Changes in rat uterine and cervical phospholipase A2 activity following progesterone agonist or antagonist administration at term.

Our previous study revealed that a fall in plasma progesterone (P(4)) level was associated with a transient increase in cytosolic phospholipase A(2) (PLA(2)) activity and prostaglandin F(2)alpha level in the rat uterus and cervix during natural parturition. This study determined the changes in the PLA(2) activities during modulated occurrence of delivery by P(4) antagonist or agonist late in pregnancy. In rats undergoing P(4) antagonist-induced preterm delivery, the PLA(2) activities of both uterine and cervical cytosol significantly decreased 12 h after the challenge and tended to be attenuated within 72 h. The plasma P(4) level altered in a similar pattern. Blockade of delivery by chronic treatment with P(4) agonist was not associated with changes in uterine PLA(2) activity compared with that in normally delivering rats, although there was a persistent rise in cervical PLA(2) activity. The obtained data indicates that the PLA(2) activities in rat uterine and cervical cytosol are not regulated solely by P(4) and that delivery can occur without activation of this enzyme.