Ischemic bowel: the protective effect of free-radical anion scavengers

Recent data indicates that the free-radical anion superoxide (O2-), an unstable cytotoxic form of oxygen, is implicated in the pathogenesis of ischemic bowel following reperfusion after low flow states. This report evaluates the effect of free radical scavengers on survival in an animal model with bowel ischemia. At laparotomy, the superior mesenteric artery (SMA) of 79 weanling rats (90 g) was occluded for one minute and released. Animals were divided into three experimental groups: group I acted as controls (n = 41), group II, received thiopental 5 mg/kg IV (n = 19), group III, received methohexital 2.5 mg/kg IV (n = 19). At one week animals were evaluated for mortality, mean survival time, evidence of bowel necrosis or perforation, and bowel appearance on scanning electron microscopy (EM). Mortality was 63.5% (26/41) in group I, 19 had necrotic bowel and 7 had gross perforation; 31.6% in group II (6/19) (p less than .05 versus control), with one necrotic bowel and 5 perforations; and 57.9% in group III (11/19) where 7 had necrotic bowel and 4 had perforations (p NS v control). Survival time (mean +/- SD in days) post SMA occlusion was 3.2 +/- 1.9 for group I; 4.0 +/- 1.7 for group II; and 2.5 +/- 2.0 for group III. EM showed mucosal destruction worsened by the duration of reperfusion, decreased by thiopental but not by methohexital. Thiopental, a free radical anion scavenger was cytoprotective in this animal model, as it decreased mortality and the incidence of bowel necrosis and perforation. These data support the thesis that following low flow states bowel ischemia may be related to a reperfusion injury due to the release of toxic free radical anions.