Exercise induces lipoprotein lipase and GLUT-4 protein in muscle independent of adrenergic-receptor signaling

Decreased pancreatic amylase activity after acute high-intensity exercise and its effects on post-exercise muscle glycogen recovery

Our prior results showed that an acute bout of endurance exercise for 6 h, but not 1 h, decreased pancreatic amylase activity, indicating that acute endurance exercise may affect carbohydrate digestive capacity in an exercise duration-dependent manner. Here, we investigated the effects of acute endurance exercise of different intensities on mouse pancreatic amylase activity. Male C57BL/6J mice performed low- or high-intensity running exercise for 60 min at either 10 (Ex-Low group) or 20 m/min (Ex-High group). The control group comprised sedentary mice. Immediately after acute exercise, pancreatic amylase activity was significantly decreased in the Ex-High group and not the Ex-Low group in comparison with the control group. To determine whether the decreased amylase activity induced by high-intensity exercise influenced muscle glycogen recovery after exercise, we investigated the rates of muscle glycogen resynthesis in Ex-High group mice administered either oral glucose or starch solution (2.0 mg/g body weight) immediately after exercise. The starch-fed mice exhibited significantly lower post-exercise glycogen accumulation rates in the 2-h recovery period compared with the glucose-fed mice. This difference in the glycogen accumulation rate was absent for starch- and glucose-fed mice in the sedentary (no exercise) control group. Furthermore, the plasma glucose AUC during early post-exercise recovery (0-60 min) was significantly lower in the starch-fed mice than in the glucose-fed mice. Thus, our findings suggest that acute endurance exercise diminishes the carbohydrate digestive capacity of the pancreas in a manner dependent on exercise intensity, with polysaccharides leading to delayed muscle glycogen recovery after exercise.

Association of physical activity and trajectories of physical activity with cardiovascular disease

INTRODUCTION

Prolonged sedentary life existence is associated with increased incidence of cardiovascular disease (CVD), coronary heart disease (CHD), obesity, type 2 diabetes mellitus (T2DM), hypertension, heart failure (HF), and all-cause mortality. On the contrary, regular exercise is known from antiquity to be associated with beneficial cardiovascular (CV) effects and decreased mortality.

AREAS COVERED

The cardiovascular (CV) benefits of exercise have been confirmed by many studies, but the trajectories of the different modes of PA are not well recognized. In order to examine the different modalities of exercise and its long-term trajectories, a Medline search of the English literature was conducted between 2015 and 2022 and 60 pertinent papers were selected for review.

EXPERT OPINION

Careful review of the selected papers showed that the beneficial CV effects of PA are mediated through several favorable modifications of molecular and clinical factors. Also, any type of physical activity in conjunction with lifestyle adjustments is associated with decreased incidence of CVD, CHD, obesity, T2DM, hypertension, HF, and all-cause mortality. In addition, the long-term trajectories regarding the duration and the level of exercise are associated with greater beneficial CV effects, with even the resumption of discontinued exercise can lead to beneficial CV effects.

Sedentary Behaviour-A Target for the Prevention and Management of Cardiovascular Disease

Cardiovascular disease (CVD) is highly prevalent and can lead to disability and premature mortality. Sedentary behaviour, defined as a low energy expenditure while sitting or lying down, has been identified as an independent risk factor for CVD. This article discusses (1) the association of total sedentary time and patterns of accumulating sedentary time with CVD risk markers, CVD incidence and mortality; (2) acute experimental evidence regarding the acute effects of reducing and breaking up sedentary time on CVD risk markers; and (3) the effectiveness of longer-term sedentary behaviour interventions on CVD risk. Findings suggest that under rigorously controlled laboratory and free-living conditions, breaking up sedentary time improves cardiovascular risk markers in individuals who are healthy, overweight or obese, or have impaired cardiovascular health. Breaking up sedentary time with walking may have the most widespread benefits, whereas standing breaks may be less effective, especially in healthy individuals. There is also growing evidence that sedentary behaviour interventions may benefit cardiovascular risk in the longer term (i.e., weeks to months). Reducing and breaking up sedentary time may, therefore, be considered a target for preventing and managing CVD. Further research is needed to determine the effectiveness of sedentary behaviour interventions over the long-term to appropriately inform guidelines for the management of CVD.

Exercise, Physical Activity, and Cardiometabolic Health: Pathophysiologic Insights

Physical activity and its sustained and purposeful performance-exercise-promote a broad and diverse set of metabolic and cardiovascular health benefits. Regular exercise is the most effective way to improve cardiorespiratory fitness, a measure of one's global cardiovascular, pulmonary and metabolic health, and one of the strongest predictors of future health risk. Here, we describe how exercise affects individual organ systems related to cardiometabolic health, including the promotion of insulin and glucose homeostasis through improved efficiency in skeletal muscle glucose utilization and enhanced insulin sensitivity; beneficial changes in body composition and adiposity; and improved cardiac mechanics and vascular health. We subsequently identify knowledge gaps that remain in exercise science, including heterogeneity in exercise responsiveness. While the application of molecular profiling technologies in exercise science has begun to illuminate the biochemical pathways that govern exercise-induced health promotion, much of this work has focused on individual organ systems and applied single platforms. New insights into exercise-induced secreted small molecules and proteins that impart their effects in distant organs ("exerkines") highlight the need for an integrated approach towards the study of exercise and its global effects; efforts that are ongoing.

High-intensity interval exercise in the cold regulates acute and postprandial metabolism

High-intensity interval exercise (HIIE) has been shown to be more effective than moderate-intensity exercise for increasing acute lipid oxidation and lowering blood lipids during exercise and postprandially. Exercise in cold environments is also known to enhance lipid oxidation; however, the immediate and long-term effects of HIIE exercise in cold are unknown. The purpose of this study was to examine the effects cold stress during HIIE on acute exercise metabolism and postprandial metabolism. Eleven recreationally active individuals (age: 23 ± 3 yr, weight: 80 ± 9.7 kg, V̇O_2peak: 39.2 ± 5.73 mL·kg^-1·min^-1) performed evening HIIE sessions (10 × 60 s cycling, 90% V̇O_2peak interspersed with 90 s active recovery, 30% V̇O_2peak) in thermoneutral (HIIE-TN, control; 21°C) and cold environment (HIIE-CO; 0°C), following a balanced crossover design. The following morning, participants consumed a high-fat meal. Indirect calorimetry was used to assess substrate oxidation, and venous blood samples were obtained to assess changes in noncellular metabolites. During acute exercise, lipid oxidation was higher in HIIE-CO (P = 0.002) without differences in V̇O₂ and energy expenditure (P ≥ 0.162) between conditions. Postprandial V̇O₂, lipid and CHO oxidation, plasma insulin, and triglyceride concentrations were not different between conditions (P > 0.05). Postprandial blood LDL-C levels were higher in HIIE-CO 2 h after the meal (P = 0.003). Postprandial glucose area under curve was 49% higher in HIIE-CO versus HIIE-TN (P = 0.034). Under matched energy expenditure conditions, HIIE demonstrated higher lipid oxidation rates during exercise in the cold; but only marginally influenced postprandial lipid metabolism the following morning. In conclusion, HIIE in the cold seemed to be less favorable for postprandial lipid and glycemic responses.NEW & NOTEWORTHY This is the first known study to investigate the effects of cold ambient temperatures on acute metabolism during high-intensity interval exercise, as well as postprandial metabolism the next day. We observed that high-intensity interval exercise in a cold environment does change acute metabolism compared to a thermoneutral environment; however, the addition of a cold stimulus was less favorable for postprandial metabolic responses the following day.

Impaired postprandial glucose and no improvement in other cardiometabolic responses or cognitive function by breaking up sitting with bodyweight resistance exercises: a randomised crossover trial

The effects of breaking up sitting with resistance exercise on cardiometabolic health and cognitive function in young healthy adults are unknown. This study evaluated the acute effects of breaking up sitting with bodyweight resistance exercise on postprandial glucose, lipids, blood pressure and cognitive function. A randomised crossover design was used. Twelve normal-weight participants aged 25 ± 6 years took part in two, 5 h conditions: (1) uninterrupted sitting (SIT), and (2) sitting with 3 min of bodyweight resistance exercise breaks every 30 min (REX). Dietary intake was standardised across conditions. Linear mixed models were used to compare outcomes between conditions. Postprandial glucose was significantly higher in the REX condition than in SIT (incremental area under the curve 346.3 [95% confidence interval: 233.9, 458.7] and 256.9 [144.4, 369.3] mmol/L∙5 h, respectively, p = 0.045). Blood pressure, lipids and cognitive function outcomes were not different between conditions (p ≥ 0.05). This study suggests that breaking up sitting with bodyweight resistance exercise does not benefit cardiometabolic health or cognitive function acutely in young healthy adults. The longer-term effects of breaking up sitting with resistance exercise warrants investigation to appropriately inform public health guidelines.

The Importance of Fatty Acids as Nutrients during Post-Exercise Recovery

It is well recognized that whole-body fatty acid (FA) oxidation remains increased for several hours following aerobic endurance exercise, even despite carbohydrate intake. However, the mechanisms involved herein have hitherto not been subject to a thorough evaluation. In immediate and early recovery (0–4 h), plasma FA availability is high, which seems mainly to be a result of hormonal factors and increased adipose tissue blood flow. The increased circulating availability of adipose-derived FA, coupled with FA from lipoprotein lipase (LPL)-derived very-low density lipoprotein (VLDL)-triacylglycerol (TG) hydrolysis in skeletal muscle capillaries and hydrolysis of TG within the muscle together act as substrates for the increased mitochondrial FA oxidation post-exercise. Within the skeletal muscle cells, increased reliance on FA oxidation likely results from enhanced FA uptake into the mitochondria through the carnitine palmitoyltransferase (CPT) 1 reaction, and concomitant AMP-activated protein kinase (AMPK)-mediated pyruvate dehydrogenase (PDH) inhibition of glucose oxidation. Together this allows glucose taken up by the skeletal muscles to be directed towards the resynthesis of glycogen. Besides being oxidized, FAs also seem to be crucial signaling molecules for peroxisome proliferator-activated receptor (PPAR) signaling post-exercise, and thus for induction of the exercise-induced FA oxidative gene adaptation program in skeletal muscle following exercise. Collectively, a high FA turnover in recovery seems essential to regain whole-body substrate homeostasis.

Interventions to promote cardiometabolic health and slow cardiovascular ageing

Cardiovascular ageing and the atherosclerotic process begin very early in life, most likely in utero. They progress over decades of exposure to suboptimal or abnormal metabolic and hormonal risk factors, eventually culminating in very common, costly, and mostly preventable target-organ pathologies, including coronary heart disease, stroke, heart failure, aortic aneurysm, peripheral artery disease, and vascular dementia. In this Review, we discuss findings from preclinical and clinical studies showing that calorie restriction (CR), intermittent fasting, and adjusted diurnal rhythm of feeding, with adequate intake of specific macronutrients and micronutrients, are powerful interventions not only for the prevention of cardiovascular disease but also for slowing the accumulation of molecular damage leading to cardiometabolic dysfunction. Furthermore, we discuss the mechanisms through which a number of other nondietary interventions, such as regular physical activity, mindfulness-based stress-reduction exercises, and some CR-mimetic drugs that target pro-ageing pathways, can potentiate the beneficial effects of a healthy diet in promoting cardiometabolic health.

Association between skeletal muscle mass and serum concentrations of lipoprotein lipase, GPIHBP1, and hepatic triglyceride lipase in young Japanese men

Background

Two important regulators for circulating lipid metabolisms are lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL). In relation to this, glycosylphosphatidylinositol anchored high-density lipoprotein binding protein 1 (GPIHBP1) has been shown to have a vital role in LPL lipolytic processing. However, the relationships between skeletal muscle mass and lipid metabolism, including LPL, GPIHBP1, and HTGL, remain to be elucidated. Demonstration of these relationships may lead to clarification of the metabolic dysfunctions caused by sarcopenia. In this study, these relationships were investigated in young Japanese men who had no age-related factors; participants included wrestling athletes with abundant skeletal muscle.

Methods

A total of 111 young Japanese men who were not taking medications were enrolled; 70 wrestling athletes and 41 control students were included. The participants’ body compositions, serum concentrations of lipoprotein, LPL, GPIHBP1 and HTGL and thyroid function test results were determined under conditions of no extreme dietary restrictions and exercises.

Results

Compared with the control participants, wrestling athletes had significantly higher skeletal muscle index (SMI) (p < 0.001), higher serum concentrations of LPL (p < 0.001) and GPIHBP1 (p < 0.001), and lower fat mass index (p = 0.024). Kruskal–Wallis tests with Bonferroni multiple comparison tests showed that serum LPL and GPIHBP1 concentrations were significantly higher in the participants with higher SMI. Spearman’s correlation analyses showed that SMI was positively correlated with LPL (ρ = 0.341, p < 0.001) and GPIHBP1 (ρ = 0.309, p = 0.001) concentration. The serum concentrations of LPL and GPIHBP1 were also inversely correlated with serum concentrations of triglyceride (LPL, ρ = − 0.198, p = 0.037; GPIHBP1, ρ = − 0.249, p = 0.008). Serum HTGL concentration was positively correlated with serum concentrations of total cholesterol (ρ = 0.308, p = 0.001), low-density lipoprotein-cholesterol (ρ = 0.336, p < 0.001), and free 3,5,3′-triiodothyronine (ρ = 0.260, p = 0.006), but not with SMI.

Conclusions

The results suggest that increased skeletal muscle mass leads to improvements in energy metabolism by promoting triglyceride-rich lipoprotein hydrolysis through the increase in circulating LPL and GPIHBP1.

Exercise Increases Glucose Transporter-4 Levels on Peripheral Blood Mononuclear Cells

PURPOSE

Glucose transporter 4 (GLUT4) plays a key role in the pathophysiology of type 2 diabetes. Glucose transporter 4 is upregulated in response to exercise, enhancing cellular glucose transport in skeletal muscle tissue. This mechanism appears to remain intact in individuals with insulin resistance. Details of the mechanism are poorly understood and are challenging to study due to the invasive nature of muscle biopsy. Peripheral blood mononuclear cells (PBMC) have documented insulin-sensitive GLUT4 activity and may serve as a proxy tissue for studying skeletal muscle GLUT4. The purpose of this study was to investigate whether GLUT4 in PBMC is affected by conditioning.

METHODS

We recruited 16 student athletes from the cross-country running and skiing teams and fifteen sedentary students matched for age and sex from the University of Alaska Fairbanks. Peripheral blood mononuclear cells were collected with mononuclear cell separation tubes. The GLUT4 concentrations were measured using a commercially available enzyme linked immunosorbent assay. Additionally, correlations between PBMC GLUT4 and common indicators of insulin resistance were examined.

RESULTS

Results indicate significantly higher PBMC GLUT4 levels in conditioned athletes than in their sedentary counterparts, similar to what has been documented in myocytes. Females were observed to have higher PBMC GLUT4 levels than males. Correlations were not detected between PBMC GLUT4 and hemoglobin A1c, glucose, insulin, homeostatic model assessment of insulin resistance, body mass index, or body fat.

CONCLUSIONS

This study provides evidence to support exploration of PBMC as a proxy tissue for studying GLUT4 response to exercise or other noninsulin factors.

Exercise and GLUT4 in human subcutaneous adipose tissue

To examine the effect of acute and chronic exercise on adipose tissue GLUT4 expression, a total of 20 healthy, male subjects performed one of two studies. Ten subjects performed cycle ergometer exercise for 60 min at 73 ± 2% VO2 peak and abdominal adipose tissue samples were obtained immediately before and after exercise and after 3 h of recovery. Another 10 subjects completed 10 days of exercise training, comprising a combination of six sessions of 60 min at 75% VO2 peak and four sessions of 6 × 5 min at 90% VO2 peak, separated by 3 min at 40% VO2 peak. Abdominal adipose tissue and vastus lateralis muscle samples were obtained before training and 24 h after the last training session. A single bout of exercise did not change adipose tissue GLUT4 mRNA; however, there was a small, but significant, reduction in adipose tissue GLUT4 protein expression 3 h after exercise. There were no changes in adipose tissue GLUT4 or COX-IV expression following exercise training. In contrast, skeletal muscle GLUT4 and COX-IV were increased by 47% and 44%, respectively following exercise training. The exercise training-induced increase in GLUT4 expression was similar in both type I and type IIa single muscle fibers. Our results indicate that neither a single exercise bout, nor 10 days of exercise training, increased adipose tissue GLUT4, in contrast with the increases observed in skeletal muscle GLUT4 expression.

Exosomes as Mediators of the Systemic Adaptations to Endurance Exercise

Habitual endurance exercise training is associated with multisystemic metabolic adaptations that lower the risk of inactivity-associated disorders such as obesity and type 2 diabetes mellitus (T2DM). Identification of complex systemic signaling networks responsible for these benefits are of great interest because of their therapeutic potential in metabolic diseases; however, specific signals that modulate the multisystemic benefits of exercise in multiple tissues and organs are only recently being discovered. Accumulated evidence suggests that muscle and other tissues have an endocrine function and release peptides and nucleic acids into the circulation in response to acute endurance exercise to mediate the multisystemic adaptations. Factors released from skeletal muscle have been termed myokines and we propose that the total of all factors released in response to endurance exercise (including peptides, nucleic acids, and metabolites) be termed, "exerkines." We propose that many of the exerkines are released within extracellular vesicles called exosomes, which regulate peripheral organ cross talk. Exosomes (30-140 nm) and larger microvesicles [MVs] (100-1000 nm) are subcategories of extracellular vesicles that are released into the circulation. Exosomes contain peptides and several nucleic acids (microRNA [miRNA], messenger RNA [mRNA], mitochondrial DNA [mtDNA]) and are involved in intercellular/tissue exchange of their contents. An acute bout of endurance exercise increases circulating exosomes that are hypothesized to mediate organ cross talk to promote systemic adaptation to endurance exercise. Further support for the role of exosomes (and possibly MVs) in mediating the systemic benefits of exercise comes from the fact that the majority of the previously reported myokines/exerkines are found in extracellular vesicles databases (Vesiclepedia and ExoCarta). We propose that exosomes isolated from athletes following exercise or exosomes bioengineered to incorporate one or many of known exerkines will be therapeutically useful in the treatment of obesity, T2DM, and other aging-associated metabolic disorders.

Role of AMP-Activated Protein Kinase for Regulating Post-exercise Insulin Sensitivity

Skeletal muscle insulin resistance precedes development of type 2 diabetes (T2D). As skeletal muscle is a major sink for glucose disposal, understanding the molecular mechanisms involved in maintaining insulin sensitivity of this tissue could potentially benefit millions of people that are diagnosed with insulin resistance. Regular physical activity in both healthy and insulin-resistant individuals is recognized as the single most effective intervention to increase whole-body insulin sensitivity and thereby positively affect glucose homeostasis. A single bout of exercise has long been known to increase glucose disposal in skeletal muscle in response to physiological insulin concentrations. While this effect is identified to be restricted to the previously exercised muscle, the molecular basis for an apparent convergence between exercise- and insulin-induced signaling pathways is incompletely known. In recent years, we and others have identified the Rab GTPase-activating protein, TBC1 domain family member 4 (TBC1D4) as a target of key protein kinases in the insulin- and exercise-activated signaling pathways. Our working hypothesis is that the AMP-activated protein kinase (AMPK) is important for the ability of exercise to insulin sensitize skeletal muscle through TBC1D4. Here, we aim to provide an overview of the current available evidence linking AMPK to post-exercise insulin sensitivity.

The effect of exercise intensity and excess postexercise oxygen consumption on postprandial blood lipids in physically inactive men

Reductions in postprandial lipemia have been observed following aerobic exercise of sufficient energy expenditure. Increased excess postexercise oxygen consumption (EPOC) has been documented when comparing high- versus low-intensity exercise. The contribution of EPOC energy expenditure to alterations in postprandial lipemia has not been determined. The purpose of this study was to evaluate the effects of low- and high-intensity exercise on postprandial lipemia in healthy, sedentary, overweight and obese men (age, 43 ± 10 years; peak oxygen consumption, 31.1 ± 7.5 mL·kg^-1·min^-1; body mass index, 31.8 ± 4.5 kg/m²) and to determine the contribution of EPOC to reductions in postprandial lipemia. Participants completed 4 conditions: nonexercise control, low-intensity exercise at 40%-50% oxygen uptake reserve (LI), high-intensity exercise at 70%-80% oxygen uptake reserve (HI), and HI plus EPOC re-feeding (HI+EERM), where the difference in EPOC energy expenditure between LI and HI was re-fed in the form of a sports nutrition bar (Premier Nutrition Corp., Emeryville, Calif., USA). Two hours following exercise participants ingested a high-fat (1010 kcals, 99 g sat fat) test meal. Blood samples were obtained before exercise, before the test meal, and at 2, 4, and 6 h postprandially. Triglyceride incremental area under the curve was significantly reduced following LI, HI, and HI+EERM when compared with nonexercise control (p < 0.05) with no differences between the exercise conditions (p > 0.05). In conclusions, prior LI and HI exercise equally attenuated postprandial triglyceride responses to the test meal. The extra energy expended during EPOC does not contribute significantly to exercise energy expenditure or to reductions in postprandial lipemia in overweight men.

The potential of endurance exercise-derived exosomes to treat metabolic diseases

Endurance exercise-mediated multisystemic adaptations are known to mitigate metabolism-related disorders such as obesity and type 2 diabetes mellitus (T2DM). However, the underlying molecular mechanisms that promote crosstalk between organs and orchestrate the pro-metabolic effects of endurance exercise remain unclear. Exercise-induced release of peptides and nucleic acids from skeletal muscle and other organs (collectively termed 'exerkines') has been implicated in mediating these systemic adaptations. Given that the extracellular milieu is probably not a hospitable environment for labile exerkines, a lipid vehicle-based mode of delivery has originated over the course of evolution. Two types of extracellular vesicles, exosomes and microvesicles, have been shown to contain proteins and nucleic acids that participate in a variety of physiological and pathological processes. Exosomes, in particular, have been shown to facilitate the exchange of peptides, microRNA, mRNA and mitochondrial DNA between cells and tissues. Intriguingly, circulatory extracellular vesicle content increases in an intensity-dependant manner in response to endurance exercise. We propose that the systemic benefits of exercise are modulated by exosomes and/or microvesicles functioning in an autocrine, paracrine and/or endocrine manner. Furthermore, we posit that native or modified exosomes, and/or microvesicles enriched with exerkines will have therapeutic utility in the treatment of obesity and T2DM.

Targeting fatty acid metabolism to improve glucose metabolism

Disturbances in fatty acid metabolism in adipose tissue, liver, skeletal muscle, gut and pancreas play an important role in the development of insulin resistance, impaired glucose metabolism and type 2 diabetes mellitus. Alterations in diet composition may contribute to prevent and/or reverse these disturbances through modulation of fatty acid metabolism. Besides an increased fat mass, adipose tissue dysfunction, characterized by an altered capacity to store lipids and an altered secretion of adipokines, may result in lipid overflow, systemic inflammation and excessive lipid accumulation in non-adipose tissues like liver, skeletal muscle and the pancreas. These impairments together promote the development of impaired glucose metabolism, insulin resistance and type 2 diabetes mellitus. Furthermore, intrinsic functional impairments in either of these organs may contribute to lipotoxicity and insulin resistance. The present review provides an overview of fatty acid metabolism-related pathways in adipose tissue, liver, skeletal muscle, pancreas and gut, which can be targeted by diet or food components, thereby improving glucose metabolism.

The effect of acute exercise on GLUT4 levels in peripheral blood mononuclear cells of sled dogs

Using sled dogs as exercise model, our objectives of this study were to (1) assess the effects of one acute bout of high-intensity exercise on surface GLUT4 concentrations on easily accessible peripheral blood mononuclear cells (PBMC) and (2) compare our findings with published research on exercise induced GLUT4 in skeletal muscle. During the exercise bout, dogs ran 5 miles at approximately 90% of VO₂ max. PMBC were collected before exercise (baseline), immediately after exercise and after 24 h recovery.GLUT4 was measured via ELISA. Acute exercise resulted in a significant increase on surface GLUT4 content on PBMC. GLUT4 was increased significantly immediately after exercise (~50%; p<0.05) and reduced slightly by 24 h post-exercise as compared to baseline (~22%; p>0.05). An effect of acute exercise on GLUT4 levels translocated to the cell membrane was observed, with GLUT4 levels not yet returned to baseline after 24 h post-exercise. In conclusion, the present investigation demonstrated that acute high-intensity exercise increased GLUT4 content at the surface of PBMC of sled dogs as it has been reported in skeletal muscle in other species. Our findings underline the potential use of peripheral blood mononuclear cell GLUT4 protein content as minimally invasive proxy to investigate relationships between insulin sensitivity, insulin resistance, GLUT4 expression and glucose metabolism.

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Acute exercise increased GLUT4 translocation in peripheral mononuclear cells

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GLUT4 translocation in peripheral mononuclear cells was insulin independent

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Mononuclear cells are a potential proxy tissue to study GLUT4 translocation

Physiological regulation of lipoprotein lipase

The enzyme lipoprotein lipase (LPL), originally identified as the clearing factor lipase, hydrolyzes triglycerides present in the triglyceride-rich lipoproteins VLDL and chylomicrons. LPL is primarily expressed in tissues that oxidize or store fatty acids in large quantities such as the heart, skeletal muscle, brown adipose tissue and white adipose tissue. Upon production by the underlying parenchymal cells, LPL is transported and attached to the capillary endothelium by the protein GPIHBP1. Because LPL is rate limiting for plasma triglyceride clearance and tissue uptake of fatty acids, the activity of LPL is carefully controlled to adjust fatty acid uptake to the requirements of the underlying tissue via multiple mechanisms at the transcriptional and post-translational level. Although various stimuli influence LPL gene transcription, it is now evident that most of the physiological variation in LPL activity, such as during fasting and exercise, appears to be driven via post-translational mechanisms by extracellular proteins. These proteins can be divided into two main groups: the liver-derived apolipoproteins APOC1, APOC2, APOC3, APOA5, and APOE, and the angiopoietin-like proteins ANGPTL3, ANGPTL4 and ANGPTL8, which have a broader expression profile. This review will summarize the available literature on the regulation of LPL activity in various tissues, with an emphasis on the response to diverse physiological stimuli.

Role of exercise in optimizing the functional status of patients with nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is frequently concomitant with obesity. This article discusses factors that influence health and functional outcomes of people who develop NAFLD, including increased burden of illness, whole body function, performance, and perception of self-efficacy. Changes in macronutrients, amount of calories consumed, and decreased physical activity all negatively influence patient outcome. The benefits of exercise in this population are also discussed. To be effective, exercise must be performed, regularly and in conjunction with dietary and other behavioral change. Therefore, a lifelong commitment to exercise, activity, and diet are needed if NAFLD is to be successfully treated.

Regulation of mitochondrial biogenesis and GLUT4 expression by exercise

Endurance exercise training can induce large increases mitochondria and the GLUT4 isoform of the glucose transporter in skeletal muscle. For a long time after the discovery in the 1960s that exercise results in an increase in muscle mitochondria, there was no progress in elucidation of the mechanisms involved. The reason for this lack of progress was that nothing was known regarding how expression of the genes-encoding mitochondrial proteins is coordinately regulated. This situation changed rapidly after discovery of transcription factors that control transcription of genes-encoding mitochondrial proteins and, most importantly, the discovery of peroxisome proliferator-gamma coactivator-1α (PGC-1α). This transcription coactivator binds to and activates transcription factors that regulate transcription of genes-encoding mitochondrial proteins. Thus, PGC-1α activates and coordinates mitochondrial biogenesis. It is now known that exercise rapidly activates and induces increased expression of PGC-1α. The exercise-generated signals that lead to PGC-1α activation and increased expression are the increases in cytosolic Ca(2+) and decreases in ATP and creatine phosphate (∼P). Ca(2+) mediates its effect by activating CAMKII, while the decrease in ∼P mediates its effect via activation of AMPK. Expression of the GLUT4 isoform of the glucose transporter is regulated in parallel with mitochondrial biogenesis via the same signaling pathways. This review describes what is known regarding the regulation of mitochondrial biogenesis and GLUT4 expression by exercise. A major component of this review deals with the physiological and metabolic consequences of the exercise-induced increase in mitochondria and GLUT4.

Exercise, GLUT4, and skeletal muscle glucose uptake

Glucose is an important fuel for contracting muscle, and normal glucose metabolism is vital for health. Glucose enters the muscle cell via facilitated diffusion through the GLUT4 glucose transporter which translocates from intracellular storage depots to the plasma membrane and T-tubules upon muscle contraction. Here we discuss the current understanding of how exercise-induced muscle glucose uptake is regulated. We briefly discuss the role of glucose supply and metabolism and concentrate on GLUT4 translocation and the molecular signaling that sets this in motion during muscle contractions. Contraction-induced molecular signaling is complex and involves a variety of signaling molecules including AMPK, Ca(2+), and NOS in the proximal part of the signaling cascade as well as GTPases, Rab, and SNARE proteins and cytoskeletal components in the distal part. While acute regulation of muscle glucose uptake relies on GLUT4 translocation, glucose uptake also depends on muscle GLUT4 expression which is increased following exercise. AMPK and CaMKII are key signaling kinases that appear to regulate GLUT4 expression via the HDAC4/5-MEF2 axis and MEF2-GEF interactions resulting in nuclear export of HDAC4/5 in turn leading to histone hyperacetylation on the GLUT4 promoter and increased GLUT4 transcription. Exercise training is the most potent stimulus to increase skeletal muscle GLUT4 expression, an effect that may partly contribute to improved insulin action and glucose disposal and enhanced muscle glycogen storage following exercise training in health and disease.

Effects of acute exercise on postprandial triglyceride response after a high-fat meal in overweight black and white adolescents

OBJECTIVE

We examined the effects of acute exercise on postprandial triglyceride (TG) metabolism following a high-fat meal in overweight black vs white adolescents.

DESIGN AND SUBJECTS

Twenty-one black and 17 white adolescents (12-18 yrs, body mass index 85th percentile) were evaluated twice, during control versus exercise trials, 1-4 weeks apart, in a counterbalanced randomized design. In the control trial, participants performed no exercise on day 1. In the exercise trial, participants performed a single bout of 60-min exercise (50% VO2 peak) on a cycle ergometer on day 1. On day 2 of both trials, participants consumed a high-fat breakfast (70% calories from fat) and blood was sampled for TG concentration in the fasted state and for 6 h postprandially.

RESULTS

There was a significant main effect of condition on postprandial peak TG concentration (P=0.01) and TG area under the curve (AUC) (P=0.003), suggesting that independent of race, peak TG and TG-AUC was lower in the exercise trial vs control trial. Including Tanner stage, gender, total fat (kg) and visceral adipose tissue (VAT) as independent variables, stepwise multiple regression analyses revealed that in whites, VAT was the strongest (P<0.05) predictor of postprandial TG-AUC, explaining 56 and 25% of the variances in TG-AUC in the control and exercise trials, respectively. In blacks, VAT was not associated with postprandial TG-AUC, independent of trial.

CONCLUSION

A single bout of aerobic exercise preceding a high-fat meal is beneficial to reduce postprandial TG concentrations in overweight white adolescents to a greater extent than black adolescents, particularly those with increased visceral adiposity.

Gender Differences in Lipoprotein Lipase Activity after Acute Exercise

OBJECTIVE

To determine whether gender differences exist in lipoprotein lipase (LPL) activity in response to exercise and/or insulin. Exercise and insulin are known modulators of LPL activity in men, but this is less clear in women. LPL activity may predict propensity for obesity; therefore, understanding its modulators is of considerable importance.

RESEARCH METHODS AND PROCEDURES

Gender differences in skeletal muscle and adipose tissue LPL activity were determined after a single bout of exercise followed by a hyperinsulinemic/euglycemic clamp and compared with an identical rest day in healthy lean men (n = 10) and women (n = 10). Muscle and adipose tissue biopsies were obtained pre- (post-exercise vs. rest) and post-clamp.

RESULTS

Basal levels of muscle and adipose tissue LPL activity were not different between men and women. There was, however, a significant gender by day interaction for muscle LPL activity (p = 0.023) and adipose tissue LPL activity (p = 0.013). In muscle, this was because of a significant increase in LPL activity on the exercise vs. rest day in men (p < 0.001) but not women. Adipose tissue LPL activity also increased significantly in men on the exercise day relative to rest day (p = 0.04) but decreased in women (p = 0.10). The hyperinulinemic/euglycemic clamp had no independent effect on tissue LPL activity, in either gender, after rest or exercise.

DISCUSSION

In the 3 to 4 hours after exercise, muscle and adipose tissue LPL activity increased significantly in men, whereas LPL activity remained unchanged in women.

Physical activity and exercise in the regulation of human adipose tissue physiology

Physical activity and exercise are key components of energy expenditure and therefore of energy balance. Changes in energy balance alter fat mass. It is therefore reasonable to ask: What are the links between physical activity and adipose tissue function? There are many complexities. Physical activity is a multifaceted behavior of which exercise is just one component. Physical activity influences adipose tissue both acutely and in the longer term. A single bout of exercise stimulates adipose tissue blood flow and fat mobilization, resulting in delivery of fatty acids to skeletal muscles at a rate well-matched to metabolic requirements, except perhaps in vigorous intensity exercise. The stimuli include adrenergic and other circulating factors. There is a period following an exercise bout when fatty acids are directed away from adipose tissue to other tissues such as skeletal muscle, reducing dietary fat storage in adipose. With chronic exercise (training), there are changes in adipose tissue physiology, particularly an enhanced fat mobilization during acute exercise. It is difficult, however, to distinguish chronic "structural" changes from those associated with the last exercise bout. In addition, it is difficult to distinguish between the effects of training per se and negative energy balance. Epidemiological observations support the idea that physically active people have relatively low fat mass, and intervention studies tend to show that exercise training reduces fat mass. A much-discussed effect of exercise versus calorie restriction in preferentially reducing visceral fat is not borne out by meta-analyses. We conclude that, in addition to the regulation of fat mass, physical activity may contribute to metabolic health through beneficial dynamic changes within adipose tissue in response to each activity bout.

Does Branched-Chain Amino Acids Supplementation Modulate Skeletal Muscle Remodeling through Inflammation Modulation? Possible Mechanisms of Action

Skeletal muscle protein turnover is modulated by intracellular signaling pathways involved in protein synthesis, degradation, and inflammation. The proinflammatory status of muscle cells, observed in pathological conditions such as cancer, aging, and sepsis, can directly modulate protein translation initiation and muscle proteolysis, contributing to negative protein turnover. In this context, branched-chain amino acids (BCAAs), especially leucine, have been described as a strong nutritional stimulus able to enhance protein translation initiation and attenuate proteolysis. Furthermore, under inflammatory conditions, BCAA can be transaminated to glutamate in order to increase glutamine synthesis, which is a substrate highly consumed by inflammatory cells such as macrophages. The present paper describes the role of inflammation on muscle remodeling and the possible metabolic and cellular effects of BCAA supplementation in the modulation of inflammatory status of skeletal muscle and the consequences on protein synthesis and degradation.

Physical activity and postprandial lipidemia: are energy expenditure and lipoprotein lipase activity the real modulators of the positive effect?

Historically, the link between elevated cholesterol and increased risk of cardiovascular disease has been based on fasting measurements. This is appropriate for total, low-density lipoprotein and high-density lipoprotein cholesterol. However, triglyceride concentrations vary considerably throughout the day in response to the regular consumption of food and drink. Recent findings indicate that postprandial triglyceride concentrations independently predict future cardiovascular risk. Potential modulators of postprandial lipidemia include meal composition and physical activity. Early cross sectional studies indicated that physically active individuals had a lower postprandial lipidemic response compared to inactive individuals. However, the effect of physical activity on postprandial lipidemia is an acute phenomenon, which dissipates within 60 h of a single bout of exercise. Total exercise induced energy expenditure, rather than duration or intensity of the physical activity is commonly reported to be a potent modulator of postprandial lipidemia. However, the pooled results of studies in this area suggest that energy expenditure exerts most of its influence on fasting triglyceride concentrations rather than on the incremental change in triglyceride concentrations seen following meal consumption. It seems more likely that energy expenditure is one component of a multifactorial list of mediators that may include local muscle contractile activity, and other yet to be elucidated mechanisms.

Normal adaptations to exercise despite protection against oxidative stress

It has been reported that supplementation with the antioxidant vitamins C and E prevents the adaptive increases in mitochondrial biogenesis and GLUT4 expression induced by endurance exercise. We reevaluated the effects of these antioxidants on the adaptive responses of rat skeletal muscle to swimming in a short-term study consisting of 9 days of vitamins C and E with exercise during the last 3 days and a longer-term study consisting of 8 wk of antioxidant vitamins with exercise during the last 3 wk. The rats in the antioxidant groups were given 750 mg·kg body wt(-1)·day(-1) vitamin C and 150 mg·kg body wt(-1)·day(-1) vitamin E. In rats euthanized immediately after exercise, plasma TBARs were elevated in the control rats but not in the antioxidant-supplemented rats, providing evidence for an antioxidant effect. In rats euthanized 18 h after exercise there were large increases in insulin responsiveness of glucose transport in epitrochlearis muscles mediated by an approximately twofold increase in GLUT4 expression in both the short- and long-term treatment groups. The protein levels of a number of mitochondrial marker enzymes were also increased about twofold. Superoxide dismutases (SOD) 1 and 2 were increased about twofold in triceps muscle after 3 days of exercise, but only SOD2 was increased after 3 wk of exercise. There were no differences in the magnitudes of any of these adaptive responses between the control and antioxidant groups. These results show that very large doses of antioxidant vitamins do not prevent the exercise-induced adaptive responses of muscle mitochondria, GLUT4, and insulin action to exercise and have no effect on the level of these proteins in sedentary rats.

Dietary exercise as a novel strategy for the prevention and treatment of metabolic syndrome: effects on skeletal muscle function

A sedentary lifestyle can cause metabolic syndrome to develop. Metabolic syndrome is associated with metabolic function in the skeletal muscle, a major consumer of nutrients. Dietary exercise, along with an adequate diet, is reported to be one of the major preventive therapies for metabolic syndrome; exercise improves the metabolic capacity of muscles and prevents the loss of muscle mass. Epidemiological studies have shown that physical activity reduces the risk of various common diseases such as cardiovascular disease, diabetes, and cancer; it also helps in reducing visceral adipose tissue. In addition, laboratory studies have demonstrated the mechanisms underlying the benefits of single-bout and regular exercise. Exercise regulates the expression/activity of proteins associated with metabolic and anabolic signaling in muscle, leading to a change in phenotype. The extent of these changes depends on the intensity, the duration, and the frequency of the exercise. The effect of exercise is also partly due to a decrease in inflammation, which has been shown to be closely related to the development of various diseases. Furthermore, it has been suggested that several phytochemicals contained in natural foods can improve nutrient metabolism and prevent protein degradation in the muscle.

Prolonged exercise-induced stimulation of skeletal muscle glucose uptake is due to sustained increases in tissue perfusion and fractional glucose extraction

CONTEXT

The mechanisms behind the positive effects of physical activity on glucose metabolism in skeletal muscle and the time course of the effects need to be more elucidated.

OBJECTIVE

The aim was to examine the prolonged effects of an acute bout of one-legged exercise on local skeletal muscle glucose utilization and tissue perfusion.

DESIGN AND SETTING

Interstitial glucose concentration, local tissue perfusion, glucose uptake, and effects of insulin infusion were studied 12 h after an acute bout of exercise and without prior exercise.

PARTICIPANTS

Ten healthy subjects, five women and five men, participated in the study.

INTERVENTION

Microdialysis measurements, (133)Xe clearance, and a 2-h hyperinsulinemic euglycemic clamp were performed on two occasions.

MAIN OUTCOME MEASURES

We measured interstitial glucose concentration and tissue perfusion in the quadriceps femoris muscle of both legs.

RESULTS

Tissue perfusion (3.3 ± 0.6 ml × 100 g(-1) × min(-1) vs. 1.4 ± 0.2 ml × 100 g(-1) × min(-1); P = 0.007) and basal glucose uptake (2.3 ± 0.5 μmol × 100 g(-1) × min(-1) vs. 0.9 ± 0.2 μmol × 100 g(-1) × min(-1); P = 0.006) were increased in the leg that had exercised compared to the resting leg; the findings in the resting leg were comparable to those in the control experiment without prior exercise. The relative effect of insulin on fractional skeletal muscle glucose uptake was the same in all experimental settings, and insulin did not affect tissue perfusion.

CONCLUSIONS

The prolonged stimulatory effect of physical exercise on skeletal muscle glucose uptake was mediated via vascular effects combined with an increase in basal glucose transport independent of enhancement of insulin responses.

Skeletal muscle insulin resistance: roles of fatty acid metabolism and exercise

The purpose of this review is to provide information about the role of exercise in the prevention of skeletal muscle insulin resistance, that is, the inability of insulin to properly cause glucose uptake into skeletal muscle. Insulin resistance is associated with high levels of stored lipids in skeletal muscle cells. Aerobic exercise training decreases the amounts of these lipid products and increases the lipid oxidative capacity of muscle cells. Thus, aerobic exercise training may prevent insulin resistance by correcting a mismatch between fatty acid uptake and fatty acid oxidation in skeletal muscle. Additionally, a single session of aerobic exercise increases glucose uptake by muscle during exercise, increases the ability of insulin to promote glucose uptake, and increases glycogen accumulation after exercise, all of which are important to blood glucose control. There also is some indication that resistance exercise may be effective in preventing insulin resistance. The information provided is intended to help clinicians understand and explain the roles of exercise in reducing insulin resistance.

The role of FoxO in the regulation of metabolism

Forkhead proteins, and FoxO1 in particular, play a significant role in regulating whole body energy metabolism. Glucose homeostasis is achieved by adjusting endogenous glucose production as well as glucose uptake by peripheral tissues in response to insulin. In the fasted state, the liver is primarily responsible for maintaining glucose levels, with FoxO1 playing a key role in promoting the expression of gluconeogenic enzymes. Following feeding, pancreatic beta cells secrete insulin, which promotes the uptake of glucose by peripheral tissues including skeletal muscle and adipose tissue, and can in part suppress gluconeogenic enzyme expression in the liver. In addition to directly regulating metabolism, FoxO1 also plays a role in the formation of both adipose tissue and skeletal muscle, two major organs that are critical for maintaining energy homeostasis. The importance of FoxO1 in energy homeostasis is particularly striking under conditions of metabolic dysfunction or insulin resistance. In obese or diabetic states, FoxO1-dependent gene expression promotes some of the deleterious characteristics associated with these conditions, including hyperglycemia and glucose intolerance. In addition, the increase in pancreatic beta cell mass that normally occurs in response to a rise in insulin demand is blunted by nuclear FoxO1 expression. However, under these same pathophysiological conditions, FoxO1 expression may help drive the expression of genes involved in combating oxidative stress, thereby preserving cellular function. FoxO1 may also be involved in promoting the switch from carbohydrate to fatty acid as the major energy source during starvation.

Rapid upregulation of GLUT-4 and MCT-4 expression during 16 h of heavy intermittent cycle exercise

In this study, we have investigated the hypothesis that an exercise protocol designed to repeatedly induce a large dependence on carbohydrate and large increases in glycolytic flux rate would result in rapid increases in the principal glucose and lactate transporters in working muscle, glucose transporter (GLUT)-4 and monocarboxylate transporter (MCT)4, respectively, and in activity of hexokinase (Hex), the enzyme used to phosphorylate glucose. Transporter abundance and Hex activity were assessed in homogenates by Western blotting and quantitative chemiluminescence and fluorometric techniques, respectively, in samples of tissue obtained from the vastus lateralis in 12 untrained volunteers [peak aerobic power (V̇o2peak) = 44.3 ± 2.3 ml·kg−1·min−1] before cycle exercise at repetitions 1 (R1), 2 (R2), 9 (R9), and 16 (R16). The 16 repetitions of the exercise were performed for 6 min at ∼90% V̇o2peak, once per hour. Compared with R1, GLUT-4 increased ( P < 0.05) by 28% at R2 and remained elevated ( P < 0.05) at R9 and R16. For MCT-4, increases ( P < 0.05) of 24% were first observed at R9 and persisted at R16. No changes were observed in GLUT-1 and MCT-1 or in Hex activity. The ∼17- to 24-fold increase ( P < 0.05) in muscle lactate observed at R1 and R2 was reduced ( P < 0.05) to an 11-fold increase at R9 and R16. It is concluded that an exercise protocol designed to strain muscle carbohydrate reserves and to result in large increases in lactic acid results in a rapid upregulation of both GLUT-4 and MCT-4.

Effect of exercise duration on postprandial hypertriglyceridemia in men with metabolic syndrome

We examined the effect of exercise on postprandial hypertriglyceridemia (PHTG) and insulin resistance in individuals with metabolic syndrome. Subjects were 10 hypertriglyceridemic men with insulin resistance [age = 35.0 ± 1.8 yr, body weight = 90.7 ± 3.3 kg, fasting triglyceride (TG) = 2.6 ± 0.4 mmol/l, peak oxygen consumption (V̇o2peak) = 36.0 ± 1.3 ml−1·kg−1·min−1, and homeostatic model assessment of insulin resistance (HOMA-IR)= 3.1 ± 0.3]. Each participant performed a control trial (Ctr; no exercise) and three exercise trials at 60% of their V̇o2peakfor 30 min (30 min-Ex), 45 min (45 min-Ex) and 60 min (60 min-Ex). All subjects had a fat meal in each trial. In the exercise trials, the subject jogged on a treadmill for a designated duration of 12 h before ingestion of a fat meal. Blood samples were taken at 0 h (before the meal) and at 2, 4, 6, and 8 h after the meal. The plasma TG, area score under TG concentration curve over an 8-h period (TG AUC) after the meal, and HOMA-IR were analyzed. The TG AUC scores in both the 45 min-Ex and 60 min-Ex were 31 and 33% lower, respectively, than Ctr ( P < 0.02). There were no significant differences in TG AUC scores between the 30 min-Ex and the Ctr ( P > 0.05). There were no trial differences in the fasting plasma glucose concentration ( P > 0.05). HOMA-IR values in the 30 min-Ex, 45 min-Ex, and 60 min-Ex trials were lower than the Ctr ( P < 0.03), but no significant differences were found in HOMA-IR among the exercise trials. The results suggest that for physically inactive individuals with metabolic syndrome, exercising at moderate intensity for 45 min effectively attenuates PHTG while exercise for 30 min is sufficient to improve insulin action.

A single bout of brisk walking increases basal very low-density lipoprotein triacylglycerol clearance in young men

Very low-density lipoprotein triacylglycerol (VLDL-TG) turnover rate was evaluated in the morning, 12 hours after a single bout of brisk walking (90 minutes at approximately 60% of VO2max; EXE), compared to a resting control period (CON) in 10 recreationally active men. VLDL-TG fractional catabolic rate was calculated from the decay in isotopic enrichment after a bolus injection of [2H5]glycerol. Plasma VLDL-TG concentration was 24% lower in the morning after the EXE trial compared to control (0.47+/-0.04 and 0.36+/-0.04 mmol L(-1), for CON and EXE, respectively; P<.01). Serum insulin (7.4+/-0.7 and 5.6+/-0.4 mIU L(-1), CON and EXE, respectively; P<.05) and plasma glucose (5.6+/-0.1 and 5.4+/-0.1 mmol/L, CON and EXE, respectively; P<.05) concentrations were also significantly lower in the EXE trial. Insulin sensitivity (homeostasis model assessment [HOMA] index) was improved by 27% in EXE compared with the CON trial (P<.05).VLDL-apolipoprotein B-100 and plasma fatty acid concentrations were similar in the two trials. Hepatic VLDL-TG secretion rates were not significantly affected by exercise (13.1+/-1.2 and 13.2+/-1.6 micromol.min(-1) for the CON and EXE trials, respectively), whereas VLDL-TG clearance rate increased by 36% (28.1+/-1.3 and 38.1+/-3.5 mL.min(-1) for the CON and EXE trials, respectively; P<.05). It is concluded that the decrease in fasting plasma VLDL-TG concentration observed 12 hours after brisk walking is related mainly to increased VLDL-TG clearance from plasma.

Calorie restriction or exercise: effects on coronary heart disease risk factors. A randomized, controlled trial

Coronary heart disease (CHD) risk factors and the risk of CHD increase with increased adiposity. Fat loss induced by negative energy balance improves all metabolic CHD risk factors. To determine whether fat loss induced by long-term calorie restriction (CR) or increased energy expenditure induced by exercise (EX) has different effects on CHD risk factors in nonobese subjects, we conducted a 1-yr controlled trial involving 48 nonobese subjects who were randomly assigned to one of three groups: CR, 20% CR diet (n = 18); EX, 20% increase in energy expenditure through daily exercise with no increase in energy intake (n = 18); or HL, healthy lifestyle guidelines (n = 10). Subjects were 29 women and 17 men aged 57 +/- 3 yr, with BMI 27.3 +/- 2.0 kg/m(2). Assessments included total body fat by DEXA, lipoproteins, blood pressure, HOMA-IR, C-reactive protein (CRP), and estimated 10-yr CHD risk score. Body fat decreased by 6.3 +/- 3.8 kg in CR, 5.6 +/- 4.4 kg in EX, and 0.4 +/- 1.7 kg in HL, which corresponded to reductions of 24.9, 22.3, and 1.2% of baseline body fat mass, respectively. These CR- and EX-induced energy deficits were accompanied by reductions in most of the major CHD risk factors, including plasma LDL-cholesterol, total cholesterol/HDL ratio, HOMA-IR index, and CRP concentrations that were similar in the two intervention groups. Data from the present study provide evidence that CR- and EX-induced negative energy balance result in substantial and similar improvements in the major risk factors for CHD in normal-weight and overweight middle-aged adults.

Divergent response of metabolite transport proteins in human skeletal muscle after sprint interval training and detraining

Skeletal muscle primarily relies on carbohydrate (CHO) for energy provision during high-intensity exercise. We hypothesized that sprint interval training (SIT), or repeated sessions of high-intensity exercise, would induce rapid changes in transport proteins associated with CHO metabolism, whereas changes in skeletal muscle fatty acid transporters would occur more slowly. Eight active men (22 +/- 1 yr; peak oxygen uptake = 50 +/- 2 ml.kg(-1).min(-1)) performed 4-6 x 30 s all-out cycling efforts with 4-min recovery, 3 days/wk for 6 wk. Needle muscle biopsy samples (vastus lateralis) were obtained before training (Pre), after 1 and 6 wk of SIT, and after 1 and 6 wk of detraining. Muscle oxidative capacity, as reflected by the protein content of cytochrome c oxidase subunit 4 (COX4), increased by approximately 35% after 1 wk of SIT and remained higher compared with Pre, even after 6 wk of detraining (P < 0.05). Muscle GLUT4 content increased after 1 wk of SIT and remained approximately 20% higher compared with baseline during detraining (P < 0.05). The monocarboxylate tranporter (MCT) 4 was higher after 1 and 6 wk of SIT compared with Pre, whereas MCT1 increased after 6 wk of training and remained higher after 1 wk of detraining (P < 0.05). There was no effect of training or detraining on the muscle content of fatty acid translocase (FAT/CD36) or plasma membrane associated fatty acid binding protein (FABPpm) (P > 0.05). We conclude that short-term SIT induces rapid increases in skeletal muscle oxidative capacity but has divergent effects on proteins associated with glucose, lactate, and fatty acid transport.

Acute exercise and GLUT4 expression in human skeletal muscle: influence of exercise intensity

To examine the influence of exercise intensity on the increases in vastus lateralis GLUT4 mRNA and protein after exercise, six untrained men exercised for 60 min at 39 ± 3% peak oxygen consumption (V̇o2 peak) (Lo) or 27 ± 2 min at 83 ± 2% V̇o2 peak(Hi) in counterbalanced order. Preexercise muscle glycogen levels were not different between trials (Lo: 408 ± 35 mmol/kg dry mass; Hi: 420 ± 43 mmol/kg dry mass); however, postexercise levels were lower ( P < 0.05) in Hi (169 ± 18 mmol/kg dry mass) compared with Lo (262 ± 35 mmol/kg dry mass). Thus calculated muscle glycogen utilization was greater ( P < 0.05) in Hi (251 ± 24 mmol/kg) than in Lo (146 ± 34). Exercise resulted in similar increases in GLUT4 gene expression in both trials. GLUT4 mRNA was increased immediately at the end of exercise (∼2-fold; P < 0.05) and remained elevated after 3 h of postexercise recovery. When measured 3 h after exercise, total crude membrane GLUT4 protein levels were 106% higher in Lo (3.3 ± 0.7 vs. 1.6 ± 0.3 arbitrary units) and 61% higher in Hi (2.9 ± 0.5 vs. 1.8 ± 0.5 arbitrary units) relative to preexercise levels. A main effect for exercise was observed, with no significant differences between trials. In conclusion, exercise at ∼40 and ∼80% V̇o2 peak, with total work equal, increased GLUT4 mRNA and GLUT4 protein in human skeletal muscle to a similar extent, despite differences in exercise intensity and duration.

Effect of 2-month detraining on body composition and insulin sensitivity in young female dancers

OBJECTIVE

To investigate the effect of 2-month detraining on body composition and glucose tolerance for female collegiate dancers.

DESIGN

Longitudinal study of dancers who stopped their regular training for 2 months.

SUBJECTS

16 female collegiate dancers (age: 19.7 +/-0.11 year, body mass index (BMI): 20.7 +/- 0.56 kg/m(2)).

MEASUREMENTS

BMI, waist-to-hip ratio (WHR), oral glucose tolerance test (OGTT), insulin response during OGTT, and blood lipids at baseline and after a 2-month detraining.

RESULTS

Glucose tolerance was not significantly affected by the detraining, but the fasted insulin and insulin levels during OGTT were significantly elevated. Fasted free fatty acid (FFA) and triglyceride levels were significantly elevated without change in cholesterol level. BMI was not significantly altered during this detraining period, but the waist circumference and WHR ratio were significantly elevated.

CONCLUSION

Only a 2-month cessation of regular training in female dancers significantly elevated basal and postprandial insulin levels and triglycerides, and were associated with increased basal FFA. This result appears to be partly related to the increased central fatness but not body mass, indicating that the early development of obesity due to reduced physical activity may not necessarily reflect on weight status. A warning is thus warranted for those young women who depend on weight measurement for body fat status monitoring.

Lipid metabolism response to a single, prolonged bout of endurance exercise in healthy young men

To discover the alterations in lipid metabolism linked to postexercise hypotriglyceridemia, we measured lipid kinetics, lipoprotein subclass distribution and lipid transfer enzymes in seven healthy, lean, young men the day after 2 h of cycling and rest. Compared with rest, exercise increased fatty acid rate of appearance and whole body fatty acid oxidation by approximately 65 and 40%, respectively (P < 0.05); exercise had no effect on VLDL-triglyceride (TG) secretion rate, increased VLDL-TG plasma clearance rate by 40 +/- 8%, and reduced VLDL-TG mean residence time by approximately 40 min and VLDL-apolipoprotein B-100 (apoB-100) secretion rate by 24 +/- 8% (all P < 0.05). Exercise also reduced the number of VLDL but almost doubled the number of IDL particles in plasma (P < 0.05). Muscle lipoprotein lipase content was not different after exercise and rest, but plasma lipoprotein lipase concentration increased by approximately 20% after exercise (P < 0.05). Plasma hepatic lipase and lecithin:cholesterol acyltransferase concentrations were not affected by exercise, whereas cholesterol ester transfer protein concentration was approximately 10% lower after exercise than after rest (P = 0.052). We conclude that 1) greater fatty acid availability after exercise does not stimulate VLDL-TG secretion, probably because of the increase in fatty acid oxidation and possibly also fatty acid use for restoration of tissue TG stores; 2) reduced secretion of VLDL-apoB-100 lowers plasma VLDL particle concentration; and 3) increased VLDL-TG plasma clearance maintains low plasma TG concentration but is not accompanied by similar increases in subsequent steps of the delipidation cascade. Acutely, therefore, the cardioprotective lowering of plasma TG and VLDL concentrations by exercise is counteracted by a proatherogenic increase in IDL concentration.

Effect of Exercise Timing on Postprandial Lipemia in Hypertriglyceridemic Men

We investigated the effect of exercise timing on attenuation of postprandial hyper-triglyceridemia (PHTG) in individuals with hypertriglyceridemia (HTG). Subjects were 10 males (TG = 290.1 ± 28.5 mg/dl). Each subject performed a control trial (Ctr), 12-hr premeal exercise trial (12-hr Pre), and 24-hr premeal exercise trial (24-hr Pre). In each trial, subjects had a fat-rich meal. In the exercise trials they jogged on a treadmill at 60% of their [Formula: see text] for 1 hr at a designated time. Blood samples were taken at 0 (immediately before the fat meal), and at 2, 4, 6, 8, and 24 hrs after the meal. The results indicated that plasma TG concentrations in 12-hr Pre were lower than in Ctr and 24-hr Pre (p <  0.03). The area score under the TG concentration curve (TG AUC score) in 12-hr Pre was 37% and 33% lower than in 24-hr Pre and Ctr (p <  0.02), respectively. Insulin concentrations in 12-hr Pre were lower than Ctr and 24-hr Pre (p <  0.001). The plasma nonesterified fatty acid (NEFA) concentration was higher in 12-hr Pre than in both 24-hr Pre and Ctr (p <  0.003). There were no trial differences in both HDLtot-Ch and HDL2-Ch. These results suggest that exercising 12 hrs prior to a fat-meal intake significantly reduces PHTG response whereas exercising 24 hrs prior to the meal does not attenuate PHTG in hypertriglyceridemic men. The effect of an acute exercise bout on PHTG lowering may be short-lived and diminished by 24 hrs. Key words: high-density lipoprotein cholesterol, triglyceride, lipoprotein lipase, insulin

Effect of short-term training on GLUT-4 mRNA and protein expression in human skeletal muscle

Six untrained, male subjects (23 +/- 1 years old, 84 +/- 5 kg, (O(2)peak)= 3.7 +/- 0.8 l min(-1)) exercised for 60 min at 75 +/- 1%(O(2)peak) on 7 consecutive days. Muscle samples were obtained before the start of cycle exercise training and 24 h after the first and seventh exercise sessions and analysed for citrate synthase activity, glycogen and glucose transporter 4 (GLUT-4) mRNA and protein expression. Exercise training increased (P < 0.05) citrate synthase by approximately 20% and muscle glycogen concentration by approximately 40%. GLUT-4 mRNA levels 24 h after the first and seventh exercise sessions were similar to those measured before the start of exercise training. In contrast, GLUT-4 protein expression was increased after 7 days of exercise training (12.4 +/- 1.5 versus 3.4 +/- 1.0 arbitray units (a.u.), P < 0.05) and although it tended to be higher 24 h after the first exercise session (6.0 +/- 3.0 versus 3.4 +/- 1.0 a.u.), this was not significantly different (P= 0.09). These results support the suggestion that the adaptive increase in skeletal muscle GLUT-4 protein expression with short-term exercise training arises from the repeated, transient increases in GLUT-gene transcription following each exercise bout leading to a gradual accumulation of GLUT-4 protein, despite GLUT-4 mRNA returning to basal levels between exercise stimuli.

Exercise and myocyte enhancer factor 2 regulation in human skeletal muscle

Overexpression of GLUT4 in skeletal muscle enhances whole-body insulin action. Exercise increases GLUT4 gene and protein expression, and a binding site for the myocyte enhancer factor 2 (MEF-2) is required on the GLUT4 promoter for this response. However, the molecular mechanisms involved remain elusive. In various cell systems, MEF-2 regulation is a balance between transcriptional repression by histone deacetylases (HDACs) and transcriptional activation by the nuclear factor of activated T-cells (NFAT), peroxisome proliferator-activated receptor-gamma coactivator 1 (PGC-1), and the p38 mitogen-activated protein kinase. The purpose of this study was to determine if these same mechanisms regulate MEF-2 in contracting human skeletal muscle. Seven subjects performed 60 min of cycling at approximately 70% of VO2(peak). After exercise, HDAC5 was dissociated from MEF-2 and exported from the nucleus, whereas nuclear PGC-1 was associated with MEF-2. Exercise increased total and nuclear p38 phosphorylation and association with MEF-2, without changes in total or nuclear p38 protein abundance. This result was associated with p38 sequence-specific phosphorylation of MEF-2 and an increase in GLUT4 mRNA. Finally, we found no role for NFAT in MEF-2 regulation. From these data, it appears that HDAC5, PGC-1, and p38 regulate MEF-2 and could be potential targets for modulating GLUT4 expression.

Time course of GLUT4 and AMPK protein expression in human skeletal muscle during one month of physical training

Endurance training elicits profound adaptations of skeletal muscle, including increased expression of several proteins. The 5'-AMP activated protein kinase (AMPK) may be one of these, considering the fact that acute exercise increases AMPK activity. Eight young (26 +/- 1 year) lean, healthy males endurance trained one leg (while the other leg remained resting) on an ergometer bicycle for 30 min/day for four weeks (workload corresponding to approximately 70% of maximal oxygen uptake). Muscle biopsies were obtained approximately 18 h after the previous training session. On day eight GLUT4 protein expression was 36% higher in trained (T) compared with untrained (UT) (P < 0.05), but no further increase was seen at day 14 and 30 despite continuously increasing absolute workloads. Expression of AMPKalpha2 and actin did not change with training. In contrast, expression of AMPKalpha1 was 27% higher in T vs. UT muscle (P < 0.05) (measured only on day 30).

CONCLUSIONS

GLUT4 protein expression increases substantially after seven days of endurance training with no further increase with prolonged training at progressively increasing workloads. AMPKalpha1 and alpha2 behave differently in their expression in response to endurance training. AMPKalpha1 protein content is increased after one month of training, while no change in AMPKalpha2 and actin expression was detected over the time course of the training period.

Effects of prior exercise on postprandial lipemia: a quantitative review

The purpose of this report is to synthesize the results from studies examining the effect of exercise on postprandial lipemia to summarize the existing data and provide direction for future research. A quantitative review of the literature was performed using meta-analytic methods to quantify the effect sizes. Moderator analyses were performed to examine features of the studies that could potentially influence the effect of exercise on postprandial lipemia. Thirty-eight effects from 555 people were retrieved from 29 studies. The mean weighted effect was moderate as indicated by Cohen's d (d = -0.57; 95% confidence interval [CI], -0.71 to -0.43), indicating that people who perform exercise before meal ingestion exhibit a 0.5 standard deviation reduction in the postprandial triglyceride (TG) response relative to persons in comparison groups. There was no significant effect of study design, gender, age, type of meal ingested, exercise intensity, exercise duration, or timing of exercise on the postprandial response (P >.05). There was, however, significant variation in the effect sizes, for women for exercise performed within 24 hours of meal ingestion, and for exercise performed more than 24 hours before meal ingestion (P <.01). For studies that reported the energy expenditure of exercise, there was a significant relationship between effect size and energy expenditure (r = -.62, P =.02). Results from this quantitative review of the literature suggest that exercise has a moderate effect on the postprandial lipemic response and that the energy expenditure of prior exercise may play a role in the magnitude of this effect. Other factors that may affect the response remain to be clarified.

A forty-year memoir of research on the regulation of glucose transport into muscle

This historical review describes the research on the regulation of glucose transport in skeletal muscle conducted in my laboratory and in collaboration with a number of colleagues in other laboratories. This research includes studies of stimulation of glucose transport, GLUT4 translocation, and GLUT4 expression by exercise/muscle contractions, the role of Ca(2+) in these processes, and the interactions between the effects of exercise and insulin. Among the last are the additive effects of insulin and contractions on glucose transport and GLUT4 translocation and the increases in muscle insulin sensitivity and responsiveness induced by exercise.