Mice with gene disruption of both endothelial and neuronal nitric oxide synthase exhibit insulin resistance.

Abstract

Studies from our laboratory using acute pharmacologic blockade of nitric oxide synthase (NOS) activity have suggested that nitric oxide (NO) has an important role in regulating carbohydrate metabolism. We now report on insulin sensitivity in mice with targeted disruptions in endothelial NOS (eNOS) and neuronal NOS (nNOS) genes compared with their wild-type (WT) counterparts. Mice underwent hyperinsulinemic-euglycemic clamp studies after a 24-h fast, during an insulin infusion of 20 mU · k g -1 · min -1 . Glucose levels were measured at baseline and every 10 min during the clamp. Insulin levels were measured at baseline and at the end of the clamp study. Glucose infusion rates (GIRs) during the last 30 min of the clamp study were in a steady state. Tritiated glucose infusion was used to measure rates of endogenous glucose output (EGO) both at baseline and during steady-state euglycemia. Glucose disposal rates (GDRs) were computed from the GIR and EGO. Fasting and steady-state glucose and insulin levels were comparable in the 3 groups of mice. No differences in fasting EGO were noted between the groups. GIR was significantly reduced (37%, P = 0.001) in the eNOS knockout (KO) mice compared with the WT mice, with values for the nNOS mice being intermediate. EGO was completely suppressed in the nNOS and WT mice during insulin infusion, but not in the eNOS mice. Even so, the eNOS mice displayed significantly reduced whole-body GDRs compared with those of the WT mice ( 8 2 . 6 7 ± 10.77 vs. 103.67 ± 3.47 m g · k g -1 · min -1 , P = 0.03). eNOS KO mice are insulin resistant at the level of the liver and peripheral tissues, whereas the nNOS KO mice are insulin resistant only in the latter. These data indicate that NO plays a role in modulating insulin sensitivity and carbohydrate metabolism and that the eNOS isoform may play a dominant role relative to nNOS. Diabetes 49:XXX-XXX, 2000 N itric oxide (NO) has emerged as an important molecule with diverse biological functions. In the blood vessels, NO mediates endotheliumdependent vasodilation (1-3) in response to diverse stimuli such as shear stress (4-6), insulin (7), acetylcholine (8,9), and bradykinin (3,10). In the central nervous system (CNS) and peripheral nervous tissue, NO is an unusual neurotransmitter (11-13). NO is generated when the amino acid L-arginine is converted to citrulline by the enzyme NO synthase (NOS) (14,15). Three separate genes encode the known isoforms of NOS (16): endothelial NOS (eNOS or NOS III) and neuronal NOS (nNOS or NOS II) catalyze the constitutive production of NO in a calcium-dependent manner predominantly in the blood vessels and neural tissues, respect i v e l y. The third isoform, inducible NOS (iNOS or NOS I) is located in macrophages and catalyzes NO formation in i n flammatory cells.Intravenous administration of N G -m o n o m e t h y l -L-a r g i n i n e (L-NMMA), a competitive inhibitor of all NOS isoforms, acutely induces hypertension and insulin resistance in rats ( 1 7 ) . M o r e r e c e n t l y, we reported that acute pharm...

Association of - 786T-C mutation of endothelial nitric oxide synthase gene with insulin resistance

“…Skeletal muscle glucose uptake is enhanced by insulin-mediated vasodilation and the decrease in local blood flow can result in insulin resistance [1][2][3][4][5]. However, several reports deny a major role of endothelial NO production in determining insulin sensitivity [6,7].Recently eNOS knockout mice have been reported to be insulin resistant [8]. These mice have also shown a decrease in whole-body and muscle-glucose uptake as well as the simultaneous decrease in the local blood flow [9].…”

“…Recently eNOS knockout mice have been reported to be insulin resistant [8]. These mice have also shown a decrease in whole-body and muscle-glucose uptake as well as the simultaneous decrease in the local blood flow [9].…”

Systemic inhibition of nitric oxide synthesis in non-diabetic individuals produces a significant deterioration in glucose tolerance by increasing insulin clearance and inhibiting insulin secretion

“…The physiological relevance of this effect has not been assessed either in experimental animals or in humans. Finally, in anaesthetised rats, blocking NO synthesis selectively in the central nervous system with an intracerebroventricular L-NAME infusion produced a mild impairment of both peripheral insulin sensitivity and arginine-induced insulin secretion [13].…”

Nitric oxide vs insulin secretion, action and clearance

“…Admittedly, whether conclusions from an acute experiment can apply to a long-term impairment of NO bioavailability remains disputable. Moreover, mice with genetic disruption of endothelial NO synthase, used as a model of chronic NO deficiency, exhibit insulin resistance (IR) in the liver and peripheral tissues [2]. Nevertheless, it can be speculated that depressed insulin secretion and enhanced insulin degradation, when superimposed on concomitant IR, might further impair glucose tolerance and accelerate the development of type 2 diabetes mellitus under conditions associated with reduced NO bioavailability.…”