Adenine nucleotide and IMP contents of the quadriceps muscle in man after exercise

Subjects performed submaximal and maximal bicycle exercise. Work time was between 2 and 15 min. Muscle biopsies were taken from m. quadriceps femoris at rest, immediately after termination of exercise and in some cases during the recovery period. Samples were analyzed for lactate, ATP, ADP, AMP, inorganic phosphate, creatine phosphate, creatine and IMP. The decrease in creatine phosphate and ATP/ADP ratio, as well as the increase in lactate were similar to previous investigations. Total adenine nucleotide content (TAN=ATP+ADP+AMP) decreased after maximal exercise with about 15% but was unchanged after submaximal exercise. The decrease in TAN after maximal exercise was corresponded by a similar increase in muscle IMP content. After 30 min of recovery TAN was restored to the basal value and IMP had decreased correspondingly. The physiological importance of adenine nucleotide degradation and IMP accumulation is discussed as well as the regulatory properties of the involved enzymes. The amount of energy which is liberated when 1 mol of ATP is hydrolysed to ADP has been calculated to decrease from 54 kJ at rest to 50 kJ after exhaustive exercise. It is suggested that the energy yield in the hydrolysation of ATP, rather than the amount of available ATP, is limiting for muscle contraction.     

The time course of phosphorylcreatine resynthesis during recovery of the quadriceps muscle in man

Summary The time course of phosphorylcreatine (PC) resynthesis in the human m. quadriceps femoris was studied during recovery from exhaustive dynamic exercise and from isometric contraction sustained to fatigue. The immediate postexercise muscle PC content after either form of exercise was 15–16% of the resting muscle content. The time course of PC resynthesis during recovery was biphasic exhibiting a fast and a slow recovery component. The half-time for the fast component was 21–22 s but this accounted for a smaller fraction of the total PC restored during recovery from the isometric contraction than after the dynamic exercise. The half-time for the slow component was in each case more than 170 s. After 2 and 4 min recovery the total amounts of PC resynthesized after the isometric exercise were significantly lower than from the dynamic exercise.Occlusion of the circulation to the quadriceps completely abolished the resynthesis of PC. Restoration of resynthesis occurred only after release of occlusion.     

Regulation of glycogen resynthesis in muscles of rats following exercise.

Following a strenuous bout of exercise, glycogen repletion occurred most rapidly in the fast-twitch red type of muscle, least rapidly in fast-twitch white, and at an intermediate rate in slow-twitch red muscle. There was a linear correlation between glycogen synthase I activity and the rate of glycogen synthesis in the three types of muscle. This finding helps explain the differences between the rates of glycogen resynthesis in the three muscle types, and supports the view that glycogen synthase activity is the most important factor determining the rate of glycogen synthesis when substrate supply is adequate. There was an inverse correlation between muscle glycogen concentration and percent glycogen synthase I. Plasma insulin concentration was low and norepinephrine and glucagon concentrations were elevated in the postexercise period. The finding that rapid glycogen synthesis occurred despite a hormonal milieu conducive to glycogenolysis provides evidence that a low glycogen concentration is a potent stimulus to glycogen synthesis that overrides the effects of low insulin, and high norepinephrine and glucagon levels.     

The effect of exercise training on glycogen,glycogen synthase and phosphorylase in muscle and liver

Summary It is thought that exercise training in both man and the rat results in a protective effect against the depletion of carbohydrate stores during exercise (glycogen-sparing). However there has been no comprehensive study of the effects of training on glycogen anabolic and catabolic enzymes with liver or muscle. The aim of this study was to examine whether changes in these enzymes occur and whether these changes may provide an explanation for the glycogen-sparing which results from exercise training.Male rats were trained by a treadmill running program at three different workloads. In addition, there were three control groups: free eating (SF), food restricted (SR), and one SF with a single bout of exercise prior to sacrifice.Exercise training was associated with a 60–150% increase in glycogen synthase and phosphorylase and a 50–70% increase in glycogen content in soleus, an intermediate muscle, but not in extensor digitorum longus (EDL), a white muscle nor in liver. The increase in glycogen synthase and phosphorylase in intermediate muscle was proportional to the degree of training and there was a significant correlation between glycogen content, glycogen synthase, and phosphorylase activity in intermediate muscle. Cytochrome c oxidase activity, an indicator of respiratory capacity, increased 50% in gastrocnemius of trained rats and was significantly correlated with glycogen synthase and phosphorylase in soleus.These results indicate a significant effect of exercise training on glycogen anabolic and catabolic enzymes in intermediate muscle, with no significant effects in white muscle or liver. The changes do not provide an explanation for glycogen-sparing, but are consistent with improved capacity of intermediate muscle for rapid glycogen mobilisation and repletion.     

Modulation of ATP/ADP concentration at the endothelial surface by shear stress: effect of flow-induced ATP release

The adenine nucleotides ATP and ADP induce the production of vasoactive compounds in vascular endothelial cells (ECs). Therefore, knowledge of how flow affects the concentration of ATP and ADP at the EC surface may be important for understanding shear stress-mediated vasoregulation. The concentration of ATP and ADP is determined by convective and diffusive transport as well as by hydrolysis of these nucleotides by ectonucleotidases at the EC surface. Previous mathematical modeling has demonstrated that for steady flow in a parallel plate flow chamber, the combined ATP+ADP concentration does not change considerably over a wide range of shear stress. This finding has been used to argue that the effect of flow on adenine nucleotide transport could not account for the dependence of endothelial responses to ATP on the magnitude of applied shear stress. The present study extends the previous modeling to include pulsatile flow as well as flow-induced endothelial ATP release. Our results demonstrate that flow-induced ATP release has a pronounced effect on nucleotide concentration under both steady and pulsatile flow conditions. While the combined ATP+ADP concentration at the EC surface in the absence of flow-induced ATP release changes by only 10% over the wall shear stress range 0.1-10 dyne/cm ^-2, inclusion of this release leads to a concentration change of 34% –106% over the same shear stress range, depending on how ATP release is modeled. These results suggest that the dependence of various endothelial responses to shear stress on the magnitude of the applied shear stress may be partially attributable to flow-induced changes in cell-surface adenine nucleotide concentration. © 2001 Biomedical Engineering Society. PAC01: 8716Ac, 8716Uv, 8719Uv, 8715Vv, 8710+e     

The effect of glycogen availability on power output and the metabolic response to repeated bouts of maximal,isokinetic exercise in man

The relationship of glycogen availability to performance and blood metabolite accumulation during repeated bouts of maximal exercise was examined in 11 healthy males. Subjects performed four bouts of 30 s maximal, isokinetic cycling exercise at 100 rev · min^–1, each bout being separated by 4 min of recovery. Four days later, all subjects cycled intermittently to exhaustion [mean (SEM) 106 (6) min] at 75% maximum oxygen uptake Subjects were then randomly assigned to an isoenergetic low-carbohydrate (CHO) diet [7.8 (0.6)% total energy intake,n = 6] or an isoenergetic high-CHO diet [81.5 (0.4)%,n = 5], for 3 days. On the following day, all subjects performed 30 min cycling at 75% and, after an interval of 2 h, repeated the four bouts of 30 s maximal exercise. No difference was seen when comparing total work production during each bout of exercise before and after a high-CHO diet. After a low-CHO diet, total work decreased from 449 (20) to 408 (31) J · kg^–1 body mass in bout 1 (P < 0.05), from 372 (15) to 340 (18) J · kg^–1 body mass in bout 2 (P < 0.05), and from 319 (12) to 306 (16) J · kg^t-1 body mass in bout 3 (P < 0.05), but was unchanged in bout 4. Blood lactate and plasma ammonia accumulation during maximal exercise was lower after a low-CHO diet (P < 0.001), but unchanged after a high-CHO diet. In conclusion, muscle glycogen depletion impaired performance during the initial three, but not a fourth bout of maximal, isokinetic cycling exercise. Irrespective of glycogen availability, prolonged submaximal exercise appeared to have no direct effect on subsequent maximal exercise performance.     

The effect of praziquantel on calcium in Hymenolepis diminuta

Praziquantel (PZ) at concentrations down to 5 × 10^?8 M induced a rapid contraction of Hymenolepis diminuta musculature. This effect was accompanied by a strong inhibition of ⁴⁵Ca²⁺ incorporation which showed some dependence on Ca²⁺ concentration. Ca²⁺ efflux experiments showed that PZ markedly stimulated the release of Ca²⁺ from tapeworms preloaded with ⁴⁵Ca²⁺, with the effluxed Ca²⁺ being derived from a small fast pool and a larger slow pool. This stimulatory effect appeared, like PZ-induced muscle contraction, to be independent of external Ca²⁺. By carrying out ⁴⁵Ca²⁺ exchange experiments under near equilibrium conditions and atomic absorption spectroscopy it could be demonstrated that PZ resulted in a net excretion of endogenous Ca²⁺. In PZ-induced contracted worms adenylate nucleotide levels and the adenylate energy charge were not significantly different from those of untreated control worms. Also, PZ had no effect on Ca²⁺-stimulated ATPase activity of the tapeworm's tegumental brush border. Nor did the drug alter the activities of Ca²⁺-ATPases in whole homogenates of worms or mitochondria, microsomal or soluble fractions. Although the mechanism of PZ-induced changes in Ca²⁺ transport was not elucidated, it is suggested that the sustained release of endogenous Ca²⁺ may affect the sequence of excitation-contraction coupling and that such interference may cause the observed massive contraction of the tapeworm's musculature.     

Anaerobic chemical changes and mechanical output during isometric tetani of rat skeletal muscle in situ

The time course was examined of the energy-rich phosphate usage and exerted isometric tetanic force in electrically stimulated rat quadriceps muscle. The maximal rate of energy-rich phosphate usage was calculated from the changes in the intramuscular concentrations of phosphocreatine, lactate, ATP and inosine monophosphate (IMP) and was somewhat higher than those calculated on the basis of exercise in vivo. The IMP concentration increased directly from the onset of the contraction until after about 11 s it remained constant. The increase in the IMP concentration coincided with a decrease in the ATP concentration. The relationship between mechanical output and energy usage was examined in two wasy (i) by calculating the ratio time integral of the force (FTI) and the total energy-rich usage (P _tot) and (ii) by calculating the ratio Force (F _t) to the energy flux (dP _tot/dt) at a certain timet.Whereas the ratio FTI/P _tot showed a hyperbolic relationship, the ratioF _t/(dP _tot/dt) showed a parabolic relationship From the latter finding and from the results described in the literature it is concluded that the ratio mechanical output/energy-rich phosphate usage depends on the conditions under which exercise is carried out. Recovery under aerobic conditions from a maximal tetanic isometric contraction sustained for 15 s was slow compared to results of experiments in vivo.     

Muscle glycogen resynthesis, signalling and metabolic responses following acute exercise in exercise-trained pigs carrying the PRKAG3 mutation

Hampshire pigs carrying the PRKAG3 mutation in the AMP-activated protein kinase (AMPK) γ3 subunit exhibit excessive skeletal muscle glycogen storage and an altered glycogen synthesis signalling response following exercise. AMPK plays an important role as a regulator of carbohydrate and fat metabolism in mammalian cells. Exercise-trained muscles are repeatedly exposed to glycogen degradation and resynthesis, to which the signalling pathways adapt. The aim of this study was to examine the effect of acute exercise on glycogen synthesis signalling pathways, and the levels of insulin and other substrates in blood in exercise-trained pigs with and without the PRKAG3 mutation. After 5 weeks of training, pigs performed two standardized treadmill exercise tests, and skeletal muscle biopsies were obtained immediately after exercise and 3 h postexercise in the first test, and 6 h postexercise in the second test. The PRKAG3 mutation carriers had higher glycogen storage, and resynthesis of glycogen was faster after 3 h but not after 6 h of recovery. Alterations in the concentrations of insulin, glucose, lactate and free fatty acids after exercise did not differ between the genotypes. The carriers showed a lower expression of AMPK and increased phosphorylation of Akt Ser(473) after exercise, compared with non-carriers. Acute exercise stimulated the phosphorylation of AS160 in both genotypes, and the phosphorylation of GSK3α Ser(21) and ACC Ser(79) in the non-carriers. In conclusion, exercise-trained pigs carrying the PRKAG3 mutation show an altered Akt and AMPK signalling response to acute exercise, indicating that glucose metabolism is associated with faster resynthesis of muscle glycogen in this group.     

Effect of diet on muscle glycogen and blood glucose utilization during a short-term exercise in man

7 subjects were studied at rest and during a 6 min submaximal exercise (65% of Vo₂, max) on two occasions, the first preceded by a fat rich diet and the second by a carbohydrate rich diet. Oxygen uptake and respiratory exchange ratio (R) were measured at rest and heart rate both at rest and during exercise. Arterial-femoral venous differences for oxygen, glucose, lactate and β-hydroxybutyrate and arterial concentrations of free fatty acids were measured at rest and during exercise. Changes in muscle glycogen (in 6 subjects) and lactate concentration were determined by biopsies from m. quadriceps femoris taken before and immediately after exercise. Muscle glycogen decreased less during exercise after the fat than after the carbohydrate diet in 5 of the 6 subjects, whereas blood glucose extraction by the exercising legs did not change with diet. Muscle lactate accumulation and release were smaller after the fat diet. In conclusion, the muscle glycogen utilization during a short-term exercise appeared to be lower after the fat than after the carbohydrate diet, but not the concomitant blood glucose extraction. These differences between diets were similar to those observed after a more prolonged work at the same load.     

冬虫夏草醇提取物对大鼠缺血再灌注过程心肌保护作用研究

目的和方法：观察冬虫夏草对缺血再灌注过程心肌保护作用。采用Ｌａｎｇｅｎｄｏｒｆ非循环式离体心脏灌流方法，与正常对照组、缺血再灌组、刺五加注射液用药组相对比，研究了冬虫夏草醇提取物对大鼠心肌缺血－再灌注过程脂质过氧化产物（ＭＤＡ）和腺嘌呤核苷酸含量的影响。结果：冬虫夏草醇提取物显著降低了再灌注心肌的ＭＤＡ水平（Ｐ＜０．０１）及显著提高了心肌中腺嘌呤核苷酸含量（Ｐ＜００１）。结论：冬虫夏草可通过改善心肌的能量代谢减少缺血再灌注损伤，对心肌的保护作用明显优于刺五加注射液     

Dependence of lactate removal on muscle metabolism in man

Summary If lactate is primarily oxidized in skeletal muscle in man, it is expected that lactate uptake would increase linearly with increasing muscle metabolism (VO₂). Therefore, lactate removal was investigated (N=9) after 6 min exercise bouts (90% VO₂ max), at rest, and during 30 min of recovery exercise, when the relative intensities were constant to equate lactate production while permitting exercise metabolism (VO₂) to vary. Recovery exercises were therefore conducted at 26.8% VO₂ max for arm exercise, 26.8% VO₂ max for leg exercise, and 29% VO₂ max for combined arm and leg exercise. These exercise intensities were calculated from VO₂ max values established separately for each of the three modes of exercise. Lactate removal was slowest at rest (p<0.05). Removal during leg recovery was faster than during the arm condition (p<0.05), but the leg removal was not different from the combined arm and leg condition (p>0.05). The VO₂ cost of the arm (0.73±0.04 l/min), leg (1.04±0.05 l/min) and combined arm and leg exercise (1.23±0.10 l/min) were distinctly different from each other (p<0.05). There was a high correlation (r=0.92) between VO₂ cost, and the lactate removal rates of the corresponding recovery conditions. These findings indicate that lactate increases proportionately with the metabolically active muscle mass, providing exercise remains aerobic. Thus in man, it appears that lactate removal from the blood during recovery exercise occurs primarily in skeletal muscle.     

The repeated bout effect of reduced-load eccentric exercise on elbow flexor muscle damage

In this study we investigated the extent to which an initial eccentric exercise consisting of two (2ECC) or six maximal eccentric actions (6ECC) of the elbow flexors would produce a similar effect to 24 maximal eccentric actions (24ECC), on a second bout of 24ECC performed 2 weeks later. Male students (n=34) were assigned to one of three groups, and with their non-dominant arm performed either 2ECC (n=12), 6ECC (n=10), or 24ECC (n=12) as a first bout of exercise. Two weeks later all groups performed 24ECC. Maximal isometric strength, range of motion, upper arm circumference, muscle soreness, plasma creatine kinase activity and myoglobin concentration were assessed before, immediately after, and for 4 days after exercise. Changes in all variables were compared between the bouts and groups by a two-way repeated measures analysis of variance. All variables changed significantly (P<0.05) after 2ECC, 6ECC, and 24ECC, but the amount of change after 2ECC and 6ECC was significantly smaller (P<0.05) than both 6ECC and 24ECC, and 24ECC, respectively. After the second bout, the 6ECC and 24ECC groups showed a profound repeated bout effect, and no significant differences were found between the groups. All variables except muscle soreness were significantly (P<0.05) larger after the second bout for the 2ECC group, however the changes observed after 24ECC were significantly smaller (P<0.01) than those observed after the first 24ECC of the 24ECC group. These results suggest that it is not necessary to conduct a high number of eccentric actions in the first bout to elicit a repeated bout effect in a subsequent bout performed some time later. Electronic Publication     

Selective glycogen depletion in skeletal muscle fibres of man following sustained contractions

1. Six healthy males performed sustained contractions with different tensions related to their maximal voluntary contraction (MVC). The isometric exercise consisted of efforts to extend the knee when flexed at an angle of 90 degrees .2. Biopsy samples were taken from the lateral portion of M. quadriceps femoris before and after different periods (6-45 min) during a series of sustained contractions. Total glycogen content was determined on each muscle sample. In order to evaluate whether the glycogen depletion occurred preferentially in slow twitch (ST) or fast twitch (FT) fibres, serial sections of the muscle samples were stained for myofibrillar ATPase and glycogen (PAS reaction).3. In all experiments a selective glycogen depletion was observed. At low tensions, the ST fibres and at higher tensions the FT fibres became glycogen depleted. The critical tension at which this conversion in glycogen depletion from ST to FT fibres took place was 20% MVC.4. It is concluded that at sustained contractions of less than 20% MVC there is a major reliance upon ST fibres and above that level a primary dependence upon FT fibres. It is further suggested that restriction of blood flow and thus availability of oxygen at forces higher than 20% MVC may be the explanation for the present findings.     

Resynthesis of glycogen in different muscle fibre types after prolonged exhaustive exercise in man

The rate of glycogen resynthesis was examined in different muscle fibre types after prolonged exhaustive exercise. Six subjects exercised to exhaustion at 75% of VO2 max, and muscle biopsies were taken after 0, 90 and 180 min of recovery. Glucose drinks (1.4, 0.7 and 0.7 g kg-1 body wt) were taken at time 0, 60 and 120 min. Photometric determination of periodic acid-Schiff stain intensity revealed a 65% faster rate of glycogen resynthesis in type IIA and IIAB as compared to type I fibres during the first 90 min. Thereafter no differences between the various fibre types were detected. No differences in the rate of glycogen resynthesis were observed between the subgroups of type II muscle fibres. These results suggest that there was a slower acceleration of glycogen resynthesis in type I compared to type II fibres. In all fibre types a positive relationship between rate of synthesis and glycogen concentration was observed. It is suggested that the size of the glycogen molecule and hence the number of available terminal glucosyl units is a major determinant of rate of resynthesis.     

Moderate exercise training promotes adaptations in coronary blood flow and adenosine production in normotensive rats

OBJECTIVES:

Aerobic exercise training prevents cardiovascular risks. Regular exercise promotes functional and structural adaptations that are associated with several cardiovascular benefits. The aim of this study is to investigate the effects of swimming training on coronary blood flow, adenosine production and cardiac capillaries in normotensive rats.

METHODS:

Wistar rats were randomly divided into two groups: control (C) and trained (T). An exercise protocol was performed for 10 weeks and 60 min/day with a tail overload of 5% bodyweight. Coronary blood flow was quantified with a color microsphere technique, and cardiac capillaries were quantified using light microscopy. Adenine nucleotide hydrolysis was evaluated by enzymatic activity, and protein expression was evaluated by western blot. The results are presented as the means ± SEMs (p<0.05).

RESULTS:

Exercise training increased the coronary blood flow and the myocardial capillary-to-fiber ratio. Moreover, the circulating and cardiac extracellular adenine nucleotide hydrolysis was higher in the trained rats than in the sedentary rats due to the increased activity and protein expression of enzymes, such as E-NTPDase and 5′-nucleotidase.

CONCLUSIONS:

Swimming training increases coronary blood flow, number of cardiac capillaries, and adenine nucleotide hydrolysis. Increased adenosine production may be an important contributor to the enhanced coronary blood flow and angiogenesis that were observed in the exercise-trained rats; collectively, these results suggest improved myocardial perfusion.     

Carbohydrate feeding and glycogen synthesis during exercise in man

In 7 male cyclists glycogen synthesis during exercise and rest was studied. Each subject did two exercise trials (A and B), in random order. In both trials, after determining the maximal workload (W _max), intermittent exercise was given to exhaustion. After the exhaustive exercise and taking a muscle biopsy the subjects either exercised at 40%W _max for 3 h (trial A) or rested for 3 h (trial B), during which they consumed approximately 21 of a 25% malto-dextrine drink in both trials. After 3 h rest (trial A) or 3 h of mild exercise (trial B) a second muscle biopsy was taken for total glycogen and histochemistry (ATPase and PAS). Blood glucose and insulin levels were elevated during the first 2 h of exercise (p<0.05). Glycogen depletion was most pronounced in type I and to a less extent in type IIA fibers. In trial A muscle glycogen increased from 136±66 to 199±71 mmol/kg DW, and in trial B from 145±56 to 257±79 mmol/kg DW. During exercise glycogen repletion was restricted to type IIA and IIB fibers, whereas during rest glycogen synthesis occurred both in type I and type II fibers. The present study demonstrates that oral carbohydrate administered during exercise may not only provide substrate for energy metabolism, but can also be utilized for glycogen synthesis in the non-active muscle fibers.