Alpha-hypophamine; manufactured versions – syntocinon and pitocin (both synthetic oxytocin); carbetocin (an analogue of oxytocin with similar structure)
Oxytocin is a hormone which is produced in the hypothalamus and is secreted into the bloodstream by the posterior pituitary gland. Secretion depends on electrical activity of neurons in the hypothalamus; it is released into the blood when these cells are activated.
The two main actions of oxytocin in the body are contraction of the womb (uterus) during childbirth and lactation, the process of making and releasing milk from the breast. Oxytocin stimulates the uterine muscles to contract during labour, and also increases production of prostaglandins, which increase the contractions further. Manufactured oxytocin is sometimes given to induce labour if it has not started naturally or it can be used to strengthen contractions to help childbirth. In addition, manufactured oxytocin can be used to speed up delivery of the placenta after the baby has been born, and can reduce the risk of heavy bleeding by contracting the uterus. During breastfeeding, oxytocin promotes the movement of milk through the ducts in the breast, allowing it to be excreted via the nipple. Oxytocin is also present in men, playing a role in sperm transport and production of testosterone by the testes.
In the brain, oxytocin acts as a chemical messenger and has an important role in human behaviours including sexual arousal, recognition, trust, romantic attachment and mother–infant bonding. As a result, oxytocin has been called the 'love hormone'.
Oxytocin production and secretion is controlled by a positive feedback mechanism whereby release of the hormone causes an action that stimulates more of its own release. For example, when contraction of the uterus starts during childbirth, oxytocin is released. This stimulates more contractions and more oxytocin to be released. In this way, contractions increase in intensity and frequency.
There is also a positive feedback involved in the milk-ejection reflex. Stimulation of the nipple during breastfeeding leads to increased oxytocin production and secretion into the blood, which then causes milk to be secreted from the breast. The positive feedback cycle is maintained until the baby stops suckling. The production of oxytocin during childbirth is also self-limiting; namely the release of the hormone is stopped once the baby is delivered.
Currently, the implications of having too much oxytocin are not clear. High levels have been associated with benign prostatic hyperplasia, a condition which affects the prostate gland in more than half of men over the age of 60. This may cause difficulty in passing urine. It may be possible to treat this condition by manipulating oxytocin levels; however, more research is needed before any possible treatments are available.
Similarly, it is not fully understood at present if there are any implications of having too little oxytocin in the body. A lack of oxytocin in a mother who is breastfeeding would prevent the milk-ejection reflex and prevent milk from being produced.
Low oxytocin levels have been linked to autism and autistic spectrum disorders (e.g. Asperger syndrome) – a key element of these disorders being poor social functioning. Giving oxytocin has also been shown to help babies with Prader Willi Syndrome who have problems with feeding. Some scientists believe oxytocin could be used to treat these disorders. Low oxytocin has been linked to depressive symptoms and it has been proposed as a treatment for depression. However, there is not enough evidence at present to support its use for any of these conditions.
Last reviewed: Oct 2023
