Effects of Testicular and Ovarian Inhibin-Like Activity, Using In Vitro and In Vivo Systems

Inhibin-like activities in charcoal-treated bovine follicular fluid (FF) and medium from cultured Sertoli cells (SCCM) were assayed in an in vitro bioassay system, using cultured pituitary cells. Addition of both fluids resulted in parallel dose-dependent decreases of the concentration of follicle-stimulating hormone (FSH) in the medium, both in the presence or absence of luteinizing hormone-releasing hormone (LH-RH).
A single injection of FF into immature and adult male and female rats resulted in decreased peripheral levels of FSH, but not of LH, after 4 or 8 h. This decrease was larger and occurred faster in adult female rats than in prepubertal female animals. Injection of FF into adult female rats, immediately after unilateral ovariectomy (ULO) prevented the specific increase of FSH levels, occurring in control animals. This suppression could not be obtained after treatment with steroids.
Daily treatment of adult female or immature male rats for periods longer than 5 days did not result in prolonged suppression of circulating FSH concentrations; LH levels were significantly increased. The female animals showed cyclic vaginal smear changes and normal ovulation; in the male rats testis weight and numbers of spermatogenic cells were reduced.
It is concluded that testicular and ovarian inhibin-like activities have similar properties. Injections of FF into male and female rats cause similar effects on FSH and LH. The effect of FF in ULO-animals suggests that inhibin could play a role in the short-term regulation of the number of developing follicles in the ovary. Injection of FF into male rats causes a probably transient impairment of spermatogenesis through an initial suppression of FSH.