noun, plural: oxytocins
An antidiuretic peptide hormone (chemical formula: C46H66N12O12S2) produced chiefly by the magnocellular neurosecretory cells of the paraventricular nucleus of the supraoptic nucleus of the hypothalamus, and then stored and released by the posterior pituitary into the bloodstream to reach target cells to exert its effects (e.g. uterine wall contraction and ejection of milk)
Oxytocin is a peptide hormone (1007 D) that is secreted from the posterior pituitary. The posterior pituitary is not glandular unlike the anterior pituitary. Nonetheless, it also releases hormones. Apart from oxytocin, vasopressin is also released from it. Oxytocin is similar to vasopressin in several aspects, e.g. structure. Both oxytocin and vasopressin are nonapeptides with a single disulfide bridge.
It is produced by the magnocellular neurosecretory cells of the paraventricular nucleus of the supraoptic nucleus of the hypothalamus. The axons of these cells terminate in the posterior pituitary. Oxytocin is stored in Herring bodies at the axon terminals. Thus, oxytocin is released from the posterior pituitary into the circulation in order to reach target cells where it exerts its effects, such as the induction of the smooth muscle contraction of the uterine wall (during labor) and the stimulation of nipples (for milk ejection). The action of oxytocin is an example of a positive feedback loop. Uterine contractions stimulate the release of oxytocin and the effect of the oxytocin is to increase uterine contractions. This loop continues throughout labour. The concentration of oxytocin is associated with estrogen level. When estrogen level is increased, the expression of oxytocin receptors in the brain is also increased. This results in the increase in the number of circulating oxytocin.
Non-neural sources of oxytocin are corpus luteum and placenta in females. In males, the interstitial cells of Leydig produce oxytocin. Other non-neural sources in both sexes are retina, adrenal medulla, thymus, and pancreas.
Oxytocin has also gained the moniker, love hormone. It is because it appears to have a role in forming pair bonding, ingroup bonding, and romantic attachment. It also seems to have anti-depressant effects; a deficiency of oxytocin appears to be involved in the pathology of clinical depression in humans.
Pitocin, a synthetic oxytocin, is a medication used to induce and/or speed up labor and to stimulate breast milk production.