IMPAIRMENT OF BACTERIAL CLEARANCE INDUCED BY NOREPINEPHRINE INFUSION IN RABBITS

Objective: Purpose of the study was to investigate the potential influ ence of norepinephrine (NE) on immune functions in terms of systemic a nd organ-specific bacterial clearance in rabbits. Design. To enable qu antification of the clearance process, defined numbers of exogenous Es cherichia coli (1.3 x 10(8) CFU) were injected intravenously 60 min af ter starting the NE infusion at a low dose (1 mu g/kg per min, n = 6), causing an increase (30 mmHg) in mean arterial pressure without affec ting the oxygen uptake, and at a higher dose (7.5 mu g/kg per min, n = 6), resulting in a marked decrease (20%) in oxygen uptake, after infu sion of NaCl solution (control, n = 6). In additional experiments (n = 6) NE (1 mu g/kg per min) was tested in endotoxemia induced by simult aneous infusion of endotoxin (40 mu g/kg per h). Parameters monitored were arterial pressure, oxygen uptake, and rates of bacterial eliminat ion from the blood. At 180 min after E. coli injection, the animals we re sacrificed, and tissue samples of liver, kidney, spleen, and lung w ere collected for bacterial counts. Results: NE infusion resulted in a dose-dependent prolonged elimination of the injected E. coli from the blood and in significantly higher (p < 0.05) numbers of CFU in liver and lung compared to the controls. Significant impairment of bacterial clearance was found after shock-producing endotoxemia, whereas simult aneous infusion of NE and endotoxin caused only a slightly delayed blo od clearance of the injected bacteria. Conclusion. NE dose dependently affected bacterial clearance, which might be due to ischemia-derived hypoxic impairment of the phagocytosis and lysis function of the retic uloendothelial system, whereas NE improved elimination of bacteria in a state of endotoxic shock.