Thermoregulation during prolonged exercise in heat: alterations with beta-adrenergic blockade

1987 ◽  
Vol 63 (3) ◽  
pp. 930-936 ◽  
Author(s):  
B. J. Freund ◽  
M. J. Joyner ◽  
S. M. Jilka ◽  
J. Kalis ◽  
J. M. Nittolo ◽  
...  
Keyword(s):  
Prolonged Exercise ◽  
Beta Blockers ◽  
Cycle Ergometer ◽  
Beta Blockade ◽  
Adrenergic Blockade ◽  
Sweat Loss ◽  
Double Blind ◽  
Beta Adrenergic ◽  
Cardiovascular Drift ◽  
Placebo Trial

Thermoregulation and cardiovascular drift were studied under conditions of prolonged exercise in a warm environment (dry bulb temperature 31.7 +/- 0.3 degrees C, rh 44.7 +/- 4.7%) during beta-adrenergic blockade. Fourteen subjects performed 90-min rides on a cycle ergometer at a work rate equivalent to 40% of their control maximal O2 uptake under each of three treatments provided in a randomized double-blind manner: atenolol (100 mg/day), propranolol (160 mg/day), and a placebo. Exercise during the propranolol trial resulted in significantly higher forearm vascular resistance values and significantly lower forearm blood flows (FBF) compared with the placebo trial. However, the significantly lower FBF during propranolol did not significantly alter the rectal temperature (Tre) response to prolonged exercise. In addition, both beta-blockers produced lower FBF for any given Tre, suggesting that beta-adrenergic blockade affects FBF through nonthermal factors. The slight differences in Tre, despite the large differences in FBF between the various treatments, are apparently the result of an enhanced sweat loss and a lower mean skin temperature during exercise with beta-blockade. The uncoupling of FBF and sweat loss provides evidence of independent regulation. The reduction in FBF at any given Tre was concomitant to lower blood pressure values during beta-blockade and suggests that baroreflexes provide significant input to the control of skin blood flow when both pressure and temperature maintenance are simultaneously challenged.

Effect of beta-blockade on the drift in O2 consumption during prolonged exercise

1988 ◽  
Vol 64 (2) ◽  
pp. 753-758 ◽  
Author(s):  
J. K. Kalis ◽  
B. J. Freund ◽  
M. J. Joyner ◽  
S. M. Jilka ◽  
J. Nittolo ◽  
...  
Keyword(s):  
Heart Rate ◽  
Minute Ventilation ◽  
Cycle Ergometer ◽  
Beta Blockade ◽  
Adrenergic Blockade ◽  
Maximal Heart Rate ◽  
O2 Consumption ◽  
Double Blind ◽  
Cycle Ergometer Test ◽  
Ergometer Test

The effect of beta-adrenergic blockade on the drift in O2 consumption (VO2 drift) typically observed during prolonged constant-rate exercise was studied in 14 healthy males in moderate heat at 40% of maximal O2 consumption (VO2max). After an initial maximum cycle ergometer test to determine the subjects' control VO2max, subjects were administered each of three medications: placebo, atenolol (100 mg once daily), and propranolol (80 mg twice daily), in a randomized double-blind fashion. Each medication period was 5 days in length and was followed by a 4-day washout period. On the 3rd day of each medication period, subjects performed a maximal cycle ergometer test. On the final day of each medication period, subjects exercised at 40% of their control VO2max for 90 min on a cycle ergometer in a warm (31.7 +/- 0.3 degrees C) moderately humid (44.7 +/- 4.7%) environment. beta-Blockade caused significant (P less than 0.05) reductions in VO2max, maximal minute ventilation (VEmax), maximal heart rate (HRmax), and maximal exercise time. Significantly greater decreases in VO2max, VEmax, and HRmax were associated with the propranolol compared with the atenolol treatment. During the 90-min submaximal rides, beta-blockade significantly reduced heart rate. Substantially lower values for O2 consumption (VO2) and minute ventilation (VE) were observed with propranolol compared with atenolol or placebo. Furthermore, VO2 drift and HR drift were observed under atenolol and placebo conditions but not with propranolol. Respiratory exchange ratio decreased significantly over time during the placebo and atenolol trials but did not change during the propranolol trial.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of beta-adrenergic blockade on the control of sweating in humans

1986 ◽  
Vol 61 (5) ◽  
pp. 1701-1705 ◽  
Author(s):  
G. W. Mack ◽  
L. M. Shannon ◽  
E. R. Nadel
Keyword(s):  
Skin Temperature ◽  
Sweat Rate ◽  
Energy Balance Equation ◽  
Cycle Ergometer ◽  
Beta Blockade ◽  
Evaporative Heat Loss ◽  
Adrenergic Blockade ◽  
Beta Adrenergic ◽  
Local Skin ◽  
Ergometer Exercise

To evaluate the role of beta-adrenergic receptors in the control of human sweating, we studied six subjects during 40 min of cycle-ergometer exercise (60% maximal O2 consumption) at 22 degrees C 2 h after oral administration of placebo or nonselective beta-blockade (BB, 80 mg propranolol). Internal temperature (esophageal temperature, Tes), mean skin temperature (Tsk), local chest temperature (Tch), and local chest sweat rate (msw) were continuously recorded. The control of sweating was best described by the slope of the linear relationship between msw and Tes and the threshold Tes for the onset of sweating. The slope of the msw-Tes relationship decreased 27% (P less than 0.01), from 1.80 to 1.30 mg X cm-2 X min-1 X degree C-1 during BB. The Tes threshold for sweating (36.8 degrees C) was not altered as the result of BB. These data suggest that BB modified the control of sweating via some peripheral interaction. Since Tsk was significantly (P less than 0.05) reduced during BB exercise, from a control value of 32.8 to 32.2 degrees C, we evaluated the influence of the reduction in local skin temperature (Tsk) in the altered control of sweating. Reductions in Tch accounted for only 45% of the decrease in the slope of the msw-Tes relationship during BB. Since evaporative heat loss requirement during exercise with BB, as estimated from the energy balance equation, was also reduced 18%, compared with control exercise, we concluded that during BB the reduction in sweating at any Tes is the consequence of both a decrease in local Tsk and a direct effect on sweat gland.

Effect of beta-adrenergic blockade on lactate turnover in exercising dogs

1984 ◽  
Vol 57 (6) ◽  
pp. 1754-1759 ◽  
Author(s):  
B. Issekutz
Keyword(s):  
Plasma Glucose ◽  
Lactate Production ◽  
Hormonal Control ◽  
Glucose Turnover ◽  
Beta Blockade ◽  
Adrenergic Blockade ◽  
Metabolic Clearance ◽  
Beta Adrenergic ◽  
Indwelling Catheters ◽  
Lactate Turnover

Dogs with indwelling catheters in the jugular vein and in the carotid artery ran on the treadmill (slope: 15%, speed: 133 m/min). Lactate turnover and glucose turnover were measured using [U-14C]lactate and [3-3H]glucose as tracers, according to the primed constant-rate infusion method. In addition, the participation of plasma glucose in lactate production (Ra-L) was measured with [U-14C]glucose. Propranolol was given either (A) before exercise (250 micrograms/kg, iv) or (B) in form of a primed infusion administered to the dog running at a steady rate. Measurements of plasma propranolol concentration showed that in type A experiments plasma propranolol fell in 45 min below the lower limit of the complete beta-blockade. In the first 15 min of work Ra-L rose rapidly; then it fell below that of the control (exercise) values. During steady exercise, the elevated Ra-L was decreased by propranolol infusion close to resting values. beta-Blockade doubled the response of glucose production, utilization, and metabolic clearance rate to exercise. In exercising dogs approximately 40-50% of Ra-L arises from plasma glucose. This value was increased by the blockade to 85-90%. It is concluded that glycogenolysis in the working muscle has a dual control: 1) an intracellular control operating at the beginning of exercise, and 2) a hormonal control involving epinephrine and the beta-adrenergic receptors.

Effects of beta-blockade on exercise capacity of trained and untrained men: a hemodynamic comparison

1986 ◽  
Vol 60 (4) ◽  
pp. 1429-1434 ◽  
Author(s):  
M. J. Joyner ◽  
B. J. Freund ◽  
S. M. Jilka ◽  
G. A. Hetrick ◽  
E. Martinez ◽  
...  
Keyword(s):  
Stroke Volume ◽  
Treadmill Exercise ◽  
Cardiovascular Fitness ◽  
Beta Blockade ◽  
Adrenergic Blockade ◽  
O2 Uptake ◽  
Double Blind ◽  
Beta 2 ◽  
Male Subjects ◽  
Submaximal Heart Rate

To study the effects of cardiovascular fitness on hemodynamic responses to exercise during beta-adrenergic blockade (BAB), submaximal [60% of maximum O2 uptake (VO2max)] and maximal treadmill exercise data were collected in 11 trained (T, VO2max 63.3 ml X kg-1 X min-1, 26.8 yr) and 11 untrained (UT, VO2max 44.5 ml X kg-1 X min-1, 25.0 yr) male subjects. Subjects completed two maximal control tests followed by a randomized, double-blind series of maximal tests after 1-wk treatments with placebo (PLAC), propranolol (PROP, 160 mg/day, beta 1- and beta 2-blockade), and atenolol (ATEN, 100 mg/day, beta 1-blockade). Treatments were separated by 1-wk washout periods. At 60% of control VO2max T and UT subjects experienced no reductions in O2 uptake (VO2) with either drug. Submaximal heart rate (HR, beats/min) was 134.8 PLAC, 107.0 PROP, 107.9 ATEN (P less than 0.05 both drugs vs. PLAC) in T subjects and 141.1 PLAC, 106.1 PROP, and 105.0 ATEN (P less than 0.05 both drugs vs. PLAC) in UT subjects. Cardiac output (1/min) for T was 17.3 PLAC, 16.9 PROP, 16.5 ATEN (P less than 0.05 ATEN vs. PLAC in T only) and for UT it was 12.2 (PLAC), 11.7 (PROP), 11.5 (ATEN) (P less than 0.05 both drugs vs. PLAC in UT). Stroke volume increased from 129.8 ml (PLAC) to 158.6 (PROP) and 156.2 (ATEN) in T (P less than 0.05 both drugs vs. PLAC) and from 86.8 (PLAC) to 110.0 (PROP) and 109.8 (ATEN) (P less than 0.05 both drugs vs. PLAC) in UT. The increases in stroke volume (SV) were similar in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-adrenergic blockade alters whole-body leucine metabolism in humans

1989 ◽  
Vol 67 (1) ◽  
pp. 221-225 ◽  
Author(s):  
L. S. Lamont ◽  
D. G. Patel ◽  
S. C. Kalhan
Keyword(s):  
Skeletal Muscle ◽  
Blocking Agent ◽  
Whole Body ◽  
Beta Blockade ◽  
Adrenergic System ◽  
Adrenergic Blockade ◽  
Beta Adrenergic ◽  
Leucine Metabolism ◽  
Leucine Oxidation ◽  
Tracer Dilution

This study examined the effects of a nonselective beta-blocking agent on whole-body leucine metabolism in humans. Five normal, healthy subjects (4 male, 1 female) underwent a 6-h primed, constant-rate infusion of L-[1–13C]leucine after 5 days of twice daily oral use of 80 mg propranolol and a placebo. Leucine turnover was determined by tracer dilution and leucine oxidation by 13C enrichment of the expired CO2. Propranolol decreased the total daily energy expenditure from 1,945 +/- 177.5 to 1,619 +/- 92.5 kcal/day (P less than 0.05). A fasting associated decrease in blood glucose and an attenuated rise in free fatty acids and ketones were observed during beta-blockade. Propranolol also increased plasma leucine concentrations (73.1 +/- 8.7 to 103.4 +/- 7.3 mumol/l; P less than 0.05) and leucine oxidation (13.2 +/- 1.2 to 17.1 +/- 1.3 mumol.kg-1.h-1; P less than 0.05), although leucine turnover was not significantly altered (100.5 +/- 7.3 vs. 126.0 +/- 12.3 mumol.kg-1.h-1). In addition, the urinary urea nitrogen-to-creatinine ratio was greater during propranolol administration (0.24 +/- 0.04 vs. 0.34 +/- 0.02 mol/g; P less than 0.05). These data suggest that the beta-adrenergic system plays a role in the modulation of whole-body leucine metabolism in humans. Whether these changes are the result of a direct effect on skeletal muscle or an indirect effect mediated by altering the fuel supply to skeletal muscle cannot be discriminated by the present study.

The Effects of Ingesting Polylactate or Glucose Polymer Drinks during Prolonged Exercise

1991 ◽  
Vol 1 (3) ◽  
pp. 249-256 ◽  
Author(s):  
Thomas D. Fahey ◽  
James D. Larsen ◽  
George A. Brooks ◽  
William Colvin ◽  
Steven Henderson ◽  
...  
Keyword(s):  
Perceived Exertion ◽  
Prolonged Exercise ◽  
Venous Blood ◽  
Sodium Lactate ◽  
Cycle Ergometer ◽  
Fluid Replacement ◽  
Double Blind ◽  
Sodium Potassium ◽  
Glucose Polymer ◽  
Skin Temperatures

Five trained, fasted male cyclists rode a cycle ergometer three times at 50% of,max for 180 min. Using a balanced order, double-blind procedure,subjects were given either a solution containing polylactate (PL: 80% polylactate, 20% sodium lactate, in 7% solution with water), glucose polymer (GP: multidextrin in 7% solution with water), or control (C: water sweetened with aspartame) 5 min before exercise and at 20-min intervals during exercise. Venous blood samples were taken at rest and at 20-min intervals during exercise. In general, PL and GP rendered similar results except that pH and bicarbonate () were higher in PL. There were no differences between treatments in perceived exertion, sodium, potassium, chloride, lactate, heart rate, oxygen consumption, rectal temperature, or selected skin temperatures. These data show that polylactate may help maintain blood glucose and enhance blood buffering capacity during prolonged exercise and could be a useful component in an athletic fluid replacement beverage.

Effect of selective and nonselective beta-blockade on skeletal muscle excitability and fatiguability

1994 ◽  
Vol 76 (6) ◽  
pp. 2461-2466 ◽  
Author(s):  
C. M. Cupido ◽  
A. L. Hicks ◽  
R. S. McKelvie ◽  
D. G. Sale ◽  
A. J. McComas
Keyword(s):  
Skeletal Muscle ◽  
Knee Extensors ◽  
Beta Blockade ◽  
Double Blind ◽  
M Wave ◽  
Fatigue Protocol ◽  
Placebo Trial ◽  
Double Blind Design ◽  
Voluntary Contractions ◽  
Muscle Excitability

The effects of beta-blockade on skeletal muscle excitability and fatiguability during exercise were examined. Ten healthy males (mean age 21.9 +/- 1.1 yr) performed a 4-min fatigue protocol consisting of intermittent isometric voluntary contractions of the knee extensors in one leg. Subjects performed the exercise after treatment with placebo, 100 mg metoprolol, or an equipotent dose of propranolol (60 mg, n = 1; 80 mg, n = 8; 100 mg, n = 1) twice a day for 76 h before testing according to a randomized double-blind design. The evoked twitch torque, maximal voluntary torque, and maximal M-wave amplitude were unaffected by the beta-blockade treatments before fatigue. During the placebo trial, there were significant reductions in the evoked and voluntary torques (77 +/- 15 and 55 +/- 11%, respectively) after the fatigue protocol; however, both the voluntary electromyogram and evoked M waves were well maintained throughout fatigue. The beta-blockade treatments had no significant effect on torque or electromyogram activity over the course of the exercise. Thus, despite evidence for an impairment of dynamic exercise performance with beta 1- and beta 1,2-blockade, there appears to be no effect of these agents on muscle excitability and fatiguability during isometric muscle activity.

Glucose-induced decrease in glucagon and pinephrine responses to exercise in man

1977 ◽  
Vol 42 (4) ◽  
pp. 525-530 ◽  
Author(s):  
H. Galbo ◽  
N. J. Christensen ◽  
J. J. Holst
Keyword(s):  
Prolonged Exercise ◽  
Glucagon Secretion ◽  
Glucose Infusion ◽  
Nonesterified Fatty Acid ◽  
Adrenergic Blockade ◽  
Plasma Glucagon ◽  
Beta Adrenergic ◽  
Propranolol Administration ◽  
Glycogen Utilization ◽  
Exercise Induced

Seven men ran at 60% of individual maximal oxygen uptake to exhaustion during beta-adrenergic blockade with propranolol or without drugs. After propranolol administration the increases during exercise in plasma glucagon and epinephrine concentrations as well as the decrease in plasma glucose concentrations were faster than in control experiments. When euglycemia was maintained by glucose infusion during beta-adrenergic blockade, glucagon and epinephrine responses to exercise, although not abolished, were markedly reduced. The diminution of the exercise-induced decline in glucose concentrations correlated significantly with the diminution of the glucagon as well as the epinephrine responses. Thus decreased glucose concentrations may significantly enhance the secretion of glucagon and epinephrine during prolonged exercise in man. Since the diminution of the glucagon response produced by glucose infusion was not accompanied by significant alterations in the levels of nonesterified fatty acid (NEFA) and glycerol, increased glucagon secretion does not seem to be a major determinant of lipolysis during exercise in man. During glucose infusion, glycogen utilization rates in muscle (n = 4) tended to decrease, whereas carbohydrate combustion rate and concentrations of norepinephrine, insulin, alanine, and lactate were unchanged.

Effects of beta-adrenergic blockade on O2 uptake during submaximal and maximal exercise

1983 ◽  
Vol 54 (4) ◽  
pp. 901-905 ◽  
Author(s):  
P. A. Tesch ◽  
P. Kaiser
Keyword(s):  
Heart Rate ◽  
Maximal Exercise ◽  
Pulmonary Ventilation ◽  
Submaximal Exercise ◽  
Beta Blockade ◽  
Adrenergic Blockade ◽  
Maximal Heart Rate ◽  
O2 Consumption ◽  
O2 Uptake ◽  
Beta Adrenergic

Changes in cardiorespiratory variables and perceived rate of exertion (RPE) were studied in 13 trained men performing cycling exercise before and after beta-adrenergic blockade. Propranolol (Inderal, 80 mg) was administered orally 2 h prior to standardized maximal and submaximal exercises. Muscle biopsies were obtained from vastus lateralis at rest for subsequent histochemical analyses of muscle fiber type distribution and capillary supply. During submaximal exercise O2 consumption decreased from 2.76 to 2.59 l . min-1 following blockade (P less than 0.01), whereas heart rate decreased from 157 to 113 beats . min-1 (P less than 0.001). Maximal O2 uptake was lowered from 3.79 to 3.26 l . min-1 (P less than 0.001) and maximal heart rate was reduced from 192 to 142 beats . min-1 (P less than 0.001) as a result of the blockade. Pulmonary ventilation was unaltered in both exercise conditions. “Local” RPE was higher (P less than 0.001) than “central” RPE after beta-blockade in both submaximal and maximal exercise. During normal condition this difference did not appear. Changes in both local and central RPE during submaximal exercise were positively correlated to changes in O2 uptake. Individual variations in the metabolic profile of the exercising muscle had no influence on beta-blockade-induced changes in O2 uptake. It is concluded that blockade of beta-adrenergic receptors reduces O2 consumption during submaximal (approximately 73% maximal O2 uptake) and maximal exercise in habitually trained men.

Effects of beta-adrenergic blockade on ventilation and gas exchange during exercise in humans

1983 ◽  
Vol 54 (5) ◽  
pp. 1306-1313 ◽  
Author(s):  
E. S. Petersen ◽  
B. J. Whipp ◽  
J. A. Davis ◽  
D. J. Huntsman ◽  
H. V. Brown ◽  
...  
Keyword(s):  
Heart Rate ◽  
Gas Exchange ◽  
Time Constant ◽  
Minute Ventilation ◽  
Work Rate ◽  
Beta Blockade ◽  
Adrenergic Blockade ◽  
O2 Uptake ◽  
Beta Adrenergic ◽  
Co2 Partial Pressure

The effects of beta-adrenergic blockade induced by intravenous propranolol hydrochloride (0.2 mg/kg) on ventilatory and gas exchange responses to exercise were studied during tests in which the work rate was either increased progressively or maintained at a constant load in six healthy young male subjects. Heart rate during exercise decreased by about 20% and cardiac output, as estimated by a modification of the method of Kim et al. (J. Appl. Physiol. 21: 1338–1344, 1966), by about 15%. The relation between work rate and O2 uptake (VO2) was unaffected by propranolol, whereas maximal O2 uptake (VO2max) decreased by 5% and the anaerobic threshold, estimated noninvasively, was lowered by 23%. The relations between CO2 output (VCO2) and end-tidal CO2 partial pressure (PCO2) and between VCO2 and minute ventilation (VE) were both unaffected. The time constants for changes of VO2, VCO2, and VE during on-transients from unloaded pedaling to either a moderate (ca. 50% VO2max) or a heavy (ca. 67% VO2max) work rate in the control studies were in agreement with previously reported values, i.e., 42, 60, and 69 s, respectively. beta-Blockade was associated with a significantly increased time constant for VO2 of 61 s but with less consistent and insignificant changes for VCO2 and VE. There was a small but significant increase of the time constant for heart rate from 40 to 45 s. It is concluded that propranolol exerts its primary influence during exercise on the cardiovascular system without any discernible effect on ventilatory control.

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