Inhibiting NOS blocks microvascular recruitment and blunts muscle glucose uptake in response to insulin

Abstract

. Inhibiting NOS blocks microvascular recruitment and blunts muscle glucose uptake in response to insulin. Am J Physiol Endocrinol Metab 285: E123-E129, 2003; 10.1152/ajpendo.00021.2003.-We examined the effects of inhibiting nitric oxide synthase with N -nitro-L-arginine-methyl ester (L-NAME) on total hindlimb blood flow, muscle microvascular recruitment, and hindlimb glucose uptake during euglycemic hyperinsulinemia in vivo in the rat. We used two independent methods to measure microvascular perfusion. In one group of animals, microvascular recruitment was measured using the metabolism of exogenously infused 1-methylxanthine (1-MX), and in a second group contrast-enhanced ultrasound (CEU) was used. Limb glucose uptake was measured by arterial-venous concentration differences after 2 h of insulin infusion. Saline alone did not alter femoral artery flow, glucose uptake, or 1-MX metabolism. Insulin (10 mU ⅐ min Ϫ1 ⅐ kg Ϫ1 ) significantly increased hindlimb total blood flow (0.69 Ϯ 0.02 to 1.22 Ϯ 0.11 ml/min, P Ͻ 0.05), glucose uptake (0.27 Ϯ 0.05 to 0.95 Ϯ 0.08 mol/min, P Ͻ 0.05), 1-MX uptake (5.0 Ϯ 0.5 to 8.5 Ϯ 1.0 nmol/min, P Ͻ 0.05), and skeletal muscle microvascular volume measured by CEU (10.0 Ϯ 1.6 to 15.0 Ϯ 1.2 video intensity units, P Ͻ 0.05). Addition of L-NAME to insulin completely blocked the effect of insulin on both total limb flow and microvascular recruitment (measured using either 1-MX or CEU) and blunted glucose uptake by 40% (P Ͻ 0.05). We conclude that insulin specifically recruits flow to the microvasculture in skeletal muscle via a nitric oxide-dependent pathway and that this may be important to insulin's overall action to regulate glucose disposal. capillary recruitment; nitric oxide; nitric oxide synthase; muscle blood flow THERE IS ABUNDANT EVIDENCE that insulin augments total limb blood flow in humans (2, 29, 33) and experimental animals (20, 22) in a time-and dose-dependent fashion. It has been suggested that this action of insulin could, by facilitating the delivery of glucose and itself to muscle, contribute to insulin's overall action on glucose disposal (3), although this remains controversial (33).Substantial evidence suggests that nitric oxide (NO) is involved in insulin's action to increase limb blood flow in humans (5,8,25,26,29). NO in muscle is produced by nitric oxide synthase (NOS), located in both vascular endothelium (28) and myocytes (16). Inhibition of NO production by N -mono-methyl-L-arginine (L-NMMA) can fully abolish the effect of insulin to increase limb total blood flow in humans (4,5,26,29). In one study, this agent partially blocked (ϳ25%) insulin-mediated glucose uptake as well (5). Baron et al. (6) have also reported that, in the rat, L-NMMA increases mean arterial pressure and reduces whole body glucose infusion rate in a dose-dependent fashion during a euglycemic insulin clamp (12 mU⅐min Ϫ1 ⅐kg Ϫ1). Using intravital microscopy, Chen and Messina (8) demonstrated that insulin induces vasodilation of firstorder arterioles in rat cremaster and that the addition...

Acute glucosamine-induced insulin resistance in muscle in vivo is associated with impaired capillary recruitment

“…Similarly, other studies have shown that endothelium-dependent vasodilation was impaired in thoracic aorta rings from rats infused with glucosamine and that this was a result of the inhibition of NOS by glucosamine [19]. Since both the insulin-mediated increases in total flow [15,36] and capillary recruitment [16] have been suggested to be NOSdependent, this could be the mechanism for the glucosamine-mediated inhibition of capillary recruitment and total flow. The effects of glucosamine on gene expression in endothelial cells [37] should also be considered, if longer-term exposure occurs.…”

“…When infused locally [15], inhibitors of nitric oxide synthase (NOS) block insulin-mediated increases in blood flow, and also block insulin-mediated capillary recruitment when infused systemically [16]. For capillary recruitment, the higher sensitivity to insulin [17] and the fact that time course studies show capillary recruitment to be the earliest change caused by insulin in vivo [18] suggest that endothelial cells, in particular endothelial nitric oxide synthase (eNOS), are the source of nitric oxide (NO).…”

Vascular and metabolic effects of methacholine in relation to insulin action in muscle

“…There are two major effectors of muscle glucose uptake, insulin and exercise, and both have been claimed to involve some dependency on NO [1][2][3]26]. In rats, insulin-mediated increase in limb blood flow is blocked by systemically administered NO synthase inhibitors [27,28], as is insulin-mediated capillary recruitment [27,28] and glucose uptake [27,28], although the latter is controversial in humans [24,29,30]. However, since a centrally injected NO synthase inhibitor can mimic the insulin resistance and hypertension seen with systemic NO synthase inhibitors [31], a local mechanism involving endothelial insulin receptors, endothelial NO synthase and NO-dependent vasodilatation is far from clear.…”

Epigallocatechin Gallate, a Green Tea Polyphenol, Mediates NO-dependent Vasodilation Using Signaling Pathways in Vascular Endothelium Requiring Reactive Oxygen Species and Fyn

“…This leads to increased blood flow to skeletal muscle resulting in increased delivery of glucose and insulin to metabolic targets of insulin action (2). These vasodilator actions of insulin contribute significantly to insulin-mediated glucose uptake (3)(4)(5)(6). Synergistic relationships between insulin sensitivity and endothelial function are reinforced because insulin signaling pathways in skeletal muscle, adipose tissue, and liver promoting metabolic actions of insulin are shared in common with insulin signaling pathways in vascular endothelium promoting vasodilator actions of insulin (1).…”