Tissue kallikrein in human placenta in early and late gestation

This study was addressed to identify kallikrein mRNA and protein in early, preterm, and term human placenta and to evaluate their temporospatial patte rn. Kallikrein mRNA was expressed in syncytio/cytotrophoblasts and in the e ndothelial cells of the floating villi, with a greater intensity in early s amples (isolated spontaneous abortions and ectopic pregnancies). Cytotropho blasts at the base of the anchoring villi, maternal decidua and decidual ar teries, endothelial cells of chorionic and basal plate blood vessels, and t he amniotic epithelium presented a positive signal. Tissue kallikrein was p redominantly observed in syncytiotrophoblasts and had a greater immunoreact ivity in first-trimester samples. Intraarterial trophoblasts, blood vessels of the floating villi, basal and chorionic plates, and the amniotic epithe lium showed positive immunoreactivity. The sites and variations of the tiss ue kallikrein mRNA and protein in the human placenta, in different stages o f pregnancy, support the hypothesis that this enzyme may participate in the establishment and maintenance of placental blood flow through vasodilation , platelet antiaggregation, cell proliferation, and trophoblast invasion.