Oxytocin
Oxytocin is a nine-amino-acid cyclic peptide synthesized in hypothalamic supraoptic and paraventricular neurons and released from the posterior pituitary. It acts through a single Gq-coupled oxytocin receptor, raising intracellular calcium. Classically, distending uterine mechanoreceptors trigger reflex oxytocin discharge that intensifies labor contractions, while suckling evokes pulsatile release driving milk let-down through myoepithelial contraction. Synthetic oxytocin is a first-line uterotonic for labor induction and postpartum hemorrhage prevention, and atosiban, an oxytocin receptor antagonist, is used to arrest preterm labor. Beyond reproduction, oxytocin modulates social bonding, trust, stress and pair-bond behaviors, inspiring research into social deficits in autism and related conditions.
