Hormones: Oxytocin

Oxytocin is a hormone that acts on organs in the body (including the breast and uterus) and as a chemical messenger in the brain controlling key aspects of the reproductive system including childbirth and lactation, and aspects of human behaviour.


Alternative names for oxytocin

Alpha-hypophamine; manufactured versions – carbetocin, syntocinon and pitocin.


What is oxytocin?

Oxytocin 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 excited.

The two main actions of oxytocin in the body are contraction of the womb (uterus) during childbirth and lactation. Oxytocin stimulates the uterine muscles to contract 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 aid childbirth. In addition, manufactured oxytocin is often given to speed up delivery of the placenta and reduce the risk of heavy bleeding by contracting the uterus. During breastfeeding, oxytocin promotes the movement of milk into the breast, allowing it to be excreted by the nipple. Oxytocin is also present in men, playing a role in sperm movement and production of testosterone by the testes.

More recently, oxytocin has been suggested to be an important player in social behaviour.

In the brain, oxytocin acts as a chemical messenger and has been shown to be important in human behaviours including sexual arousal, recognition, trust, anxiety and mother-infant bonding. As a result, oxytocin has been called the ‘love hormone’ or ‘cuddle chemical’.

Many research projects are undertaken, looking at the role of oxytocin in addiction, brain injury, anorexia and stress amongst other topics.

How is oxytocin controlled?

Oxytocin is controlled by a positive feedback mechanism where release of the hormone causes an action which stimulates more of its own release.  When contraction of the uterus starts, for example, oxytocin is released which 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. When a baby sucks at the breast of its mother, the stimulation leads to oxytocin secretion into the blood which then causes milk to be let down into the breast. Oxytocin is also released into the brain to help stimulate further oxytocin secretion. These processes are self-limiting; production of the hormone is stopped after the baby is delivered or when the baby stops feeding.

What happens if I have too much oxytocin?

At present, the implications of having too much oxytocin are not clear. High levels have been linked to benign prostatic hyperplasia, a condition which affects the prostate in more than half of men over the age of 50. 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.


What happens if I have too little oxytocin?

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 nursing mother would prevent the milk-ejection reflex and prevent breastfeeding.

Low oxytocin levels have been linked to autism and autistic spectrum disorders (eg, Asperger syndrome) – a key element of these disorders being poor social functioning. Some scientists believe oxytocin could be used to treat these disorders. In addition, low oxytocin has been linked to depressive symptoms and it has been proposed as a treatment for depressive disorders. However, there is not enough evidence at present to support its use for any of these conditions.

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