Progesterone induction of phospholipid methylation and arachidonic acid turnover during the first meiotic division in amphibian oocytes.

Progesterone is the physiological stimulus that acts at the amphibian oocyte plasma membrane to induce the meiotic divisions. Rana oocytes were preincubated with [3H]-arachidonic acid, [3H]-methionine and/or [14C]choline. Total and plasma membrane phospholipids were monitored during the first 2 h after induction with progesterone. A transient increase in methylation of phosphatidylethanolamine during the first 10 minutes coincided with an increased Ca2+ efflux and was followed by increased arachidonic acid incorporation into phosphatidylcholine during a period of increasing membrane conductance. The labeled phospholipids disappeared sequentially 5-90 min after the hormone stimulus, suggesting that activation of phospholipases A2 and/or C occur as part of a cascade of membrane events.