Mechanisms of gastric mucosal injury and protection.

This article emphasizes and reviews the premise that because the pathogenesis of acute gastric mucosal injury is multifactorial, several protective mechanisms should also be considered in analyzing gastric mucosal defense. The first part of the article reviews the pathogenesis of acute gastric mucosal injury by major etiologic factors such as hypoxia and chemical and biological agents, and emphasizes the common endogenous mediators of damage (e.g, endothelins, leukotrienes, thromboxane, platelet-activating factor, monoamines, free radicals, proteases, ammonia, hydrochloric acid, and bile acids--in decreasing potency). The second part of the review is devoted to the gastroprotective mechanisms that are analyzed by anatomical (histologic) location and biochemical processes. The endogenous mediators of acute gastroprotection include prostaglandins, sulfhydryl (SH) compounds, non-SH antioxidants, polyamines, and epidermal growth factor, whereas the protective and mediatory role of glucocorticoids, somatostatin, pentagastrin, histamine, gangliosides, and calcitonin gene-related peptide need further studies. A list of endogenous and exogenous chemicals that exert biphasic, damaging, and protective effects on the gastric mucosa in also included. The final common pathway of acute gastroprotection at the structural and functional level seems to be the preservation of subepithelial microvascular integrity leading to maintenance of mucosal blood flow that allows the energy-dependent rapid restitution (cell migration) from surviving gastric neck cells to repair the superficial epithelial defect. Very new data on the contribution of a histodilutional barrier and release of proteases to gastroprotective processes are also discussed.