Nitric oxide (NO) plays a major role in the regulation of cardiovascular and metabolic homeostasis, as evidenced by insulin resistance and arterial hypertension in endothelial NO synthase (eNOS) null mice. Extrapolation of these findings to humans is difficult, however, because eNOS gene deficiency has not been reported. eNOS gene polymorphism and impaired NO synthesis, however, have been reported in several cardiovascular disease states and could predispose to insulin resistance. High-fat diet induces insulin resistance and arterial hypertension in normal mice. To test whether partial eNOS deficiency facilitates the development of insulin resistance and arterial hypertension during metabolic stress, we examined effects of an 8-week high-fat diet on insulin sensitivity (euglycemic clamp) and arterial pressure in eNOS(+/-) mice. When fed a normal diet, these mice had normal insulin sensitivity and were normotensive. When fed a high-fat diet, however, eNOS(+/-) mice developed exaggerated arterial hypertension and had fasting hyperinsulinemia and a 35% lower insulin-stimulated glucose utilization than control mice. The partial deletion of the eNOS gene does not alter insulin sensitivity or blood pressure in mice. When challenged with nutritional stress, however, partial eNOS deficiency facilitates the development of insulin resistance and arterial hypertension, providing further evidence for the importance of this gene in linking metabolic and cardiovascular disease.

Impaired glucose tolerance (IGT) is characterized by insulin resistance. Recently, defects in the insulinsignaling cascade have been implicated in the pathogenesis of insulin resistance. To study insulin signaling in IGT, we used human skeletal muscle cells in primary culture from patients with IGT and control subjects. In these cultured myotubes, we assessed insulin-induced 2-deoxyglucose uptake and early steps of the metabolic insulin-signaling cascade. Myotubes in culture from patients with IGT had insulin-induced glucose uptake that was roughly 30 -50% less than that from control subjects. This insulin resistance was associated with impaired insulin receptor substrate (IRS)-2-associated phosphatidylinositol 3 (PI3) kinase activation and IRS-2 tyrosine phosphorylation as well as significantly decreased protein kinase C (PKC)-/ activation in response to insulin. IRS-1-associated PI3 kinase activation and insulin receptor autophosphorylation were comparable in the two groups. Protein expression levels for the insulin receptor, IRS-1, IRS-2, the p85 regulatory subunit of PI3 kinase, Akt, PKC-/, GLUT1, and GLUT4 were also similar in the two groups. In conclusion, myotubes from patients with IGT have impaired insulininduced glucose uptake. This is associated with impaired IRS-2-associated PI3 kinase activation and PKC-/ activation. Our results suggest that these defects may contribute to insulin resistance in IGT patients.

Increased eNO and pulmonary iNOS expression in eNOS null mice. S. Cook, P. Vollenweider, B. Ménard, M. Egli, P. Nicod, U. Scherrer. #ERS Journals Ltd 2003. ABSTRACT: Nitric oxide (NO) is a major regulatory molecule of the cardiovascular system; however, measurement of vascular NO synthesis in vivo represents a major challenge. NO stemming from the lower respiratory tract has been used as a marker of vascular endothelial function. Experimental evidence for this concept is lacking. Therefore, the aim of the present study was to investigate this relationship.Lower respiratory tract exhaled NO concentration, together with systemic and pulmonary artery pressure, was measured in endothelial nitric oxide synthase (NOS) (eNOS) null mice (eNOS-/-). Similar studies were performed in inducible NOS (iNOS) null mice (iNOS-/-).Defective endothelial NO synthesis in eNOS-/-mice (evidenced by systemic and pulmonary hypertension) was associated with augmented exhaled NO levels (12.5¡1.9 versus 9.8¡1.2 parts per billion (ppb), eNOS-/-versus wild type), whereas normal endothelial NO synthesis in iNOS-/-mice was associated with decreased exhaled NO levels (4.3 ¡ 1.5 ppb). Augmented exhaled NO levels in eNOS-/-mice were associated with upregulation of iNOS expression in the lung.These results indicate that inducible nitric oxide synthase is a major determinant of gaseous nitric oxide production in the lung, and lower respiratory tract exhaled nitric oxide does not always represent a marker of vascular endothelial nitric oxide synthesis. Since the late 1980s, nitric oxide (NO) has emerged as a major regulator of the cardiovascular system [1]. Measurement of vascular endothelial nitric oxide synthase (NOS) (eNOS) activity and its final product NO in vivo still represents a major challenge, because the small amount of NO produced by the endothelium is rapidly scavenged by haemoglobin and then inactivated. To date, the contribution of NO to the regulation of vascular tone has been assessed by indirect methods, examining specific modifications of physiological responses induced by NOS inhibitors and NO donors, and/or measuring levels of NO metabolites or cyclic guanosine monophosphate [2].NO is present in the exhaled air of many animal species and humans [3], but its origin and physiological function are incompletely understood. In the respiratory tract, all three NOS isoforms are expressed in tissues close to the airways. Although there is consensus that under normal conditions, a large proportion of the exhaled NO is synthesised by inducible NOS (iNOS) located in the epithelial cells of the upper respiratory tract [4,5], the origin and function of lower respiratory tract exhaled NO is incompletely understood. It has been claimed that exhaled NO stemming from the lower respiratory tract represents a marker of vascular endothelial NO synthesis [6][7][8][9][10][11][12]. Experimental evidence for this concept is lacking, however, and studies in humans, using pharmacological NOS inhibitors, suggest that eNOS barely albeit significantly, cont...