The effects of acute or chronic ingestion of propranolol or metoprolol on the metabolic and hormonal responses to prolonged, submaximal exercise in hypertensive men

Role of the sympathoadrenergic system in adipose tissue metabolism during exercise in humans

1. The relative roles of sympathetic nerve activity and circulating catecholamines for adipose tissue lipolysis during exercise are not known. 2. Seven paraplegic spinal cord injured (SCI, injury level T3-T5) and seven healthy control subjects were studied by microdialysis and (133)xenon washout in clavicular (Cl) and in umbilical (Um) (sympathetically decentralized in SCI) subcutaneous adipose tissue during 1 h of arm cycling exercise at approximately 60 % of the peak rate of oxygen uptake. 3. During exercise, adipose tissue blood flow (ATBF) and interstitial glycerol, lactate and noradrenaline concentrations increased significantly in both groups. Plasma catecholamine levels increased significantly less with exercise in SCI than in healthy subjects. The exercise-induced increase in interstitial glycerol concentration in subcutaneous adipose tissue was significantly lower in SCI compared with healthy subjects (SCI: 25 +/- 12 % (Cl), 36 +/- 20 % (Um); healthy: 60 +/- 17 % (Cl), 147 +/- 45 % (Um)) and the increase in ATBF was significantly lower (Cl) or similar (Um) in SCI compared with healthy subjects (SCI: 1.2 +/- 0.3 ml (100 g)(-1) min(-1) (Cl), 1.0 +/- 0.3 ml (100 g)(-1) min(-1) (Um); healthy: 2.8 +/- 0.7 ml (100 g)(-1) min(-1) (Cl), 0.6 +/- 0.3 ml (100 g)(-1) min(-1) (Um)). Accordingly, in both adipose tissues lipolysis increased less in SCI compared with healthy subjects, indicating that circulating catecholamines are important for the exercise-induced increase in subcutaneous adipose tissue lipolysis. In SCI subjects, the exercise-induced increase in subcutaneous adipose tissue lipolysis was not lower in decentralized than in sympathetically innervated adipose tissue. During exercise the interstitial noradrenaline and adrenaline concentrations were lower in SCI compared with healthy subjects (P < 0.05) and always lower than arterial plasma catecholamine concentrations (P < 0.05). 4. It is concluded that circulating catecholamines are important for the exercise-induced increase in subcutaneous adipose tissue lipolysis while sympathetic nerve activity is not.

Regulation of fatty acid delivery in vivo

Adipose tissue triacylglycerol (TG) constitutes by far the largest energy store in the body. In order for this TG to be used as a substrate for oxidative metabolism, it has to be exported from adipose tissue and transported to the tissues where it will be used. Following hydrolysis of stored TG, non-esterified fatty acids (NEFA) leave the adipocyte and enter the plasma. Unlike tissues such as skeletal muscle which extract plasma NEFA, in adipose tissue the flow of fatty acids across the cell membrane is bi-directional, outward in times of net fat mobilization such as fasting and exercise, and inward during the postprandial period. Factors regulating NEFA delivery in vivo include hormonal and nervous stimulation of lipolysis, and a variety of factors, local and systemic, which oppose this by suppressing lipolysis. Adipose tissue blood flow (ATBF) is also important. ATBF is increased in states of fat mobilization and fat deposition, although there is evidence that during strenuous exercise the increase in ATBF is not sufficient for export of all the NEFA made available from lipolysis. There are well-documented regional variations in lipolysis. The intra-abdominal depots appear to have the highest rates of TG turnover, the subcutaneous abdominal an intermediate rate, and the gluteal-femoral depots to have relatively sluggish turnover. However, much of the evidence for this derives from studies of isolated adipocytes, and confirmation in vivo is much needed. There are links between abdominal fat deposition and risk of cardiovascular disease which may be mediated through increased fatty acid delivery from abdominal fat depots. The ability of exercise specifically to decrease intra-abdominal fat stores may be yet another health benefit of regular exercise.

On the trail of potassium in heat injury

In both classical and exertional heatstroke and in various animal models of human heat injury, clinical manifestations have included observations of normokalemia, hyperkalemia, and hypokalemia. This review attempts to address these observations as well as the role of potassium and potassium depletion in heat injury with an emphasis on the integration of information from the level of transmembrane potassium transport mechanisms to systems physiology. Under moderate conditions of passive heat exposure or exercise in the heat, the adaptive capacity of the Na-K pump (Na+-K+ ATPase activity) and cotransport mechanisms can ordinarily accommodate the attendant increased efflux of intracellular K+ and influx of extracellular Na+ to maintain ionic equilibrium. Several factors affecting transmembrane K+ kinetics include protracted K+ deficiency, extreme hyperthermia, dehydration, and excessive exertion. These could elicit reduced membrane potentials and conductance, futile cycling of the Na-K pump with concomitant energy depletion and greatly increased metabolic heat production, reduced arteriolar vasodilation, altered neurotransmitter release, or cell swelling, each of which could contribute to the pathophysiology of heat injury. This review represents a preliminary attempt to link transmembrane K+ pathophysiology with clinical heat injury.

The effect of acute vs chronic treatment with beta-adrenoceptor blockade on exercise performance, haemodynamic and metabolic parameters in healthy men and women

1. Variable results have been reported on the effect of beta-adrenoceptor blockers on maximal oxygen uptake (VO2 max) and exercise endurance. This may in part be due to different subject populations, but it could also be due to an adaption of metabolic and haemodynamic responses to exercise during chronic treatment with beta-adrenoceptor blockers. The present study was therefore carried out to examine the effect of acute and chronic administration of the non-selective beta-adrenoceptor blocker propranolol on both peak VO2 and exercise performance in the same subjects. Since the effect of beta-adrenoceptor blockade has not been properly investigated in women, eight healthy women were compared with seven men. Progressive bicycle exercise to exhaustion was performed after propranolol 0.15 mg kg-1 i.v. (acute) or 80 mg three times daily for 2 weeks (chronic) or placebo given according to a double-blind crossover design. 2. Mean (s.e. mean) peak VO2, was significantly reduced from 42.3 (1.6) ml min-1 kg-1 during placebo to 40.3 (1.2, P < 0.05) ml min-1 kg-1 after acute and 39.1 (1.2, P < 0.001) ml min-1 kg-1 after chronic propranolol treatment. No significant difference in peak VO2 between the two propranolol treatment regimens was observed (mean difference 1.2, 95% CI -0.1 to 2.4 ml min-1 kg-1). There was no treatment interaction with gender. 3. Cumulative work, 163 (9.3) kJ, was significantly reduced by acute, 148 (7.7, P < 0.001) kJ, and chronic, 147 (7.6, P < 0.001) kJ, administration of propranolol since the time to exhaustion was reduced by 5.3% and 5.3%, respectively. There was no significant difference between the two regimens of propranolol (mean difference 0.2, 95% CI -6.7 to 7.0 kJ) or between the sexes. Maximal knee extensor and handgrip strengths were not affected by propranolol. 4. Whereas sex did not influence ventilatory, haemodynamic or metabolic parameters, some differences were observed between acute and chronic propranolol treatment. During submaximal exercise oxygen uptake was reduced by approximately 2% and RER values increased by 0.04-0.05 after chronic treatment in contrast to no effect of acute propranolol treatment. Heart rate and systolic blood pressure were reduced significantly more after chronic compared with acute propranolol treatment; peak heart rate being 186 (2.2), 147 (2.3) and 134 (2.3) beats min-1, and peak systolic blood pressure being 189 (7), 171 (4) and 161 (4) mmHg after placebo, acute and chronic propranolol administration, respectively. Also the exercise induced rise in potassium and lactate levels were modified differentially; the rise in potassium concentration was less after chronic compared with acute propranolol treatment and lactate levels were reduced only after chronic administration of propranolol. In contrast, ventilation, which was unchanged after propranolol during submaximal exercise, was reduced to similar extent at exhaustion from 108 (6.4) to 97 (7.2) and 96 (5.9) l min-1 after acute and chronic propranolol administration, respectively. Diastolic blood pressure and subjective perception of fatigue were similar across the treatment regimens. 5. The study has demonstrated that acute and chronic administration of propranolol result in different haemodynamic and metabolic response to exercise, although endurance and peak oxygen consumption were reduced to the same extent. The response to propranolol was not significantly different between men and women.

Beta-blockade and lipolysis during endurance exercise

Inhibition of adipose tissue lipolysis may be involved in the impairment of endurance capacity after administration of a beta-adrenoceptor blocker. During endurance exercise, no significant decrease in plasma glycerol and free fatty acid (NEFA) concentrations after beta-adrenoceptor blockade is found. However, the levels during recovery from exhaustion are lower after beta-adrenoceptor blockade. This study was designed to investigate whether the lower levels after exercise are due to beta-adrenoceptor blockade or to the shorter time to exhaustion after administration of a beta-adrenoceptor blocker. In a single-blind study, 11 well-trained male subjects (age 23 (0.9) y) performed a cycle ergometer test at 70% Wmax until exhaustion 2 h after intake of 80 mg propranolol. One week later, the test was repeated after intake of placebo and was stopped at the time of exhaustion in the previous test. Average exercise time was 24 min. During exercise plasma glucose was lower, whereas plasma lactate and the respiratory exchange ratio were significantly higher when the subjects were on propranolol. Glycerol and NEFA concentrations during exercise were not significantly different between the two conditions. Despite an identical exercise time, glycerol and NEFA concentrations during recovery were significantly lower after propranolol treatment. In conclusion, lipolysis is inhibited during exercise after propranolol, probably causing a shift from fat to carbohydrate combustion.

Effects of selective beta 2-adrenoceptor blockade on serum potassium and exercise performance in normal men

1. The differential effects of beta-adrenoceptor subtypes on potassium fluxes and exercise capacity were compared in eight healthy young men using single oral doses of the selective beta 2-adrenoceptor antagonist ICI-118551, the selective beta 1-adrenoceptor antagonist atenolol or the non-selective beta-adrenoceptor antagonist propranolol. The study was randomized, double-blind and placebo controlled. 2. Potassium in the venous effluent from the exercising muscles increased progressively with increasing exercise intensity. This response was augmented by propranolol, whereas neither atenolol nor ICI-118551 modified the response. After exercise potassium concentration fell exponentially with no difference between the treatment regimens. 3. Cumulative work was significantly reduced by ICI-118551 (6.4%, P = 0.04) and by propranolol (12.4%, P less than 0.01), whereas the reduction with atenolol (5.6%) did not reach statistical significance. 4. Atenolol and propranolol reduced peak heart rate by 23% and 29%, and peak systolic blood pressure by 9% and 11% respectively during maximal exercise. ICI-118551 caused a non-significant reduction in heart rate during submaximal exercise, with a significant reduction at maximum exercise (6% reduction), whereas systolic blood pressure was not different from placebo. Diastolic blood pressures were similar across all treatment regimens. 5. Similar glucose concentrations were obtained at baseline and at exhaustion during all treatment regimens. Lactate concentrations were comparable for any given exercise intensity irrespective of treatment regimens. Propranolol reduced lactate concentrations from the exercising muscles at maximum exercise in proportion to the reduction of maximal exercise capacity. 6. The subjective perception of fatigue was not affected by either beta 1- or beta 2-adrenoceptor blockade.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in plasma free fatty acids and glycerols during prolonged exercise in trained and hypertensive persons taking propranolol and pindolol

The extent to which lipolysis is attenuated during prolonged submaximal exercise during beta blockade was determined in 12 normotensive endurance-trained and 12 hypertensive sedentary men using nonselective drugs with and without intrinsic sympathomimetic activity (ISA). Initially, subjects performed a graded treadmill test to determine maximal oxygen uptake (VO2max). This was followed by 2-hour walks at 25 and 45% of the subject's VO2max under each of 3 treatments: pindolol (ISA), propranolol (non-ISA) and placebo. The distribution of medication was randomized and double blinded. Blood samples taken at rest and every 30 minutes during the 2-hour walks were analyzed to determine the concentrations of free fatty acids (FFA) and glycerol. On the basis of the respective changes in FFA, glycerols and the respiratory exchange ratio, beta-adrenergic blockade did not attenuate lipolysis in the untrained hypertensive subjects when compared with the placebo administration. However, beta blockade did demonstrate a tendency to attenuate lipolysis in the trained, normotensive subjects when compared with results after placebo administration. This was particularly evident at 30 minutes of exercise, when both glycerol and FFA concentrations were not increased above resting values under both conditions of beta blockade. No differences between pindolol and propranolol were observed. Therefore, a beta-blocking agent with ISA properties appears to have no clear benefit with respect to lipid metabolism during low and moderate intensity exercise. Furthermore, these data demonstrate that beta blockade does not inhibit exercise-induced lipolysis at low and moderate intensities of exercise as formerly believed, and is unlikely to be the cause of fatigue normally observed during work in patient populations taking beta-blocking medication.

Exercise testing and training with beta-adrenergic blockade: role of the drug washout period in "unmasking" a training effect

To determine whether or not a training effect can be achieved with beta-adrenergic blockade and whether there is a difference between selective and nonselective therapy, we recruited 40 healthy subjects (16 women, 24 men) to participate in a 9-week exercise training program. After a baseline exercise treadmill test, subjects were randomized to oral therapy groups of atenolol, 50 mg daily (AT 50), atenolol, 100 mg daily (AT 100), propranolol, 80 mg twice a day (Prop), or placebo. Repeat exercise tests were performed at week 1, week 8, and at week 9, with week 8 to 9 being a 1-week drug-free washout period. At week 8, maximal oxygen consumption (Max VO2), when compared with baseline levels, was increased slightly in AT 50 (4.2%) and Prop (2.4%), decreased in AT 100 (5.3%), and increased significantly in the placebo group (12.7%). After washout, Max VO2 increased significantly compared with baseline in AT 50, AT 100, and Prop (9.8%, 10.8%, and 9.8%, respectively). We conclude that there is no significant difference between selective and nonselective beta-blockade therapy in the development of a training effect. This effect, however, may not become apparent until the drug is withdrawn.

The importance of potassium and lactate for maximal exercise performance during beta blockade

Changes in femoral vein pH, lactate, glucose and potassium were studied in a double-blind randomized, short-term, dynamic cycle ergometry exercise test on six healthy male subjects after administration of non-selective (timolol), beta-1-selective (atenolol) beta blocker or placebo. The exercise intensity was increased in steps of 200 kpm/min every 2 min until exhaustion. During submaximal exercise, potassium concentrations in blood from the exercising leg muscles increased progressively with increasing exercise intensity, and was significantly higher for any given exercise level following timolol as compared to placebo administration. The potassium concentrations following atenolol were in-between those of timolol and placebo. Despite reduced working capacity after non-selective beta blockade, almost identical potassium concentrations were reached at exhaustion irrespective of treatment regimens (placebo: 6.3, range 5.8-6.8 mmol/l; atenolol: 6.5, range 6.1-7.3 mmol/l and timolol: 6.4, range 6.2-6.8 mmol/l). The increase in s-lactate concentrations was similar across all treatments, and rose in proportion to the increase in the exercise intensity. A biphasic increase in lactate was observed with identical breaking points (anaerobic threshold) irrespective of treatment regimens. There was no difference in glucose concentrations between the treatment regimens. The marked increase in serum potassium during maximal exercise coincides with leg muscle fatigue and may, by its effect on the muscle cell membrane potential, limit the maximal working capacity following beta blockers. The rise in serum potassium may curtail the use of maximal exercise test as an index of cardiac performance in healthy young subjects.

A comparison of the effects of flosequinan, a new vasodilator, and propranolol on sub-maximal exercise in healthy volunteers

1. The effects of steady state flosequinan, a new vasodilator, and propranolol, on glucose mobilisation, lipolysis and plasma potassium concentration during sub-maximal exercise testing were investigated in a double-blind, randomised, three-way crossover study in 12 healthy volunteers. 2. Plasma glucose, potassium and free fatty acid concentration during and after exercise on flosequinan were similar to those on placebo. Exercise heart rates were 7% (+9.2 beats min-1) higher on flosequinan compared with placebo (P less than 0.05). During exercise on propranolol plasma glucose concentrations were comparable with those on placebo but plasma potassium concentrations were higher (mean increase 0.26 mmol l-1, P less than 0.01) whereas free fatty acid concentrations were lower (mean decrease 0.10 mmol 1-1, P less than 0.01). As expected the heart rate on exercise was 25% less (-35 beats min-1) on propranolol (P less than 0.05). 3. These data suggest that, in contrast to propranolol, flosequinan does not adversely affect the mobilisation of the two major sources of energy during sub-maximal exercise.

Difference between beta-1-selective and non-selective beta-blockade during continuous and intermittent exercise

Limiting factors of maximal exercise performance are not clearly defined. In order to differentiate between various factors, maximal exercise was studied during continuous (n = 12) and intermittent (n = 9) exercise. The non-selective beta-blocker timolol (10 mg b.i.d. for 5 days) was compared double-blind and placebo controlled with the beta-1-selective beta-blocker metoprolol (100 mg b.i.d. for 5 days), with respect to effect on maximal exercise tolerance. Total cumulated work was comparable during continuous and intermittent exercise. Timolol and metoprolol reduced maximal exercise performance. No difference was observed between the two beta-blockers during intermittent exercise. The non-selective beta-blocker caused a greater reduction in exercise performance (10.4%) than the beta-1-selective beta-blocker (4.7%) (P less than 0.05) during continuous exercise. Maximal heart rate was higher with metoprolol than timolol during continuous exercise. The non-selective beta-blocker caused a slightly greater inhibition of lipolysis than the beta-1 selective one. No significant differences in glucose concentrations were observed between the treatment regimens. Exercise caused a marked increase in serum potassium concentrations. Beta-blockade caused further increase in potassium at any given workload. This study indicates that maximal working capacity is comparable during continuous and intermittent exercise. Beta-1-selective and non-selective beta-blockade reduce the maximal working capacity, non-selective more than beta-1-selective. Substrate availability was not responsible for the beta-blocker induced reduction of the working capacity. The rate of rise in serum potassium was significantly higher during beta-blockade and may, therefore, be a limiting factor for the maximal working capacity.

Beta-adrenoceptor blockade and exercise. An update

Blockade of beta-adrenoceptors interferes with haemodynamic and metabolic adaptations and ion balance during dynamic exercise. After administration of a beta-blocker exercise heart rate is reduced. Exercise cardiac output and blood pressure are reduced also, but to a lesser extent than heart rate. At submaximal exercise intensities blood flow to the active skeletal muscle is also reduced. The availability of non-esterified fatty acids for energy production is decreased, due to inhibition of beta-adrenoceptor-mediated adipose tissue lipolysis, and possibly also of intramuscular triglyceride breakdown. During submaximal exercise muscle glycogenolysis is unaffected, but there are indications that the maximal glycogenolytic rate at high exercise intensities is decreased. In normally fed subjects plasma glucose concentration is maintained at a normal level during submaximal endurance exercise after beta-blocker administration, although lower glucose concentrations are found in fasting subjects and during high intensity exercise after beta-blocker administration. Plasma lactate concentrations tend to be somewhat lower after beta-blocker administration while plasma potassium concentration during exercise is increased. beta-Blocker administration may also interfere with thermoregulation during prolonged exercise. Maximal aerobic exercise capacity is reduced in normotensive and probably also in hypertensive subjects after beta-blocker administration. Submaximal endurance performance is impaired to a much more important extent in both groups of subjects. In patients with coronary artery disease, on the other hand, symptom-limited exercise capacity is improved during beta-blocker treatment. Studies on trainability during beta-blocker treatment show inconsistent results in healthy subjects, although the majority of studies suggest a similar training-induced increase in VO2max during placebo and beta-blocker treatment. In patients with coronary artery disease the training effects are also similar in patients treated with beta-blockers and those without. The negative effects of beta-blockers on maximal and especially submaximal exercise capacity should be considered when prescribing beta-blockers to physically active hypertensive patients. The negative influence is shared by all types of beta-blockers, although the impairment of submaximal exercise capacity is more pronounced with non-selective than with beta 1-selective beta-blockers. beta-Blockers with intrinsic sympathomimetic activity have similar effects during exercise to those without intrinsic sympathomimetic activity.

Post-exercise hypotension: the effects of epanolol or atenolol on some hormonal and cardiovascular variables in hypertensive men

1 Eight men with primary hypertension were treated for 3 weeks with placebo, epanolol (200 mg or 400 mg), or atenolol 100 mg in a randomised cross-over study. Each active treatment period was preceded by a 3 week placebo treatment period and both investigators and subjects were blind to the active drug sequence. 2 At the end of each period, measurements were made of resting cardiovascular (heart rate, blood pressure, forearm blood flow) and biochemical variables (plasma renin, angiotensin II, aldosterone, adrenaline, noradrenaline, vasopressin, sodium and potassium concentrations and osmolality). Responses to exercise (including gas exchange, sweat rate, and ratings of perceived exertion) and the reflex cardiovascular adjustments to distal body subatmospheric pressure were also assessed. 3 The reduction of exercise-induced tachycardia by epanolol 400 mg was comparable to that of atenolol. There was very little difference in the effects of atenolol or epanolol 400 mg on resting blood pressure, but in both cases blood pressures were usually significantly lower than with epanolol 200 mg. 4 Although each active treatment influenced the renin-angiotensin system and circulating levels of catecholamines, the exercise-induced reduction in blood pressure was unaffected. Thus, the hypotensive effects of pharmacological and non-pharmacological interventions were additive.

Exercise-induced hyperkalaemia: effects of beta-adrenoceptor blocker vs diuretic

Four groups of eight normotensive male volunteers performed a 60 min bicycle exercise test before and after 2 weeks of either placebo, hydrochlorothiazide (HCTZ, 25 mg day-1), pindolol (PIND, 10 mg day-1) or both drugs in combination using a double-blind, randomized design. During exercise on placebo serum potassium increased by 0.8 mmol l-1. HCTZ significantly decreased potassium levels at rest and during exercise by 0.2 mmol l-1. PIND did not affect resting potassium levels but potentiated the increase by 0.4 mmol l-1 at the end of exercise, and delayed the return to normal of serum potassium after exercise. The addition of HCTZ to PIND offset the potentiating effect of PIND on exercise-induced hyperkalaemia (only after prolonged exercise) and accelerated the return to baseline after exercise. The results indicate that the hypokalaemic effect of HCTZ can oppose the hyperkalaemic effect of PIND during prolonged physical exercise and particularly during recovery.

Adverse reactions and interactions with beta-adrenoceptor blocking drugs

beta-Blocking drugs are widely used throughout the world and serious adverse reactions are relatively uncommon. Most of those which do occur are pharmacologically predictable and may be avoided by ensuring that patients who are to be given beta-blockers do not have a predisposition to the development of bronchospasm, cardiac failure or peripheral ischaemia. In some situations, the use of a beta 1-selective blocking drug may reduce the risk of a severe adverse reaction, but there is little evidence that other ancillary properties such as partial agonist activity are of relevance in this context. Long term experience with many of the beta-blockers in current use suggests that unpredictable major adverse reactions such as the practolol oculomucocutaneous syndrome are unlikely to be repeated, although some of these drugs may be associated with immunological disturbances and some have been implicated in the development of retroperitoneal fibrosis. beta-Blocking drugs appear to be associated with a number of subjective side effects including muscle fatigue, peripheral coldness and some neurological symptoms. These side effects are highly subjective and are therefore difficult to quantify and it is not known whether they are of major importance in terms of their effect upon patients' overall well-being. It cannot be assumed that simply because such side effects can be elicited that they do, in fact, matter. However, because beta-blockers are often prescribed for patients who have no symptoms and for whom the benefits of therapy are generally small, such side effects would be of considerable importance if they had an overall effect upon quality of life. There are theoretical reasons to suppose that the incidence and severity of such side effects may be related to the ancillary properties of the individual drugs, but there is little evidence that parameters such as beta 1-selectivity, or partial agonist activity are clinically important determinants of the severity of these side effects. Lipophilicity, however, may be associated with an increased incidence of neurological symptoms. beta-Blocking drugs may cause a variety of metabolic disturbances including an increase in serum VLDL-cholesterol concentrations. However, long term studies have not shown that such disturbances are associated with an increased risk of cardiovascular disease, indicating that such metabolic changes may not be of major importance in practice. beta-Blocking drugs may be involved in a number of interactions with other drugs, but few of these have been shown to be of clinical significance.(ABSTRACT TRUNCATED AT 400 WORDS)

Plasma catecholamines following exercise in hypertensives treated with pindolol: comparison with placebo and metoprolol

This study re-examines the proposal that beta-adrenoceptor blockers with intrinsic sympathomimetic activity decrease plasma noradrenaline levels. Thirteen patients (aged 29-65 years) with uncomplicated essential hypertension were randomly allocated to a three period, double-blind cross-over trial. The treatment periods, each of 3 weeks duration, were composed of placebo, pindolol (5 mg twice daily) and metoprolol (100 mg twice daily), dispensed in identical capsules. At the end of each treatment period, patients were exercised on a bicycle ergometer to a predetermined workload. Blood pressure and heart rate were measured before, immediately on completion of exercise and after 10 min post-exercise rest. Blood samples for plasma noradrenaline and adrenaline determination were also collected at these times. Blood pressures were similar during treatment with pindolol and metoprolol. As expected, heart rate was consistently lower during metoprolol treatment. Basal, pre-exercise plasma noradrenaline and adrenaline were similar at the end of each treatment period. However, the increase following exercise was significantly greater during metoprolol treatment. The post-exercise increase during pindolol treatment was indistinguishable from that in the placebo period. These findings, in a randomised placebo-controlled study, therefore demonstrate that pindolol does not influence basal or exercise-stimulated plasma noradrenaline and adrenaline concentrations. This is best explained by a lack of effect of pindolol on the plasma clearance of catecholamines, which is impaired by beta-adrenoceptor blockers devoid of intrinsic sympathomimetic activity.

Blood pressure and catecholamines following exercise during selective beta-blockade in hypertension

This study examines and compares the hemodynamic and sympathoadrenal response to bicycle exercise in hypertensive subjects during two weeks' treatment with a cardio-selective (metoprolol) and nonselective (propranolol) beta-blocker. The increase in plasma norepinephrine and epinephrine concentration following exercise was augmented to a similar degree with each beta-blocker. Pre-exercise blood pressure and heart rate were similar for the two drugs. However immediately after exercise and particularly after resting for 20 min post exercise, diastolic blood pressure was lower during metoprolol treatment. Systolic blood pressure was also lower 20 min post exercise during metoprolol treatment. These observations indicate that cardio-selective beta-blockers offer advantages in blood pressure control during exercise through intact vascular beta 2-adrenoceptors opposing sympathetically mediated vasoconstriction.

Exercise performance and beta-blockade

beta-Adrenoceptor blockers (beta-blockers) are common first-choice drugs in the treatment of various cardiovascular disorders. Physical exercise performed during single-dose administration of beta-blockers, however, is associated with an increased rate of perceived exertion; an effect which appears to be partly reduced with long term treatment. Although clinical doses of beta-blockade may reduce heart rate by 30 to 35%, during maximal exercise cardiac output is not equally reduced. Accordingly, most studies have demonstrated increased stroke volume after beta-blockade. This reduction in heart rate is typically accompanied by a decreased VO2max (5 to 15%) in both patients and healthy, trained subjects. This smaller reduction in VO2max, as compared with the decrease in cardiac output, is the result of a partly compensating increased arteriovenous O2 difference. Work capacity as reflected by the ability to perform intense short term or more prolonged steady-state exercise is also impaired following beta-blockade. beta-Adrenoceptors can be subdivided into types beta 1- and beta 2. Blockers which are specific for either beta 1-receptors (beta 1-selective blockers) or both beta 1- and beta 2 receptors (non-selective blockers) differ with regard to their effect on exercise performance. Exercise performance ability, irrespective of exercise intensity and duration, is impaired to a greater extent following non-selective than beta 1-selective blockade at equal reductions in heart rate. This response stems from a decreased energy flux through glycogenolysis during non-selective blockade treatment. Individuals receiving beta-blockade medication therefore show greater adaptive response to physical conditioning during treatment with beta 1-selective than non-selective blockade probably because of greater training intensity with the former therapy. Neither psychomotor performance nor muscular strength and power is negatively affected by beta-blockade. Nevertheless, the ability to perform athletic events requiring high levels of motor control under emotional stress but not high levels of aerobic or anaerobic energy release, is probably increased during beta-blockade.

Exercise and beta-blocking agents

Beta-adrenoceptor-blocking agents produce noticeable effects on exercise performance. In patients with coronary heart disease, exercise capacity may in some cases increase during beta-blockade. Training effects (increased functional capacity, increased maximal oxygen uptake) may be somewhat attenuated in relatively healthy individuals taking beta-blockers, although with vigorous exercise programs, physiologic adaptations to exercise probably do occur.

The effects of acute or chronic ingestion of propranolol or metoprolol on the physiological responses to prolonged, submaximal exercise in hypertensive men

We have studied the physiological responses to 50 min of intermittent, moderate exercise in hypertensive men after the ingestion of a single dose of placebo, propranolol or metoprolol, and also after 28 days treatment. In addition, subjective assessments of mood were made during the last 7 days of each period of chronic treatment. Heart rate and blood pressure, both at rest and during exercise, were significantly reduced by a single dose of propranolol or metoprolol; more marked effects were observed after chronic treatment. Ventilation and gas exchange during exercise were only slightly disturbed by single doses of propranolol or metoprolol, whereas chronic treatment had no effect. Perceived exertion scores were increased after a single dose of either drug, compared to placebo, and the effect of propranolol was greater than that of metoprolol. With chronic treatment there were fewer differences between the perceived exertion scores during exercise, although 'leg' fatigue remained greater after propranolol than after placebo. Sweating from the forehead during exercise was enhanced by a single dose of either beta-adrenoceptor antagonist, with propranolol having the greater effect. After chronic treatment the effect of propranolol was diminished, whereas the effect of metoprolol was maintained. Very few disturbances of mood were found after chronic ingestion of the beta-adrenoceptor antagonists.