Possible roles for prostaglandins E2 and F2 alpha in seasonal changes in ovarian steroidogenesis in the frog (Rana esculenta).

Concentrations of PGE2, PGF2 alpha, androgens and oestradiol in plasma, and ovary weights were measured in the female frog, Rana esculenta, during the annual breeding cycle. Experiments were carried out in vivo to study the effects of PGE2 and PGF2 alpha on plasma sex steroids during the following stages: pre-reproduction (April), reproduction (May), post-reproduction (June) and recovery (October). Experiments were performed in vitro during these stages to evaluate the effects of these two prostaglandins on the secretion of ovarian steroids. Concentrations of PGE2 were low in plasma during winter hibernation, the reproduction and post-reproduction stages, whereas they were high during the pre-reproduction and recovery stages. PGE2 treatment in vivo increased androgen secretion in April, whereas PGF2 alpha treatment increased oestradiol secretion in June and October. In experiments in vitro, PGE2 increased androgen secretion and decreased oestradiol secretion from ovaries collected in April, whereas PGF2 alpha increased oestradiol secretion from ovaries collected in October. These results suggest that a seasonal increase in plasma PGE2 may inhibit breeding activity, probably by stimulating ovarian androgen secretion, whereas, as previously reported, a seasonal increase in plasma PGF2 alpha may inhibit breeding, by stimulating ovarian oestradiol secretion.