The prostaglandin synthase inhibiting ability of maternal plasma and the onset of human labor.

Using an enzyme incubation-radioimmunoassay technique we have cross-sectionally studied the prostaglandin synthase inhibiting ability of plasma in relation to human pregnancy. The inhibitory potency of human plasma did not change with the onset of pregnancy, at parturition or during the puerperium. A significant decrease in potency did occur however in the third trimester of pregnancy. This preparturient decrease raises the possibility of a role in the onset of human labor for the factor(s) causing the inhibition.