Immunohistochemical studies on opioid peptides in the human placenta

The demonstration of the immunoreactive proopiomelanocortin (POMC) peptides beta-endorphin (beta-E), beta-lipotropin (beta-LPH), alpha-melanotropin (alpha-MSH), and corticotropin (ACTH) in the human placenta or in tissue cultures of placental origin using radioimmuno-, bio-, or radioreceptor assay suggested that opioid peptide hormones or their precursors are synthesized in the placenta. In order to test this hypothesis, we tried to localize opioid peptides immunohistochemically. On neighbouring sections of the placenta which were incubated with antisera against beta-E, beta-LPH, alpha-MSH, ACTH, BAM-12 P, BAM-22 P, Heptapeptide, alpha-Neoendorphin and Dynorphin 1-17, the immunoperoxidase method was used. The placenta and the pituitary of perfusion-fixed rats were used for controls. The negative immunohistochemical findings in the human and rat placenta do not support the view that beta-E, beta-LPH, alpha-MSH and ACTH are synthesized in the syncytiotrophoblast of this organ. The site of origin of proopiomelanocortin peptides which are present in the maternal and the fetal plasma most likely is the maternal and fetal pituitary.