SEASONAL-CHANGES IN PLASMA-CONCENTRATIONS OF SEX STEROIDS IN THE SALAMANDER HYNOBIUS-NIGRESCENS

Changes in plasma concentrations of androgens, estradiol-17β, and progesterone were examined throughout the year in Hynobius nigrescens. The highest mean concentration of androgens (312.7 ng/ml) was found in males in the process of spermiation and having just entered the breeding pond in early spring. Plasma estradiol-17β concentration was at its base level in females both before and after the animals had entered the pond. Plasma progesterone concentrations were low throughout the year except during the aquatic phase in March when females possessed some ova within the coelom and many ova in the oviducts and ovisacs after the completion of ovulation. During the terrestrial phase, or nonbreeding season, plasma concentrations of androgens and estradiol-17β were in approximate correspondence with the development of sex accessory structures. This is the first documentation of plasma concentrations of sex steroids in hynobiid salamanders. © 1993 by Academic Press, Inc.