Recent studies indicate that the stomach is a target organ injured during sepsis and/or multiple organ failure. Systemic inflammatory mediators released under these conditions may be responsible for gastric microvascular injury, an initiating event in the reduction of mucosal defense against luminal acid. The goal of this application is to examine the role of inflammatory mediators in the pathogenesis of gastric microvascular injury, as evidenced by increased vascular permeability, vasoconstriction, and capillary stasis. Using a canine ex vivo perfused gastric segment as the experimental model, the proposed, studies are designed to: 1) examine the effects of endotoxin, FMLP (formyl-leucyl-methionyl-phenylalanine, a chemotactic peptide released from bacteria), and tumor necrosis factor on the gastric microcirculation. We postulate that the mechanism of microvascular injury by these agents is mainly due to activation of neutrophils, which in turn cause physical obstruction, free radical generation and protease secretion, 2) evaluate the role of gastric hypercontractility in the pathogenesis of gastric microvascular injury. We propose that endotoxin, platelet-activating factor (PAF), and thromboxane A2 stimulate gastric contractions which increase vascular resistance with consequent mucosal ischemia, and 3) assess gastric microvascular injury by these inflammatory mediators released endogenously in an experimental model of intestinal ischemia/reperfusion.
The first aim will be achieved by assessing the relationship between activation of neutrophils and changes in gastric vascular resistance, vascular permeability, and filtration during administration of endotoxin, FMLP, and tumor necrosis factor. The effects of these mediators on microvascular injury will also be examined in the absence of circulating neutrophils by using Leukopak filters, which remove 9799% of neutrophils in a single passage. In addition, further studies will examine the significance of neutrophil aggregation, free radical secretion, and adherence to endothelial cells in the mechanism of neutrophil-induced microvascular injury. The second goal will be accomplished by assessing the degree of gastric contractions induced by endotoxin, PAF, and thromboxane A2, and its effect on gastric vascular resistance. The role of various neurotransmitters (i.e., acetylcholine, substance P, serotonin) in gastric contractions stimulated by these mediators will also be examined. The third objective will be pursued by correlating the degree of microvascular injury with inhibitors of endogenously released mediators during intestinal/ischemia reperfusion, including: a) polymyxin B which inactivates endotoxin, b) Leukopak filters, c) BMI 3505, a specific receptor antagonist to thromboxane A2, and d) MoAb #05-106, a monoclonal antibody which binds tumor necrosis factor. These proposed studies will provide new information regarding mechanisms involved in gastric microvascular injury, an initiating event in stress gastritis. Since the stomach is one of the organs adversely affected in patients with sepsis and/or multiple organ failure, a better understanding of gastric microcirculatory changes may be beneficial to our knowledge regarding other organ dysfunctions.
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