Insulin increases glucose disposal into muscle. In addition, in vivo insulin elicits distinct nitric oxide synthase-dependent vascular responses to increase total skeletal muscle blood flow and to recruit muscle capillaries (by relaxing resistance and terminal arterioles, respectively). In the current study, we compared the temporal sequence of vascular and metabolic responses to a 30-min physiological infusion of insulin (3 mU ⅐ min ؊1 ⅐ kg ؊1 , euglycemic clamp) or saline in rat skeletal muscle in vivo. We used contrast-enhanced ultrasound to continuously quantify microvascular volume. Insulin recruited microvasculature within 5-10 min (P < 0.05), and this preceded both activation of insulin-signaling pathways and increases in glucose disposal in muscle, as well as changes in total leg blood flow. Moreover, L-NAME (N -nitro-L-arginine-methyl ester), a specific inhibitor of nitric oxide synthase, blocked this early microvascular recruitment (P < 0.05) and at least partially inhibited early increases in muscle glucose uptake (P < 0.05). We conclude that insulin rapidly recruits skeletal muscle capillaries in vivo by a nitric oxidedependent action, and the increase in capillary recruitment may contribute to the subsequent glucose uptake.

. 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...

The vascular system controls the delivery of nutrients and hormones to muscle, and a number of hormones may act to regulate muscle metabolism and contractile performance by modulating blood flow to and within muscle. This review examines evidence that insulin has major hemodynamic effects to influence muscle metabolism. Whole body, isolated hindlimb perfusion studies and experiments with cell cultures suggest that the hemodynamic effects of insulin emanate from the vasculature itself and involve nitric oxide-dependent vasodilation at large and small vessels with the purpose of increasing access for insulin and nutrients to the interstitium and muscle cells. Recently developed techniques for detecting changes in microvascular flow, specifically capillary recruitment in muscle, indicate this to be a key site for early insulin action at physiological levels in rats and humans. In the absence of increases in bulk flow to muscle, insulin may act to switch flow from nonnutritive to the nutritive route. In addition, there is accumulating evidence to suggest that insulin resistance of muscle in vivo in terms of impaired glucose uptake could be partly due to impaired insulin-mediated capillary recruitment. Exercise training improves insulin-mediated capillary recruitment and glucose uptake by muscle.

In vivo measurement of interface pressure is encouraged when clinical and experimental outcomes of compression treatment are to be evaluated.

Insulin-induced increases in blood flow are hypothesized to enhance overall glucose uptake by skeletal muscle. Whether the insulin-mediated changes in blood flow are associated with altered blood flow distribution and increased capillary recruitment in skeletal muscle is not known. In the present study, the effects of insulin on hemodynamic parameters in rat skeletal muscle in vivo were investigated. Mean arterial blood pressure, heart rate, femoral blood flow, hind leg vascular resistance, and glucose uptake were measured in control and euglycemic insulin-clamped (10 mU x min(-1) x kg[-1]) anesthetized rats. Blood flow distribution within the hind leg muscles was assessed by measuring the metabolism of 1-methylxanthine (1-MX), an exogenously added substrate for capillary xanthine oxidase. Insulin treatment had no effect on heart rate but significantly increased arterial blood pressure (12 mmHg) and femoral blood flow (80%) and decreased hind leg vascular resistance (31%). Changes were similar in magnitude and in time of onset to those reported in humans. Insulin treatment increased hind leg glucose uptake approximately fourfold and also increased hind leg 1-MX metabolism by 50%, suggesting increased exposure to endothelial xanthine oxidase. To ascertain whether the increased 1-MX metabolism was simply due to increased bulk femoral blood flow, epinephrine was infused at a dose (0.125 microg x min(-) x kg[-1]) chosen to match the insulin-induced increase in femoral blood flow. This dose of epinephrine had no significant effects on arterial blood pressure or heart rate but increased femoral blood flow and lowered hind leg vascular resistance to a similar extent as insulin. Epinephrine did not significantly alter 1-MX metabolism as compared with control animals. These results demonstrate that insulin increases total hind leg blood flow and metabolism of 1-MX, suggesting a recruitment of capillary blood flow in rat hind leg not mimicked by epinephrine.

Supraphysiological doses of insulin enhance total limb blood flow and recruit capillaries in skeletal muscle. Whether these processes change in response to physiological hyperinsulinemia is uncertain. To examine this, we infused either saline (n ‫؍‬ 6) or insulin (euglycemic clamp, 3.0 mU ⅐ min ؊1 ⅐ kg ؊1 , n ‫؍‬ 9) into anesthetized rats for 120 min.

Future descriptions of compression bandages should include the subbandage pressure range measured in the medial gaiter area, the number of layers, and a specification of the bandage components and of the elastic property (stiffness) of the final bandage.

Insulin has an exercise-like action to increase microvascular perfusion of skeletal muscle and thereby enhance delivery of hormone and nutrient to the myocytes. With insulin resistance, insulin's action to increase microvascular perfusion is markedly impaired. This review examines the present status of these observations and techniques available to measure such changes as well as the possible underpinning mechanisms. Low physiological doses of insulin and light exercise have been shown to increase microvascular perfusion without increasing bulk blood flow. In these circumstances, blood flow is proposed to be redirected from the nonnutritive route to the nutritive route with flow becoming dominant in the nonnutritive route when insulin resistance has developed. Increased vasomotion controlled by vascular smooth muscle may be part of the explanation by which insulin mediates an increase in microvascular perfusion, as seen from the effects of insulin on both muscle and skin microvascular blood flow. In addition, vascular dysfunction appears to be an early development in the onset of insulin resistance, with the consequence that impaired glucose delivery, more so than insulin delivery, accounts for the diminished glucose uptake by insulin-resistant muscle. Regular exercise may prevent and ameliorate insulin resistance by increasing "vascular fitness" and thereby recovering insulin-mediated capillary recruitment.