Regulation of quail oviduct phospholipase A2 activity by estradiol.

The phospholipase A2 (PLA2) activity was measured in the oviduct of immature and estradiol benzoate (EB)-treated quails. The pH profiles demonstrate the presence of two PLA2 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 oviduct and poorly stimulated by estradiol; and an alkaline isoform, optimally active at pH 8-9.5 and calcium dependent, with little activity in the immature tissue but markedly stimulated by EB. After EB injection, PLA2 activation occurs at first during the prereplicative period of oviduct cells (+172% at 6 h), it is dose dependent from 0.01 to 1 mg/kg EB and can be prevented by cycloheximide together with ornithine decarboxylase activation. Moreover, estradiol was inactive on cell-free extracts of immature oviducts. These results suggest that EB increases PLA2 activity through gene activation and de novo protein synthesis. The correlation between the early stimulation of PLA2 activity and the proliferation of oviduct cells is discussed.

In vivo inhibition of basal and estrogen-induced phospholipase A2 activities by the triphenylethylene antiestrogen, tamoxifen, in immature quail oviduct.

The effects of tamoxifen on oviductal phospholipase A2 activity were studied in immature quails. Injected alone, from 0.1 to 10 mg/kg tamoxifen significantly reduced basal phospholipase A2 activity 6 h after the injection, independently of the dose used. At 24 h, maximal inhibition (-50%) was observed with 0.1 mg/kg tamoxifen, while higher doses were less effective. Combined with estradiol benzoate, tamoxifen reduced even below the control value (1 mg/kg for 24 h) the increase in phospholipase A2 activity induced by estrogen.