Caffeine mouth rinse enhances performance,fatigue tolerance and reduces muscle activity during moderate-intensity cycling

We investigated the effects of caffeine mouth rinse on endurance performance, muscle recruitment (i.e., electromyographic activity of the vastus lateralis and rectus femoris), rating of perceived effort and heart rate. Twelve physically-active healthy men cycled at 80% of their respiratory compensation point until task failure. The participants rinsed their mouths for 10 seconds with placebo (PLA, 25 mL of a solution composed of non-caloric mint essence) or caffeine (CAF, 25 mL of 1.2% of anhydrous caffeine concentration with non-caloric mint essence) every 15 minutes of exercise. Time until exhaustion increased 17% (effect size = 0.70) in CAF compared to PLA (p = 0.04). The wavebands of low-frequency electromyographic activity (EMG) of the vastus lateralis and rectus femoris was lower in CAF group than PLA at 50% of the time until exhaustion (p = 0.04). The global EMG signal was lower in CAF group than PLA at 100% of the time until exhaustion (p = 0.001). The rating of perceived effort pooled was higher in CAF mouth rinse (p = 0.001) than PLA group. No effect was found on the heart rate between the groups (p > 0.05). Caffeine mouth rinse increases endurance performance, rating of perceived effort and decreases muscle activity during a moderate-intensity exercise.     

Endurance treadmill training in rats alters CRH activity in the hypothalamic paraventricular nucleus at rest and during acute running according to its period

Running training on the treadmill increases the resting hypothalamic corticotropin-releasing hormone (CRH) content in rats, though is still unknown whether and how it occurs in the parvocellular region of the hypothalamic paraventricular nucleus (PVN) where is a predominant region of pituitary-adrenal activity and where CRH and arginine vasopressin (AVP) are colocalized. We thus aimed at examining whether treadmill training would alter the CRH and AVP mRNA levels in the PVN at rest and during acute running with different lengths of a training regime. Male Wistar rats were subjected to treadmill running (approximately 25 m/min, 60 minutes/day, 5 times/week) for training regimes of 0, 1, 2 or 4 weeks. All training regimes induced an adrenal hypertrophy. Plasma corticosterone levels before acute running increased with lengthening the training period. Four weeks of training produced a significant increase in the resting CRH, but not AVP, mRNA levels in the PVN though relatively shorter training regimes did not. Acute responses of lactate and ACTH release were reduced after 2 and 4 weeks of training, respectively. The responsive PVN CRH mRNA level to acute running decreased with 4 weeks of training but increased with relatively shorter training regimes. These results indicate that running training changes the PVN CRH biosynthetic activity with the regime lasting for 4 weeks, which follows adaptive changes in adrenal functions. Thus, running training-induced changes in hypothalamic CRH activity would originate from the PVN and be induced according to the training period.     

The effect of severe eccentric exercise-induced muscle damage on plasma elastase, glutamine and zinc concentrations

The aim of this study was to determine if severe exercise-induced muscle damage alters the plasma concentrations of glutamine and zinc. Changes in plasma concentrations of glutamine, zinc and polymorphonuclear elastase (an index of phagocytic cell activation) were examined for up to 10 days following eccentric exercise of the knee extensors of one leg in eight untrained subjects. The exercise bout consisted of 20 repetitions of electrically stimulated eccentric muscle actions on an isokinetic dynamometer. Subjects experienced severe muscle soreness and large increases in plasma creatine kinase activity indicative of muscle fibre damage. Peak soreness occurred at 2 days post-exercise and peak creatine kinase activity [21714 (6416) U · l⁻¹, mean (SEM)] occurred at 3 days post-exercise (P < 0.01 compared with pre-exercise). Plasma elastase concentration was increased at 3 days post-exercise compared with pre-exercise (P < 0.05), and is presumably indicative of ongoing phagocytic leucocyte infiltration and activation in the damaged muscles. There were no significant changes in plasma zinc and glutamine concentrations in the days following eccentric exercise. We conclude that exercise-induced muscle damage does not produce changes in plasma glutamine or zinc concentrations despite evidence of phagocytic neutrophil activation. Accepted: 3 November 1997     

Serum hormone concentrations during prolonged training in elite endurance-trained and strength-trained athletes

A study of 1 year was performed on nine elite endurance-trained athletes (swimmers) and on eight elite strength-trained athletes (weightlifters) in order to examine the effects of training on the endocrine responses and on physical performance capacity. The measurements for the determination of serum hormone concentrations were performed at about 4-month intervals during the course of the year. The primary findings demonstrated that during the first and most intensive training period of the year in preparing for the primary competitions similar but statistically insignificant changes were observed in the concentrations of serum testosterone, free testosterone and cortisol in both the endurance-trained and strength-trained groups. After that period the changes in hormonal response over the year were infrequent and minor. A significant (p less than 0.01) decrease occurred in the strength-trained group in serum-free testosterone during the second period, which was characterized by the highest overall amount of training. Over the entire year the concentrations of serum hormones remained statistically unaltered in both groups. Slight but statistically insignificant increases of 1.2% +/- 0.8% and 2.1% +/- 5.1% were observed in the competitive performances over the year in the endurance-trained and strength-trained groups, respectively. The present findings in the two groups of elite athletes, who differed greatly with regard to the type of physiological loading, demonstrated that the overall hormonal responses both during the most intensive and during prolonged training periods were rather similar and the infrequent small changes remained well within the normal physiological range.(ABSTRACT TRUNCATED AT 250 WORDS)     

Recent developments on the regulation and structure of glutamine synthetase enzymes from selected bacterial groups

Abstract: The structure of glutamine synthetase (GS) enzymes from diverse bacterial groups fall into three distinct classes. GSI is the typical bacterial GS, GSII is similar to the eukaryotic GS and is found together with GSI in plant symbionts and Streptomyces , while GSIII has been found in two unrelated anaerobic rumen bacteria. In most cases, the structural gene for GS enzyme is regulated in response to nitrogen. However, different regulatory mechanisms, to ensure optimal utilization of nitrogen substrates, control the GS enzyme in each class.     

Endurance training without weight loss lowers systemic, but not muscle, oxidative stress with no effect on inflammation in lean and obese women

Obesity is associated with oxidative stress. Endurance training (ET) in healthy individuals increases antioxidant enzyme activity and decreases oxidative stress, whereas its effects on oxidative status in obese humans have yet to be determined. We investigated the effects of obesity and ET on markers of oxidative stress, antioxidant defense, and inflammation. Obese (n=12) and lean (n=12) women underwent 12 weeks of ET with blood, 24-h urine, and muscle biopsies collected prior to and following training for determination of oxidative stress (urinary 8-hydroxy-2-deoxyguanosine and 8-isoprostanes, muscle protein carbonyls, and 4-hydroxynonenal), antioxidant enzyme protein content (muscle CuZnSOD, MnSOD, and catalase), and inflammation (C-reactive protein, leptin, adiponectin, interleukin-6). Obese women had elevated urinary 8-hydroxy-2-deoxyguanosine (P=0.03), muscle protein carbonyls (P=0.03), and 4-hydroxynonenal (P<0.001); serum C-reactive protein (P=0.01); and plasma leptin (P=0.0001) and interleukin-6 (P=0.03). ET decreased urinary 8-hydroxy-2-deoxyguanosine (P=0.006) and 8-isoprostanes (P=0.02) in all subjects and CuZnSOD protein content (P=0.04) in obese women, in the absence of changes in body weight or composition. ET without weight loss decreases systemic oxidative stress, but not markers of inflammation, in obese women.     

Blood amino acids concentration during insulin induced hypoglycemia in rats: the role of alanine and glutamine in glucose recovery

Summary. Our purpose was to determine the blood amino acid concentration during insulin induced hypoglycemia (IIH) and examine if the administration of alanine or glutamine could help glycemia recovery in fasted rats. IIH was obtained by an intraperitoneal injection of regular insulin (1.0 U/kg). The blood levels of the majority of amino acids, including alanine and glutamine were decreased (P < 0.05) during IIH and this change correlates well with the duration than the intensity of hypoglycemia. On the other hand, the oral and intraperitoneal administration of alanine (100 mg/kg) or glutamine (100 mg/kg) accelerates glucose recovery. This effect was partly at least consequence of the increased capacity of the livers from IIH group to produce glucose from alanine and glutamine. It was concluded that the blood amino acids availability during IIH, particularly alanine and glutamine, play a pivotal role in recovery from hypoglycemia.     

Decreases in motor unit firing rate during sustained maximal-effort contractions in young and older adults

Previous studies have suggested that older adults may be more resistant to muscular fatigue than young adults. We sought to determine whether motor unit firing rate might be a factor that determines the response to fatiguing exercise in young and older subjects. Motor unit recordings and muscular forces were obtained from the tibialis anterior (TA) muscle of 11 young and 8 older individuals. Maximal voluntary force was first measured during maximal-effort dorsiflexion contractions. Each subject then performed a series of 15 maximal isometric contractions, with each contraction lasting 30 s. A 10-s rest period separated the fatiguing contractions. As a result of the fatiguing exercise, both subject groups demonstrated a significant loss in maximal force. The force decline was less in the older adults (20.4%) than in the young adults (33.8%). As expected, prior to muscle fatigue, maximal firing rates in the TA muscle were greater in the young (28.1 ± 5.8 imp/s) than in the older adults (22.3 ± 4.8 imp/s). The decrease in motor unit firing rate with fatigue was also greater in the young adults (34.9%), than in the older adults (22.0%). These results suggest that the greater fatigue-resistance exhibited by older individuals might be explained by the fact that the decline in motor unit firing rate during fatigue is greater in young persons than it is in older adults.     

Purification and partial characterization of alanine dehydrogenase from Streptomyces aureofaciens

Alanine dehydrogenase was purified to near homogeneity from cell-free extract of Streptomyces aureofaciens, which produces tetracycline. The molecular weight of the enzyme determined by size-exclusion high-performance liquid chromatography was 395 000. The molecular weight determined by sodium dodecyl sulfate gel electrophoresis was 48 000, indicating that the enzyme consists of eight subunits with similar molecular weight. The isoelectric point of alanine dehydrogenase is 6.7. The pH optimum is 10.0 for oxidative deamination of L-alanine and 8.5 for reductive amination of pyruvate. K _M values were 5.0 mM for L-alanine and 0.11 mM for NAD⁺. K _M values for reductive amination were 0.56 mM for pyruvate, 0.029 mM for NADH and 6.67 mM for NH₄Cl.Abbreviation AlaDH alanine dehydrogenase     

Alanine and glutamine synthesis and release from skeletal muscle. II. The precursor role of amino acids in alanine and glutamine synthesis.

The synthesis and release of alanine and glutamine have been studied in the intact rat epitrochlaris skeletal muscle preparation. Aspartate, cysteine, leucine, valine, methionine, isoleucine, serine, theronine, and glycine increased significantly the formation and release of alanine from muscle. Cysteine, leucine, valine, methionine, isoleucine, tyrosine, lysine, and phenylalanine increased the rate of glutamine synthesis. Only ornithine, arginine, and tryptophan were without effect on the synthesis of either alanine or glutamine. Half-maximal stimulation of alanine and glutamine formation by added amino acids was observed with concentrations ranging between 0.5 and 1.0 mM. Increases in alanine and glutamine formation were not accompanied by changes in pyruvate production or glucose uptake. The progressive decline in alanine and glutamine synthesis noted on prolonged incubation was prevented by the addition of amino acids to the incubation medium. Stimulation of alanine synthesis by added amino acids was unaffected by inhibition of glycolysis with iodoacetate. Inhibition of alanine aminotransferase with aminooxyacetate significantly decreased alanine formation. Pyruvate and ammonium chloride did not increase further the rate of either alanine or glutamine formation above that produced by added amino acids. These data indicate that most amino acids are precursors for alanine and glutamine synthesis in skeletal muscle. A general mechanism is presented for the de novo formation of alanine from amino acids in skeletal muscle, and the importance of proteolysis for the supply of amino acid precursors for alanine and glutamine synthesis is discussed.     

Fatty acids and glycerol or lactate are required to induce gluconeogenesis from alanine in isolated rabbit renal cortical tubules

Summary In isolated rabbit renal cortical tubules, glucose synthesis from 1 mM alanine is negligible, while the amino acid is metabolized to glutamine and glutamate. The addition of 0.5 mM octanoate plus 2 mM glycerol induces incorporation of [U-¹⁴C]Alnine into glucose and decreases glutamine synthesis, whereas oleate and palmitate in the presence of glycerol are less potent than octanoate. Gluconeogenesis is also significantly accelerated when glycerol is substituted by lactate. In view of an increase in¹⁴CO₂ fixation and elevation of both cytosolic and mitochondrial NADH/NAD⁺ ratios, the activation of glucose formation from alanine upon the addition of glycerol and octanoate is likely due to (i) stimulation of pyruvate carboxylation, (ii) increased availability of NADH for glyceraldehyde-3-phosphate dehydrogenase and (iii) elevation of mitochondrial redox state causing a diminished provision of ammonium for glutamine synthesis. The induction of gluconeogenesis in the presence of alanine, glycerol and octanoate is not related to cell volume changes. The results presented in this paper show the importance of free fatty acids and glycerol for regulation of renal gluconeogenesis from alanine. The possible physiological significance of the data is discussed.     

Proton efflux in human skeletal muscle during recovery from exercise

In recovery from exercise, phosphocreatine resynthesis results in the net generation of protons, while the net efflux of protons restores pH to resting values. Because proton efflux rate declines as pH increases, it appears to have an approximately linear pH-dependence. We set out to examine this in detail using recovery data from human calf muscle. Proton efflux rates were calculated from changes in pH and phosphocreatine concentration, measured by ³¹P magnetic resonance spectroscopy, after incremental dynamic exercise to exhaustion. Results were collected post hoc into five groups on the basis of end-exercise pH. Proton efflux rates declined approximately exponentially with time. These were rather similar in all groups, even when pH changes were small, so that the apparent rate constant (the ratio of efflux rate to pH change) varied widely. However, all groups showed a consistent pattern of decrease with time; the halftimes of both proton efflux rate and the apparent rate constant were longer at lower pH. At each time-point, proton efflux rates showed a significant pH-dependence [slope 17 (3) mmol · l⁻¹ · min⁻¹ · pH unit⁻¹ at the start of recovery, mean (SEM)], but also a significant intercept at resting pH [16 (3) mmol · l⁻¹ · min⁻¹ at the start of recovery]. The intercept and the slope both decreased with time, with halftimes of 0.37 (0.06) and 1.4 (0.4) min, respectively. We conclude that over a wide range of end-exercise pH, net proton efflux during recovery comprises pH-dependent and pH-independent components, both of which decline with time. Comparison with other data in the literature suggests that lactate/proton cotransport can be only a small component of this initial recovery proton efflux. Accepted: 5 May 1997     

Comparison of incremental and steady state tests of endurance training

To compare the results obtained by incremental or constant work load exercises in the evaluation of endurance conditioning, a 20-week training programme was performed by 9 healthy human subjects on the bicycle ergometer for 1 h a day, 4 days a week, at 70-80% VO2max. Before and at the end of the training programme, (1) the blood lactate response to a progressive incremental exercise (18 W increments every 2nd min until exhaustion) was used to determine the aerobic and anaerobic thresholds (AeT and AnT respectively). On a different day, (2) blood lactate concentrations were measured during two sessions of constant work load exercises of 20 min duration corresponding to the relative intensities of AeT (1st session) and AnT (2nd session) levels obtained before training. A muscle biopsy was obtained from vastus lateralis at the end of these sessions to determine muscle lactate. AeT and AnT, when expressed as % VO2max, increased with training by 17% (p less than 0.01) and 9% (p less than 0.05) respectively. Constant workload exercise performed at AeT intensity was linked before training (60% VO2max) to a blood lactate steady state (4.8 +/- 1.4 mmol.l-1) whereas, after training, AeT intensity (73% VO2max) led to a blood lactate accumulation of up to 6.6 +/- 1.7 mmol.l-1 without significant modification of muscle lactate (7.6 +/- 3.1 and 8.2 +/- 2.8 mmol.kg-1 wet weight respectively). It is concluded that increase in AeT with training may reflect transient changes linked to lower early blood lactate accumulation during incremental exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

Uptake and release for glutamine and glutamate in a crude synaptosomal fraction from rat brain

[14C]Glutamine uptake in a crude synaptosomal (P2) fraction, (representing the sum of [¹⁴C]glutamine accumulated and [¹⁴C]glutamate formed by hydrolysis), is distinct from glutamate uptake. Glutamine uptake is Na⁺-independent and unaffected by the Na⁺–K⁺-ATPase inhibitor ouabain, whereas glutamate uptake is Na⁺-dependent and inhibited by ouabain. The uptake of both glutamine and glutamate is unaffected by the gamma-glutamyltransferase inhibitor, Acivicin. This indicates that glutamine uptake is not mediated by a carrier, as distinct from that of glutamate, and also not linked to gamma-glutamyl-transferase. Na⁺ affects the distribution of glutamine-derived glutamate by increasing the synaptosomal content and reducing that of the medium. When glutamate release from synaptosomes preloaded with [¹⁴C]glutamate is measured by superfusion technique in order to prevent reuptake, Na⁺ has been found to inhibit release in a non-depolarizing medium (Ringer buffer with no Ca²⁺) of the [¹⁴C]glutamate as well as of endogenous glutamate. The specific activity of the [¹⁴C]glutamine-derived glutamate in the incubation medium is much higher than that in the synaptosomes, indicating that there exists a readily releasable pool of newly formed glutamate in addition to another pool. The latter glutamate pool is partially reduced by Na⁺.Special Issue Dedicated to Dr. Abel Lajtha.     

以结核分枝杆菌丙氨酸消旋酶为靶点的抗结核药物筛选及其与D-环丝氨酸的共结晶

【目的】阐释结核分枝杆菌丙氨酸消旋酶原有抑制剂D-环丝氨酸的作用机制,建立丙氨酸消旋酶抑制剂的高通量筛选模型,并用此模型筛选到新的抑制剂分子。【方法】将结核分枝杆菌中丙氨酸消旋酶基因克隆到pET-28a表达载体中,在大肠杆菌BL21(DE3)菌株中得到可溶性的大量表达。表达后的蛋白质通过镍离子亲和层析和阴离子交换层析得到纯化,一方面将纯化后的蛋白和D-环丝氨酸共结晶以解析其抑制剂作用的分子机制。另一方面建立并优化丙氨酸消旋酶抑制剂的高通量筛选体系,用D-环丝氨酸验证体系的可行性并用该体系筛选本实验室药物库中的384种小分子片段、792种化合物及2 200种中药样品。【结果】得到的共晶晶体衍射能力2.50?,晶体空间群为P41212,晶胞参数a=b=163.92?,c=57.44?。结构分析表明,D-环丝氨酸进入活性位点之后与磷酸吡哆醛相互作用形成磷酸吡哆胺,使得磷酸吡哆醛的C4?原子与K42之间的相互作用被破坏,从而改变了结核分枝杆菌丙氨酸消旋酶的活性中心氢键网络。同时经D-环丝氨酸验证建立的抑制剂筛选体系可行,获得阳性化合物分子2个。【结论】依据我们所建立的高通量筛选体系可以有效地为结核分枝杆菌丙氨酸消旋酶筛选到可信的抑制剂分子。     

Changes in voluntary and electrically induced contractions during strength training and detraining

To elucidate the changes in neuro-muscular function during strength training and detraining, five male subjects underwent progressive isotonic strength training of their calf muscles three times a week for 8 weeks with additional detraining for the same periods. Electrically evoked twitch contractions were induced in the triceps surae muscles of each subject every 4 weeks during the training and detraining periods. At the same time, maximal voluntary isometric contractions (MVC) and the maximal girth of the calf (MGC) were measured. During the training period, MVC increased significantly from 98.4 to 129.6 Nm (31.7%, P less than 0.01) for the first 4 weeks of training but MGC showed little increase. Neither of the changes correlated with each other. Twitch contraction parameters, i.e. maximal twitch torque (Pt), maximal rate of torque development (max dT/dt) and rate of relaxation (relax dT/dt) showed no statistical change. During detraining, on the contrary, a large and significant increase (22.5%, P less than 0.01) was observed in max dT/dt without any changes in Pt and relax dT/dt. The MVC/Pt showed both significant increases during training and decreases during detraining. Our data suggest that short term strength training as employed in the present study does not induce changes in the contractile properties of the muscle during training, but may significantly affect the rate of force development during the subsequent detraining period, indicating the possible existence of complex post-training muscle adaptation.     

Effects of isokinetic training of the knee extensors on high-intensity exercise performance and skeletal muscle buffering

Twenty-three subjects isokinetically trained the right and left quadriceps femoris, three times per week for 16 weeks; one group (n=13) trained at an angular velocity of 4.19 rad · s^–1 and a second group (n=10), at 1.05 rad · s^–1. A control group (n=10) performed no training. Isometric endurance time at 60% quadriceps maximum voluntary contraction (MVC), mean power output and work done (W) during all-out cycling, and the muscle buffer value (B) and carnosine concentration of biopsy samples from the vastus lateralis, were all assessed before and after training. The two training groups did not differ significantly from each other in their training response to any of these variables (P < 0.05). No significant difference in either 60% MVC endurance time or impulse [(endurance time × force) at 60% MVC] was observed for any group after the 16 week period (P > 0.05). However, the post-training increase (9%) in W during high-intensity cycling was greater in the training group than in the control group (P=0.04). NeitherB nor carnosine concentration showed any significant change following training (P=0.56 andP=0.37, respectively). It is concluded that 16 weeks of isokinetic training of the knee extensors enables subjects to do more work during high-intensity cycling. Although the precise adaptations responsible for the improved performance have yet to be identified, they are unlikely to include an increase inB.     

Repetitive static muscle contractions in humans —a trigger of metabolic and oxidative stress?

Repetitive static exercise (RSE) is a repetitive condition of partial ischaemia/reperfusion and may therefore be connected to the formation of oxygen-derived free radicals and tissue damage. Seven subjects performed two-legged intermittent knee extension exercise repeating at 10 s on and 10 s off at a target force corresponding to about 30% of the maximal voluntary contraction force. The RSE was continued for 80 min (n = 4) or to fatigue (n = 3). Four of the subjects also performed submaximal dynamic exercise (DE) at an intensity of about 60% maximal oxygen uptake (VO2max) for the same period. Whole body oxygen uptake (VO2) increased gradually with time during RSE (P less than 0.05), indicating a decreased mechanical efficiency. This was further supported by a slow increase in leg blood flow (P less than 0.05) and leg oxygen utilization (n.s.) during RSE. In contrast, prolonged RSE had no effect on VO2 during submaximal cycling. Maximal force (measured in six additional subjects) declined gradually during RSE and was not completely restored after 60 min of recovery. After 20 and 80 min (or at fatigue) RSE phosphocreatine (PC) dropped to 74% and 60% of the initial value, respectively. A similar decrease in PC occurred during DE. Muscle and arterial lactate concentrations remained low during both RSE and DE. The three subjects who were unable to continue RSE for 80 min showed no signs of a more severe energy imbalance than the other subjects. A continuous release of K+ occurred during both RSE and DE.(ABSTRACT TRUNCATED AT 250 WORDS)     

Corticospinal responses of resistance-trained and un-trained males during dynamic muscle contractions

Little is known regarding the modulation and the plasticity of the neural pathway interconnecting elements of the central nervous system and skeletal muscle in resistant-trained individuals. The aim of the study was to compare corticospinal and spinal responses measured during dynamic muscle contractions of the tibialis anterior in resistance trained (RT) and un-trained (UT) males. Nine UT and 10 RT male volunteers reported to the laboratory 24 h following a familiarisation session. Motor evoked potentials (MEPs) and the cortical silent period were evoked using transcranial magnetic stimulation at a range of contraction intensities and was delivered as the ankle passed 90° during shortening and lengthening contractions. The Hoffmann reflex (H-reflex) and V-waves were evoked with peripheral nerve stimulation. Despite the RT group being significantly stronger during shortening (28%; P = 0.023: CI = 1.27–15.1 N m), lengthening (25%; P = 0.041: CI = 0.27–17.0 N m) and isometric muscle actions (20%; P = 0.041; CI = 0.77–14.9 N m), no differences between the groups existed for corticospinal or spinal variables. Lack of detectable differences between RT and UT individuals may be linked to minimal exposure to task specific, isolated high intensity resistance training of the TA muscle.