[The regulation of FSH release by the testis. Studies on inhibin]

The FSH release from the hypophysis is suggested to be particularly regulated by a testicular hormone called inhibin. Origin, structure and target organs of inhibin are unknown. Experiments to test some hypotheses in this field are described. Adult male rats, prenatally treated with busulfan, show only Sertoli cells in the semiferous tubules. Experimental cryptorchidism and orchidectomy, however, leads to an increase in FSH levels as observed in normal animals. This indicates the role of Sertoli cells in FSH regulation. Ligation of efferent ducts of testes leads to an increase of FSH levels, too, indicating that an FSH-inhibiting principle cannot be absorbed. Interstitial testis fluid (ITF) of normal rats was applicated to immature female rats. Their FSH release is inhibited, visible in the lower ovarian weight gain following additional hCG-administration. Orchidectomized animals react with a decrease of FSH levels to the application of ITF. Therefore ITF seems to contain a FSH-inhibiting factor. Androgen binding protein-content of epididymes, however, is increased after repeated injections of ITF. It is concluded that testis (probably the Sertoli cells) produces a FSH-inhibiting factor, but ITF contains only small amounts of inhibin.