INSULIN-RECEPTORS IN SYNCYTIOTROPHOBLAST AND FETAL ENDOTHELIUM OF HUMAN PLACENTA - IMMUNOHISTOCHEMICAL EVIDENCE FOR DEVELOPMENTAL-CHANGES IN DISTRIBUTION PATTERN

The localisation of insulin receptors (IR) was investigated on cryosec tions of human non-pathologic first trimester and full term placentae by indirect immunohistochemistry with three different monoclonal antib odies (MABS). In placentae from 6 to 10 weeks post-menstruation (p-m.) , only syncytiotrophoblast was stained, predominantly that of mesenchy mal villi and syncytial sprouts, which are areas of high proliferative activity. In placentae from 11 to 14 weeks p-m., endothelial cells co mmenced to react with the IR MABS and the syncytiotrophoblast was less intensely labelled than at weeks 6 to 10 p-m. In term placentae, the microvillous membrane of the syncytiotrophoblast showed only patches o f weak immunoreactivity. In contrast, the endothelial cells in the pla centa but not in the umbilical cord were strongly stained. The amnioti c epithelium in the chorionic plate and fibroblasts in the stroma were conspicuously labelled. The data indicate: (I) the receptor density o n villous syncytiotrophoblast decreases and that of fetal endothelium increases throughout gestation; (2) syncytiotrophoblast of human term placentae expresses a low level per unit area of surface IR; and (3) t he majority of TR in human term placentae is located in fetal endothel ium. Apart from yet unknown functional effects of maternal and fetal i nsulin at the placental barrier, the results suggest a growth promotin g effect on the trophoblast of maternal insulin in first trimester as well as developmental effects of fetal insulin on the fete-placental v essels at term.