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 flows, blood gases, and bladder epithelial PO2, a marker of organ perfusion. The animals received either saline or endotoxin at doses of 1, 10 and 100 mg/kg body wt. Blood pressure changed significantly in all three endotoxin groups, though only the 100 mg/kg group showed significant changes in arterial PCO2, arterial PO2, and body temperature compared with controls. Whereas aortic and renal blood flow rose significantly in the two lower-dose groups, an approximate one-third fall occurred in the 100 mg/kg group (P < 0.001). Notwithstanding these macrocirculatory hemodynamic changes, both bladder epithelial PO2 and arterial base deficit rose significantly in all groups, though only the base deficit showed a progressive dose response. This model illustrates that responses to endotoxin are dose dependent but with changing patterns for different variables. The consistent finding of an elevated tissue PO2 in endotoxemia, regardless of dose, is suggestive of defective cellular oxygen metabolism.