Prostaglandins mediate skeletal muscle arteriole dilation in hyperdynamic bacteremia

Live Escherichia coli bacteremia during the high cardiac output (hyperdynamic) phase of sepsis causes constriction of large arterioles but dilation of small arterioles in skeletal muscle. This study examines the role of dilator prostaglandins, serotonin, and histamine in these differential microvascular responses in the decerebrate rat that avoids the effects of drug anesthesia. Topical application of meclofenamate, a prostaglandin synthesis inhibitor, to the cremaster muscle 60 min after induction of E. coli bacteremia enhanced the constriction of large arterioles from 20 +/- 8 to 46 +/- 9% less than baseline and blunted the dilation of small arterioles from 39 +/- 9 to 17 +/- 7% above baseline values in the cremaster microcirculation. Induction of E. coli bacteremia after pretreatment of the cremaster with meclofenamate constricted large arterioles to 40 +/- 4% less than baseline and small arterioles to 31 +/- 4% less than baseline. This indicates that prostaglandins initiate small arteriole dilation in response to E. coli, but some other dilator factor is activated by prostaglandins to maintain small arteriole dilation during E. coli bacteremia. Topical application of cyproheptadine, an antagonist of both histamine and serotonin receptors, to the cremaster muscle did not alter the E. coli-induced constriction of large arterioles or the dilation of small arterioles in the cremaster microcirculation.