Effect of sex, testosterone propionate and trienbolone acetate on the rate of growth and myofibrillar protein degradation in growing young rats.

Abstract

The urinary output of N tau-methylhistidine (3-methylhistidine: 3-Mehis) was determined to evaluate the effect of testosterone propionate (TP, 1 mg/100g body weight per day) and trienbolone acetate (3-oxo-17 beta-hydroxy-4,9,11-estratriene acetate, TBA 1 mg/100g body weight per day) on the rate of myofibrillar protein breakdown in young growing intact and adrenalectomized (AdX) male and female rats. Injections were given subcutaneously for 14 days. Body weight changes were recorded daily throughout the experiment. Compared with the intact control rats, male-AdX rats had a significant (p less than 0.05) reduction in both growth and 3-Mehis output (and, therefore, a reduction in the rate of myofibrillar protein degradation). Administration of the anabolic steroids to these rats had no significant effect on growth but increased the rate of 3-Mehis output to the normal range in the case of TP, and above the normal range (p less than 0.05) in the case of TBA. However, compared with the intact female rats, female-AdX rats showed a significant (p less than 0.05) increase in 3-Mehis output. Administration of either TP or TBA to these animals significantly (p less than 0.05) increased growth and reduced 3-Mehis output. The response of myofibrillar protein degradation in AdX rats to TP or TBA administration is strongly dependent on the sex of the animals. The anabolic action of TP and TBA, especially in female rats, may be mediated through an antagonistic effect to the catabolic effects of oestrogens and glucocorticoids.