PROLACTIN

From Big Medical Encyclopedia

PROLACTIN (synonym: lactogenic hormone, luteotropic hormone, lyuteotropin, mammotropin) — the hormone of the proteinaceous nature produced by a front share of a hypophysis has wide biological activity. The item stimulates growth and development of mammary glands (see. Mammary gland ), activates lactation (see), stimulates growth and function sebaceous glands (see) and growth of internals. The item regulates reproductive processes, stimulates manifestation of a maternal instinct. At male individuals of P. stimulates growth of a prostate (see. Prostate ) and seed bubbles (see). One of the most known effects of P. is stimulation under its influence of proliferation of cells of a ferruterous epithelium of walls of a craw of birds and secretions of a so-called milk, a cut is used for feeding of baby birds. At bony fishes of P. stimulates education on a body surface of slime, edges it is eaten by whitebaits. All this is to some extent similar to P.'s stimulation to function of mammary glands at mammals. Finds luteotropic effect in many rodents of P. and supports function yellow body (see).

On chemical structure of P. represents simple protein (see. Proteinaceous and peptide hormones ), apprx. 50% of a peptide chain in a molecule P. it is curtailed in the form of an alpha spiral. The peptide chain of P. consists of 199 amino-acid remains and contains three disulfide bridges (— S — S-bonds).

The item is formed in acidophilic cells of a front share hypophysis (see). It is synthesized on the ribosomes connected with cytoplasmic membranes of a cytoplasmic reticulum in the form of a preprolaktin, the high-molecular predecessor, from to-rogo later enzymatic eliminating of N-trailer so-called alarm peptide the molecule of active hormone is formed. The item collects in a front share of a hypophysis where its concentration reaches 1 — 2 mg on 1 g of fabric.

Prolactin represents the most important, though not only, the factor defining growth and development of mammary glands. Synergists P. in this respect are somatotropic hormone (see), is oestrogenic (see) and progesterone (see). Lactotropic function of a hypophysis is controlled hypothalamus (see). The item — the only anterior pituitary hormone, secretion to-rogo constantly is suppressed with a hypothalamus and sharply increases after release of a hypophysis from hypothalamic control. Among the substances found in a hypothalamus the direct braking impact on P.'s secretion by a hypophysis is exerted by dopamine. In a hypothalamus are available as well secretagogues of P. K to them the tireotropinrileasing-factor, or tiroliberin, the specific activator of secretion of thyritropic hormone which stimulates as well P.'s secretion (see belongs. Hypothalamic neurohormones ). In a hypothalamus both other stimulators and inhibitors of secretion of P. which nature is not found out yet are found. In experiences of in vitro the braking influence leu enkephalin is shown (see. Opiates endogenous ) on P.'s synthesis by a hypophysis. The direct activating impact on secretion by P.'s hypophysis is rendered by estrogen which, besides, causes decrease in contents prolactin - the inhibiting factors in a hypothalamus that also promotes increase in secretion of the Item. Some pharmaceuticals strengthening effect of dopamine (ergokornin, bromergokriptin), slow down secretion P. Bromergokriptin (Parlodelum) in medicine apply to treatment of the galactorrhoea (the spontaneous expiration of milk from mammary glands) caused by hypersecretion P. Aminazin (Chlorpromazinum) and Reserpinum, on the contrary, stimulate P.'s secretion, most likely, oppressing allocation by a hypothalamus prolactin - the inhibiting factors. Increase in secretion of P. a hypophysis is caused by stressful factors, sexual intercourse, mechanical irritations of a neck of uterus and irritation of nerve terminations in nipples of mammary glands.

In comparison with other belkovopeptidny hormones the speed of exchange of P. in an organism is not really high and time of his semi-life makes apprx. 20 — 30 min.

At the heart of molecular mechanisms biol, P.'s actions its linkng with the specific receptors which are located on a surface of cellular membranes lies. In addition to a mammary gland, such receptors are found in a liver and in many other fabrics producing steroid hormones or sensitive to them. Contacting specific receptors in a mammary gland, P. causes phosphorylation of nuclear proteins (the mechanism of this phosphorylation is not clear yet), activates a transcription and synthesis of a protein kinase, template-RNA, responsible for biosynthesis of enzyme (KF 2. 7. 1. 37), which, catalyzing phosphorylation of proteins of membranes, and also phosphorylation of ribosomes and chromatin, causes changes in a metabolism of a mammary gland.

Oncogenous action of P. is connected with the influence on exchange stimulating it in tissues of mammary glands; long introduction of P. an experimental animal causes not only acceleration of growth and development of mammary glands, but also formation of tumors. Estrogen which after long introduction by an experimental animal, in addition to stimulation of secretion of P. a hypophysis, finds direct oncogenous impact on a mammary gland possess similar action. Other substances increasing P.'s secretion such as Reserpinum, also had oncogenous effect on a mammary gland in an experiment.

The item together with corticosteroids (see) induces and supports a lactation in a puerperal period. It is shown that addition to culture of tissue of mammary gland of mix P., corticosteroids and insulin causes increase in synthesis of casein and lactose, the main nutritious components of milk.

Disturbance of lactotropic function of a hypophysis is expressed in uncontrollable decrease or increase in formation of the Item. Insufficient secretion of P. causes an underdevelopment of mammary glands and disturbance of their function. Patol, increase in secretion of P. leads to a galactorrhoea (see. Lactation ). Sometimes it results from emergence of the tumor of a hypophysis producing the Item. Dysfunction of a hypothalamus is the frequent reason of increase in secretion of P. (see. Hypothalamic syndrome ).

P.'s maintenance in biol, substrates (blood serum, etc.) define by means of biological, biochemical, physical and chemical and radio of immunological methods.

Biol, methods of definition of P. consist in its detection on discoloration of pigment cells at small fishes of Gillichthus mirabilis in an injection site of hormone, on increase in survival of gipofizektomirovanny small fishes of Piccilia latipina after introduction of P. by it, on P.'s stimulation proliferation of cells of a ferruterous epithelium and secretion of a milk in a craw of pigeons, on luteotropic effect of P. on gipofizektomirovanny rats. At addition P. or supporting him biol, liquids to culture of tissue of mammary gland in fabric note specific gistol, and biochemical, changes.

As biochemical, an indicator of presence of P. in biol, substrate use activity N-atsetillak-tozaminsintetazy, the lactose participating in synthesis in tissues of a mammary gland, and intensity of synthesis of casein in a mammary gland which is stimulated

with P. Kachestvenno and quantitatively it is possible to define P.'s maintenance in tissue of a hypophysis also by electrophoretic division of extract from a hypophysis in poliakrilamidny * gel (see. Electrophoresis ).

Radio immunological method (see) is the most highly sensitive and widely used method of definition of P. in biol, liquids. With its help a specification on P.'s maintenance in blood of animals and the person is obtained and considerable volume a wedge, researches is carried out. Nonpregnant women have P.'s maintenance in blood determined by this method fluctuates from 10 to 40 ng/ml and does not change depending on a stage of a menstrual cycle. During pregnancy P.'s maintenance begins to grow in blood with the first trimester and gradually increases in process of increase in duration of gestation, reaching a maximum (200 — 220 ng/ml) before childbirth. After the delivery P.'s maintenance in blood decreases to 100 — 30 ng/ml and increases after each feeding of the child on average to 200 — 300 ng/ml. During pregnancy P.'s maintenance in an amniotic fluid (2000 ng/ml p more) is extremely high whereas in blood of the pregnant woman during the same period P.'s maintenance in comparison with norm can be increased very few. High concentration of P. (200 ng/ml) is defined in blood at newborns and remains P. raised in comparison with content in blood of adults within several weeks after the birth. At a galactorrhoea P.'s maintenance in blood reaches 120 ng/ml and more. At the same time cases of extremely high concentration of P. in blood of nonpregnant women with a tumor of a hypophysis (to 3000 ng/ml) are described in which noticeable signs of a galactorrhoea were not found. It demonstrates that P. is the necessary, but not the only factor defining emergence of a galactorrhoea.

At women apply prolactin which is the drug P. emitted from hypophyses of cattle and pigs and promotes strengthening of a lactation in a puerperal period to treatment of a hypolactation, stimulating lactogenesis and laktopoez. Amount of drug, to the corresponding 70 — 100 conventional units of activity (PIECE), dissolve in 1 ml of a sterile distilled water just before use and enter intramusculary (1 — 2 time a day). Course of treatment of 5 — 6 days.

Form of release: the sterile lyophilized powder in hermetically the corked bottles on 100 and 200 PIECES.

Store in the place protected from light at t ° 15 — 20 °.

See also Gonadotropic hormones .

Bibliography: Biochemistry of hormones and hormonal regulation, under the editorship of N. A. Yudaye-va, page 44, M., 1976; Hormones in blood, ed. by of Page H. Gray a. \. H. T. James, v. 1, p. 280, L. a. o., 1979; Lactogenic hormones, ed. by G. E. W. Wolstenholme a. J. Knight, Edinburgh — L., 1972; Methods in investigative and diagnostic endocrinology, ed. by S. A. Berson a. R. S. Ya-low, v. 2, p. 559, N. Y., 1973.

Yu. A. Pankov.

Яндекс.Метрика