Dissociation between adipose nitric oxide synthase expression and tissue metabolism

Context: Nitric oxide synthase ( NOS) expression in adipose tissue is increased in obese subjects. The functional relevance is not known. Objective: The objective was to compare adipose tissue metabolism between obese men with greater or lower adipose endothelial NOS (eNOS) or inducible NOS (iNOS) expression. Design: The design was an open-labeled prospective study. Setting: The study took place at an academic clinical research center. Patients: The patients included 14 obese ( 32 +/- 0.6 kg/m(2)) and eight normal-weight ( 23 +/- 2 kg/m(2)) healthy men. Intervention: Microdialysis catheters in abdominal sc adipose tissue and in vastus lateralis were perfused with N-omega- nitro-L-arginine methyl ester (L-NAME) or N-omega-nitro-D-arginine methyl ester (DNAME). Then, incremental isoproterenol concentrations were added to the perfusate. Main Outcome Measures: Microdialysate glycerol was the main outcome measure. Results: Tissue perfusion and microdialysate glycerol concentrations at baseline and during isoproterenol stimulation were similar in obese men with high or low eNOS or iNOS expression during both L-NAME and D-NAME. During D-NAME, basal and maximal isoproterenol stimulated glycerol were similar in lean and in obese men. However, in lean men, the dose-response relationship between isoproterenol and glycerol was shifted towards the left (P < 0.0001). NOS inhibition with L-NAME had no effect on basal or isoproterenol-stimulated glycerol in the obese group in skeletal muscle or in adipose tissue. In contrast, L- NAME augmented the lipolytic response in lean subjects in both tissues. Conclusions: Differences in eNOS and iNOS mRNA expression at the adipose tissue level may have a limited effect on lipolysis and tissue perfusion. The lower resting lipolysis in adipose tissue of obese compared with nonobese subjects cannot be explained by a tonic nitric oxide effect.