The effect of exercise and insulin on AS160 phosphorylation and 14-3-3 binding capacity in human skeletal muscle

AS160 is an Akt substrate of 160 kDa implicated in the regulation of both insulin- and contraction-mediated GLUT4 translocation and glucose uptake. The effects of aerobic exercise and subsequent insulin stimulation on AS160 phosphorylation and the binding capacity of 14-3-3, a novel protein involved in the dissociation of AS160 from GLUT4 vesicles, in human skeletal muscle are unknown. Hyperinsulinemic-euglycemic clamps were performed on seven men at rest and immediately and 3 h after a single bout of cycling exercise. Skeletal muscle biopsies were taken before and after the clamps. The insulin sensitivity index calculated during the final 30 min of the clamp was 8.0 +/- 0.8, 9.1 +/- 0.5, and 9.2 +/- 0.8 for the rest, postexercise, and 3-h postexercise trials, respectively. AS160 phosphorylation increased immediately after exercise and remained elevated 3 h after exercise. In contrast, the 14-3-3 binding capacity of AS160 and phosphorylation of Akt and AMP-activated protein kinase were only increased immediately after exercise. Insulin increased AS160 phosphorylation and 14-3-3 binding capacity and insulin receptor substrate-1 and Akt phosphorylation, but the response to insulin was not enhanced by prior exercise. In conclusion, the 14-3-3 binding capacity of AS160 is increased immediately after acute exercise in human skeletal muscle, but this is not maintained 3 h after exercise completion despite sustained AS160 phosphorylation. Insulin increases AS160 phosphorylation and 14-3-3 binding capacity, but prior exercise does not appear to enhance the response to insulin.     

Time dependent effects of dexamethasone on serum insulin level and insulin receptors in rat liver and erythrocytes

The effects of glucocorticoid excess on regulation of insulin receptors were investigated in dexamethasone-treated rats. Glucocorticoid excess was produced by administration of dexamethasone (0.5 mg/100 g b.w.) 30 min, 4, 12, 18, 24, 42 or 70 h before experiments. This treatment caused time-dependent changes of glucose and insulin concentration in blood, as well as in amounts of specific insulin binding and insulin receptors of liver cells and erythrocytes. The time intervals in which dexamethasone produced the increase in insulin concentration were accompanied with decrease in insulin binding to receptors in membranes of liver cells, while significant changes in insulin binding to receptors of erythrocytes were not observed under the same experimental conditions. The effect is maximal 18 and 42 h after dexamethasone treatment that increase insulin blood level by about 85% and 60%, respectively. Receptor analysis revealed that changes in specific binding of insulin could be due to significant changes in amount of binding sites on cell surface rather than to mild alteration in receptor affinity. These findings suggest that besides the changes in insulin level, the alterations in insulin receptor number and affinity may play a major role in the states of altered insulin sensitivity which accompany glucocorticoid excess.     

The erythrocyte insulin receptor response to insulin induced hypoglycaemia

The response of the erythrocyte insulin receptor to a prolonged intravenous infusion of insulin has been measured in normal individuals during hypoglycaemia and when hypoglycaemia was prevented by the concurrent infusion of glucose. When euglycaemia was maintained, mean (+/- S.D.) specific insulin binding following the 5 hour insulin infusion was unchanged (6.9 +/- 2.1 to 6.65 +/- 2.2% bound per 2.25 X 10(9) erythrocytes). In the presence of mild hypoglycaemia, mean (+/- SD) specific insulin binding rose from 6.6 +/- 2.3 to 7.6 +/- 2.5% bound per 2.25 X 10(9) erythrocytes (P less than 0.01), after 5 hours. This increase was due to increased receptor affinity. It was not correlated with the increase in the concentration of any individual counter-regulatory hormone. Initial insulin receptor binding correlated strongly with the subsequent decline in plasma glucose concentration (r = 0.9527; P less than 0.01). Thus, acute hyperinsulinaemia, when associated with hypoglycaemia, does not result in downregulation of insulin receptors on erythrocytes but rather results in increased receptor binding. Consequently, the insulin receptor may not play an active role in protecting the individual against acute hypoglycaemia.     

Resistance and aerobic exercise: the influence of mode on the relationship between IL-6 and glucose tolerance in young men who are obese

Regular exercise lowers indicators of disease risk including some inflammatory cytokines; however, the relationship between different modes of acute exercise, cytokine levels, and subsequent glucose tolerance is unclear. The purpose was to determine the effects of resistance (RES) and aerobic (AER) exercises on interleukin-6 (IL-6) and its association with glucose tolerance 24 hours after exercise. After testing for 1 repetition maximum (1RM) and VO2peak, 10 obese (body mass index > 30 kg · m(-2)), untrained men aged 18-26 years completed 3 protocols: 60 minutes of RES, AER, and a resting (CON) condition. The RES was 2 sets of 8 repetitions and a third set to fatigue at 80% 1RM of 8 lifts using all major muscle groups. The AER was 60 minutes of cycling at 70% of VO2peak. On day 1, subjects completed the 60-minute exercise or resting protocol, and on day 2, they completed an oral glucose tolerance test (OGTT). Blood was collected before and after exercise, at 2 and 7 hour postexercise, and before and every 30 minutes during the OGTT and was analyzed for IL-6, glucose and insulin. Postexercise IL-6 was greater in RES (8.01 ± 2.08 pg · mL(-1)) vs. in AER (4.26 ± 0.27 pg · mL(-1)), and both were greater than in CON (1.61 ± 0.18 pg · mL(-1)). During the OGTT, there were no differences in glucose or insulin between conditions for single time points or as area under the curve. The RES caused greater IL-6 levels immediately after exercise that may be related to the greater active muscle mass compared to AER. Neither exercise produced enhanced glucose removal compared to control; thus, despite the greater elevation in IL-6 in RES, for these exercise conditions and this population, this cytokine did not influence glucose tolerance.     

Changes in prolactin and testosterone levels induced by acute physical exertion in young female athletes

In order to establish the influence of acute atypical exercise on prolactin and testosterone levels in young female athletes the authors selected a group of 13 short distance runners who were subjected to exercise on a cycle ergometer. Hormone levels were measured before the test, just after the end of test, 30 and 90 minutes thereafter. Significant increase in testosterone concentration appeared immediately after the exercise and 90 minutes after completion of a test testosterone level returned to preexercise levels. Unlike the results of other authors statistically significant decrease in plasma prolactin concentration was found 90 minutes after the end of test.     

Plasma ghrelin is altered after maximal exercise in elite male rowers

The aim of the present investigation was to investigate plasma ghrelin response to acute maximal exercise in elite male rowers. Eight elite male rowers performed a maximal 6000-m rowing ergometer test (mean performance time: 19 mins 52 secs; 1192.1 +/- 16.4 secs), and venous blood samples were obtained before, immediately after, and after 30 mins of recovery. In addition to ghrelin concentration, leptin, insulin, growth hormone, insulin-like growth factor-1 (IGF-1), testosterone, cortisol, and glucose values were measured. Ghrelin was significantly increased immediately after the exercise (+24.4%; P < 0.05) and was not significantly different than baseline after 30 mins of recovery. Leptin was significantly decreased immediately after the exercise (- 15.8%; P < 0.05) and remained significantly decreased after the first 30 mins of recovery. No changes occurred in insulin concentrations. Growth hormone, IGF-1, and testosterone values were significantly increased and decreased to the pre-exercise level immediately after the exercise and after the first 30 mins of recovery, respectively. Cortisol and glucose values were significantly increased immediately after the exercise and remained significantly increased during the first 30 mins of recovery. There were no relationships between plasma ghrelin and other measured blood parameters after the exercise, nor were changes in ghrelin related to changes in other measured blood biochemical values after the exercise. In conclusion, these results suggest that acute negative energy balance induced by specific maximal short-term exercise elicits a metabolic response with opposite changes in ghrelin and leptin concentrations in elite male athletes.     

Changes in Prolactin and Testosterone Levels Induced by Acute Physical Exertion in Young Female Athletes

In order to establish the influence of acute untypical exercise on prolactin and testosterone levels in young female athletes, the authors selected a group of 13 short distance runners who were subjected to exercise on a cycle ergometer. Hormone levels were measured before the test, just after the end of the test, and 30 and 90 minutes thereafter. A significant increase in the testosterone concentration appeared immediately after the exercise, and 90 minutes after the completion of a test, the testosterone level had returned to the preexercise levels. Unlike the results of other authors, a statistically significant decrease in the plasma prolactin concentration was found 90 minutes after the end of the test.     

Whole body hyperthermia of rats decreases insulin binding to erythrocytes

125I-insulin binding to rat erythrocytes was studied to investigate the effect of whole body hyperthermia on the insulin receptor. Heat treatment of rats at 42 degrees C for 15 min caused a significant decrease (48.7% of control) in 125I-insulin binding to rat erythrocytes. Scatchard analysis showed that the decreased binding resulted from a decrease in the number of the insulin receptors rather than from a decrease in receptor affinity. The decreased receptor number for insulin showed no evidence of recovery, 2 h and 8 h after the hyperthermia. Plasma insulin levels remained lower than the control, up to 8 h after the hyperthermia, whereas plasma glucose, which decreased immediately after the hyperthermia, increased higher than the control, 8 h after the hyperthermia. The low plasma insulin level and decreased number of insulin receptor are believed to be possible factors for the elevation of plasma glucose.     

Degradation and internalization of bound insulin in human erythrocytes.

Internalization and degradation of insulin by human erythrocytes were studied. Erythrocytes were incubated with 125I-insulin at 4 degrees C, 15 degrees C, and 37 degrees C for varying time intervals. These erythrocytes were then subjected to a low pH wash to release bound insulin followed by TCA precipitation. After 4, 22, and 24 hours of insulin binding at 4 degrees C, 92 to 95% of the bound 125I-insulin was dissociable and 92 to 98% of the extractable insulin was undegraded. After 3.5 hours of incubation at 15 degrees, 82% of the bound insulin was dissociable and 60% of this was intact. However, after 60, 90, 120, and 180 minutes of incubation at 37 degrees C, only 42, 34, 24, and 37%, respectively, of the bound insulin was dissociable. The undissociated insulin in the 37 degrees C studies was considered to be intracellular. With increasing time of incubation at 37 degrees C, the extractability of cell bound insulin and the proportion of undegraded dissociable insulin were decreased. When 125I-insulin binding was 95% blocked by preincubating the erythrocytes with anti-insulin receptor antibody, 95% of the degradation of 125I-insulin was also blocked. These studies indicate that mature human erythrocytes degrade internalized insulin and this process is time, temperature, and insulin receptor dependent.     

Effects of different macronutrient consumption following a resistance-training session on fat and carbohydrate metabolism

The effect of consuming meals of different macronutrient content on substrate oxidation following resistance exercise was examined in 9 resistance-trained men (26.2 +/- 2.4 years). Subjects completed 3 resistance exercise bouts of 8 exercises and 1 warm-up set (50% of 10 repetition maximum [RM]), which were followed by 3 sets of 10 repetitions (72.7 +/- 1.9% 10RM), with 60 seconds of rest between sets. Forty-five minutes after exercise, subjects consumed meals of high fat (HF, 37% carbohydrate, 18% protein, and 45% fat), high carbohydrate (HC, 79% carbohydrate, 20% protein, and 1% fat), or water (CON). Fat and carbohydrate oxidation were determined at 15-minute periods after meal consumption for 165 minutes. Blood was collected at preexercise (pre), premeal (0 minutes), and 15, 30, 45, 60, 90, 120, 150, and 180 minutes postmeal and was analyzed for insulin, glucose, triacylglycerols, and glycerol. There were no significant differences among the meal conditions for fat and carbohydrate oxidation. Insulin and glucose concentrations were significantly higher (p < 0.05) following HC at 15, 30, 45, 60, and 90 minutes compared to HF and CON. Triacylglycerol concentrations were significantly higher (p < 0.05) following HF at 90, 120, 150, and 180 minutes compared to HC and CON. Fat and carbohydrate oxidation were not affected by differences in macronutrient meal consumption after an acute bout of resistance training. Different macronutrient consumption does influence insulin, glucose, and triacylglycerol concentrations after resistance exercise.     

Effect of a pre-exercise energy supplement on the acute hormonal response to resistance exercise

The effect of a pre-exercise energy sport drink on the acute hormonal response to resistance exercise was examined in eight experienced resistance trained men. Subjects were randomly provided either a placebo (P: maltodextrin) or the supplement (S: combination of branched chain amino acids, creatine, taurine, caffeine, and glucuronolactone). Subjects performed 6 sets of no more than 10 repetitions of the squat exercise at 75% of their 1 repetition maximum (1RM) with 2 minutes of rest between sets. Blood draws occurred at baseline pre-exercise, immediately post- (IP), 15 minutes post- (15P), and 30-minutes post (30P) exercise for measurement of serum growth hormone, total and free testosterone, cortisol, and insulin concentrations. Although significant differences were seen only at set 5, the total number of repetitions and training volume tended (p = 0.08) to be higher with S compared to P. Serum growth hormone and insulin concentrations were significantly higher at 15P and IP, respectively, in S compared to P. Results suggest that a pre-exercise energy S consumed 10 minutes before resistance exercise can enhance acute exercise performance by increasing the number of repetitions performed and the total volume of exercise. The enhanced exercise performance resulted in a significantly greater increase in both growth hormone and insulin concentrations, indicating an augmented anabolic hormone response to this pre-exercise S.     

Effect of acute high-intensity interval exercise on postexercise biventricular function in mild heart failure

We studied the acute effect of high-intensity interval exercise on biventricular function using cardiac magnetic resonance imaging in nine patients [age: 49 ± 16 yr; left ventricular (LV) ejection fraction (EF): 35.8 ± 7.2%] with nonischemic mild heart failure (HF). We hypothesized that a significant impairment in the immediate postexercise end-systolic volume (ESV) and end-diastolic volume (EDV) would contribute to a reduction in EF. We found that immediately following acute high-intensity interval exercise, LV ESV decreased by 6% and LV systolic annular velocity increased by 21% (both P < 0.05). Thirty minutes following exercise (+30 min), there was an absolute increase in LV EF of 2.4% (P < 0.05). Measures of preload, left atrial volume and LV EDV, were reduced immediately following exercise. Similar responses were observed for right ventricular volumes. Early filling velocity, filling rate, and diastolic annular velocity remained unchanged, while LV untwisting rate increased 24% immediately following exercise (P < 0.05) and remained 18% above baseline at +30 min (P < 0.05). The major novel findings of this investigation are 1) that acute high-intensity interval exercise decreases the immediate postexercise LV ESV and increases LV EF at +30 min in patients with mild HF, and this is associated with a reduction in LV afterload and maintenance of contractility, and 2) that despite a reduction in left atrial volume and LV EDV immediately postexercise, diastolic function is preserved and may be modulated by enhanced LV peak untwisting rate. Acute high-intensity interval exercise does not impair postexercise biventricular function in patients with nonischemic mild HF.     

Acute forced exercise increases Bdnf IV mRNA and reduces exploratory behavior in C57BL/6J mice

Acute exercise has been shown to improve memory in humans. Potential mechanisms include increased Bdnf expression, noradrenergic activity and modification of glutamate receptors. Because mice are commonly used to study exercise and brain plasticity, it is important to explore how acute exercise impacts behavior in this model. C57BL/6J mice were assigned to three groups: control, moderate‐intensity running, and high‐intensity running. Control mice were placed on a stationary treadmill for 30 minutes and moderate‐ and high‐intensity mice ran for 30 minutes at 12 and 15‐17 m/min, respectively. Mice were sacrificed immediately after running and the hippocampus removed. Total Bdnf, Bdnf exon IV, and glutamate receptor subunits were quantified with quantitative polymerase chain reaction. Total and phosphorylated GluR1 (Ser845 and Ser831) protein was quantified following immunoblotting. Utilizing the same protocol for control and high‐intensity running, object location memory was examined in a separate cohort of mice. Anxiety‐like behavior was assessed in the open field task (OFT) in a third cohort of mice that were separated into four groups: control‐saline, control‐DSP‐4, acute exercise‐saline, and acute exercise‐DSP‐4. DSP‐4 was used to lesion the central noradrenergic system. We observed higher Bdnf IV mRNA in high‐intensity runners compared to controls, but no effects of acute exercise on memory. In the OFT, runners traveled less distance and spent more time grooming than controls. DSP‐4 did not attenuate the effects of exercise. A single bout of exercise increases Bdnf IV mRNA in an intensity‐dependent manner; however, high‐intensity running reduces exploratory behavior in C57BL/6J mice.     

The effect of brief physical exercise on free radical scavenging enzyme systems in human red blood cells

Eleven sedentary male students were studied, using a bicycle ergometer, for 30 min at about 75% of their maximal oxygen uptake, to observe the effects of brief physical exercise on free radical scavenging system enzymes of the erythrocytes. Of the enzymes examined, only total glutathione reductase activity showed a significant elevation immediately after exercise and appeared to remain high at 30 min after exercise. The results suggest that acute physical exercise has some effects on red blood cell glutathione reductase activity, which is related primarily to maintenance of reduced glutathione.     

Effect of tetrahydrocurcumin on insulin receptor status in type 2 diabetic rats: studies on insulin binding to erythrocytes

Curcumin is the most active component of turmeric. It is believed that curcumin is a potent antioxidant and anti-inflammatory agent. Tetrahydrocurcumin (THC) is one of the major metabolites of curcumin, and exhibits many of the same physiological and pharmacological activities as curcumin and, in some systems, may exert greater antioxidant activity than curcumin. Using circulating erythrocytes as the cellular mode, the insulin-binding effect of THC and curcumin was investigated. Streptozotocin (STZ)-nicotinamide-induced male Wistar rats were used as the experimental models. THC (80 mg/kg body weight) was administered orally for 45 days. The effect of THC on blood glucose, plasma insulin and insulin binding to its receptor on the cell membrane of erythrocytes were studied. Mean specific binding of insulin was significantly lowered in diabetic rats with a decrease in plasma insulin. This was due to a significant decrease in mean insulin receptors. Erythrocytes from diabetic rats showed a decreased ability for insulin-receptor binding when compared with THC-treated diabetic rats. Scatchard analysis demonstrated that the decrease in insulin binding was accounted for by a decrease in insulin receptor sites per cell, with erythrocytes of diabetic rats having less insulin receptor sites per cell than THC-treated rats. High affinity (K d1), low affinity (K d2) and kinetic analyses revealed an increase in the average receptor affinity of erythrocytes from THC-treated rats compared with those of diabetic rats. These results suggest that acute alteration of the insulin receptor on the membranes of erythrocytes occurred in diabetic rats. Treatment with THC significantly improved specific insulin binding to the receptors, with receptor numbers and affinity binding reaching near-normal levels. Our study suggests the mechanism by which THC increases the number of total cellular insulin binding sites resulting in a significant increase in plasma insulin. The effect of THC is more prominent than that of curcumin.     

How muscle insulin sensitivity is regulated: testing of a hypothesis

Muscle contractions induce an increase in glucose transport. The acute effect of muscle contractions on glucose transport is independent of insulin and reverses rapidly after cessation of exercise. As the acute increase in glucose transport reverses, a marked increase in the sensitivity of muscle to insulin occurs. The mechanism for this phenomenon is unknown. We hypothesize that an increase in insulin sensitivity is a general phenomenon that occurs during reversal of an increase in cell surface GLUT4 induced by any stimulus, not just exercise. To test this hypothesis, epitrochlearis, rat soleus, and flexor digitorum brevis muscles were incubated for 30 min with a maximally effective insulin concentration (1.0 mU/ml). Muscles were allowed to recover for 3 h in the absence of insulin. Muscles were then exposed to 60 microU/ml insulin for 30 min followed by measurement of glucose transport. Preincubation with 1.0 mU/ml insulin resulted in an approximately 2-fold greater increase in glucose transport 3.5 h later in response to 60 microU/ml insulin than that which occurred in control muscles treated with 60 microU/ml insulin. Pretreatment of muscles with combined maximal insulin and exercise stimuli greatly amplified the increase in insulin sensitivity. The increases in glucose transport were paralleled by increases in cell surface GLUT4. We conclude that stimulation of glucose transport by any agent is followed by an increase in sensitivity of glucose transport to activation that is mediated by translocation of more GLUT4 to the cell surface.     

Cationic concentrations and transmembrane fluxes in erythrocytes of humans during exercise

The effect of exercise on the intraerythrocyte cationic concentrations and transmembrane fluxes such as the Na+-K+-adenosinetriphosphatase (ATPase) pump, the Na+-K+ cotransport, and the Na+-Li+ countertransport system was studied in 11 normal male volunteers. All subjects performed an uninterrupted incremental exercise test on a bicycle ergometer, starting at an initial work load of 20% of the subjects' maximal exercise capacity, as determined in a pretest. The work rate was increased with an additional 20% each 6 min up to a final work load of 80%. Blood samples were taken at rest, at 60 and 80% of maximal exercise capacity, and 1, 2, 3, 4, 5, and 30 min after cessation of exercise. At moderate exercise (60% of maximal exercise capacity) the intraerythrocyte potassium concentration was not changed, but at severe exercise (80% of maximal exercise capacity) it was decreased. After exercise the intraerythrocyte potassium concentration returned to base line within 2 min. Exercise did not affect the intraerythrocyte concentrations of sodium and magnesium. The activity of the Na+-K+-ATPase pump and the Na+-K+ cotransport in the erythrocytes during and after exercise was no different from the resting level. The activity of the Na+-Li+ countertransport system on the contrary tended to decrease during exercise. It is concluded that exercise is accompanied by a leakage of potassium out of the erythrocytes without major alterations in the active red cell cationic fluxes.     

Exercise increases serum Hsp72 in humans

Recent evidence suggests that heat shock proteins (Hsps) may have an important systemic role as a signal to activate the immune system. Since acute exercise is known to induce Hsp72 (the inducible form of the 70-kDa family of Hsp) in a variety of tissues including contracting skeletal muscle, we hypothesized that such exercise would result in the release of Hsp72 from stressed cells into the blood. Six humans (5 males, 1 female) ran on a treadmill for 60 minutes at a workload corresponding to 70% of their peak oxygen consumption. Blood was sampled from a forearm vein at rest (R), 30 minutes during exercise, immediately postexercise (60 minutes), and 2, 8, and 24 hours after exercise. These samples were analyzed for serum Hsp72 protein. In addition, plasma creatine kinase (CK) was measured at these time points as a crude marker of muscle damage. With the exception of the sample collected at 30 minutes, muscle biopsies (n = 5 males) were also obtained from the vastus lateralis at the time of blood sampling and analyzed for Hsp72 gene and protein expression. Serum Hsp72 protein increased from rest, both during and after exercise (0.13 0.10 vs 0.87+/-0.24 and 1.02+/-0.41 ng/mL at rest, 30 and 60 minutes, respectively, P < 0.05, mean SE). In addition, plasma CK was elevated (P < 0.05) 8 hours postexercise. Skeletal muscle Hsp72 mRNA expression increased 6.5-fold (P < 0.05) from rest 2 hours postexercise, and although there was a tendency for Hsp72 protein expression to be elevated 2 and 8 hours following exercise compared with rest, results were not statistically significant. The increase in serum Hsp72 preceded any increase in Hsp72 gene or protein expression in contracting muscle, suggesting that Hsp72 was released from other tissues or organs. This study is the first to demonstrate that acute exercise can increase Hsp72 in the peripheral circulation, suggesting that during stress these proteins may indeed have a systemic role.     

长程运动诱发试验的两种方法在诊断低钾性周期性麻痹中的比较

摘要 目的：探究长程运动诱发试验（exercise test, ET）的两种方法在诊断低钾性周期性麻痹患者的价值比较。方法：选择2018年2月~2020年3月我院住院和门诊的72例低钾性周期性麻痹患者,根据ET检测的方法分为观察组和对照组,对比两组ET检测在运动后即刻、运动后的10、20、30、40、50、60 min的双侧尺神经进行复合肌肉动作电位（compound muscle action potential,cMAP）波幅和ET阳性率;以临床诊断结果为金指标,分析两组ET诊断价值。结果：两组的ET检测的阳性发生率对比无显著性差异（P>0.05）。两组波幅降低百分比在运动后即刻以及运动后的10、20、30、40、50、60 min对比无差异(P>0.05),在20 min后观察组波幅降低百分比趋势稍比对照组慢。临床诊断结果阳性68例,阳性率为94.44 %。观察组ET检测的特异性为50.0 %,灵敏度为88.23 %,对照组ET检测的特异性为25.0 %,灵敏度为80.88 %,观察组的特异性和灵敏度均优于对照组。结论：长程运动诱发试验是低钾型周期性麻痹诊断中重要的辅助诊断方法之一,且运动持续50 s,休息10 s,只做1个循环的方法,简单、快捷,可供临床诊断时优先选择。