Objective   To observe the effects of norepinephrine on the activation of macrophages induced by LPS and to explore its possible molecular mechanisms.     Methods   The peritoneal macrophages collected from male SD rats were pretreated by norepinephrine at different concentrations for 1 h

or norepinephrine at the dose of 10 ng/ml for a period ranging from 0.5 h to 5 h

and then treated by LPS for another 1 h. The phagocytic capacities and TNF-α secretion abilities of macrophages were measured. The CD14

SR

and TLR4 mRNA expression levels were evaluated by semi-quantitative RT-PCR.     Results   Norepinephrine at low concentrations (2 ng/ml~10 ng/ml) predominantly enhanced the phagocytic capacities and the TNF-α secretion abilities of peritoneal macrophages induced by LPS

but it had no effects on these functions at higher concentrations (50 ng/ml~100 ng/ml). Besides

norepinephrine at low concentrations improved CD14 and SR mRNA expression levels of peritoneal macrophages

but it had no effects at higher concentrations. Further more

norepinephrine had no effects on TLR4 mRNA expression at the observed concentrations.     Conclusion   Norepinephrine at a suitable concentration can enhance the activation of macrophages induced by LPS

which may be associated with the elevated expressions of CD14 and SR mRNA.