The time course of the energy metabolism after reperfusion, the relationship between the conversion of xanthine dehydrogenase to xanthine oxidase (D-to-O conversion) during ischemia, and the changes of the energy metabolism after reperfusion were studied using an ischemia-reperfusion model in the small intestine of the rat. The rat jejunum underwent an occlusion of the superior mesenteric artery and vein for either 30 minutes (group 1, n = 6) or 90 minutes (group 2, n = 6) with collateral interruption, and then it was reperfused. The contents of the adenine nucleotides in the small intestine of the rat were measured by high-performance liquid chromatography (HPLC) before ischemia, and 30, 60, and 90 minutes of ischemia, as well as 30, 60, 120, and 180 minutes after reperfusion. The recovery level of adenosine triphosphate (ATP) in group 1 (6.05 ± 0.80 μmol/g dry weight) 30 minutes after reperfusion was significantly higher than that in group 2 (2.28 ± 1.12 μmol/g dry weight) (P < .001). In addition, the ATP content after reperfusion in group 2 did not change from 30 to 180 minutes after reperfusion. The D-to-O conversion during ischemia in group 1 was not significantly greater than that before ischemia; however, that of group 2 did increase significantly during ischemia (P < .005). These results suggest that the tissue damage from ischemia-reperfusion injury after reperfusion under 90 minutes' ischemia is accomplished within the first 30 minutes after reperfusion. Therefore, the ATP level at 30 minutes after reperfusion may be useful for the evaluation of intestinal viability. Thus, the conversion of the xanthine oxidase enzyme system might play an important role in the expression of ischemia-reperfusion injury.
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