Endocrine Abstracts

Human placenta expresses a large variety of regulatory factors which are involved in the control of local hormone production, throughout paracrine and/or autocrine mechanisms. Their action may occur in the same tissue where they originate, as well as in the contiguous tissues (fetal membranes, uterus).

By using primary cultures, cell lines, or tissue explants (incubated or perifused) it has been shown that neuropeptides, growth factors, cytokines modulate the release of protein (hCG, hPL) and steroid hormones (progesterone, estradiol), and that a correlation with the regulation of the hypothalamus-pituitary axis exists.

Corticotropin-releasing factor (CRF) is a neuropeptide os 41 amino acids released from the medial eminence of the hypothalamus, acting at the pituitary corticotroph cells to stimulate the release of ACTH and related peptides in response to stress events. Urocortin is a 40-amino acid peptide that belongs to the CRF family and displays 45% sequence homology with rat and human CRF. Recently, two new members of the CRF family have been discovered: urocortin 2 (UCN2) and urocortin 3 (UCN3). UCN 2 shows moderate homology to human CRF (34%) and 37% to respectively.

Placental CRF and urocortins may act an multiple targets: 1) to stimulate ACTH, prostaglandins and oxytocin secretion (involved in the mechanisms leading to parturition); 2) to induce a relaxant effect on utero-placental vasculature and (regulate the utero-placental blood flow); 3) to modulate myometrial contractility. In addition to paracrine actions, CRF and urocortins are measurable in maternal circulation as classical hormones, and change during physiological and pathological (preeclampsia, preterm birth) pregnancy have been described.