Effect of blood volume on plasma volume shift during exercise

To assess the relationship between blood volume (BV) and the reduction in plasma volume (PV) during exercise in individual variations, we measured BV and changes in PV in thirteen male volunteers during treadmill exercise until exhaustion. The lactate threshold (LT), as a predictor of aerobic exercise capacity, was calculated from the exercise intensity at the point of plasma lactate concentration buildup to 4 mmol. The relationship of peak VO₂ with BV indicated a significant positive correlation. The strong positive relation between the shifts in PV and total PV, and resulted in a maintenance of the circulating BV.     

Plasma volume changes during and after acute variations of body hydration level in humans

This study examined plasma volume changes (deltaPV) in humans during periods with or without changes in body hydration: exercise-induced dehydration, heat-induced dehydration and glycerol hyperhydration. Repeated measurements of plasma volume were made after two injections of Evans blue. Results were compared to deltaPV calculated from haematocrit (Hct) and blood haemoglobin concentration ([Hb]). Eight well-trained men completed four trials in randomized order: euhydration (control test C), 2.8% dehydration of body mass by passive controlled hyperthermia (D) and by treadmill exercise (60% of their maximal oxygen uptake, VO2max) (E), and hyperhydration (H) by glycerol ingestion. The Hct, [Hb], plasma protein concentrations and plasma osmolality were measured before, during and after the changes in body hydration. Different Hct and [Hb] reference values were obtained to allow for posture-induced variations between and during trials. The deltaPV values calculated after two Evans blue injections were in good agreement with deltaPV calculated from Hct and [Hb]. Compared to the control test, mean plasma volume declined markedly during heat-induced dehydration [-11.4 (SEM 1.7)%] and slightly during exercise-induced dehydration [-4.2 (SEM 0.9)%] (P < 0.001 compared to D), although hyperosmolality was similar in these two trials. Conversely, glycerol hyperhydration induced an increase in plasma volume [+7.5 (SEM 1.0)%]. These results would indicate that, for a given level of dehydration, plasma volume is dramatically decreased during and after heat exposure, while it is better maintained during and after exercise.     

Slow volume changes in calf and thigh during cycle ergometer exercise

To study the transcapillary fluid movements in the human lower limb in the upright body position and during muscle exercise, the slow changes in thigh and calf volumes were measured by mercury-in-rubber-strain gauge plethysmography. Measurements were carried out on 20 healthy volunteers while sitting, standing and doing cycle ergometer exercise at intensities of 50 and 100-W. A plethysmographic recording of slow extravascular volume changes during muscle exercise was possible because movement artefacts were eliminated by low-pass filtering. While standing and sitting the volumes of both thigh and calf increased due to enhanced transcapillary filtration. While standing the mean rate of increase was 0.13%.min-1 in the calf and 0.09%.min-1 in the thigh. During cycle ergometer exercise at 50 and 100 W, the calf volume decreased with a mean rate of -0.09.min-1. In contrast, the thigh volume did not change significantly during exercise at 50 W and increased at 100 W. Most of the increase occurred during the first half of the experimental period i.e. between min 2 and 12, amounting to +0.6%. Thus, simultaneous measurements revealed opposite changes in the thigh and calf. This demonstrates that the conflicting findings reported in the literature may have occurred because opposite changes can occur in different muscle groups of the working limb at the same time. Lowered venous pressure, increased lymph flow and increased tissue pressure in the contracting muscle are considered to have caused the reduction in calf volume during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

Maximal power and torque-velocity relationship on a cycle ergometer during the acceleration phase of a single all-out exercise

Seven subjects pedalled on a Monark cycle ergometer as fast as possible for approximately 7 s against four different resistances which corresponded to braking torques (T _B) equal to 19, 38, 57 and 76 N · m at the crank level. Exercise periods were separated by 5-min recovery periods. Pedal velocity was recorded every 50 ms by means of a disc with 360 slots fixed on the flywheel, passing in front of a photo-electric cell linked to a microcomputer which processed the data. Every 50 ms, the time necessary to perform half a pedal revolution (t _1/2) was computed by adding the 50-ms periods necessary to reach 669 slots (the number of slots corresponding to half a pedal revolution). To measuret _1/2 to an accuracy better than 50 ms, this time was computed by a linear interpolation of the time-slot number relationship. Power (P) was averaged duringt ₁₂ by adding the power dissipated against braking torque and the power necessary to accelerate the flywheel. The torque-velocity (T-) relationship was studied during the acceleration phase of a sprint against a single TB by computing every 50 ms the relationship between and T (N · m), equal to the sum ofT _B and the torque necessary to accelerate the flywheel at the same time. The T- relationships calculated from the acceleration phase of a single all-out exercise were linear and similar to the previously described relationships between peak velocity and braking force. These relationships can be expressed as follows: = _0,acc (1 –T/T _0,acc) where is pedal velocity,T the torque exerted on the crank andT _0,acc and _0,acc have the dimensions of maximal torque and maximal velocity respectively. Based on this model, maximal power (P _max,acc) is calculated as 0.257_{0, acc} T _{0, acc}. Maximal powerP _max,acc measured with the acceleration method was independent of braking torqueT _B and slightly higher thanP _max calculated from the relationship between peak velocity andT _B.     

Alterations in plasma volume, electrolytes and protein during incremental exercise at different pedal speeds

We investigated the effects of pedal speed on changes in plasma volume, electrolytes and protein during incremental exercise. Ten adult males participated in two, 30 minute incremental cycle ergometer exercise tests at room temperature (22° C, rh=56%). Exercise load was increased from 20 to 70% of peak . Five minutes were spent at each of six stages which were equally spaced in exercise intensity. Subjects pedaled at 50 (50 RPM) and 90 (90 RPM) rev · min^–1. Venous blood samples were drawn prior to exercise and during the last minute of each stage. Relative plasma volume changes showed a progressive hemoconcentration during the exercise. There were no significant differences due to pedal speed as plasma volume loss averaged –7.3% during exercise. [Na+], [Cl–], and [K+] increased significantly during exercise but were not influenced by pedal speed. Changes in plasma protein and albumin concentrations indicated that there was a loss of globulin from the vascular volume in both conditions and an addition of albumin to the plasma in 50 RPM. The difference in plasma albumin dynamics was possibly related to an effect of pedal speed on movement of fluid in the lymphatic vessels of the legs.This work was supported in part by Grants from the Theresa Monaco Endowment of the University of Houston College of Education and Nautilus Sports/Medical Industries     

Fluid replacement beverages and maintenance of plasma volume during exercise: role of aldosterone and vasopressin

Previous experiments have demonstrated that consumption of a glucose polymer-electrolyte (GP-E) beverage is superior to water in minimizing exercise-induced decreases in plasma volume (PV). We tested the hypothesis that elevated plasma concentrations of vasopressin and/or aldosterone above that seen with water ingestion may explain this observation. Six trained cyclists performed 115 min of constant-load exercise (approximately 65% of maximal oxygen consumption) on a cycle ergometer on two occasions with 7 days separating experiments. Ambient conditions were maintained relatively constant for both exercise tests (29-30 degrees C; 58-66% relative humidity). During each experiment, subjects consumed 400 ml of one of the following beverages 20 min prior to exercise and 275 ml immediately prior to and every 15 min during exercise: (1) distilled water or (2) GP-E drink contents = 7% carbohydrate (glucose polymers and fructose; 9 mmol.l-1 sodium; 5 mmol.l-1 potassium; osmolality 250 mosmol.l-1). No significant difference (P > 0.05) existed in mean skin temperature, rectal temperature, oxygen consumption, carbon dioxide production or the respiratory exchange ratio between treatments. Further, no significant differences existed in plasma osmolality and plasma concentrations of sodium, potassium, chloride or magnesium between treatments. Plasma volume was better maintained (P < 0.05) in the GP-E trial at 90 and 120 min of exercise when compared to the water treatment. No differences existed in plasma levels of vasopressin or aldosterone between treatments at any measurement period. Further, the correlation coefficients between plasma concentrations of vasopressin and aldosterone and change in PV during exercise were 0.42 (P < 0.05) and 0.16 (P > 0.05), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Gastric emptying during walking and running: effects of varied exercise intensity

Gastric emptying is increased during running (50%-70% maximal aerobic uptake, VO2max) as compared to rest. Whether this increase varies as a function of mode (i.e. walking vs running) and intensity of treadmill exercise is unknown. To examine the gastric emptying characteristics of water during treadmill exercise performed over a wide range of intensities relative to resting conditions, 10 men ingested 400 ml of water prior to each of six 15 min exercise bouts or 15 min of seated rest. Three bouts of walking exercise (1.57 m.s-1) were performed at increasing grades eliciting approximately 28%, 41% or 56% of VO2max. On a separate day, three bouts of running (2.68 ms-1) exercise were performed at grades eliciting approximately 57%, 65% or 75% of VO2max. Gastric emptying was increased during treadmill exercise at all intensities excluding 75% VO2max as compared to rest. Gastric emptying was similar for all intensities during walking and at 57% and 65% VO2max during running. However, running at 74% VO2max decreased the volume of original drink emptied as compared to all lower exercise intensities. Stomach secretions were markedly less during running as compared to walking and rest. These data demonstrate that gastric emptying is similarly increased during both moderate intensity (approximately 28%-65% VO2max) walking or running exercise as compared to resting conditions. However, gastric emptying decreases during high intensity exercise. Increases in gastric emptying during moderate intensity treadmill exercise may be related to increases in intragastric pressure brought about by contractile activity of the abdominal muscles.     

Functional role of AMP-activated protein kinase in the heart during exercise

AMP-activated protein kinase (AMPK) plays a critical role in maintaining energy homeostasis and cardiac function during ischemia in the heart. However, the functional role of AMPK in the heart during exercise is unknown. We examined whether acute exercise increases AMPK activity in mouse hearts and determined the significance of these increases by studying transgenic (TG) mice expressing a cardiac-specific dominant-negative (inactivating) AMPKalpha2 subunit. Exercise increased cardiac AMPKalpha2 activity in the wild type mice but not in TG. We found that inactivation of AMPK did not result in abnormal ATP and glycogen consumption during exercise, cardiac function assessed by heart rhythm telemetry and stress echocardiography, or in maximal exercise capacity.     

Plasma volume in acute hypoxia: comparison of a carbon monoxide rebreathing method and dye dilution with Evans' blue

Exposure to acute hypoxia is associated with changes in body fluid homeostasis and plasma volume (PV). This study compared a dye dilution technique using Evans' blue (PV_Evans') with a carbon monoxide (CO) rebreathing method (PV_CO) for measurements of PV in ten normal subjects at sea level and again 24 h after rapid passive ascent to high altitude (4,350 m). Hypobaric hypoxia decreased arterial oxygen saturation to 79 (74–83)% (mean with 95% confidence intervals). The PV_Evans' remained unchanged from 3.49 (3.30–3.68) l at sea level to 3.46 (3.24–3.68) l at high altitude. In contrast PV_CO decreased from 3.39 (3.17–3.61) l at sea level to 3.04 (2.75–3.33) l at high altitude (P < 0.05). Compared with sea level, this resulted in an increase of the mean bias between the two methods [from 0.11 (−0.05–0.27) l at sea level to 0.43 (0.26–0.60) l at high altitude] so that the ratio between PV_Evans' and PV_CO increased from 1.04 (0.99–1.09) at sea level to 1.15 (1.06–1.24) at high altitude (P < 0.05). In conclusion, the two methods were not interchangeable as measures of hypoxia-induced changes in PV. The mechanism responsible for the bias remains unknown, but it is suggested that the results may reflect a redistribution of albumin caused by the combined effects in hypoxia of both an increased capillary permeability to albumin and a decrease in PV. As a result, the small perivascular compartment of albumin beyond the endothelium may increase without changes in the overall albumin distribution volume. Accepted: 31 October 1997     

Effects of order of presentation of exercise intensities and of sauna baths on perceived exertion during treadmill running

Thirteen male subjects performed a running test on the treadmill consisting of four standard exercise intensities [65%, 75%, 85%, 95% maximal O2 uptake (VO2 max)] presented in ascending, descending or random order. At the end of each exercise intensity, O2 consumption, heart rate (fc), venous blood lactate concentration [( Ia]b) and perceived exertion were assessed. This last variable was determined according to the Borg nonlinear CR-20 scale. The same variables were also determined during exercise at a standard intensity (65% or 95% VO2 max) performed before and after a Finnish sauna bath. Ratings of perceived exertion showed a good test-retest reliability (r = 0.77); they were the same when the exercise intensity was expressed in relative (%VO2 max) or absolute (speed) terms, and were independent of the order of presentation of the exercise. The latter had no effect on fc either but it did, however, influence [Ia]b, which was significantly higher in the descending, as compared to the ascending or random modes of presentation. The sauna bath increased fc at a given exercise intensity, but left perceived exertion and [Ia]b unchanged. It was concluded that at least under the present experimental conditions, fc and venous [Ia]b do not play a major role as determinants of perceived exertion.     

Leg kinematics and muscle activity during treadmill running in the cockroach, Blaberus discoidalis: II. Fast running

We have combined kinematic and electromyogram (EMG) analysis of running Blaberus discoidalis to examine how middle and hind leg kinematics vary with running speed and how the fast depressor coxa (Df) and fast extensor tibia (FETi) motor neurons affect kinematic parameters. In the range 2.5–10 Hz, B. discoidalis increases step frequency by altering the joint velocity and by reducing the time required for the transition from flexion to extension. For both Df and FETi the timing of recruitment coincides with the maximal frequency seen for the respective slow motor neurons. Df is first recruited at the beginning of coxa-femur (CF) extension. FETi is recruited in the latter half of femur-tibia (FT) extension during stance. Single muscle potentials produced by these fast motor neurons do not have pronounced effects on joint angular velocity during running. The transition from CF flexion to extension was abbreviated in those cycles with a Df potential occurring during the transition. One effect of Df activity during running may be to phase shift the beginning of joint extension so that the transition is sharpened. FETi is associated with greater FT extension at higher running speeds and may be necessary to overcome high joint torques at extended FT joint angles. Accepted: 24 May 1997     

Effects of exercise training on plasma cytokine and chemokine levels, and thermoregulation

Pyrogenic factors may include the proinflammatory cytokines such as interleukin (IL)-1β, IL-6, tumor necrosis factor-alpha (TNF-α), and IL-8 (chemokine). Exercise also causes cytokinemia that might result in pyrogenically mediated body temperature elevation. The aim of the present study was to determine the effect of exercise training on exercise-induced plasma concentrations of IL-1β, IL-6, TNF-α, and IL-8. Messenger RNA levels of these factors were also evaluated in peripheral blood leukocytes. We also observed the relationship between cykokines, chemokines, and sweating after exercise. Nine tennis athletes (n=9) and untrained sedentary control subjects (n=10) ran for 1 h at 75% intensity of VO_2max. Venous blood samples were analyzed for plasma concentrations and mRNA expression in leukocytes of cytokines and chemokine of interest. Sweat volume was calculated by measuring body weight changes. Leukocyte mRNA expression and plasma protein levels of IL-1β, IL-6, TNF-α, and IL-8 immediately increased after exercise in both groups, but to a much greater extent in the athletic group. However, mRNA expression and plasma protein level for IL-6 and TNF-α, unlike IL-1β and IL-8, decreased more quickly in the athletic group compared to the control group during the recovery period. Compared to the control group, greater sweat loss volumes, and lower body temperatures in athletic group were observed at all time points. In conclusion, exercise training improved physical capacity and sweating function so that body temperature was more easily regulated during and after exercise. This may due to improved production of specific cytokine and chemokine in sweating during exercise.     

Ventilatory threshold and work efficiency during exercise on cycle and paddling ergometers in young female kayakists

The aim of this study was to assess the effects of increasing specific (paddling erogmeter) and non-specific (cycle ergometer) exercise on parameters relating to the ventilatory threshold (Th_vent) and work efficiency in 11 young female flat-water kayakists. When these trained subjects were tested using non-specific workloads, their oxygen uptake (VO₂) values at Th_vent, as a percentage ofVO_2max (%VO_2max), were close to those of untrained subjects [74.2 (5.6) %VO_2max, mean (SD)]. However, when we tested the same subjects using specific exercise, we recorded values typical of highly trained athletes [84.8 (4.7) %VO_2max). For the non-specific exercise on the cycle erogmeter, we recorded work efficiency values close to those of untrained subjects [22.3 (2.5) %]; however, for the specific exercise on the paddling ergometer, we recorded much lower values [13.4 (3.0) %] both at the level of Th_vent. The work efficiency at two warm-up submaximal exercise loads on the paddling ergometer was non-significantly lower than values at Th_vent [12.3 (2.8) % and 12.9 (2.9) % respectively]. Significant correlations were found between maximal-performanceVO₂ (ml · kg^–1 · min^–1) and performance at Th_vent during paddling and race performance (0.623, 0.630 and 0.648 respectively, allP<0.05). Because the results of both specific and non-specific submaximal exercise tests are different, we suggest caution in the interpretation of physiological variables that may be sensitive to training status. The evaluation of Th_vent and work efficiency as supplementary parameters during laboratory studies enables the determination of the effectiveness of the training process and the specific adaptation of the subjects.     

Plasma lactate, GH and GH-binding protein levels in exercise following BCAA supplementation in athletes

Summary. Branched chain amino acids (BCAA) stimulate protein synthesis, and growth hormone (GH) is a mediator in this process. A pre-exercise BCAA ingestion increases muscle BCAA uptake and use. Therefore after one month of chronic BCAA treatment (0.2 g kg⁻¹ of body weight), the effects of a pre-exercise oral supplementation of BCAA (9.64 g) on the plasma lactate (La) were examined in triathletes, before and after 60 min of physical exercise (75% of VO₂max). The plasma levels of GH (pGH) and of growth hormone binding protein (pGHBP) were also studied. The end-exercise La of each athlete was higher than basal. Furthermore, after the chronic BCAA treatment, these end-exercise levels were lower than before this treatment (8.6 ± 0.8 mmol L⁻¹ after vs 12.8 ± 1.0 mmol L⁻¹ before treatment; p < 0.05 [mean ± std. err.]). The end-exercise pGH of each athlete was higher than basal (p < 0.05). Furthermore, after the chronic treatment, this end-exercise pGH was higher (but not significantly, p = 0.08) than before this treatment (12.2 ± 2.0 ng mL⁻¹ before vs 33.8 ± 13.6 ng mL⁻¹ after treatment). The end-exercise pGHBP was higher than basal (p < 0.05); and after the BCAA chronic treatment, this end-exercise pGHBP was 738 ± 85 pmol L⁻¹ before vs 1691 ± 555 pmol L⁻¹ after. pGH/pGHBP ratio was unchanged in each athlete and between the groups, but a tendency to increase was observed at end-exercise. The lower La at the end of an intense muscular exercise may reflect an improvement of BCAA use, due to the BCAA chronic treatment. The chronic BCAA effects on pGH and pGHBP might suggest an improvement of muscle activity through protein synthesis. Received January 5, 1999 / Accepted June 17, 1999     

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.     

Time–frequency and principal-component methods for the analysis of EMGs recorded during a mildly fatiguing exercise on a cycle ergometer

Electromyographic signals contain the information on muscle activity and have to be frequently averaged, compared, classified or details need to be extracted. A time–frequency analysis, based on wavelets, was previously presented. The analysis transformed an EMG signal into an EMG-intensity-pattern showing the intensities at any point in time for the frequencies filtered out by the wavelets. The purpose of the present study was:

1. to define and apply a new EMG-pattern-space for the analysis of EMG-intensity-patterns; and

2. to determine the variation of EMG-intensity-patterns while getting mildly fatigued by cycling on a cycle-ergometer.

The coordinates spanning the pattern space were principal components of the measured EMG-intensity-patterns. A point in pattern-space thus represented an EMG-intensity-pattern. Fatigue resulted in points moving along a line in pattern space. The line was characterized by an intercept at time 0 and a slope. Thus mild fatigue caused a shift from an initial intensity-pattern representing the intercept to a final intensity-pattern adding gradually larger amounts of the pattern representing the slope. The intensity-pattern of the slope revealed the physiologically important individual strategies for coping with mild fatigue. Changes were observed at different times and at different frequencies during the cycling movement.     

The relationship between plasma potassium concentration and muscle torque during recovery following intense exercise

The present study investigated the relationship between plasma potassium ion concentration ([K⁺]) and skeletal muscle torque during three different 15-min recovery periods after fatigue induced by four 30-s sprints. Four males and one female completed the multiple sprint exercise on three separate days; recovery was passive, i.e. no cycling exercise (PRec), active cycling at 30% peak oxygen consumption O_2peak (30% Rec) and active cycling at 60% O_2peak (60% Rec). Plasma [K⁺] was measured from blood sampled from an antecubital vein of subjects at rest and at 0, 3, 5, 10 and 15 min into each recovery. Isokinetic leg strength was measured at rest and at 1, 6, 11 and 16 min during each recovery. Following the exhaustive sprints, [K⁺] increased significantly from an average mean (SEM) resting value of 3.81 (0.07) mmol · l⁻¹ to 4.48 (0.19) mmol · l⁻¹ (P < 0.01). In all recovery conditions, plasma [K⁺] returned to resting levels within 3 min following the fourth sprint. However, in the two active recovery conditions plasma [K⁺] increased over the remainder of the recovery periods to 4.36 (0.12) mmol · l⁻¹ in the 30% Rec condition and 4.62 (0.12) mmol · l⁻¹ in the 60% Rec condition, the latter being significantly higher than the former (P < 0.01). The maximum torque measured following the sprints decreased significantly, on average, to 61.1 (8.36)% of peak levels (P < 0.01). After 15 min of recovery, maximum torque was highest in the 30% Rec condition at 92.13 (3.06)% of peak levels (P < 0.01), compared to 85.23 (3.64)% and 85.71 (0.82)% for the PRec and 60% Rec conditions, respectively. In contrast to the significant differences in plasma [K⁺] across all three recovery conditions, muscle torque recovery was significantly different in only the 30% Rec condition. In summary, recovery of peak levels of muscle torque following fatiguing exercise does not appear to follow changes in plasma [K⁺]. Accepted: 18 October 1996     

Changes in protein kinase and protein phosphatase properties during the cycle of asparaginase activity in Leptosphaeria michotti

Regulation of the cyclic activity of asparaginase (obtained as a purified protein complex) by a reversible auto-phosphorylation process has been previously reported in the fungus Leptosphaeria michotii (West) Sacc. In the present study, the protein complex was purified in the presence of either a mixture of 3 protein phosphatase inhibitors (fluoride, vanadate and molybdate) or EGTA, during the cycle of asparaginase activity, and the protein kinase and protein phosphatase activities characterized. (I) At the phase of increasing asparaginase activity, a Ca²⁺/calmodulin-dependent kinase activity was identified by (a) its inhibition by calmidazolium, reversed by calmodulin, and its inhibition by EGTA, but not by poly(Glu/Tyr 4:1)n. dichloro-(ribofuranosyl)-benzimidazole or polylysine (b) an increasing level of calmodulin bound to the complex, as estimated by enzyme-linked immunosorbent assay (ELISA). (2) At the phase of decreasing asparaginase activity, the Ca²⁺-calmodulin-dependent kinase activity disappeared and a little calmodulin remained associated with the complex: phosphorylation of the complex was increased several-fold by 1 nM okadaic acid and 25 nM inhibitor-2, and was not affected by EGTA, indicating a protein phosphatase-2A-like activity. (3) When asparaginase activity was low, a little calmodulin was bound to the complex. The kinase could phosphorylate casein and phosvitin. was inhibited by poly(Glu/Tyr 4:1)n. dichloro-(ribofuranosyl)-benzimidazole and heparin, stimulated by polylysine and not affected by calmidazolium or EGTA, just as a casein kinase 2. A Ca²⁺-dependent but calmodulin-independent protein phosphatase activity, not affected by okadaic acid and inhibitor-2. was then identified. We postulate the presence in the complex, of (a) only one protein kinase and one protein phosphatase, whose properties could change during the cycle of asparaginase activity: (b) two Ca²⁺/-binding proteins: first calmodulin, which could bind to Ca²⁺ and the casein kinase-2 form to give a Ca²⁺/calmodulin-dependent kinase, which could become Ca²⁺/calmodulin-independent following an auto-phosphorylation process: second a protein homologous to calmodulin, able to bind to the protein phosphatase-2A catalytic subunit to give a protein phosphatase-2B catalytic subunit.     

Influence of acute plasma volume expansion on VO2 kinetics, VO2 peak, and performance during high-intensity cycle exercise.

The purpose of this study was to examine the influence of acute plasma volume expansion (APVE) on oxygen uptake (V(O2)) kinetics, V(O2peak), and time to exhaustion during severe-intensity exercise. Eight recreationally active men performed "step" cycle ergometer exercise tests at a work rate requiring 70% of the difference between the gas-exchange threshold and V(O2max) on three occasions: twice as a "control" (Con) and once after intravenous infusion of a plasma volume expander (Gelofusine; 7 ml/kg body mass). Pulmonary gas exchange was measured breath by breath. APVE resulted in a significant reduction in hemoglobin concentration (preinfusion: 16.0 +/- 1.0 vs. postinfusion: 14.7 +/- 0.8 g/dl; P < 0.001) and hematocrit (preinfusion: 44 +/- 2 vs. postinfusion: 41 +/- 3%; P < 0.01). Despite this reduction in arterial O(2) content, APVE had no effect on V(O2) kinetics (phase II time constant, Con: 33 +/- 15 vs. APVE: 34 +/- 12 s; P = 0.74), and actually resulted in an increased V(O2peak) (Con: 3.90 +/- 0.56 vs. APVE: 4.12 +/- 0.55 l/min; P = 0.006) and time to exhaustion (Con: 365 +/- 58 vs. APVE: 424 +/- 64 s; P = 0.04). The maximum O(2) pulse was also enhanced by the treatment (Con: 21.3 +/- 3.4 vs. APVE: 22.7 +/- 3.4 ml/beat; P = 0.04). In conclusion, APVE does not alter V(O2) kinetics but enhances V(O2peak) and exercise tolerance during high-intensity cycle exercise in young recreationally active subjects.