Endogenous nitric oxide is implicated in the regulation of lipolysis through antioxidant-related effect

We studied the influence of nitric oxide (NO) endogenously produced by adipocytes in lipolysis regulation. Diphenyliodonium (DPI), a nitric oxide synthase (NOS) inhibitor, was found to completely suppress NO synthesis in intact adipocytes and was thus used in lipolysis experiments. DPI was found to decrease both basal and dibutyryl cAMP (DBcAMP)-stimulated lipolysis. Inhibition of DBcAMP-stimulated lipolysis by DPI was prevented by S-nitroso-N-acetylpenicillamine (SNAP), a NO donor. This antilipolytic effect of DPI was also prevented by two antioxidants, ascorbate or diethyldithiocarbamic acid (DDC). Preincubation of isolated adipocytes with DPI (30 min) before exposure to DBcAMP almost completely abolished the stimulated lipolysis. Addition of SNAP or antioxidant during DPI preincubation restored the lipolytic response to DBcAMP, whereas no preventive effects were observed when these compounds were added simultaneously to DBcAMP. Exposure of isolated adipocytes to an extracellular generating system of oxygen species (xanthine/xanthine oxidase) or to H2O2 also resulted in an inhibition of the lipolytic response to DBcAMP. H2O2 or DPI decreased cAMP-dependent protein kinase (PKA) activation. The DPI effect on PKA activity was prevented by SNAP, ascorbate, or DDC. These results provide clear evidence that 1) the DPI antilipolytic effect is related to adipocyte NOS inhibition leading to PKA alterations, and 2) endogenous NO is required for the cAMP lipolytic process through antioxidant-related effect.