Evidence for a major role o inhibin in the feedback control of FSH in the male rat

Summary. Adult rats (16\p=n-\18/group)received a single intratesticular injection of 25, 100 or 400\g=m\lglycerol solution (7:3 in distilled water, v/v). Half of the rats in each group were given implants of testosterone, a testosterone-filled Silastic capsule (1 \m=.\5cm length) to provide serum values of testosterone within the normal range. After 1 week all animals were killed by decapitation. Serum concentrations of gonadotrophins, testos-terone and immunoactive inhibin as well as testicular concentrations of testosterone and bioactive inhibin were determined. Testicular histology was studed in Paraplast-embedded tissue stained with PAS and haematoxylin\p=n-\eosin.Glycerol treatment caused a dose-dependent ablation of spermatogenesis in a distinct area around the site of injection. Serum concentrations of FSH increased proportionally with increasing spermatogenic damage while serum LH and testosterone remained unaltered except with the highest glycerol dose. The rise in serum FSH was significantly correlated with serum (r = \m=-\0\m=.\70,P < 0\m=.\001)and testicular (r = \m=-\0\m=.\66,P < 0\m=.\001)concentrations of inhibin. A less pronounced correlation was found between LH and serum inhibin (r = 0\m=.\48).No correlation was found between the concentrations of LH and testicula