Maintenance of complete but quantitatively reduced spermatogenesis in hypophysectomized monkeys by testosterone alone

In order to investigate whether testosterone can maintain spermatogenesis in the absence of FSH in primates, four cynomolgus monkeys were hypophysectomized and implanted with 20 5-cm-long testosterone-filled silastic capsules within 45 min of pituitary ablation. Thereafter the serum levels of testosterone were elevated about 9-fold over presurgical levels. Testicular volumes declined to 60% of presurgical values. Testicular concentrations of testosterone were 50-180% of presurgical levels. Germ cell numbers were reduced to 30-50% of presurgical values and germ cell ratios suggested that the reduced numbers of all advanced germ cells were due to a decrease in the efficiency of proliferation of B spermatogonia. A fifth monkey was left untreated following hypophysectomy. Its serum testosterone was as low as that of castrated monkeys, and the testicular volume declined to 30% of that before surgery. Primitive spermatogonia were the only germ cells present 13 weeks after surgery. Thus, in primates testosterone alone maintains the complete process of spermatogenesis, however, spermatogonial proliferation is impaired in the absence of FSH.