Whole body metabolic effects of prolonged endurance training in combination with erythropoietin treatment in humans: a randomized placebo controlled trial

Erythropoietin (Epo) administration improves aerobic exercise capacity and insulin sensitivity in renal patients and also increases resting energy expenditure (REE). Similar effects are observed in response to endurance training. The aim was to compare the effects of endurance training with erythropoiesis-stimulating agent (ESA) treatment in healthy humans. Thirty-six healthy untrained men were randomized to 10 wk of either: 1) placebo ( n = 9), 2) ESA ( n = 9), 3) endurance training ( n = 10), or 4) ESA and endurance training ( n = 8). In a single-blinded design, ESA/placebo was injected one time weekly. Training consisted of biking for 1 h at 65% of wattmax three times per week. Measurements performed before and after the intervention were as follows: body composition, maximal oxygen uptake, insulin sensitivity, REE, and palmitate turnover. Uncoupling protein 2 (UCP2) mRNA levels were assessed in skeletal muscle. Fat mass decreased after training ( P = 0.003), whereas ESA induced a small but significant increase in intrahepatic fat ( P = 0.025). Serum free fatty acid (FFA) levels and palmitate turnover decreased significantly in response to training, whereas the opposite pattern was found after ESA. REE corrected for lean body mass increased in response to ESA and training, and muscle UCP2 mRNA levels increased after ESA ( P = 0.035). Insulin sensitivity increased only after training ( P = 0.011). In conclusion: 1) insulin sensitivity is not improved after ESA treatment despite improved exercise capacity, 2) the calorigenic effects of ESA may be related to increased UCP2 gene expression in skeletal muscle, and 3) training and ESA exert opposite effects on lipolysis under basal conditions, increased FFA levels and liver fat fraction was observed after ESA treatment.

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Sex Differences in the Metabolic Effects of Testosterone in Sheep

Endocrinology ◽

10.1210/en.2011-1634 ◽

2012 ◽

Vol 153 (1) ◽

pp. 123-131 ◽

Cited By ~ 19

Author(s):

Scott D. Clarke ◽

Iain J. Clarke ◽

Alexandra Rao ◽

Michael A. Cowley ◽

Belinda A. Henry

Keyword(s):

Skeletal Muscle ◽

Protein Kinase ◽

Uncoupling Protein ◽

Specific Effect ◽

Metabolic Effects ◽

Mrna Levels ◽

Nonesterified Fatty Acids ◽

Glucose Levels ◽

Amp Activated Protein Kinase ◽

The Brain

Adiposity is regulated in a sexually divergent manner. This is partly due to sex steroids, but the differential effects of androgens in males and females are unclear. We investigated effects of testosterone on energy balance in castrated male (n = 6) and female sheep (n = 4), which received 3 × 200 mg testosterone implants for 2 wk or blank implants (controls). Temperature probes were implanted into retroperitoneal fat and skeletal muscle. Blood samples were taken to measure metabolites and insulin. In males, muscle and fat biopsies were collected to measure uncoupling protein (UCP) mRNA and phosphorylation of AMP-activated protein kinase and Akt. Testosterone did not change food intake in either sex. Temperature in muscle was higher in males than females, and testosterone reduced heat production in males only. In fat, however, temperature was higher in the castrate males compared with females, and there was no effect of testosterone treatment in either sex. Preprandial glucose levels were lower, but nonesterified fatty acids were higher in females compared with males, irrespective of testosterone. In males, the onset of feeding increased UCP1 and UCP3 mRNA levels in skeletal muscle, without an effect of testosterone. During feeding, testosterone reduced glucose levels in males only but did not alter the phosphorylation of AMP-activated protein kinase or Akt in muscle. Thus, testosterone maintains lower muscle and fat temperatures in males but not females. The mechanism underlying this sex-specific effect of testosterone is unknown but may be due to sexual differentiation of the brain centers controlling energy expenditure.

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Early postnatal oestradiol exposure causes insulin resistance and signs of inflammation in circulation and skeletal muscle

Journal of Endocrinology ◽

10.1677/joe-08-0534 ◽

2009 ◽

Vol 201 (1) ◽

pp. 49-58 ◽

Cited By ~ 11

Author(s):

Camilla Alexanderson ◽

Elias Eriksson ◽

Elisabet Stener-Victorin ◽

Malin Lönn ◽

Agneta Holmäng

Keyword(s):

Insulin Resistance ◽

Skeletal Muscle ◽

Adipose Tissue ◽

Insulin Sensitivity ◽

Uncoupling Protein ◽

Female Rats ◽

Whole Body ◽

Low Grade ◽

Expression Of Genes ◽

Genes Encoding

Early postnatal events can predispose to metabolic and endocrine disease in adulthood. In this study, we evaluated the programming effects of a single early postnatal oestradiol injection on insulin sensitivity in adult female rats. We also assessed the expression of genes involved in inflammation and glucose metabolism in skeletal muscle and adipose tissue and analysed circulating inflammation markers as possible mediators of insulin resistance. Neonatal oestradiol exposure reduced insulin sensitivity and increased plasma levels of monocyte chemoattractant protein-1 (MCP-1) and soluble intercellular adhesion molecule-1. In skeletal muscle, oestradiol increased the expression of genes encoding complement component 3 (C3), Mcp-1, retinol binding protein-4 (Rbp4) and transforming growth factor β1 (Tgfβ1). C3 and MCP-1 are both related to insulin resistance, and C3, MCP-1 and TGFβ1 are also involved in inflammation. Expression of genes encoding glucose transporter-4 (Glut 4), carnitine-palmitoyl transferase 1b (Cpt1b), peroxisome proliferator-activated receptor δ (Ppard) and uncoupling protein 3 (Ucp3), which are connected to glucose uptake, lipid oxidation, and energy uncoupling, was down regulated. Expression of several inflammatory genes in skeletal muscle correlated negatively with whole-body insulin sensitivity. In s.c. inguinal adipose tissue, expression of Tgfβ1, Ppard and C3 was decreased, while expression of Rbp4 and Cpt1b was increased. Inguinal adipose tissue weight was increased but adipocyte size was unaltered, suggesting an increased number of adipocytes. We suggest that early neonatal oestrogen exposure may reduce insulin sensitivity by inducing chronic, low-grade systemic and skeletal muscle inflammation and disturbances of glucose and lipid metabolism in skeletal muscle in adulthood.

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Two weeks of early time-restricted feeding (eTRF) improves skeletal muscle insulin and anabolic sensitivity in healthy men

American Journal of Clinical Nutrition ◽

10.1093/ajcn/nqaa192 ◽

2020 ◽

Vol 112 (4) ◽

pp. 1015-1028

Author(s):

Robert Jones ◽

Pardeep Pabla ◽

Joanne Mallinson ◽

Aline Nixon ◽

Tariq Taylor ◽

...

Keyword(s):

Skeletal Muscle ◽

Weight Loss ◽

Insulin Sensitivity ◽

Temporal Distribution ◽

Early Time ◽

Metabolic Effects ◽

Whole Body ◽

Intermittent Fasting ◽

Restricted Feeding ◽

Branched Chain

ABSTRACT Background Altering the temporal distribution of energy intake (EI) and introducing periods of intermittent fasting (IF) exert important metabolic effects. Restricting EI to earlier in the day [early time-restricted feeding (eTRF)] is a novel type of IF. Objectives We assessed the chronic effects of eTRF compared with an energy-matched control on whole-body and skeletal muscle insulin and anabolic sensitivity. Methods Sixteen healthy males (aged 23 ± 1 y; BMI 24.0 ± 0.6 kg·m−2) were assigned to 2 groups that underwent either 2 wk of eTRF (n = 8) or control/caloric restriction (CON:CR; n = 8) diet. The eTRF diet was consumed ad libitum and the intervention was conducted before the CON:CR, in which the diet was provided to match the reduction in EI and body weight observed in eTRF. During eTRF, daily EI was restricted to between 08:00 and 16:00, which prolonged the overnight fast by ∼5 h. The metabolic responses to a carbohydrate/protein drink were assessed pre- and post-interventions following a 12-h overnight fast. Results When compared with CON:CR, eTRF improved whole-body insulin sensitivity [between-group difference (95% CI): 1.89 (0.18, 3.60); P = 0.03; η2p = 0.29] and skeletal muscle uptake of glucose [between-group difference (95% CI): 4266 (261, 8270) μmol·min−1·kg−1·180 min; P = 0.04; η2p = 0.31] and branched-chain amino acids (BCAAs) [between-group difference (95% CI): 266 (77, 455) nmol·min−1·kg−1·180 min; P = 0.01; η2p = 0.44]. eTRF caused a reduction in EI (∼400 kcal·d−1) and weight loss (−1.04 ± 0.25 kg; P = 0.01) that was matched in CON:CR (−1.24 ± 0.35 kg; P = 0.01). Conclusions Under free-living conditions, eTRF improves whole-body insulin sensitivity and increases skeletal muscle glucose and BCAA uptake. The metabolic benefits of eTRF are independent of its effects on weight loss and represent chronic adaptations rather than the effect of the last bout of overnight fast. This trial was registered at clinicaltrials.gov as NCT03969745.

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Human skeletal muscle PPARα expression correlates with fat metabolism gene expression but not BMI or insulin sensitivity

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00232.2003 ◽

2004 ◽

Vol 286 (2) ◽

pp. E168-E175 ◽

Cited By ~ 18

Author(s):

Junlong Zhang ◽

D. I. W. Phillips ◽

Chunli Wang ◽

Christopher D. Byrne

Keyword(s):

Skeletal Muscle ◽

Lipid Metabolism ◽

Insulin Sensitivity ◽

Uncoupling Protein ◽

Acid Oxidation ◽

Peroxisome Proliferator ◽

Mrna Levels ◽

Peroxisome Proliferator Activated Receptor ◽

Few Data

Peroxisome proliferator-activated receptor-α (PPARα) is a key regulator of fatty acid oxidation in skeletal muscle, but few data exist from humans in vivo. To investigate whether insulin sensitivity in skeletal muscle and body mass index (BMI) were associated with skeletal muscle expression of PPARα and with important genes regulating lipid metabolism in humans in vivo, we undertook hyperinsulinemic-euglycemic clamps and measured PPARα mRNA levels and mRNA levels of lipid regulating PPARα response genes in skeletal muscle biopsies. mRNA levels were measured in 16 men, using a novel highly sensitive and specific medium throughput quantitative competitive PCR that allows reproducible measurement of multiple candidate mRNAs simultaneously. mRNA levels of PPARα were positively correlated with mRNA levels of CD36 ( r = 0.77, P = 0.001), lipoprotein lipase ( r = 0.54, P = 0.024), muscle-type carnitine palmitoyltransferase-I ( r = 0.54, P = 0.024), uncoupling protein-2 ( r = 0.63, P = 0.008), and uncoupling protein-3 ( r = 0.53, P = 0.026), but not with measures of insulin sensitivity, BMI, or GLUT4, which plays an important role in insulin-mediated glucose uptake. Thus our data suggest that in humans skeletal muscle PPARα expression and genes regulating lipid metabolism are tightly linked, but there was no association between both insulin sensitivity and BMI with PPARα expression in skeletal muscle.

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Impaired Skeletal Muscle β-Adrenergic Activation and Lipolysis Are Associated with Whole-Body Insulin Resistance in Rats Bred for Low Intrinsic Exercise Capacity

Endocrinology ◽

10.1210/en.2009-0158 ◽

2009 ◽

Vol 150 (11) ◽

pp. 4883-4891 ◽

Cited By ~ 38

Author(s):

Sarah J. Lessard ◽

Donato A. Rivas ◽

Zhi-Ping Chen ◽

Bryce J. van Denderen ◽

Matthew J. Watt ◽

...

Keyword(s):

Insulin Resistance ◽

Skeletal Muscle ◽

Insulin Sensitivity ◽

Protein Content ◽

Exercise Capacity ◽

Metabolic Health ◽

Whole Body ◽

Receptor Protein ◽

Endurance Capacity ◽

Triacylglycerol Lipase

Rats selectively bred for high endurance running capacity (HCR) have higher insulin sensitivity and improved metabolic health compared with those bred for low endurance capacity (LCR). We investigated several skeletal muscle characteristics, in vitro and in vivo, that could contribute to the metabolic phenotypes observed in sedentary LCR and HCR rats. After 16 generations of selective breeding, HCR had approximately 400% higher running capacity (P < 0.001), improved insulin sensitivity (P < 0.001), and lower fasting plasma glucose and triglycerides (P < 0.05) compared with LCR. Skeletal muscle ceramide and diacylglycerol content, basal AMP-activated protein kinase (AMPK) activity, and basal lipolysis were similar between LCR and HCR. However, the stimulation of lipolysis in response to 10 μm isoproterenol was 70% higher in HCR (P = 0.004). Impaired isoproterenol sensitivity in LCR was associated with lower basal triacylglycerol lipase activity, Ser660 phosphorylation of HSL, and β2-adrenergic receptor protein content in skeletal muscle. Expression of the orphan nuclear receptor Nur77, which is induced by β-adrenergic signaling and is associated with insulin sensitivity, was lower in LCR (P < 0.05). Muscle protein content of Nur77 target genes, including uncoupling protein 3, fatty acid translocase/CD36, and the AMPK γ3 subunit were also lower in LCR (P < 0.05). Our investigation associates whole-body insulin resistance with impaired β-adrenergic response and reduced expression of genes that are critical regulators of glucose and lipid metabolism in skeletal muscle. We identify impaired β-adrenergic signal transduction as a potential mechanism for impaired metabolic health after artificial selection for low intrinsic exercise capacity.

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Erythropoietin administration acutely stimulates resting energy expenditure in healthy young men

Journal of Applied Physiology ◽

10.1152/japplphysiol.01391.2011 ◽

2012 ◽

Vol 112 (7) ◽

pp. 1114-1121 ◽

Cited By ~ 14

Author(s):

Britt Christensen ◽

Mikkel H. Vendelbo ◽

Thomas Krusenstjerna-Hafstrøm ◽

Michael Madsen ◽

Steen B. Pedersen ◽

...

Keyword(s):

Insulin Sensitivity ◽

Energy Expenditure ◽

Young Men ◽

Resting Energy Expenditure ◽

Fat Oxidation ◽

Metabolic Effects ◽

Whole Body ◽

Mrna Levels ◽

Substrate Metabolism ◽

Resting Energy

Treatment with recombinant human erythropoietin (rHuEpo) improves insulin sensitivity in patients with end-stage renal disease, and animal studies indicate that Epo increases fat oxidation. However, the metabolic effects of rHuEpo have never been experimentally studied in healthy humans. The aim was to investigate the effects of an acute rHuEpo bolus on substrate metabolism and insulin sensitivity in healthy young men. Ten healthy young men were studied in a single-blinded, randomized crossover design with a 2-wk washout period receiving 400 IU/kg rHuEpo or placebo. Substrate metabolism was evaluated by indirect calorimetry and tracer infusions, and insulin sensitivity by a hyperinsulinemic euglycemic clamp; and PCR and Western blotting measured protein expression and content, respectively. Resting energy expenditure (REE) increased significantly after rHuEpo [basal: 1,863.3 ± 67.2 (kcal/day) (placebo) vs. 2,041.6 ± 81.2 (rHuEpo), P < 0.001; clamp: 1,903.9 ± 68.3 (placebo) vs. 2,015.7 ± 114.4 (rHuEpo), P = 0.03], but the increase could not be explained by changes in mRNA levels of uncoupling protein 2 or 3. Fat oxidation in the basal state tended to be higher after rHuEpo but could not be explained by changes in mRNA levels of CPT1 and PPARα or AMPK and ACC protein phosphorylation. Insulin-stimulated glucose disposal, glucose metabolism, and whole body and forearm protein metabolism did not change significantly in response to rHuEpo. In conclusion, a single injection of rHuEpo acutely increases REE in healthy human subjects. This calorigenic effect is not accompanied by distinct alterations in the pattern of substrate metabolism or insulin sensitivity.

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Abstract P645: Chronic Angiotensin-(1-7) Improves Whole-Body Insulin Sensitivity in High-Fat Fed Mice by Enhancing Skeletal Muscle Glucose Uptake

Hypertension ◽

10.1161/hyp.66.suppl_1.p645 ◽

2015 ◽

Vol 66 (suppl_1) ◽

Author(s):

Ian M Williams ◽

David H Wasserman ◽

Italo Biaggioni ◽

Amy C Arnold

Keyword(s):

Blood Pressure ◽

Skeletal Muscle ◽

Body Weight ◽

Insulin Sensitivity ◽

Glucose Uptake ◽

Hepatic Glucose Production ◽

Metabolic Effects ◽

Whole Body ◽

High Fat ◽

Sites Of Action

Angiotensin (Ang)-(1-7) is a vasodilatory peptide implicated in the pathophysiology of hypertension, in part by opposing deleterious Ang II cardiovascular actions. Recent studies show that Ang-(1-7) restoration lowers blood pressure and improves glycemic control in animal models of cardiometabolic syndrome. The tissue-specific sites of action and blood pressure dependence for these metabolic effects, however, remain unclear. We hypothesized that Ang-(1-7) improves insulin sensitivity by enhancing peripheral glucose delivery. To test this hypothesis, adult male C57BL/6 mice were placed on standard chow or 60% high-fat diet for 11 weeks, with Ang-(1-7) [400 ng/kg/min] or saline given during the last 3 weeks of diet by subcutaneous osmotic mini-pump. Hyperinsulinemic (4 mU/kg/min) euglycemic clamps were performed in conscious, unrestrained mice at the end of the treatment period. High-fat fed mice exhibited modest hypertension (systolic blood pressure: 137±3 high-fat vs. 123±5 mmHg chow; p=0.043), which was not altered by Ang-(1-7) infusion (141±4 mmHg; p=0.516). Body weight, body composition, and fasting plasma glucose and insulin levels were not significantly different following Ang-(1-7) treatment in chow or high-fat fed mice. Ang-(1-7) increased the glucose infusion rate (GIR) needed to maintain euglycemia in high-fat fed mice (steady-state GIR: 31±5 Ang-(1-7) vs. 16±1 mg/kg/min vehicle; p=0.017) indicating enhanced whole-body insulin sensitivity, with no significant effect in chow fed mice. The improvement in insulin sensitivity in high-fat fed mice was due to an enhanced rate of whole-body glucose disappearance (R d : 34±5 Ang-(1-7) vs. 20±2 mg/kg/min vehicle; p=0.049), with increased rates of glucose uptake in gastrocnemius, vastus, and soleus muscle. There was no effect of Ang-(1-7) on insulin-mediated suppression of hepatic glucose production. Our data shows that Ang-(1-7) has direct insulin-sensitizing effects on skeletal muscle, which are independent of changes in body weight or systemic blood pressure. These overall findings provide new insight into mechanisms by which Ang-(1-7) improves insulin action, and provide further support to targeting this peptide for treatment of cardiometabolic disease.

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Myostatin propeptide mutation of the hypermuscular Compact mice decreases the formation of myostatin and improves insulin sensitivity

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00216.2016 ◽

2017 ◽

Vol 312 (3) ◽

pp. E150-E160 ◽

Cited By ~ 5

Author(s):

Tamas Kocsis ◽

Gyorgy Trencsenyi ◽

Kitti Szabo ◽

Julia Aliz Baan ◽

Geza Muller ◽

...

Keyword(s):

Skeletal Muscle ◽

Insulin Sensitivity ◽

Genetic Background ◽

Negative Regulator ◽

Metabolic Effects ◽

Muscle Size ◽

Whole Body ◽

Rab Gtpase ◽

Wild Type ◽

Absolute Size

The TGFβ family member myostatin (growth/differentiation factor-8) is a negative regulator of skeletal muscle growth. The hypermuscular Compact mice carry the 12-bp Mstn(Cmpt-dl1Abc) deletion in the sequence encoding the propeptide region of the precursor promyostatin, and additional modifier genes of the Compact genetic background contribute to determine the full expression of the phenotype. In this study, by using mice strains carrying mutant or wild-type myostatin alleles with the Compact genetic background and nonmutant myostatin with the wild-type background, we studied separately the effect of the Mstn(Cmpt-dl1Abc) mutation or the Compact genetic background on morphology, metabolism, and signaling. We show that both the Compact myostatin mutation and Compact genetic background account for determination of skeletal muscle size. Despite the increased musculature of Compacts, the absolute size of heart and kidney is not influenced by myostatin mutation; however, the Compact genetic background increases them. Both Compact myostatin and genetic background exhibit systemic metabolic effects. The Compact mutation decreases adiposity and improves whole body glucose uptake, insulin sensitivity, and 18FDG uptake of skeletal muscle and white adipose tissue, whereas the Compact genetic background has the opposite effect. Importantly, the mutation does not prevent the formation of mature myostatin; however, a decrease in myostatin level was observed, leading to altered activation of Smad2, Smad1/5/8, and Akt, and an increased level of p-AS160, a Rab-GTPase-activating protein responsible for GLUT4 translocation. Based on our analysis, the Compact genetic background strengthens the effect of myostatin mutation on muscle mass, but those can compensate for each other when systemic metabolic effects are compared.

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Effect of training on insulin binding to rat skeletal muscle sarcolemmal vesicles

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1986.250.5.e570 ◽

1986 ◽

Vol 250 (5) ◽

pp. E570-E575

Author(s):

G. K. Grimditch ◽

R. J. Barnard ◽

S. A. Kaplan ◽

E. Sternlicht

Keyword(s):

Skeletal Muscle ◽

Insulin Sensitivity ◽

Exercise Training ◽

Insulin Binding ◽

Whole Body ◽

Rat Skeletal Muscle ◽

Binding Studies ◽

Muscle Enzyme ◽

Intravenous Glucose ◽

High Affinity

We examined the hypothesis that the exercise training-induced increase in skeletal muscle insulin sensitivity is mediated by adaptations in insulin binding to sarcolemmal (SL) insulin receptors. Insulin binding studies were performed on rat skeletal muscle SL isolated from control and trained rats. No significant differences were noted between groups in body weight or fat. An intravenous glucose tolerance test showed an increase in whole-body insulin sensitivity with training, and specific D-glucose transport studies on isolated SL vesicles indicated that this was due in part to adaptations in skeletal muscle. Enzyme marker analyses revealed no differences in yield, purity, or contamination of SL membranes between the two groups. Scatchard analyses indicated no significant differences in the number of insulin binding sites per milligram SL protein on the high-affinity (15.0 +/- 4.1 vs. 18.1 +/- 6.4 X 10(9)) or on the low-affinity portions (925 +/- 80 vs. 884 +/- 106 X 10(9)) of the curves. The association constants of the high-affinity (0.764 +/- 0.154 vs. 0.685 +/- 0.264 X 10(9) M-1) and of the low affinity sites (0.0096 +/- 0.0012 vs. 0.0102 +/- 0.0012 X 10(9) M-1) also were similar. These results do not support the hypothesis that the increased sensitivity to insulin after exercise training is due to changes in SL insulin receptor binding.

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Transcriptional regulation of gene expression in human skeletal muscle during recovery from exercise

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.2000.279.4.e806 ◽

2000 ◽

Vol 279 (4) ◽

pp. E806-E814 ◽

Cited By ~ 351

Author(s):

Henriette Pilegaard ◽

George A. Ordway ◽

Bengt Saltin ◽

P. Darrell Neufer

Keyword(s):

Skeletal Muscle ◽

Exercise Training ◽

Human Skeletal Muscle ◽

Molecular Mechanisms ◽

Uncoupling Protein ◽

Pyruvate Dehydrogenase Kinase ◽

Heme Oxygenase 1 ◽

Metabolic Efficiency ◽

Vastus Lateralis Muscle ◽

Mrna Levels

Exercise training elicits a number of adaptive changes in skeletal muscle that result in an improved metabolic efficiency. The molecular mechanisms mediating the cellular adaptations to exercise training in human skeletal muscle are unknown. To test the hypothesis that recovery from exercise is associated with transcriptional activation of specific genes, six untrained male subjects completed 60–90 min of exhaustive one-legged knee extensor exercise for five consecutive days. On day 5, nuclei were isolated from biopsies of the vastus lateralis muscle of the untrained and the trained leg before exercise and from the trained leg immediately after exercise and after 15 min, 1 h, 2 h, and 4 h of recovery. Transcriptional activity of the uncoupling protein 3 (UCP3), pyruvate dehydrogenase kinase 4 (PDK4), and heme oxygenase-1 (HO-1) genes (relative to β-actin) increased by three- to sevenfold in response to exercise, peaking after 1–2 h of recovery. Increases in mRNA levels followed changes in transcription, peaking between 2 and 4 h after exercise. Lipoprotein lipase and carnitine pamitoyltransferase I gene transcription and mRNA levels showed similar but less dramatic induction patterns, with increases ranging from two- to threefold. In a separate study, a single 4-h bout of cycling exercise ( n = 4) elicited from 5 to >20-fold increases in UCP3, PDK4, and HO-1 transcription, suggesting that activation of these genes may be related to the duration or intensity of exercise. These data demonstrate that exercise induces transient increases in transcription of metabolic genes in human skeletal muscle. Moreover, the findings suggest that the cumulative effects of transient increases in transcription during recovery from consecutive bouts of exercise may represent the underlying kinetic basis for the cellular adaptations associated with exercise training.

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