TESTOSTERONE PROMOTES THE CONVERSION OF ROUND SPERMATIDS BETWEEN STAGE-VII AND STAGE-VIII OF THE RAT SPERMATOGENIC CYCLE

Several spermatogenic cell types have been reported to be responsive t o testosterone (T) in vivo. We have proposed that the principal action of T is to facilitate the maturation of round to elongated spermatids during spermiogenesis. To identify T-dependent cell types during sper miogenesis, round spermatid populations were counted using stereologic al techniques in adult rats after T withdrawal and replacement. The nu mber of round spermatids per testis in stages I-III, IV-VI, VII, and V III of the spermatogenic cycle were determined and, based on the known duration of each stage, the hourly production rates of round spermati d populations calculated. Sprague-Dawley rats received 3 cm T and 0.4 cm estradiol implants (TE treatment) for 11 weeks to suppress LH, test icular T levels, and spermatogenesis. To restore sperm production, hig h-dose T (24 cm) implants were then given, and animals were perfused 0 , 2, 4, and 7 days later. Total testicular T levels were suppressed to 2.9% of control levels by TE treatment and significantly increased (P < 0.05) after 2 days of high-dose T, to remain between 7-12% of contr ol. The hourly production rates of round spermatids between stages I a nd VII were suppressed to 29-35% of control by TE treatment and remain ed unchanged by high-dose T administration. Stage VIII round spermatid hourly production rates however, were markedly reduced to 5% of contr ol by TE treatment and increased significantly (P < 0.05) to 27% of co ntrol after 4 days of high-dose T. The efficiency of conversion of spe rmatids through spermiogenesis was estimated from the ratios of the ho urly production rates of successive spermatid groups. The conversion o f spermatids between stages I-VII of the cycle did not differ from con trol regardless of the treatment. However, the conversion of round spe rmatids between stages VII and VIII was markedly suppressed to 16% of control by TE treatment and was then normalized after 4 days of high-d ose T administration. We conclude that the conversion of round spermat ids between stages VII and VIII is a highly T-dependent step during sp ermiogenesis.