Deep muscle-proteomic analysis of freeze-dried human muscle biopsies reveals fiber type-specific adaptations to exercise training.

Skeletal muscle conveys several of the health-promoting effects of exercise; yet the underlying mechanisms are not fully elucidated. Studying skeletal muscle is challenging due to its different fiber types and the presence of non-muscle cells. This can be circumvented by isolation of single muscle fibers. Here, we develop a workflow enabling proteomics analysis of pools of isolated muscle fibers from freeze-dried human muscle biopsies. We identify more than 4000 proteins in slow- and fast-twitch muscle fibers. Exercise training alters expression of 237 and 172 proteins in slow- and fast-twitch muscle fibers, respectively. Interestingly, expression levels of secreted proteins and proteins involved in transcription, mitochondrial metabolism, Ca2+ signaling, and fat and glucose metabolism adapts to training in a fiber type-specific manner. Our data provide a resource to elucidate molecular mechanisms underlying muscle function and health, and our workflow allows fiber type-specific proteomic analyses of snap-frozen non-embedded human muscle biopsies.

Near-normalization of glycaemic control with glucagon-like peptide-1 receptor agonist treatment combined with exercise in patients with type 2 diabetes.

AIMS: To investigate the effects of exercise in combination with a glucagon-like peptide-1 receptor agonist (GLP-1RA), liraglutide, or placebo for the treatment of type 2 diabetes. METHODS: Thirty-three overweight, dysregulated and sedentary patients with type 2 diabetes were randomly allocated to 16 weeks of either exercise and liraglutide or exercise and placebo. Both groups had three supervised 60-minute training sessions per week including spinning and resistance training. RESULTS: Glycated haemoglobin (HbA1c) levels dropped by a mean ± standard deviation of 2.0% ± 1.2% (from 8.2% ± 1.4%) in the exercise plus liraglutide group vs 0.3% ± 0.9% (from 8.0% ± 1.2%) in the exercise plus placebo group ( P < .001), and body weight was reduced more with liraglutide (-3.4 ± 2.9 kg vs -1.6 ± 2.3 kg; P < .001). Compared with baseline, similar reductions were seen in body fat (exercise plus liraglutide: -2.5% ± 1.4% [ P < .001]; exercise plus placebo: -2.2% ± 1.9% [ P < .001]) and similar increases were observed in maximum oxygen uptake (exercise plus liraglutide: 0.5 ± 0.5 L O2 /min [ P < .001]; exercise plus placebo: 0.4 ± 0.4 L O2 /min [ P = .002]). Greater reductions in fasting plasma glucose (-3.4 ± 2.3 mM vs -0.3 ± 2.6 mM, P < .001) and systolic blood pressure (-5.4 ± 7.4 mm Hg vs -0.6 ± 11.1 mm Hg, P < .01) were seen with exercise plus liraglutide vs exercise plus placebo. The two groups experienced similar increases in quality of life during the intervention. CONCLUSIONS: In obese patients with type 2 diabetes, exercise combined with GLP-1RA treatment near-normalized HbA1c levels and caused a robust weight loss when compared with placebo. These results suggest that a combination of exercise and GLP-1RA treatment is effective in type 2 diabetes.

Obesity augments the age-induced increase in mitochondrial capacity for H2O2 release in Zucker fatty rats.

AIM: Mitochondrial dysfunction has been suggested to play a significant role in obesity and insulin resistance. The aim of the present study was to investigate if changes in obesity and insulin resistance were related to similar changes in mitochondrial capacity for hydrogen peroxide release in Zucker diabetic fatty rats and their lean littermates. METHODS: Thirty-four rats were used in this study. Rats were either lean or obese Zucker rats killed at 5-6 (young) or 12-14 (adults) weeks of age. Mitochondria were isolated from soleus muscles; respiration and release of hydrogen peroxide were determined and related to citrate synthase activity to determine intrinsic mitochondrial function. Mitochondrial-specific super-oxide dismuthase (MnSOD) protein content was determined in isolated mitochondria and muscle homogenate. Catalase protein content was determined in muscle homogenate. RESULTS: Young lean and obese rats had a higher mitochondrial respiration when using palmitoyl-l-carnitine as substrate compared with adult lean and obese rats. The obese strain had higher mitochondrial hydrogen peroxide release but only in the adult animals. In both lean and obese animals, increased age was associated with increased mitochondrial hydrogen peroxide release. MnSOD tended to be higher in the obese strain in the isolated mitochondria. Regardless of age, catalase protein content was significantly lower in the obese rats. CONCLUSIONS: This study shows that the augmented increase in obesity and insulin resistance seen in Zucker diabetic fatty rats is associated with increased capacity for mitochondrial hydrogen peroxide release.

Factors regulating fat oxidation in human skeletal muscle.

In modern societies, oversupply of calories leads to obesity and chronic metabolic stress, which may lead to development of disease. Oversupply of calories is often associated with elevated plasma lipid concentrations and accumulation of lipids in skeletal muscle leading to decreased insulin sensitivity. Consequently, enhanced fat oxidation might be beneficial in counteracting lipid accumulation. Exercise is the most effective way to increase fat oxidation, because it increases metabolic rate. Lipid metabolism can also be altered by dietary manipulations. Thus, a fat rich diet leads to increased potential for fat oxidation by increasing the content of several of the proteins in the fat oxidative pathway. The regulation of both exercise and diet induced lipid oxidation will be discussed in this review.

Contraction-induced skeletal muscle FAT/CD36 trafficking and FA uptake is AMPK independent.

The aim of this study was to investigate the molecular mechanisms regulating FA translocase CD36 (FAT/CD36) translocation and FA uptake in skeletal muscle during contractions. In one model, wild-type (WT) and AMP-dependent protein kinase kinase dead (AMPK KD) mice were exercised or extensor digitorum longus (EDL) and soleus (SOL) muscles were contracted, ex vivo. In separate studies, FAT/CD36 translocation and FA uptake in response to muscle contractions were investigated in the perfused rat hindlimb. Exercise induced a similar increase in skeletal muscle cell surface membrane FAT/CD36 content in WT (+34%) and AMPK KD (+37%) mice. In contrast, 5-aminoimidazole-4-carboxamide ribonucleoside only induced an increase in cell surface FAT/CD36 content in WT (+29%) mice. Furthermore, in the perfused rat hindlimb, muscle contraction induced a rapid (1 min, +15%) and sustained (10 min, +24%) FAT/CD36 relocation to cell surface membranes. The increase in cell surface FAT/CD36 protein content with muscle contractions was associated with increased FA uptake, both in EDL and SOL muscle from WT and AMPK KD mice and in the perfused rat hindlimb. This suggests that AMPK is not essential in regulation of FAT/CD36 translocation and FA uptake in skeletal muscle during contractions. However, AMPK could be important in regulation of FAT/CD36 distribution in other physiological situations.

Increased rate of whole body lipolysis before and after 9 days of bed rest in healthy young men born with low birth weight.

Individuals born with low birth weight (LBW) are at risk of developing type 2 diabetes mellitus (T2D), which may be precipitated by physical inactivity. Twenty-two LBW subjects and twenty-three controls were studied before and after bed rest by the hyperinsulinemic euglycemic clamp combined with indirect calorimetry and infusion of stable isotope tracers and preceded by an intravenous glucose tolerance test. LBW subjects had a similar body mass index but elevated abdominal obesity compared with controls. The basal rate of whole body lipolysis (WBL) was elevated in LBW subjects with and without correction for abdominal obesity before and after bed rest (all P = 0.01). Skeletal muscle hormone-sensitive lipase (HSL) protein expression and phosphorylation at Ser565 were similar in the two groups. Bed rest resulted in a decrease in WBL and an increased skeletal muscle HSL Ser565 phosphorylation indicating a decreased HSL activity in both groups. All subjects developed peripheral insulin resistance in response to bed rest (all P < 0.0001) with no differences between groups. LBW subjects developed hepatic insulin resistance in response to bed rest. In conclusion, increased WBL may contribute to the development of hepatic insulin resistance when exposed to bed rest in LBW subjects. Nine days of bed rest causes severe peripheral insulin resistance and reduced WBL and skeletal muscle HSL activity, as well as a compensatory increased insulin secretion, with no differences in LBW subjects and controls.

Prolactin suppresses malonyl-CoA concentration in human adipose tissue.

Prolactin is best known for its involvement in lactation, where it regulates mechanisms that supply nutrients for milk production. In individuals with pathological hyperprolactinemia, glucose and fat homeostasis have been reported to be negatively influenced. It is not previously known, however, whether prolactin regulates lipogenesis in human adipose tissue. The aim of this study was to investigate the effect of prolactin on lipogenesis in human adipose tissue in vitro. Prolactin decreased the concentration of malonyl-CoA, the product of the first committed step in lipogenesis, to 77+/-6% compared to control 100+/-5% (p=0.022) in cultured human adipose tissue. In addition, prolactin was found to decrease glucose transporter 4 ( GLUT4) mRNA expression, which may cause decreased glucose uptake. In conclusion, we propose that prolactin decreases lipogenesis in human adipose tissue as a consequence of suppressed malonyl-CoA concentration in parallel with decreased GLUT-4 expression. In the lactating woman, this regulation in adipose tissue may enhance the provision of nutrients for the infant instead of nutrients being stored in adipose tissue. In hyperprolactinemic individuals, a suppressed lipogenesis could contribute to an insulin resistant state with consequences for the health.

Impact of carbohydrate supplementation during endurance training on glycogen storage and performance.

AIM: Glucose ingestion may improve exercise endurance, but it apparently also influences the transcription rate of several metabolic genes and it alters muscle metabolism during an acute exercise bout. Therefore, we investigated how chronic training responses are affected by glucose ingestion. METHODS: In previously untrained males performance and various muscular adaptations were evaluated before and after 8 weeks of supervised endurance training conducted either with (n = 8; CHO group) or without (n = 7; placebo) glucose supplementation. RESULTS: The two groups achieved similar improvements in maximal oxygen uptake and peak power output during incremental cycling (both parameters elevated by 17% on average) and both groups lost approximately 3 kg of fat mass during the 8 weeks of training. An equal reduction in respiratory exchange ratio (0.02 units) during submaximal exercise was observed in both groups. Beta-hydroxyacyl-CoA-dehydrogenase activity was increased in both groups, however, to a larger extent in the placebo group (45 +/- 11%) than CHO (23 +/- 9%, P < 0.05). GLUT-4 protein expression increased by 74 +/- 14% in the placebo group and 45 +/- 14% in CHO (both P < 0.05), while resting muscle glycogen increased (P < 0.05) to a larger extent in the placebo group (96 +/- 4%) than CHO (33 +/- 2%). CONCLUSION: These results show that carbohydrate supplementation consumed during exercise training influences various muscular training adaptations, but improvements in cardiorespiratory fitness and reductions in fat mass are not affected.

Potential role of TBC1D4 in enhanced post-exercise insulin action in human skeletal muscle.

AIMS/HYPOTHESIS: TBC1 domain family, member 4 (TBC1D4; also known as AS160) is a cellular signalling intermediate to glucose transport regulated by insulin-dependent and -independent mechanisms. Skeletal muscle insulin sensitivity is increased after acute exercise by an unknown mechanism that does not involve modulation at proximal insulin signalling intermediates. We hypothesised that signalling through TBC1D4 is involved in this effect of exercise as it is a common signalling element for insulin and exercise. METHODS: Insulin-regulated glucose metabolism was evaluated in 12 healthy moderately trained young men 4 h after one-legged exercise at basal and during a euglycaemic-hyperinsulinaemic clamp. Vastus lateralis biopsies were taken before and immediately after the clamp. RESULTS: Insulin stimulation increased glucose uptake in both legs, with greater effects (approximately 80%, p < 0.01) in the previously exercised leg. TBC1D4 phosphorylation, assessed using the phospho-AKT (protein kinase B)substrate antibody and phospho- and site-specific antibodies targeting six phosphorylation sites on TBC1D4, increased at similar degrees to insulin stimulation in the previously exercised and rested legs (p < 0.01). However, TBC1D4 phosphorylation on Ser-318, Ser-341, Ser-588 and Ser-751 was higher in the previously exercised leg, both in the absence and in the presence of insulin (p < 0.01; Ser-588, p = 0.09; observed power = 0.39). 14-3-3 binding capacity for TBC1D4 increased equally (p < 0.01) in both legs during insulin stimulation. CONCLUSION/INTERPRETATION: We provide evidence for site-specific phosphorylation of TBC1D4 in human skeletal muscle in response to physiological hyperinsulinaemia. The data support the idea that TBC1D4 is a nexus for insulin- and exercise-responsive signals that may mediate increased insulin action after exercise.

The effect of exercise on postprandial lipidemia in type 2 diabetic patients.

To elucidate if postprandial exercise can reduce the exaggerated lipidemia seen in type 2 diabetic patients after a high-fat meal. Two mornings eight type 2 diabetic patients (males) (58 +/- 1.2 years, BMI 28.0 +/- 0.9 kg m(-2)) and seven non-diabetic controls ate a high-fat breakfast (680 kcal m(-2), 84% fat). On one morning, 90 min later subjects cycled 60 min at 57% VO(2max). Biopsies from quadriceps muscle and abdominal subcutaneous adipose tissue were sampled after exercise or equivalent period of rest and arterialized blood for 615 min. Postprandial increases in serum total-triglyceride (TG) (incremental AUC: 1,702 +/- 576 vs. 341 +/- 117 mmol l(-1) 600 min), chylomicron-TG (incremental AUC: 1,331 +/- 495 vs. 184 +/- 55 mmol l(-1) 600 min) and VLDL-TG as well as in insulin (incremental AUC: 33,946 +/- 7,414 vs. 13,670 +/- 3,250 pmol l(-1) 600 min), C-peptide and glucose were higher in diabetic patients than in non-diabetic controls (P < 0.05). In diabetic patients these variables were reduced (P < 0.05) by exercise (total-TG incremental AUC being 1,110 +/- 444, chylomicron-TG incremental AUC 1,043 +/- 474 mmol l(-1) 600 min and insulin incremental AUC 18,668 +/- 4,412 pmol l(-1) 600 min). Lipoprotein lipase activity in muscle (11.0 +/- 2.0 vs. 24.1 +/- 3.4 mU g per wet weight, P < 0.05) and post-heparin plasma at 615 min were lower in diabetic patients than in non-diabetic controls, but did not differ in adipose tissue and did not change with exercise. In diabetic patients, 210 min after exercise oxygen uptake (P < 0.05) and fat oxidation (P < 0.1) were still higher than on non-exercise days. In type 2 diabetic patients, after a high-fat meal exercise reduces the plasma concentrations of triglyceride contained in both chylomicrons and VLDL as well as insulin secretion. This suggests protection against progression of atherosclerosis and diabetes.

Evaluation of intramyocellular lipid breakdown during exercise by biochemical assay, NMR spectroscopy, and Oil Red O staining.

The study compared the net decline of intramyocellular lipids (IMCL) during exercise (n = 18) measured by biochemical assay (BIO) and Oil Red O (ORO) staining on biopsy samples from vastus lateralis muscle and by (1)H-MR spectroscopy (MRS) sampled in an 11 x 11 x 18-mm(3) voxel in the same muscle. IMCL was measured before and after a 2-h cycling bout ( approximately 75% V(.)(O(2) peak)). ORO and MRS measurements showed substantial IMCL use during exercise of 31 +/- 12 and 47 +/- 6% of preexercise IMCL content. In contrast, use of BIO for IMCL determination did not reveal an exercise-induced breakdown of IMCL (2 +/- 9%, P = 0.29) in young healthy males. Correlations between different measures of exercise-induced IMCL degradation were low. Coefficients were 0.48 for MRS vs. ORO (P = 0.07) and were even lower for BIO vs. MRS (r = 0.38, P = 0.13) or ORO (r = 0.08, P = 0.78). This study demonstrates that different methods to measure IMCL in human muscles can result in different conclusions with regard to exercise-induced IMCL changes. MRS has the advantage that it is noninvasive, however, not fiber type specific and hampered by an at least 30-min delay in measurements after exercise completion and may overestimate IMCL use. BIO is the only quantitative method but is subject to variation when biopsies have different fiber type composition. However, BIO yields lower IMCL breakdown compared with ORO and MRS. ORO has the major advantage that it is fiber type specific, and it therefore provides information that is not available with the other methods.

Regulation of oxidative enzyme activity and eukaryotic elongation factor 2 in human skeletal muscle: influence of gender and exercise.

AIM: To investigate gender-related differences in the responses of oxidative enzymes and eukaryotic elongation factor-2 (eEF2) to exercise. METHODS: The influence of exercise (90 min, 60%VO(2peak)) on citrate synthase (CS) and beta-hydroxyacyl-CoA dehydrogenase (HAD) activity and mRNA content, together with eEF2 expression and phosphorylation at rest, were assessed in skeletal muscle of untrained (UT) and endurance trained (ET) females and males. RESULTS: Citrate synthase and HAD mRNA were higher in females than in males (27% and 48%, respectively, P < 0.05) whereas CS and HAD activity did not differ between females and males (NS). In females only, CS activity was enhanced (P < 0.05) by 90 min exercise. Resting CS mRNA content did not differ between UT and ET but, nevertheless, CS activity was 56% higher in ET than in UT volunteers (P < 0.001). HAD mRNA and activity were not influenced by training status (NS). In UT, CS mRNA was enhanced 37% (P < 0.05) by exercise whereas exercise did not change CS mRNA in ET (NS). eEF2 expression was 31% higher (P < 0.05) and eEF2 Thr56 phosphorylation (which leads to translation inhibition) was 24% lower (P < 0.05) in females than in males. eEF2 expression and phosphorylation were unaffected by training status (NS). CONCLUSION: Basal transcriptional, translational, and/or post-translational control of CS and HAD seems to be gender-dependent. Also, gender differences in translation and/or post-translational protein modification of CS occur during exercise. Accordingly, the potential for peptide-chain elongation, based on eEF2 expression and phosphorylation, appears to be higher in females than in males.

Studies of plasma membrane fatty acid-binding protein and other lipid-binding proteins in human skeletal muscle.

The first putative fatty acid transporter identified was plasma membrane fatty acid-binding protein (FABPpm). Later it was demonstrated that this protein is identical to the mitochondrial isoform of the enzyme aspartate aminotransferase. In recent years data from several cell types have emerged, indicating that FABPpm plays a role in the transport of long-chain saturated and unsaturated fatty acids. In the limited number of studies in human skeletal muscle it has been demonstrated that dietary composition and exercise training can influence the content of FABPpm. Ingestion of a fat-rich diet induces an increase in FABPpm protein content in human skeletal muscle in contrast to the decrease seen during consumption of a carbohydrate-rich diet. A similar effect of a fat-rich diet is also observed for cytosolic fatty acid-binding protein and fatty acid translocase/CD36 protein expression. Exercise training up regulates FABPpm protein content in skeletal muscle, but only in male subjects; no significant differences were observed in muscle FABPpm content in a cross-sectional study of female volunteers of varying training status, even though muscle FABPpm content did not depend on gender in the untrained state. A higher utilization of plasma long-chain fatty acids during exercise in males compared with females could explain the gender-dependent influence of exercise training on FABPpm. The mechanisms involved in the regulation of the function and expression of FABPpm protein remain to be clarified.

Interstitial glycerol concentrations in human skeletal muscle and adipose tissue during graded exercise.

AIM: It is not clear how lipolysis changes in skeletal muscle and adipose tissue during exercise of different intensities. We aimed at estimating this by microdialysis and muscle biopsy techniques. METHODS: Nine healthy, young men were kicking with both legs at 25% of maximal power (Wmax) for 45 min and then simultaneously with one leg at 65% and the other leg at 85% Wmax for 35 min. RESULTS: Glycerol concentrations in skeletal muscle and adipose tissue interstitial fluid and in arterial plasma increased (P<0.001) during low intensity exercise and increased (P<0.05) even more during moderate intensity exercise. The difference between interstitial muscle and arterial plasma water glycerol concentration, which indicates the direction of the glycerol flux, was positive (P<0.05) at rest (21 +/- 9 microM) and during exercise at 25% Wmax (18 +/- 6 microM). The difference decreased (P<0.05) with increasing exercise intensity and was not significantly different from zero during exercise at 65% (-11 +/- 17 microM) and 85% (-12 +/- 13 microM) Wmax. In adipose tissue, the difference between interstitial and arterial plasma water glycerol increased (P<0.001) with increasing intensity. The net triacylglycerol breakdown, measured chemically from the biopsy, did not differ significantly from zero at any exercise intensity although directional changes were similar to microdialysis changes. CONCLUSIONS: Skeletal muscle releases glycerol at rest and at low exercise intensity but not at higher intensities. This can be interpreted as skeletal muscle lipolysis peaking at low exercise intensities but could also indicate that glycerol is taken up in skeletal muscle at a rate which is increasing with exercise intensity.

Utilization of long-chain fatty acids in human skeletal muscle during exercise.

Long-chain fatty acids (LCFA) are important sources of energy in contracting skeletal muscle: during the course of endurance exercise the contribution of LCFA in energy metabolism increases whereas when the intensity of exercise increases, the energy need is covered more and more by carbohydrates. Although this has been known for nearly 100 years, the mechanisms controlling fatty acid uptake and oxidation during various exercise modes are still not completely elucidated. Besides passive diffusion, data suggest that both membrane-associated and cytosolic fatty acid binding proteins are involved in the uptake of LCFA into skeletal muscle. However, data from human studies suggest that the regulation of fatty acid utilization in skeletal muscle during exercise lies mainly within the entrance into the mitochondria or metabolism within the mitochondria. Although possible compartmentalization within the cell makes definitive conclusions difficult, available evidence suggests that changes in malonyl CoA concentration in muscle do not play a major regulatory role in controlling LCFA oxidation during exercise in man. In contrast, it is suggested that the availability of free carnitine may play a major regulatory role in oxidation of LCFA during exercise.

A possible role for AMP-activated protein kinase in exercise-induced glucose utilization: insights from humans and transgenic animals.

Exercise-induced glucose uptake in skeletal muscle is mediated by an insulin-independent mechanism, but the actual signals to glucose transport in response to muscle contraction have not been identified. The 5'-AMP-activated protein kinase (AMPK) has emerged as a putative mediator of contraction-induced glucose transport, although no conclusive evidence has been provided so far. Recent experiments in AMPK transgenic mice suggest that glucose transport induced by 5-amino-4-imidazolecarboxamide riboside (AICAR) or hypoxia is mediated by AMPK. In contrast, contraction-induced glucose transport in rodent skeletal muscle induced by electrical stimulation in vitro or in situ is not influenced or is only partially reduced by abolishing both or one of the catalytic AMPK subunits. This is compatible with exercise studies done in humans, where no tight correlation is found between AMPK activity and glucose uptake during exercise. Taken together, these results question an essential role of AMPK in exercise-induced glucose uptake and imply that one or more additional pathways are involved in mediating glucose transport in skeletal muscle during exercise.

Fat utilization during exercise: adaptation to a fat-rich diet increases utilization of plasma fatty acids and very low density lipoprotein-triacylglycerol in humans.

1. This study was carried out to test the hypothesis that the greater fat oxidation observed during exercise after adaptation to a high-fat diet is due to an increased uptake of fat originating from the bloodstream. 2. Of 13 male untrained subjects, seven consumed a fat-rich diet (62 % fat, 21 % carbohydrate) and six consumed a carbohydrate-rich diet (20 % fat, 65 % carbohydrate). After 7 weeks of training and diet, 60 min of bicycle exercise was performed at 68 +/- 1 % of maximum oxygen uptake. During exercise [1-(13)C]palmitate was infused, arterial and venous femoral blood samples were collected, and blood flow was determined by the thermodilution technique. Muscle biopsy samples were taken from the vastus lateralis muscle before and after exercise. 3. During exercise, the respiratory exchange ratio was significantly lower in subjects consuming the fat-rich diet (0.86 +/- 0.01, mean +/- S.E.M.) than in those consuming the carbohydrate-rich diet (0.93 +/- 0.02). The leg fatty acid (FA) uptake (183 +/- 37 vs. 105 +/- 28 micromol min(-1)) and very low density lipoprotein-triacylglycerol (VLDL-TG) uptake (132 +/- 26 vs. 16 +/- 21 micromol min(-1)) were both higher (each P < 0.05) in the subjects consuming the fat-rich diet. Whole-body plasma FA oxidation (determined by comparison of (13)CO(2) production and blood palmitate labelling) was 55-65 % of total lipid oxidation, and was higher after the fat-rich diet than after the carbohydrate-rich diet (13.5 +/- 1.2 vs. 8.9 +/- 1.1 micromol min(-1) kg(-1); P < 0.05). Muscle glycogen breakdown was significantly lower in the subjects taking the fat-rich diet than those taking the carbohydrate-rich diet (2.6 +/- 0.5 vs. 4.8 +/- 0.5 mmol (kg dry weight)(-1) min(-1), respectively; P < 0.05), whereas leg glucose uptake was similar (1.07 +/- 0.13 vs. 1.15 +/- 0.13 mmol min(-1)). 4. In conclusion, plasma VLDL-TG appears to be an important substrate source during aerobic exercise, and in combination with the higher plasma FA uptake it accounts for the increased fat oxidation observed during exercise after fat diet adaptation. The decreased carbohydrate oxidation was apparently due to muscle glycogen sparing and not to diminished plasma glucose uptake.

Moderate exercise, postprandial lipemia, and skeletal muscle lipoprotein lipase activity.

One mechanism by which prior exercise decreases the plasma triacylglycerol (TG) response to dietary fat may involve enhanced clearance of TG-rich lipoproteins. The purpose of the present study was to examine the influence of moderate intensity exercise on postprandial lipemia and muscle lipoprotein lipase (LPL) activity. Eight physically active, normolipidemic men aged 27.0 years (SD 4.2), body mass index 24.5 kg. m(-2) (SD 1.3), participated in 2 oral fat-tolerance tests with different preceding conditions. The afternoon before one test ( approximately 16 hours), subjects cycled for 90 minutes at 62.3% (SD 1.7%) of maximal oxygen uptake. Before the other test, subjects refrained from exercise. Samples of muscle, venous blood, and expired air were obtained in the fasted state. Subjects then consumed a high-fat meal (1.4 g fat, 1.2 g carbohydrate, 0.2 g protein, 73 kJ energy per kg body mass) before further blood and expired air samples were collected until 6 hours. The 6-hour areas under the TG concentration v time curves for plasma and for the chylomicron-rich fraction were lower (P <.05) after exercise (plasma, 7.91 [SE 1.09] v 5.72 [SE 0.47] mmol. L(-1). h; chylomicron-rich fraction, 1.98 [SE 0.51] v 0.92 [SE 0.16] mmol. L(-1). h). Muscle LPL activity was not significantly influenced by prior exercise, but the 4 subjects who had higher muscle LPL activity after exercise also had the most noticeable decreases in postprandial lipemia. The difference in lipemia between trials was inversely related to the difference in LPL activity (rho = -.79, P <.05). In the fasted state and postprandially, carbohydrate oxidation was lower after exercise (P <.05). Thus moderate exercise attenuates postprandial lipemia, possibly by altering muscle LPL activity.

Effect of creatine supplementation on creatine and glycogen content in rat skeletal muscle.

The effects of high dose creatine feeding (5 g kg(-1) BW day(-1), 5 days) on creatine content, glucose transport, and glycogen accumulation in white gastrocnemius, red gastrocnemius and soleus muscles of the rat was investigated. Isolated rat hindquarters of creatine fed and control rats were perfused with a standard medium containing either insulin alone (0, 100 or 20 000 microU mL(-1)) or in combination with creatine (2 or 10 mmol L(-1)). Furthermore, plasma insulin concentration was measured in normal rats during creatine feeding, as well as in anaesthetized rats during intravenous creatine infusion. Five days of creatine feeding increased (P < 0.05) total creatine content in soleus (+ 20%) but not in red gastrocnemius (+15%, n.s.) and white gastrocnemius (+ 10%, n.s.). In parallel, glycogen content was markedly elevated (P < 0.05) in soleus (+ 40%), less (P < 0.05) in red gastrocnemius (+ 15%), and not in white gastrocnemius (+ 10%, n.s.). Glucose transport rate, muscle GLUT-4 content, glycogen synthase activity in perfused muscles and glycogen synthesis rate were not significantly altered by creatine feeding in either muscle type. Furthermore, high dose creatine feeding raised (P < 0.05) plasma creatine concentration fivefold but did not alter circulating insulin level. It is concluded that short-term high dose creatine feeding enhances creatine disposal and glycogen storage in rat skeletal muscle. However, the creatine and glycogen response to creatine supplementation is markedly greater in oxidative than in glycolytic muscles.