REGULATION OF QUAIL OVIDUCT PHOSPHOLIPASE A(2) ACTIVITY BY ESTRADIOL

The phospholipase A(2)(PLA(2)) activity was measured in the oviduct of immature and estradiol benzoate (EB)-treated quails. The pH profiles d emonstrate the presence of two PLA(2) isoforms in the avian oviduct: a neutral isoform, optimally active at pH 7-7.5 and calcium independent , responsible for most of the hydrolytic activity in the immature ovid uct and poorly stimulated by estradiol; and an alkaline isoform, optim ally active at pH 8-9.5 and calcium dependent, with little activity in the immature tissue but markedly stimulated by EB. After EB injection , PLA(2) activation occurs at first during the prereplicative period o f oviduct cells (+172% at 6h), it is dose dependent from 0.01 to 1 mg/ kg EB and can be prevented by cycloheximide together with ornithine de carboxylase activation. Moreover, estradiol was inactive on cell-free extracts of immature oviducts. These results suggest that EB increases PLA(2) activity through gene activation and de novo protein synthesis . The correlation between the early stimulation of PLA(2) activity and the proliferation of oviduct cells is discussed.