Phospholipase A2 activity is increased in guinea pig uterine cervix in late pregnancy and at parturition

Abstract

Release of arachidonic acid from phospholipids by phospholipases A2 (PLA2) is the rate-limiting step in prostaglandin (PG) synthesis. PGE2 and PGF2 alpha are essential intermediates in interstitial collagenase-mediated degradation of type I collagen, a key step in cervical dilatation at parturition. We demonstrate that PLA2 is present in cytosolic fractions of guinea pig cervix and PLA2 activity is increased during cervical dilatation at parturition. In the cervix of nonpregnant animals, PLA2 activity against phosphatidylcholine (PC) and phosphatidylethanolamine (PE) was 13 +/- 6 and 49 +/- 27 pmol.min-1.mg protein-1, respectively. Levels were similar at day 25 of pregnancy. At day 50, PLA2-PC increased to 190 +/- 54 pmol.min-1.mg-1, and PLA2-PE rose to 592 +/- 127 pmol.min-1.mg-1. At parturition (68 +/- 2 days) there were further increases of 49-67%. PLA2 activity declined toward basal levels 2 days postpartum. Almost 50% of the enhanced cytosolic PLA2 (cPLA2) activity at day 50 or at parturition was of high molecular mass and was identified as the "85-kDa cPLA2." Increases in cPLA2 activity at these time points were not, however, associated with increases in cPLA2 protein or phosphorylation of cPLA2, compared with nonpregnant animals. This study suggests that multiple PLA2 enzymes, including cPLA2, are involved in cervical dilatation at parturition.