Seasonal changes in plasma testosterone and 5 alpha-dihydrotestosterone levels in the adult male newt, Cynops pyrrhogaster pyrrhogaster.

Seasonal changes in plasma levels of testosterone (T) and 5 alpha-dihydrotestosterone (DTH) were examined in the adult male Japanese red-bellied newt. The concentration of plasma T increased significantly (p less than 0.05) from January to February and decreased drastically from April to July when it reached its minimum. After the summer decline, plasma T increase rapidly from July to October (P less than 0.05) and reached its maximum in October. Concerning the seasonal fluctuation of plasma DHT levels, three peaks were observed; one, the highest peak, appeared in the middle of May, and two lower peaks in early spring (Feb.-March) and autumn (Sept.-Oct.). In this report, the role of plasma T and DHT in the reproductive cycle is discussed.