Can spermatogenesis be maintained quantitatively in intact adult rats with exogenously administered...

It is well established that testosterone (T) is required to maintain spermatogenesis in the mammalian testis, presumably acting through a receptor mechanism, as elsewhere. It is puzzling, however, that the T concentration that is required to maintain spermatogenesis quantitatively in intact adult rats (15-20 ng/ml) is well in excess of the concentration required to saturate testicular androgen receptors. If, indeed, T regulation of spermatogenesis is mediated through the androgen receptor, 5 alpha-dihydrotestosterone (DHT) would be expected to more effectively maintain spermatogenesis than T because of its greater affinity for, and slower rate of dissociation from, the androgen receptor. To test this hypothesis experimentally, the quantitative relationship between the intratesticular concentration of exogenously administered DHT and the maintenance of germ cell production was examined in intact rats in which endogenous T production was suppressed. To this end, rats received increasing doses of DHT via polydimethylsiloxane implants of 6-36 cm in length for 8 weeks. In each DHT-treated rat, serum luteinizing hormone (LH) concentration was reduced to below the limit of detectability by radioimmunoassay (RIA), and intratesticular T concentration was reduced by > 90%. Serum and intratesticular DHT concentrations increased with increasing implant size. The serum and intratesticular concentrations of 5 alpha-androstane-3 alpha, 17 beta-diol(3 alpha-Diol) were consistently higher than DHT concentrations because of conversion of DHT to 3 alpha-Diol. Spermatogenesis was maintained qualitatively in some rats that received implants of 6 cm, in most rats that received implants of 12 cm, and in all rats that received implants of 18 cm.(ABSTRACT TRUNCATED AT 250 WORDS)