Objective  

Purpose of the study was to investigate the potential influence of norepinephrine (NE) on immune functions in terms of systemic and organ-specific bacterial clearance in rabbits.

Design  

To enable quantification of the clearance process, defined numbers of exogenousEscherichia coli (1.3×10⁸ CFU) were injected intravenously 60 min after starting the NE infusion at a low dose (1 g/kg per min,n=6), causing an increase (30 mmHg) in mean arterial pressure without affecting the oxygen uptake, and at a higher dose (7.5 g/kg per min,n=6), resulting in a marked decrease (20%) in oxygen uptake, after infusion of NaCl solution (control,n=6). In additional experiments (n=6) NE (1 g/kg per min) was tested in endotoxemia induced by simultaneous infusion of endotoxin (40 g/kg per h). Parameters monitored were arterial pressure, oxygen uptake, and rates of bacterial elimination from the blood. At 180 min afterE. coli injection, the animals were sacrificed, and tissue samples of liver, kidney, spleen, and lung were collected for bacterial counts.

Results  

NE infusion resulted in a dose-dependent prolonged elimination of the injectedE. 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="" shockproducing="" endotoxemia,="" whereas="" simultaneous="" infusion="" of="" ne="" and="" endotoxin="" caused="" only="" a="" slightly="" delayed="" blood="" clearance="" of="" the="" injected="">

Conclusion  

NE dose dependently affected bacterial clearance, which might be due to ischemia-derived hypoxic impairment of the phagocytosis and lysis function of the reticuloendothelial system, whereas NE improved elimination of bacteria in a state of endotoxic shock.