The distribution of pregnancy-associated prostaglandin synthetase inhibitor in the human placenta.
The distribution of pregnancy-associated prostaglandin synthetase inhibitor (PAPSI) has been studied in 181 human placentae and early products of conception using a peroxidase-antiperoxidase (PAP) immunohistological method. PAPSI was detected in amniotic epithelium throughout all stages of gestation. Extravillous trophoblast was PAPSI-positive throughout gestation. Villous trophoblast was PAPSI-positive in the first 12 weeks of gestation, when PAPSI was localized to syncytiotrophoblast but not to cytotrophoblast. Villous syncytio- and cytotrophoblast were both PAPSI-negative from 12 weeks to term. Fetal and maternal polymorphs contained PAPSI at all stages of gestation, as did villous Hofbauer cells. The significance of these findings is discussed in relation to putative functions of PAPSI, particularly the maintenance of pregnancy and control of onset of parturition.