title: Nitric oxide inhibits isoproterenol-stimulated adipocyte lipolysis through oxidative inactivation of the beta-agonist.
abstract: Nitric oxide has been implicated in the inhibition of catecholamine-stimulated lipolysis in adipose tissue by as yet unknown mechanisms. In the present study, it is shown that the nitric oxide donor, 2,2-diethyl-1-nitroso-oxyhydrazine, antagonized isoproterenol (isoprenaline)-induced lipolysis in rat adipocytes, freshly isolated from white adipose tissue, by decreasing the potency of the beta-agonist without affecting its efficacy. These data suggest that nitric oxide did not act downstream of the beta-adrenoceptor but reduced the effective concentration of isoproterenol. In support of the latter hypothesis, we found that pre-treatment of isoproterenol with nitric oxide abolished the lipolytic activity of the catecholamine. Spectroscopic data and HPLC analysis confirmed that the nitric oxide-mediated inactivation of isoproterenol was in fact because of the modification of the catecholamine through a sequence of oxidation reactions, which apparently involved the generation of an aminochrome. Similarly, aminochrome was found to be the primary product of isoproterenol oxidation by 3-morpholinosydnonimine and peroxynitrite. Finally, it was shown that nitric oxide released from cytokine-stimulated adipocytes attenuated the lipolytic effect of isoproterenol by inactivating the catecholamine. In contrast with very recent findings, which suggest that nitric oxide impairs the beta-adrenergic action of isoproterenol through intracellular mechanisms and not through a chemical reaction between NO and the catecholamine, we showed that nitric oxide was able to attenuate the pharmacological activity of isoproterenol in vitro as well as in a nitric oxide-generating cellular system through oxidation of the beta-agonist. These findings should be taken into account in both the design and interpretation of studies used to investigate the role of nitric oxide as a modulator of isoproterenol-stimulated signal transduction pathways.
authors.affiliation: Departmento de Estructura y Función de Proteínas, Centro de Investigaciones Biológicas (CSIC), Velázquez 144, 28006 Madrid, Spain.
authors.forename: P
authors.initials: P
authors.lastname: Klatt
authors.forename: J
authors.initials: J
authors.lastname: Cacho
authors.forename: M D
authors.initials: MD
authors.lastname: Crespo
authors.forename: E
authors.initials: E
authors.lastname: Herrera
authors.forename: P
authors.initials: P
authors.lastname: Ramos
mesh_terms: D016475:3T3 Cells; D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D002395:Catecholamines / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D004305:Dose-Response Relationship, Drug; D005260:Female; D006834:Hydrazines / Q000494:pharmacology; D045563:Indolequinones; D007211:Indoles / Q000737:chemistry; D007545:Isoproterenol / Q000737:chemistry / Q000378:metabolism*; D008066:Lipolysis; D051379:Mice; D008981:Molsidomine / Q000031:analogs & derivatives / Q000494:pharmacology; D009566:Nitrates / Q000494:pharmacology; D009569:Nitric Oxide / Q000494:pharmacology*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D009589:Nitrogen Oxides; D010100:Oxygen / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction; D013053:Spectrophotometry; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: D002395:Catecholamines; D006834:Hydrazines; D045563:Indolequinones; D007211:Indoles; D009566:Nitrates; D020030:Nitric Oxide Donors; D009589:Nitrogen Oxides; D014409:Tumor Necrosis Factor-alpha; C039642:peroxynitric acid; D009569:Nitric Oxide; C091584:aminochrome 1; C002385:linsidomine; C084012:1,1-diethyl-2-hydroxy-2-nitrosohydrazine; D008981:Molsidomine; D007545:Isoproterenol; D010100:Oxygen