Dissociation of qualitative and quantitative effects of the suppression of testicular testosterone upon spermatogenesis

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Abstract
The present study examined the quantitative and qualitative effects of suppressed testicular testosterone concentration upon spermatogenesis. Adult male rats were given sc implants of 0.5- to 5-cm long testosterone filled silastic capsules (TC) for 10 weeks. Testicular testosterone concentrations were suppressed to below 5% of the control level in rats receiving 1.5- to 5-cm TC implants. Spermatogenesis was arrested at early spermatids in rats given 1.5-cm TC implants, but was maintained in those given 3- or 5-cm TC implants. The number of A1 spermatogonia was 10-15% higher in rats bearing 0.75- to 1.5-cm TC implants, while a 5-15% reduction in preleptotene spermatocytes was noted in rats receiving 1.5-cm or longer TC implants. Linear regression analysis revealed a significant negative correlation between the number of A1 spermatogonia and the percent yield of preleptotene spermatocytes. This result illustrates the presence of a negative feedback mechanism in the regulation of A1 spermatogonia. The lack of a correlation between the quantitative changes in germ cell number and the hormonal states suggests that factors or local mechanisms independent of the concentration of hormones are involved in the regulation of germ cell differentiation.

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