CHARACTERIZATION OF HYPOTHERMIC INTESTINAL ISCHEMIA-REPERFUSION INJURY IN DOGS

Abstract

The effects of 48 hr of hypothermic (4 degrees C ischemia) and short-term reperfusion. (I-R) on intestinal function and metabolism were studied in dogs utilizing Collins flush alone or with the putative cytoprotectant amino acid, glycine. Intestinal blood flow after hypothermic ischemia in Collins-flushed segments briefly rose at reperfusion, rapidly declined after 5 min, and plateaued over the 60-minute reperfusion period. Paired intestinal segments flushed with 5 mM glycine demonstrated parallel changes in blood flow over the reperfusion period, but the blood flow values were significantly higher (100-300%), relative to the Collins segments. Intestinal oxygen consumption (VO2) was about 50% of normal nonischemic intestinal segments at all times after reperfusion. The glycine-flushed intestinal segments significantly consumed about 100% more oxygen, relative to the paired control intestines. Intestinal fluid and protein flux into the lumen significantly increased after I-R in both glycine- and Collins-flushed segments. Mucosal tissue myeloperoxidase (MPO) activity, a biochemical marker of neutrophils, significantly increased after 48 hr of cold ischemia with Collins flush and 1 hr of reperfusion, relative to tissue obtained before ischemia. The reperfusion-induced increase in MPO activity was abolished in intestinal segments flushed with glycine. Mucosal synthesis of the chemoattractant leukotriene B4 (LTB4) significantly increased after I-R and glycine flush abolished these increases. Nitric oxide synthesis by mucosal tissue in Collins-flushed segments subjected to 48 hr of hypothermic ischemia and 1 hr of reperfusion was significantly higher, compared with nonischemic tissue or mucosal tissue subjected to cold ischemia without reperfusion. Glycine flush did not alter this pattern of NO synthesis. Light microscopic analysis in both Collins- and glycine-flushed segments revealed that intestinal hypothermic ischemia and reperfusion caused significant morphologic changes characterized by loss of villus epithelium, decreased villus height, and venous congestion. These data indicate that glycine significantly improve oxygenation after hypothermic ischemia and reperfusion and prevented the I-R-induced increase in tissue neutrophil infiltration and leukotriene synthesis.