Testis

Gonadotropin Independent Proliferation of the Pale Type A Spermatogonia in the Adult Rhesus Monkey (Macaca mulatta)

Abstract
The goal of this study was to examine the relative roles of testosterone (T) and FSH in the proliferation and differentiation of type Ap spermatogonia in the rhesus monkey (Macaca mulatta). Twenty adult male monkeys were treated with daily injections of a GnRH-receptor (R) antagonist, acyline, to suppress endogeneous gonadotropin secretion during an experiment comprising three phases. Phase 1 established a chronic hypogonadotropic state marked by a profound decrease in testicular size. During phase 2, half of the monkeys were implanted with T-filled capsules and the other half received control implants. T treatment produced circulating T levels of approximately 15 ng/mL and normal testicular T content. At the end of phase 2, monkeys were fitted with indwelling iv catheters and housed in remote sampling cages for the final phase. During phase 3, five monkeys from the T- and non T-treated groups were stimulated with recombinant hFSH. The remaining five monkeys from each group received an infusion of vehicle. On the last day of FSH or vehicle infusion, monkeys were bilaterally castrated after receiving an iv bolus of bromodeoxyuridine (BrdU). BrdU labeling of Ap spermatogonia was robust in the hypogonadotropic group, and was uninfluenced by treatment with T and FSH, either alone or in combination. In contrast, both T and FSH stimulated spermatogonial differentiation and this effect was amplified by combined treatment. We conclude that: (1) marked Ap spermatogonial proliferation occurs constitutively and in a gonadotropin independent manner and, (2) differentiation of Ap into B spermatogonia is absolutely gonadotropin dependent and may be driven by either T or FSH.

Key words: Testis • Follicle-stimulating hormone • Luteinizing hormone • Spermatogenesis • Testosterone

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