Oxytocin is a peptide hormone which is synthesized as an inactive precursor in nerve cell bodies in the supraoptic nucleus and paraventricular nucleus of the hypothalamus. The precursor protein is progressively hydrolyzed to produce oxytocin and its carrier protein neurophysin I. Together with neurophysin I, it is packaged into neurosecretory vesicles and transported axonally to the nerve endings in the neurohypophysis, where it is either stored or secreted into the bloodstream.
Oxytocin is also produced by some neurons of the hypothalamus that project to other parts of the brain and to the spinal cord.
Oxytocin is best known for roles in female reproduction as its release causes smooth muscle contraction during parturition and lactation. It is also involved in cognition, tolerance, adaptation, and complex sexual and maternal behavior.
Oxytocin is used as a medication to facilitate childbirth.