Paracrinology of endometrial neuropeptides: corticotropin-releasing hormone and opioids.

Human endometrium possesses remarkable secretory properties and the characteristics of a neuroendocrine organ. Epithelial cells of human endometrium express the corticotropin-releasing hormone (CRH) and opioid peptide precursors genes (i.e., proopiomelanocortin, proenkephalin, and prodynorphin) and their end products. Endometrial neuropeptides are under the control of ovarian steroid hormones and locally produced prostanoids and cytokines. Additionally, neuropeptides participate in local paracrine regulatory loops, facilitating communication between endometrial epithelial and stromal cells as well as the interaction between endometrial and myometrial cells. In view of the proinflammatory cytokine properties of CRH, we postulate that endometrial CRH may participate in intrauterine inflammatory and vascular processes associated with stromal cell decidualization and blastocyst implantation. Additionally, given the myorelaxant actions of opioids these endometrial neuropeptides may participate in the control of myometrial contractility.