noun, plural: prolactins
A peptide hormone secreted by lactotropic cell in the anterior pituitary of vertebrates, and, in female mammals, is involved chiefly in milk production
Prolactin (PRL) is one of the hormones produced by the anterior pituitary. It is particularly produced and released by the lactotropic cells. Lactotropic cells are acidophilic cells in the anterior pituitary. These cells synthesize PRL on endoplasmic reticulum-bound ribosomes as preprolactin that has N-termnal signal peptide cleaved from the mature form. The conversion of preprolactin to prolactin has been much used as an assay for membrane insertion. The cells secrete PRL in response to hormones (e.g. thyrotropin-releasing hormone) from the endocrine neurons in the hypothalamus. Some of the factors influencing prolactin secretion are mating, estrogen treatment, ovulation, nursing, and eating. PRL is a peptide hormone and in humans it is encoded by the PRL gene. Another important regulator of PRL is dopamine from tuberoinfundibulum neurons of the arcuate nucleus that acts as prolactin-inhibitory hormone. The dopamine acts on the D2 receptors on the surface of the lactotropic cells resulting in the inhibition of prolactin secretion.
In female mammals, PRL stimulates growth of the mammary glands and lactation after parturition. It stimulates the mammary glands to produce milk. PRL may also be involved in the production of progesterone by the corpus luteum. It has a role in the regulation of the immune system (e.g. acting in a cytokine-like manner) and in the pancreatic development as well. It is also an important regulator of metabolism. For instance, it may act as a growth factor binding to cytokine-like receptors thereby influencing hematopoiesis, angiogenesis, and blood clotting. The physiological function of PRL, therefore, may occur in an endocrine, paracrine, or autocrine fashion. It reacts with prolactin receptors and with various cytokine receptors.
In fish, PRL variants, e.g. prolactin A and prolactin B, are presumed to be associated with the regulation of water and salt balance.