Bicarbonate secretion

Ursodiol may slow progression of liver disease. It improves bile flow and may displace toxic bile acids that accumulate in a cholestatic liver, stimulate bicarbonate secretion into the bile, offer a cytoprotective effect, and reduce elevated liver tests. Ursodiol is typically dosed at 15 to 20 mg/kg per day in two divided doses and may be rounded to the nearest tablet size.5,7... 

Prostaglandins, one of the most important epithelial growth factors, inhibit gastric acid secretion and have numerous mucosal protective effects, the most important of which include the stimulation of both mucus and phospholipid production, promotion of bicarbonate secretion, and increased mucosal cell turnover. Damage to the mucosal defense system is the primary method by which HP or NSAIDs cause peptic ulcers. 

Prostaglandins, through their effects on mucous cell secretion, basal bicarbonate secretion, and mucosal growth, are important factors in gastric healing and protection. Inhibition of prostaglandin production by NSAIDs compromises these important protective mechanisms. Finally, the antiplatelet effects of NSAIDs may worsen bleeding complications associated with PUD. 

At pH 4 most bacteria are killed within 30 min, and at physiological luminal pH, 99% of bacteria are killed within 5 min [14], Certain bacteria, like lactobacilli, are more acid-resistant, and some microbes survive the hostile gastric environment by colonizing luminal niches at the mucosal surface, protected by gastric bicarbonate secretion. This is the case for Helicobacter pylori, related spiral-... 

There is also a gradient from the low luminal pH through the mucus layer, under which gastric bicarbonate secretion maintains neutral conditions. Mechanically, this is explained by the acid secretion occurring like small finger-like ejections penetrating the thick gel-like mucus layer into the gastric lumen [27]. 

Dalenback J, Mellander A, Olbe L, Sjovall H Motility-related cyclic fluctuations of interdigestive gastric acid and bicarbonate secretion in man. A source of substantial variability in gastric secretion studies. Scand J Gastroenterol 1993 28 943-948. 

Alterations in mucosal defense induced by HP or NSAIDs are the most important cofactors in peptic ulcer formation. Mucosal defense and repair mechanisms include mucus and bicarbonate secretion, intrinsic epithelial cell defense, and mucosal blood flow. Maintenance of mucosal integrity and repair is mediated by endogenous prostaglandin production. 

EP3 A mediator of febrile response to pyrogens [19], duodenal bicarbonate secretion [20], suppression of allergic inflammation [21], urinary concentration [22]... 

K. Takeuchi, H. Urawa, S. Kato, O. Fururkawa, H. Araki, Y. Sugimoto, A. Ichikawa, F. Ushikubi, S. Narumiya, Impaired duodenal bicarbonate secretion and mucosal integrity in mice lacking prostaglandin E-receptor subtype EP3, Gastroenterology 117 (1999) 1128. 

A variety of beneficial effects have been attributed to sucralfate, but the precise mechanism of action is unclear. It is believed that the negatively charged sucrose sulfate binds to positively charged proteins in the base of ulcers or erosion, forming a physical barrier that restricts further caustic damage and stimulates mucosal prostaglandin and bicarbonate secretion. 

Misoprostol has both acid inhibitory and mucosal protective properties. It is believed to stimulate mucus and bicarbonate secretion and enhance mucosal blood flow. In addition, it binds to a prostaglandin receptor on parietal cells, reducing histamine-stimulated cAMP production and causing modest acid inhibition. Prostaglandins have a variety of other actions, including stimulation of intestinal electrolyte and fluid secretion, intestinal motility, and uterine contractions. 

When the acidic stomach contents reach the small intestine, they are neutralized by bicarbonate secreted by the pancreas, and pan creatic a-amylase continues the process of starch digestion. 

The active Irunsport of chloride has also been demonstrated across ihe wall of the IVog stomach, rat ileum, dog ileum, and the human ileum. Experiments have produced a double exchange model in which bicarbonate secretion and chloride absorption are linked hy an isoelectric mechanism to hydrogen ion secretion and sodium absorption across the human ileum. In 1972. a group of researchers proposed a similar model of coupled transport... 

The major clinical applications of acetazolamide involve carbonic anhydrase-dependent bicarbonate transport at sites other than the kidney. The ciliary body of the eye secretes bicarbonate from the blood into the aqueous humor. Likewise, formation of cerebrospinal fluid by the choroid plexus involves bicarbonate secretion into the cerebrospinal fluid. Although these processes remove bicarbonate from the blood (the direction opposite to that in the proximal tubule), they are significantly inhibited by carbonic anhydrase inhibitors, which in both cases dramatically alter the pH and quantity of fluid produced. 

Pancreatic bicarbonate secretion is also diminished in exocrine pancreatic insufficiency. There may thus be insufficient intraduodenal buffer protection for enzymes against denaturation by gastric acid emptied with postprandial chyme. Indeed, intraluminal pH may decrease below 4.0, which results in irreversible destruction of lipase. 

Pharmaceutical inhibition of gastric acid output (proton pump inhibitor, H2 receptor blocker) may have beneficial effects when combined with an unprotected pancreatin preparation, not only by protection of enzymes during their gastric passage, but also by increasing duodenal pH and thereby improving enzymatic action. (Note that, in chronic pancreatitis, duodenal pH is lower due to impairment of pancreatic bicarbonate secretion, see above). 

The Heidenhain pouch preparation was used by Carter and Grossman (1978), Kauffman et al. (1980) to study the effect of luminal pH on acid secretion evoked by topical and parenteral stimulants and the effect of topical and intravenous 16,16-dimethyl prostaglandin E2 on gastric bicarbonate secretion. 

The secretion after injection of the test compound is compared with the pre-test values. Secretin increases pancreatic volume and bicarbonate secretion in a dose-dependent manner and can be ideally used as reference secretagogue. 

Glad et al. (1996) tested the influence of gastrinreleasing peptide on acid-induced secretin release and pancreatobiliary and duodenal bicarbonate secretion in Danish country strain pigs weighing between 22 and 30 kg. The animals, starved overnight with free... 

Stimulation of bicarbonate secretion, gall-bladder emptying and inhibition of gut motility... 

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