Oxytocin

What is oxytocin?

Oxytocin is a natural hormone that manages key aspects of the female and male reproductive systems, including labor and delivery and lactation, as well as aspects of human behavior. Your hypothalamus makes oxytocin, but your posterior pituitary gland stores and releases it into your bloodstream.

Hormones are chemicals that coordinate different functions in your body by carrying messages through your blood to your organs, muscles and other tissues. These signals tell your body what to do and when to do it.

Your hypothalamus is the part of your brain that controls functions like blood pressure, heart rate, body temperature and digestion.

Your pituitary gland is a small, pea-sized endocrine gland located at the base of your brain below your hypothalamus.

Synthetic forms of oxytocin

Healthcare providers use synthetic (manufactured) forms of oxytocin — Syntocinon® and Pitocin® — to induce labor in childbirth if it hasn’t started naturally or to strengthen contractions. Healthcare providers also use synthetic oxytocin to speed up delivery of the placenta (the third stage of labor) and reduce the risk of heavy bleeding (postpartum hemorrhage).

What is the function of oxytocin?

The two main physical functions of oxytocin are to stimulate uterine contractions in labor and childbirth and to stimulate contractions of breast tissue to aid in lactation after childbirth.

Oxytocin also acts as a chemical messenger in your brain and has an important role in many human behaviors and social interactions, including:

Sexual arousal.

Recognition.

Trust.

Romantic attachment.

Parent-infant bonding.

The effects of oxytocin on your brain are complex. Scientists are currently researching the role of oxytocin in various conditions, including:

Addiction.

Anorexia.

Anxiety.

Autism spectrum disorder.

Depression.

Post-traumatic stress disorder (PTSD).

Oxytocin and uterine contractions

During labor, when the fetus’s body (usually head) pushes against your cervix, the nerve impulses from this stimulation travel to your brain and stimulate your pituitary gland to release oxytocin into your bloodstream. The oxytocin travels to your uterus and stimulates contractions.

These uterine contractions, in turn, cause your pituitary gland to release more oxytocin, leading to an increase in both the intensity and frequency of contractions. Oxytocin also increases the production of prostaglandins (a group of lipids with hormone-like actions), which move labor along and increase the contractions even more. This enables you to carry out vaginal delivery completely.

Oxytocin and lactation

Once your baby is born, oxytocin promotes lactation by causing contractions of the myoepithelial cells in the alveolar ducts of your breasts. These contractions move milk through your breast tissue.

When your baby sucks at your breast, oxytocin secretion causes the milk to release so your baby can feed. As long as your baby keeps sucking, your pituitary gland continues releasing oxytocin. Once your baby stops feeding, the release of oxytocin stops until the next feeding.

Oxytocin in males

In males, oxytocin plays a part in ejaculation. The hormone contracts the vas deferens to push sperm and semen forward for ejection. Oxytocin also affects the production of testosterone (a sex hormone) in the testes.

How are oxytocin levels controlled?

Oxytocin is one of a few hormones that have a positive feedback loop. This means that the release of oxytocin leads to actions that stimulate your pituitary gland to release even more of it.

Most hormones create negative feedback loops after they’re released, meaning your body releases less of the hormone after it has its effect on your body.

With uterine contractions in childbirth, pressure on your cervix from the fetus baby stimulates your pituitary to release oxytocin. The release continues until your baby is born. With lactation and breastfeeding, your baby’s sucking stimulates your pituitary to release oxytocin to push milk through your breast tissue. The release continues until your baby stops feeding and will restart when your baby feeds again.

What happens when oxytocin levels are low?

Having lower-than-normal levels of oxytocin is rare.

Low levels of oxytocin could stop uterine contractions during the birthing process and prevent milk ejection after giving birth. Although it’s rare, the most common cause of lower-than-normal oxytocin levels is panhypopituitarism, a condition in which all the levels of hormones your pituitary gland releases are below normal.

Low oxytocin levels have been linked to autism spectrum disorder and depressive symptoms. Scientists are still researching the connection between oxytocin and these conditions, and the potential of using synthetic oxytocin as a treatment.

What happens when oxytocin levels are high?

Having higher-than-normal oxytocin levels is very rare for females and is called oxytocin toxicity. It results in an overactive uterus, causing an increase in uterine muscle mass (hypertrophy), which limits pregnancy due to not being enough space in your uterus to hold your fetus.

For males, high levels of oxytocin have been linked to benign prostatic hyperplasia (BPH). BPH is a condition in which the prostate, a walnut-sized body part made of glandular and muscular tissue, grows in size.

The prostate surrounds part of the urethra, which is the tube that carries urine and sperm out of the body. BPH can make it difficult to pee (urinate). It affects more than half males over the age of 60.