CARDIORESPIRATORY AND TISSUE OXYGEN DOSE-RESPONSE TO RAT ENDOTOXEMIA

The dose response to-endotoxin (Escherichia coli serotype 127:B8) was assessed in a spontaneously breathing, halothane-anesthetized, Sprague -Dawley rat model monitoring blood pressure, aortic and renal blood fl ows, blood gases, and bladder epithelial Po-2, a marker of organ perfu sion. The animals received either saline or endotoxin at doses of 1, 1 0 and 100 mg/kg body wt. Blood pressure changed significantly in all t hree endotoxin groups, though only the 100 mg/kg group showed signific ant-changes in arterial Pco(2), arterial Po-2, and body temperature co mpared with controls. Whereas aortic and renal blood flow rose signifi cantly in the two lower-dose groups, an approximate one-third fall occ urred in the 100 mg/kg group (P < 0.001). Notwithstanding these macroc irculatory hemodynamic changes, both bladder epithelial Po-2 and arter ial base deficit rose significantly in all groups, though only the bas e deficit showed a progressive dose response. This model illustrates t hat responses to-endotoxin are dose dependent but with changing patter ns for different variables. The consistent finding of an elevated tiss ue Po-2 in endotoxemia, regardless of dose, is suggestive of defective cellular oxygen metabolism.