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(also, lactogenic hormone), in mammals, a hormone that controls lactation.
Prolactin is a protein with a molecular weight of 23–24 × 103. In 1969, C. Lee and his colleagues (USA) established the primary structure of prolactin in sheep; 198 radicals of 18 amino acids form a polypeptide chain with three internal disulfide (—S—S—) bonds, which must be preserved for hormonal activity. Prolactin is synthesized in special acidophilic cells of the anterior lobe of the pituitary gland; its formation is controlled by a special substance that is produced in the hypothalamus. In women, the concentration of prolactin in the blood increases during pregnancy from 5–10 to 200 nanograms per milliliter; sucking during breast-feeding further stimulates the secretion of prolactin.
The mechanism of action of prolactin consists in binding with a specific receptor in the plasma membrane of the secretory alveolar cell, which results in the activation of the enzyme protein kinase and the biosynthesis of various types of ribonucleic acids (RNA); subsequently, the synthesis of milk proteins and their secretion into the ducts of the mammary gland is induced. Prolactin has also been found in males, although its functions are not clear.
In mammals, prolactin also promotes the formation of the maternal instinct; in some mammals, for example, rats and mice, prolactin promotes the functioning of the ovarian corpus luteum, which is the derivation of the term “luteotropic hormone,” the earlier name for prolactin.
In lower vertebrates, such as fish and amphibians, the functions of hormones analogous to prolactin are extremely varied; they control, for example, osmoregulation, water metabolism, skin pigmentation, and migration during the reproductive period.
REFERENCESSovremennye voprosy endokrinologii, issue 4. Moscow, 1972. Pages 30–34.
Lactogenic Hormones. Edited by G. E. Wolstenholme and J. Knight. Edinburgh-London, 1972.
Cowie, A. T. The Physiology of Lactation. London, 1971.
B. V. POKROVSKII