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Abstract

Objective

To evaluate and compare oxidative processes during ischemia and reperfusion of the equine large colon and jejunum.

Animals

2 groups of 6 anesthetized horses undergoing a terminal procedure.

Procedure

Isolated loops of large colon and jejunum were subjected to 2 hours of ischemia, followed by 2 hours of reperfusion. Tissue specimens were taken after 105 minutes of ischemia and 10, 30, 60, and 120 minutes of reperfusion. Mesenteric arterial and venous blood samples were collected for blood gas analysis at the same times to evaluate ischemia and reoxygenation. Oxidative processes in tissues were evaluated by use of biochemical assays for malondialdehyde and conjugated dienes and by use of the manganese-diaminobenzidine histochemical technique for localized superoxide generation.

Results

Significant quantities of malondialdehyde and conjugated dienes were detected in the jejunum after 60 and 120 minutes of reperfusion together with histochemical evidence of superoxide generation in jejunal endothelial cells and in submucosal neutrophils and eosinophils.

Conclusions

Oxidative processes do not appear to have an appreciable role in inducing damage in the equine large colon during reperfusion after 2 hours of ischemia. In contrast to the jejunum, reactive oxygen species are not generated in measurable quantities in the large colon subsequent to ischemia and reperfusion.

Clinical Relevance

Free radical scavengers are not likely to be effective in prevention of equine colonic mucosal deterioration after ischemia. (Am J Vet Res 1998;59:340–346)

Free access
in American Journal of Veterinary Research

SUMMARY

The scavenging of superoxide radicals by endogenous and therapeutically administered superoxide dismutases may prevent superoxide-mediated oxidative stress leading to lipid peroxidation, membrane lysis, and cell death in a wide variety of normal and pathologic states. Simple inorganic manganous salts such as MnCl2 also have superoxide dismutase-like activity and are extremely inexpensive, compared with enzymatic superoxide dismutase preparations. In this study, we explored the use of Mn salts as antioxidant drugs. We used the percentage of inhibition of nitroblue tetrazolium reduction by superoxide as a measure of the amount of superoxide dismutase-like activity. We found concentration-related increases in superoxide scavenging activity in simple buffer solutions upon addition of 1.25, 2.5, and 5.0 μM MnSO4. To determine whether Mn salts can inhibit oxidative damage in tissues, we used an in vitro model of lipid peroxidation in ischemic and reoxygenated rat liver slices. Concentrations of 10, 100, and 1000 μmoles MnCl2/L of buffer significantly decreased indicators of lipid peroxidation believed to be initiated by intracellular superoxide. We then determined the effectiveness of MnCl2 as a superoxide scavenger in conscious horses by measuring the superoxide scavenging ability of equine plasma before and during intravenous infusions of 1.0 L volumes of 0.9% slaine solution containing 0, 12.5, or 25 mM MnCl2. Plasma Mn concentrations, which were determined by atomic absorption spectrophotometry, increased as a function of time and dose. Intravenously administered MnCl2 concomitantly produced dose-related increases in superoxide scavenging ability of equine plasma at 15, 30, 45, and 60 minutes after the onset of infusion, compared with preinfusion control values. Heart rate and blood pressure of the treated horses, which were monitored to measure toxicity of MnCl2, gradually increased in both treatment groups. Clinical adverse effects of MnCl2 administration included defecation, pawing, hyperexcitability, flank watching, and sweating. The results of this study indicate that simple Mn salts may scavenge superoxide radicals in vivo with minimal adverse reactions and at a trivial cost.

Free access
in American Journal of Veterinary Research