In vitro synthesis and release of inhibin in response to FSH stimulation by isolated segments of seminiferous tubules from normal adult male rats.

The production of inhibin by isolated segments of seminiferous tubules from adult male rats cultured in vitro was investigated using a heterologous specific radioimmunoassay. Increasing lengths of tubules (5, 10, 20 and 40 cm) maintained in culture for 4 or 5 days produced increasing amounts of inhibin in vitro. A dose-dependent increase in inhibin production was observed after stimulation with ovine follicle-stimulating hormone (FSH)-s17 (0.1-1000 ng/ml). The tubule segments remain sensitive to FSH stimulation for up to 20 days of culture despite a progressive decline in basal inhibin production, resulting in an increase in the magnitude of the response to FSH stimulation between 0-5, 5-10 and 10-20 days of culture. In the presence of the protein synthesis inhibitor, cycloheximide (50 micrograms/ml), both basal and FSH-stimulated inhibin secretion are inhibited. Testosterone (10(-8)-10(-5) M) does not affect basal inhibin production, although inhibition of the FSH-induced production of inhibin occurred at only the highest dose of testosterone used (10(-5) M). These data demonstrate that the production of inhibin by segments of seminiferous tubules from adult male rats can be used to study the control of inhibin secretion.