[Cellular and molecular mechanisms of the gastric mucosa: injury of the mucosa and the protective action of antacids]

Gastrointestinal mucosa is exposed to many substances, some made by their own body as HCl, pepsin, etc, others from exogenous origin as NSAIDs, alcohol etc. that injury the mucosa. The body has build protective mechanism against the injury that we describe in the article. We know antacids acts neutralizing the acid a now we know it work as a powerful stimulant of the mucosal protection. This is called cytoprotection and is described in the article.

Is arachidonic acid protected gastric mucosa more resistant to rechallenge with a second dose of ethanol?

In our previous studies we found that pretreatment with arachidonic acid protects the gastric mucosa against ethanol-induced injury. In the present experiments we studied whether: gastric mucosa protected with arachidonic acid against ethanol injury is more resistant to a subsequent second ethanol injury, and whether a second ethanol dose produces further damage of the nonprotected damaged gastric mucosa in a control group. We found that: rechallenge with a second ethanol dose increases the extent of gastric mucosal necrosis in control rats; once protected (with arachidonic acid) the gastric mucosa is more resistant to subsequent ethanol rechallenge but some deep necrosis occurs and restoration of the surface epithelium is somewhat impaired when compared to the initial injury and repair. Thus, pretreatment of the gastric mucosa with a prostaglandin precursor dietary essential fatty acid confers excellent protection against alcohol damage with some residual protective activity against a subsequent rechallenge with alcohol.

Translocation of MAP (Erk-1 and -2) kinases to cell nuclei and activation of c-fos gene during healing of experimental gastric ulcers

We examined localization of extracellular signal regulated kinases (Erk) 1 and 2, and c-fos mRNA expression in normal and ulcerated gastric mucosa in rats at 1, 3 and 7 days after gastric ulcer induction. In normal gastric mucosa immunofluorescence signal for Erk-1 and Erk-2 was detectable in surface epithelial, neck and some glandular cells. In gastric mucosa of the ulcer margin, almost all epithelial cells displayed strong Erk-1 and Erk-2 immunoreactivity in the basolateral membranes and the cytoplasm. In addition 19+/-3% of cells showed nuclear localization of the Erk-1 and -2 signal. The c-fos mRNA expression was increased by 790+/-14% and 220+/-10%, respectively in gastric ulcer at 3 and 7 days after ulcer induction. Since in in vitro models nuclear translocation of Erk-1 and -2 triggers cell proliferation, our finding indicates relevance of this mechanism to gastric ulcer healing.

Alcohol injury to the normal human gastric mucosa: endoscopic, histologic and functional assessment

In 15 healthy volunteers, we studied the effect of intragastric administration of 100 ml 40% alcohol (in 10 experimental subjects) or isotonic saline (in 5 control subjects) on endoscopic appearance of the gastric mucosa, mucosal histology, luminal pH, and gastric mucosal potential difference. We found that a single dose of 40% alcohol produces rapid endoscopic changes (congestion and focal hemorrhagic lesions) and prominent histologic changes (exfoliation of the surface epithelium, edema of the lamina propria and hemorrhagic lesions associated with mucosal microvascular damage). The histologic changes were seen as early as 5 minutes after alcohol administration and occurred coincidentally with functional changes, which consisted of a sudden increase in luminal pH and a drop in the mucosal potential difference. The present study correlates the time sequence of the endoscopic, histological, and functional changes of the gastric mucosa following acute alcohol injury in normal human volunteers. This study confirms that many of the previous observations in animal models are also seen in normal human volunteers.

Phenazone metabolism during perfusion of isolated guinea pig liver

After 3 hr of perfusion of isolated guinea pig liver with a medium containing 407 ng/ml of phenazone, the drug concentration in the bile was 1.5 times higher than the initial concentration in the perfusion fluid. This indicates that in addition to phenazone metabolism, liver eliminates the drug by active releasing it to the bile. The active release is responsible for depression of phenazone concentration during the perfusion in approx. 6%. The remaining loss of phenazone is due to its hepatic metabolism.

Expression of nerve growth factor in rat stomach. Implications for interactions between endothelial, neural and epithelial cells

This study was aimed to determine the expression and localization of nerve growth factor (NGF) in the gastric mucosa. Transmural gastric specimens were obtained from euthanized rats.

STUDIES

1) expression of NGF and TrkA receptor by Western blotting; 2) histological evaluation of gastric wall architecture; 3) expression of NGF using immunostaining. Immunostaining showed strong and differential expression of NGF in neural elements of gastric myenteric and submucosal plexuses; in epithelial cells: mainly in chief and progenitor cells, in enterochromaffin-like (ECL) cells; and, in endothelial cells (ECs) lining blood vessels. We concluded that NGF expression in neural elements, epithelial cells and endothelial cells of blood vessels indicated a complex local interaction between neural, epithelial and endothelial cells that regulated gastric mucosal homeostasis and, likely, the protection against gastric injury and ulcer healing.

The mechanism of protective, therapeutic and prophylactic actions of sucralfate

Sucralfate, a non-systemic drug, speeds the healing of peptic ulcers, prevents their recurrence and prevents stress ulcerations in critically ill patients. In animal experiments sucralfate protects the gastric mucosa against damage produced by ulcerogenic and necrotizing agents. Sucralfate does not inhibit gastric acid secretion and has a minimal neutralizing capacity. The basis for the acute protective action of sucralfate is its effect on the normal gastric mucosa enhancing the natural defensive mechanisms, stimulating mucus, bicarbonate and prostaglandin release and mucosal cell renewal. Therapeutic action of sucralfate is most likely the result of A) local action on ulcerated areas of the mucosa by formation of a protective barrier reducing pepsin and H+injury; B) binding of pepsin and bile acids; and C) trophic effect on the entire mucosa which facilitates healing and re-epithelialization. Long term prophylactic efficacy of sucralfate is probably due to its chronic trophic action on the gastric mucosa. Quantitive and qualitative increase in the surface epithelial and proliferative zone cells enhance the defensive capabilities of the mucosa increasing mucus, bicarbonate, and prostaglandin release and cell renewal.

Effect of secretin on gastric parietal cell ultrastructure in man

The effect of secretin on parietal cell ultrastructure and on gastric mucosal potential difference have not been reported. In five healthy subjects, we studied the effect of intravenous injection of 2 clinical units per kg. of secretin on parietal cell canalicular and tubulovesicular membrane areas. In addition, we studied the effect of secretin on serum secretin levels and gastric mucosal potential difference. Biopsies of gastric mucosa for light and electron microscopy were obtained prior to and 15 and 30 minutes after secretin injection. Electron micrographs of 140 parietal cells were analyzed by the Loud quantitative method. Fifteen minutes following secretin administration, parietal cell canalicular membrane area decreased from a basal value of 4.37 +/- 0.43 per cent to 3.17 +/- 0.28 per cent (p less than 0.01). The number and length of microvilli also significantly decreased. Tubulovesicular membrane area increased from 9.32 +/- 0.7 per cent to 9.74 +/- 0.6 per cent (p greater than 0.05). The effect of secretin on canalicular membrane area was short lived, with recovery to nearly basal level at 30 minutes. Nuclear membrane area did not change at 15 and 30 minutes after secretin. After injection, serum secretin increased from a mean basal value of 15 to 2800 pg. per ml. at 15 minutes, falling to 130 pg. per ml. at 30 minutes. Gastric potential difference following secretin injection rose from -43 +/- 2 mv. to -54 +/- 2 mv. (p less than 0.01) within 10 minutes. In conclusion, a pharmacologic dose of secretin alters gastric parietal cell ultrastructure and causes significant elevation of gastric mucosal potential difference.

Cellular mechanisms, interactions, and dynamics of gastric ulcer healing

An ulcer is a deep, focal defect in the gastric or duodenal wall penetrating through the entire thickness of mucosa and muscularis mucosae. Ulcer healing (i.e., the reconstruction of the muscularis mucosae and mucosal architecture) is an active process of filling the mucosal defect with proliferating and migrating epithelial cells and connective tissue. Mucosa adjacent to the ulcer creater forms a healing zone. Gastric glands in this zone dilate and the epithelial cells lining these glands dedifferentiate, express epidermal growth factor (EGF) receptor, and proliferate. The proliferation is triggered by local activation of genes encoding for EGF and its receptor. From the ulcer margin, proliferating epithelial cells migrate onto the granulation tissue to cover (re-epithelialize) the ulcer and bud into granulation tissue to reconstruct gastric glands in the ulcer scar. Re-epithelialization and reconstruction of epithelial structures are under control of EGF and related peptides produced locally by regenerating cells. Granulation tissue at the ulcer base (whose growth is regulated, at least in part, by fibroblast growth factors) supplies microvessels for restoration of the microvascular network and connective tissue for restoration of the lamina propria within the mucosal scar. The ulcer healing reflects a dynamic interaction between the epithelial component from the healing zone at the ulcer margin and the connective tissue component (including microvessels) originating from the granulation tissue.