MELANOTSITOSTIMULIRUYUSHCHY HORMONE (grech, melas, melanos black, dark + kytos, receptacle, cell + lat. stimulare to drive, induce; synonym: melanotropny hormone, Melonotropinum) — the hormone of an intermediate part of a hypophysis relating to group of proteinaceous and peptide hormones and defiant in vivo and in vitro dispersion of pigmental granules — melanosy in melanocytes, edges is shown by visible darkening of skin.
Increase in contents beta melanotsitostimuliruyushchego hormone in a blood plasma is noted at patients with addisonovy disease (see), Itsenko's disease — Cushing (see. Itsenko — Cushing a disease ) and an ectopic AKTG-syndrome (see. Adrenocorticotropic hormone ).
Intermediate part of a hypophysis of mammals contains two kinds of polypeptide having melanotsitostimuliruyushchy activity: alpha and beta melanotsitostimuliruyushchiye hormones. alpha and Melanotsitostimuliruyushchy hormone of various animals consists of 13 amino-acid remains, the sequence of an arrangement to-rykh is identical to the sequence of 1 — 13 N-trailer site of molecule AKTG, N-trailer serine is acetylated, and C-trailer valine amidirovan. In a hypophysis of the person, free of accurately expressed intermediate part, 19-chlenny peptide, similar alpha melanotsitostimuliruyushchemu to hormone is found; its primary structure is not established.
Beta and Melanotsitostimuliruyushchy hormone has specific specificity. At the majority of mammals beta melanotsitostimuliruyushchy hormone — 18-chlenny peptide, the sequence of an arrangement of the amino-acid remains in Krom it is identical to the sequences 41 — 58 in molecules beta and gamma lipotropinov. Existence of close structural interrelation between an alpha melanotsitostimuliruyushchim hormone and AKTG, on the one hand, both p-melanotsitostimuliruyushchim hormone and beta and gamma lipotropinami — from another, allows to consider that the alpha-melanotsitostimuliruyushchy hormone is formed as a result of enzymic hydrolysis of AKTG and the subsequent modification of the corresponding fragment whereas beta melanotsitostimuliruyushchy hormone is formed during the splitting by tripsinopodobny enzyme beta lipotropina and an intermediate product of hydrolysis — gamma lipotropina.
In addition to alpha and beta melanotsitostimuliruyushchikh hormones, melanotsitostimuliruyushchy activity also their predecessors who are formed in an adenohypophysis have: AKTG, beta and gamma lipotropiny, to-rye contain the general heptapeptide kernel causing their melanotsitostimuliruyushchy activity.
M.'s secretion is regulated by c. N of page, exerting generally tonic inhibitory impact. From a hypothalamus the peptides possessing at nek-ry animals are emitted with the action stimulating or slowing down M.'s secretion. Catecholamines take part in regulation of secretion of M. of. Oppression of release of M. of under the influence of catecholamines (adrenaline, noradrenaline and dopamine) is mediated, apparently, by alpha and adrenergic or dofaminergichesky receptors whereas stimulation of secretion — beta and adrenergic receptors. M.'s release is stimulated also with acetylcholine through cholinergic receptors.
The most studied property M. of — so-called pigmental effect: The m of causes darkening of skin in the person and various animals, and also induces decolourizations of integuments at amphibiouses and darkening of wool at mice. These influences of M. of are partially connected with regulation of the movement of pigmental granules in various chromatophores. The exact mechanism of regulation is unknown. It is supposed that through the receptor on a plasma membrane of a target cell leads M. to activation of adenylatecyclase and increase in cells of quantity of cyclic AMF, to-ry in turn through stimulation of a protein kinase activates microthreads, inactivates microtubules and causes thereby dispersion melanosy. The m of regulates the movement of pigmental granules in the presence of ions of sodium and calcium. Generally pigmental effect of M. of at mammals is caused by stimulation of a melanogenesis in melanocytes of epidermis and hair follicles. Increase in number and the size of melanocytes is carried out through activation of a tyrosinase and is mediated by cyclic AMF. It is established what in in cells of a melanoma of M. of eliminates oppression of a tyrosinase, in normal cells the mechanism of activation of this enzyme is unknown.
Others biol, functions M. of at the person and mammals are not absolutely clear. It is supposed that M., stimulating education and regeneration of rhodopsin, participates in adaptation of eyes to darkness, and also, stimulating a lipogenesis in sebaceous glands, regulates development of a product rich with lipids. the alpha and Melanotsitostimuliruyushchy hormone cosecreted by an intermediate part of a hypophysis of a fruit stimulates growth of a uterus and, influencing sebaceous glands of a fruit, takes part in development of vernix caseosa protecting his skin from influence of an amniotic fluid. Disturbances of regulation of function of sebaceous glands in the pre-natal period can have significant effect on activity of these glands at adults and be the reason of such diseases as an inflammation of sebaceous glands, a hirsutism. Administration of synthetic drugs alpha melanotsitostimuliruyushchego hormone healthy and to persons with signs of a hypopituitarism causes change of the nek-ry behavioural reactions connected with manifestation of emotions and attention, motivation of acts, training and memory; these effects of M. of are caused by direct effect of peptide on c. N of page, most likely on limbic system.
Immunoreactive M. is found in a brain though its identity is not proved to M. The m of or is transported by cerebrospinal liquid from a hypophysis in other departments of a brain, or formed in a brain of predecessors.
All peptides containing the general heptapeptide kernel cause dispersion a melanophore and darkening of leather of a frog, and also stimulate at them formation of corticosteroids. These effects are used for definition biol. M.'s activities of.
Drug M. of — Intermedinum (see) it is used in a wedge, practice.
Bibliography: Biochemistry of hormones and hormonal regulation, under the editorship of N. A. Yudayev, M., 1976; The M e l N and to B. E. Interludes, Chisinau, 1973, bibliogr.; To a s t i n A. J. and. o. Behavioral aspects of melanocyte-stimulating hormone (MSH), Progr. Brain Res., v. 39, p. 461, 1973; bibliogr.; Melanocyte stimulating hormone, ed. by F. J. H. Tilders a. o., Basel, 1977; S i 1-m a n R. E. a. o. Human fetal pituitary peptides and parturition, Nature (Lond.), v. 260, p. 716, 1976.
3. F. Utesheva.