TRENBOLONE ACETATE AND TESTOSTERONE STIMULATE GROWTH IN RATSTHROUGH DIFFERENT MECHANISMS
Trenbolone acetate (TBA) is a synthetic anabolic androgen currently undergoingregistration for use in Australia. In addition to stimulating growth in cattleand sheep, it is effective in female, but not in male rats. Corticosteroidhormones are well-known to retard growth rate at high concentrations, andThomas and Rodway (1982) have found reduced plasma concentrations of cataboliccorticosteroid hormones in TBA-treated female rats and sheep. The aim of thepresent study was to examine the adrenal response of male rats to TBA and tocompare in females the effects of TBA and testosterone.
Wistar rats (7-8 weeks old) were housed individually, allowed free access to astandard laboratory diet, and maintained on a$2 h light 12 h darkness cyclewith lights on at 0700 h. Animals were weighed and injected at 1000 h dailyfor five d a y s . Steroids were dissolved in peanut oil, and injectedsubcutaneously. Male rats (n=8) received either peanut oil (0.2 ml), or TBA(O-8 mg/kg) t females (n=16) received either peanut oil, TBA (0.8 mg/kg), ortestosterone propionate (0.8 mg/kg). Rats were killed at 1700 h, the time ofday when plasma concentrations of corticosterone peak. Blood was collected andplasma was analysed for corticosterone and ACTH concentration.
Table 1 Growth rate (g/day) and plasma concentrations of corticosterone(nmol/l) and ACTH (ng/l) in rats treated daily for 5 days with
androgenic anabolic steroids
Proc. Aust. Soc. Anim. Prod. Vol. 18
In male rats, TBA caused no significant increase in growth rate, and nosignificant change in plasma concentrations of corticosterone. In contrast,female rats treated with TBA showed asignificant (PxO.05) improvement ingrowth rate (97%), and a significant (P<o.os) reduction="" in="" plasmaconcentrations="" of="" corticosterone="" (45%).="" this="" result="" suggests="" that="" tba="" promotesgrowth="" female="" rats="" through="" the="" suppression="" adrenal="" activity.="" testosteronetreatment="" caused="" an="" increase="" growth="" also.="" however,="" thegrowth="" response="" females="" to="" testosterone="" was="" significantly="" (p<o.os)="" less="" thanto="" tba,="" and="" accompanied="" by="" plasma="" concentrations="" ofcorticosterone="" (52%).="" promotegrowth="" different="" mechanisms,="" totestosterone="" <="" span="">may be constrained by increased plasma concentrations ofcorticosterone. Plasma concentrations of ACTH were not altered significantly byeither treatment. Thus, the adrenal gland is a more likely site of action thanthe pituitary, for the inhibitory effect of TBA and for the stimulatory actionof testosterone on plasma corticosterone. It is concluded that the suppressionof adrenal activity by anticatabolic agents can have a profound influence ongrowth in normal female rats.</o.os)>
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M.N. SILLENCE* and M.L. MATTHEWS*
Trenbolone acetate (TBA) is a synthetic anabolic androgen currently undergoingregistration for use in Australia. In addition to stimulating growth in cattleand sheep, it is effective in female, but not in male rats. Corticosteroidhormones are well-known to retard growth rate at high concentrations, andThomas and Rodway (1982) have found reduced plasma concentrations of cataboliccorticosteroid hormones in TBA-treated female rats and sheep. The aim of thepresent study was to examine the adrenal response of male rats to TBA and tocompare in females the effects of TBA and testosterone.
Wistar rats (7-8 weeks old) were housed individually, allowed free access to astandard laboratory diet, and maintained on a$2 h light 12 h darkness cyclewith lights on at 0700 h. Animals were weighed and injected at 1000 h dailyfor five d a y s . Steroids were dissolved in peanut oil, and injectedsubcutaneously. Male rats (n=8) received either peanut oil (0.2 ml), or TBA(O-8 mg/kg) t females (n=16) received either peanut oil, TBA (0.8 mg/kg), ortestosterone propionate (0.8 mg/kg). Rats were killed at 1700 h, the time ofday when plasma concentrations of corticosterone peak. Blood was collected andplasma was analysed for corticosterone and ACTH concentration.
Table 1 Growth rate (g/day) and plasma concentrations of corticosterone(nmol/l) and ACTH (ng/l) in rats treated daily for 5 days with
androgenic anabolic steroids
Proc. Aust. Soc. Anim. Prod. Vol. 18
In male rats, TBA caused no significant increase in growth rate, and nosignificant change in plasma concentrations of corticosterone. In contrast,female rats treated with TBA showed asignificant (PxO.05) improvement ingrowth rate (97%), and a significant (P<o.os) reduction="" in="" plasmaconcentrations="" of="" corticosterone="" (45%).="" this="" result="" suggests="" that="" tba="" promotesgrowth="" female="" rats="" through="" the="" suppression="" adrenal="" activity.="" testosteronetreatment="" caused="" an="" increase="" growth="" also.="" however,="" thegrowth="" response="" females="" to="" testosterone="" was="" significantly="" (p<o.os)="" less="" thanto="" tba,="" and="" accompanied="" by="" plasma="" concentrations="" ofcorticosterone="" (52%).="" promotegrowth="" different="" mechanisms,="" totestosterone="" <="" span="">may be constrained by increased plasma concentrations ofcorticosterone. Plasma concentrations of ACTH were not altered significantly byeither treatment. Thus, the adrenal gland is a more likely site of action thanthe pituitary, for the inhibitory effect of TBA and for the stimulatory actionof testosterone on plasma corticosterone. It is concluded that the suppressionof adrenal activity by anticatabolic agents can have a profound influence ongrowth in normal female rats.</o.os)>
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M.N. SILLENCE* and M.L. MATTHEWS*
