OBJECTIVE— Recent observations indicate that the delivery of nitric oxide by endothelial nitric oxide synthase (eNOS) is not only critical for metabolic homeostasis, but could also be important for mitochondrial biogenesis, a key organelle for free fatty acid (FFA) oxidation and energy production. Because mice deficient for the gene of eNOS (eNOS^−/−) have increased triglycerides and FFA levels, in addition to hypertension and insulin resistance, we hypothesized that these knockout mice may have decreased energy expenditure and defective β-oxidation.

RESEARCH DESIGN AND METHODS— Several markers of mitochondrial activity were assessed in C57BL/6J wild-type or eNOS^−/− mice including the energy expenditure and oxygen consumption by indirect calorimetry, in vitro β-oxidation in isolated mitochondria from skeletal muscle, and expression of genes involved in fatty acid oxidation.

RESULTS— eNOS^−/− mice had markedly lower energy expenditure (−10%, P < 0.05) and oxygen consumption (−15%, P < 0.05) than control mice. This was associated with a roughly 30% decrease of the mitochondria content (P < 0.05) and, most importantly, with mitochondrial dysfunction, as evidenced by a markedly lower β-oxidation of subsarcolemmal mitochondria in skeletal muscle (−30%, P < 0.05). Finally, impaired mitochondrial β-oxidation was associated with a significant increase of the intramyocellular lipid content (30%, P < 0.05) in gastrocnemius muscle.

CONCLUSIONS— These data indicate that elevated FFA and triglyceride in eNOS^−/− mice result in defective mitochondrial β-oxidation in muscle cells.