Abstract-Our objective was to determine the precise role of endothelial nitric oxide synthase (eNOS) as a modulator of cardiac O 2 consumption and to further examine the role of nitric oxide (NO) consumption in tissues taken from iNOS (Ϫ/Ϫ) (Ϫ28Ϯ4%), wild-type eNOS (ϩ/ϩ) (Ϫ22Ϯ4%), and heterozygous eNOS(ϩ/Ϫ) (Ϫ22Ϯ5%) but not homozygous eNOS (Ϫ/Ϫ) (Ϫ3Ϯ4%) mice. Responses to bradykinin in iNOS (Ϫ/Ϫ) and both wild-type and heterozygous eNOS mice were attenuated after NOS blockade with N-nitro-L-arginine methyl ester (L-NAME) (Ϫ2Ϯ5%, Ϫ3Ϯ2%, and Ϫ6Ϯ5%, respectively, PϽ0.05). In contrast, S-nitroso-N-acetyl-penicillamine (SNAP, 10Ϫ4 mol/L), which releases NO spontaneously, induced decreases in myocardial O 2 consumption in all groups of mice, and such responses were not affected by L-NAME. In addition, pretreatment with bacterial endotoxin elicited a reduction in basal O 2 consumption in tissues taken from normal but not iNOS (Ϫ/Ϫ)-deficient mice. Our results indicate that the pivotal role of eNOS in the control of myocardial O 2 consumption and modulation of mitochondrial respiration by NO may have an important role in pathological conditions such as endotoxemia in which the production of NO is altered. . Their initial observations demonstrated that activated mouse peritoneal macrophages severely inhibited O 2 consumption in numerous tumor cell lines obtained from different tissues and animal species in cultures by an unknown mechanism. Evidence now suggests that the macrophage-induced cytotoxic effect on mitochondrial metabolism is NO related. 2,3 NO inhibits respiration by nitrosylating the iron-sulfur centers of aconitase, complexes I and II of the electron transport chain, and through a very potent reversible alteration in the activity of cytochrome c oxidase. 4 -6 Recently, we and others have provided direct evidence to suggest that under physiological conditions NO plays a modulatory role on mitochondrial respiration and tissue O 2 consumption. For instance, L-arginine analogues, which are nonspecific inhibitors of the 3 isoforms of nitric oxide synthase (NOS), 7 increase O 2 consumption in whole body, 8 heart, skeletal muscle, and kidney both in vivo 9 -12 and in vitro. [12][13][14] We have interpreted our previous studies to suggest that endothelial nitric oxide synthase (eNOS), the most highly expressed isoform of NOS in vascular tissue under physiological conditions, is responsible for the control of tissue O 2 consumption by NO. However, we have yet to determine which isoform of NOS regulates mitochondrial O 2 consumption, because almost all cells are capable of expressing all 3 different NOS isoforms. Studies of the effects of bacterial endotoxins have attributed a substantial role for inducible nitric oxide synthase (iNOS) in the development of shock and perhaps other pathological states. To address the role of NO in both physiological and pathophysiological states in the control of mitochondrial respiration, we used tissues from mice deficient in iNOS and eNOS and 3 additional groups, ie, control C57B...

Background-Our objective for this study was to investigate whether nitric oxide (NO) modulates tissue respiration in the failing human myocardium. Methods and Results-Left ventricular free wall and right ventricular tissue samples were taken from 14 failing explanted human hearts at the time of transplantation. Tissue oxygen consumption was measured with a Clark-type oxygen electrode in an airtight stirred bath containing Krebs solution buffered with HEPES at 37°C (pH 7.4). Rate of decrease in oxygen concentration was expressed as a percentage of the baseline, and results of the highest dose are indicated. Bradykinin (10 Ϫ4 mol/L, Ϫ21Ϯ5%), amlodipine (10 Ϫ5 mol/L, Ϫ14Ϯ5%), the ACE inhibitor ramiprilat (10 Ϫ4 mol/L, Ϫ21Ϯ2%), and the neutral endopeptidase inhibitor thiorphan (10 Ϫ4 mol/L, Ϫ16Ϯ5%) all caused concentrationdependent decreases in tissue oxygen consumption. Responses to bradykinin (Ϫ2Ϯ6%), amlodipine (Ϫ2Ϯ4%), ramiprilat (Ϫ5Ϯ6%), and thiorphan (Ϫ4Ϯ7%) were significantly attenuated after NO synthase blockade with N-nitro-L-arginine methyl ester (10 Ϫ4 mol/L; all PϽ0.05). Ϫ4 mol/L, Ϫ34Ϯ5%) and nitroglycerin (10 Ϫ4 mol/L, Ϫ21Ϯ5%), also decreased tissue oxygen consumption in a concentration-dependent manner. However, the reduction in tissue oxygen consumption in response to S-nitroso-Nacetyl-penicillamine (Ϫ35Ϯ7%) or nitroglycerin (Ϫ16Ϯ5%) was not significantly affected by N-nitro-L-arginine methyl ester. Conclusions-These results indicate that the modulation of oxygen consumption by both endogenous and exogenous NOis preserved in the failing human myocardium and that the inhibition of kinin degradation plays an important role in the regulation of mitochondrial respiration. (Circulation. 1999;100:1291-1297.)Key Words: nitric oxide Ⅲ oxygen Ⅲ heart failure T he vast amount of ATP produced by the cardiac mitochondria is used mainly for cardiac muscle contraction. Abnormalities of mitochondria in cardiomyocytes in heart failure have been well documented in both animals [1][2][3][4] and human studies, 5-7 which provided structural and metabolic evidence of mitochondrial dysfunction. Mitochondrial DNA damage with increased mitochondrial DNA deletion in patients with heart failure has also been reported, 8,9 a defect associated with the impairment of oxidative phosphorylation. 10 On the other hand, normal mitochondrial metabolism has also been documented in chronic heart failure. 11,12 However, the role of nitric oxide (NO) in the control of mitochondrial metabolism is not well established. Our laboratory and others have demonstrated that attenuation of NO production increases whole-body or organ oxygen consumption. [13][14][15][16] The initial observation of the interaction between NO and mitochondrial enzymes was reported in cell culture studies of macrophage-induced cytotoxicity of neoplastic cells. 17,18 The activated macrophage induced reduction of electron transfer by inactivating iron-sulfur-containing complexes I and II of the respiratory chain and aconitase in the Krebs cycle. This effect was shown to b...

The acute inhibition of NO synthase by NLA causes a switch from fatty acids to lactate and glucose utilization by the heart which can be reversed by a NO donor, suggesting an important regulatory action of NO on cardiac metabolism.