Effects of an aromatase inhibitor on testosterone-induced inhibition of thymus growth in immature female rats

Abstract

ABSTRACT The hypothesis was tested that the inhibitory action of testosterone on thymus growth is mediated by its metabolism to oestradiol. Immature female rats were given s.c. implants of silicone elastomer tubing containing 5 or 20 mg testosterone alone, or together with 25 or 50 mg of an aromatase inhibitor 1,4,6-androstatriene-3,17-dione (ATD). Some rats received implants containing 5 mg oestradiol or 5 mg dihydrotestosterone (DHT). After 14 days the thymus was removed and weighed. Body weight gain was similar in animals treated with empty implants, or 5 mg testosterone or DHT, or with ATD alone. The combination of testosterone and ATD significantly increased body weight gain, and oestradiol significantly decreased it. Thymus growth was inhibited by both doses of testosterone and by oestradiol, but not by DHT. ATD alone did not inhibit thymus growth, nor did the lower dose of ATD inhibit the action of testosterone. The higher dose of ATD did, however, significantly reduce the inhibitory action of testosterone on the thymus. The inhibitory action of testosterone on the growing thymus may be due, at least in part, to its conversion to oestradiol. J. Endocr. (1988) 119, 65–67