What do prolactin and oxytocin do in the body?
During breastfeeding, prolactin and oxytocin work together for milk production and release, but they can also play a role in the experience of postpartum anxiety, postpartum depression, or even postpartum psychosis.Below are other relevant biological functions of prolactin:
- Breast development during puberty
- Breast health throughout life
- Production of breast alveoli
- Stimulates the production of milk in the breast alveoli
- Menstuation, including the absence of menstruation
- Headaches (in males)
- Decreased libido (in males)
- Decreased production of sperm (in males)
Prolactin and Oxytocin During Breastfeeding
The two hormones that directly impact breastfeeding are prolactin and oxytocin. These two hormones are both secreted by the pituitary gland and they work together. Prolactin is released by the anterior lobe of the pituitary gland while the posterior lobe releases oxytocin.Prolactin
During pregnancy, prolactin levels in the blood increase and stimulate the growth of breast tissue to prepare it for the production of milk. Milk is not secreted by the breast alveoli at this time though because high estrogen and progesterone levels prevent it. After delivery though, as estrogen and progesterone levels rapidly fall, prolactin is no longer blocked and milk begins being secreted.
When a baby suckles at the breast, prolactin levels increase to stimulate the production of milk. About 30 minutes after the baby begins suckling, prolactin levels are highest (so as to promote the production of milk for the next feeding). During the first few weeks of breastfeeding, the more the baby suckles, the more prolactin (and the more milk) is produced. After this initial period of breast-feeding though, the relationship between the amount of prolactin and the amount of milk produced become looser and less of a 1-to-1 connection.
Prolactin is manufactured at night so nighttime breastfeeding is extremely helpful to promote breastmilk production naturally. In many mothers, prolactin can produce a sleepy or relaxed feeling, so nighttime feedings can actually make some mothers feel more restful. But in mothers who have experienced high levels of trauma in their lives, prolactin production can be distressing–essentially it can have the opposite effect to cause anxiety, depression, or other symptoms of mental illness.
It should also be noted that suckling affects the release of Gonadotropin Releasing Hormone, Follicle Stimulating Hormone, and Luteinizing Hormone. Through its effects on these hormones, suckling and breastfeeding often causes a suppression of menstruation and ovulation.
Oxytocin
While prolactin causes the production of milk, oxytocin causes the breast alveoli to contract such that milk flows into the ducts and is ejected from the nipples. Oxytocin is thus responsible for the milk letdown reflex (also known as the “oxytocin reflex”). Whatever milk has been produced in the breast as a result of prolactin is released for the current feed by oxytocin.
Oxytocin also has powerful psychological effects on mothers and has been shown to impact “mothering” behavior in animals. In humans, oxytocin can cause mothers to experience a state of calmness and stress reduction. As a neuropeptide, oxytocin levels can alter human behaviors associated with attachment, stress, anxiety, and social affiliation. The amygdala has been identified as an important target for oxytocin effects and on the connectivity of the amygdala with the medial frontal cortex, an area of the brain that regulates the emotions and social cognition. Oxytocin is thought to increase emotional bonding between mother and child. Skin-to-skin contact between mother and baby after delivery promotes secretion of oxytocin as well as prolactin.
The release of oxytocin occurs when a mother expects to feed her baby though is also occurs when the baby is suckling. The milk letdown reflex is conditioned over time to occur in response to the mother’s sensations, feelings, intuitions, and situations that cause the mother to think lovingly of the baby. A mother who feels severe physical or emotional pain may have an oxytocin reflex that becomes inhibited. Her milk may stop flowing as a result. Emotional support, comfort, and relaxation can help oxytocin to release properly and for milk to flow properly as a result. However, mothers who don’t receive support may still be able to produce and release milk.
The Oxytocin Reflex / Milk Letdown Reflex involves:
- A tingling sensation in the breasts before or shortly after beginning a feeding
- Milk flowing from the breasts in response to the baby crying
- Milk flowing from the breasts in response to the mother thinking of the baby
- Milk flowing from the other breast during a feeding
- Milk flowing from the breast if suckling is interrupted
- Uterine pain or blood flow from the uterus
- The mother feeling thirsty while breastfeeding the baby
- Slow, deep sucks and swallowing by the baby due to the flow of milk into his or her mouth.
In summary, prolactin and oxytocin work together to produce and release milk for breastfeeding, but they also work together in regard to causing symptoms of postpartum depression, postpartum anxiety, and postpartum psychosis.
Click here to read more about D-MER / Dysphoric Milk Ejection Reflex and how prolactin and oxytocin play a role in this mental health issue that occurs during the postpartum period.
Resources:
• Faron-Gorecka, A. et al. (2023). The Involvement of Prolactin in Stress-Related Disorders. Retrieved January 14, 2024 from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9959798/
• Molitch, M. E. (2005). Medication-Induced Hyperprolactinemia. Retrieved January 15, 2024 from https://www.mayoclinicproceedings.org/article/S0025-6196(11)61587-5/fulltext
• Augustine, R. A. et al. (2017). Prolactin regulation of oxytocin neurone activity in pregnancy and lactation. Retrieved January 15, 2024 from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5451702/
• Retrieved January 15, 2024 from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6874414/
• Bramness, . G. et al. (2012). Amphetamine-induced psychosis-a separate diagnostic entity or primary psychosis triggered in the vulnerable? Retrieved January 22, 2024 from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3554477/
• Lake, C. R. et al. (1987). Cyclothymic disorder and bromocriptine: predisposing factors for postpartum mania? Retrieved January 22, 2024 from https://pubmed.ncbi.nlm.nih.gov/3690486/
• Torner, L. (2016). Actions of Prolactin in the Brain: From Physiological Adaptations to Stress and Neurogenesis to Psychopathology. Retrieved January 22, 2024 from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4811943/
• McNeilly, A. S. et al. (1983). Release of oxytocin and prolactin in response to suckling. Retrieved January 22, 2024 from https://pubmed.ncbi.nlm.nih.gov/6402061/
• Zinaman, M. J. et al. (1992). Acute prolactin and oxytocin responses and milk yield to infant suckling and artificial methods of expression in lactating women. Retrieved January 22, 2024 from https://pubmed.ncbi.nlm.nih.gov/1741218/
• Al-Chalabi, M. et al. (2023). Physiology, Prolactin. Retrieved January 22, 2024 from https://www.ncbi.nlm.nih.gov/books/NBK507829/
• Brody, S. and Kruger, T. H. C. (2006). The post-orgasmic prolactin increase following intercourse is greater than following masturbation and suggests greater satiety. Retrieved January 23, 2024 from https://pubmed.ncbi.nlm.nih.gov/16095799/
• Minakami, H. et al. (1985). Effects of progesterone on prolactin secretion in hypogonadal women. Retrieved January 24, 2024 from https://pubmed.ncbi.nlm.nih.gov/4092671/
• Allen, M. J. & Sandeep, S. (2023). Physiology, Adrenocorticotropic Hormone (ACTH). Retrieved January 24, 2024 from https://www.ncbi.nlm.nih.gov/books/NBK500031/
• WHO (2009). Infant and Young Child Feeding: Model Chapter for Textbooks for Medical Students and Allied Health Professionals. Retrieved February 11, 2024 from https://www.ncbi.nlm.nih.gov/books/NBK148970/
• Sripada, C. S. et al. (2013). Oxytocin enhances resting-state connectivity between amygdala and medial frontal cortex. Retrieved February 11, 2024 from https://pubmed.ncbi.nlm.nih.gov/22647521/
