Mucosal vascular stasis precedes loss of viability of endothelial cells in rat acetic acid colitis

The hypothesis that a significant reduction in colonic mucosal perfusion, and hence ischemic injury, precedes the development of mucosal ulceration and inflammation is tested in this report. The microcirculatory changes in the rat colonic mucosa within 1 hr of topical exposure to 10% acetic acid were assessed. Colonic mucosal blood flow signals measured by laser Doppler flowmetry were, significantly reduced to 61±8, 52±10, and 37±13% (mean±SEM) of baseline values at 1 min, 4 min, and 10 min after the colonic mucosa was exposed to 10% acetic acid, respectively, but not in controls exposed to saline. After the start of application of 10% acetic acid (for 4 min),in vivo microscopy studies demonstrated that colonic mucosal ischemia (stasis of the red blood cells in the mucosal capillaries) occurred at 9±5 min (mean±SEM). Evidence of endothelial cell death, (failure to exclude a fluorescent dye, propidium iodide, by endothelial cells) developed at 25±10 min (mean±SEM). These findings indicate that within minutes after contact of the colonic mucosa with 10% acetic acid, colonic mucosal ischemia develops, followed shortly by death of endothelial cells. The data do not establish a cause-and-effect relationship between the reductions, in mucosal blood flow and loss of endothelial cell viability in response to acetic acid. Nevertheless, because these events occur at such an early time point, they may play a pathogenetic role in the development of the subsequent inflammatory and ulcerative changes in this animal model of colitis. Further studies to define the potential causal relationships between these parameters are warranted.