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GHRP-6 (Growth Hormone Releasing Hexapeptide 6)
Chemical Name: L-histidyl-D-tryptophyl-L-alanyl-L-tryptophyl-D-phenylalanyl-L-Lysinamide
Molecular Weight: 873.014 g/mol
Formula: C46H56N12O6
Half Life: 15 – 60 minutes
[h=3]Overview and History of GHRP-6[/h]GHRP-6 (Growth Hormone Releasing Hexapeptide 6) is a peptide hormone (also referred to as a protein hormone) that belongs to a category known as HGH (Human Growth Hormone) secretagogues. That is to say that these peptide hormones will act in such a way in the body so as to stimulate secretion of Human Growth Hormone. Furthermore, GHRP-6 is a member of a category of HGH secretagogues known as Ghrelin mimetics, which are all various Growth Hormone Releasing Hexapeptide analogues. The peptides in this family include: GHRP-6, GHRP-2, Hexarelin, and Ipamorelin. They are referred to as Ghrelin mimetics because they mimic the actions of the endogenous hormone Ghrelin, whereby they will attach to the GH secretagogue receptor at the anterior pituitary gland[1]. Other activities of Ghrelin involve its activity as a hunger-stimulating peptide hormone, which easily explains the ability for many of the GHRPs to stimulate appetite to various degrees. It is very important to note that GHRP-6, as well as the other Ghrelin mimetics previously mentioned are very distinctly different peptide hormones from Growth Hormone Releasing Hormones (GHRH), such as Mod GRF 1-29 (CJC-1295 without DAC). GHRH peptides such as Mod GRF -129, and GHRP peptides such as GHRP-6, are very different classes of GH secretagogues that function through very different receptors and pathways. Therefore, the two should not be confused with one another.
GHRP-6 is a first generation GHRP, and like all other HGH secretagogues, it is a very new compound that is currently undergoing clinical trials. Therefore, the extent of gathered knowledge on this peptide is currently very minimal, but the medical establishment and its scientists are hopeful of holding a better understanding of these peptides over the next several years of research. There are many aspects of GHRP-6 and other HGH secretagogues that are not fully or completely understood, and this point must be made absolutely clear prior to delving further into this profile. New discoveries in regards to these peptides will no doubt be made over the coming years, in both clinical as well as anecdotal settings. It is the bodybuilding and performance enhancing drug using community to therefore develop logical and rational approaches to its use, supported as much as possible by proper clinical and scientific data (whenever possible).
GHRP operates via the same pathways as other GHRPs, such as GHRP-2 and Ipamorelin with some distinct differences. Almost all GHRPs will stimulate hunger simply by virtue of the fact that they are Ghrelin mimetics, but GHRP-6 has demonstrated both anecdotally as well as clinically to stimulate the largest hunger increases in comparison to all other GHRPs[2]. Studies on GHRP-6 have also demonstrated, when administered after the recent consumption of food, will exhibit lipogenic (fat-storing) properties[3]. The same study had also demonstrated the vast difference in HGH output from the pituitary gland when combined with a GHRH analogue (a 77% increase in HGH output) compared to administration alone. The consumption of carbohydrates and fats too soon before or after administration of GHRP-6 (or any GHRP) has been shown to blunt HGH release from the pituitary gland as well[4]. The aforementioned study has also demonstrated that the presence of acetylcholine in the brain will amplify the amount of HGH released via its inhibitory effects on somatostatin (a hormone that inhibits HGH release from the pituitary gland). In addition, this peptide (as well as GHRP-2) has demonstrated the ability to increase Cortisol and Prolactin secretion alongside HGH secretion, although the level of secretion of these two hormones are said to only become a concern in the higher dose ranges[5]. Insulin has demonstrated in studies to amplify the HGH response to GHRP-6 as well[6].
What does all of this mean for GHRP-6 and how it can be used? This will be further explained in the GHRP-6 doses section of this profile, but in the meantime, a few key points can be summarized:
– Proper timing of GHRP-6 doses surrounding meals should be executed so as to ensure maximal HGH release from the pituitary gland.
– GHRP Ghrelin mimetics, such as GHRP-6, should be administered in combination with a GHRH (such as Mod GRF 1-29) in order to initiate and amplify a greater pulse of HGH from the pituitary compared to GHRP-6 used solitarily on its own. The effects of a GHRH analogue with a GHRP are synergistic in their effects on the pituitary gland in amplifying the release of HGH from the pituitary.
– GHRP-6 will elevate Cortisol and Prolactin levels less significantly than GHRP-2, but does so very minimally as evidenced by studies[7]. More on this will be explained in the GHRP-6 doses section of this profile.
[h=3]Chemical Characteristics of GHRP-6[/h]GHRP-6 is a protein/peptide hormone consisting of a polypeptide chain of 6 amino acids. This polypeptide chain that makes up GHRP-6 contains unnatural D-amino acids, which were created synthetically specifically for the application of Human Growth Hormone release from the pituitary gland, making GHRP-6 known as a “true” HGH secretagogue. GHRP-6, as well as all other GHRPs, will interact with receptors on the pituitary gland[8] [9] [10] (and in many extents, on the hypothalamus as well[11] [12]) that are distinctly different receptors from the ones that GHRH interacts with. GHRP-6 will stimulate the HGH secretagogue receptor (recently renamed as the Ghrelin receptor), not the GHRH receptor. Through this interaction, GHRP-6 will stimulate a pulsatile release of HGH from the pituitary gland, which is most intense within the first 30 minutes, and lasts several hours (with the actual half-life of GHRP-6 itself being between 15 to 60 minutes)[13].
[h=3]Properties of GHRP-6[/h]Because GHRP stimulates the secretion and release of HGH from the pituitary gland in a pulsatile manner, the effects resulting from GHRP-6 are very similar from what would be expected from synthetic HGH administration over the long term (see the Human Growth Hormone profile here), although the amount of time that the released human growth hormone will remain in circulation is of a far less amount of time than synthetic Human Growth Hormone does. HGH levels will only remain raised for several hours, with the most significant amounts of HGH release only occurring within the first 30 minutes of administration. It is because of this that multiple administrations of GHRP are recommended throughout the day in order to maintain steady and/or high HGH levels on a consistent and regular basis.
Typical effects of HGH would be experienced throughout use of GHRP-6: body fat reduction, muscle mass increases, strength increases, stamina increases, and increased rate of healing, sleep quality improvement, and general increased well-being and health.
GHRP-6 References:
[1] Growth hormone-releasing peptides: clinical and basic aspects. Argente J, García-Segura LM, Pozo J, Chowen JA. Horm Res. 1996;46(4-5):155-9.
[2] Acute central ghrelin and GH secretagogues induce feeding and activate brain appetite centers. Lawrence CB, Snape AC, Baudoin FM, Luckman SM. Endocrinology. 2002 Jan;143(1):155-62.
[3] Effect of growth hormone (GH)-releasing hormone (GHRH), atropine, pyridostigmine, or hypoglycemia on GHRP-6-induced GH secretion in man. Peñalva A, Carballo A, Pombo M, Casanueva FF, Dieguez C. J Clin Endocrinol Metab. 1993 Jan;76(1):168-71.
[4] Growth hormone-releasing peptides and their analogs. Camanni F, Ghigo E, Arvat E. Front Neuroendocrinol. 1998 Jan;19(1):47-72.
[5] Ipamorelin, the first selective growth hormone secretagogue. Raun K, Hansen BS, Johansen NL, Thøgersen H, Madsen K, Ankersen M, Andersen PH. Eur J Endocrinol. 1998 Nov;139(5):552-61.
[6] Ghrelin–a hormone with multiple functions. Korbonits M, Goldstone AP, Gueorguiev M, Grossman AB (2004). Frontiers in neuroendocrinology 25 (1): 27–68. doi:10.1016/j.yfrne.2004.03.002.
[7] Human Fetal Pituitary Expresses Functional Growth Hormone-Releasing Peptide Receptors. Ilan Shimon, Xinmin Yan, and Shlomo Melmed. JCEM 1998 83: 174-178; doi:10.1210/jc.83.1.174.
[8] On the in vitro and in vivo activity of a new synthetic hexapeptide that acts on the pituitary to specifically release growth hormone. Bowers CY, Momany FA, Reynolds GA, Hong A. 1984 Endocrinology. 114:1537–1545.
[9] Effect of a new synthetic hexapeptide to selectively stimulate growth hormone release in healthy human subjects. Ilson BE, Jorkasky DK, Curnow RT, Stote RM. 1989 J Clin Endocrinol Metab. 69:212–214.
[10] On the actions of the growth hormone-releasing hexapeptide, GHRP. Bowers CY, Sartor AO, Reynolds GA, Badger TM. 1991 Endocrinology. 128:2027–2035.
[11] Blocked growth hormone-releasing peptide (GHRP-6)-induced GH secretion and absence of the synergic action of GHRP-6 plus GH-releasing hormone in patients with hypothalamopituitary disconnection: evidence that GHRP-6 main action is exerted at the hypothalamic level. V Popovic, S Damjanovic, D Micic, M Djurovic, C Dieguez, and F F Casanueva. JCEM 1995 80: 942-7; doi:10.1210/jc.80.3.942.
[12] Systemic administration of growth hormone-releasing peptide activates hypothalamic arcuate neurons. Dickson SL, Leng G, Robinson ICAF. 1993 Neurosci Lett. 53:303–306.
[13] Pharmacokinetic study of Growth Hormone-Releasing Peptide 6 (GHRP-6) in nine male healthy volunteers. Cabrales A, Gil J, Fernández E, Valenzuela C, Hernández F, García I, Hernández A, Besada V, Reyes O, Padrón G, Berlanga J, Guillén G, González LJ. Eur J Pharm Sci. 2013 Jan 23;48(1-2):40-6. doi: 10.1016/j.ejps.2012.10.006. Epub 2012 Oct 23.
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[h=1]GHRP-6 Cycles[/h]
Because GHRP-6 is a peptide hormone that will amplify the release of HGH from the pituitary gland, it makes sense that GHRP-6 cycles would generally be suited for cutting cycles and fat loss. Unfortunately, there is one aspect of GHRP-6 that tends to make it more suitable instead for bulking and mass gaining cycles for most people. That aspect is the ability for GHRP-6 to induce the most intense appetite stimulation in users that nothing else compares to. It has been demonstrated both clinically as well as anecdotally that in most users and mammals, GHRP-6 tends to stimulate what can only be described as agonizing hunger. Therefore, GHRP-6 cycles are said to often be best suited for periods of mass gaining and bulking. With that being said, GHRP-6 cycles can indeed be geared towards fat loss, but only if the individual can muster enough discipline and willpower to be able to fight the urge to eat too many calories.
GHRP-6, through its ability to amplify HGH release, can provide a solid amount of fat loss during phases of dieting. However, the majority of users will find that GHRP-6 is more often useful for bulking, and many users will often put on a significant amount of weight through its hunger inducing effects alone. The HGH releasing effect of GHRP-6 will indeed further support muscle growth and strength increases as well in conjunction with a caloric surplus that is often easily achieved with the use of GHRP-6. It must be made very clear, however, that the key determining factor as to whether or not one will lose fat or gain muscle during GHRP-6 cycles is the factor of diet and training. GHRP-6 can easily facilitate a caloric surplus or a caloric deficit and carry the results in either direction quite easily.
Because of the inherent nature of the compound and what it does, GHRP-6 cycles cannot be broken down and categorized into the typical three user tiers of cycles (i.e. beginner cycles, intermediate cycles, advanced cycles). As with nearly all HGH secretagogues, GHRP-6 cycles can only essentially be categorized into the following three cycle types:
– GHRP-6 cycles for muscle growth and fat loss
– GHRP-6 cycles for fat loss
– GHRP-6 cycles for anti-aging and general well-being
The determining factor in which of these three cycle types are engaged in or achieved is the user’s GHRP-6 dosing scheme, as well as the diet and training regimen of the user. It is important to understand that as with all Human Growth Hormone based compounds, cycles are in the long-term and must be treated as such. Synthetic HGH as well as HGH secretagogues such as GHRP-6 must be run in periods of at least 4 – 6 months or longer in order to experience any appreciable effects. The reason being is because Human Growth Hormoneis by nature a hormone that exhibits steady and cumulative effects on the body and body composition. Various changes and results can be seen sooner than others (such as the fat loss effects, within a matter of weeks) and other effects much later (such as the muscle growth and strength gaining effects, within a matter of months).
GHRP-6 cycles for the purpose of both muscle growth as well as fat loss require the administration of at least 100mcg of GHRP-6 at least three times per day for 4 – 6 months. Often times it is recommended that for even more pronounced and greater muscle growth and fat loss that the administration frequency is increased to above 3 times per day (ideally 4 – 5 injections per day). Such GHRP-6 cycles would ensure constant pulses of HGH that would be as close as possible to synthetic HGH administration.
GHRP-6 cycles that express fat loss exclusively in users would involve the administration of 100mcg of GHRP-6 two to three times daily for 4 – 6 months. Some small amounts of muscle and strength gaining might possibly be experienced in rare situations, provided nutrition and training accommodates this.
Anti-aging and general well ness cycles of GHRP-6 involve 1 – 2 injections daily of 100mcg GHRP-6 in each injection. A minimal administration protocol of GHRP-6 such as this one will induce a much smaller overall release of HGH from the pituitary gland, but just enough to ensure the positive health and well-being benefits, especially in older individuals.
GHRP-6 cycles are almost always conducted in tandem with a GHRH such as Mod GRF 1-29 (CJC-1295 without DAC) so as to maximize HGH output, which has been previously explained in great detail in this profile. GHRP-6 can also be utilized with anabolic steroids in much the same way that synthetic HGH can be utilized with them in order to provide a synergistic effect on muscle growth as well as fat loss. Synthetic HGH itself can and often is combined with HGH secretagogues such as GHRP-6, which allows the user to experience what would be considered higher overall blood plasma levels of HGH without having to utilize as much synthetic HGH. The manner in which this would typically work is the administration of exogenous synthetic HGH at a dose of 4iu immediately upon rising in the morning, followed by administrations of GHRP-6 mid-day (with another optional HGH administration 30 minutes after that), and then finally another GHRP-6 administration immediately before going to bed. Such a protocol in a GHRP-6 cycle ensures maximum benefit of HGH and is much more cost effective for the user than resorting to larger doses of synthetic HGH alone. The other benefit is the ability for the user to maintain pituitary function during the use of synthetic HGH, which would normally cause a shutdown of endogenous HGH production via the negative feedback loop. The use of HGH secretagogues such as GHRP-6 prior to bed would ensure the pituitary gland is still manufacturing endogenous HGH.
[h=1]GHRP-6 Doses[/h]
It should be noted right off the bat that GHRP-6 doses are often normally (and ideally) combined with doses of a GHRH analogue, such as Mod GRF 1-29 (CJC-1295 without DAC) due to the synergistic effects and compatibility between the two, as previously mentioned in this profile. With that being said, the proper GHRP-6 doses do not change whether or not it is utilized with a GHRH. If an effective GHRP-6 dose is 100mcg, for example, then 100mcg of GHRP-6 should be administered whether the user is utilizing it alone or with Mod GRF 1-29. The term/phrase “saturation dose” or “saturation doses” can be heard a lot when peptides are discussed. A saturation dose is defined as a dose that will completely (or near completely) saturate the peptide’s target receptors. In GHRP-6’s case, this means the Ghrelin receptors located on the hypothalamus and the anterior pituitary.
From the examination of many studies, the saturation GHRP-6 doses have been determined to be 1mcg per kg of body weight, and an average dose of approximately 100mcg without concern for bodyweight[1] [2] [3] [4]. That is to say that a 100mcg saturation dose of GHRP-6 will fully saturate receptors, and that 200mcg will only provide 50% additional effectiveness, and a 300mcg dose will provide only 25% additional effectiveness, and so on and so forth. This is very much the case with almost all GHRPs and GHRH analogues, as it seems to be the nature of these peptides.
One common concern when it comes to GHRP-6 doses (or the doses of any Ghrelin mimetic/GHRP) is the fact that it has been found to exhibit the ability to induce secretion of Cortisol and Prolactin. While many studies have indeed demonstrated this[5], they have also demonstrated that the Prolactin and Cortisol increases in most test subjects were not altered at all at GHRP-6 doses of 100mcg or less[6] [7]. GHRP-6 doses that are increased above 100mcg will exhibit increased Cortisol and Prolactin secretion, but minimally. As the dose is further increased, it stands to reason that the Cortisol and Prolactin secretions will increase as well.
GHRP-6 doses are measured in mcg (micrograms), and it is very important to make note of this distinction due to the fact that the common measurement of most other performance enhancing drugs is that of mg (milligrams). Synthetic Human Growth Hormone (HGH) is measured in iu (international units).
Medical GHRP-6 Doses
GHRP-6 is not currently yet approved for medical use and is still in the phase of clinical trials. As such, there exist no officially determined prescription medical doses currently available.
GHRP-6 Doses for Performance and Physique Enhancement
It is both impractical and impossible to categorize GHRP-6 doses into the typical three tiers of users (beginner, intermediate, and advanced) due to the inherent nature of the type of substance and hormone. The saturation doses of GHRP-6 should elicit significant increases in HGH levels in the body in a pulsatile manner that is adequate enough to ensure any performance and physique enhancing goals desired by any individual. The difference in which goals might be more attainable than others is the frequency of dosing. GHRP-6 exhibits a varying half-life of approximately 15 – 60 minutes after injection, and will stimulate a large pulse of HGH from the pituitary gland that will last several hours but is most intense and achieves its peak at approximately 30 minutes. Therefore, in order to simulate higher and steadier blood plasma levels of HGH, it is necessary to administer GHRP-6 doses multiple times daily (depending on the user’s goals).
As a result, a general guideline for the purpose of achieving performance and physique enhancement is that of 100mcg administered three times per day. Each injection should be spaced evenly apart in order to achieve substantial HGH levels throughout the day due to the short half-life of GHRP-6 as well as the pulsatile manner of the HGH release that it causes. For greater results that would include more pronounced muscle gain and fat loss, more frequent injections would be required above the three times per day protocol. More details concerning the specific administration timing will be described shortly.
GHRP-6 doses can be administered subcutaneously (SQ) or intramuscularly (IM). There is not much difference between the two, with intramuscular seemingly resulting in a slightly quicker release from the injection site. The majority of individuals prefer to administer it subcutaneously for varying reasons, however.
It is important to understand that GHRP-6 doses on its own provides considerable HGH release from the pituitary gland, but is nowhere near as effective as the potential HGH release resultant from GHRP-6 combined with a GHRH such as Mod GRF 1-29 (CJC-1295 without DAC). Studies have demonstrated that the combination of GHRP-6 and a GHRH analogue such as Mod GRF 1-29 will generate a 77% increase in HGH output compared to GHRP-6 administration alone[8]. Other studies have gone so far as to explicitly state that GHRP-6 requires GHRH in order to stimulate maximal HGH stimulation as evidenced by the fact that in test subjects, the inclusion of a GHRH can increase HGH output by an additional 81 – 95%[9].
In general summary of the synergistic effect of both: a GHRH analogue (such as Mod GRF 1-29) will serve to initiate and carry forward the pulse of HGH from the pituitary gland, while the GHRP (such as GHRP-6) will serve to amplify this pulse.
Female GHRP-6 Doses
GHRP-6 is not a sex-specific hormone and therefore carries no androgenic effects that would present any issues. Therefore, female GHRP-6 doses are the exact same for all individuals, regardless of gender.
Proper Administration and Timing of GHRP-6 Doses
GHRP-6 is normally always manufactured as lyophilized (freeze-dried) powder contained in vials in amounts of 5mg. Some companies might manufacture amounts greater or lesser than 5mg per vial, but the standard is generally 5mg/vial. The lyophilized powder contained within the vial will need to be reconstituted with bacteriostatic water in order for it to be injected. After reconstitution, the solution must then be refrigerated in storage. If left in hot environments or in room temperature environments for extended periods of time, the protein structure will degrade and become ineffective. For reconstitution, users will typically mix 3ml of bacteriostatic water with the powder gently. However, users can and do frequently reconstitute the powder with less (or more) water which will yield different concentrations of GHRP-6. For example, reconstitution of 5mg of powder with 3ml of water will yield GHRP-6 doses of 166mcg per 0.1ml (or 10iu on an insulin syringe).
As with any GHRP or GHRH, administration of GHRP-6 doses should be done no sooner than 2 hours following the last meal containing carbohydrates or fats, and no sooner than 30 minutes prior to the next consumption of carbohydrates or fats. As evidenced by studies referenced in the introduction of this profile, the consumption of fats and carbohydrates will significantly blunt (but not eliminate) HGH release. HGH pulses will generally reach their peak by about 30 minutes following injection, after which it is then acceptable to consume a meal containing carbohydrates and fats.
As previously explained, multiple GHRP-6 doses are required throughout the day due to the pulsatile nature of the HGH release, and the administration of these doses are typically administered on average 3 times daily spaced evenly apart. More administrations are acceptable for greater effects on physique and performance, but it is advised that approximately 3 hours in between each injection is ensured so as to allow the pituitary gland to restore its storage of HGH. The most common protocol is as follows:
100mcg immediately upon waking up
100mcg immediately following the end of a workout
100mcg immediately before bed
It has been previously explained that some individuals will elect to administer GHRP-6 doses twice daily, and some more than three times daily. Twice daily administration of at least 100mcg (typically upon awaking and before sleeping) will yield anti-aging and general health benefits. 3 times daily administration should yield general health benefits, fat loss, and muscle gain. 4 times daily or greater administration should provide more pronounced muscle gains and fat loss.
Finally, studies have determined that GHRP-6 administered alone stimulated an HGH release of 40 ng/ml in test subjects[10]. The same study determined that when combined with a GHRH (such as Mod GRF 1-29), the resultant HGH release was determined to be 130 ng/ml.
Expectations and Results from GHRP-6 Doses
Results and expectations from an HGH secretagogue such as GHRP-6 should be all of the same effects that any other form of Human Growth Hormone would provide. This includes fat loss, muscle mass increases, strength gains, healing and repair of joints and connective tissue, and a plethora of other benefits and changes. An important note to make is that the effects from any HGH application, whether it be an endogenous release from a GHRH or synthetic HGH administration, will all occur rather steadily over a longer period of use. Dramatic results within weeks are never to be expected, but with proper nutrition and training, dramatic performance and physique changes should occur steadily over the course of several months of application. For more information on HGH specific results and expectations, please see the Human Growth Hormone profile.
GHRP-6 References:
[1] Blockade of the growth hormone (GH) receptor unmasks rapid GH-releasing peptide-6-mediated tissue-specific insulin resistance. Peñalva A, Carballo A, Pombo M, Casanueva FF, Dieguez C. J Clin Endocrinol Metab. 1993 Jan;76(1):168-71.
[2] Blocked growth hormone-releasing peptide (GHRP-6)-induced GH secretion and absence of the synergic action of GHRP-6 plus GH-releasing hormone in patients with hypothalamopituitary disconnection: evidence that GHRP-6 main action is exerted at the hypothalamic level. V Popovic, S Damjanovic, D Micic, M Djurovic, C Dieguez, and F F Casanueva. JCEM 1995 80: 942-7; doi:10.1210/jc.80.3.942.
[3] Growth Hormone (GH) Response to GH-Releasing Peptide-6 in Type 1 Diabetic Patients with Exaggerated GH-Releasing Hormone-Stimulated GH Secretion. Pablo F. Catalina, Federico Mallo, M. Amelia Andrade, Ricardo V. García-Mayor, and Carlos Diéguez. JCEM 1998 83: 3663-3667; doi:10.1210/jc.83.10.3663.
[4] Massive growth hormone (GH) discharge in obese subjects after the combined administration of GH-releasing hormone and GHRP-6: evidence for a marked somatotroph secretory capability in obesity. F Cordido, A Peñalva, C Dieguez, and F F Casanueva. JCEM 1993 76: 819-23; doi:10.1210/jc.76.4.819.
[5] Pathophysiology of the neuroregulation of growth hormone secretion in experimental animals and the human. Giustina A, Veldhuis JD. 1998 Endocr Rev. 19:717–797.
[6] Human Fetal Pituitary Expresses Functional Growth Hormone-Releasing Peptide Receptors. Ilan Shimon, Xinmin Yan, and Shlomo Melmed. JCEM 1998 83: 174-178; doi:10.1210/jc.83.1.174.
[7] The Impact of Cranial Irradiation on GH Responsiveness to GHRH Plus GH-Releasing Peptide-6. Vera Popovic, Sandra Pekic, Ivana Golubicic, Mira Doknic, Carlos Dieguez and Felipe F. Casanueva. JCEM 2002 87: 2095-2099; doi:10.1210/jc.87.5.2095.
[8] Effect of growth hormone (GH)-releasing hormone (GHRH), atropine, pyridostigmine, or hypoglycemia on GHRP-6-induced GH secretion in man. Peñalva A, Carballo A, Pombo M, Casanueva FF, Dieguez C. J Clin Endocrinol Metab. 1993 Jan;76(1):168-71.
[9] Growth Hormone (GH)-Releasing Peptide-6 Requires Endogenous Hypothalamic GH-Releasing Hormone for Maximal GH Stimulation. Naushira Pandya, Roberta DeMott-Friberg, Cyril Y. Bowers, Ariel L. Barkan and Craig A. Jaffe. The Journal of Clinical Endocrinology & Metabolism April 1, 1998 vol. 83 no. 4 1186-1189.
[10] Inhibition of growth hormone release after the combined administration of GHRH and GHRP-6 in patients with Cushing’s syndrome. Leal-Cerro A, Pumar A, Garcia-Garcia E, Dieguez C, Casanueva FF. Clin Endocrinol (Oxf). 1994 Nov;41(5):649-54
Chemical Name: L-histidyl-D-tryptophyl-L-alanyl-L-tryptophyl-D-phenylalanyl-L-Lysinamide
Molecular Weight: 873.014 g/mol
Formula: C46H56N12O6
Half Life: 15 – 60 minutes
[h=3]Overview and History of GHRP-6[/h]GHRP-6 (Growth Hormone Releasing Hexapeptide 6) is a peptide hormone (also referred to as a protein hormone) that belongs to a category known as HGH (Human Growth Hormone) secretagogues. That is to say that these peptide hormones will act in such a way in the body so as to stimulate secretion of Human Growth Hormone. Furthermore, GHRP-6 is a member of a category of HGH secretagogues known as Ghrelin mimetics, which are all various Growth Hormone Releasing Hexapeptide analogues. The peptides in this family include: GHRP-6, GHRP-2, Hexarelin, and Ipamorelin. They are referred to as Ghrelin mimetics because they mimic the actions of the endogenous hormone Ghrelin, whereby they will attach to the GH secretagogue receptor at the anterior pituitary gland[1]. Other activities of Ghrelin involve its activity as a hunger-stimulating peptide hormone, which easily explains the ability for many of the GHRPs to stimulate appetite to various degrees. It is very important to note that GHRP-6, as well as the other Ghrelin mimetics previously mentioned are very distinctly different peptide hormones from Growth Hormone Releasing Hormones (GHRH), such as Mod GRF 1-29 (CJC-1295 without DAC). GHRH peptides such as Mod GRF -129, and GHRP peptides such as GHRP-6, are very different classes of GH secretagogues that function through very different receptors and pathways. Therefore, the two should not be confused with one another.
GHRP-6 is a first generation GHRP, and like all other HGH secretagogues, it is a very new compound that is currently undergoing clinical trials. Therefore, the extent of gathered knowledge on this peptide is currently very minimal, but the medical establishment and its scientists are hopeful of holding a better understanding of these peptides over the next several years of research. There are many aspects of GHRP-6 and other HGH secretagogues that are not fully or completely understood, and this point must be made absolutely clear prior to delving further into this profile. New discoveries in regards to these peptides will no doubt be made over the coming years, in both clinical as well as anecdotal settings. It is the bodybuilding and performance enhancing drug using community to therefore develop logical and rational approaches to its use, supported as much as possible by proper clinical and scientific data (whenever possible).
GHRP operates via the same pathways as other GHRPs, such as GHRP-2 and Ipamorelin with some distinct differences. Almost all GHRPs will stimulate hunger simply by virtue of the fact that they are Ghrelin mimetics, but GHRP-6 has demonstrated both anecdotally as well as clinically to stimulate the largest hunger increases in comparison to all other GHRPs[2]. Studies on GHRP-6 have also demonstrated, when administered after the recent consumption of food, will exhibit lipogenic (fat-storing) properties[3]. The same study had also demonstrated the vast difference in HGH output from the pituitary gland when combined with a GHRH analogue (a 77% increase in HGH output) compared to administration alone. The consumption of carbohydrates and fats too soon before or after administration of GHRP-6 (or any GHRP) has been shown to blunt HGH release from the pituitary gland as well[4]. The aforementioned study has also demonstrated that the presence of acetylcholine in the brain will amplify the amount of HGH released via its inhibitory effects on somatostatin (a hormone that inhibits HGH release from the pituitary gland). In addition, this peptide (as well as GHRP-2) has demonstrated the ability to increase Cortisol and Prolactin secretion alongside HGH secretion, although the level of secretion of these two hormones are said to only become a concern in the higher dose ranges[5]. Insulin has demonstrated in studies to amplify the HGH response to GHRP-6 as well[6].
What does all of this mean for GHRP-6 and how it can be used? This will be further explained in the GHRP-6 doses section of this profile, but in the meantime, a few key points can be summarized:
– Proper timing of GHRP-6 doses surrounding meals should be executed so as to ensure maximal HGH release from the pituitary gland.
– GHRP Ghrelin mimetics, such as GHRP-6, should be administered in combination with a GHRH (such as Mod GRF 1-29) in order to initiate and amplify a greater pulse of HGH from the pituitary compared to GHRP-6 used solitarily on its own. The effects of a GHRH analogue with a GHRP are synergistic in their effects on the pituitary gland in amplifying the release of HGH from the pituitary.
– GHRP-6 will elevate Cortisol and Prolactin levels less significantly than GHRP-2, but does so very minimally as evidenced by studies[7]. More on this will be explained in the GHRP-6 doses section of this profile.
[h=3]Chemical Characteristics of GHRP-6[/h]GHRP-6 is a protein/peptide hormone consisting of a polypeptide chain of 6 amino acids. This polypeptide chain that makes up GHRP-6 contains unnatural D-amino acids, which were created synthetically specifically for the application of Human Growth Hormone release from the pituitary gland, making GHRP-6 known as a “true” HGH secretagogue. GHRP-6, as well as all other GHRPs, will interact with receptors on the pituitary gland[8] [9] [10] (and in many extents, on the hypothalamus as well[11] [12]) that are distinctly different receptors from the ones that GHRH interacts with. GHRP-6 will stimulate the HGH secretagogue receptor (recently renamed as the Ghrelin receptor), not the GHRH receptor. Through this interaction, GHRP-6 will stimulate a pulsatile release of HGH from the pituitary gland, which is most intense within the first 30 minutes, and lasts several hours (with the actual half-life of GHRP-6 itself being between 15 to 60 minutes)[13].
[h=3]Properties of GHRP-6[/h]Because GHRP stimulates the secretion and release of HGH from the pituitary gland in a pulsatile manner, the effects resulting from GHRP-6 are very similar from what would be expected from synthetic HGH administration over the long term (see the Human Growth Hormone profile here), although the amount of time that the released human growth hormone will remain in circulation is of a far less amount of time than synthetic Human Growth Hormone does. HGH levels will only remain raised for several hours, with the most significant amounts of HGH release only occurring within the first 30 minutes of administration. It is because of this that multiple administrations of GHRP are recommended throughout the day in order to maintain steady and/or high HGH levels on a consistent and regular basis.
Typical effects of HGH would be experienced throughout use of GHRP-6: body fat reduction, muscle mass increases, strength increases, stamina increases, and increased rate of healing, sleep quality improvement, and general increased well-being and health.
GHRP-6 References:
[1] Growth hormone-releasing peptides: clinical and basic aspects. Argente J, García-Segura LM, Pozo J, Chowen JA. Horm Res. 1996;46(4-5):155-9.
[2] Acute central ghrelin and GH secretagogues induce feeding and activate brain appetite centers. Lawrence CB, Snape AC, Baudoin FM, Luckman SM. Endocrinology. 2002 Jan;143(1):155-62.
[3] Effect of growth hormone (GH)-releasing hormone (GHRH), atropine, pyridostigmine, or hypoglycemia on GHRP-6-induced GH secretion in man. Peñalva A, Carballo A, Pombo M, Casanueva FF, Dieguez C. J Clin Endocrinol Metab. 1993 Jan;76(1):168-71.
[4] Growth hormone-releasing peptides and their analogs. Camanni F, Ghigo E, Arvat E. Front Neuroendocrinol. 1998 Jan;19(1):47-72.
[5] Ipamorelin, the first selective growth hormone secretagogue. Raun K, Hansen BS, Johansen NL, Thøgersen H, Madsen K, Ankersen M, Andersen PH. Eur J Endocrinol. 1998 Nov;139(5):552-61.
[6] Ghrelin–a hormone with multiple functions. Korbonits M, Goldstone AP, Gueorguiev M, Grossman AB (2004). Frontiers in neuroendocrinology 25 (1): 27–68. doi:10.1016/j.yfrne.2004.03.002.
[7] Human Fetal Pituitary Expresses Functional Growth Hormone-Releasing Peptide Receptors. Ilan Shimon, Xinmin Yan, and Shlomo Melmed. JCEM 1998 83: 174-178; doi:10.1210/jc.83.1.174.
[8] On the in vitro and in vivo activity of a new synthetic hexapeptide that acts on the pituitary to specifically release growth hormone. Bowers CY, Momany FA, Reynolds GA, Hong A. 1984 Endocrinology. 114:1537–1545.
[9] Effect of a new synthetic hexapeptide to selectively stimulate growth hormone release in healthy human subjects. Ilson BE, Jorkasky DK, Curnow RT, Stote RM. 1989 J Clin Endocrinol Metab. 69:212–214.
[10] On the actions of the growth hormone-releasing hexapeptide, GHRP. Bowers CY, Sartor AO, Reynolds GA, Badger TM. 1991 Endocrinology. 128:2027–2035.
[11] Blocked growth hormone-releasing peptide (GHRP-6)-induced GH secretion and absence of the synergic action of GHRP-6 plus GH-releasing hormone in patients with hypothalamopituitary disconnection: evidence that GHRP-6 main action is exerted at the hypothalamic level. V Popovic, S Damjanovic, D Micic, M Djurovic, C Dieguez, and F F Casanueva. JCEM 1995 80: 942-7; doi:10.1210/jc.80.3.942.
[12] Systemic administration of growth hormone-releasing peptide activates hypothalamic arcuate neurons. Dickson SL, Leng G, Robinson ICAF. 1993 Neurosci Lett. 53:303–306.
[13] Pharmacokinetic study of Growth Hormone-Releasing Peptide 6 (GHRP-6) in nine male healthy volunteers. Cabrales A, Gil J, Fernández E, Valenzuela C, Hernández F, García I, Hernández A, Besada V, Reyes O, Padrón G, Berlanga J, Guillén G, González LJ. Eur J Pharm Sci. 2013 Jan 23;48(1-2):40-6. doi: 10.1016/j.ejps.2012.10.006. Epub 2012 Oct 23.
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[h=1]GHRP-6 Cycles[/h]
Because GHRP-6 is a peptide hormone that will amplify the release of HGH from the pituitary gland, it makes sense that GHRP-6 cycles would generally be suited for cutting cycles and fat loss. Unfortunately, there is one aspect of GHRP-6 that tends to make it more suitable instead for bulking and mass gaining cycles for most people. That aspect is the ability for GHRP-6 to induce the most intense appetite stimulation in users that nothing else compares to. It has been demonstrated both clinically as well as anecdotally that in most users and mammals, GHRP-6 tends to stimulate what can only be described as agonizing hunger. Therefore, GHRP-6 cycles are said to often be best suited for periods of mass gaining and bulking. With that being said, GHRP-6 cycles can indeed be geared towards fat loss, but only if the individual can muster enough discipline and willpower to be able to fight the urge to eat too many calories.
GHRP-6, through its ability to amplify HGH release, can provide a solid amount of fat loss during phases of dieting. However, the majority of users will find that GHRP-6 is more often useful for bulking, and many users will often put on a significant amount of weight through its hunger inducing effects alone. The HGH releasing effect of GHRP-6 will indeed further support muscle growth and strength increases as well in conjunction with a caloric surplus that is often easily achieved with the use of GHRP-6. It must be made very clear, however, that the key determining factor as to whether or not one will lose fat or gain muscle during GHRP-6 cycles is the factor of diet and training. GHRP-6 can easily facilitate a caloric surplus or a caloric deficit and carry the results in either direction quite easily.
Because of the inherent nature of the compound and what it does, GHRP-6 cycles cannot be broken down and categorized into the typical three user tiers of cycles (i.e. beginner cycles, intermediate cycles, advanced cycles). As with nearly all HGH secretagogues, GHRP-6 cycles can only essentially be categorized into the following three cycle types:
– GHRP-6 cycles for muscle growth and fat loss
– GHRP-6 cycles for fat loss
– GHRP-6 cycles for anti-aging and general well-being
The determining factor in which of these three cycle types are engaged in or achieved is the user’s GHRP-6 dosing scheme, as well as the diet and training regimen of the user. It is important to understand that as with all Human Growth Hormone based compounds, cycles are in the long-term and must be treated as such. Synthetic HGH as well as HGH secretagogues such as GHRP-6 must be run in periods of at least 4 – 6 months or longer in order to experience any appreciable effects. The reason being is because Human Growth Hormoneis by nature a hormone that exhibits steady and cumulative effects on the body and body composition. Various changes and results can be seen sooner than others (such as the fat loss effects, within a matter of weeks) and other effects much later (such as the muscle growth and strength gaining effects, within a matter of months).
GHRP-6 cycles for the purpose of both muscle growth as well as fat loss require the administration of at least 100mcg of GHRP-6 at least three times per day for 4 – 6 months. Often times it is recommended that for even more pronounced and greater muscle growth and fat loss that the administration frequency is increased to above 3 times per day (ideally 4 – 5 injections per day). Such GHRP-6 cycles would ensure constant pulses of HGH that would be as close as possible to synthetic HGH administration.
GHRP-6 cycles that express fat loss exclusively in users would involve the administration of 100mcg of GHRP-6 two to three times daily for 4 – 6 months. Some small amounts of muscle and strength gaining might possibly be experienced in rare situations, provided nutrition and training accommodates this.
Anti-aging and general well ness cycles of GHRP-6 involve 1 – 2 injections daily of 100mcg GHRP-6 in each injection. A minimal administration protocol of GHRP-6 such as this one will induce a much smaller overall release of HGH from the pituitary gland, but just enough to ensure the positive health and well-being benefits, especially in older individuals.
GHRP-6 cycles are almost always conducted in tandem with a GHRH such as Mod GRF 1-29 (CJC-1295 without DAC) so as to maximize HGH output, which has been previously explained in great detail in this profile. GHRP-6 can also be utilized with anabolic steroids in much the same way that synthetic HGH can be utilized with them in order to provide a synergistic effect on muscle growth as well as fat loss. Synthetic HGH itself can and often is combined with HGH secretagogues such as GHRP-6, which allows the user to experience what would be considered higher overall blood plasma levels of HGH without having to utilize as much synthetic HGH. The manner in which this would typically work is the administration of exogenous synthetic HGH at a dose of 4iu immediately upon rising in the morning, followed by administrations of GHRP-6 mid-day (with another optional HGH administration 30 minutes after that), and then finally another GHRP-6 administration immediately before going to bed. Such a protocol in a GHRP-6 cycle ensures maximum benefit of HGH and is much more cost effective for the user than resorting to larger doses of synthetic HGH alone. The other benefit is the ability for the user to maintain pituitary function during the use of synthetic HGH, which would normally cause a shutdown of endogenous HGH production via the negative feedback loop. The use of HGH secretagogues such as GHRP-6 prior to bed would ensure the pituitary gland is still manufacturing endogenous HGH.
[h=1]GHRP-6 Doses[/h]
It should be noted right off the bat that GHRP-6 doses are often normally (and ideally) combined with doses of a GHRH analogue, such as Mod GRF 1-29 (CJC-1295 without DAC) due to the synergistic effects and compatibility between the two, as previously mentioned in this profile. With that being said, the proper GHRP-6 doses do not change whether or not it is utilized with a GHRH. If an effective GHRP-6 dose is 100mcg, for example, then 100mcg of GHRP-6 should be administered whether the user is utilizing it alone or with Mod GRF 1-29. The term/phrase “saturation dose” or “saturation doses” can be heard a lot when peptides are discussed. A saturation dose is defined as a dose that will completely (or near completely) saturate the peptide’s target receptors. In GHRP-6’s case, this means the Ghrelin receptors located on the hypothalamus and the anterior pituitary.
From the examination of many studies, the saturation GHRP-6 doses have been determined to be 1mcg per kg of body weight, and an average dose of approximately 100mcg without concern for bodyweight[1] [2] [3] [4]. That is to say that a 100mcg saturation dose of GHRP-6 will fully saturate receptors, and that 200mcg will only provide 50% additional effectiveness, and a 300mcg dose will provide only 25% additional effectiveness, and so on and so forth. This is very much the case with almost all GHRPs and GHRH analogues, as it seems to be the nature of these peptides.
One common concern when it comes to GHRP-6 doses (or the doses of any Ghrelin mimetic/GHRP) is the fact that it has been found to exhibit the ability to induce secretion of Cortisol and Prolactin. While many studies have indeed demonstrated this[5], they have also demonstrated that the Prolactin and Cortisol increases in most test subjects were not altered at all at GHRP-6 doses of 100mcg or less[6] [7]. GHRP-6 doses that are increased above 100mcg will exhibit increased Cortisol and Prolactin secretion, but minimally. As the dose is further increased, it stands to reason that the Cortisol and Prolactin secretions will increase as well.
GHRP-6 doses are measured in mcg (micrograms), and it is very important to make note of this distinction due to the fact that the common measurement of most other performance enhancing drugs is that of mg (milligrams). Synthetic Human Growth Hormone (HGH) is measured in iu (international units).
Medical GHRP-6 Doses
GHRP-6 is not currently yet approved for medical use and is still in the phase of clinical trials. As such, there exist no officially determined prescription medical doses currently available.
GHRP-6 Doses for Performance and Physique Enhancement
It is both impractical and impossible to categorize GHRP-6 doses into the typical three tiers of users (beginner, intermediate, and advanced) due to the inherent nature of the type of substance and hormone. The saturation doses of GHRP-6 should elicit significant increases in HGH levels in the body in a pulsatile manner that is adequate enough to ensure any performance and physique enhancing goals desired by any individual. The difference in which goals might be more attainable than others is the frequency of dosing. GHRP-6 exhibits a varying half-life of approximately 15 – 60 minutes after injection, and will stimulate a large pulse of HGH from the pituitary gland that will last several hours but is most intense and achieves its peak at approximately 30 minutes. Therefore, in order to simulate higher and steadier blood plasma levels of HGH, it is necessary to administer GHRP-6 doses multiple times daily (depending on the user’s goals).
As a result, a general guideline for the purpose of achieving performance and physique enhancement is that of 100mcg administered three times per day. Each injection should be spaced evenly apart in order to achieve substantial HGH levels throughout the day due to the short half-life of GHRP-6 as well as the pulsatile manner of the HGH release that it causes. For greater results that would include more pronounced muscle gain and fat loss, more frequent injections would be required above the three times per day protocol. More details concerning the specific administration timing will be described shortly.
GHRP-6 doses can be administered subcutaneously (SQ) or intramuscularly (IM). There is not much difference between the two, with intramuscular seemingly resulting in a slightly quicker release from the injection site. The majority of individuals prefer to administer it subcutaneously for varying reasons, however.
It is important to understand that GHRP-6 doses on its own provides considerable HGH release from the pituitary gland, but is nowhere near as effective as the potential HGH release resultant from GHRP-6 combined with a GHRH such as Mod GRF 1-29 (CJC-1295 without DAC). Studies have demonstrated that the combination of GHRP-6 and a GHRH analogue such as Mod GRF 1-29 will generate a 77% increase in HGH output compared to GHRP-6 administration alone[8]. Other studies have gone so far as to explicitly state that GHRP-6 requires GHRH in order to stimulate maximal HGH stimulation as evidenced by the fact that in test subjects, the inclusion of a GHRH can increase HGH output by an additional 81 – 95%[9].
In general summary of the synergistic effect of both: a GHRH analogue (such as Mod GRF 1-29) will serve to initiate and carry forward the pulse of HGH from the pituitary gland, while the GHRP (such as GHRP-6) will serve to amplify this pulse.
Female GHRP-6 Doses
GHRP-6 is not a sex-specific hormone and therefore carries no androgenic effects that would present any issues. Therefore, female GHRP-6 doses are the exact same for all individuals, regardless of gender.
Proper Administration and Timing of GHRP-6 Doses
GHRP-6 is normally always manufactured as lyophilized (freeze-dried) powder contained in vials in amounts of 5mg. Some companies might manufacture amounts greater or lesser than 5mg per vial, but the standard is generally 5mg/vial. The lyophilized powder contained within the vial will need to be reconstituted with bacteriostatic water in order for it to be injected. After reconstitution, the solution must then be refrigerated in storage. If left in hot environments or in room temperature environments for extended periods of time, the protein structure will degrade and become ineffective. For reconstitution, users will typically mix 3ml of bacteriostatic water with the powder gently. However, users can and do frequently reconstitute the powder with less (or more) water which will yield different concentrations of GHRP-6. For example, reconstitution of 5mg of powder with 3ml of water will yield GHRP-6 doses of 166mcg per 0.1ml (or 10iu on an insulin syringe).
As with any GHRP or GHRH, administration of GHRP-6 doses should be done no sooner than 2 hours following the last meal containing carbohydrates or fats, and no sooner than 30 minutes prior to the next consumption of carbohydrates or fats. As evidenced by studies referenced in the introduction of this profile, the consumption of fats and carbohydrates will significantly blunt (but not eliminate) HGH release. HGH pulses will generally reach their peak by about 30 minutes following injection, after which it is then acceptable to consume a meal containing carbohydrates and fats.
As previously explained, multiple GHRP-6 doses are required throughout the day due to the pulsatile nature of the HGH release, and the administration of these doses are typically administered on average 3 times daily spaced evenly apart. More administrations are acceptable for greater effects on physique and performance, but it is advised that approximately 3 hours in between each injection is ensured so as to allow the pituitary gland to restore its storage of HGH. The most common protocol is as follows:
100mcg immediately upon waking up
100mcg immediately following the end of a workout
100mcg immediately before bed
It has been previously explained that some individuals will elect to administer GHRP-6 doses twice daily, and some more than three times daily. Twice daily administration of at least 100mcg (typically upon awaking and before sleeping) will yield anti-aging and general health benefits. 3 times daily administration should yield general health benefits, fat loss, and muscle gain. 4 times daily or greater administration should provide more pronounced muscle gains and fat loss.
Finally, studies have determined that GHRP-6 administered alone stimulated an HGH release of 40 ng/ml in test subjects[10]. The same study determined that when combined with a GHRH (such as Mod GRF 1-29), the resultant HGH release was determined to be 130 ng/ml.
Expectations and Results from GHRP-6 Doses
Results and expectations from an HGH secretagogue such as GHRP-6 should be all of the same effects that any other form of Human Growth Hormone would provide. This includes fat loss, muscle mass increases, strength gains, healing and repair of joints and connective tissue, and a plethora of other benefits and changes. An important note to make is that the effects from any HGH application, whether it be an endogenous release from a GHRH or synthetic HGH administration, will all occur rather steadily over a longer period of use. Dramatic results within weeks are never to be expected, but with proper nutrition and training, dramatic performance and physique changes should occur steadily over the course of several months of application. For more information on HGH specific results and expectations, please see the Human Growth Hormone profile.
GHRP-6 References:
[1] Blockade of the growth hormone (GH) receptor unmasks rapid GH-releasing peptide-6-mediated tissue-specific insulin resistance. Peñalva A, Carballo A, Pombo M, Casanueva FF, Dieguez C. J Clin Endocrinol Metab. 1993 Jan;76(1):168-71.
[2] Blocked growth hormone-releasing peptide (GHRP-6)-induced GH secretion and absence of the synergic action of GHRP-6 plus GH-releasing hormone in patients with hypothalamopituitary disconnection: evidence that GHRP-6 main action is exerted at the hypothalamic level. V Popovic, S Damjanovic, D Micic, M Djurovic, C Dieguez, and F F Casanueva. JCEM 1995 80: 942-7; doi:10.1210/jc.80.3.942.
[3] Growth Hormone (GH) Response to GH-Releasing Peptide-6 in Type 1 Diabetic Patients with Exaggerated GH-Releasing Hormone-Stimulated GH Secretion. Pablo F. Catalina, Federico Mallo, M. Amelia Andrade, Ricardo V. García-Mayor, and Carlos Diéguez. JCEM 1998 83: 3663-3667; doi:10.1210/jc.83.10.3663.
[4] Massive growth hormone (GH) discharge in obese subjects after the combined administration of GH-releasing hormone and GHRP-6: evidence for a marked somatotroph secretory capability in obesity. F Cordido, A Peñalva, C Dieguez, and F F Casanueva. JCEM 1993 76: 819-23; doi:10.1210/jc.76.4.819.
[5] Pathophysiology of the neuroregulation of growth hormone secretion in experimental animals and the human. Giustina A, Veldhuis JD. 1998 Endocr Rev. 19:717–797.
[6] Human Fetal Pituitary Expresses Functional Growth Hormone-Releasing Peptide Receptors. Ilan Shimon, Xinmin Yan, and Shlomo Melmed. JCEM 1998 83: 174-178; doi:10.1210/jc.83.1.174.
[7] The Impact of Cranial Irradiation on GH Responsiveness to GHRH Plus GH-Releasing Peptide-6. Vera Popovic, Sandra Pekic, Ivana Golubicic, Mira Doknic, Carlos Dieguez and Felipe F. Casanueva. JCEM 2002 87: 2095-2099; doi:10.1210/jc.87.5.2095.
[8] Effect of growth hormone (GH)-releasing hormone (GHRH), atropine, pyridostigmine, or hypoglycemia on GHRP-6-induced GH secretion in man. Peñalva A, Carballo A, Pombo M, Casanueva FF, Dieguez C. J Clin Endocrinol Metab. 1993 Jan;76(1):168-71.
[9] Growth Hormone (GH)-Releasing Peptide-6 Requires Endogenous Hypothalamic GH-Releasing Hormone for Maximal GH Stimulation. Naushira Pandya, Roberta DeMott-Friberg, Cyril Y. Bowers, Ariel L. Barkan and Craig A. Jaffe. The Journal of Clinical Endocrinology & Metabolism April 1, 1998 vol. 83 no. 4 1186-1189.
[10] Inhibition of growth hormone release after the combined administration of GHRH and GHRP-6 in patients with Cushing’s syndrome. Leal-Cerro A, Pumar A, Garcia-Garcia E, Dieguez C, Casanueva FF. Clin Endocrinol (Oxf). 1994 Nov;41(5):649-54
