Hormonal regulation of a rat seminiferous tubule factor which inhibits LH action on interstitial cells

The cytosol from rat testes or seminiferous tubules contains a factor that markedly reduces the responsiveness of interstitial cells to stimulation by LH. It was noted previously that the inhibitor cannot be found until 35 days of age, suggesting that gonadotrophic stimulation of the testes is of importance for its formation. In the present studies, treatment of intact 20-day-old rats with FSH or with a combination of FSH and LH caused a premature appearance of the inhibitory activity. LH alone had a weak effect. However, hypophysectomy at 20 or 35 days of age did not influence the inhibitor content of the testes. Moreover, when the Leydig cells of adult rats were destroyed selectively by treatment with ethylene dimethane sulphonate, inhibitor levels were unchanged. It is suggested that induction of the Leydig cell inhibitor is under the control of FSH. However, once induced, its regulation seems to be independent of the pituitary gland. In separate experiments, ligation of the efferent ducts of the testes in adult animals did not cause any accumulation of inhibitory activity in the ligated testes, nor could the inhibitor be traced in the caput epididymis. Thus, it does not seem to be secreted into the epididymis, but rather may act as a paracrine factor in the testis.