PLASMA-MEMBRANE MEDIATED ACTION OF PROGESTERONE IN AMPHIBIAN (RANA-DYBOWSKII) OOCYTE MATURATION

The mechanism of progesterone action within the ovarian follicle was i nvestigated in Rana dybowskii, by using immobilized progesterone. Fluo rescein isothiocyanate-labeled progesterone 3-O-carboxymethyloxime-BSA (P-BSA) was localized on the outside surface of the denuded oocyte, w hich indicated that P-BSA did not cross the barrier of cell surface. P rogesterone-BSA induced germinal vesicle breakdown (GVBD) of denuded o ocytes in a dose-dependent manner but failed to induce GVBD of follicl e wall-enclosed oocytes. The time course of P-BSA-induced GVBD in denu ded oocytes was similar to that observed with progesterone. Furthermor e, both P-BSA and progesterone induced oocyte maturation in the presen ce of RU486, a well-known nuclear progesterone receptor antagonist. Tr eatment of denuded oocytes with P-BSA resulted in a threefold increase in inositol triphosphate (IP3) and a fourfold increase in diacylglyce rol levels within 10 min. Additionally protein kinase C (PKC) activity was markedly increased by 30 min of incubation following exposure to P-BSA. Such changes were not observed in denuded oocytes exposed to be ta-estradiol-6-O-carboxymethyloxime-BSA, which failed to induce GVBD. These results suggest that progesterone acts initially at the oocyte s urface where it triggers generation of membrane-mediated second messen gers during oocyte maturation in amphibians. (C) 1998 Academic Press.