Hypothalamo-pituitary-testicular Function in Male Japanese Monkeys (Macaca fuscata) in Non-mating Season

We examined seasonal changes in serum testosterone and LH, and investigated mechanisms of reduction of testicular function in non-mating season in male Japanese monkeys. Blood samples were collected monthly throughout one year in 5 males, and hCG and LH-RH were administered to 5 and 3 animals, respectively, in non-mating and mating season. Serum testosterone and LH were measured by RIA. Serum testosterone showed the obvious seasonal changes, being low in March to August and high in October to February. Also we found the seasonal changes in LH being low in May to August and high in September to February. When hCG was administered to 5 monkeys in mating season (January), serum testosterone levels increased markedly 30 to 180 min after single administration and showed further increases after continuous administrations for four days. However, in non-mating season (August), serum testosterone showed a little increase for the same treatment as in mating season. These data showed that the reserve ability of testosterone secretion in testis in non-mating season decreased obviously in contrast to mating season. The increase of serum LH and testosterone levels in 3 males in non-mating season (July) after LH-RH single administration were less than those in mating season (December) . In intermediate period (September) between non-mating season and mating season, LH showed higher level than that in mating season but the testosterone level was the same extent as in non-mating season. These data showed that the secretive functions of pituitary LH and testicular testosterone were low conditions in non-mating season, and that in intermediate period the secretive function of pituitary LH was getting to active, but that the secretive function of testicular testosterone remained in depressive condition yet. These findings suggested that one reason for the reduction in testicular function in non-mating season was a decline in secretive function of hypothalamic LH-RH.