Gastric secretion amino acids

Figure 5-13. Effects of imidazole derivatives on gastric secretion of acid in dogs and susceptibility of diamine oxidase (DAO) and inhibitability of the enzyme by amino-guanidine (AMG). (From Lin TM, Alphin RS, Henderson FG, et al. The role of histamine in gastric hydrochloric acid secretion. Ann NY Acad Sci 99 30-44, 1962.)...

CCK is found in the digestive tract and the central and peripheral nervous systems. In the brain, CCK coexists with DA. In the peripheral nervous system, the two principal physiological actions of CCK are stimulation of gaU. bladder contraction and pancreatic enzyme secretion. CCK also stimulates glucose and amino acid transport, protein and DNA synthesis, and pancreatic hormone secretion. In the CNS, CCK induces hypothermia, analgesia, hyperglycemia, stimulation of pituitary hormone release, and a decrease in exploratory behavior. The CCK family of neuropeptides has been impHcated in anxiety and panic disorders, psychoses, satiety, and gastric acid and pancreatic enzyme secretions. 

The histamine H2-receptor (359 amino acids) is best known for its effect on gastric acid secretion. Histamine H2-receptor activation, in conjunction with gastrin and acetylcholine from the vagus, potently stimulate acid secretion from parietal cells. High concentrations of histamine are also present in cardiac tissues and can stimulate positive chronotropic and inotropic effects via H2-receptor stimulation and activation of adenylyl... 

There are two main classes of proteolytic digestive enzymes (proteases), with different specificities for the amino acids forming the peptide bond to be hydrolyzed. Endopeptidases hydrolyze peptide bonds between specific amino acids throughout the molecule. They are the first enzymes to act, yielding a larger number of smaller fragments, eg, pepsin in the gastric juice and trypsin, chymotrypsin, and elastase secreted into the small intestine by the pancreas. Exopeptidases catalyze the hydrolysis of peptide bonds, one at a time, fi"om the ends of polypeptides. Carboxypeptidases, secreted in the pancreatic juice, release amino acids from rhe free carboxyl terminal, and aminopeptidases, secreted by the intestinal mucosal cells, release amino acids from the amino terminal. Dipeptides, which are not substrates for exopeptidases, are hydrolyzed in the brush border of intestinal mucosal cells by dipeptidases. 

CCK, a 33 amino acid regulatory peptide hormone, regulates motility, pancreatic enzyme secretion, gastric emptying, and gastric acid... 

In general, ethanol in low to moderate amounts, is relatively benign to most body systems. A moderate amount of ethanol causes peripheral vasodilation, especially of cutaneous vessels, and stimulates the secretion of salivary and gastric fluids the latter action may aid digestion. On the other hand, ethanol consumption in high concentrations, as found in undiluted spirits, can induce hemorrhagic lesions in the duodenum, inhibit intestinal brush border enzymes, inhibit the uptake of amino acids, and limit the absorption of vitamins and minerals. In addition, ethanol can reduce blood testosterone levels, resulting in sexual dysfunction. 

As the acidic stomach contents pass into the small intestine, the low pH triggers secretion of the hormone secretin into the blood. Secretin stimulates the pancreas to secrete bicarbonate into the small intestine to neutralize the gastric HC1, abruptly increasing the pH to about 7. (All pancreatic secretions pass into the small intestine through the pancreatic duct.) The digestion of proteins now continues in the small intestine. Arrival of amino acids in the upper part of the intestine (duodenum) causes release into the blood of the hormone... 

Mammals have two isozymes of prostaglandin H2 synthase, COX-1 and COX-2. These have different functions but closely similar amino acid sequences (60% to 65% sequence identity) and similar reaction mechanisms at both of their catalytic centers. COX-1 is responsible for the synthesis of the prostaglandins that regulate the secretion of gastric mucin, and COX-2 for the prostaglandins that mediate inflammation, pain, and fever. Aspirin inhibits both isozymes about equally, so a dose sufficient to reduce inflammation also risks stomach irritation. Much research is aimed at developing new NSAIDs that inhibit COX-2 specifically, and several such drugs have become available. 

Other products from histidine include the hormonal substance histamine formed by decarboxylation, the oxidation product, imidazole acetic acid, and N5- and A/c-methylhistidines. Histamine plays a role in release of gastric secretions and allergic responses (Chapter 5). Drugs (antihistamines) that inhibit its release are in widespread use. The unusual amino acid diphthamide has an unknown function in pro-... 

Protein digestion starts in the mouth and continues in your stomach and small intestines. This is due to pepsin, which is secreted in the saliva and obviously the gastric juice, followed by pancreatic enzymes, then absorbed by the mucosal cells in the small intestines. In short, the digestive system breaks down protein into its peptide amino acid structures so they can be absorbed in the small intestine via the... 

As linear polypeptides, VIP (vasoactive intestinal polypeptide)105), PHI (peptide HI H = N-terminal His, I = C-terminal lie) lo6107) and GIP (gastric inhibitory polypeptide consisting of 43 amino acids)108) are structurally similar to secretin and glucagon. VIP and PHI act as vasodilators, exert hyperglycemic effects, and affect the smooth muscle of the gallbladder. GIP completely blocks gastric secretion. 

Orexin A (from the Greek orexis, "appetite") is a 33 amino acid neuropeptide connected by two disulfide bridges. Orexin A is a powerful stimulant forfood intake and gastric juice secretion. Scientists are studying orexin A to learn more about the regulation of appetite and eating, hoping to learn more about causes and potential treatments for anorexia nervosa. 

Gastric secretion represents a very complex naixture of electrolytes, water, carbohydrates, proteins, peptides, and amino acids, which are partly in solution and partly in more or less stable suspension. The large molecular materials of gastric secretion include enzymes, mucosubstances, serum proteins, peptides and products of proteolytic degradation of gastric proteins and mucoproteins, and blood group substances. 

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