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

We studied the influence ofnitric oxide (NO) endogenously produced by adipocytes in lipolysisregulation. Diphenyliodonium (DPI), a nitric oxide synthase (NOS)inhibitor, was found to completely suppress NO synthesis in intactadipocytes and was thus used in lipolysis experiments. DPI was found todecrease both basal and dibutyryl cAMP (DBcAMP)-stimulatedlipolysis. Inhibition of DBcAMP-stimulated lipolysis by DPI wasprevented by S-nitroso-N-acetyl-penicillamine (SNAP), a NO donor. This antilipolytic effect of DPI was also preventedby two antioxidants, ascorbate or diethyldithiocarbamic acid (DDC).Preincubation of isolated adipocytes with DPI (30 min) before exposureto DBcAMP almost completely abolished the stimulated lipolysis.Addition of SNAP or antioxidant during DPI preincubation restored thelipolytic response to DBcAMP, whereas no preventive effects wereobserved when these compounds were added simultaneously to DBcAMP.Exposure of isolated adipocytes to an extracellular generating systemof oxygen species (xanthine/xanthine oxidase) or toH₂O₂ also resulted in an inhibition of thelipolytic response to DBcAMP. H₂O₂ or DPIdecreased cAMP-dependent protein kinase (PKA) activation. The DPIeffect on PKA activity was prevented by SNAP, ascorbate, or DDC. Theseresults provide clear evidence that 1) the DPI antilipolyticeffect is related to adipocyte NOS inhibition leading to PKAalterations, and 2) endogenous NO is required for the cAMPlipolytic process through antioxidant-related effect.