SEASONAL-CHANGES IN PLASMA PROSTAGLANDIN-F2-ALPHA AND SEX-HORMONES IN THE MALE WATER FROG, RANA-ESCULENTA

Prostaglandin F2α (PGF2α), progesterone, androgens (testosterone + dihydrotestosterone), and 17β-estradiol were measured in the plasma of male frogs, Rana esculenta, by radioimmunoassays. Plasma concentrations of PGF2α. were higher from October to December and peaked in March (prereproduction) and in June (postreproduction). Plasma progesterone levels were relatively low but showed an increase from October to December and in June. Plasma androgen titres rapidly increased in early spring, started to fall during the reproductive period (May), and were lowest in July. 17β-Estradiol levels peaked in March and in June. The annual profile of the plasma PGFα levels was positively correlated with those of progesterone and androgens, while it was not correlated to the estradiol plasma pattern, except in March and June. The increase in plasma PGF2α in the autumn may be related to gonadal recovery. The simultaneous increases in PGF2α and 17β-estradiol, both in March and June, suggest a PGF2α dependent estradiol synthesis, a possibility also supported by the increased plasma 17β-estradiol previously observed in PGF2α treated postreproductive females. The effects of captivity and castration on plasma PGF2α concentrations were also studied during the annual cycle. Captivity was associated with a reduced PGF2α titre, while castration did not modify prostaglandin synthesis, which may point to an extragonadal source of plasma PGF2α. © 1991.