Radical production during in vivo intestinal ischemia and reperfusion in the cat

Free radical formation was studied with electron spin resonance during 2 h of intestinal ischemia in the cat, at a blood flow less than 5 ml.min-1.100 g-1, followed by 30-min reperfusion. A modification of the spin trapping technique was used to stabilize highly reactive free radicals. The rate of secondary radical formation was 0.32 +/- 0.06 mumol.min-1.100 g intestine-1 before ischemia and increased to a maximum of 0.66 +/- 0.09 mumol.min-1.100 g-1 during the first minutes of reperfusion (mean +/- SE, n = 5). This could be prevented either by maintaining intestinal blood flow at 8-15 ml.min-1.100 g-1, by administering allopurinol before and during ischemia, or by perfusing the intestinal lumen with an O2-saturated buffer solution during ischemia, resulting in maximum rates of radical production during reperfusion of 0.37 +/- 0.04 (n = 6), 0.33 +/- 0.04 (n = 5), and 0.39 +/- 0.13 mumol.min-1.100 g-1 (n = 5), respectively. The results demonstrate that free radicals are produced in the intestine during reperfusion after a period of reduced blood flow below a certain critical level, and that inhibition of xanthine oxidase and prevention of hypoxia will eliminate this radical production.