OBJECTIVE-We have previously shown in humans that local infusion of a nitric oxide synthase (NOS) inhibitor into the femoral artery attenuates the increase in leg glucose uptake during exercise without influencing total leg blood flow. However, rodent studies examining the effect of NOS inhibition on contraction-stimulated skeletal muscle glucose uptake have yielded contradictory results. This study examined the effect of local infusion of an NOS inhibitor on skeletal muscle glucose uptake (2-deoxyglucose) and capillary blood flow (contrastenhanced ultrasound) during in situ contractions in rats. RESEARCH DESIGN AND METHODS-Male hoodedWistar rats were anesthetized and one hindleg electrically stimulated to contract (2 Hz, 0.1 ms) for 30 min while the other leg rested. After 10 min, the NOS inhibitor N G -nitro-L-arginine methyl ester (L-NAME) (arterial concentration of 5 mol/l) or saline was infused into the epigastric artery of the contracting leg.RESULTS-Local NOS inhibition had no effect on blood pressure, heart rate, or muscle contraction force. Contractions increased (P Ͻ 0.05) skeletal muscle NOS activity, and this was prevented by L-NAME infusion. NOS inhibition caused a modest significant (P Ͻ 0.05) attenuation of the increase in femoral blood flow during contractions, but importantly there was no effect on capillary recruitment. NOS inhibition attenuated (P Ͻ 0.05) the increase in contraction-stimulated skeletal muscle glucose uptake by ϳ35%, without affecting AMP-activated protein kinase (AMPK) activation. CONCLUSIONS-NOS inhibition attenuated increases in skel-etal muscle glucose uptake during contraction without influencing capillary recruitment, suggesting that NO is critical for part of the normal increase in skeletal muscle fiber glucose uptake during contraction. Diabetes 56:2885-2892, 2007

Aims/hypothesis Plasma levels of endothelin-1 are frequently elevated in patients with hypertension, obesity and type 2 diabetes. We hypothesise that this vasoconstrictor may prevent full perfusion of muscle, thereby limiting delivery of insulin and glucose and contributing to insulin resistance. Materials and methods The acute effects of endothelin-1 on insulin-mediated haemodynamic and metabolic effects were examined in rats in vivo. Endothelin-1 (50 pmol min −1 kg −1 for 2.5 h) was infused alone, or 30 min prior to a hyperinsulinaemic-euglycaemic insulin clamp (10 mU min −1 kg −1 for 2 h). Insulin clamps (10 or 15 mU min −1 kg −1 ) were performed after 30 min of saline infusion. Results Endothelin-1 infusion alone increased plasma endothelin-1 11-fold (p<0.05) and blood pressure by 20% (p<0.05). Endothelin-1 alone had no effect on femoral blood flow, capillary recruitment or glucose uptake, but endothelin-1 with 10 mU min −1 kg −1 insulin caused a decrease in insulin clearance from 0.35±0.6 to 0.19± 0.02 ml/min (p=0.02), resulting in significantly higher plasma insulin levels (10 mU min −1 kg −1 insulin: 2,120± 190 pmol/l; endothelin-1+10 mU min −1 kg −1 insulin: 4,740± 910 pmol/l), equivalent to 15 mU min −1 kg −1 insulin alone (4,920±190 pmol/l). The stimulatory effects of equivalent doses of insulin on femoral blood flow, capillary recruitment and glucose uptake were blocked by endothelin-1.Conclusions/interpretation Endothelin-1 blocks insulin's haemodynamic effects, particularly capillary recruitment, and is associated with decreased muscle glucose uptake and glucose infusion rate. These findings suggest that elevated endothelin-1 levels may contribute to insulin resistance of muscle by increasing vascular resistance and limiting insulin and glucose delivery.

Insulin has vascular actions within the skeletal muscle microcirculation (capillary recruitment) that enhance its own access and that of glucose to the muscle cells. Obesity and insulin resistance are associated with dysregulated vascular function within muscle and a loss of insulin-mediated capillary recruitment. Furthermore, agents that impair insulin's vascular actions to recruit capillaries lead to acute insulin resistance in terms of muscle glucose uptake. Together these data suggest a strong connection between the loss of insulin-mediated capillary recruitment and the development of insulin resistance. This review examines the mechanisms involved in insulin-mediated capillary recruitment and the vascular defects associated with obesity and insulin resistance that may impair the capillary recruiting process. Understanding the mechanisms of insulin-mediated capillary recruitment and its impairment may lead to new treatment avenues to prevent the progression of obesity to diabetes.

The Warburg effect is a metabolic phenomenon characterized by increased glycolytic activity, decreased mitochondrial oxidative phosphorylation, and the production of lactate. This metabolic phenotype is characterized in rapidly proliferative cell types such as cancerous cells and embryonic stem cells. We hypothesized that a Warburg-like metabolism could be achieved in other cell types by treatment with pharmacological agents, which might, in turn, facilitate nuclear reprogramming. The aim of this study was to treat fibroblasts with CPI-613 and PS48 to induce a Warburg-like metabolic state. We demonstrate that treatment with both drugs altered the expression of 69 genes and changed the level of 21 metabolites in conditioned culture media, but did not induce higher proliferation compared to the control treatment. These results support a role for the reverse Warburg effect, whereby cancer cells induce cancer-associated fibroblast cells in the surrounding stroma to exhibit the metabolically characterized Warburg effect. Cancer-associated fibroblasts then produce and secrete metabolites such as pyruvate to supply the cancerous cells, thereby supporting tumor growth and metastasis. While anticipating an increase in the production of lactate and increased cellular proliferation, both hallmarks of the Warburg effect, we instead observed increased secretion of pyruvate without changes in proliferation.

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Contrast-enhanced ultrasound (CEU) has been used to measure muscle microvascular perfusion in vivo in response to exercise and insulin. In the present study we address whether CEU measurement of capillary volume is influenced by bulk flow and if measured capillary filling rate allows discrimination of different flow pattern changes within muscle. Three in vitro models were used: (i) bulk flow rate was varied within a single length of capillary tubing; (ii) at constant bulk flow, capillary volume was increased 3-fold by joining lengths of capillary in series, and compared to a single length; and (iii) at constant bulk flow, capillary volume was increased by sharing flow between a number of lengths of identical capillaries in parallel. The contrast medium for CEU was gas-filled albumin microbubbles. Pulsing interval (time) versus acoustic-intensity curves were constructed and from these, capillary volume and capillary filling rate were calculated. CEU estimates of capillary volume were not affected by changes in bulk flow. Furthermore, as CEU estimates of capillary volume increased, measures of capillary filling rate decreased, regardless of whether capillaries were connected in series or parallel. Therefore, CEU can detect a change in filling rate of the microvascular volume under measurement, but it can not be used to discriminate between different flow patterns within muscle that might account for capillary recruitment in vivo.

Introduction: Various pressures exist for curricular change, including economic forces, burgeoning knowledge, broadening learning outcomes, and improving quality and outcomes of learning experiences. In an Australian 5-year undergraduate medical course, staff were asked to reduce teaching hours by 20% to alleviate perceived overcrowded preclinical curriculum, achieve operating efficiencies and liberate time for students' self-directed learning.Methods: A case study design with mixed methods was used to evaluate outcomes.Results: Teaching hours were reduced by 198 hours (14%) overall, lectures by 153 hours (19%) and other learning activities by 45 hours (7%). Summative assessment scores did not change significantly after the reductions: 0.4% increase, 1.5% decrease and 1.7% increase in Years 1, 2 and 3, respectively. The percentage of students successfully completing their academic year did not change significantly: 94.4% before and 93.3% after the reductions.Student evaluations from eVALUate surveys changed little, except workload was perceived to be more reasonable. Conclusions:Teaching hours, particularly lectures, can be moderately reduced with little impact on student learning outcomes or satisfaction with an undergraduate medical course.

Skeletal muscle contributes to ~40% of total body mass and has numerous important mechanical and metabolic roles in the body. Skeletal muscle is a major site for glucose disposal following a meal. Consequently, skeletal muscle plays an important role in postprandial blood glucose homeostasis. Over the past number of decades, research has demonstrated that insulin has an important role in vasodilating the vasculature in skeletal muscle in response to an insulin infusion (hyperinsulinaemic‐euglycaemic clamp) or following the ingestion of a meal. This vascular action of insulin is pivotal for glucose disposal in skeletal muscle, as insulin‐stimulated vasodilation increases the delivery of both glucose and insulin to the myocyte. Notably, in insulin‐resistant states such as obesity and type 2 diabetes, this vascular response of insulin in skeletal muscle is significantly impaired. Whereas the majority of work in this field has focussed on the action of insulin alone on skeletal muscle microvascular blood flow and myocyte glucose metabolism, there is less understanding of how the consumption of a meal may affect skeletal muscle blood flow. This is in part due to complex variations in glucose and insulin dynamics that occurs postprandially—with changes in humoral concentrations of glucose, insulin, amino acids, gut and pancreatic peptides—compared to the hyperinsulinaemic‐euglycaemic clamp. This review will address the emerging body of evidence to suggest that postprandial blood flow responses in skeletal muscle may be a function of the nutritional composition of a meal.