Distribution of inhibin in testes of neonatal, pubertal, and adult rats

Localization of inhibin in human testes by immunoperoxidase technique

Immunohistological studies on the localization of inhibin in human testes were carried out to investigate the cell types involved in inhibin synthesis/storage. The paraffin embedded testicular tissues were stained by an indirect immunoperoxidase technique. Specific antiserum to human testicular inhibin generated against the homogenous preparation of human testicular inhibin at our laboratory was used as the first antibody. Inhibin was found to be localized in Sertoli cells, spermatogonia, and primary spermatocytes. A weak positive reaction was also observed in spermatids. Interestingly, Leydig cells showed positive reaction indicating presence of inhibin in these cells too.

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

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 follicle-stimulating hormone (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 being markedly displaced to the right as the age increased, leading to a fivefold 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, thus 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. Moreover, SCM reversed the stimulatory effect of 17 beta-estradiol on both spontaneous and LHRH-induced LH and FSH release, whereas the stimulatory effect of progesterone on FSH release was 50-80% inhibited. The present data show that inhibin activity of Sertoli cell origin can exert marked interactions with sex steroids in the control of gonadotropin secretion. These data also demonstrate that the inhibin component is an important factor in sexual maturation of the rat and that high FSH levels of 10-day-old rats could suggest a modulation by a nonandrogenic factor of gonadotropin secretion in developing rats.