Effects of carbohydrate feedings on plasma free tryptophan and branched-chain amino acids during prolonged cycling

Summary Brain serotonin (5-hydroxytryptamine, 5-HT) has been suggested to be involved in central fatigue during prolonged exercise. Changes in the ratio of plasma free tryptophan (free Trp) to branched-chain amino acids (BCAA) are associated with altered brain 5-HT synthesis. The purposes of this study were to describe systematically the effects of prolonged exercise on changes in plasma free Trp and BCAA and to examine the effects of carbohydrate (CHO) feedings on these same variables. Eight well-trained men [ _max = 57.8 (SE 4.1) ml kg^–1 min^–1] cycled for up to 255 min at a power output corresponding toVO₂ at lactate threshold (approximately 68%VO_2max) on three occasions separated by at least 1 week. Subjects drank 5 ml kg^–1 body wt^–1 of either a water placebo, or a liquid beverage containing a moderate (6% CHO) or high (12% CHO) concentration of carbohydrate beginning at min 14 of exercise and every 30 min thereafter. Exercise time to fatigue was shorter in subjects receiving placebo [190 (SE 4) min] as compared to 6% CHO [235 (SE 10) min] and 12% CHO [234 (SE 9) min] (P<0.05). Glucose and insulin decreased in the placebo group, and free Trp, free-Trp/BCAA, and free fatty acids increased approximately five- to sevenfold (P < 0.05). These changes were attenuated in a dose-related manner by the carbohydrate drinks. Plasma free Trp and plasma free fatty acids were highly correlated (r=0.86,P<0.001). Plasma BCAA did not change in the placebo group, but decreased slightly in those receiving 6% CHO and 12% CHO (P<0.05). No differences in heart rate, , plasma volume and respiratory exchange ratio were found. The results indicate that free Trp and free Trp/BCAA increase progressively during prolonged cycling to fatigue. This response was attenuated by CHO feedings. Changes in plasma free fatty acids probably play a prominent role in these responses.     

The effect of acute branched-chain amino acid supplementation on prolonged exercise capacity in a warm environment

Eight males were recruited to examine the effect of branched-chain amino acid (BCAA) supplementation on exercise capacity in a glycogen-depleted state in a warm environment. Following a exercise and dietary regimen designed to reduce glycogen availability, subjects returned to the laboratory the following morning and remained seated for 2 h, before cycling to volitional exhaustion at 50% O₂ peak in a warm environment [30.0 (0.2)°C; mean (SD)]. Four 250 ml aliquots of a 12 g l^–1 BCAA solution or placebo were ingested at 30 min intervals prior to exercise, with an additional 150 ml consumed every 15 min throughout exercise. BCAA ingestion had no effect on exercise capacity [placebo 103.9 (26.9) min; BCAA 111.0 (29.2) min; P=0.129). No difference in heart rate (P=0.345), core temperature (P=0.628), or weighted mean skin temperature (P=0.114) was apparent between trials. Ingestion of the BCAA solution produced a marked increase in plasma BCAA immediately prior to exercise [+1126 (158) mol l^–1; P<0.001) with this difference maintained throughout. Consequently, a significant reduction in the plasma concentration ratio of free tryptophan to BCAA was observed during the BCAA trial when compared to the placebo (P<0.001). Plasma ammonia concentration was significantly elevated during exercise throughout the BCAA trial (P<0.001), with no change from rest apparent during the placebo trial (P=0.608). Blood glucose (P=0.114) and lactate (P=0.836) concentrations were not different between trials. Ingestion of a BCAA solution prior to, and during, prolonged exercise in glycogen-depleted subjects did not influence exercise capacity in a warm environment.     

Influence of a 36 h fast followed by refeeding with glucose,glycerol or placebo on metabolism and performance during prolonged exercise in man

Summary Five men were studied during exercise to exhaustion on an electrically braked cycle ergometer at 70% of % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVq0xe9tqqrpepC0xbbL8F4rqqrFfpeea0xe9sq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0Firpepe0de9vr0-vr% 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaKaaGkqadAfaga% GaaOWaaSbaaSqaaiaab+eadaWgaaqccawaaiaabkdacaqGGaGaaeyB% aiaabggacaqG4baameqaaaWcbeaaaaa!3C9E!\[\dot V_{{\text{O}}_{{\text{2 max}}} } \]. The four experimental treatments were as follows: fasted for 36 h (A); fasted (36 h) and refed with glucose (B) or glycerol (C); postabsorptive (overnight fast, D). In B and C the subjects were given a drink containing glucose or glycerol (lg per kg body weight) 45 min before starting exercise. A placebo drink was given 45 min before exercise on treatments A and D. Despite an increased availability of circulating free fatty acids, -hydroxybutyrate and glycerol exercise time to exhaustion was significantly lower after fasting (treatment A 77.7±6.8 min) compared with treatment D (119.5±5.8 min). Refeeding with glucose or glycerol did not significantly improve performance (92.4±11.8 min and 80.8±3.6 min respectively) compared with treatment A and lowered circulating levels of FFA and — HB during exercise compared with A. Despite the probability of low liver glycogen levels after fasting, none of the subjects became hypoglycaemic (blood glucose <4 mmol · l^–1) during exercise and their blood lactate concentrations were not high at exhaustion. Plasma levels of branched chain amino acids (BCAA) decreased progressively during exercise on treatments A, B and C and were considerably lower at exhaustion compared with treatment D. Falling plasma concentrations of BCAA during prolonged exercise may be implicated in the generation of central fatigue.     

Administration of branched-chain amino acids during sustained exercise — effects on performance and on plasma concentration of some amino acids

Summary Previous studies have shown that sustained exercise in human subjects causes an increase in the plasma concentration ratio of free tryptophan: other large neutral amino acids [including the branched-chain amino acids (BCAA)]. This should favour the transport of tryptophan into the brain and also the synthesis of 5-hydroxytryptamine, which is thought to contribute to fatigue during prolonged exercise. A mixture of the three BCAA was given to subjects during a 30-km cross-country race or a marathon (42.2 km) and the effects on mental and physical performances were measured. The mental performance, measured as the performance in the Stroop Colour and Word Test (CWT), was improved after, as compared to before the 30-km cross-country race when a BCAA supplement was given during the race, whereas the CWT scores were similar before and after in the placebo group. The running performance in the marathon was improved for the slower runners (3.05 h–3.30 h) when BCAA was taken during the race; however, there was no significant effect on the performance in the faster runners (<3.05 h). The results showed that both mental and physical performance was improved by an intake of BCAA during exercise. In addition, the effects of exercise on the plasma concentration of the aromatic amino acids were altered when a BCAA supplement was given during the marathon.     

Effects of dietary leucine supplementation on exercise performance

Branched chain amino acids (BCAA), particularly leucine, have been suggested to be ergogenic for both endurance and strength/power performance. This study investigated the effects of dietary leucine supplementation on the exercise performance of outrigger canoeists. Thirteen (ten female, three male) competitive outrigger canoeists [aged 31.6 (2.2) year, VO_2max 47.1 (2.0) ml kg⁻¹ min⁻¹] underwent testing before and after 6-week supplementation with either capsulated L-leucine (45 mg kg⁻¹ d⁻¹; n=6) or placebo (cornflour; n=7). Testing included anthropometry, 10 s upper body power and work and a row to exhaustion at 70–75% maximal aerobic power where perceived exertion (RPE), heart rate (HR) and plasma BCAA and tryptophan concentrations were assessed. Leucine supplementation resulted in significant increases in plasma leucine and total BCAA concentrations. Upper body power and work significantly increased in both groups after supplementation but power was significantly greater after leucine supplementation compared to the placebo [6.7 (0.7) v. 6.0 (0.7) W kg⁻¹]. Rowing time significantly increased [77.6 (6.3)–88.3 (7.3) min] and average RPE significantly decreased [14.5 (1.5)–12.9 (1.4)] with leucine supplementation while these variables were unchanged with the placebo. Leucine supplementation had no effect on the plasma tryptophan to BCAA ratio, HR or anthropometric variables. Six weeks’ dietary leucine supplementation significantly improved endurance performance and upper body power in outrigger canoeists without significant change in the plasma ratio of tryptophan to BCAA.Parts of this work have previously been presented in abstract form: Crowe MJ, Weatherson JN (2002) The effects of dietary L-leucine supplementation on exercise performance. Sports Medicine and Science at the Extremes. Australian Conference of Science and Medicine in Sport. 12–16 October, Melbourne, Australia     

Influence of supplementation with branched-chain amino acids in combination with resistance exercise on p70S6 kinase phosphorylation in resting and exercising human skeletal muscle

Aim: Skeletal muscle growth is thought to be regulated by the mammalian target of rapamycin (mTOR) pathway, which can be activated by resistance exercise and branched-chain amino acids (BCAA). The major aim of the present study was to distinguish between the influence of resistance exercise and BCAA on key enzymes considered to be involved in the regulation of protein synthesis, including p70^S6 kinase (p70^S6k). Methods: Nine healthy subjects (four men and five women) performed unilateral resistance exercise on two occasions separated by 1 month. Subjects were randomly supplied either a mixture of BCAA or flavoured water. Muscle biopsies were taken from both resting and exercising muscle before, after and 1 h after exercise. Results: Phosphorylation of Akt was unaltered by either resistance exercise and/or BCAA supplementation whereas mTOR phosphorylation was enhanced (P < 0.05) to a similar extent in both exercising and resting muscle following exercise in the absence (70–90%) and presence of BCAA supplementation (80–130%). Phosphorylation of p70^S6k was unaffected by resistance exercise alone; however, BCAA intake increased (P < 0.05) this phosphorylation in both legs following exercise. In resting muscle, a 5- and 16-fold increase in p70^S6k was observed immediately after and 1 h after exercise, respectively, as compared to 11- and 30-fold increases in the exercising muscle. Phosphorylation of eukaryotic elongation factor 2 was attenuated 1 h after exercise (P < 0.05) in both resting (10–40%) and exercising muscle (30–50%) under both conditions. Conclusion: The present findings indicate that resistance exercise and BCAA exert both separate and combined effects on the p70^S6k phosphorylation in an Akt-independent manner.     

Zum Mechanismus der ökonomischen Halteleistung eines glatten Muskels (Byssus retractor anterior,Mytilus edulis)

Summary Freeze-dried fibre-bundles (GF) of the anterior byssus retractor muscle (ABRM) ofMytilus develop in Ca²⁺-containing ATP-salt-solution almost the same isometric tension as the surviving muscle and maintain the same tension remnant when Ca²⁺ is deprived. The ratio ATPase/tension of Ca²⁺-activated GF (0.15 mcal/sec × kg tension × cm fibre at 20°C, determined from ATPase measurements) corresponds to the heat of maintenance of living muscle in tetanus (0.07 mcal/see × kg × cm), while it is nearly zero when GF are in the catch state in Ca²⁺-free solution.Contrary to isometric tension and tension remnant, the energy expenditure and speed of tension development depend on temperature (Q ₁₀3); moreover the ratio ATPase/tension of Ca²⁺-activated GF decreases to 70% as the extent of the caught state increases in the course of three successive periods of contraction. But it increases again to the former level when the catch is abolished.These findings are discussed in relation to the Paramyosin-theory of catch. With regard to the typical ultrastructure of caught muscle fibres it is suggested that their increased economy is based on interaction of the thick paramyosinfilaments.

     

Plasma FFA responses to prolonged walking in untrained men and women

Summary Gender differences in plasma FFA responses to 90 min of treadmill walking at 35% were investigated in six men and six women following an overnight fast. The subjects represented average values for maximal oxygen uptake and body fat percentage for age and gender. Mean plasma FFA concentration at 45 and 90 min of exercise were significantly (P<0.05) higher for women (0.82 mmol·l^–01, 0.88 mmol·l^–01) than men (0.42 mmol·l^–01, 0.59 mmol·l^–1). Lower R values for women throughout the exercise period indicated a greater percentage fat in total metabolism than for men while the FFA/glycerol results supported greater lipolytic activity for women. The uniformity of percent fat in metabolism for women from rest to exercise showed that FFA release from adipose tissue increased rapidly with the onset of exercise which was not the case for men. Comparison of metabolic data as well as a statistical analysis (ANCOVA) controlling for the influence of and percentage body fat on FFA plasma concentration suggested that gender differences in FFA responses to prolonged submaximal exercise can be expected to occur in untrained subjects.     

Effect of carnitine loading on long-chain fatty acid oxidation,maximal exercise capacity,and nitrogen balance

Summary Carnitine has a potential effect on exercise capacity due to its role in the transport of long-chain fatty acids into the mitochondria for-oxidation, the export of acyl-coenzyme A compounds from mitochondria and the activation of branched-chain amino acid oxidation in the muscle. We studied the effect of carnitine supplementation on palmitate oxidation, maximal exercise capacity and nitrogen balance in rats. Daily carnitine supplementation (500 mg - kg^–1 body mass for 6 weeks) was given to 30 rats, 15 of which were on an otherwise carnitine-free diet (group 1) and 15 pair-fed with a conventional pellet diet (group II). A control group (group III,n = 6) was fed ad libitum the pellet diet. Palmitate oxidation was measured by collecting¹⁴CO₂ after an intraperitoneal injection of [1-¹⁴C]palmitate and exercise capacity by swimming to exhaustion. After carnitine supplementation carnitine concentrations in serum were supranormal [group I, total 150.8 (SD 48.5), free 78.9 (SD 18.4); group II, total 170.9 (SD 27.9), free 115.8 (SD 24.6) gmol·1^–1] and liver carnitine concentrations were normal in both groups [group I, total 1.6 (SD 0.3), free 1.2 (SD 0.2); group II, total 1.3 (SD 0.3), free 0.9 (SD 0.2) mol·g^–1 dry mass]. In muscle carnitine concentrations were normal in group I [total 3.8 (SD 1.2), free 3.2 (SD 1.0) mol · g^–1 dry mass] and increased in group II [total 6.6 (SD 0.5), free 4.9 (SD 0.9) mol·g^–1 dry mass]. Despite the difference in muscle carnitine concentrations there were no differences among the groups in cumulative palmitate oxidation after 3 h [group I, 39.7 (SD 11.6)%, group II, 29.6 (SD 14.0)%; group III, 36.5 (SD 10.8)% of injected activity] or swimming time to exhaustion [group I, 9.7 (SD 2.9); group II, 8.4 (SD 3.6); group III, 7.1 (SD 2.8) h]. A borderline increase in nitrogen balance was observed in group II. We concluded that increasing carnitine tissue concentrations by carnitine supplementation had no effect on palmitate oxidation and maximal exercise capacity in the rats studied.     

An energy balance of front crawl

With the aim of computing a complete energy balance of front crawl, the energy cost per unit distance (C= v^–1, where is the metabolic power and v is the speed) and the overall efficiency (_o=W_tot/C, where W_tot is the mechanical work per unit distance) were calculated for subjects swimming with and without fins. In aquatic locomotion W_tot is given by the sum of: (1) W_int, the internal work, which was calculated from video analysis, (2) W_d, the work to overcome hydrodynamic resistance, which was calculated from measures of active drag, and (3) W_k, calculated from measures of Froude efficiency (_F). In turn, _F=W_d/(W_d+W_k) and was calculated by modelling the arm movement as that of a paddle wheel. When swimming at speeds from 1.0 to 1.4 m s^–1, _F is about 0.5, power to overcome water resistance (active body drag × v) and power to give water kinetic energy increase from 50 to 100 W, and internal mechanical power from 10 to 30 W. In the same range of speeds increases from 600 to 1,200 W and C from 600 to 800 J m^–1. The use of fins decreases total mechanical power and C by the same amount (10–15%) so that _o (overall efficiency) is the same when swimming with or without fins [0.20 (0.03)]. The values of _o are higher than previously reported for the front crawl, essentially because of the larger values of W_tot calculated in this study. This is so because the contribution of W_int to W_tot was taken into account, and because _F was computed by also taking into account the contribution of the legs to forward propulsion.     

Lactoferrin,lysozyme, and β2-Microglobulin levels in cerebrospinal fluid

The CSF levels of lactoferrin, lysozyme, and ₂-microglobulin ( ₂ ) were measured in patients with evident, probable, or possible inflammatory CNS reactions and compared to those found in neurologically apparently healthy patients. Patients with viral CNS infections had significantly raised ₂ and lysozyme levels but normal lactoferrin levels, indicating a local activation of lymphocytes and monocytes but not of granulocytes. Patients with bacterial CNS infections had significantly raised levels of all three cell markers, but the increase of lysozyme and lactoferrin was relatively more pronounced than that of ₂ , indicating that the inflammatory response to bacterial agents is dominated by monocytes and granulocytes. Patients with primary or secondary malignant brain tumors were characterized by a moderate increase of ₂ and a considerable increase in both lysozyme and lactoferrin, i.e., the same protein pattern as observed in bacterial CNS infection. The lysozyme levels were moderately increased in half the patients with benign cerebral tumors while the levels of ₂ and lactoferrin were normal, indicating that benign and malignant brain tumors induce different local inflammatory CNS reactions. Half the patients with pituitary gland adenoma had elevated ₂ and lysozyme levels but normal lactoferrin levels, suggesting that immunological mechanisms are associated with the adenoma development. Patients with MS had moderately but significantly raised CSF levels of ₂ and lysozyme and a third of them also had raised levels of lactoferrin, a protein pattern suggesting a low-active inflammatory process in CNS involving mononuclears and granulocytes. A similar protein pattern was found in Guillain-Barré syndrome. In cerebrosarcoidosis we noted considerably increased lysozyme and ₂ but normal lactoferrin levels, consistent with the idea that the sarcoid granuloma mass is dominated by monocytic inflammatory cells. The data obtained indicate a clinical value of lactoferrin, lysozyme, and ₂ as differential indices of inflammatory cell reactions taking place in various CNS processes.     

Effects of serine protease inhibitor,tame, on IL-1β in LPS-stimulated human monocytes: Relationship between synthesis and release of a 33-kDa precursor and the 17-kDa biologically active species

LPS stimulation of human monocytes in vitro induced release of the 17-kDa mature IL-1 (mIL-1) but did not result in release of precursor IL-1 (pIL-1). In contrast, the presence of a serine protease inhibitor, N-(p-toluene sulfonyl)-L-arginine methyl ester (TAME; 10 mM) for 6 or 18 h was associated with the LPS-stimulated release of the 33-kDa pIL-1 as well. These effects were initially discerned from observations that the fraction of the total IL-1 produced (as detected by ELISA) that was released from monocytes increased in the presence of TAME, and immunoblot assays confirmed that this fraction was predominantly 33-kDa IL-1. A global decrease in monocyte protein synthesis was also observed after prolonged (18-h) exposure to TAME and was associated with a decrease in IL-1 synthesis, predominantly affecting 31-kDa pIL-1, and a dose-dependent inhibition of TNF- production. Parallel examination of lactate dehydrogenase (LDH) release indicated thatpIL-1 release was unrelated to cell lysis. These results demonstrate that TAME-inhibitable serine proteases are probably involved in the production and eventual proteolysis of the 33-kDa pIL-1 in situ but are probably not mechanistically related to either maturation of the IL-1 molecule or signaling of IL-1 release. IL-1 release appears to be dependent on the amount of total IL-1 synthesized. Serine proteolysis may constitute a degradative pathway for excess precursor, which, if interfered with, could result in release of the higher-molecular-weight forms of IL-1.     

Influence of a 24 h fast on high intensity cycle exercise performance in man

Summary The influence of a 24 h fast on endurance performance and the metabolic response to maximal cycle exercise was investigated in 6 healthy men (mean±SD: age = 21±7 years; weight = 73±10 kg; = 46±10 ml·kg^–1·min^–1). Subjects performed in randomised order two exercise bouts to exhaustion separated by one week. Test rides were performed in fasted (F) and post-absorptive (normal-diet, ND) conditions on an electrically braked cycle ergometer at a workload equivalent to 100% of . Acid-base status and selected metabolites were measured on arterialised venous blood at rest prior to exercise and at intervals for 15 mins following exercise. Exercise time to exhaustion was shorter after F compared with ND (p<0.01). Pre-exercise blood bicarbonate (HCO₃ ^–) concentration, and base excess (BE) were lower after F compared with ND (p<0.05). Prior to exercise, circulating concentrations of free fatty acids (FFA), gb-hydroxybutyrate (B-HB) and glycerol were higher after F compared with ND (p<0.01) but blood glucose and lactate concentration were not different. On the F treatment, after exercise, blood pH, HCO₃ ^–, and BE were all significantly higher (p<0.01) than on ND; blood lactate concentration was significantly lower for the whole of the post-exercise period after F compared with ND (p<0.01). Circulating levels of FFA and B-HB after exercise on the F treatment fell but levels of these substrates were not altered by exercise after ND. Blood glucose and glycerol concentrations increased following exercise on both treatments. The present study provides evidence that a 24 h fast is detrimental to high-intensity exercise performance and possibly influences the metabolic response following maximal cycle exercise. These changes may be related to the altered pre-exercise acid-base status and/or a change in the pattern of substrate utilisation.     

Regional differences in the lipolytic response of the subcutaneous fat depots to prolonged exercise and severe energy deficiency

Summary After five days of almost continuous strenuous combat exercise and energy deficiency, 12 well-trained young men had a mean body fat loss of 2.7 kg and the average fat cell size was reduced from 0.34 g to 0.24 g. No significant changes were found in the total number of fat cells. For the group as a whole, the decrease in fat cell size was most pronounced in the gluteal subcutaneous region, followed by the abdominal region. No significant decrease in fat cell size was encountered in tissue samples from the femoral site. Before the course, and on the last day, the subjects accomplished a short-term bicycle exercise at 50% of the individual's . On day 5, positive correlations were found between the fat cell weights estimated in the gluteal tissue samples and the pre-exercise free fatty acid (FFA) levels (r=0.87, p<0.01), and also with the plasma free glycerol obtained five minutes after the bicycle exercise (r=0.93, p<0.001). These correlations were not apparent in the control experiment performed before the course. Further, no such relationship was found between the plasma metabolites and the fat cell size of the other body sites investigated. This finding may indicate that gluteal fat deposits are more important for energy provision than abdominal and, especially, femoral deposits.     

Blood metabolites during prolonged exercise in swimming and leg cycling

Summary This study was designed to compare the influence of two modes of exercise (swimming and leg cycling) on the blood concentrations of metabolic substrates and metabolites during a 45-min exercise period. Eight college students (mean age=21.6±1.2 year) exercised at 70% of O₂ max, in water using the front crawl on one occasion, and on a cycle ergometer using the legs on another. Blood samples were drawn at 0,15, 30, and 45 min and analyzed for free fatty acids, glycerol, glucose, pyruvate, and lactate concentrations. Mean oxygen uptakes (2.23 vs 2.12 l·min^–1) and heart rates (152 vs 150 b·min^–1) for cycling and swimming respectively were not significantly different. Lactate and pyruvate were significantly (p<0.01) higher during swimming as compared to cycling. Free fatty acids, glycerol, and glucose were not significantly different between the two modes of exercise (p>0.05). Assuming venous blood concentrations provide some indication of metabolic events, these data are compatible with a tendency to a higher relative carbohydrate oxidation rate during swimming as compared to cycling during prolonged exercise at the same relative work intensities.Supported by grand from C.A.F.I.R., Université de Montréal     

Effects of training on plasma FFA during exercise in women

Summary The purpose of this study was to investigate the effects of training on plasma FFA concentrations in women during 60 min of work. All subjects (n=10) exercised at 55% of their initial VO_{2 max} for 60 min on a bicycle ergometer. Five subjects then participated in a training program, consisting of bicycling five days per week for four weeks while five control subjects remained inactive. Following the training or control period, all 10 subjects repeated the initial 1-h test at the same absolute work load. The training program resulted in a 14% increase in VO_{2 max} and a decreased resting HR (p<0.05). The submaximal exercise HR and R were also lower following training (p<0.05). Plasma FFA were significantly lower (p<0.05) during exercise in the experimental group following training. The average increase in plasma FFA during the 60 min bicycle test was 0.22 mol/l, from 0.48 mol/l at rest to 0.70 mol/l after 60 min of exercise prior to training. After training the same absolute work load resulted in an increased plasma FFA of only 0.10 mol/l from 0.29 to 0.39 mol/l. No significant changes due to training were observed for glycerol or lactate. The results suggest that the metabolic response of women is similar to men during exercise before and after training. Possible mechanisms for the decreased plasma FFA response after training are discussed.     

Catecholamines,lymphocyte subsets,and cyclic adenosine monophosphate production in mononuclear cells and CD4+ cells in response to submaximal resistance exercise

We examined the effect of 30 min of submaximal resistance exercise on free and sulphoconjugated plasma catecholamine concentrations determined by high performance (-pressure) liquid chromatography separation, the distribution of circulating lymphocytes quantified by flow cytometry, and isoproterenol induced cyclic adenosine monophosphate (cAMP) production in mononuclear cells (MNL) and CD4⁺ cells. Venous blood samples were taken before, immediately after and 45 min after exercise. Resistance exercise increased free plasma adrenaline (A) and noradrenaline (NA) concentrations, whereas sulphoconjugated catecholamine concentrations remained unchanged. Exercise induced leucocytosis and lymphocytosis was predominantly manifested by an increase in the number of total lymphocytes, monocytes, CD3⁺, CD8⁺ cells and CD3^– CD16/CD56^– cells. Redistribution resulted in a decrease in the CD4^–: CD8⁺ ratio. The total number and distribution of lymphocytes returned to baseline after 45-min rest. An exercise-induced increase in the number of CD3^– CD16/CD56⁺ cells was significantly correlated with the increase in plasma NA (r = 0.66;P = 0.035), indicating a NA dependent process of redistribution. The cAMP-production in MNL was significantly elevated after resistance exercise, when cells were stimulated with 1 mol·1^–1 isoproterenol [pre-exercise 16.5 (SD 3.3); postexercise 21.6 (SD 9.8); 45 min postexercise 10.7 (SD 2.8)]. The cAMP production in CD4⁺ cells was not affected by exercise. Therefore, it is discussed whether redistribution is responsible for the exercise induced increase in cAMP production in MNL.     

Carbohydrate and fat metabolism of unacclimatized men during and after submaximal exercise in cool and hot environments

Summary Changes in levels of plasma lactate, pyruvate, glucose, free fatty acids (FFA), glycerol and 3-hydroxybutyrate during muscular exercise and recovery in cool (ambient temperature T _a = 23 C and water vapor pressure P _w = 13 mb) and hot environments (T _a = 40 C, P _w = 30 mb) were measured in six subjects. Arterial blood samples were collected at fixed time intervals during an initial resting phase of 75 min, an exercise period of 20 min and a recovery period of 125 min. Exercise consisted in pedaling a bicycle ergometer in the supine position at a work load that raised the heart pulse rate to nearly 140 beats min^–1 in the cool condition. Heart rate and rectal temperature were significantly higher during exercise and recovery in the hot environment. For samples collected at corresponding times in the cool and the hot conditions, the deviations of the observed blood parameters from their mean values during the whole resting phase seldom differed. However, for the exercise phase as a whole, the mean increases of lactate, pyruvate and glycerol were significantly greater and the mean decrease of glucose significantly smaller, in the hot condition, while the mean decreases of FFA and 3-hydroxybutyrate did not differ significantly. Related to their corresponding mean resting values, the mean changes in all six blood parameters measured were significantly larger during recovery in the hot condition than in the cool. These results verify the enhanced anaerobic metabolism in hot environment already described by previous authors, and show an adipokinetic and hyperglycemic effect of acute exposure to heat.     

Influence of environmental temperature on exercise-induced inspiratory muscle fatigue

Exercise in the heat has detrimental effects on circulation that might negatively influence endurance performance. If blood is diverted away from the inspiratory muscles to the skin during exercise in the heat, exercise-induced inspiratory muscle fatigue might be exacerbated. Thus, we hypothesised that prolonged heavy endurance exercise in the heat would impair exercise performance and exacerbate inspiratory muscle fatigue compared to exercise in a thermo-neutral environment. Using a crossover design, seven male endurance trained subjects [mean (SEM) maximum oxygen uptake = 62.2 (1.5) ml·kg^–1·min^–1] were assigned at random to either a group that exercised in the heat at an ambient temperature of 35°C (H) or a group that exercised in the cool at 15°C (C). Maximum inspiratory mouth pressure at zero flow (P ₀), pressure normalised maximum relaxation rate (MRR/P ₀), time constant for the pressure decay (), and maximum inspiratory flow at 30% P ₀ ( ₃₀) were assessed immediately before and reassessed within 2, 30, and 60 min of completing a pre-loaded time trial [40 min at 65% peak power, plus ~30 min time trial] on a cycle ergometer . Group H completed the time trial 432 (135) s slower than group C [2,285 (180) vs 1,852 (122) s, respectively; =24 (8)%, P=0.0094]. Repeat measurements within 2 min post-exercise revealed significant declines in P ₀, MRR/P ₀, , and ₃₀ from baseline values, but no between-group differences were observed. In conclusion, heavy sustained exercise in the heat impaired subsequent time-trial performance but did not exacerbate inspiratory muscle fatigue in endurance-trained subjects.     

Inhibition of the release of soluble tumor necrosis factor receptors in experimental endotoxemia by an anti-tumor necrosis factor-α antibody

The role of tumor necrosis factor- in the shedding of soluble tumor necrosis factor receptors in endotoxemia was investigated. The appearance of the soluble tumor necrosis factor receptors was assessed in four healthy volunteers following an intravenous injection of tumor necrosis factor- and in eight chimpanzees after intravenous administration of endotoxin in the absence or presence of concurrent treatment with a neutralizing anti-tumor necrosis factor- monoclonal antibody. Injection of tumor necrosis factor- in humans elicited a significant, instantaneous (after 15 min) increase in the plasma concentrations of both types of soluble tumor necrosis factor receptors. In chimpanzees, treatment with the anti-tumor necrosis factor- antibody completely neutralized endotoxin-induced tumor necrosis factor- activity. The release of soluble tumor necrosis factor receptors was strongly (80–90%) inhibited in the presence of the neutralizing antibody. Our results indicate that tumor necrosis factor- is a prime mediator of endotoxin-induced release of its own soluble receptors.