Acute inactivity impairs glycemic control but not blood flow to glucose ingestion

Physiology of sedentary behavior

Sedentary behaviors (SB) are characterized by low energy expenditure while in a sitting or reclining posture. Evidence relevant to understanding the physiology of SB can be derived from studies employing several experimental models: bed rest, immobilization, reduced step count, and reducing/interrupting prolonged SB. We examine the relevant physiological evidence relating to body weight and energy balance, intermediary metabolism, cardiovascular and respiratory systems, the musculoskeletal system, the central nervous system, and immunity and inflammatory responses. Excessive and prolonged SB can lead to insulin resistance, vascular dysfunction, shift in substrate use toward carbohydrate oxidation, shift in muscle fiber from oxidative to glycolytic type, reduced cardiorespiratory fitness, loss of muscle mass and strength and bone mass, and increased total body fat mass and visceral fat depot, blood lipid concentrations, and inflammation. Despite marked differences across individual studies, longer term interventions aimed at reducing/interrupting SB have resulted in small, albeit marginally clinically meaningful, benefits on body weight, waist circumference, percent body fat, fasting glucose, insulin, HbA1c and HDL concentrations, systolic blood pressure, and vascular function in adults and older adults. There is more limited evidence for other health-related outcomes and physiological systems and for children and adolescents. Future research should focus on the investigation of molecular and cellular mechanisms underpinning adaptations to increasing and reducing/interrupting SB and the necessary changes in SB and physical activity to impact physiological systems and overall health in diverse population groups.

Accumulated Short Bouts of Walking in Older Adults With Type 2 Diabetes: Effects on Glycosylated Hemoglobin (HbA1c) and Homeostasis Model Assessment of Insulin Resistance (HOMA-IR)

The current study examined the effects of accumulated short bouts of walking on glycosylated hemoglobin (HbA1c) and homeostasis model assessment of insulin resistance (HOMA-IR) of older adults with type 2 diabetes. Differences in variables between models of accumulated bouts of walking and 10,000 steps were also investigated. Sedentary participants (N = 38) were randomized into one of three groups: accumulated 10-minute bouts of walking at 100 steps/min (10/100MW), accumulated 10,000 steps (10KS), or control. HbA1c, HOMA-IR, blood lipids, and cardiorespiratory fitness (VO2max) were assessed before and after the intervention. VO2max, HbA1c, and HOMA-IR in the 10/100MW and 10KS groups showed significant and comparable improvements postintervention compared to preintervention (p < 0.05). Furthermore, the change in average daily step count was significantly associated with the change in HbA1c of the two walking groups (r = -0.61 for 10KS and r = -0.63 for 10/100MW; p < 0.05). Accumulated short bouts of walking at 100 steps/min and 10,000 steps daily improved HbA1c and HOMA-IR of older adults with type 2 diabetes. [Research in Gerontological Nursing, 16(5), 250-258.].

Short-term removal of exercise impairs glycemic control in older adults: A randomized trial

Postprandial glycemia (PPG) predicts cardiovascular disease, and short-term physical inactivity increases PPG in young, active adults. Whether this occurs in older, active adults who may be more prone to bouts of inactivity is unknown. This study determined if postprandial interstitial glucose (PPIG) was impaired in active older adults following the removal of exercise for 3 days (NOEX) compared to active young adults. In this randomized, crossover study, 11 older (69.1 ± 1.9 years) and 9 young (32.8 ± 1.8 years) habitually active (≥90 min/week of exercise) adults completed 3-days of NOEX and 3-days of normal habitual exercise (EX), separated by ≥1 week. Diet was standardized across phases. Glycemic control (3-day average) was assessed via continuous glucose monitoring during both phases. Significant main effects of age and phase were detected (p < 0.05), but no interaction was found for steps/day (p > 0.05) (old EX: 6283 ± 607, old NOEX: 2380 ± 382 and young EX: 8798 ± 623, young NOEX: 4075 ± 516 steps/day). Significant main effects of age (p = 0.002) and time (p < 0.001) existed for 1-h PPIG, but no effect of phase or interactions was found (p > 0.05). Significant main effects (p < 0.05) of age (old: 114 ± 1 mg/dl, young: 106 ± 1 mg/dl), phase (NOEX: 112 ± 1 mg/dl, EX: 108 ± 1 mg/dl), and time (0 min: 100 ± 2, 30 min: 118 ± 2, 60 min: 116 ± 2, 90 min: 111 ± 2, 120 min: 108 ± 2 mg/dl) in 2-h PPIG were detected, but no interaction was found (p > 0.05). However, only significant main effects of phase (NOEX: 14 ± 1 and EX:12 ± 1, p > 0.05) were found for 24-h blood glucose standard deviation. Older adults appear to have impaired glycemic control compared to young adults and exercise removal impairs glycemic control in both populations. Yet, the impairment in glycemic control with exercise removal is not different between old and young adults.

Insights into the development of insulin resistance: Unraveling the interaction of physical inactivity, lipid metabolism and mitochondrial biology

While impairments in peripheral tissue insulin signalling have a well-characterized role in the development of insulin resistance and type 2 diabetes (T2D), the specific mechanisms that contribute to these impairments remain debatable. Nonetheless, a prominent hypothesis implicates the presence of a high-lipid environment, resulting in both reactive lipid accumulation and increased mitochondrial reactive oxygen species (ROS) production in the induction of peripheral tissue insulin resistance. While the etiology of insulin resistance in a high lipid environment is rapid and well documented, physical inactivity promotes insulin resistance in the absence of redox stress/lipid-mediated mechanisms, suggesting alternative mechanisms-of-action. One possible mechanism is a reduction in protein synthesis and the resultant decrease in key metabolic proteins, including canonical insulin signaling and mitochondrial proteins. While reductions in mitochondrial content associated with physical inactivity are not required for the induction of insulin resistance, this could predispose individuals to the detrimental effects of a high-lipid environment. Conversely, exercise-training induced mitochondrial biogenesis has been implicated in the protective effects of exercise. Given mitochondrial biology may represent a point of convergence linking impaired insulin sensitivity in both scenarios of chronic overfeeding and physical inactivity, this review aims to describe the interaction between mitochondrial biology, physical (in)activity and lipid metabolism within the context of insulin signalling.

Detrimental effects of physical inactivity on peripheral and brain vasculature in humans: Insights into mechanisms, long-term health consequences and protective strategies

The growing prevalence of physical inactivity in the population highlights the urgent need for a more comprehensive understanding of how sedentary behaviour affects health, the mechanisms involved and what strategies are effective in counteracting its negative effects. Physical inactivity is an independent risk factor for different pathologies including atherosclerosis, hypertension and cardiovascular disease. It is known to progressively lead to reduced life expectancy and quality of life, and it is the fourth leading risk factor for mortality worldwide. Recent evidence indicates that uninterrupted prolonged sitting and short-term inactivity periods impair endothelial function (measured by flow-mediated dilation) and induce arterial structural alterations, predominantly in the lower body vasculature. Similar effects may occur in the cerebral vasculature, with recent evidence showing impairments in cerebral blood flow following prolonged sitting. The precise molecular and physiological mechanisms underlying inactivity-induced vascular dysfunction in humans are yet to be fully established, although evidence to date indicates that it may involve modulation of shear stress, inflammatory and vascular biomarkers. Despite the steady increase in sedentarism in our societies, only a few intervention strategies have been investigated for their efficacy in counteracting the associated vascular impairments. The current review provides a comprehensive overview of the evidence linking acute and short-term physical inactivity to detrimental effects on peripheral, central and cerebral vascular health in humans. We further examine the underlying molecular and physiological mechanisms and attempt to link these to long-term consequences for cardiovascular health. Finally, we summarize and discuss the efficacy of lifestyle interventions in offsetting the negative consequences of physical inactivity.

The impact of preconditioning exercise on the vascular response to an oral glucose challenge

Exercise elicits direct benefits to insulin sensitivity but may also indirectly improve glucose uptake by hemodynamic conditioning of the vasculature. The purpose of this study was to examine the modifying effect of 3 different types of exercise on the vascular response to an oral glucose challenge. Twenty healthy adults (9 women, 11 men; aged 23 ± 3 years) completed a standard oral glucose tolerance test (OGTT) at rest, as well as 1.5 hours after moderate continuous cycling exercise (30 min; 65% peak oxygen consumption), high-intensity interval cycling exercise (10 × 1 min at 90% peak heart rate), and lower-load higher-repetition resistance exercise (25-35 repetitions/set, 3 sets). Brachial and superficial femoral artery blood flow, conductance, and oscillatory shear index were measured throughout the OGTT. Regardless of rested state or exercise preconditioning, the OGTT induced reductions in brachial artery blood flow and conductance (p < 0.001), and transient increases in brachial and superficial femoral artery oscillatory shear index and retrograde blood flow (p < 0.01). Continuous cycling and resistance exercise were followed with a small degree of protection against prolonged periods of oscillatory flow. Our findings imply transient peripheral vasoconstriction and decreased limb blood flow during a standard OGTT, for which prior exercise was unable to prevent in healthy adults. Novelty: We investigated the impact of continuous, interval, and resistance exercise on the hemodynamic response to an OGTT. Our findings suggest decreased upper-limb blood flow during an OGTT is not prevented by prior exercise in healthy adults.

High-glucose mixed-nutrient meal ingestion impairs skeletal muscle microvascular blood flow in healthy young men

Oral glucose ingestion leads to impaired muscle microvascular blood flow (MBF), which may contribute to acute hyperglycemia-induced insulin resistance. We investigated whether incorporating lipids and protein into a high-glucose load would prevent postprandial MBF dysfunction. Ten healthy young men (age, 27 yr [24, 30], mean with lower and upper bounds of the 95% confidence interval; height, 180 cm [174, 185]; weight, 77 kg [70, 84]) ingested a high-glucose (1.1 g/kg glucose) mixed-nutrient meal (10 kcal/kg; 45% carbohydrate, 20% protein, and 35% fat) in the morning after an overnight fast. Femoral arterial blood flow was measured via Doppler ultrasound, and thigh MBF was measured via contrast-enhanced ultrasound, before meal ingestion and 1 h and 2 h postprandially. Blood glucose and plasma insulin were measured at baseline and every 15 min throughout the 2-h postprandial period. Compared with baseline, thigh muscle microvascular blood volume, velocity, and flow were significantly impaired at 60 min postprandial (-25%, -27%, and -46%, respectively; all P < 0.05) and to a greater extent at 120 min postprandial (-37%, -46%, and -64%; all P < 0.01). Heart rate and femoral arterial diameter, blood velocity, and blood flow were significantly increased at 60 min and 120 min postprandial (all P < 0.05). Higher blood glucose area under the curve was correlated with greater MBF dysfunction (R² = 0.742; P < 0.001). Ingestion of a high-glucose mixed-nutrient meal impairs MBF in healthy individuals for up to 2 h postprandial.

Metabolic Implications of Diet and Energy Intake during Physical Inactivity

PURPOSE

Physical inactivity is associated with disruptions in glucose metabolism and energy balance, whereas energy restriction may blunt these adverse manifestations. During hypocaloric feeding, higher-protein intake maintains lean mass which is an important component of metabolic health. This study determined whether mild energy restriction preserves glycemic control during physical inactivity and whether this preservation is more effectively achieved with a higher-protein diet.

METHODS

Ten adults (24 ± 1 yr) consumed a control (64% carbohydrate, 20% fat, 16% protein) and higher-protein diet (50% carbohydrate, 20% fat, 30% protein) during two 10-d inactivity periods (>10,000 → ~5000 steps per day) in a randomized crossover design. Energy intake was decreased by ~400 kcal·d to account for reduced energy expenditure associated with inactivity. A subset of subjects (n = 5) completed 10 d of inactivity while consuming 35% excess of their basal energy requirements, which served as a positive control condition (overfeeding+inactivity).

RESULTS

Daily steps were decreased from 12,154 ± 308 to 4275 ± 269 steps per day (P < 0.05) which was accompanied by reduced V˙O2max (-1.8 ± 0.7 mL·kg·min, P < 0.05), independent of diet conditions. No disruptions in fasting or postprandial glucose, insulin, and nonesterified fatty acids in response to 75 g of oral glucose were observed after inactivity for both diet conditions (P > 0.05). Overfeeding+inactivity increased body weight, body fat, homeostasis model assessment of insulin resistance, and 2-h postprandial glucose and insulin concentrations (P < 0.05), despite no changes in lipid concentrations.

CONCLUSIONS

We show that independent of diet (normal vs higher-protein), mild energy restriction preserves metabolic function during short-term inactivity in healthy subjects. That is, metabolic deterioration with inactivity only manifests in the setting of energy surplus.

Quantification of Mitochondrial Oxidative Phosphorylation in Metabolic Disease: Application to Type 2 Diabetes

Type 2 diabetes (T2D) is a growing health concern with nearly 400 million affected worldwide as of 2014. T2D presents with hyperglycemia and insulin resistance resulting in increased risk for blindness, renal failure, nerve damage, and premature death. Skeletal muscle is a major site for insulin resistance and is responsible for up to 80% of glucose uptake during euglycemic hyperglycemic clamps. Glucose uptake in skeletal muscle is driven by mitochondrial oxidative phosphorylation and for this reason mitochondrial dysfunction has been implicated in T2D. In this review we integrate mitochondrial function with physiologic function to present a broader understanding of mitochondrial functional status in T2D utilizing studies from both human and rodent models. Quantification of mitochondrial function is explained both in vitro and in vivo highlighting the use of proper controls and the complications imposed by obesity and sedentary lifestyle. This review suggests that skeletal muscle mitochondria are not necessarily dysfunctional but limited oxygen supply to working muscle creates this misperception. Finally, we propose changes in experimental design to address this question unequivocally. If mitochondrial function is not impaired it suggests that therapeutic interventions and drug development must move away from the organelle and toward the cardiovascular system.

Skeletal muscle ceramides do not contribute to physical-inactivity-induced insulin resistance

Physical inactivity increases the risk to develop type 2 diabetes, a disease characterized by a state of insulin resistance. By promoting inflammatory state, ceramides are especially recognized to alter insulin sensitivity in skeletal muscle. The present study was designed to analyze, in mice, whether muscle ceramides contribute to physical-inactivity-induced insulin resistance. For this purpose, we used the wheel lock model to induce a sudden reduction of physical activity, in combination with myriocin treatment, an inhibitor of de novo ceramide synthesis. Mice were assigned to 3 experimental groups: voluntary wheel access group (Active), a wheel lock group (Inactive), and wheel lock group treated with myriocin (Inactive-Myr). We observed that 10 days of physical inactivity induces hyperinsulinemia and increases basal insulin resistance (HOMA-IR). The muscle ceramide content was not modified by physical inactivity and myriocin. Thus, muscle ceramides do not play a role in physical-inactivity-induced insulin resistance. In skeletal muscle, insulin-stimulated protein kinase B phosphorylation and inflammatory pathway were not affected by physical inactivity, whereas a reduction of glucose transporter type 4 content was observed. Based on these results, physical-inactivity-induced insulin resistance seems related to a reduction in glucose transporter type 4 content rather than defects in insulin signaling. We observed in inactive mice that myriocin treatment improves glucose tolerance, insulin-stimulated protein kinase B, adenosine-monophosphate-activated protein kinase activation, and glucose transporter type 4 content in skeletal muscle. Such effects occur regardless of changes in muscle ceramide content. These findings open promising research perspectives to identify new mechanisms of action for myriocin on insulin sensitivity and glucose metabolism.

A nutrient cocktail prevents lipid metabolism alterations induced by 20 days of daily steps reduction and fructose overfeeding: result from a randomized study

Physical inactivity and sedentary behaviors are independent risk factors for numerous diseases. We examined the ability of a nutrient cocktail composed of polyphenols, omega-3 fatty acids, vitamin E, and selenium to prevent the expected metabolic alterations induced by physical inactivity and sedentary behaviors. Healthy trained men ( n = 20) (averaging ∼14,000 steps/day and engaged in sports) were randomly divided into a control group (no supplementation) and a cocktail group for a 20-day free-living intervention during which they stopped exercise and decreased their daily steps (averaging ∼3,000 steps/day). During the last 10 days, metabolic changes were further triggered by fructose overfeeding. On days 0, 10, and 20, body composition (dual energy X-ray), blood chemistry, glucose tolerance [oral glucose tolerance test (OGTT)], and substrate oxidation (indirect calorimetry) were measured. OGTT included 1% fructose labeled with (U-¹³C) fructose to assess liver de novo lipogenesis. Histological changes and related cellular markers were assessed from muscle biopsies collected on days 0 and 20. While the cocktail did not prevent the decrease in insulin sensitivity and its muscular correlates induced by the intervention, it fully prevented the hypertriglyceridemia, the drop in fasting HDL and total fat oxidation, and the increase in de novo lipogenesis. The cocktail further prevented the decrease in the type-IIa muscle fiber cross-sectional area and was associated with lower protein ubiquitination content. The circulating antioxidant capacity was improved by the cocktail following the OGTT. In conclusion, a cocktail of nutrient compounds from dietary origin protects against the alterations in lipid metabolism induced by physical inactivity and fructose overfeeding. NEW & NOTEWORTHY This is the first study to test the efficacy of a novel dietary nutrient cocktail on the metabolic and physiological changes occurring during 20 days of physical inactivity along with fructose overfeeding. The main findings of this study are that 1) reduction in daily steps leads to decreased insulin sensitivity and total fat oxidation, resulting in hyperlipemia and increased de novo lipogenesis and 2) a cocktail supplement prevents the alterations on lipid metabolism.

Oral glucose challenge impairs skeletal muscle microvascular blood flow in healthy people

Skeletal muscle microvascular (capillary) blood flow increases in the postprandial state or during insulin infusion due to dilation of precapillary arterioles to augment glucose disposal. This effect occurs independently of changes in large artery function. However, acute hyperglycemia impairs vascular function, causes insulin to vasoconstrict precapillary arterioles, and causes muscle insulin resistance in vivo. We hypothesized that acute hyperglycemia impairs postprandial muscle microvascular perfusion, without disrupting normal large artery hemodynamics, in healthy humans. Fifteen healthy people (5 F/10 M) underwent an oral glucose challenge (OGC, 50 g glucose) and a mixed-meal challenge (MMC) on two separate occasions (randomized, crossover design). At 1 h, both challenges produced a comparable increase (6-fold) in plasma insulin levels. However, the OGC produced a 1.5-fold higher increase in blood glucose compared with the MMC 1 h postingestion. Forearm muscle microvascular blood volume and flow (contrast-enhanced ultrasound) were increased during the MMC (1.3- and 1.9-fold from baseline, respectively, P < 0.05 for both) but decreased during the OGC (0.7- and 0.6-fold from baseline, respectively, P < 0.05 for both) despite a similar hyperinsulinemia. Both challenges stimulated brachial artery flow (ultrasound) and heart rate to a similar extent, as well as yielding comparable decreases in diastolic blood pressure and total vascular resistance. Systolic blood pressure and aortic stiffness remained unaltered by either challenge. Independently of large artery hemodynamics, hyperglycemia impairs muscle microvascular blood flow, potentially limiting glucose disposal into skeletal muscle. The OGC reduced microvascular blood flow in muscle peripherally and therefore may underestimate the importance of skeletal muscle in postprandial glucose disposal.

Influence of physical inactivity on arterial compliance during a glucose challenge

NEW FINDINGS

What is the central question of this study? To understand better the effects of acute hyperglycaemia on arterial stiffness in healthy young individuals, we assessed arterial stiffness in physically active men before and after reduced ambulatory physical activity to decrease insulin sensitivity. What is the main finding and its importance? During an oral glucose tolerance test, we identified an increase in leg arterial stiffness (i.e. reduced femoral artery compliance) only when subjects were inactive for 5 days (<5000 steps day^-1 ) and not when they were engaging in regular physical activity (>10,000 steps day^-1 ). These results demonstrate the deleterious consequence of acute reductions in daily physical activity on the response of the peripheral vasculature to acute hyperglycaemia.

ABSTRACT

Acute hyperglycaemia has been shown to augment indices of arterial stiffness in patients with insulin resistance and other co-morbidities; however, conflicting results exist in healthy young individuals. We examined whether acute hyperglycaemia after an oral glucose tolerance test (OGTT) increases arterial stiffness in healthy active men before and after reduced ambulatory physical activity to decrease insulin sensitivity. High-resolution arterial diameter traces acquired from Doppler ultrasound allowed an arterial blood pressure (BP) waveform to be obtained from the diameter trace within a cardiac cycle. In 24 subjects, this method demonstrated sufficient agreement with the traditional approach for assessing arterial compliance using applanation tonometry. In 10 men, continuous recordings of femoral and brachial artery diameter and beat-to-beat BP (Finometer) were acquired at rest, 60 and 120 min of an OGTT before and after 5 days of reduced activity (from >10,000 to <5000 steps day^-1 ). Compliance and β-stiffness were quantified. Before the reduction in activity, the OGTT had no effect on arterial compliance or β-stiffness. However, after the reduction in activity, femoral compliance was decreased (rest, 0.10 ± 0.03 mm²  mmHg^-1 versus 120 min OGTT, 0.06 ± 0.02 mm²  mmHg^-1 ; P < 0.001) and femoral β-stiffness increased (rest, 8.7 ± 2.7 a.u. versus 120 min OGTT, 15.3 ± 6.5 a.u.; P < 0.001) during OGTT, whereas no changes occurred in brachial artery compliance (P = 0.182) or stiffness (P = 0.892). Insulin sensitivity (Matsuda index) was decreased after the reduction in activity (P = 0.002). In summary, in young healthy men the femoral artery becomes susceptible to acute hyperglycaemia after 5 days of reduced activity and the resultant decrease in insulin sensitivity, highlighting the strong influence of daily physical activity levels on vascular physiology.

Transition from physical activity to inactivity increases skeletal muscle miR-148b content and triggers insulin resistance

This study investigated miR‐148b as a potential physiological actor of physical inactivity‐induced effects in skeletal muscle. By using animal and human protocols, we demonstrated that the early phase of transition toward inactivity was associated with an increase in muscle miR‐148b content, which triggered the downregulation of NRAS and ROCK1 target genes. Using human myotubes, we demonstrated that overexpression of miR‐148b decreased NRAS and ROCK1 protein levels, and PKB phosphorylation and glucose uptake in response to insulin. Increase in muscle miR‐148b content might thus participate in the decrease in insulin sensitivity at the whole body level during the transition toward physical inactivity.

Role of Inactivity in Chronic Diseases: Evolutionary Insight and Pathophysiological Mechanisms

This review proposes that physical inactivity could be considered a behavior selected by evolution for resting, and also selected to be reinforcing in life-threatening situations in which exercise would be dangerous. Underlying the notion are human twin studies and animal selective breeding studies, both of which provide indirect evidence for the existence of genes for physical inactivity. Approximately 86% of the 325 million in the United States (U.S.) population achieve less than the U.S. Government and World Health Organization guidelines for daily physical activity for health. Although underappreciated, physical inactivity is an actual contributing cause to at least 35 unhealthy conditions, including the majority of the 10 leading causes of death in the U.S. First, we introduce nine physical inactivity-related themes. Next, characteristics and models of physical inactivity are presented. Following next are individual examples of phenotypes, organ systems, and diseases that are impacted by physical inactivity, including behavior, central nervous system, cardiorespiratory fitness, metabolism, adipose tissue, skeletal muscle, bone, immunity, digestion, and cancer. Importantly, physical inactivity, itself, often plays an independent role as a direct cause of speeding the losses of cardiovascular and strength fitness, shortening of healthspan, and lowering of the age for the onset of the first chronic disease, which in turn decreases quality of life, increases health care costs, and accelerates mortality risk.

Obesity, type 2 diabetes, and impaired insulin-stimulated blood flow: role of skeletal muscle NO synthase and endothelin-1

Increased endothelin-1 (ET-1) and reduced endothelial nitric oxide phosphorylation (peNOS) are hypothesized to reduce insulin-stimulated blood flow in type 2 diabetes (T2D), but studies examining these links in humans are limited. We sought to assess basal and insulin-stimulated endothelial signaling proteins (ET-1 and peNOS) in skeletal muscle from T2D patients. Ten obese T2D [glucose disposal rate (GDR): 6.6 ± 1.6 mg·kg lean body mass (LBM)^-1·min^-1] and 11 lean insulin-sensitive subjects (Lean GDR: 12.9 ± 1.2 mg·kg LBM^-1·min^-1) underwent a hyperinsulinemic-euglycemic clamp with vastus lateralis biopsies taken before and 60 min into the clamp. Basal biopsies were also taken in 11 medication-naïve, obese, non-T2D subjects. ET-1, peNOS (Ser1177), and eNOS protein and mRNA were measured from skeletal muscle samples containing native microvessels. Femoral artery blood flow was assessed by duplex Doppler ultrasound. Insulin-stimulated blood flow was reduced in obese T2D (Lean: +50.7 ± 6.5% baseline, T2D: +20.8 ± 5.2% baseline, P < 0.05). peNOS/eNOS content was higher in Lean under basal conditions and, although not increased by insulin, remained higher in Lean during the insulin clamp than in obese T2D (P < 0.05). ET-1 mRNA and peptide were 2.25 ± 0.50- and 1.52 ± 0.11-fold higher in obese T2D compared with Lean at baseline, and ET-1 peptide remained 2.02 ± 1.9-fold elevated in obese T2D after insulin infusion (P < 0.05) but did not increase with insulin in either group (P > 0.05). Obese non-T2D subjects tended to also display elevated basal ET-1 (P = 0.06). In summary, higher basal skeletal muscle expression of ET-1 and reduced peNOS/eNOS may contribute to a reduced insulin-stimulated leg blood flow response in obese T2D patients.

NEW & NOTEWORTHY

Although impairments in endothelial signaling are hypothesized to reduce insulin-stimulated blood flow in type 2 diabetes (T2D), human studies examining these links are limited. We provide the first measures of nitric oxide synthase and endothelin-1 expression from skeletal muscle tissue containing native microvessels in individuals with and without T2D before and during insulin stimulation. Higher basal skeletal muscle expression of endothelin-1 and reduced endothelial nitric oxide phosphorylation (peNOS)/eNOS may contribute to reduced insulin-stimulated blood flow in obese T2D patients.

From physical inactivity to immobilization: Dissecting the role of oxidative stress in skeletal muscle insulin resistance and atrophy

In the literature, the terms physical inactivity and immobilization are largely used as synonyms. The present review emphasizes the need to establish a clear distinction between these two situations. Physical inactivity is a behavior characterized by a lack of physical activity, whereas immobilization is a deprivation of movement for medical purpose. In agreement with these definitions, appropriate models exist to study either physical inactivity or immobilization, leading thereby to distinct conclusions. In this review, we examine the involvement of oxidative stress in skeletal muscle insulin resistance and atrophy induced by, respectively, physical inactivity and immobilization. A large body of evidence demonstrates that immobilization-induced atrophy depends on the chronic overproduction of reactive oxygen and nitrogen species (RONS). On the other hand, the involvement of RONS in physical inactivity-induced insulin resistance has not been investigated. This observation outlines the need to elucidate the mechanism by which physical inactivity promotes insulin resistance.

A Trial of Lifestyle Modification on Cardiopulmonary, Inflammatory, and Metabolic Effects among Obese with Chronic Kidney Disease

BACKGROUND

The feasibility and benefits of lifestyle intervention in chronic kidney disease (CKD) patients who are obese has not been well studied. We examined the early effects of an exercise plus weight loss intervention on body composition, exercise capacity, metabolic parameters and kidney function in obese subjects with CKD.

METHODS

Nine subjects (median age 57 years, body mass index (BMI) 43.9) underwent a lifestyle intervention program that included supervised aerobic exercise (i.e. ∼85% maximum heart rate) and dietary counseling (500 kcal reduction in daily caloric intake). Body composition (iDXA), exercise capacity (maximal oxygen consumption), quality of life, insulin resistance (Matsuda index), inflammation (high sensitivity C-reactive protein), adipokines (leptin and total adiponectin) and kidney function (iothalamate glomerular filtration rate) were measured at baseline and after 12 weeks of the intervention. Changes in parameters were compared using the Wilcoxon signed-rank test.

RESULTS

After 12 weeks of intervention, there was a significant decrease in BMI and fat mass (median -4.9 kg (25th-75th percentile -5.9 to -3.0)). There was a significant increase in exercise capacity (3.7 ml/kg/min (3.0-4.7)), along with improvements in insulin sensitivity (0.55 (0.43-1.2)), total adiponectin (780.9 μg/ml (262.1-1,497.1)) and leptin (-5.1 ng/ml (-14.5 to -3.3)). There were improvements in biomarkers of kidney disease very quality of life measures, but kidney function remained unchanged.

CONCLUSION

Lifestyle modification is feasible in obese patients with CKD and produces weight loss that is related to improvements in exercise capacity, insulin resistance and adipokines. Whether lifestyle-induced weight loss and fitness can be sustained and whether it will mediate improvements in kidney function over time merits further investigation.

The influence of reduced insulin sensitivity via short-term reductions in physical activity on cardiac baroreflex sensitivity during acute hyperglycemia

Reduced insulin sensitivity and impaired glycemic control are among the consequences of physical inactivity and have been associated with reduced cardiac baroreflex sensitivity (BRS). However, the effect of reduced insulin sensitivity and acute hyperglycemia following glucose consumption on cardiac BRS in young, healthy subjects has not been well characterized. We hypothesized that a reduction in insulin sensitivity via reductions in physical activity would reduce cardiac BRS at rest and following an oral glucose tolerance test (OGTT). Nine recreationally active men (23 ± 1 yr; >10,000 steps/day) underwent 5 days of reduced daily physical activity (RA5) by refraining from planned exercise and reducing daily steps (<5,000 steps/day). Spontaneous cardiac BRS (sequence technique) was compared at rest and for 120 min following an OGTT at baseline and after RA5. A substudy (n = 8) was also performed to independently investigate the influence of elevated insulin alone on cardiac BRS using a 120-min hyperinsulinemic-euglycemic clamp. Insulin sensitivity (Matsuda index) was significantly reduced following RA5 (BL 9.2 ± 1.3 vs. RA5 6.4 ± 1.1, P < 0.001). Resting cardiac BRS was unaffected by RA5 and significantly reduced during the OGTT similarly at baseline and RA5 (baseline 0 min, 28 ± 4 vs. 120 min, 18 ± 4; RA5 0 min, 28 ± 4 vs. 120 min, 21 ± 3 ms/mmHg). Spontaneous cardiac BRS was also reduced during the hyperinsulinemic-euglycemic clamp (P < 0.05). Collectively, these data demonstrate that acute elevations in plasma glucose and insulin can impair spontaneous cardiac BRS in young, healthy subjects, and that reductions in cardiac BRS following acute hyperglycemia are unaffected by reduced insulin sensitivity via short-term reductions in physical activity.