Follicle-stimulating hormone stimulates spermatogenesis in the adult monkey.

A 2-fold increase in the numbers of germinal cells was observed in the seminiferous epithelium of cynomolgus monkeys treated with 15 IU FSH twice a day during 28 days. No effect was seen after 7 days of treatment. After 16 days only the numbers of Apale (Ap) spermatogonia had increased to 200% of the control level while the numbers of B spermatogonia, spermatocytes, and spermatids had increased less (160%, 129%, and 100% of the control level, respectively). In the rhesus monkey after the same dose of FSH an increase in the number of Ap spermatogonia to 152% was found after 16 days. When a dose of 25 IU FSH was administered to cynomolgus monkeys three times per week for 16 days the number of Ap spermatogonia increased to only 131% of the control level. After all treatments no effect on the number of Adark (Ad) spermatogonia was found. It was concluded that the increased levels of plasma FSH caused a specific increase in the number of Ap spermatogonia. The increased number of A spermatogonia gave rise to an increase in the number of B spermatogonia after 16 days of treatment which in turn produced more spermatocytes between 16 and 28 days of treatment. If the FSH was administered for a period of 28 days the number of round spermatids also showed a 2-fold increase. These findings indicate a correlation between plasma FSH levels and the numbers of germinal cells in the seminiferous epithelium. In monkeys treated with 450 IU human CG daily no effect on the numbers of the A spermatogonia was observed.