Differential microvascular response to cyclooxygenase blockade in the rat small intestine during acute bacteremia.

To determine whether arachidonic acid metabolites are mediators of regional blood flow changes during sepsis, we examined the effects of cyclooxygenase blockade on intestinal microvascular diameters and blood flow during acute bacteremia, induced in the rat by the intravenous injection of 10(9) live Escherichia coli. Mean arterial pressure, cardiac output, intestinal microvascular diameters, and blood flow were measured in the presence or absence of a topically applied selective cyclooxygenase inhibitor (mefenamate). Bacteremia caused a diffuse constriction of both arterioles and venules and a concomitant 50% decrease in blood flow. Treatment with mefenamate did not affect baseline intestinal microvascular tone or bacteremia-induced arteriolar constriction and hypoperfusion, but did reverse an intense venular constriction. Our results suggest that the small intestinal microcirculation has a differential response to cyclooxygenase products of arachidonic acid metabolism during acute bacteremia. They appear not to be mediators of the intestinal arteriolar constriction and hypoperfusion observed during acute E. coli bacteremia, but profoundly influence the mesenteric venular constriction. These observations support the concept that microvascular control mechanisms are different not only between but within organ specific vascular beds.