Nitric oxide inhibits isoproterenol-stimulated adipocyte lipolysis through oxidative inactivation of the beta-agonist

• Published in: Biochemical journal 2000-10, Vol.351 Pt 2 (2), p.485-493
• Main Authors: Klatt, P, Cacho, J, Crespo, M D, Herrera, E, Ramos, P
• Format: Article
• Language: English
• Subjects: 3T3 Cells; Adipocytes - metabolism; Animals; Catecholamines - metabolism; Chromatography, High Pressure Liquid; Dose-Response Relationship, Drug; Female; Hydrazines - pharmacology; Indolequinones; Indoles - chemistry; Isoproterenol - chemistry; Isoproterenol - metabolism; Lipolysis; Mice; Molsidomine - analogs & derivatives; Molsidomine - pharmacology; Nitrates - pharmacology; Nitric Oxide - pharmacology; Nitric Oxide Donors - pharmacology; Nitrogen Oxides; Oxygen - metabolism; Rats; Rats, Wistar; Signal Transduction; Spectrophotometry; Time Factors; Tumor Necrosis Factor-alpha - metabolism; Ultraviolet Rays
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/0264-6021:3510485

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.