Modulation of gonadotropin secretion by Sertoli cell inhibin, LHRH, and sex steroids

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Abstract
Sertoli cell culture media (SCM) from 10-, 20-, 30-, 35-, and 40-day-old male Wistar rats were assayed to determine the inhibin activity in anterior pituitary cells in culture. In agreement with previous data, SCM did not affect the luteinizing hormone (LH) spontaneous release at all ages studied, whereas it inhibited specifically FSH spontaneous release by 40% for the 40-day-old rats. Younger animals (10-, 20-, and 30-day-old) showed a 60% inhibition of the FSH basal release. The inhibin activity was also different at all stages studied, the IC50 [50% inhibitory concentration] being markedly displaced to the right as the age increased, leading to a 5-fold difference between 10- and 30- to 40-day-old rats. The same pattern was observed when the LH and FSH responses to 0.3 nM LH-releasing hormone (LHRH) were studied. SCM from 35 day old rats did not alter total LH, whereas total FSH was markedly reduced, suggesting a reduced FSH synthesis in the presence of inhibin. SCM exerts an additive inhibitory effect with dihydrotestosterone on the LH response to LHRH, whereas it reverses the stimulatory effect of the androgen on spontaneous and LHRH-induced FSH release. SCM reversed the stimulatory effect of 17.beta.-estradiol on both spontaneous and LHRH-induced LH and FSH release; the stimulatory effect of progesterone on FSH release was 50-80% inhibited. Inhibin activity of Sertoli cell origin can exert marked interactions with sex steroids in the control of gonadotropin secretion. The inhibin component is an important factor in sexual maturation of the rat and high FSH levels of 10 day old rats could suggest a modulation by a nonandrogenic factor of gonadotropin secretion in developing rats.