Prolactin (PRL) also known as luteotropic hormone (LTH) is a protein that in humans is encoded by the PRL gene.
Prolactin is a peptide hormone discovered by Dr. Henry Friesen, primarily associated with lactation.
In breastfeeding, the act of an infant suckling the nipple stimulates the production of oxytocin which stimulates the “milk let-down” reflex, which fills the breast with milk via a process called lactogenesis, in preparation for the next feed.
Pituitary prolactin secretion is regulated by neuroendocrine neurons in the hypothalamus, the most important ones being the neurosecretory tuberoinfundibulum (TIDA) neurons of the arcuate nucleus, which secrete dopamine to act on the dopamine-2 receptors of lactotrophs, causing inhibition of prolactin secretion.
Thyrotropin-releasing factor (thyrotropin-releasing hormone) has a stimulatory effect on prolactin release. (Wikipedia)
Prolactin has several function:
- The most important of which is to stimulate the mammary glands to produce milk (lactation). Increased serum concentrations of prolactin during pregnancy cause enlargement of the mammary glands of the breasts and increases the production of milk. However, the high levels of progesterone during pregnancy act directly on the breasts to stop ejection of milk. It is only when the levels of this hormone fall after childbirth that milk ejection is possible. Sometimes, newborn babies (males as well as females) secrete a milky substance from their nipples. This substance is commonly known as Witch’s milk. This is caused by the fetus being affected by prolactin circulating in the mother just before birth, and usually stops soon after birth.
- Another effect is to provide the body with sexual gratification after sexual acts. The hormone represses the effect of dopamine, which is responsible for sexual arousal, thus causing the male’s refractory period. The amount of prolactin can be an indicator for the amount of sexual satisfaction and relaxation. Unusually high amounts are suspected to be responsible for impotence and loss of libido.
- Prolactin has been found to stimulate proliferation of oligodendrocyte precursor cells. These cells differentiate into oligodendrocytes, the cells responsible for the formation of myelin coatings on axons in the central nervous system.
- Other possible functions of prolactin include the surfactant synthesis of the foetal lungs at the end of the pregnancy and immune tolerance of the fetus by the maternal organism during pregnancy.
Sometimes the level of prolactine couls be increases – it called hyperprolactinemia.
Hyperprolactinemia is one of causes of dysfunction of the menstrual cycle.
Prolactin is a hormone produced by the pituitary gland, which lies under the brain in the skull. Increased levels of prolactin will occur for several reasons. They occur naturally in pregnancy and lactation but will also be raised in stress. This hormone stimulates lactation in women and its presence in concentrations higher than normal in non-lactating women is termed as “hyperprolactinemia”. Excess of the hormone prolactin can also lead to metabolic imbalances.
High prolactin levels in the blood in non-lactating women may be due to several factors:
- The prolactin producing cells in the pituitary may be hyperactive;
- Certain drugs such as tranquilizers, oestrogens (including oestrogens in birth control pills), pain killers and alcohol may cause a rise in prolactin levels;
- Stress also induces hyperprolactinemia;
- Certain diseases – raised prolactin may be due to liver or kidney disease, ovarian disease such as polycystic ovary syndrome (PCOS);
- A rare type of endocrine tumor in the pituitary gland – “prolactin” producing cells in the pituitary form a cluster – a non cancerous tumor resulting in excess production of prolactin. In cases of very high concentrations of prolactin in non-lactating women, a computed tomography scan needs to be carried out to exclude the pituitary adenoma.
Hyperprolactinemia and lactation
- Amenorrhea (absence of the menstrual cycles and periods);
- Galactorrhea (lactation in non-pregnant and non-breastfeeding women);
- Menstrual disorders (rare cycles, irregular cycles);
- Decreased libido (decreased sexual needs);
- Osteoporosis (lack of calcium in bones).
Can hyperprolactinemia affect a woman’s fertility?
Lactating women do not ovulate. Therefore women with hyperprolactinemia also have ovulatory disorders and following infertility.
Hyperprolactinemia is best treated with a drug called ergo-bromocriptine. The dose of the drug is adjusted depending upon “how high” the levels of prolactin are. Regular intake of the drug will result in the drop in hormone levels and normal ovulation. These women may either ovulate on their own or may need ovulation inducing drugs. It is strongly recommended for women with very high prolactin levels to seek the advice of a neurologist.
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