The long term goal of this research is to understand the mechanisms and cellular control of intestinal secretion, processes that play a fundamental role in the pathophysiology of diarrheal diseases. In the next granting period, the hypothesis to be explored is that the immune system, along with the enteric nervous system and the hormonal system, is one of three intercommunicating systems controlling intestinal water and electrolyte transport.
The specific aims are to define and characterize: 1) the stimuli and inhibitors of intestinal eicosanoid production in the normal and germ-free rat colon and in a human colonic carcinoma (T-84-cell line; 2) the intestinal secretory response to eicosanoids of both the cyclooxygenase and lipoxygenase pathways; 3) the cellular source and secretory profiles of eicosanoids from gut inflammatory cells (intraepithelial lymphocytes, intestinal macrophages, mucosal mast cells, and intestinal polymorphonuclear leukocytes), from mesenchymal cells (fibroblasts, endothelial cells, and muscle), and from the intestinal epithelial cells; 4) the secretary and histological consequences of interactions between the inflammatory, mesenchymal and the epithelial cells; and 5) intestinal eicosanoid production in animal models of intestinal inflammation: a) chemotactic peptide (rat, fMLP), b) bacterial invasion (rat salmonellosis), c) toxigenic bacterial colonization (porcine, E coli STa), d) viral infection (porcine rotavirus) and e) parasitic infestation (porcine cryptosporidiosis). Eicosanoid responses to non-specific inflammatory cells stimuli (A23187 or phorbol esters) and to specific stimuli (bradykinin, platelet activating factor, chemotactic peptide, complement fragment C5a, anti-IgE, LTB4 and oxy-radicals) will be quantitated by radioimmunoassay following high performance liquid chromatography purification of extracts of tissue, purified inflammatory cells and incubation fluid. Electrophysiologic and isotope flux measurements in Ussing chambered intestine will define the responses to inflammatory cell stimuli and secretion of mediators. Changes in eicosanoid production by neurotransmitters/hormones will define how the three systems communicate. Reconstitution of inflammatory cells, fibroblasts, and epithelial cells will define the interaction of effector, intermediate, and target cells. The inflammatory models will characterize eicosanoid production in idiopathic and infectious intestinal inflammation. These studies should clarify a new area of gut electrolyte transport physiology and should shed light on the pathophysiology of inflammatory bowel disease and infectious diarrheas.
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