Effect of varying light intensity on maximal power production and selected metabolic variables

This study was designed to examine the effect of exposure to two levels of light intensity (bright; 5000 lux, dim; 50 lux) prior to supramaximal cycle exercise on performance and metabolic alterations. The exercise was performed after bright and dim light exposure for 90 minutes. Ten male long-distance runners volunteered to take part in the study. They performed 45-sec supramaximal exercise using a cycle ergometer in a 500-lux. Mean power output was measured during the exercise. Lactate and ammonia in the blood and epinephrine and norepinephrine concentrations in plasma were measured at rest immediately after bright and dim light exposures and after the exercise. Bright and dim light exposure prior to exercise did not significantly affect the power output during the exercise. Blood glucose concentration immediately after exercise and plasma epinephrine during the resting period were significantly lower after bright light exposure compared with dim light exposure (p < 0.05). No significant difference was found in blood lactate, ammonia, or plasma norepinephrine levels after exercise following bright and dim light exposures. This study demonstrated that bright light stimulation prior to supramaximal exercise decreases glucose and epinephrine levels, but is not related to physical performance.     

Plasma catecholamine and lactate response during graded exercise with varied glycogen conditions.

The relationships between the lactate threshold (TLa), plasma catecholamines, and ventilatory threshold (TVE) were examined under normal and glycogen-depleted conditions. Nine male subjects performed a graded exercise test on a bicycle ergometer in a normal glycogen (NG) state and in a glycogen-depleted (GD) state to determine if manipulation of muscle glycogen content would affect their ventilatory, lactate, and catecholamine responses. High correlations were found between plasma lactate and the two catecholamines, epinephrine (r = 0.964) and norepinephrine (r = 0.965) under both conditions. The GD protocol resulted in a shift in the TLa to a later work rate; inflections in epinephrine and norepinephrine shifted in a coordinated manner. TVE and TLa occurred at similar work loads under NG conditions [67.2 +/- 1.5 and 65.6 +/- 2.3% maximal oxygen consumption (VO2max), respectively], but TLa occurred at a later work load (75.3 +/- 1.9% VO2max) compared with TVE (68.3 +/- 1.6% VO2max) under GD conditions. These results suggest a causal relationship between plasma lactate and epinephrine during a graded exercise test under the glycogen conditions studied. Although an association existed between ventilation and lactate, this relationship was not as strong.     

Effect of increased central blood volume with water immersion on plasma catecholamines during exercise

To examine the influence of an increase in central blood volume with head-out water immersion (WI) on the sympathoadrenal response to graded dynamic exercise, nine healthy men underwent upright leg cycle exercise on land and with WI. Plasma norepinephrine and epinephrine concentrations were used as indexes of overall sympathoadrenal activity. Oxygen consumption (VO2), heart rate, systolic blood pressure, and plasma concentrations of norepinephrine, epinephrine, and lactate were determined at work loads corresponding to approximately 40, 60, 80, and 100% peak VO2. Peak VO2 did not differ on land and with WI. Plasma norepinephrine concentration was reduced (P less than 0.05) at 80 and 100% peak VO2 with WI and on land, respectively. Plasma epinephrine and lactate concentrations were similar on land and with WI at the three submaximal work stages, but both were reduced (P less than 0.05) at peak exertion with WI. Heart rate was lower (P less than 0.05) at the three highest work intensities with WI. These results suggest that the central shift in blood volume with WI reduces the sympathoadrenal response to high-intensity dynamic exercise.     

The ventilation, lactate and electromyographic thresholds during incremental exercise tests in normoxia, hypoxia and hyperoxia

These experiments examined the effect of hypoxia and hyperoxia on ventilation, lactate concentration and electromyographic activity during an incremental exercise test in order to determine if coincident chances in ventilation and electromyographic activity occur during an incremental exercise test, despite an enhancement or reduction of peripheral chemoreceptor activity. In addition, these experiments were completed to determine if electromyographic activity and ventilation are enhanced or reduced in response to the inspiration of oxygen-depleted and oxygen-enriched air, respectively. Seven subjects performed three incremental exercise tests, until volitional exhaustion was achieved, while inspiring air with a fractional concentration of oxygen of either 66%, 21% or 17%. In addition, another single subject completed two tests while inspiring air with a fractional concentration of either 17% or 21%. During the tests, ventilation, mixed expired oxygen and carbon dioxide, arterialized venous blood and the electromyographic activity from the vastus lateralis were sampled. From these values ventilation, electromyographic and lactate thresholds were detected during normoxia, hypoxia and hyperoxia. The results showed that although ventilation and lactate concentration were significantly less during hyperoxia as compared to normoxia or hypoxia, the carbon dioxide production values were not significantly different between the normoxic, hypoxic and hyperoxic conditions. For a particular condition, the time, carbon dioxide production and oxygen consumption values that corresponded to the ventilation and electromyographic thresholds were not significantly different, but the values corresponding to the lactate threshold were significantly less than those for the electromyographic and ventilation thresholds. Comparisons between the three conditions showed that the time, carbon dioxide production and oxyen consumption values corresponding to each of these thresholds were not significantly different. These findings have led us to conclude that the changes in lactate concentration observed during exercise may not be directly related to the fractional concentration of inspired oxygen, and that the peripheral chemoreceptors may not be the sole mediators of the first ventilatory threshold. It is suggested that this threshold may be mediated by an increase in neural activity originating from higher motor centers or the exercising limbs, induced in response to the need to progressively recruit fast twitch muscle fibers as exercise power output is increased and as individual muscle fibers begin to fatigue.     

Increased blood ammonia in hypoxia during exercise in humans

The effect of acute hypoxia on blood concentration of ammonia ([NH3]b) and lactate (la-]b) was studied during incremental exercise(IE), and two-step constant workload exercises (CE). Fourteen endurance-trained subjects performed incremental exercise on a cycle ergometer under normoxic (21% O2) and hypoxic (10.4% O2) conditions. Eight endurance-trained subjects performed two-step constant workload exercise at sea level and at a simulated altitude of 5000 m (hypobaric chamber, P(B)=405 Torr; P(O2)=85 Torr) in random order. In normoxia, the first step lasted 25 minutes at an intensity of 85 % of the individual ventilatory anaerobic threshold (AT(vent), ind) at sea level. This reduced workload was followed by a second step of 5 minutes at 115% of their AT(vent), ind. This test was repeated into a hypobaric chamber, at a simulated altitude of 5,000 m. The first step in hypoxia was at an intensity of 65 % of AT(vent), ind., whereas workload for the second step at simulated altitude was the same as that of the first workload in normoxia (85 % of AT(vent), ind). During IE, [NH3]b and [la-]b were significantly higher in hypoxia than in normoxia. Increases in these metabolites were highly correlated in each condition. The onset of [NH3]b and [la-]b accumulation occurred at different exercise intensity in normoxia (181W for lactate and 222W for ammonia) and hypoxia (100W for lactate and 140W for ammonia). In both conditions, during CE, [NH3]b showed a significant increase during each of the two steps, whereas [la-]b increased to a steady-state in the initial step, followed by a sharp increase above 4 mM x L(-1) during the second. Although exercise intensity was much lower in hypoxia than in normoxia, [NH3]b was always higher at simulated altitude. Thus, for the same workload, [NH3]b in hypoxia was significantly higher (p<0.05) than in normoxia. Our data suggest that there is a close relationship between [NH3]b and [la-]b in normoxia and hypoxia during graded intensity exercises. The accumulation of ammonia in blood is independent of that of lactate during constant intense exercise. Hypoxia increases the concentration of ammonia in blood during exercise.     

Early adaptations in blood substrates, metabolites, and hormones to prolonged exercise training in man.

This study was designed to investigate the effect of short-term, submaximal training on changes in blood substrates, metabolites, and hormonal concentrations during prolonged exercise at the same power output. Cycle training was performed daily by eight male subjects (VO2max = 53.0 +/- 2.0 mL.kg-1.min-1, mean +/- SE) for 10-12 days with each exercise session lasting for 2 h at an average intensity of 59% of VO2max. This training protocol resulted in reductions (p less than 0.05) in blood lactate concentration (mM) at 15 min (2.96 +/- 0.46 vs. 1.73 +/- 0.23), 30 min (2.92 +/- 0.46 vs. 1.70 +/- 0.22), 60 min (2.96 +/- 0.53 vs. 1.72 +/- 0.29), and 90 min (2.58 +/- 1.3 vs. 1.62 +/- 0.23) of exercise. The reduction in blood lactate was also accompanied by lower (p less than 0.05) concentrations of both ammonia and uric acid. Similarly, following training lower concentrations (p less than 0.05) were observed for blood beta-hydroxybutyrate (60 and 90 min) and serum free fatty acids (90 min). Blood glucose (15 and 30 min) and blood glycerol (30 and 60 min) were higher (p less than 0.05) following training, whereas blood alanine and pyruvate were unaffected. For the hormones insulin, glucagon, epinephrine, and norepinephrine, only epinephrine and norepinephrine were altered with training. For both of the catecholamines, the exercise-induced increase was blunted (p less than 0.05) at both 60 and 90 min. As indicated by the changes in blood lactate, ammonia, and uric acid, a depression in glycolysis and IMP formation is suggested as an early adaptive response to prolonged submaximal exercise training.     

Effects of pre-exercise listening to slow and fast rhythm music on supramaximal cycle performance and selected metabolic variables

We examined the effect of listening to two different types of music (with slow and fast rhythm), prior to supramaximal cycle exercise, on performance, heart rate, the concentration of lactate and ammonia in blood, and the concentration of catecholamines in plasma. Six male students participated in this study. After listening to slow rhythm or fast rhythm music for 20 min, the subjects performed supramaximal exercise for 45 s using a cycle ergometer. Listening to slow and fast rhythm music prior to supramaximal exercise did not significantly affect the mean power output. The plasma norepinephrine concentration immediately before the end of listening to slow rhythm music was significantly lower than before listening (p < 0.05). The plasma epinephrine concentration immediately before the end of listening to fast rhythm music was significantly higher than before listening (p < 0.05). The type of music had no effect on blood lactate and ammonia levels or on plasma catecholamine levels following exercise. In conclusion, listening to slow rhythm music decreases the plasma norepinephrine level, and listening to fast rhythm music increases the plasma epinephrine level. The type of music has no impact on power output during exercise.     

Influence of cold exposure on blood lactate response during incremental exercise

This study examined the effect of acute exposure of the whole body to cold on blood lactate response during incremental exercise. Eight subjects were tested with a cycle ergometer in a climatic chamber, room temperature being controlled either at 24 degrees C (MT) or at -2 degrees C (CT). The protocol consisted of a step increment in exercise intensity of 30 W every 2 min until exhaustion. Oxygen consumption (VO2) was measured at rest and during the last minute of each exercise intensity. Blood samples were collected at rest and at exhaustion for estimations of plasma norepinephrine (NE), epinephrine (E), free fatty acid (FFA) and glucose concentrations, during the last 15 s of each exercise step and also during the 1st, 4th, 7th, and the 10th min following exercise for the determination of blood lactate (LA) concentration. The VO2 was higher during CT than during MT at rest and during nearly every exercise intensity. At CT, lactate anaerobic threshold (LAT), determined from a marked increase of LA above resting level, increased significantly by 49% expressed as absolute VO2, and 27% expressed as exercise intensity as compared with MT. The LA tended to be higher for light exercise intensities and lower for heavy exercise intensities during CT than during MT. The E and NE concentrations increased during exercise, regardless of ambient temperature. Furthermore, at rest and at exhaustion E concentrations did not differ between both conditions, while NE concentrations were greater during CT than during MT. Moreover, an increase off FFA was found only during CT.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of plasma catecholamines on the lactate threshold during graded exercise

This investigation examined the relationship among plasma catecholamines, the blood lactate threshold (TLa), and the ventilatory threshold (TVE) in highly trained endurance athletes. Six competitive cyclists and six varsity cross-country runners performed a graded exercise test via two different modalities: treadmill running and bicycle ergometry. Although maximal oxygen consumption (VO2 max) did not differ significantly for the cyclists for treadmill running and cycling (64.6 +/- 1.0 and 63.5 +/- 0.4 ml O2.kg-1-min-1, respectively), both TLa and TVE occurred at a relatively earlier work load during the treadmill run. The opposite was true for the runners as TLa and TVE appeared at an earlier percent of VO2max during cycling compared with treadmill running (60.0 +/- 1.7 vs. 75.0 +/- 4.0%, respectively, TLa). The inflection in plasma epinephrine shifted in an identical manner and occurred simultaneously with that of TLa (r = 0.97) regardless of the testing protocol or training status. Although a high correlation (r = 0.86) existed for the shift in TVE and TLa, this relationship was not as strong as was seen with plasma epinephrine. The results suggest that a causal relationship existed between the inflection in plasma epinephrine and TLa during a graded exercise test. This association was not as strong for TVE and TLa.     

Lactate determination in exercise testing using an electrochemical analyser: with or without blood lysis?

The practical use of lactate electrochemical analysers in exercise testing has not been adequately examined. Initial studies have reported differences in lactate concentration between that measured spectrophotometrically and that measured electrochemically. The study described here was undertaken to compare, using the statistical technique of Bland and Altman (1986), two widely available methods of measuring lactate using lysed and non-lysed blood samples and the lactate thresholds derived from the measured lactate values using a log-log transform technique. Thirteen normal, healthy young adults (11 male) undertook progressive exercise tests to exhaustion. Arterialised venous blood samples were taken each minute and the lactate concentration therein was measured both spectrophotometrically and electrochemically and either with or without lysis of the blood samples. The lactate concentrations measured in lysed blood using both methods (182 pairs) were in close agreement. The electrochemical values obtained using non-lysed blood were systematically lower than spectrophotometric values (206 pairs), the difference becoming progressively greater at higher lactate concentrations. Results for the lactate threshold comparisons are given as mean difference (limits of agreement with 95% probability). Lactate thresholds (12 pairs) derived from lysed blood lactate concentrations measured spectrophotometrically and electrochemically were not significantly different -30 (240) ml O2 x min(-1). Lactate thresholds (11 pairs) derived from lysed spectrophotometric and non-lysed electrochemical measurements were also not significantly different + 20 (250) ml O2 x min(-1). Thus, despite the difference in the measured lactate concentrations, the derived lactate thresholds are in agreement and, therefore, electrochemical analysers can be used for lactate threshold determination using the log-log transform technique without sample lysis.     

The influence of dietary manipulation on plasma ammonia accumulation during incremental exercise in man

The influence of a pattern of exercise and dietary manipulation, intended to alter carbohydrate (CHO) availability, on pre-exercise acid-base status and plasma ammonia and blood lactate accumulation during incremental exercise was investigated. On three separate occasions, five healthy male subjects underwent a pre-determined incremental exercise test (IET) on an electrically braked cycle ergometer. Each IET involved subjects exercising for 5 min at 30%, 50%, 70% and 95% of their maximal oxygen uptake (VO2max) and workloads were separated by 5 min rest. The first IET took place after 3 days of normal dietary CHO intake. The second and third tests followed 3 days of low or high CHO intake, which was preceded by prolonged exercise to exhaustion in an attempt to deplete muscle and liver glycogen stores. Acid-base status and plasma ammonia and blood lactate levels were measured on arterialised venous blood samples immediately prior to and during the final 15 s of exercise at each workload and for 40 min following the completion of each IET. Three days of low CHO intake resulted in the development of a mild metabolic acidosis in all subjects. Plasma ammonia (NH3) accumulation on the low-CHO diet tended to be greater than normal at each exercise workload. Values returned towards resting levels during each recovery period. After the normal and high-CHO diets plasma NH3 levels did not markedly increase above resting values until after exercise at 95% VO2max. Plasma NH3 levels after the high-CHO diet were similar to those after the normal CHO diet.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma catecholamines in the aorta and the phrenicoabdominal vein in exercising dogs

Plasma epinephrine and norepinephrine concentrations were measured in the aorta and phrenicoabdominal vein in five dogs at rest and during short-duration mild- and moderate-intensity exercise and during prolonged mild-intensity exercise. Plasma epinephrine and norepinephrine concentrations increased with exercise in both the aorta and the phrenicoabdominal vein. Plasma epinephrine concentration was much higher in the phrenicoabdominal vein than in the aorta (24-43 times). Plasma epinephrine concentrations in the aorta and phrenicoabdominal vein were significantly correlated (r = 0.88). This confirms that peripheral epinephrine concentration is a reliable index of the activity of the adrenal medulla during exercise. The epinephrine-to-norepinephrine ratio in the phrenicoabdominal vein was stable (4:1) throughout the experimental protocol, suggesting that the proportion of the two amines released by the adrenal medulla did not vary through this range of adrenal activity in dogs.     

Lactate removal ability and graded exercise in humans

Venous lactate concentrations of nine athletes were recorded every 5 s before, during, and after graded exercise beginning at a work rate of 0 W with an increase of 50 W every 4th min. The continuous model proposed by Hughson et al. (J. Appl. Physiol. 62: 1975-1981, 1987) was well fitted with the individual blood lactate concentration vs. work rate curves obtained during exercise. Time courses of lactate concentrations during recovery were accurately described by a sum of two exponential functions. Significant direct linear relationships were found between the velocity constant (gamma 2 nu) of the slowly decreasing exponential term of the recovery curves and the times into the exercise when a lactate concentration of 2.5 mmol/l was reached. There was a significant inverse correlation between gamma 2 nu and the rate of lactate increase during the last step of the exercise. In terms of the functional meaning given to gamma 2 nu, these relationships indicate that the shift to higher work rates of the increase of the blood lactate concentration during graded exercise in fit or trained athletes, when compared with less fit or untrained ones, is associated with a higher ability to remove lactate during the recovery. The results suggest that the lactate removal ability plays an important role in the evolution pattern of blood lactate concentrations during graded exercise.     

The effect of different blood sampling sites and analyses on the relationship~ between exercise intensity and 4.0 mmol ·1? blood lactate concentration

The aim of the study was to examine whether the difference in lactate concentration in different blood fractions is of practical importance when using blood lactate as a test variable of aerobic endurance capacity. Ten male firefighters performed submaximally graded exercise on a cycle ergometer for 20-25 min. Venous and capillary blood samples were taken every 5 min for determination of haematocrit and lactate concentrations in plasma, venous and capillary blood. At the same time, expired air was collected in Douglas bags for determination of the oxygen consumption. A lactate concentration of 4.0 mmol.l-1 was used as the reference value to compare the oxygen consumption and exercise intensity when different types of blood specimen and sampling sites were used for lactate analysis. At this concentration the exercise intensity was 17% lower (P less than 0.01) when plasma lactate was compared to venous blood lactate, and 12% lower (P less than 0.05) when capillary blood lactate was used. Similar discrepancies were seen in oxygen consumption. The results illustrated the importance of standardizing sampling and handling of blood specimens for lactate determination to enable direct comparisons to be made among results obtained in different studies.     

Acute anemia increases lactate production and decreases clearance during exercise

We evaluated whether elevated blood lactate concentration during exercise in anemia is the result of elevated production or reduced clearance. Female Sprague-Dawley rats were made acutely anemic by exchange transfusion of plasma for whole blood. Hemoglobin and hematocrit were reduced 33%, to 8.6 +/- 0.4 mg/dl and 26.5 +/- 1.1%, respectively. Blood lactate kinetics were studied by primed continuous infusion of [U-14C]lactate. Blood flow distribution during rest and exercise was determined from injection of 153Gd- and 113Sn-labeled microspheres. Resting blood glucose (5.1 +/- 0.2 mM) and lactate (1.9 +/- 0.02 mM) concentrations were not different in anemic animals. However, during exercise blood glucose was lower in anemic animals (4.0 +/- 0.2 vs. 4.6 +/- 0.1 mM) and lactate was higher (6.1 +/- 0.4 vs. 2.3 +/- 0.5 mM). Blood lactate disposal rates (turnover measured with recyclable tracer, Ri) were not different at rest and averaged 136 +/- 5.8 mumol.kg-1.min-1. Ri was significantly elevated in both control (260.9 +/- 7.1 mumol.kg-1.min-1) and anemic animals (372.6 +/- 8.6) during exercise. Metabolic clearance rate (MCR = Ri/[lactate]) did not differ during rest (151 +/- 8.2 ml.kg-1.min-1); MCR was reduced more by exercise in anemic animals (64.3 +/- 3.8) than in controls (129.2 +/- 4.1). Plasma catecholamine levels were not different in resting rats, with pooled mean values of 0.45 +/- 0.1 and 0.48 +/- 0.1 ng/ml for epinephrine (E) and norepinephrine (NE), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

狗在运动中的肌糖原消耗与无氧阈的关系

本实验测定了5条狗的无氧阈值,运动耐受时间、衰竭时的血乳酸浓度及运动中的肌糖原消耗量。结果如下:无氧阈值,1.与运动耐受时间呈正相关(r=0.947,P<0.02);2.与运动中肌糖原消耗量呈负相关(r=-0.959,P<0.01);3.与衰竭时的血乳酸浓度呈负相关(r=-0.942,P<0.02)。实验结果提示,无氧阈值是反映机体耐力的可靠指标。而运动中肌糖原消耗少,血乳酸积累程度轻,可能是无氧阈值之所以能够反映机体耐力的物质基础。     

Comparison of blood and saliva lactate level after maximum intensity exercise

Several studies have described high correlation of salivary and blood lactate level during exercise. Measuring the effectiveness and intensity of training, lactate concentration in blood, and lately in saliva are used.The aim of our study was to evaluate the correlation between the concentration and timing of salivary and blood lactate level in endurance athletes and non-athletes after a maximal treadmill test, and to identify physiological and biochemical factors affecting these lactate levels.Sixteen volunteers (8 athletes and 8 non-athletes) performed maximal intensity (Astrand) treadmill test. Anthropometric characteristics, body composition and physiological parameters (heart rate, RR-variability) were measured in both studied groups. Blood and whole saliva samples were collected before and 1, 4, 8, 12, 15, 20 min after the exercise test. Lactate level changes were monitored in the two groups and two lactate peaks were registered at different timeperiods in athletes. We found significant correlation between several measured parameters (salivary lactate - total body water, salivary lactate - RR-variability, maximal salivary lactate - maximal heart rate during exercise, salivary- and blood lactate -1 min after exercise test). Stronger correlation was noted between salivary lactate and blood lactate in athletes, than in controls.     

The effects of a glycogen loading regimen on acid-base status and blood lactate concentration before and after a fixed period of high intensity exercise in man

Six healthy male subjects exercised after an overnight fast for a fixed 3 min period at a workload equivalent to 100% of their maximal oxygen uptake ( ) on 3 separate occasions. The first test took place after subjects had consumed a mixed diet (43±3% carbohydrate (CHO), 41±5% fat and 16±3% protein) for 3 days, and was followed 2 h later by prolonged cycling to exhaustion at 77±3% to deplete muscle glycogen stores. Following this, subjects consumed a low CHO diet (4±1% CHO, 63±5% fat and 33±6% protein) for the remainder of the day and for the subsequent 2 days; on the morning of the next day a second high intensity test took place. Finally subjects followed a 3 day high CHO diet (73±7% CHO, 17±6% fat and 10±1% protein) before their last test. Acid-base status and selected metabolites were measured on arterialised-venous blood at rest prior to exercise and at intervals for 15 min following exercise. Prior to exercise, plasma pH and blood lactate concentration were higher (p<0.05) after the high CHO diet when compared with the low CHO diet. Pre-exercise plasma bicarbonate, blood PCO₂ and blood base excess were all higher after the high (p<0.001,p<0.01,p<0.01 respectively) and normal (p<0.05,p<0.05,p<0.05 respectively) CHO diets when compared with the low CHO diet. During the post-exercise period there were no differences in plasma pH or blood base excess between the three experimental situations; plasma bicarbonate was higher (p<0.05) at 2 min post-exercise after the high CHO diet when compared with the low CHO diet; blood PCO₂ was higher throughout the post-exercise period after the high CHO diet when compared with the low CHO diet and at 2 min post-exercise was higher after the normal CHO diet than after the low CHO diet (p<0.5). The post-exercise blood lactate concentration after the high CHO diet was at all times higher than the corresponding values recorded after the normal CHO diet and until 15 min post-exercise was significantly higher than the values recorded after the low CHO diet. The present experiment further substantiates the view that a pattern of dietary and exercise manipulation can significantly influence the acid-base status of the blood and by doing so may influence high intensity exercise performance.     

Epinephrine-induced changes in muscle carbohydrate metabolism during exercise in male subjects

Epinephrine increases glycogenolysis in resting skeletal muscle, but less is known about the effects of epinephrine on exercising muscle. To study this, epinephrine was given intraarterially to one leg during two-legged cycle exercise in nine healthy males. The epinephrine-stimulated (EPI) and non-stimulated (C) legs were compared with regard to glycogen, glucose, glucose 6-phosphate (G6P), alpha-glycerophosphate (alpha-GP), and lactate contents in muscle biopsies taken before and after the 45-min submaximal exercise, as well as brachial arterial-femoral venous (a-fv) differences for epinephrine, norepinephrine, lactate, glucose, and O2 during exercise. During exercise the arterial plasma epinephrine concentration was 4.8 +/- 0.8 nmol/l and the femoral venous epinephrine concentrations were 10.3 +/- 2.1 and 3.9 +/- 0.6 nmol/l, respectively, in the EPI and C leg. During exercise the a-fv difference for lactate was greater (-0.41 +/- 0.14 vs. -0.21 +/- 0.14 mmol/l; P less than 0.001), and the a-fv difference for glucose was smaller (0.07 +/- 0.12 vs. 0.24 +/- 0.12 mmol/l; P less than 0.01) in the EPI than in the C leg, but the a-fv differences for O2 were similar. Muscle glycogen depletion (137 +/- 63 vs. 99 +/- 43 mmol/kg dry muscle; P less than 0.1) and the muscle concentrations of glucose (P less than 0.05), alpha-GP (P less than 0.1), G6P (P greater than 0.1), and lactate (P greater than 0.1) tended to be higher in the EPI than the C leg after exercise. These findings suggest that physiological concentrations of epinephrine may enhance muscle glycogenolysis during submaximal exercise in male subjects.     

AMINO ACIDS AND CEREBRAL EXCITABILITY1

Abstract— —Seizure threshold, measured with hexafluorodiethyl ether, was shown to be reduced in immature albino rats fed a diet containing excess tryptophan. Similar diets containing excess glycine, serine, leucine, valine or lysine had no effect on seizure threshold. Previous studies had shown phenylalanine, tyrosine and methionine to enhance cerebral excitability with the same technique. The increased cerebral excitability was shown to occur within 24 hr following diet supplementation with phenylalanine. Brain concentration of hexafluorodiethyl ether was identical in control and experimental animals, although the experimental animals had lowered seizure thresholds; this established an alteration in cerebral excitability rather than variation in tissue penetration by the convulsant. Alterations were found in blood and brain ammonia in serine, lysine and methionine supplemented animals. Brain glutamate and glutamine were lowered in methionine-supplemented animals; however, it was concluded that this effect was not causally related to the increased cerebral excitability.