Oxytocin receptor (OXTR) belongs to the vasopressin/oxytocin family of GPCRs and binds cyclic nonapeptide hormones. The oxytocin receptor functions primarily during labor and lactation. There is a dramatic increase in the number of oxytocin receptors just before the onset of labor causing the uterine muscles to become exceedingly sensitive to oxytocin. OXTR causes an inward membrane current that results in smooth muscle contraction during labor and milk ejection during lactation. OXTR also plays a role in natriuresis, kaliuresis and may have an antistress effect. References: The UniProt Consortium. Nucleic Acids Res. 47: D506-515 (2019); Nucleic Acids Res. 2016 Jan 4;44(D1):D733-45, PMID:26553804