Abstract
The response of the testis to exogenous gonadotropins was examined by determining serum testosterone (T) levels and by observing histopathological changes of the testes using 5–7 month-old males. After a single combined injection of 100 IU plus 15 IU human menopausal gonadotropin (hMG) or 500 IU human chorionic gonadotropin (hCG) plus 15 IU hMG, the serum T levels reached peak values 72 h after administration. During repeated aministration of the combined injection of 100 IU hCG plus 15 IU hMG at five 3-day intervals (Day 0, 3, 6, 9, 12), the serum T levels reached peak values 3 days after the first injection, which were about 3 times higher than the mean serum T levels of adult monkeys. The serum T levels decreased gradually on subsequent days of treatment. Three days after the fifth injection (Day 15), the T levels were equal to the T levels of adult monkeys. The testicular volumes on Day 15 were significantly higher than those on the first day of injection. The histopathological examination of the testes (210, 238 mg) obtained from two treated males revealed hyperplasia and hypertrophy of the Leydig cells and spermatogonias, spermatocytes, and mitotic germinal cells were observed in the seminiferous tubule. Only spermatogonia were found in the one testis (150 mg) obtained from an untreated male. From the above results, it was confirmed that the testes of infant cynomolgus monkeys produced T levels in the same way as the testes of adult monkeys in response to the administration of exogenous gonadotropins. Additionally, the initiation of the spermatogenetic process in the testes of infant monkeys was stimulated by exogenous gonadotropins, therefore suggesting that this method could become a useful means to evaluate the testicular function of infant males.