Regulation of oxytocin receptors and oxytocin receptor signaling.

The oxytocin (OT) -oxytocin receptor (OTR) system plays a key role in many aspects of mammalian reproduction as well as several other physiological processes such as bond pairing and cardiovascular homeostasis. To manifest these diverse physiological roles, the transcription and expression of the OTR is tightly regulated within reproductive, cardiovascular, and neuronal tissues. The expression of the OTR within the mammalian uterus is regulated during gestation with a peak at the day of delivery. The control of this dramatic increase in expression is mediated in rodent species by a combination of stretch, classical steroid hormone stimulation, and repression. In the human uterus events are less clear, although a prominent role for inflammatory-related rapid-response genes and novel transcription factors such as hMafF (human homologue of chicken musculoaponeurotic fibrosarcoma oncogene family protein F) have been put forward. In the uterus the potent uterotonic actions of OT are mediated by the OTR through G-protein activation to stimulate phospholipase C activity. The activated OTR increases contraction frequency and increases force by sensitizing the contractile apparatus of the myocytes to calcium. This review summarizes the current knowledge of the complex regulation of OTR transcription in the myometrium and the intracellular signaling mechanisms through which OT mediates its potent stimulatory effects.