Prolactin

Clinic

• PRL also known as lactotropin is secreted from the pituitary gland in response to eating, mating, estrogen treatment, ovulation and nursing.
• It is secreted heavily in pulses in between these events.
• It plays an essential role in
  • Metabolism
  • Regulation of the immune system
  • Pancreatic development
  • Milk production
  • Growth, differentiating and anti-apoptotic factor.
  • Hematopoiesis and angiogenesis and is involved in the regulation of blood clotting

Regulation

• Pituitary prolactin secretion is regulated by endocrine neurons in hypothalamus
• Dopamine through D₂ receptors of lactotrophs causes inhibition of prolactin secretion.
• TRH has a stimulatory effect on prolactin release
• Prolactin is the only anterior pituitary hormone whose principal control is inhibitory.

Function

• It stimulates the mammary glands to produce milk (lactation)
• Increased serum concentrations of prolactin during pregnancy cause enlargement of the mammary glands and prepare for milk production, which normally starts when levels of progesterone fall by the end of pregnancy and a suckling stimulus is present.
• Prolactin plays an important role in maternal behavior.

• In general, dopamine inhibits prolactin but this process has feedback mechanisms.
• Elevated levels of prolactin decrease the levels of sex hormones (Estrogen in women and testosterone in men). The effects of mildly elevated levels of prolactin are much more variable, in women, substantially increasing or decreasing estrogen levels.

• Prolactin is sometimes classified as a gonadotropin although in humans it has only a weak luteotropic effect while the effect of suppressing classical gonadotropic hormones is more important.
• Prolactin within the normal reference ranges can act as a weak gonadotropin, but at the same time suppresses GnRH secretion.
• Physiologic levels of prolactin in males enhance luteinizing hormone-receptors in Leydig cells, resulting in testosterone secretion, which leads to spermatogenesis.

• Prolactin also stimulates proliferation of oligodendrocyte precursor cells. These cells differentiate into oligodendrocytes, the cells responsible for the formation of myelin coatings on axons in CNS
• Other actions include contributing to pulmonary surfactant synthesis of the fetal lungs at the end of the pregnancy and immune tolerance of the fetus by the maternal organism during pregnancy. Prolactin promotes neurogenesis in maternal and fetal brains.

Hyperprolactinaemia

• It is the presence of abnormally high levels of prolactin in the blood.
• Hyperprolactinemia inhibits the secretion of GnRH from hypothalamus, which inhibits the release of FSH and LH from the pituitary gland and results in hypogonadism.
• Hyperprolactinemia may cause
  • Galactorrhea
  • Infertility
  • Abnormal menstrual period
  • Hypogonadism
  • Erectile dysfunction
  • Gynecomastia

• 17% of PCOS have Hyperprolactinaemia

• Long-term hyperprolactinaemia can lead Osteoporosis / Osteolysis
• Etiology: In many people, elevated prolactin levels remain unexplained and may represent a form of hypothalamic–pituitary–adrenal axis dysregulation.