Microvascular permeability and endothelial cell morphology associated with low-flow ischemia/reperfusion injury in the equine jejunum

Robin M. Dabareiner From the Marion duPont Scott Equine Medical Center, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Leesburg, VA 22075 (Dabareiner, White, Sullins), and the Departments of Surgery (Snyder, Pascoe, Harmon, Woliner, Pinney) and Medicine and Epidemiology (Gardner), School of Veterinary Medicine, University of California, Davis, CA 95616.

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Jack R. Snyder From the Marion duPont Scott Equine Medical Center, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Leesburg, VA 22075 (Dabareiner, White, Sullins), and the Departments of Surgery (Snyder, Pascoe, Harmon, Woliner, Pinney) and Medicine and Epidemiology (Gardner), School of Veterinary Medicine, University of California, Davis, CA 95616.

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Nathaniel A. White From the Marion duPont Scott Equine Medical Center, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Leesburg, VA 22075 (Dabareiner, White, Sullins), and the Departments of Surgery (Snyder, Pascoe, Harmon, Woliner, Pinney) and Medicine and Epidemiology (Gardner), School of Veterinary Medicine, University of California, Davis, CA 95616.

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John R. Pascoe From the Marion duPont Scott Equine Medical Center, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Leesburg, VA 22075 (Dabareiner, White, Sullins), and the Departments of Surgery (Snyder, Pascoe, Harmon, Woliner, Pinney) and Medicine and Epidemiology (Gardner), School of Veterinary Medicine, University of California, Davis, CA 95616.

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Faye A. Harmon From the Marion duPont Scott Equine Medical Center, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Leesburg, VA 22075 (Dabareiner, White, Sullins), and the Departments of Surgery (Snyder, Pascoe, Harmon, Woliner, Pinney) and Medicine and Epidemiology (Gardner), School of Veterinary Medicine, University of California, Davis, CA 95616.

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Ian Gardner From the Marion duPont Scott Equine Medical Center, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Leesburg, VA 22075 (Dabareiner, White, Sullins), and the Departments of Surgery (Snyder, Pascoe, Harmon, Woliner, Pinney) and Medicine and Epidemiology (Gardner), School of Veterinary Medicine, University of California, Davis, CA 95616.

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Michael J. Woliner From the Marion duPont Scott Equine Medical Center, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Leesburg, VA 22075 (Dabareiner, White, Sullins), and the Departments of Surgery (Snyder, Pascoe, Harmon, Woliner, Pinney) and Medicine and Epidemiology (Gardner), School of Veterinary Medicine, University of California, Davis, CA 95616.

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Diane Pinney From the Marion duPont Scott Equine Medical Center, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Leesburg, VA 22075 (Dabareiner, White, Sullins), and the Departments of Surgery (Snyder, Pascoe, Harmon, Woliner, Pinney) and Medicine and Epidemiology (Gardner), School of Veterinary Medicine, University of California, Davis, CA 95616.

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K. E. Sullins From the Marion duPont Scott Equine Medical Center, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Leesburg, VA 22075 (Dabareiner, White, Sullins), and the Departments of Surgery (Snyder, Pascoe, Harmon, Woliner, Pinney) and Medicine and Epidemiology (Gardner), School of Veterinary Medicine, University of California, Davis, CA 95616.

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SUMMARY

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 blood 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, which was determined when the ratio of lymphatic protein to plasma protein concentration reached a constant minimal value as lymph flow rate increased (filtration-independent lymph flow rate), which occurred at venous pressure of 30 mm of Hg. Full-thickness jejunal biopsy specimens were obtained at the beginning and end of each experiment, and were prepared for light microscopy to estimate tissue volume (edema) and for transmission electron microscopy to evaluate capillary endothelial cell morphology.

The osmotic reflection coefficient for normal equine jejunum was 0.19 ± 0.06, and increased significantly (P < 0.0001) to 0.48 ± 0.05 after the ische- mia/reperfusion period. Microscopic evaluation revealed a significant increase (P < 0.0001) in submucosal and serosal volume and capillary endothelial cell damage in horses that underwent ischemia/reperfusion injury. Results indicate that ischemia/re-perfusion of the equine jejunum caused a significant increase in microvascular permeability.

SUMMARY

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 blood 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, which was determined when the ratio of lymphatic protein to plasma protein concentration reached a constant minimal value as lymph flow rate increased (filtration-independent lymph flow rate), which occurred at venous pressure of 30 mm of Hg. Full-thickness jejunal biopsy specimens were obtained at the beginning and end of each experiment, and were prepared for light microscopy to estimate tissue volume (edema) and for transmission electron microscopy to evaluate capillary endothelial cell morphology.

The osmotic reflection coefficient for normal equine jejunum was 0.19 ± 0.06, and increased significantly (P < 0.0001) to 0.48 ± 0.05 after the ische- mia/reperfusion period. Microscopic evaluation revealed a significant increase (P < 0.0001) in submucosal and serosal volume and capillary endothelial cell damage in horses that underwent ischemia/reperfusion injury. Results indicate that ischemia/re-perfusion of the equine jejunum caused a significant increase in microvascular permeability.

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