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    Default Anabolic Steroids Muscle Growth. The Difference of Anabolic and Androgenic Steroids

    I. Use of Suprapharmacologic Doses of Anabolic/Androgenic Steroids (AAS)
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    ABSTRACT
    I. Use of Suprapharmacologic Doses of...
    II. Anabolic Steroids
    III. Androstenedione
    IV. Do Anabolic Steroids Increase Muscle...
    V. Challenging the Conventional Wisdom:...
    VI. Mechanism of Anabolic Effect in...
    VI. Other Consequences of...
    VII. Conclusions
    REFERENCES

    People have been taking testosterone to restore "vitality" since the efficacy of some hormonal component of the testes was first described by Brown-Sequard in 1889. He reported the reversal of his own aging by self-injection of a testicular extract, thereby stimulated a flurry of experimentation into the putative anti-aging effects of testicular hormones long before the identity of testosterone was confirmed. The first use to improve athletic performance occurred shortly thereafter, in 1896. A contemporary of Brown-Sequard self-administered testicular extract, then measured his finger strength. Athletes have been using purified testosterone since it was first available (see a review of this early history in Yesalis et al., 2000). The modern use of anabolic steroids in athletic competition dates from the Olympic competitions during the Cold War era. Russian athletes were putatively the first to use anabolic steroids to improve athletic performance in international competitions. Although the International Olympic Committee banned use of anabolic agents in 1964, the practice spread and probably reached its pinnacle in the athletic programs in Germany during the 1970s (Yesalis et al., 2000).

    Medical use of testicular extract began in the late 1800s. Clinical use of supraphysiological doses of AAS in eugonadal patients for anabolic benefit started in the 1940s. High-dose AAS regimens have been used to promote muscle deposition after burns, surgery, radiation therapy, and aging-related sarcopenia (muscle wasting). Recent uses include treating wasting in human immunodeficiency virus (HIV) and contraception (Bhasin et al., 1996,1997; Amory and Bremner, 2000).


    II. Anabolic Steroids
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    ABSTRACT
    I. Use of Suprapharmacologic Doses of...
    II. Anabolic Steroids
    III. Androstenedione
    IV. Do Anabolic Steroids Increase Muscle...
    V. Challenging the Conventional Wisdom:...
    VI. Mechanism of Anabolic Effect in...
    VI. Other Consequences of...
    VII. Conclusions
    REFERENCES

    All steroids that are anabolic are derivatives of testosterone and are androgenic as well as anabolic, as they stimulate growth and function of male reproductive tract. Individual drugs vary in their balance of anabolic:androgen activity but none of the currently available drugs are purely anabolic. All the anabolic steroids currently used are derivatives of testosterone or are structural modifications of testosterone that influence its pharmacokinetics, bioavailability, or balance of androgenic to anabolic activity. These include testosterone itself, all of the derivatives that are used clinically, as well as numerous plant products that at least claim to possess anabolic actions.

    The testosterone derivatives available in the United States comprise several groups: 1) endogenously produced androgens or their precursors, including testosterone and androstenedione; 2) synthetic derivatives of testosterone with altered metabolic or receptor-binding characteristics; and 3) various uncharacterized plant or animal materials. Testosterone actions represent the combination of several activities. First, it binds to the androgen receptor to exert its androgenic activity. Second, it is 5reduced in some target tissues (including the male urogenital tract, skin, liver, and sebaceous glands) to dihydrotestosterone (DHT), which also acts on the androgen receptor. Finally, it can be aromatized to estradiol and exert estrogenic activities. The latter two actions are highly undesirable in anabolic drugs, 5 reduction because it decreases the ratio of anabolic:androgenic activity and aromatization because of the feminizing side effects.

    Structural and pharmacokinetic properties have been reviewed extensively (Wilson, 1988,1996) and are abstracted briefly here (see Figures 1 and 2).




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    FIG. 1. Model testosterone structure. [Reprinted with permission from Wilson JD 1998 Androgen abuse by athletes. Endocr Rev 9:181–191. Copyright The Endocrine Society.]



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    FIG. 2. Structures of several anabolic steroids. [Reprinted with permission from Wilson JD 1998 Androgen abuse by athletes. Endocr Rev 9:181–191. Copyright The Endocrine Society.]

    1. Testosterone as an injectable form, a transdermal patch, skin cream, and a micronized oral preparation
    2. 17-ß esters of testosterone:testosterone cypionate, propionate, enanthate, and undecanoate. Esterification at this site renders the steroid more fat soluble and delays absorption into the circulation. All but the undecanoate must be injected. Nandrolone 17-ß esters also exist.

    3. 17- derivatives (methyltestosterone, methandrostenolone, norethandrolone, fluoxymesterone, danazol, oxandrolone, stanozol). These derivatives resist metabolism in the liver, so are orally active. This modification is associated with significant hepatic toxicities.

    4. Modifications of the A, B, or C rings (mesterolone, nortestosterone, methenolone, fluoxymesterone, methandrostenolone, northandrolone, danazol, nandrolone, stanozol). These modifications achieve a number of goals, including a) slow metabolism; b) enhanced affinity for the androgen receptor (19-nortestosterone); c) resistance to aromatization to estradiol (fluoxymesterone, 19 nortestosterone); and d) decreased binding of metabolites to androgen receptor (5-reduced metabolites of 19-nortestosterone, 7-19- nortestosterone).

    Structure:activity modifications that limit either conversion to DHT and/or to estradiol partially target specific testosterone derivatives to specific activities. Agents such as fluoxymesterone and 19-nortestosterone (nandrolone) that resist aromatization lack the feminizing side effects of testosterone. 19-nortestosterone possesses another characteristic that increases its anabolic activity because its 5-reduced metabolite has poor affinity for the androgen receptor. Similarly, alpha-methyl-19-nortestosterone is not a substrate for 5 reductase (Sundaram et al., 1995).

    Finally, a number of "natural products" that are purported to exhibit anabolic qualities are marketed freely in the United States due to the exemption of "natural products" from U.S. Food and Drug Administration regulation. Most of these are steroid precursors. Androstenedione and norandrostenedione are two widely marketed precursors. Marketers claim that they are converted into testosterone and nortestosterone (nandrolone). While a small percentage is, indeed, converted, the total amount produced is likely far below that which would have any anabolic activity in a eugonadal male. Finally, there are undefined mixtures with catchy names like "Horny Goat Weed" and "Testicular Extract" that are derived from both plant and animal materials and contain absolutely unknown ingredients.

    All of the drugs listed above possess both anabolic and androgenic activities; none are absolutely selective. However, this ratio varies across a broad range. Table I shows the approximate anabolic:androgenic ratio of a number of clinically used AAS. The range is fairly narrow by clinical standards. All anabolic steroids are virilizing if administered for long enough at high enough doses.



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    TABLE I Anabolic:Androgenic Ratio for Selected Anabolic Drugs

    These values are based on data collected in the 1950s and 1960s from bioassays of varying degrees of specificity and accuracy (see excellent historical review in Kochakian, 1976). Typically, the ability of a test drug to stimulate growth of a skeletal muscle and a reproductive target (prostate gland) was assessed. Two classic methods for establishing anabolic efficacy were the stimulation of growth of the levator ani muscle in the castrated rodent and stimulation of whole-body nitrogen retention in a castrated animal. Neither of these are ideal measures. The levator ani muscle may actually reflect androgenic efficacy of AAS because it can be viewed as part of the reproductive system. Its use as a bioassay for "anabolic" activity has been questioned. While the nitrogen-retention assay is better, it provides an extremely indirect measure of muscle deposition.
    There has been virtually no investigation of the relative anabolic and androgenic properties of AAS since the mid-1970s and none using more modern tools to assess androgen receptor activity. One major goal of this chapter is to summarize recent developments in the molecular pharmacology of androgen receptors that are opening this area up for pharmaceutical development.
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