Clinical significance of melatonin receptors in the human myometrium

Objective: To review and update the research on melatonin receptor expression in the human myometrium, in particular as it pertains to uterine contractility at labor. Design: Summary of previous studies with the addition of new data on the transcriptional regulation of melatonin receptor expression in human myometrial cells. Setting: Not applicable. Patient(s): Late-term pregnant volunteers. Intervention(s): Biopsy collection for in vitro analyses provided the original data. More recently, uterine contractions in late-term pregnant volunteers were assessed before, during, and after acute white-light exposure. Main Outcome Measure(s): Melatonin receptor signaling in myometrial cells and uterine contractions in late-term pregnant volunteers. Result(s): Melatonin acts through the MTNR1B melatonin receptor that is expressed in the myometrium at late term to synergistically enhance oxytocin-dependent signaling and contractions. Acute inhibition of endogenous melatonin levels with light reversibly suppresses uterine contractions. Conclusion(s): These results point to a significant role for circulating melatonin in the timing and degree of uterine contractions in late-term pregnancy. Understanding the regulation of melatonin receptors remains a future objective. ((C)2014 by American Society for Reproductive Medicine.)