Exercise induced augmentation of myocardial oxygen extraction in spite of normal coronary dilatory capacity in dogs

Summary Myocardial O₂-extraction rate was studied during exercise induced augmentation of cardiac work in dogs.The O₂-extraction rate at rest was 75% of arterial content. Progressive levels of exercise increased the animals' O₂-consumption from 7 ml/min · kg up to 91 ml/min · kg. Cardiac output rose from 108 ml/min · kg at rest to 484 ml/min · kg at the highest exercise level. The increase in myocardial O₂-consumption from 9 ml/min·100 g at rest up to 57 ml/min·100 g at the highest exercise level was met by an increase in coronary flow from 59 to 256 ml/min·100 g and a rise of myocardial AVDO₂ from 15 to 22 Vol%. Thus the latter contributed 40% to the augmented myocardial O₂-requirements.Coronary venous O₂-saturation decreased to 9% saturation during highest levels of exercise. This low value was not the result of a limited coronary dilatory capacity, of inadequate state of exercise training, or of a relative underperfusion of the inner layers of the left ventricle.Thus, augmentation of myocardial O₂-extraction rate seems to be a mechanism of physiological relevance during exercise induced elevation of myocardial O₂-requirements in dogs and may be explained by capillary recruitment in the myocardium.Supported by Deutsche Forschungsgemeinschaft     

Oxygen transport and utilization in chronic nonpulsatile blood flow

Oxygen transport and utilization during rest and progressive exercise in chronic nonpulsatile blood flow was reviewed. In a chronic nonpulsatile animal model, (1) basal oxygen consumption of a 4-month old calf was 6.3±0.3 ml/kg/min; (2)PvO₂ decreased when the pump flow rate was reduced (29.6±1.0, 28.3±1.2, and 23.8±0.9 mmHg at 120, 100, and 90 ml/kg/min of pump flow, respectively); (3) serum lactate concentration increased significantly at 90 ml/kg/min of pump flow compared with other rates of pump flow. These results suggest that a critical flow level to maintain oxidative metabolism in the calf with chronic nonpulsatile flow exists between 90 and 100 ml/kg/min, andPvO₂ at the critical flow rate was between 24 and 28 mm Hg. Exercise data showed a significant correlation between O₂ delivery and the maximal O₂ consumption at each nominal flow rate, and suggested that a maximum of 78% of the oxygen delivered can be extracted and utilized during maximal exercise in animals with chronic nonpulsatile blood flow. These data suggest that chronic nonpulsatile blood flow is not a limiting factor for oxygen transport during rest and progressive exercise. However, further studies are needed to directly compare oxygen transport properties in pulsatile and nonpulsatile blood flow models.     

Metabolic and hormonal responses to prolonged physical exercise in dogs after a single fat-enriched meal

Summary Metabolic and hormonal responses to prolonged treadmill exercise in dogs fed a fat-enriched meal 4 h prior to the exercise were compared to those measured 4 h after a mixed meal or in the postabsorptive state.Ingestion of the fat-enriched meal caused significant elevations in the resting values of plasma triglyceride (TG), free fatty acid (FFA), and glycerol concentrations. A reduction of the plasma TG concentration (from 1.6±0.2 to 1.1±0.10 mmol·l^–1,P<0.005) occurred only in dogs exercising after the fat-enriched meal. No significant changes in this variable were noted in dogs fed a mixed meal, whilst in the postabsorptive state exercise caused an increase in the plasma TG level (from 0.42±0.03 to 0.99±0.11 mmol·l^–1,P<0.01). The exercise-induced elevations in plasma FFA and glycerol concentrations were the highest in the dogs given the fat-enriched meal. Plasma glycerol during exercise correlated with the initial values of circulating TG (r=0.73). The plasma FFA-glycerol ratio, at the end of exercise was lowest in the dogs taking the fat-enriched meal (1.39±0.19), suggesting an increased utilization of FFA in comparison with that in the postabsorptive state (3.27±0.37) or after a mixed meal (2.88±0.55). Basal serum insulin (IRI) concentrations were similarly enhanced in dogs fed fat-enriched and mixed meals, and they were reduced to control values within 60 min of exercise. Plasma adrenaline and noradrenaline concentrations correlated with time of exercise (r=0.84 andr=0.96, respectively) and were unaffected by the nutritional modifications.It is concluded that ingestion of a single fat-enriched meal considerably modifies the exercise-induced changes in lipid metabolism. The pattern of changes in plasma TG, FFA, and glycerol concentrations indicates an enhanced hydrolysis of plasma chylomicron-TG, suggesting that this lipid source may contribute markedly to exercise metabolism.This work was supported by the Polish Academy of Sciences within the Project 10.4     

Enhanced glucose availability for working muscles reduces exercise hyperthermia in dogs

Summary Body temperature and metabolic responses to 2 h treadmill exercise in dogs given glucose intravenously (25–30 mg·kg^–1· min^–1 throughout the run) were compared with those measured in the same animals with elevated plasma FFA concentrations (soya bean oil ingestion+intravenous heparin) and in control experiments (24 h fasting). In comparison with control conditions enhanced glucose availability for the working muscles caused a reduction in the exercise-induced increases in both rectal (by 0.9± 0.11° C) and muscle (by 0.9±0.16° C) temperatures, a lower rate of oxygen uptake (by 16%) and an elevated respiratory exchange ratio. A tendency towards enhanced body temperature responses to exercise, accompanied by increases inV _{O 2} and cardiac frequency was noted in dogs with elevated plasma FFA concentrations as compared with the control animals. The estimated amount of heat effectively dissipated from the body, expressed as a fraction of heat load (thermoregulatory efficiency) was significantly higher in dogs infused with glucose (0.962±0.0035), than in the controls (0.947± 0.0043) and those with elevated plasma FFA concentrations (0.931±0.0029).It is concluded that the increased contribution of carbohydrates to the energy yield during exercise results in a marked attenuation of hyperthermia, associated with a reduced metabolic rate and improved thermoregulatory efficiency.This work was supported by the Polish Academy of Sciences within the Project 10.4.     

Ventilatory threshold during treadmill exercise in kindergarten children

Summary The cardiorespiratory response to graded treadmill exercise was studied in a group of kindergarten children, aged 5 to 6 years. From the non-linear change of pulmonary ventilation with increasing exercise intensity a ventilatory threshold was determined which averaged 28.1±4.9 (SD) ml O₂·min^–1·kg^–1. A significant correlation was established between this ventilatory threshold (ml O₂·min^–1) and the physical working capacity at a heart rate of 170 beats per min (PWC₁₇₀, ml O₂·min^–1):r=0.93,p<0.001. These data show that a ventilatory threshold can be obtained in young children which is an objective index of cardiorespiratory performance capacity.     

Changes in carotid blood flow and electrocardiogram in humans during and after walking on a treadmill

Blood flow velocity in the common carotid artery and the electrocardiogram were measured simultaneously by telemetry in seven male subjects during 20-min walking on a treadmill at an exercise intensity corresponding to a mean oxygen uptake of 26.0 (SD 2.9) ml · kg ^–1 · min ^–1. The mean cardiac cycle was shortened from 0.814 (SD 0.103) s to 0.452 (SD 0.054) s during this exercise. Of this shortening, 73% was due to shortening of the diastolic period and 27% to shortening of the systolic period. In the relatively small shortening of the mean systolic period [from 0.377 (SD 0.043) s to 0.268 (SD 0.029) s], the isovolumetric contraction time was shortened by 56%. During exercise, the heart rate (f _c) increased by 79.4% [from 74.3 (SD 9.3) beats · min ^–1 to 133.3 (SD 14.8) beats · min ^–1], and the peak blood velocity (S₁) in the common carotid artery increased by 56.1% [from 0.82 (SD 0.10) m · s^–1 to 1.28 (SD 0.11) m · s^–1]. After exercise, the S₁ decreased rapidly to the resting level. The f _c decreased more slowly, still being higher than the initial resting level 5 min after exercise. The diastolic velocity wave and the end-diastolic foot decreased during exercise. The blood flow rate in the carotid artery increased transiently by 13.5% at the beginning of exercise [from 5.62 (SD 0.63) ml · s^–1 to 6.38 (SD 0.85) ml · s^–1] and by 26.5% at the end of the exercise period [from 5.62 (SD 0.63) ml · s^–1 to 7.11 (SD 1.34) ml · s^–1]. The increase of blood flow in the carotid artery at the onset of exercise may have been mainly related to cerebral activation, and partly to an increase of blood flow to the skin of the head. The physiological significance for cerebral function of the increase of blood flow in the artery after the end of exercise is unknown.     

The possible role of acetate in exercise hyperemia in dog skeletal muscle

The possible role of acetate in the genesis of exercise hyperemia was studied in five series of dogs. Intraarterial infusion of an isomotic solution of sodium acetate at 0.76 ml/min in the dog forelimb decreased the resistance to flow through skeletal muscle by 48%, primarily by decreasing resistance to flow through small vessels. Skin lymph flow and lymph protein concentration were unaffected. The hindlimb of the conscious dog took up acetate at rest (A-V difference, _58.3±19.6 nmoles/ml) and put out acetate during treadmill exercise (A-V difference, –105.6±20.12 nmoles/ml); femoral venous blood acetate concentration increased by 145 nmoles/ml (control 195 nmoles/ml). In the gracilis muscle of the anesthetized dog, simulated exercise at 0.5, 1.0 or 2.0 Hz increased acetate tissue content (72, 248 and 442 nmoles/g, respectively), output (18,899, and 1,830 nmoles/100 g/min, respectively) and venous cencentration (82, 49 and 39 nmoles/ml, respectively) and changes in tissue acetate content correlated with changes in vascular resistancer=0.75,P<0.001. Intraarterial infusion of an isosmotic solution of sodium acetate in the quiescent gracilis muscle perfused at constant flow produced a significant (6%) decrease in resistance when arterial blood acetate was increased by a calculated 96 nmoles/ml. These studies suggest that acetate might be included among those metabolites that contribute to exercise hyperemia.Supported by grants CO7610 and CO7635 from the Uniformed Services University. Preliminary communications included Physiologist 21:115, 1978, Federation Procedings 39:270, 1980 and Physiologist 23:156, 1980     

Short-term effects of oral enoximone on hemodynamics,exercise capacity,anaerobic threshold,and arrhythmias in congestive heart failure

Summary Enoximone, a phosphodiesterase-inhibitor, is a potent inotropic vasodilator agent that causes a marked improvement in hemodynamics in patients with congestive heart failure. The acute effects of oral enoximone on rest and exercise hemodynamics, ejection fraction, aerobic metabolism, exercise capacity, and arrhythmias were studied in 11 patients with moderate to moderately severe dilative cardiomyopathy after 8 days of enoximone (100 mg tid) in addition to baseline therapy (diuretics and digitalis).The cardiac index increased from 2.44±0.45 to 2.72±0.50 l/min/m² (p<0.01) at rest and from 4.00±0.96 to 4.75±0.95 l/min/m² (p<0.005) during exercise. Pulmonary wedge pressure decreased from 16.8±7.3 to 12.5±6.5 mmHg (p<0.005) at rest and from 28.2±8.0 to 24.5±10.3 mmHg (p< 0.05) during exercise. Systemic vascular resistance decreased from 1608±243 to 1495±300 dynes*sec*cm^–5 (p<0.05) at rest and from 1152±155 to 1027±236 dynes*sec*cm^–5 (ns) during exercise. The anaerobic threshold, which was recorded simultaneously, increased from 13.2±2.7 to 15.5± 2.5ml/kg/min VO₂ (p<0.02). The radionuclide ventriculography ejection fraction improved from 21.7±5.0 to 28.1±9.1% (p<0.01) during exercise; the changes at rest were not significant (20.8±6.2 vs 25.8±8.4%). Exercise tolerance showed an increase of 16% (492±133 to 573±135 sec, p< 0.005). The resting heart rate remained unchanged (81.8±13.4 vs 81.8±11.9). Interestingly, 24-h Holter monitoring revealed more or new repetitive arrhythmias in 9/11 patients.Short-term therapy with oral enoximone enhances ventricular performance by increasing cardiac contractility and lowering vascular resistance, both of which extend exercise tolerance and improve aerobic metabolism. Potential proarrhythmic effects need further evaluation, however.Abbreviations AMP adenosine monophosphate - PDE phosphodiesterase - VCO₂ carbon dioxide production - VPB ventricular premature beat - VE minute ventilation - VO₂ oxygen uptake Dedicated to Professor Jahrmärker on the occasion of his seventieth birthday     

Effect of increased blood fluidity through hemodilution on coronary circulation at rest and during exercise in dogs

Summary Coronary flow and myocardial oxygen consumption were measured in conscious dogs at rest and during two levels of submaximal treadmill exercise (3 and 7 km/h at 15% grade, respectively) during adaptation to progressive hemodilution with dextran 60. At rest coronary flow increased to more than seven-fold with diminishing hematocrit to 12.5% in order to cover myocardial oxygen consumption which increased from 6.5±0.3 ml/min· 100 g at hematocrit 47.5% to 13.5±0.8 ml/min· 100 g at hematocrit 12.5%. The dilatory capacity of the coronary vessels, estimated from the reactive hyperemia after a 12 sec occlusion of the left circumflex coronary artery, dropped from 602% at control to 45% at lowest hematocrit levels.During the superimposed stress of exercise coronary flow and myocardial oxygen consumption increased further, so that the dilatory capacity of the coronaries was exhausted at hematocrit levels between 16 and 22%.Myocardial oxygen consumption per unit of oxygen delivered to peripheral tissues increased substantially with progressive hemodilution. In the presence of the reduced arterial oxygen content the augmented myocardial oxygen demand limits the overall adaptability to hemodilution by an exhaustion of the coronary dilatory capacity.Supported by Deutsche Forschungsgemeinschaft.     

Increase in oxygen consumption induced by selective spinal cord cooling in the exercising pigeon

Six domestic pigeons with chronically implanted spinal thermodes were exercised on a treadmill at neutral ambient temperature. During the exercise the spinal cord was cooled to 34.7±0.4°C (mean±S.E.M.). Oxygen consumption of the pigeons increased from 28.3 ±2.1 to 61.2±3.7 ml·min^–1·kg^–1 due to exercise per se, and superimposed cooling of the spinal cord during exercise induced an additional increase in oxygen consumption to 84.9±4.5 ml·min^–1·kg^–1. The result demonstrates that cooling of the spinal cord elicits shivering in exercising pigeons at thermoneutral conditions.     

Right atrial pressure and forearm blood flow during prolonged exercise in a hot environment

Right atrial pressure (RAP) at rest is known to be reduced by an increase in skin blood flow (SkBF) in a hot environment. However, there is no clear evidence that this is so during exercise. To clarify the effect of the increase in SkBF on RAP during exercise, we measured forearm blood flow (FBF) (as an index of SkBF) and RAP continuously using a Swan-Ganz catheter in five male volunteers exercising on a cycle ergometer at 60% of peak aerobic power for 50 min in a hot environment (30°C, relative humidity 20%). Cardiac output increased from 5.5±0.21/min at rest to 17.9±1.21/min (mean±SE, P<0.01) in the first 10 min of exercise and then remained steady until the end of exercise. FBF did not change significantly during the first 5 min, but then increased from 2.7±0.5 ml/100 ml per min at rest to 10.8±1.7 ml/100 ml per min (P<0.001) by 25 min as pulmonary arterial blood temperature (T _b) rose from 37.0±0.1°C to 38.1±0.1°C (P<0.001). FBF then reached a plateau, despite a continuing increase in T _b. RAP increased significantly from 4.3±0.8 to 7.6±1.2 mm Hg (P<0.001) during the first 5 min of exercise and then gradually declined to 6.1±1.0 mm Hg by 25 min (P<0.001 vs. 5 min) and further to 5.7±1.0 mm Hg by 50 min, a value not significantly higher than at rest. This reduction in RAP during exercise was significantly correlated with the increase in FBF (r=–0.97, P<0.001) with a regression equation of RAP=–0.25×FBF+8.8. These results suggest that the decrease in RAP after 5 min exercise was caused by an increase in SkBF during exercise in a hot environment.Part of this work has been published in abstract form [FASEB J 5A1400 (1991)]     

Thermoregulation in hyperhydrated men during physical exercise

Summary The influence of hyperhydration on thermoregulatory function was tested in 8 male volunteers. The subjects performed cycle exercise in the upright position at 52%V _{O 2max} for 45 min in a thermoneutral (Ta=23° C) environment. The day after the control exercise the subjects were hyperhydrated with tap water (35 ml · kg^–1 of body weight) and then performed the same physical exercise as before.Total body weight loss was lower after hyperhydration (329±85 g) than during the control exercise (442±132 g),p<0.05. The decrease in weight loss after hyperhydration was probably due to a decrease in dripped sweat (58±64 and 157±101 g,p<0.05). With hyperhydration delay in onset of sweating was reduced from 5.8±3.2 to 3.7±2.0 min (p<0.05), and rectal temperature increased less (0.80±0.20 and 0.60±0.10° C,p<0.01). The efficiency of sweating was higher in hyperhydrated (81.4%) than in euhydrated subjects (57.1%),p<0,01. It is concluded that hyperhydration influences thermoregulatory function in exercising men by shortening the delay in onset of sweating and by decreasing the quantity of dripped sweat. As a result, the increases in body temperature in hyperhydrated exercising men are lower than in normally hydrated individuals.     

Right ventricular function in patients with chronic obstructive pulmonary disease

Summary Simultaneous right heart catheterization and radionuclide ventriculography were performed in 27 patients with a wide range of chronic obstructive pulmonary disease. Central hemodynamics and radionuclide studies were done at rest and during exercise. In the resting state the right ventricular ejection fraction (RVEF) was in the normal range (43.3±6%). During exercise a significant (p<0.001) decrease of RVEF to 38.8±6.7% occurred. The pumonary artery mean pressures were 19.9±3.8 at rest. During exercise a significant (p<0.001) increase to 41±9.8 mm Hg occurred. There was a linear relationship between pulmonary pressures and RVEF during exercise in patients with pulmonary artery pressures not exceeding 35 mm Hg. In patients with right ventricular end-diastolic wall thickness 6 mm a curvilinear relationship between these parameters could be observed with a flattening of the curve at higher pressures (>35 mm Hg) and lower ejection fractions (<35% RVEF). Radionuclide venticulography cannot substitute for right heart catheterization. Echocardiography is useful for interpretation of right ventricular ejection fractions in advanced chronic obstructive pulmonary disease.Abbreviations CI Cardiac index (l/min/m²) - CO Cardiac output (l/min) - COPD Chronic obstructive pulmonary disease - FEV₁ Forced expiratory volume in the first second (ml) - HR Heart rate (B/min) - PAd Pulmonary artery diastolic pressure (mm Hg) - PAP Pulmonary artery mean pressure (mm Hg) - PAs Pulmonary artery peak pressure (mm Hg) - PVR Pulmonary vascular resistance (dyn·s·cm^–5) - PwP Pulmonary capillary wedge pressure (mm Hg) - RAP Right arterial pressure (mm Hg) - Raw Airway resistance (cm H₂/l/s) - RNV Radionuclide ventriculogram - RV Residual volume (l) - RVEF Right ventricular ejection fraction (%) - RVEDVI Right ventricular enddiastolic volume index (ml/m²) - RVEDVI SVI RVEF (ml/m²) - RVESVI Right ventricular endsystolic index (m²/m²) - SVI Stroke volume index (ml/m²) - TLC Total lung capacity (l) - VC Vital capacity (l)     

Effects of pre-exercise carbohydrate feedings on muscle glycogen use during exercise in well-trained runners

Summary The purpose of this study was to examine the effects of pre-exercise glucose and fructose feedings on muscle glycogen utilization during exercise in six well-trained runners ( =68.2±3.4 ml·kg^–1·min^–1). On three separate occasions, the runners performed a 30 min treadmill run at 70% . Thirty minutes prior to exercise each runner ingested 75 g of glucose (trial G), 75 g of fructose (trial F) or 150 ml of a sweetened placebo (trial C). During exercise, no differences were observed between any of the trials for oxygen uptake, heart rate or perceived exertion. Serum glucose levels were elevated as a result of the glucose feeding (P<0.05) reaching peak levels at 30 min post-feeding (7.90±0.24 mmol·l^–1). With the onset of exercise, glucose levels dropped to a low of 5.89±0.85 mmol·l^–1 at 15 min of exercise in trial G. Serum glucose levels in trials F and C averaged 6.21±0.31 mmol·l^–1 and 5.95±0.23 mmol·l^–1 respectively, and were not significantly different (P<0.05). There were also no differences in serum glucose levels between any of the trials at 15 and 30 min of exercise. Muscle glycogen utilization in the first 15 min of exercise was similar in trial C (18.8±8.3 mmol·kg^–1), trial F (16.3±3.8 mmol·kg^–1) and trial G (17.0±1.8 mmol·kg^–1), and total glycogen use was also similar in trial C (25.6±7.9 mmol·kg^–1), trial F (35.4±5.7 mmol·kg^–1) and trial G (24.6±3.2 mmol·kg^–1). In contrast to previous research, these results suggest that pre-exercise feedings of fructose or glucose do not affect the rate of muscle glycogen utilization during 30 min of treadmill running in trained runners.     

Bestimmung des Anteiles der rechten Coronararterie am Coronarsinusausfluß

Zusammenfassung An Hunden in Morphin-Chloralose-Urethan-Narkose wurde der Sinusausfluß, sowie der Zustrom von Blut aus der rechten Coronararterie in den Sinus mit der Teststoffinjektionsmethode gemessen. Durch Farbstoffinjektionen bei geschlossenem Thorax abwechselnd in einen Hauptast der linken Coronararterie und in die rechte Coronararterie wurden bei peripherer Lage des Absaugkatheters im Coronarsinus Zeitkonzentrationskurven registriert. Es berechneten sich folgende Mittelwerte: für die Coronardurchblutung 87,3±7,1 ml/min · 100 g, für die mittlere Durchflußzeit in der linken Coronararterie 8,7±1,7 sec, für die mittlere Durchflußzeit in der rechten Coronararterie 10,5±0,5 sec, für die kürzeste Durchflußzeit in der linken 1,4±0,06 sec und in der rechten Coronararterie 2,5±0,33 sec, für das intracoronare Blutvolumen 12,4±1,0ml/100 g.Im Mittel stammten 1,5±0,2% des Sinusausflusses aus der rechten Kammermuskulatur. Bei normaler Coronardurchblutung wurden Werte unter 1%, bei gesteigerter (300–400 ml/min · 100 g) vorwiegend Werte zwischen 2% und 3% gemessen.

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Summary On closed chest dogs (morphin-chloralose-urethan-anesthesia) coronary sinus outflow and the fraction of blood deriving from the right coronary artery was measured with the testsubstance dilution method. While injections of testsubstance were made alternately into one mainbranch of the left coronary artery and into the right coronary artery time concentration curves were recorded from the coronary sinus blood. The following mean values were calculated: for the coronary flow 87.3±7.1 ml/min · 100 g, for the mean transit time within the left coronary artery 8.7±1.7 sec, for the mean transit time within the right coronary artery 10.5±0.5 sec, for the first appearance time in the left coronary artery 1.4±0.06 sec and in the right coronary artery 2.5±0.33 sec, for the intracoronary blood volume 12.4±1.0 ml/100 g. A mean value of 1.5±0.2% was found for the fraction of coronary sinus outflow deriving from the right ventricle muscle. At normal myocardial flow mainly values below 1%, at enhanced myocardial flow (300–400 ml/min × 100 g) mainly values between 2% and 3% were measured.

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Effect of exercise on systemic blood pressure and heart rate in horses

Summary Carotid loops were prepared in 3 horses several months prior to the experiments. Systemic blood pressure was recorded at rest and during exercise by insertion of a plastic cannula into the carotid artery. The pressure transducer was fixed at the neck of the animal. The blood pressure signal was transmitted by telemetry.When the horses were standing under the rider, the following results were obtained: heart rate 38±5 beats · min^–1, systolic pressure 115±15, disstolic pressure 83±10, mean pressure 97±12, and pulse pressure 32±9 mm Hg. During steady gallop at a mean speed of 548±90 m · min^–1, heart rate rose to 184±23 beats · min^–1, systolic pressure to 205±23, diastolic pressure to 116±12, mean pressure to 160±20 and pulse pressure to 89±19 mm Hg. These values remained stable throughout the exercise period of 5–6 min.When the horses were exercised at stepwise increasing speed from walk through trot to gallop, both the mean arterial blood pressure and the pulse pressure rose in proportion to the running speed.     

Plasma renin activity and plasma catecholamines in intact and splenectomized running and swimming beagle dogs

Summary The influence of splenectomy in the dog on plasma catecholamine levels and plasma renin activity during treadmill running and swimming was investigated. Plasma catecholamines were measured by a radioenzymatic assay and plasma renin activity by a radioimmunoassay. Exercise consistently increased plasma catecholamine levels before and after splenectomy (range of increase:3–38 pmol·ml^–1). Swimming, however, was a stronger stimulus than running. No change in the ratio between noradrenaline and adrenaline was found. In intact dogs exercise results in a marked increase in hematocrit due to splenic contraction (range of increase 3–8 volume %), while renal blood flow and plasma renin activity remain virtually constant. In splenectomized dogs, exercise has been reported to induce a decrease in renal blood flow. In contrast to this known effect on renal blood flow, splenectomy did not affect plasma renin activity in treadmill running dogs. In swimming dogs, however, plasma renin activity was increased after splenectomy (range of increase 3.3–6.9 ng·Ang I·ml^–1·h^–1). Possibly, a threshold in sympathetic tone is required to increase renin release in the dog.     

Effect of anaerobic and aerobic exercise of equal duration and work expenditure on plasma growth hormone levels

Summary Growth hormone (GH) and lactic acid levels were measured in five normal males before, during and after two different types of exercise of nearly equal total duration and work expenditure. Exercise I (aerobic) consisted of continuous cycling at 100 W for 20 min. Exercise II (anaerobic) was intermittent cycling for one minute at 285 W followed by two minutes of rest, this cycle being repeated seven times. Significant differences (P<0.01) were observed in lactic acid levels at the end of exercise protocols (20 min) between the aerobic (I) and anaerobic (II) exercises (1.96±0.33 mM·l^–1 vs 9.22±0.41 mM·l^–1, respectively). GH levels were higher in anaerobic exercise (II) than in aerobic (I) at the end of the exercise (20 min) (2.65±0.95 g·l^–1 vs 0.8±0.4 g·l^–1;P<0.10) and into the recovery period (30 min) (7.25±6.20 g·l^–1 vs 2.5±2.9 g·l^–1;P<0.05, respectively).     

The hormonal responses to repetitive brief maximal exercise in humans

Summary The responses of nine men and nine women to brief repetitive maximal exercise have been studied. The exercise involved a 6-s sprint on a non-motorised treadmill repeated 10 times with 30 s recovery between each sprint. The total work done during the ten sprints was 37,693±3,956 J by the men and 26,555±4,589 J by the women (M > F,P<0.01). This difference in performance was not associated with higher blood lactate concentrations in the men (13.96± 1.70 mmol·^–1) than the women (13.09±3.04 mmol·l^–1). An 18-fold increase in plasma adrenaline (AD) occurred with the peak concentration observed after five sprints. The peak AD concentration in the men was larger than that seen in the women (9.2 +- 7.3 and 3.7 ± 2.4 nmol · l^–1 respectively,P<0.05). The maximum noradrenaline (NA) concentration occurred after ten sprints in the men (31.6±10.9 nmol·l^–1) and after five sprints in the women (27.4 ± 20.8 nmol · l^–1). Plasma cardiodilatin (CDN) and atrial natriuretic peptide (ANP) concentrations were elevated in response to the exercise. The peak ANP concentration occurred immediately postexercise and the response of the women (10.8 ± 4.5 pmol · l^–1 was greater than that of the men (5.1 ± 2.6 pmol · l^–1,P<0.05). The peak CDN concentrations were 163 ± 61 pmol · l^–1 for the women and 135 ± 61 pmol · l^–1 for the men. No increases in calcitonin gene related peptide (CGRP) were detected in response to the exercise. These results indicate differences between men and women in performance and hormonal responses. There was no evidence for a role of CGRP in the control of the cardiovascular system after brief intermittent maximal exercise.     

Respiratory alkalosis: no effect on blood lactate decline or exercise performance

Summary It was the purpose of this study to determine the effects of respiratory alkalosis before and after high intensity exercise on recovery blood lactate concentration. Five subjects were studied under three different acid-base conditions before and after 45 s of maximal effort exercise: 1) hyperventilating room air before exercise (Respiratory Alkalosis Before=RALB, 2) hyperventilating room air during recovery (Respiratory Alkalosis After=RALA), and 3) breathing room air normally throughout rest and recovery (Control =C). RALB increased blood pH during rest to 7.65±0.03 while RALA increased blood pH to 7.57±0.03 by 40 min of recovery. Neither alkalosis treatment had a significant effect on blood lactate concentration during recovery. The peak lactate values of 12.3±1.2 mmol · L^–1 for C, 11.8±1.2 mmol · L^–1 for RALB, and 10.2±0.9 mmol · L^–1 for RALA were not significantly different, nor were the half-times (t _1/2) for the decline in blood lactate concentration; C=18.2 min, RALB=19.3 min, and RALA=18.2 min. In C, RALB and RALA, the change in base excess from rest to postexercise was greater than the concomitant increase in blood lactate concentration, suggesting the presence of a significant amount of acid in the blood in addition to lactic acid. There was no significant difference in either the total number of cycle revolutions (C=77±2, RALB=77±1) or power output at 5 s intervals between RALB and C during the 45 s. These results suggest that the possible range of respiratory alkalosis changes in intact humans may be insufficient 1) to affect recovery blood lactate concentrations, or 2) to affect intense, short-term exercise performance.