MICROVASCULAR PERMEABILITY AND ENDOTHELIAL-CELL MORPHOLOGY ASSOCIATEDWITH LOW-FLOW ISCHEMIA-REPERFUSION INJURY IN THE EQUINE JEJUNUM

Microvascular permeability of the jejunum of clinically normal equids and microvascular permeability associated with 60 minutes of ischemia (25% baseline blood flow) and subsequent reperfusion were investigated . Eight adult horses were randomly allotted to 2 equal groups: normal and ischemic/reperfusion injury. Lymphatic flow rates, mesenteric bloo d flow, and lymph and plasma protein concentrations were determined at 15-minute intervals throughout the study. Microvascular permeability was determined by estimates of the osmotic reflection coefficient, whi ch was determined when the ratio of lymphatic protein to plasma protei n concentration reached a constant minimal value as lymph flow rate in creased (filtration-independent lymph flow rate), which occurred at ve nous pressure of 30 mm of Hg. Full-thickness jejunal biopsy specimens were obtained at the beginning and end of each experiment, and were pr epared for light microscopy to estimate tissue volume (edema) and for transmission electron microscopy to evaluate capillary endothelial cel l morphology. The osmotic reflection coefficient for normal equine jej unum was 0.19 +/- 0.06, and increased significantly (P less than or eq ual to 0.0001) to 0.48 +/- 0.05 after the ischemia/reperfusion period. Microscopic evaluation revealed a significant increase (P less than o r equal to 0.0001) in submucosal and serosal volume and capillary endo thelial cell damage in horses that underwent ischemia/reperfusion inju ry. Results indicate that ischemia/reperfusion of the equine jejunum c aused a significant increase in microvascular permeability.