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1.
Jeukendrup Asker E.; Borghouts Lars B.; Saris Wim H.M.; Wagenmakers Anton J.M. 《Journal of applied physiology》1996,81(5):1952-1957
Jeukendrup, Asker E., Lars B. Borghouts, Wim H. M. Saris,and Anton J. M. Wagenmakers. Reduced oxidation rates of ingested glucose during prolonged exercise with low endogenous CHO availability. J. Appl. Physiol. 81(5):1952-1957, 1996.This study investigated the effect of endogenouscarbohydrate (CHO) availability on oxidation rates of ingested glucoseduring moderate-intensity exercise. Seven well-trained cyclistsperformed two trials of 120 min of cycling exercise in random order at57% maximal O2 consumption. Preexercise glycogen concentrations were manipulated byglycogen-lowering exercise in combination with CHO restriction[low-glycogen (LG) trial] or CHO loading[moderate-to-high-glycogen (HG) trial]. In the LG and HGtrials, subjects ingested 4 ml/kg body wt of an 8% corn-derivedglucose solution of high natural13C abundance at the start,followed by boluses of 2 ml/kg every 15 min. The third trial, in whichpotato-derived glucose was ingested, served as a control test forbackground correction. Exogenous glucose oxidation rates werecalculated from the 13C enrichmentof the ingested glucose and of the breathCO2. Total CHO oxidation was lowerin the LG trial than in the HG trial during 60-120 min of exercise[84 ± 7 (SE) vs. 116 ± 8 g;P < 0.05]. Exogenous CHOoxidation in this period was 28% lower in the LG trial compared withthe HG trial. Maximal exogenous oxidation rates were also lower(P < 0.05) in the LG trial (0.64 ± 0.05 g/min) than in the HG trial (0.88 ± 0.04 g/min). Thisdecreased utilization of exogenous glucose was accompanied by increased plasma free fatty acid levels (2-3 times higher) and lower insulin concentrations. It is concluded that glycogen-lowering exercise, performed the evening before an exercise bout, in combination with CHOrestriction leads to a reduction of the oxidation rate of ingestedglucose during moderate-intensity exercise. 相似文献
2.
Burelle Y.; Peronnet F.; Charpentier S.; Lavoie C.; Hillaire-Marcel C.; Massicotte D. 《Journal of applied physiology》1999,86(1):52-60
The purpose of this study was to compare the oxidation of[13C]glucose (100 g)ingested at rest or during exercise in six trained (TS) and sixsedentary (SS) male subjects. The oxidation of plasma glucose was alsocomputed from the volume of13CO2and13C/12Cin plasma glucose to compute the oxidation rate of glucose released from the liver and from glycogen stores in periphery (mainly muscle glycogen stores during exercise). At rest, oxidative disposal of bothexogenous (8.3 ± 0.3 vs. 6.6 ± 0.8 g/h) and liver glucose (4.4 ± 0.5 vs. 2.6 ± 0.4 g/h) was higher in TS than in SS.This could contribute to the better glucose tolerance observed at rest in TS. During exercise, for the same absolute workload [140 ± 5 W: TS = 47 ± 2.5; SS = 68 ± 3 %maximal oxygen uptake(O2 max)], [13C]glucose oxidationwas higher in TS than in SS (39.0 ± 2.6 vs. 33.6 ± 1.2 g/h),whereas both liver glucose (16.8 ± 2.4 vs. 24.0 ± 1.8 g/h) and muscle glycogen oxidation (36.0 ± 3.0 vs. 51.0 ± 5.4 g/h) were lower. For the same relative workload (68 ± 3% O2 max:TS = 3.13 ± 0.96; SS = 2.34 ± 0.60 lO2/min), exogenous glucose(44.4 ± 1.8 vs. 33.6 ± 1.2 g/h) and muscle glycogen oxidation (73.8 ± 7.2 vs. 51.0 ± 5.4 g/h) were higher in TS. However,despite a higher energy expenditure in TS, liver glucose oxidation was similar in both groups (22.2 ± 3.0 vs. 24.0 ± 1.8 g/h). Thus exogenous glucose oxidation was selectively favored in TSduring exercise, reducing both liver glucose and muscle glycogen oxidation. 相似文献
3.
Peronnet F.; Burelle Y.; Massicotte D.; Lavoie C.; Hillaire-Marcel C. 《Journal of applied physiology》1997,82(2):440-446
Péronnet, F., Y. Burelle, D. Massicotte, C. Lavoie,and C. Hillaire-Marcel. Respective oxidation of13C-labeled lactate and glucoseingested simultaneously during exercise. J. Appl.Physiol. 82(2): 440-446, 1997.The purpose ofthis experiment was to measure, by using13C labeling, the oxidation rateof exogenous lactate (25 g, as Na+,K+,Ca2+, andMg2+ salts) and glucose (75 g)ingested simultaneously (in 1,000 ml of water) during prolongedexercise (120 min, 65 ± 3% maximum oxygen uptake in 6 male subjects). The percentage of exogenous glucose and lactateoxidized were similar (48 ± 3 vs. 45 ± 5%, respectively). However, because of the small amount of oral lactate that could be tolerated without gastrointestinal discomfort, the amountof exogenous lactate oxidized was much smaller than that of exogenousglucose (11.1 ± 0.5 vs. 36.3 ± 1.3 g, respectively) andcontributed to only 2.6 ± 0.4% of the energy yield(vs. 8.4 ± 1.9% for exogenous glucose). The cumulative amount ofexogenous glucose and lactate oxidized was similar to that observedwhen 100 g of[13C]glucose wereingested (47.3 ± 1.8 vs. 50.9 ± 1.2 g, respectively). When[13C]glucose wasingested, changes in the plasma glucose13C/12Cratio indicated that between 39 and 61% of plasma glucose derived fromexogenous glucose. On the other hand, the plasma glucose 13C/12Cratio remained unchanged when[13C]lactate wasingested, suggesting no prior conversion into glucose before oxidation. 相似文献
4.
Exogenous glucose oxidation during exercise in endurance-trained and untrained subjects 总被引:4,自引:0,他引:4
Jeukendrup A. E.; Mensink M.; Saris W. H.M.; Wagenmakers A. J.M. 《Journal of applied physiology》1997,82(3):835-840
Jeukendrup, A. E., M. Mensink, W. H. M. Saris, and A. J. M. Wagenmakers. Exogenous glucose oxidation during exercise in endurance-trained and untrained subjects. J. Appl.Physiol. 82(3): 835-840, 1997.To investigate theeffect of training status on the fuel mixture used during exercise withglucose ingestion, seven endurance-trained cyclists (Tr; maximumO2 uptake 67 ± 2.3 ml · kg1 · min1)and eight untrained subjects (UTr; 48 ± 2 ml · kg1 · min1)were studied during 120 min of exercise at ~60% maximumO2 uptake. At the onset of exercise, 8 ml · kg1 · min1of an 8% naturally enriched[13C]glucose solutionwas ingested and 2 ml/kg every 15 min thereafter. Energy expenditurewas higher in Tr subjects compared with UTr subjects (3,404 vs. 2,630 kJ; P < 0.01). During the secondhour, fat oxidation was higher in Tr subjects (37 ± 2 g) comparedwith UTr subjects (23 ± 1 g), whereas carbohydrateoxidation was similar (116 ± 8 g in Tr subjects vs. 114 ± 4 g in UTr subjects). No differences were observed in exogenousglucose oxidation (50 ± 2 g in Tr subjects and 45 ± 3 g in UTr subjects, respectively). Peak exogenous glucose oxidationrates were similar in the two groups (0.95 ± 0.07 g/min in Trsubjects and 0.96 ± 0.03 g/min in UTr subjects). It is concluded that the higher energy expenditure in Tr subjects during exercise atthe same relative exercise intensity is entirely met by a higher rateof fat oxidation without changes in the rates of exogenous andendogenous carbohydrates. 相似文献
5.
Duhamel TA Green HJ Perco JG Ouyang J 《American journal of physiology. Cell physiology》2006,291(4):C607-C617
We employed a glycogen-depleting session of exercise followed by a low-carbohydrate (CHO) diet to investigate modifications that occur in muscle sarcoplasmic reticulum (SR) Ca2+-cycling properties compared with low-CHO diet alone. SR properties were assessed in nine untrained males [peak aerobic power (O2 peak) = 43.6 ± 2.6 (SE) ml·kg1·min1] during prolonged cycle exercise to fatigue performed at 58% O2 peak after 4 days of low-CHO diet (Lo CHO) and after glycogen-depleting exercise plus 4 days of low-CHO (Ex+Lo CHO). Compared with Lo CHO, Ex+Lo CHO resulted in 12% lower (P < 0.05) resting maximal Ca2+-ATPase activity (Vmax = 174 ± 12 vs. 153 ± 10 µmol·g protein1·min1) and smaller reduction in Vmax induced during exercise. A similar effect was observed for Ca2+ uptake. The Hill coefficient, defined as slope of the relationship between cytosolic free Ca2+ concentration and Ca2+-ATPase activity, was higher (P < 0.05) at rest (2.07 ± 0.15 vs. 1.90 ± 0.10) with Ex+Lo CHO, an effect that persisted throughout the exercise. The coupling ratio, defined as the ratio of Ca2+ uptake to Vmax, was 2330% elevated (P < 0.05) at rest and during the first 60 min of exercise with Ex+Lo CHO. The 27 and 34% reductions (P < 0.05) in phase 1 and phase 2 Ca2+ release, respectively, observed during exercise with Lo CHO were not altered by Ex+Lo CHO. These results indicate that when prolonged exercise precedes a short-term Lo CHO diet, Ca2+ sequestration properties and efficiency are improved compared with those during Lo CHO alone. calcium cycling; vastus lateralis; contractile activity; glycogen; phosphorylation potential 相似文献
6.
Utilization of glycogen but not plasma glucose is reduced in individuals with NIDDM during mild-intensity exercise 总被引:2,自引:0,他引:2
Colberg Sheri R.; Hagberg James M.; McCole Steve D.; Zmuda Joseph M.; Thompson Paul D.; Kelley David E. 《Journal of applied physiology》1996,81(5):2027-2033
Colberg, Sheri R., James M. Hagberg, Steve D. McCole, JosephM. Zmuda, Paul D. Thompson, and David E. Kelley. Utilization ofglycogen but not plasma glucose is reduced in individuals with NIDDMduring mild-intensity exercise. J. Appl.Physiol. 81(4): 2027-2033, 1996.To test thehypothesis that substrate utilization during mild-intensity exercisediffers in non-insulin-dependent diabetes mellitus (NIDDM) comparedwith nondiabetic subjects, seven lean healthy subjects (L), seven obesehealthy subjects (O), and seven individuals with NIDDM were studiedduring 40 min of mild-intensity cycling (40% of peakO2 uptake). Systemic utilization of plasma glucose (Glc Rd) was determined by using isotope dilution methods. Gas exchange was measured to determine rates of carbohydrate (CHO) and lipid oxidation. During exercise, when CHOoxidation was greater than Glc Rd, the net oxidation of glycogen wascalculated as the difference: CHO oxidation Glc Rd. Duringmild-intensity cycling, the respiratory exchange ratio was similaracross groups (0.87 ± 0.02, 0.85 ± 0.02, and 0.86 ± 0.01 inL, O, and NIDDM subjects, respectively), and CHO oxidation accountedfor one-half of total energy expenditure during exercise. Glc Rdincreased during exercise and was greatest in subjects with NIDDM (3.0 ± 0.2, 2.9 ± 0.2, and 4.5 ± 0.4 ml · kg1 · min1in L, O, and NIDDM subjects, respectively,P < 0.05), yet Glc Rd wasless than CHO oxidation during exercise, indicating net oxidation ofglycogen. Glycogen oxidation was greater in L and O than in NIDDMsubjects (3.4 ± 1.0, 2.5 ± 0.9, and 1.7 ± 0.8 ml · kg1 · min1;P < 0.05). In summary, duringmild-intensity exercise, NIDDM subjects have an increased Glc Rd and adecreased oxidation of muscle glycogen. 相似文献
7.
Training-induced alterations of carbohydrate metabolism in women: women respond differently from men 总被引:4,自引:0,他引:4
Friedlander Anne L.; Casazza Gretchen A.; Horning Michael A.; Huie Melvin J.; Piacentini Maria Francesca; Trimmer Jeffrey K.; Brooks George A. 《Journal of applied physiology》1998,85(3):1175-1186
We examined the hypothesis that glucose flux wasdirectly related to relative exercise intensity both beforeand after a 12-wk cycle ergometer training program [5days/wk, 1-h duration, 75% peakO2 consumption(O2 peak)] inhealthy female subjects (n = 17; age23.8 ± 2.0 yr). Two pretraining trials (45 and 65% of O2 peak)and two posttraining trials [same absolute workload (65% of oldO2 peak)and same relative workload (65% of new O2 peak)] wereperformed on nine subjects by using a primed-continuous infusion of[1-13C]- and[6,6-2H]glucose.Eight additional subjects were studied by using[6,6-2H]glucose.Subjects were studied postabsorption for 90 min of rest and 1 h ofcycling exercise. After training, subjects increased O2 peak by 25.2 ± 2.4%. Pretraining, the intensity effect on glucose kinetics wasevident between 45 and 65% ofO2 peak with rates ofappearance (Ra: 4.52 ± 0.25 vs. 5.53 ± 0.33 mg · kg1 · min1),disappearance (Rd: 4.46 ± 0.25 vs. 5.54 ± 0.33 mg · kg1 · min1),and oxidation (Rox: 2.45 ± 0.16 vs. 4.35 ± 0.26 mg · kg1 · min1)of glucose being significantly greater(P 0.05) in the 65% thanin the 45% trial. Training reducedRa (4.7 ± 0.30 mg · kg1 · min1),Rd (4.69 ± 0.20 mg · kg1 · min1),and Rox (3.54 ± 0.50 mg · kg1 · min1)at the same absolute workload (P 0.05). When subjects were tested at the same relative workload,Ra,Rd, andRox were not significantlydifferent after training. However, at both workloads after training,there was a significant decrease in total carbohydrate oxidation asdetermined by the respiratory exchange ratio. These results show thefollowing in young women: 1)glucose use is directly related to exercise intensity;2) training decreasesglucose flux for a given power output;3) when expressed asrelative exercise intensity, training does not affect the magnitude ofblood glucose flux during exercise; but4) training does reduce totalcarbohydrate oxidation. 相似文献
8.
Training-induced alterations of glucose flux in men 总被引:5,自引:0,他引:5
Friedlander Anne L.; Casazza Gretchen A.; Horning Michael A.; Huie Melvin J.; Brooks George A. 《Journal of applied physiology》1997,82(4):1360-1369
Friedlander, Anne L., Gretchen A. Casazza, Michael A. Horning, Melvin J. Huie, and George A. Brooks. Training-induced alterations of glucose flux in men. J. Appl.Physiol. 82(4): 1360-1369, 1997.We examined thehypothesis that glucose flux was directly related to relative exerciseintensity both before and after a 10-wk cycle ergometer trainingprogram in 19 healthy male subjects. Two pretraining trials [45and 65% of peak O2 consumption(O2 peak)] andtwo posttraining trials (same absolute and relative intensities as 65%pretraining) were performed for 90 min of rest and 1 h of cyclingexercise. After training, subjects increasedO2 peak by9.4 ± 1.4%. Pretraining, the intensity effect on glucose kinetics was evident with rates of appearance(Ra; 5.84 ± 0.23 vs. 4.73 ± 0.19 mg · kg1 · min1),disappearance (Rd; 5.78 ± 0.19 vs. 4.73 ± 0.19 mg · kg1 · min1),oxidation (Rox; 5.36 ± 0.15 vs. 3.41 ± 0.23 mg · kg1 · min1),and metabolic clearance (7.03 ± 0.56 vs. 5.20 ± 0.28 ml · kg1 · min1)of glucose being significantly greater(P 0.05) in the 65% than the 45%O2 peak trial. WhenRd was expressed as a percentage of total energy expended per minute(Rd E), there was nodifference between the 45 and 65% intensities. Training did reduceRa (4.63 ± 0.25),Rd (4.65 ± 0.24),Rox (3.77 ± 0.43), andRd E (15.30 ± 0.40 to12.85 ± 0.81) when subjects were tested at the same absolute workload (P 0.05). However, whenthey were tested at the same relative workload,Ra,Rd, andRd E were not different,although Rox was lowerposttraining (5.36 ± 0.15 vs. 4.41 ± 0.42, P 0.05). These results show1) glucose use is directly relatedto exercise intensity; 2) trainingdecreases glucose flux for a given power output;3) when expressed as relativeexercise intensity, training does not affect the magnitude of bloodglucose use during exercise; 4)training alters the pathways of glucose disposal. 相似文献
9.
This investigation examined the effects ofNaHCO3 loading on lactateconcentration ([La]), acid-base balance, and performance for a 603.5-m sprint task. Ten greyhounds completed aNaHCO3 (300 mg/kg body weight) andcontrol trial in a crossover design. Results are expressed as means ± SE. Presprint differences (P < 0.05) were found for NaHCO3 vs.control, respectively, for blood pH (7.47 ± 0.01 vs. 7.42 ± 0.01), HCO3 (28.4 ± 0.4 vs. 23.5 ± 0.3 meq/l), and base excess (5.0 ± 0.3 vs. 0.2 ± 0.3 meq/l). Peak blood [La] increased(P < 0.05) inNaHCO3 vs. control (20.4 ± 1.6 vs. 16.9 ± 1.3 mM, respectively). Relative to control,NaHCO3 produced a greater(P < 0.05) reduction in blood baseexcess (18.5 ± 1.4 vs. 14.1 ± 0.8 meq/l) andHCO3 (17.4 ± 1.2 vs.12.8 ± 0.7 meq/l) from presprint to postexercise. Postexercise peak muscle H+concentration ([H+])was higher (P < 0.05) inNaHCO3 vs. control (158.8 ± 8.8 vs. 137.0 ± 5.3 nM, respectively). Muscle[H+] recoveryhalf-time (7.2 ± 1.6 vs. 11.3 ± 1.6 min) and time to predosevalues (22.2 ± 2.4 vs. 32.9 ± 4.0 min) were reduced(P < 0.05) inNaHCO3 vs. control, respectively.No differences were found in blood[H+] or blood[La] recovery curves or performance times.NaHCO3 increased postexerciseblood [La] but did not reduce the muscle or blood acid-basedisturbance associated with a 603.5-m sprint or significantly affectperformance. 相似文献
10.
Wei S Rothstein EC Fliegel L Dell'Italia LJ Lucchesi PA 《American journal of physiology. Cell physiology》2001,281(5):C1542-C1550
Bursts in reactive oxygen species productionare important mediators of contractile dysfunction duringischemia-reperfusion injury. Cellular mechanisms that mediatereactive oxygen species-induced changes in cardiac myocyte functionhave not been fully characterized. In the present study,H2O2 (50 µM) decreased contractility of adultrat ventricular myocytes. H2O2 caused aconcentration- and time-dependent activation of extracellularsignal-regulated kinases 1 and 2 (ERK1/2), p38, and c-JunNH2-terminal kinase (JNK) mitogen-activated protein (MAP)kinases in adult rat ventricular myocytes. H2O2 (50 µM) caused transient activation of ERK1/2 and p38 MAP kinase thatwas detected as early as 5 min, was maximal at 20 min (9.6 ± 1.2- and 9.0 ± 1.6-fold, respectively, vs. control), and returned tobaseline at 60 min. JNK activation occurred more slowly (1.6 ± 0.2-fold vs. control at 60 min) but was sustained at 3.5 h. Theprotein kinase C inhibitor chelerythrine completely blocked JNKactivation and reduced ERK1/2 and p38 activation. The tyrosine kinaseinhibitors genistein and PP-2 blocked JNK, but not ERK1/2 and p38,activation. H2O2-inducedNa+/H+ exchanger phosphorylation was blocked bythe MAP kinase kinase inhibitor U-0126 (5 µM). These resultsdemonstrate that H2O2-induced activation of MAPkinases may contribute to cardiac myocyte dysfunction duringischemia-reperfusion. 相似文献
11.
Mitchell J. B.; Pizza F. X.; Paquet A.; Davis B. J.; Forrest M. B.; Braun W. A. 《Journal of applied physiology》1998,84(6):1917-1925
To determine the effect of carbohydrate (CHO)status on immune responses after long-duration exercise, on twooccasions, 10 men completed a glycogen-depleting bout of cycleergometry followed by 48 h of either a high-CHO diet (HiCHO; 8.0 gCHO/kg) or a low-CHO diet (LoCHO; 0.5 g CHO/kg). After the 48 h,subjects completed a 60-min ride at 75% maximalO2 uptake (EX). Blood samples were taken predepletion, pre-EX, post-EX, and 2 and 24 h post-EX and wereassayed for leukocyte number and function, glucose, glutamine, andcortisol. The glucose responses were significantly higher in the HiCHO(4.62 ± 0.26 mM) vs. the LoCHO (3.19 ± 0.15 mM) condition post-EX, and glutamine was significantly higher in the HiCHO(0.472 ± 0.036 mM) vs. the LoCHO (0.410 ± 0.025 mM)condition throughout. Cortisol levels were significantly greater in theLoCHO (587 ± 50 nM) vs. the HiCHO (515 ± 62 nM) conditionthroughout the trial. Lymphocyte proliferation (phytohemagglutinin) wassignificantly depressed after exercise. However, there was nodifference between conditions, and the depression was not correlatedwith elevations in cortisol. Circulating numbers of leukocytes,neutrophils, lymphocytes, and lymphocyte subsets were significantlygreater in the LoCHO vs. the HiCHO condition at the post-EX and 2 hpost-EX time points. These data indicate that the exercise and dietmanipulation altered the number of circulating leukocytes but did notaffect the decrease in lymphocyte proliferation that occurred afterexercise. 相似文献
12.
Microdialysis ethanol removal reflects probe recovery rather than local blood flow in skeletal muscle 总被引:2,自引:0,他引:2
Radegran G.; Pilegaard H.; Nielsen J. J.; Bangsbo J. 《Journal of applied physiology》1998,85(2):751-757
The present study compared the microdialysis ethanoloutflow-inflow technique for estimating blood flow (BF) in skeletalmuscle of humans with measurements by Doppler ultrasound of femoralartery inflow to the limb(BFFA). The microdialysis probeswere inserted in the vastus lateralis muscle and perfused with a Ringeracetate solution containing ethanol,[2-3H]adenosine (Ado),andD-[14C(U)]glucose.BFFA at rest increased from0.16 ± 0.02 to 1.80 ± 0.26 and 4.86 ± 0.53 l/minwith femoral artery infusion of Ado (AdoFA,i) at 125 and 1,000 µg · min1 · l1thigh volume (low dose and high dose, respectively;P < 0.05) and to 3.79 ± 0.37 and6.13 ± 0.65 l/min during one-legged, dynamic, thigh muscle exercisewithout and with high AdoFA,i,respectively (P < 0.05). The ethanoloutflow-to-inflow ratio (38.3 ± 2.3%) and the probe recoveries(PR) for [2-3H]Ado(35.4 ± 1.6%) and forD-[14C(U)]glucose(15.9 ± 1.1%) did not change withAdoFA,i at rest (P = not significant). During exercisewithout and with AdoFA,i, theethanol outflow-to-inflow ratio decreased(P < 0.05) to a similar level of17.5 ± 3.4 and 20.6 ± 3.2%, respectively(P = not significant), respectively,while the PR increased (P < 0.05) toa similar level (P = not significant)of 55.8 ± 2.8 and 61.2 ± 2.5% for[2-3H]Ado and to 42.8 ± 3.9 and 45.2 ± 5.1% forD-[14C(U)]glucose.Whereas the ethanol outflow-to-inflow ratio and PR correlated inverselyand positively, respectively, to the changes in BF during muscularcontractions, neither of the ratio nor PR correlated tothe AdoFA,i-induced BF increase.Thus the ethanol outflow-to-inflow ratio does not represent skeletalmuscle BF but rather contraction-induced changes in molecular transport in the interstitium or over the microdialysis membrane. 相似文献
13.
Whitley Helena A.; Humphreys S. M.; Campbell I. T.; Keegan M. A.; Jayanetti T. D.; Sperry D. A.; MacLaren D. P.; Reilly T.; Frayn K. N. 《Journal of applied physiology》1998,85(2):418-424
We studied the effects of preexercise mealcomposition on metabolic and performance-related variables duringendurance exercise. Eight well-trained cyclists (maximal oxygen uptake65.0 to 83.5 ml · kg1 · min1)were studied on three occasions after an overnight fast. They weregiven isoenergetic meals containing carbohydrate (CHO), protein (P),and fat (F) in the following amounts (g/70 kg body wt):high-carbohydrate meal, 215 CHO, 26 P, 3 F; high-fat meal, 50 CHO, 14 P, 80 F. On the third occasion subjects were studied after an overnightfast. Four hours after consumption of the meal, subjects startedexercise for 90 min at 70% of their maximal oxygen uptake, followed by a 10-km time trial. The high-carbohydrate meal compared with the high-fat meal resulted in significant decreases(P < 0.05) in blood glucose, plasmanonesterified fatty acids, plasma glycerol, plasmachylomicron-triacylglycerol, and plasma 3-hydroxybutyrate concentrations during exercise. This was accompanied by anincrease in plasma insulin (P < 0.01 vs. no meal), plasma epinephrine, and plasma growth hormoneconcentrations (each P < 0.05 vs.either of the other conditions) during exercise. Despite these large differences in substrate and hormone concentrations in plasma, substrate oxidation during the 90-min exercise period was similar inthe three trials, and there were no differences in performance on thetime trial. These results suggest that, although the availability offatty acids and other substrates in plasma can be markedly altered bydietary means, the pattern of substrate oxidation during enduranceexercise is remarkably resistant to alteration. 相似文献
14.
Turcotte Lorraine P.; Petry Carsten; Kiens Bente; Richter Erik A. 《Journal of applied physiology》1998,84(5):1788-1794
To evaluate the effects of contractions on thekinetics of uptake and oxidation of palmitate in a physiological musclepreparation, rat hindquarters were perfused with glucose (6 mmol/l),albumin-bound [1-14C]palmitate, andvarying amounts of albumin-bound palmitate (200-2,200 µmol/l) atrest and during muscle contractions. When plotted against the unboundpalmitate concentration, palmitate uptake and oxidation displayedsimple Michaelis-Menten kinetics with estimated maximal velocity(Vmax)and Michaelis-Menten constant(Km) values of42.8 ± 3.8 (SE)nmol · min1 · g1and 13.4 ± 3.4 nmol/l for palmitate uptake and 3.8 ± 0.4 nmol · min1 · g1and 8.1 ± 2.9 nmol/l for palmitate oxidation, respectively, at rest.Whereas muscle contractions increased theVmaxfor both palmitate uptake and oxidation to 91.6 ± 10.1 and 16.5 ± 2.3 nmol · min1 · g1,respectively, theKm remainedunchanged.Vmaxand Km estimates obtained from Hanes-Woolf plots (substrate concentration/velocity vs.substrate concentration) were not significantly different. In theresting perfused hindquarter, an increase in palmitate delivery from31.9 ± 0.9 to 48.7 ± 1.2 µmol · g1 · h1by increasing perfusate flow was associated with a decrease in thefractional uptake of palmitate so that the rates of uptake andoxidation of palmitate remained unchanged. It is concluded that therates of uptake and oxidation of long-chain fatty acids (LCFA) saturatewith an increase in the concentration of unbound LCFA in perfusedskeletal muscle and that muscle contractions, but not an increase inplasma flow, increase theVmaxfor LCFA uptake and oxidation. The data are consistent with the notion that uptake of LCFA in muscle may be mediated in part by a transport system. 相似文献
15.
Schepkin, V. D., I. O. Choy, and T. F. Budinger. Sodiumalterations in isolated rat heart during cardioplegic arrest. J. Appl. Physiol. 81(6):2696-2702, 1996.Triple-quantum-filtered (TQF) Na nuclearmagnetic resonance (NMR) without chemical shift reagent is used toinvestigate Na derangement in isolated crystalloid perfused rat heartsduring St. Thomas cardioplegic (CP) arrest. Theextracellular Na contribution to the NMR TQF signal of a rat heart isfound to be 73 ± 5%, as determined by wash-out experiments atdifferent moments of ischemia and reperfusion. With the use of thiscontribution factor, the estimated intracellular Na([Na+]i)TQF signal is 222 ± 13% of preischemic level after 40 min of CParrest and 30 min of reperfusion, and the heart rate pressure productrecovery is 71 ± 8%. These parameters aresignificantly better than for stop-flow ischemia: 340 ± 20% and 6 ± 3%, respectively. At 37°C, the initial delay of 15 min in[Na+]igrowth occurs during CP arrest along with reduced growth later (~4.0%/min) in comparison with stop-flow ischemia (~6.7%/min). The hypothermia (21°C, 40 min) for the stop-flow ischemia and CPdramatically decreases the[Na+]igain with the highest heart recovery for CP (~100%). These studiesconfirm the enhanced sensitivity of TQF NMR to[Na+]iand demonstrate the potential of NMR without chemical shift reagent tomonitor[Na+]iderangements. 相似文献
16.
Gisolfi C. V.; Summers R. W.; Lambert G. P.; Xia T. 《Journal of applied physiology》1998,85(5):1941-1948
To determine howosmolality of an orally ingested fluid-replacement beverage would alterintestinal fluid absorption from the duodenum and/or jejunumduring 85 min of cycle exercise (63.3 ± 0.9% peakO2 uptake) in a cool environment(22°C), seven subjects (5 men, 2 women, peakO2 uptake = 54.5 ± 3.8 ml · kg1 · min1) participated infour experiments separated by 1 wk in which they ingested a waterplacebo (WP) or one of three 6% carbohydrate (CHO) beveragesformulated to give mean osmolalities of 197, 295, or 414 mosmol/kgH2O. CHO solutions alsocontained 17-18 meq Na+ and3.2 meq K+. Nasogastric andmultilumen tubes were fluoroscopically positioned in the gastric antrumand duodenojejunum, respectively. Subjects ingested a total of 23 ml/kgbody mass of the test solution, 20% (370 ± 9 ml) of this volume 5 min before exercise and 10% (185 ± 4 ml) every 10 min thereafter.By using the rate of gastric emptying as the rate of intestinalperfusion (G. P. Lambert, R. T. Chang, D. Joensen, X. Shi, R. W. Summers, H. P. Schedl, and C. V. Gisolfi. Int. J. Sports Med. 17: 48-55, 1996), intestinal absorption was determined by segmental perfusion from the duodenum (0-25 cm) and jejunum (25-50 cm). There were no differences(P > 0.05) in gastric emptying (mean18.1 ± 1.3 ml/min) or total fluid absorption (802 ± 109, 650 ± 52, 674 ± 62, and 633 ± 74 ml · 50 cm1 · h1for WP, hypo-, iso-, and hypertonic solutions, respectively) amongbeverages; but WP was absorbed faster(P < 0.05) from the duodenum than inthe jejunum. Of the total volume of fluid ingested, 82 ± 14, 74 ± 6, 76 ± 5, and 68 ± 7% were absorbed forWP, hypo-, iso-, and hypertonic beverages, respectively. There were nodifferences in urine production or percent change in plasma volumeamong solutions. We conclude that total fluid absorption of 6%CHO-electrolyte beverages from the duodenojejunum during exercise,within the osmotic range studied, is not different from WP. 相似文献
17.
Ryschon T. W.; Jarvis J. C.; Salmons S.; Balaban R. S. 《Journal of applied physiology》1997,82(3):1024
Ryschon, T. W., J. C. Jarvis, S. Salmons, and R. S. Balaban.High-energy phosphates and tension production in rabbit tibialisanterior/extensor digitorum longus muscles. J. Appl. Physiol. 82(3): 1024-1029, 1997.The effects ofrepetitive muscle contraction on energy state and tension productionwere studied in rabbit tibialis anterior/extensor digitorum longusmuscles that had been subjected to 90 days of continuous indirectelectrical stimulation at 10 Hz. Anesthetized chronically stimulatedand control rabbits were challenged with 15 min of stimulation at 4 and15 tetani/min.Pi-to-phosphocreatine (PCr) ratio(Pi/PCr) was measured in vivo before, during, andafter acute stimulation by31P-magnetic resonancespectroscopy, and tension was recorded at the same time. AlthoughPi/PCr was low at rest, it wassignificantly higher in chronically stimulated muscle than in controlmuscle (0.20 ± 0.02 vs. 0.05 ± 0.01, P < 0.05). Stimulation of control muscle for 15 min at both 4 and 15 tetani/min induced a significant rise in Pi/PCr, whereas the sameconditions in chronically stimulated muscle did not produce anysignificant departure from initial levels. The tension produced bycontrol muscle fell to 93 ± 3% of its initial value duringstimulation at 4 tetani/min and to 61 ± 7% at 15 tetani/min,respectively. In chronically stimulated muscle, on the other hand,tension was potentiated above its initial level at both stimulationrates (135 ± 15 and 138 ± 11%, respectively) and remainedsignificantly elevated throughout each trial. The ability ofchronically stimulated muscle to sustain high levels of activity withminimal perturbations in Pi/PCr ordecrement in tension is attributable to cellular adaptations thatinclude a well-documented increase in oxidative capacity. 相似文献
18.
LY-294002-inhibitable PI 3-kinase and regulation of baseline rates of Na(+) transport in A6 epithelia 总被引:2,自引:0,他引:2
Păunescu TG Blazer-Yost BL Vlahos CJ Helman SI 《American journal of physiology. Cell physiology》2000,279(1):C236-C247
Blocker-inducednoise analysis of epithelial Na+ channels (ENaCs) was usedto investigate how inhibition of an LY-294002-sensitive phosphatidylinositol 3-kinase (PI 3-kinase) alters Na+transport in unstimulated and aldosterone-prestimulated A6 epithelia. From baseline Na+ transport rates(INa) of 4.0 ± 0.1 (unstimulated) and9.1 ± 0.9 µA/cm2 (aldosterone), 10 µM LY-294002caused, following a relatively small initial increase of transport, acompletely reversible inhibition of transport within 90 min to 33 ± 6% and 38 ± 2% of respective baseline values. Initialincreases of transport could be attributed to increases of channel openprobability (Po) within 5 min to 143 ± 17% (unstimulated) and 142 ± 10% of control (aldosterone) frombaseline Po averaging near 0.5. Inhibition oftransport was due to much slower decreases of functional channeldensities (NT) to 28 ± 4% (unstimulated)and 35 ± 3% (aldosterone) of control at 90 min. LY-294002 (50 µM) caused larger but completely reversible increases ofPo (215 ± 38% of control at 5 min) andmore rapid but only slightly larger decreases ofNT. Basolateral exposure to LY-294002 induced nodetectable effect on transport, Po or NT. We conclude that an LY-294002-sensitive PI3-kinase plays an important role in regulation of transport bymodulating NT and Po ofENaCs, but only when presented to apical surfaces of the cells. 相似文献
19.
Effect of estrogen supplementation on exercise thermoregulation in premenopausal women 总被引:1,自引:0,他引:1
Chang R.-T.; Lambert G. P.; Moseley P. L.; Chapler F. K.; Gisolfi C. V. 《Journal of applied physiology》1998,85(6):2082-2088
This studyexamined the effects of 3 days of estrogen supplementation (ES) onthermoregulation during exercise in premenopausal (20-39 yr) adultwomen during the follicular phase of the menstrual cycle. Subjects (11 control, 10 experimental) performed upright cycle ergometer exercise at60% of maximal O2 consumption ina neutral environment (25°C, 30% relative humidity) for 20 min. Subjects were given placebo (P) or -estradiol (2 mg/tablet, 3 tablets/day for 3 days). All experiments were conductedbetween 6:30 and 9:00 AM after ingestion of the last tablet. Heartrate, forearm blood flow (FBF), mean skin temperature, esophagealtemperature (Tes), and forearmsweat rate were measured. Blood analysis for estrogen and progesteronereflected the follicular phase of the menstrual cycle. MaximalO2 consumption (37.1 ± 6.2 in P vs. 38.4 ± 6.3 ml · kg1 · min1in ES) and body weight-to-surface area ratio (35.58 ± 2.85 in P vs.37.3 ± 2.7 in ES) were similar between groups. Synthesis of 70-kDaheat shock protein was not induced by 3 days of ES. Neither thethreshold for sweating (36.97 ± 0.15 in P vs. 36.90 ± 0.22°C in ES), the threshold for an increase in FBF (37.09 ± 0.22 in P vs. 37.17 ± 0.26°C in ES), the slope ofsweat rate-Tes relationship (0.42 ± 0.16 in P vs. 0.41 ± 0.17 in ES), nor the FBF-Tes relationship (10.04 ± 4.4 in P vs. 9.61 ± 3.46 in ES) was affected(P > 0.05) by 3 days of ES. Weconclude that 3 days of ES by young adult women in the follicular phaseof their menstrual cycle have no effect on heat transfer to the skin,heat dissipation by evaporative cooling, or leukocyte synthesis of70-kDa heat shock protein. 相似文献
20.
Haworth Robert S.; Sinnett-Smith James; Rozengurt Enrique; Avkiran Metin 《American journal of physiology. Cell physiology》1999,277(6):C1202
The regulation of plasma membraneNa+/H+exchanger (NHE) activity by protein kinase D (PKD), a novel proteinkinase C- and phorbol ester-regulated kinase, was investigated. Todetermine the effect of PKD on NHE activity in vivo, intracellular pH(pHi) measurements were made inCOS-7 cells by microepifluorescence using the pH indicator cSNARF-1.Cells were transfected with empty vector (control), wild-type PKD, orits kinase-deficient mutant PKD-K618M, together with green fluorescentprotein (GFP). NHE activity, as reflected by the rate of acid efflux(JH), wasdetermined in single GFP-positive cells following intracellularacidification. Overexpression of wild-type PKD had no significanteffect on JH(3.48 ± 0.25 vs. 3.78 ± 0.24 mM/min in control atpHi 7.0). In contrast,overexpression of PKD-K618M increasedJH (5.31 ± 0.57 mM/min at pHi 7.0;P < 0.05 vs. control). Transfectionwith these constructs produced similar effects also in A-10 cells,indicating that native PKD may have an inhibitory effect on NHE in bothcell types, which is relieved by a dominant-negative action ofPKD-K618M. Exposure of COS-7 cells to phorbol ester significantlyincreased JH in control cells but failed to do so in cells overexpressing either wild-type PKD (due to inhibition by the overexpressed PKD) or PKD-K618M(because basal JHwas already near maximal). A fusion protein containing the cytosolicregulatory domain (amino acids 637-815) of NHE1 (the ubiquitousNHE isoform) was phosphorylated in vitro by wild-type PKD, but with lowstoichiometry. These data suggest that PKD inhibits NHE activity,probably through an indirect mechanism, and represents a novel pathwayin the regulation of the exchanger. 相似文献