[Studies on the feedback regulation of gonadotropin concentrations in male rats. (III). The effects of testosterone and its metabolites on gonadotropin secretion from rat pituitary cells in culture].

To determine whether dihydrotestosterone (DHT) or estradiol (E2) exerts negative or positive feedback effects on rat pituitary gland, Testosterone (T) metabolite (T, DHT, 5 alpha-androstane-3 alpha, 17 beta-diol:3 alpha-diol or E2) was added to the cultured pituitary cells. Anterior pituitary glands were obtained from 6-week-old male rats. Pituitary cells were prepared by trypsin digestion and incubated with various concentrations of steroid hormones for 72 h to determine the effects of steroid hormones on basal secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH) after 48 h preculture without steroids. Then 10 nM luteinizing hormone-releasing hormone (LH-RH) with appropriate concentrations of these steroid hormones was added to the pituitary cells in culture and incubated for another 6h to determine the effects of steroid hormones on LH-RH induced gonadotropin release. After the incubation, pituitary cells were lysed with 0.1% Triton X100 to measure the intracellular gonadotropin content. The concentration of LH and FSH was determined by radioimmunoassay. T, DHT and 3 alpha-diol stimulated basal FSH but not basal LH secretion, and inhibited both the release of FSH and LH from cultured pituitary cells during incubations with LH-RH in a dose-dependent fashion. Intracellular content of both FSH and LH were increased, and total FSH and not LH was also increased by the addition of DHT in a dose-dependent manner. E2 did not exert any of such effects on pituitary cells in culture. These studies suggest that 5 alpha-reduced metabolites but not aromatized metabolite of T play an important role on feedback regulation of gonadotropin secretion at pituitary level. DHT directly acts on pituitary gland not only to stimulate the production of FSH but also to suppress FSH and LH secretion induced by LH-RH.