Regulation of nitric oxide production from macrophages by lipopolysaccharide and catecholamines

Catecholamines are elaborated in stress responses to mediate vasoconstriction, and elevate systemic vascular resistance and blood pressure. They are elaborated in disorders such as sepsis, cocaine abuse, and cardiovascular disease. The aim of the study was to determine whether catecholamines affect nitric oxide (NO) production, as NO is a vasodilator and counteracts the harmful effects of catecholamines. RAW264.7 macrophage cells were cultured with lipopolysaccharide (LPS)+/-epinephrine, norepinephrine, and dopamine at 5x10(-6)M concentrations for 24h. Supernatants were harvested for measuring NO by spectrophotometry using the Greiss reagent and cells were harvested for detecting inducible NO synthase (iNOS) by Western blot. NO production in RAW 264.7 macrophages was increased significantly by addition of LPS (0.5-10ng/ml) in a dose-dependent fashion. The NO production induced by LPS was further enhanced by epinephrine and norepinephrine, and to a lesser extent by dopamine. These increases in NO correlated with expression of iNOS protein in these cells. The enhancing effect of iNOS synthesis by epinephrine and norepinephrine on LPS-induced macrophages was down regulated by beta-adrenoceptor antagonist, propranolol, and dexamethasone. The results suggest that catecholamines have a synergic effect on LPS in induction of iNOS synthesis and NO production, and this may mediate some of the vascular effects of infection. These data support a novel role for catecholamines in disorders such as septic shock and cocaine use, and indicate that beta-adrenoceptor antagonists and glucocorticoids may be used therapeutically for modulation of the catecholamine-NO axis in disease states.