Neuropeptides and neurotransmitters in human placental villi

The human placenta contains many kinds of bioactive substances which are more or less similar to those from the hypothalamic-pituitary-gonadal axis. Most of the studies were carried out mainly with term placenta. The present study, therefore, was attempted to identify, quantify and characterize these substances in the human placenta at the early pregnancy. Using the RIA, immunohistochemistry, HPLC, tissue culture and intrauterine injection methods, we have found that: (1) many kinds of neuropeptides and neurotransmitters are present in the placental villi; (2) LH-RH, NT and SRIF positive immunoreactive granules are localized in the cytotrophoblast and those of beta-EP, 5-HT positive granules in the syncytiotrophoblast; (3) synthetic LH-RH and dynorphin (Dyn) stimulate the hCG secretion of the early placental villi in vitro, and (4) the antisera of LH-RH, NT, Dyn and NE antagonist-alpha-MPT significantly reduced the number of blastocyst implantations in the early pregnant rat. These results indicate that in the human placenta there possibly exists a self-regulation mechanism for the synthesis and secretion of placental hormones and neurotransmitters. Therefore, the human placenta can be regarded as a neuroendocrine organ.