Oxytocin is a hormone found in mammals including humans. It is synthesized in the hypothalamus by magnocellular neurosecretory cells and released from the posterior lobe of the pituitary gland. It seems to function to encourage bonding and the formation of trust between people, and is also related to the facilitation of birth, breastfeeding, and orgasm as well as the development of romantic love.
Oxytocin is a peptide of nine different amino acids: cysteine, tyrosine, isoleucine, glutamine, asparagines, cysteine, praline, leucine, glycine (abbreviated CYIQNCPLG). It is almost identical to vasopressin, with the single difference being that vasopressin has argine or lysine in the position of leucine. Oxytocin is often found bound to neurophysin, a carrier protein.
Oxytocin's physical effects on humans include uterine contractions just prior to birth that enable cervical dilation, and the contractions during the second and third stages of labor. It is also involved in the letdown reflex in breastfeeding that releases milk from the myoepithelial cells into the lactation ducts. When breastfeeding for the first few weeks, this dual action of oxytocin can cause mildly painful contractions in the uterus. It also plays a little-understood role in orgasm; oxytocin levels in the blood of both males and females are significantly elevated during sexual arousal and orgasm. It may facilitate sperm transport in ejaculation through the same mechanism it uses to induce the letdown reflex.
Perhaps even more important than the physical effects are the effects of oxytocin on the emotions. Sheep and rats who are given oxytocin antagonists after giving birth do not exhibit maternal behavior toward their newborns, and virgin sheep females given a cerebrospinal fluid injection of oxytocin show maternal behavior toward foreign lambs.
Oxytocin seems to act similarly on humans. Levels of oxytocin are high among people who state they are falling in love, and it seems to also mediate other forms of bonding like friendship and family relationships. People who have sociophobic behaviors improve after being treated with oxytocin.
In a Brave New World sort of twist, oxytocin administered nasally generates trust in humans, according to studies. Experimental subjects who have taken oxytocin are twice as likely to show high trust toward others in a study. Yet, when the same subject with the same dose is told he or she is interacting with a computer, their behavior does not change in relation to not having a dose of oxytocin. (see Kosfeld 2005). Though it's easy to see where this might have excellent application in social anxiety disorders and other behavioral problems like autism, it is also easy to see where it could be misused by manipulators.
Oxytocin can also affect different anti-stress functions, such as the reduction of blood pressure and cortisol levels, reducing anxiety, and increasing tolerance to pain. It can also inhibit the development of tolerance to addictive substances like opiates or alcohols, but it reduces the withdrawal symptoms as well in animal testing.
Applications of Oxytocin
Oxytocin analogues like Pitocin is used to encourage uterine contractions and to help placental coagulation after the baby is delivered. Oxytocin inhibitors are being used in some countries to suppress premature labour with excellent effect. And the same oxytocin nasal spray used in the trust experiments can be used to encourage the letdown of milk and easier breast feeding.
Web Resources On Oxytocin
Role in Maintenance of Relationships
Physiologic Effects of Oxytocin
Book Resources On Oxytocin
The Oxytocin Factor: Tapping the Hormone of Calm, Love, and Healing by Kerstin Uvnas Moberg, et al
Vasopressin and Oxytocin: From Genes to Clinical Applications by D. Poulain et al