AMPHIBIAN OOCYTE - A MODEL OF A POSSIBLE REGULATORY MECHANISM FOR PROSTAGLANDIN E(2) AND PROSTAGLANDIN-F2-ALPHA SYNTHESIS

To clarify the possible mechanisms regulating prostaglandin E(2) (PGE(2)) and prostaglandin F-2 alpha (PGF(2 alpha) synthesis, the effects of gonadotropin-releasing hormone (GnRH) and substance P (SP) on the release of these two prostaglandins were studied in the oocytes of the crested newt, Triturus carnifex. Full-grown oocytes of T. carnifex, heed from follicular cells, were incubated in the presence of GnRH or SP and of the inhibitors of several enzymes involved in the release of arachidonic acid (AA) and in the conversion of AA into PGE(2) and PGF(2 alpha). In parallel, the same experiments were performed on oocytes with membrane phospholipids labelled with [H-3]AA. In addition, the PGE(2)-9-ketoreductase activity was evaluated through the conversion of [H-3]PGE(2) into [H-3]PGF(2 alpha). The results showed that GnRH and SP could regulate prostaglandin synthesis through the activation of phospholipase C and diacylglycerol lipase, and through the modulation of PGE(2)-9-ketoreductase in the oocytes of T. carnifex. In particular, GnRH enhances the activity of PGE(2)-9-ketoreductase with a consequent increase in PGF(2 alpha), while SP inhibits the enzyme which leads to an increase in PGE(2). A similar mechanism could also be hypothesized for other vertebrate species.