Androgen and estrogen levels in the plasma of Pleurodeles waltl, Michah., during the annual cycle. II. Female cycle.

Sex steroid levels in the plasma of the female Pleurodeles waltl were determined by radioimmunoassay of blood samples taken monthly from each newt during an 18-month period. Estradiol-17 beta levels were relatively high (greater than 1 ng/ml) but androgen levels were higher (2-30 ng/ml). Androgen and estradiol-17 beta levels fluctuated according to season with two annual peaks, in autumn and in March. Testosterone was the principal androgen present in this plasma. Dihydrotestosterone levels were relatively low but showed slight fluctuations during the year. 4-Androstenedione and estrone levels were very low and relatively constant throughout the seasons. Fluctuations of androgen and estradiol-17 beta levels were synchronous between the several newts studied during the year. The ratio [E2-17 beta]/[Androgen] was stable during the major part of the year (0.2-0.3) except in July and August, when it reached the value of 1.0. The seasonal variations in the steroid levels were well correlated to the morphological modifications of sexual characteristics during the year.