Large colon ischemia and reperfusion in horses: Histological and functional alterations, and response of the innate immune system

Large colon volvulus is the most devastating cause of intestinal ischemia in horses and results in severe mucosal damage, barrier dysfunction, toxic shock and possibly death. Although essential for regeneration, reperfusion can exacerbate mucosal injury after ischemia. Responses to I/R involve a series of synchronized biochemical, cellular and structural changes characterized by generation of radicals, activation of immune cells, and epithelial cell degeneration and death. The objective of the study was to assess the effect of colonic I/R on functional and histological alterations, reaction of neutrophils, eosinophils, macrophages and mast cells, expression of nitrotyrosine, COX and calprotectin, and clinicopathological changes in horses.;A segment of the pelvic flexure was submitted to 1hI or 2hI followed by 30minR, 4hR, or 18hR. Mucosal biopsies before and after ischemia, and after reperfusion were processed for H&E, Luna-, TB-staining, IHC (calprotectin, CD163, nitrotyrosine), TUNEL method, and TEM. Mucosal (H&E) and epithelial damage (TB, TEM) were described and quantified. The number and distribution of mucosal neutrophils (H&E, calprotectin), eosinophils (Luna), macrophages (CD163) and mast cells (TB) were assessed. Mucosal nitrotyrosine and COX-1/-2 expression, and apoptotic cell death (TB, TUNEL) were identified. To assess mucosal barrier integrity, TER and mannitol flux were determined before and after 1hI, and after 4hR. Calprotectin (ELISA), and clinicopathological variables were evaluated in JB and CB before and after 1hI, and after 1hR, 2hR and 4hR.;Ischemia caused degeneration and detachment of epithelial cells, early apoptosis, and opening of TJ resulting in decreased TER and increased mannitol flux. Autophagy was a prominent feature in epithelial cells after 1hI. Reperfusion was characterized by apoptosis, epithelial regeneration, and restoration of TJ resulting in recovery of epithelial barrier integrity. Neutrophils infiltrated colonic mucosa after reperfusion, and macrophages, mast cells and eosinophils were activated during I/R. Ischemia caused metabolic acidosis, increased lactate, K+ and CPK, and decreased glucose in colonic venous blood. But they returned to normal after reperfusion despite activation of an inflammatory response characterized by increased neutrophil cell turn over and release of calprotectin after I/R.;Equine colonic mucosa subjected to ischemia can repair during reperfusion, despite increased mucosal inflammation. (Full text of this dissertation may be available via the University of Florida Libraries web site. Please check http://www.uflib.ufl.edu/etd.html).