Bcl-2 expression delays postpartum involution of pregnancy-induced vascular changes in the human placental bed.

In subinvolution of the placental bed, the uteroplacental (spiral) arteries that had undergone physiologic changes to accommodate the needs of the placenta and fetus during pregnancy fail to involute and avert to their nonpregnant state. Because expression of bcl-2 oncoprotein is associated with inhibition of apoptosis and prolonged cell survival, we examined its expression in third-trimester human placental bed tissue and in uterine tissue from women presenting with postpartum hemorrhage in which a diagnosis of involution or of subinvolution of the placental bed was made. bcl-2 oncoprotein was not detected in the uteroplacental arteries during the third trimester of pregnancy but was seen in involution and, more strongly, in subinvolution of the placental bed. Extravillous trophoblast was weakly stained in pregnancy and in the postpartum specimens, whereas glandular epithelium was stained to a variable degree and intensity. The findings suggest that involution and subinvolution of the placental bed are morphologic entities that lie in the spectrum between complete resolution and noninvolution of pregnancy-induced changes and that bcl-2 is associated with subinvolution of the uteroplacental arteries.