Prostaglandin F2 alpha in female water frog, Rana esculenta: plasma levels during the annual cycle and effects of exogenous PGF2 alpha on circulating sex hormones.

Prostaglandin F2 alpha (PGF2 alpha) and sex hormones (progesterone, androgens, and estradiol-17 beta) have been determined in the plasma of female water frog, Rana esculenta, utilizing radioimmunoassay methods (RIA). Plasma PGF2 alpha level increases in autumn-winter when recovery processes interest both gonad and oviduct. The PGF2 alpha plasma highest value has been recorded in October (4.52 +/- 0.58 ng/ml) and the lowest in May (1.43 +/- 0.12). The PGF2 alpha annual pattern is positively correlated to that of estradiol (but not to those of progesterone and androgens). Exogenous PGF2 alpha, injected into intact females during the various phases of the annual cycle, induces an increase of ovarian weight in frogs treated in December and February and an increase of plasma estradiol in postreproductive animals (June). Although preliminary, such results propose a putative implication of PGF2 alpha in ovarian recovery processes and in the interruption of reproductive processes in late summer.