Catecholamines decrease nitric oxide production by cytokine-stimulated hepatocytes

Background. Catecholamines are significantly elevated in inflammatory respo nses and play a regulatory role in sepsis. Nitric oxide (NO), also a key in flammatory mediator in sepsis, is produced in large amounts by the inducibl e nitric oxide synthase (iNOS) in the liver The purpose of this study was t o test the hypothesis that catecholamines play a role in the regulation of NO production by hepatocytes. Methods. Primary hepatocytes were isolated from healthy male Sprague-Dawley rats and either cultured with normal medium or stimulated with cytomix (in terleukin-1 beta, interferon-gamma, and tumor necrosis factor-alpha) in the presence or absence of epinephrine or norepinephrine at varying concentrat ions. Total RNA was isolated 6 hours after treatment and analyzed by Northe rn blotting for iNOS mRNA. Protein extracts were obtained at 12 hours and w ere analyzed by Western immunoblotting for iNOS. Cell culture supernatants were analyzed for NO, determined as the stable end-product NO2-, at 24 hour s. Results. Epinephrine and norepinephrine significantly decreased NO2- levels in stimulated hepatocytes but had no effect on iNOS mRNA or protein levels . Ae decrease in NO2- was reproduced by the adenylate cyclase stimulator, f orskolin. The catecholamine-induced decrease in NO2- was completely reverse d by the protein kinase A inhibitor Rp-8-Br-cyclic adenosine monophosphate. Conclusions. Catecholamines decrease hepatocyte Production of NO in respons e to cytokine stimulation. This effect seems to be due to post-translationa l events and appears to be mediated in part by cyclic adenosine monophospha te.