GASTRIN (Greek gaster a stomach) — the hormone produced by a mucous membrane of preferential antral department of a stomach, stimulating activity of gastric glands through blood. Causes secretion of a gastric juice, influences secretory processes and in other glands, and also went on motility. - kish. path.
Was opened by Adkins (J. S. Edkins, 1905) who showed ability of extracts from an antral part of a stomach at intravenous administration to excite gastric secretion. Originally these data did not attract interest as it was already known that various fabrics extracts are in a varying degree capable to cause secretion of a gastric juice. Again these data drew to themselves attention when it became clear that extracts from a mucous membrane of antral department of a stomach contain a histamine and other agent stimulating secretion who is not destroyed by a histaminase called later by gastrin.
A specific place among works on studying of the nature of gastrin is held Komarov's research (S. A. Komarov, 1938, 1942) which established its proteinaceous nature. R. A. Gregory and Tracey (N. J. Tracy) who developed a method of allocation and purification of hormone studied its properties and structure, and further together with G. W. Kenner and finally confirmed with Bentley (R. N. of Bentley, 1966) also a chemical structure of gastrin, having received it in the synthetic way. By them it was established that G. represents peptide about a pier. weighing 2200, consisting of 17 amino-acid remains and amide group.
In N-trailer situation in G. there is a closed group — pyroglutaminic to - that, cover the COOH end of a molecule amidirovan. Existence of 5 remains glutaminic to - you give to G. silnokisly character. An active center of hormone is the COOH trailer fragment of a molecule from 4 amino-acid remains and amide group.
From a mucous membrane of an antral part of a stomach two types of gastrins — gastrin I and gastrin II which differ only with the fact that the hydroxylic group of the rest of tyrosine in gastrin II in the 12th situation is sulphated are allocated. On the nature of action and activity gastrin II is identical to gastrin I.
Gastrins of the person and various animals are purely received (pigs, sheep, dogs). All of them are very close to each other, differ in only one-two amino-acid remains in molecular composition.
At blood serum of the person there are three types of G.: one about a pier. weighing 2200 (amide of heptadecapeptide) — about 2% of total quantity of G. make; another about a pier. weighing 7000 — is considered as the main form circulating in blood G. (more than 70% of total quantity) and, at last, the third — with even big a pier. it is powerful making 18% (believe that it. corresponds synthesized, r to a mucous membrane of intestines a form of gastrin). Under the influence of proteolytic enzymes, in particular trypsin, from the last two forms; G. with 17 amino-acid remains which hl is released. obr. also causes gastrinny activity.
G.'s concentration in blood serum decides on the help radioimmunol. techniques.
Gastrinny activity is found also in a cardial part of a stomach, but there it is rather small; G.'s presence in a small bowel is established. The mucous membrane of a duodenum has low gastrinny activity (Gregory, Tracey, 1967).
G.'s arrival in blood from a mucous membrane of antral department of a stomach is connected with action of chemical and mechanical irritants. V. V. Savich and G. P. Zeleny (1913) showed that the area of the gatekeeper is that zone from where irritants through local nervous educations cause secretion of gastric glands. It is found out that this influence is transferred with the assistance of G. Himicheskiye (hl. obr. cleavage products of protein and extractives of food), mechanical irritants, influencing nervous receptors in a mucous membrane of an antral part of a stomach, cause G. Solyanaya's release to - that, on the contrary, this process detains: at a certain acidity of contents of an antral part of a stomach G.'s secretion is slowed down. Regulation of release of G. is carried out by a vagus nerve. The food which is in an oral cavity reflex excites gastric secretion, leads to allocation of antral G. which in turn stimulates glands of a stomach.
The effect of effect of hormone is caused not only quantity and speed of its receipt in blood, but also action of other factors defining a functional condition of glands. The vagus nerve strengthens G. Pererezk's action of a nerve (e.g., a section of the bridge at dogs with the Pavlovsk ventricle) leads to considerable decrease in reaction of gastric glands for. Administration of cholinergic substance (urekholin) along with G. strengthens this reaction. Observed in this case secretory reaction nevertheless strongly differs from reaction of the Pavlovsk ventricle. G.'s introduction together with urekholiny in dogs with the Pavlovsk ventricle causes much higher secretion, than in dogs with a geydengaynovsky ventricle. It is explained, apparently, by the fact that, in addition to tonic influence, the nervous system has adaptation and trophic effect on glands, regulates exchange processes and a functional condition of glands.
G.'s ability to stimulate gastric secretion is explained by its action on obkladochny cells of gastric glands. Causes department of a gastric juice with high acidity, but with rather low content of proteolytic enzymes (pepsin and gastricsin); against the background of already developed gastric secretion G.'s introduction has the braking effect.
The question of the mechanism of action of G. on obkladochny cells of gastric glands cannot be considered as resolved yet. According to Koudu (Page F. Code, 1965), various irritants of secretion, including and G., cause local release of a histamine which in turn influences activity of gastric glands in a stomach. From this point of view, the histamine is considered as a final stimulator of obkladochny cells of gastric glands. At the same time, according to most of researchers, such representation needs confirmation.
Glikomakropeptid — a cleavage product a kappa casein pepsin — is inhibitor of action of. At introduction to blood this substance sharply slows down the gastric secretion caused
by G. G. influences also other glands went. - kish. path. In particular, it stimulates production of enzymes in a pancreas and in a nek-swarm of degree strengthens department of pancreatic juice and bicarbonates. So, G.'s introduction to dogs in the conditions of acute experience against the background of effect of secretin causes sharp increase of concentration in juice of all pancreatic enzymes (amylase, a lipase, the general proteinases). Its effect is very close to effect of pancreozymin that, apparently, is directly connected with existence in a molecule of both hormones of the same active group — amide of S-trailer tetrapeptide. In addition, G. strengthens biliary secretion; like secretin, it has gidrokholeretichesky effect on a liver though works much more weakly than secretin. Stimulates motor activity of a stomach, causes strengthening with the subsequent braking of motility of a small bowel, slows down absorption of glucose, sodium, water in a small intestine and strengthens release of potassium. However its ability to stimulate secretion of acid juice with glands of a stomach and enzymes a pancreas is most expressed.
Apply both pure natural or synthetic G., and its synthetic analogs to a research of gastric secretion. Among G.'s analogs the amide of S-trailer tetrapeptide and amide of pentapeptide (Pentagastrinum) containing in addition the rest of beta alanine is most spread. This analog has high gastrinny activity. Entered into blood or subcutaneously G. and Pentagastrinum do not cause considerable by-effects. These drugs use for assessment of a condition of gastric secretion in special clinical trials; they can be applied also in broad medical practice.
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G. K. Shlygin.