Amphibian oocyte: a model of a possible regulatory mechanism for prostaglandin E2 and prostaglandin F2 alpha synthesis.

To clarify the possible mechanisms regulating prostaglandin E2 (PGE2) and prostaglandin F2 alpha (PGF2 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, freed 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 PGE2 and PGF2 alpha. In parallel, the same experiments were performed on oocytes with membrane phospholipids labelled with [3H]AA. In addition, the PGE2-9-ketoreductase activity was evaluated through the conversion of [3H]PGE2 into [3H]PGF2 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 PGE2-9-ketoreductase in the oocytes of T. carnifex. In particular, GnRH enhances the activity of PGE2-9-ketoreductase with a consequent increase in PGF2 alpha, while SP inhibits the enzyme which leads to an increase in PGE2. A similar mechanism could also be hypothesized for other vertebrate species.