Limitation of work performance in normal adult males in the presence of beta-adrenergic blockade

Cerebral oxygenation decreases during exercise in humans with beta-adrenergic blockade

AIM

Beta-blockers reduce exercise capacity by attenuated increase in cardiac output, but it remains unknown whether performance also relates to attenuated cerebral oxygenation.

METHODS

Acting as their own controls, eight healthy subjects performed a continuous incremental cycle test to exhaustion with or without administration of the non-selective beta-blocker propranolol. Changes in cerebral blood flow velocity were measured with transcranial Doppler ultrasound and those in cerebral oxygenation were evaluated using near-infrared spectroscopy and the calculated cerebral mitochondrial oxygen tension derived from arterial to internal jugular venous concentration differences.

RESULTS

Arterial lactate and cardiac output increased to 15.3 +/- 4.2 mM and 20.8 +/- 1.5 L min(-1) respectively (mean +/- SD). Frontal lobe oxygenation remained unaffected but the calculated cerebral mitochondrial oxygen tension decreased by 29 +/- 7 mmHg (P < 0.05). Propranolol reduced resting heart rate (58 +/- 6 vs. 69 +/- 8 beats min(-1)) and at exercise exhaustion, cardiac output (16.6 +/- 3.6 L min(-1)) and arterial lactate (9.4 +/- 3.7 mM) were attenuated with a reduction in exercise capacity from 239 +/- 42 to 209 +/- 31 W (all P < 0.05). Propranolol also attenuated the increase in cerebral blood flow velocity and frontal lobe oxygenation (P < 0.05) whereas the cerebral mitochondrial oxygen tension decreased to a similar degree as during control exercise (delta 28 +/- 10 mmHg; P < 0.05).

CONCLUSION

Propranolol attenuated the increase in cardiac output of consequence for cerebral perfusion and oxygenation. We suggest that a decrease in cerebral oxygenation limits exercise capacity.

Alterations in dynamic heart rate control in the beta 1-adrenergic receptor knockout mouse

beta 1-Adrenergic receptors (beta 1-ARs) are key targets of sympathetic nervous system activity and play a major role in the beat-to-beat regulation of cardiac chronotropy and inotropy. We employed a beta 1-AR gene knockout model to test the hypothesis that beta 1-AR function is critical for maintenance of resting heart rate and baroreflex responsiveness and, on the basis of its important role in regulating chronotropy and inotropy, is also required for maximal exercise capacity. Using an awake unrestrained mouse model, we demonstrate that resting heart rate and blood pressure are normal in beta 1-AR knockouts and that the qualitative responses to baroreflex stimulation are intact. Chronotropic reserve in beta 1-AR knockouts is markedly limited, with peak heart rates approximately 200 beats/min less than wild types. During graded treadmill exercise, heart rate is significantly depressed in beta 1-AR knockouts at all work loads, but despite this limitation, there are no reductions in maximal exercise capacity or metabolic indexes. Thus, in mice, the beta 1-AR is not essential for either maintenance of resting heart rate or for maximally stressed cardiovascular performance.

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.

Effects of recombinant human erythropoietin and exercise training on exercise capacity in hemodialysis patients

The effects of recombinant human erythropoietin (rHuEPO) and exercise training on exercise capacity were evaluated in 20 hemodialysis patients. After improvement of anemia by rHuEPO (Phase I), patients were divided into 2 groups. Group 1, 10 patients, was placed in a 3-month exercise training program. Group 2, 10 patients, served as a control group (Phase 2). A symptom-limited exercise tolerance test was performed at the start of Phase 1 and before and after Phase 2. Hemoglobin (Hb) values were kept constant throughout Phase 2. In Phase 1, maximum workloads (62.0 +/- 19.1 to 76.5 +/- 25.6 W, p < 0.001), maximum O2 uptake (VO2max) (18.7 +/- 3.5 to 2.2 +/- 5.9 ml/min/kg, p < 0.01), and VO2 at anaerobic threshold (AT) (VO2AT) (8.5 +/- 2.1 to 10.2 +/- 2.9 ml/min/kg, p < 0.01) were all improved by rHuEPO. However, in Phase 2, despite unchanged Hb values and maximum workloads, VO2max (20.7 +/- 4.6 to 17.6 +/- 2.6 ml/min/kg, p < 0.05) and VO2AT (10.6 +/- 1.4 to 9.5 +/- 1.8, ml/min/kg p < 0.05) were decreased in Group 2. However, in Group 1, maximum workloads (66.7 +/- 8.2 to 81.7 +/- 7.5 W, p < 0.01) were improved, and VO2max and VO2AT were not decreased significantly in the same period. Exercise training in rHuEPO-treated hemodialysis patients resulted in an improved aerobic exercise capacity, whereas those without exercise training did not have increased capacity. Throughout the study, O2 uptakes were lower than those of nonrenal anemic patients who had similar Hb values. Maximum lactate values also remained low. In conclusion, improvement in the exercise capacity in hemodialysis patients treated with rHuEPO was minimal. Some defects were suggested in the aerobic energy production system in skeletal muscle of dialysis patients. Anemia-improved patients should participate in incremental physical activity to maintain an improved exercise capacity.

Effort blood pressure control in the course of antihypertensive treatment

In 30 patients with mild hypertension (diastolic blood pressure, 95 to 105 mmHg), the antihypertensive effect of rilmenidine 1 mg was compared in a double-blind study, with the effect of hydrochlorothiazide 25 mg. Patients not satisfactorily controlled received a combined therapy on the same doses of the two drugs used. Rilmenidine and hydrochlorothiazide induced a significant reduction (p = 0.01) of supine and erect systolic/diastolic blood pressure 23 hours after drug intake with no change in heart rate. This effect was due to a reduction in cardiac output (bioimpedance method) significant (p = 0.05) only for rilmenidine. Both drugs controlled the increase of effort systolic blood pressure in comparison with placebo on systemic vascular resistance treadmill exercise testing. Effort cardiac output was increased by each treatment in comparison with baseline values. Both at rest and on exertion, there was no effect on systemic vascular resistance induced by the two drugs. In a second group of 10 patients with moderate hypertension (diastolic blood pressure, 105 to 115 mmHg), rilmenidine 1 mg was administered in order to evaluate its efficacy and hemodynamic effects (bioimpedance and radionuclide ventriculography), at rest and during a lying cycloergometer effort test. The drug induced a significant decrease in blood pressure at rest and on exertion four hours after drug intake. This effect was due to a reduction (p = 0.05) in systemic vascular resistance, whereas cardiac output and heart rate remained unchanged. Our results show that the reduction in systolic/diastolic blood pressure induced by rilmenidine 1 mg is comparable with that induced by the well-known antihypertensive drug hydrochlorothiazide in mild hypertension. In moderate hypertension, the 1-mg dose appears to be insufficient in controlling the blood pressure in all patients. The drug exerts its antihypertensive effect through the normalization of the altered hemodynamic parameters of hypertension (high cardiac output and/or increased systemic vascular resistance). Rilmenidine also respects the physiologic increase in blood pressure and cardiac output on exertion.

Comparison of doxazosin and atenolol in mild hypertension, and effects on exercise capacity, hemodynamics and left ventricular function

The effects of once-daily therapy with doxazosin (1 to 8 mg/day) on exercise capacity, left ventricular performance and hemodynamics (radionuclide ventriculography) were compared with those of atenolol (50 to 100 mg/day) and placebo in a randomized, double-blind crossover trial in 16 patients (9 men) with mild hypertension. Both medications controlled blood pressure (BP) to a similar degree (mean BP was 150 +/- 12, 137 +/- 17 and 141 +/- 14 mm Hg for placebo, atenolol and doxazosin, respectively) but by different mechanisms. Changes during maximal semierect bicycle exercise were similar to those seen at rest. Doxazosin decreased total peripheral resistance and maintained cardiac output, whereas atenolol decreased cardiac output. Exercise capacity (136 +/- 56 watts with placebo) was maintained by doxazosin (135 +/- 56 watts) but decreased with atenolol (122 +/- 55 watts). Compared with atenolol, doxazosin slightly increased the left ventricular ejection fraction at rest and during exercise. The significance of this study is in the choice of a first-line antihypertensive agent. Both are once-a-day medications that control BP. However, doxazosin does so by improving the abnormal physiology of essential hypertension and, consequently, does not adversely affect exercise performance.

Exercise haemodynamics and maximal exercise capacity during beta-adrenoceptor blockade in normotensive and hypertensive subjects

1. The effects of atenolol administration on maximal exercise capacity and exercise haemodynamics have been compared in eight normotensive and eight mildly hypertensive subjects, matched for sex, age, body weight, and maximal oxygen uptake, and familiar with maximal exercise testing. 2. Supine and exercise blood pressure, and exercise total peripheral resistance were significantly higher, and exercise cardiac output was significantly lower in the hypertensive than in the normotensive subjects. 3. Administration of atenolol (1 X 100 mg day-1) for 3 days reduced supine and exercise systolic blood pressure, heart rate, and cardiac output, and increased exercise stroke volume. Supine and exercise diastolic blood pressure and exercise total peripheral resistance were unaffected by atenolol. The effects of atenolol did not differ in the normotensive and the hypertensive subjects. 4. Maximal work load, maximal oxygen uptake, and maximal heart rate were reduced to a similar extent in normotensive and hypertensive subjects during atenolol treatment. 5. It is concluded that there is no difference in the effects of short-term atenolol administration on exercise haemodynamics and maximal exercise capacity in normotensive and mildly hypertensive subjects.

A 31P-n.m.r. study of the acute effects of beta-blockade on the bioenergetics of skeletal muscle during contraction

1. The effects of beta-adrenoceptor antagonist administration on skeletal muscle contractile performance and bioenergetics in vivo have been investigated during unilateral sciatic nerve stimulation in the rat. 2. Two muscle stimulation protocols have been used: supramaximal stimulation at 4 Hz, or incremental supramaximal stimulation at 1, 2 and 4 Hz. Changes in high-energy phosphate concentrations were followed using 31P-n.m.r., and gastrocnemius muscle twitch characteristics were monitored continuously. 3. Under all conditions investigated, DL-propranolol administration (2.5 mg/kg body wt.) caused a significant decrease in cyclic AMP concentrations in resting and stimulated gastrocnemius muscle, prevented an increase in heart rate upon muscle stimulation, but did not affect plasma glucose, fatty acid or lactate concentrations in comparison with values obtained in control experiments. 4. Administration of DL-propranolol 5 min or 35 min before unilateral stimulation of 4 Hz had no effect on changes in muscle phosphocreatine, ATP or Pi concentrations, intracellular pH or contractile performance. 5. In contrast, animals receiving DL-propranolol 5 min before unilateral stimulation of 1, 2 and 4 Hz showed a significant deterioration in gastrocnemius muscle tension development during 2 and 4 Hz stimulation compared with control animals. Concurrent with this change in contractile performance was a higher muscle concentration of phosphocreatine, a lower concentration of Pi and no significant change in intramuscular pH compared with control experiments. 6. The changes in muscle performance and bioenergetics observed during the incremental stimulation protocol were not observed when D-propranolol was administered and could be completely circumvented by a short period of muscle stimulation of 4 Hz prior to initiation of the incremental stimulation protocol. 7. Mechanisms are discussed which may account for the failure of gastrocnemius muscle to generate the expected force during the incremental stimulation protocol in the presence of beta-blockade.

Effect of propranolol and verapamil on oxygen utilization, acidosis and fatigue during exercise in stable angina pectoris

Oxygen utilization, arterial and venous blood gas levels, hemodynamic values and exercise tolerance were compared before and after administration of propranolol and verapamil in 10 patients with stable angina pectoris. During exercise, propranolol decreased cardiac output (CO) by 22%; O2 extraction was increased and O2 consumption (VO2) did not change. With verapamil treatment, CO modestly increased (7%), O2 extraction decreased and VO2 did not change. In contrast to O2 utilization, the drugs produced opposite changes in mixed venous and arterial blood gas levels. Propranolol decreased mixed venous pH, increased CO2 tension and decreased the pH of arterial blood. Verapamil increased venous pH and decreased CO2 tension; pH of arterial blood did not change. The drugs yielded similar levels of antianginal efficacy, but patients exercised longer during verapamil therapy and were less fatigued. The hemodynamic and metabolic differences suggest that muscle perfusion during exercise influences the onset of fatigue and may help determine the choice of therapy.

Twenty-four hour effects of oxprenolol Oros and atenolol on heart rate, blood pressure, exercise tolerance and perceived exertion

The effects of oxprenolol, a non-selective beta-blocker with moderate intrinsic sympathomimetic activity (ISA), given by the Oros delivery system, on resting and exercise heart rate and blood pressure have been compared over a 24-h period with those of atenolol, a beta 1-selective blocker without ISA. The effects on maximal and submaximal exercise tolerance and perceived exertion were studied in relation to the level of beta-blockade. 9 healthy subjects were treated with placebo, atenolol, 100 mg/day and oxprenolol Oros, 16/260 mg/day in random order, each for 5 days. Progressive maximal exercise tests and submaximal endurance tests at 80% of maximum aerobic exercise capacity were performed 2, 5 and 24 h after intake of the drugs. The reduction of blood pressure 2 and 5 h after drug intake was less pronounced after oxprenolol Oros than after atenolol, but by 24 h after the last dose the effects were similar. The peak level of beta-blockade (i.e. reduction in maximal exercise heart rate) was similar after oxprenolol Oros and atenolol. The minimal level of beta-blockade 24 h after the last dose was greater after oxprenolol Oros than after atenolol. Maximal exercise capacity and submaximal exercise tolerance were impaired after both beta-blockers. The subjective feeling of exertion did not differ between placebo, atenolol and oxprenolol Oros when related to the relative work load, except after the first minute of exercise, when the rating of perceived exertion was higher after atenolol.

Effect of beta 1-selective and non-selective beta-blockade on work capacity and muscle metabolism

Six well-trained men were studied while performing a maximal bicycle exercise. The seven experiments included in this study were randomized in a double-blind cross-over fashion. On each occasion the subjects were given either placebo or 40, 80, or 160 mg propranolol (non-selective blockade) or 25,50, or 100 mg atenolol (beta 1-selective blockade). After completion of the study each subject had performed once under each of the seven treatments. Heart rate, maximal oxygen uptake (Vo2max), blood lactate and performance time to exhaustion were measured. A muscle biopsy from vastus lateralis was taken at exhaustion after placebo, 80 mg propranolol and 50 mg atenolol trials, for analysis of ATP, creatine phosphate (CP), glucose-6-phosphate (G-6-P), glucose and lactate. The performance time was reduced (P less than 0.05-0.001) with both blockers compared to placebo. At an equal heart rate reduction, Vo2max was equally reduced by both blockers. Performance time, on the other hand, was reduced to a greater extent (P less than 0.05) with propranolol. ATP and CP levels were decreased (P less than 0.05) by both drugs. G-6-P, however, was lower (P less than 0.05) with propranolol than with either placebo or atenolol. No difference was observed between placebo and atenolol. In conclusion, both beta1-selective and non-selective blockade reduced short-term maximal exercise capacity. The major limiting factor seems to be the reduction in oxygen transport. The finding that at an equivalent reduction in Vo2max propranolol reduced performance time to a greater extent than atenolol suggests that beta 2-blockade may reduce performance by mechanisms additional to those that affect oxygen transport.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-adrenoceptor blockade and intrinsic sympathomimetic activity--relevance in the treatment of ischaemic heart disease

Beta adrenoceptor blockade has become one of the major therapeutic interventions in the medical management of ischaemic heart disease over the last 15 years. A number of beta adrenoceptor blockers have been developed with differing pharmacological properties including cardioselectivity and intrinsic sympathomimetic activity (ISA). The relevance of this latter property has been in some doubt. A number of reports suggest that ISA confers haemodynamic benefits although there does not appear to be any clear therapeutic advantage. In addition it would appear that patients with severe or rest angina might benefit more from a pure beta antagonist rather than one with ISA when the beta blocker is used as monotherapy, but this situation rarely arises. This paper reviews and assesses the value of treatment of ischaemic heart disease with beta blockers possessing intrinsic sympathomimetic activity.

Beta-Blockade and Response to Exercise: Influence of Training

In brief: Beta-blockers and exercise training are recommended for treating cardiovascular disease and hypertension, and researchers have tried to determine the interaction of these two treatment modalities. Data from four studies conducted on 93 subjects over the past five years show that beta-blockade exerts a differential effect on the exercise capacity of subjects of different levels of health and fitness: It increases the capacity of angina patients; decreases the capacity of highly trained, fit individuals; and has little or no effect on the capacity of healthy, untrained individuals.

Effect of beta 1-selective and nonselective beta blockade on blood pressure relative to physical performance in men with systemic hypertension

Eleven physically active men with systemic hypertension were studied after 5 weeks of treatment with placebo, atenolol or propranolol. A double-blind, crossover randomized design was used. Blood pressure (BP), heart rate (HR), physical performance capacity, rate of perceived exertion and blood lactate concentrations were measured during rest, exercise to exhaustion and postexercise, at 8 and 24 hours after intake of the last dose. Blood pressure at rest and during exercise was similarly decreased with both drugs (8 and 24 hours), and there was no difference between 8 and 24 hours with any of the treatments. Heart rate (8 hours) was decreased similarly by both drugs, but after 24 hours, HR at increased workloads (above 120 watts) was higher with atenolol compared with propranolol. Maximal HR was lower with propranolol than atenolol at both 8 and 24 hours. Maximal exercise loads (8 and 24 hours) were 231 and 232 watts with placebo, 211 and 212 with propranolol and 228 and 227 with atenolol. That is, maximal workload was decreased with propranolol compared with placebo and atenolol at both 8 and 24 hours. No difference was found between placebo and atenolol at either 8 or 24 hours. The rate of perceived exertion values were higher with propranolol than atenolol. Blood lactate concentrations did not differ according to treatments. The results indicate that atenolol, when given in a dose that decreases resting and exercise BP to the same extent as propranolol, limits physical performance less than propranolol.

Acute response to submaximal and maximal exercise consequent to beta-adrenergic blockade: implications for the prescription of exercise

Forty-seven healthy male subjects, 17 to 34 years old, completed a test to exhaustion on a motor-driven treadmill to determine their maximal oxygen uptake. A second test was administered 2 days later during which the subject walked for 20 to 25 minutes at a steady-state level representing 60% of the maximal oxygen uptake as determined in the first test. The grade was then increased every 2 minutes until the subject reached the state of exhaustion. After the second test, the subjects were randomly assigned, in a double-blind manner, to either placebo, propranolol (160 mg/day), or atenolol (100 mg/day) treatment for 7 days. Exactly 1 week from the time of the second test, and 3 hours after the last medication, the subjects completed the final exercise test using the same treadmill protocol administered in the second test. Heart rate and systolic blood pressure at rest and during submaximal steady-state exercise were significantly reduced by both drugs, whereas diastolic pressure was unaffected. During submaximal steady-state exercise, cardiac output was reduced in both the placebo and atenolol groups, stroke volume was increased in both atenolol and propranolol groups, oxygen uptake was reduced in the atenolol group, pulmonary ventilation was reduced in both propranolol and atenolol groups, and the respiratory exchange ratio remained unchanged. With maximal exercise, treadmill time was significantly reduced with propranolol, pulmonary ventilation and heart rate were reduced significantly with both drugs, but maximal oxygen uptake remained unchanged. Thus, beta blockade does not appear to limit ability to exercise. However, there appears to be a significant advantage to using a cardioselective rather than a nonselective beta-blocking agent.

Improvement in exercise capacity and associated changes in hemodynamics and left ventricular function after the addition of metoprolol to nifedipine in patients with stable exertional angina

In 10 men with stable exertional angina, the changes in exercise capacity, hemodynamics, and left ventricular (LV) function were measured after 20 mg sublingual nifedipine (N) and again after adding 100 mg oral metoprolol (M). Nifedipine alone did not significantly improve exercise workloads (+18%) and duration (+21%), but the addition of metoprolol increased both parameters by a further 37 and 32%, respectively (both p less than 0.005 vs. N). After nifedipine the onset of angina was slightly delayed (5.14 +/- 2.41 min placebo (P), 6.00 +/- 2.31 min N, p less than 0.1) and occurred at higher workloads (36 +/- 17 W P, 43 +/- 8 W N, p less than 0.1). After the addition of metoprolol, the onset of angina was delayed substantially more (9.57 +/- 2.22 min, p less than 0.001 vs. P and N) and occurred at much higher workloads (62 +/- 20 W, p less than 0.001 vs. P and N). At rest (R) and during exercise (E), nifedipine decreased systemic vascular resistance (-36% R, -27% E, both p less than 0.001) and mean arterial pressure (-18% R, -21% E, both p less than 0.001), and increased heart rate (+15% R, +11% E, both p less than 0.001), Pulmonary artery wedge pressure on exercise increased less (22 +/- 7 mmHg P, 13 +/- 5 mmHg N, p less than 0.001). After adding metoprolol, the major change was a reduced heart rate (-25% vs. N at R and E, both p less than 0.001), and arterial pressure was unaltered. Pulmonary artery wedge pressure on exercise increased to 18 +/- 5 mmHg (p less than 0.05 vs. N). Exercise LV ejection fraction and volume did not change significantly after adding metoprolol despite marked improvement in angina. In this acute exercise study in patients with stable exertional angina, metoprolol added to nifedipine markedly improved exercise capacity by preventing the increase in heart rate seen with nifedipine. In our patients with relatively normal LV function at rest, the combination was safe and produced no deleterious effects on LV function.

Maximal aerobic power and blood pressure in normotensive subjects after acute and chronic administration of metoprolol

The acute and long-term effects of the beta 1-adrenoceptor blocking agent metoprolol on blood pressure and maximal aerobic power (Wmax) were studied in 10 healthy subjects. Progressive maximal bicycle ergometer tests were performed after intravenous administration of placebo and metoprolol (0.15 mg . kg-1 and 0.30 mg . kg-1), and at the end of 4-week treatment periods with placebo, conventional metoprolol (C-M) and slow-release metoprolol (SR-M). The reduction in maximal exercise heart rate (HRmax) was correlated with the log plasma metoprolol concentration. Despite a reduction in HRmax of 23 beats/min after 0.15 mg . kg-1 metoprolol, Wmax was unaffected. After 0.30 mg . kg-1 HRmax was reduced by 40 beats/min and Wmax by 5.0%. During chronic treatment, the reductions in HRmax and Wmax were 48 beats/min and 7.5% (C-M) and 45 beats/min and 6.9% (SR-M), respectively. Resting systolic blood pressure was not changed after acute administration of metoprolol but it was reduced during chronic beta-blocker treatment. Resting diastolic blood pressure was not affected after acute or chronic treatment. Exercise systolic blood pressure remained unchanged after 0.15 mg . kg-1 metoprolol i.v. The fall in exercise systolic pressure after 0.30 mg . kg-1 metoprolol i.v. (18 +/- 5 mmHg) was significantly smaller than that during chronic treatment (30 +/- 6 mmHg C-M; 30 +/- 6 mmHg, SR-M). During chronic metoprolol treatment a certain % HRmax corresponded to a higher % Wmax than during placebo treatment, but the shift appeared to be of minor practical importance.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of a week's beta-adrenoceptor antagonism on daytime heart-rates, subjective responses to exercise, and physical activity in normal subjects

The effects on heart rate (HR) and physical activity of 1 week's treatment with three different beta-adrenoceptor antagonists (20 mg betaxolol (Lorex); 160 mg propranolol LA; or 100 mg atenolol daily) have been compared with placebo in a double-blind study of 12 normal men. On the fifth day of each treatment a body-borne tape-recorder was worn during waking hours for recording of ECG and footfall signals. Each record was calibrated in terms of the subject's response to laboratory ergometer exercise, and a computer analysis provided objective indices of physical activity. While on beta-adrenoceptor antagonists the subjects perceived standard exercise as significantly harder than on placebo and reported more side-effects (albeit mild and transient). Ambulatory monitoring of HR showed that subjects spent 13% of their waking day at heart rates below 50 beats min-1 while on propranolol, compared with 1% on placebo and 20% on atenolol and betaxolol. On these latter drugs, the group spent as much as 10% of their waking time with HR below 45 beats min-1. The lowest individual heart-rates recorded were below 35 beats min-1. Objective indices of physical activity, such as the duration of periods spent with heart rates above the HR found at 100 W in the ergometer test, showed no differences between the treatments. This negative finding was confirmed by pedometer step counts over the whole week.

Exercise and hypertension

Hypertension is a major risk factor for atherosclerosis. In this article the authors review the use of physical activity as therapy for elevated blood pressure and explore the hemodynamic effects of exercise among patients with treated and untreated hypertension. Recommendations concerning the use of exercise in the management of hypertension are outlined.

Effects of beta-adrenoceptor blockade on exercise performance and respiratory response in healthy, physically untrained humans

The effects of propranolol 80 mg orally were compared with those of placebo on the response to a stepwise increasing exercise test in 17 healthy and physically untrained volunteers, of whom eight were female. Propranolol showed no significant effects on maximum work rate or perceived exertion rate. However, submaximal O2 uptake, CO2 output and minute ventilation tended to be lower after propranolol than after placebo. It is concluded that in subjects with a low work capacity, beta-adrenoceptor blockade does not impair maximal exercise capacity. The mechanisms underlying changes in respiratory response to exercise after propranolol are not fully explained. However, changes in substrate utilisation, the reduction in cardiac output and an alteration in respiratory drive may all be involved.

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.

Isometric muscle endurance during acute beta-adrenergic blockade

Isometric muscle endurance was measured in fourteen physically active men without (placebo) and after acute oral administration of 160 mg propranolol (Inderal). Quadriceps muscle contractions were sustained at 65% maximum voluntary contraction (MVC) to exhaustion. Muscle biopsies were obtained from m. vastus lateralis at rest for subsequent histochemical analysis for myofibrillar ATPase and amylase-PAS in order to determine fiber type composition and capillary density. The time to exhaustion was shorter (p less than 0.01) during beta-blockade (0.82 +/- 0.22) min than placebo (0.90 +/- 0.23) min. Changes in endurance time, induced by beta-blockade, were not correlated with any of the muscle morphological or histochemical variables examined. It is concluded that muscular performance is impaired as a result of beta-blockade on muscle tissue irrespective of any concomitant change in central circulation.

Intrinsic sympathomimetic activity: clinical fact or fiction?

The therapeutic importance of the ancillary pharmacologic property of partial agonist activity, or intrinsic sympathomimetic activity (ISA), of a beta-adrenoceptor antagonist is controversial. Its pharmacologic definition and accepted physiologic potential are now joined by convincing evidence that ISA may have important therapeutic implications. The ability to support basal cardiac functions while preventing the potential hazards of random sympathetic stimulation is an important attribute of this property, particularly in the damaged heart. The beneficial effects of ISA on peripheral blood flow, systemic vascular resistance and left ventricular afterload are established. Although all beta-blocking drugs are contraindicated in patients with asthma, ISA appears to be at least as important as cardioselectivity in offsetting some of the increase in airway resistance that results from beta blockade alone both at rest and during exertion. These pharmacodynamic consequences of ISA may explain the lesser reduction in exercise tolerance afforded by beta-blocking drugs with ISA than by those without. ISA may also enhance the primary oxygen-sparing effects of beta blockade in the ischemic myocardium by reducing coronary resistance, enhancing coronary blood flow, and reducing anaerobic metabolism. The adverse effects of beta-blocking drugs on blood lipids and carbohydrate metabolism also appear to be largely negated in drugs with ISA. The risks of rebound effects from abrupt withdrawal are significantly less in drugs with ISA than in those without.

Improved exercise ventilatory responses after training in coronary heart disease during long-term beta-adrenergic blockade

Exercise ventilatory responses of 7 men with well-documented myocardial infarction receiving long-term beta-adrenergic blockade were studied before and after 4 months of endurance training. Observations were obtained during graded levels of upright treadmill exercise continued until 85% of the predetermined symptom-limited heart rate (working heart frequency limit). This submaximal testing procedure revealed a significant slowing of the heart rate (p less than 0.005) together with an increased oxygen pulse (p less than 0.05) after training, for what was previously a maximal work load for the working heart frequency limit. In addition, all patients achieved an increased exercise duration and work load, accompanied by significant increases in maximal oxygen uptake (p less than 0.01), oxygen pulse (p less than 0.025), and respiratory exchange ratio, for their working heart frequency limit after exercise conditioning. These results show that prolonged physical training results in physiologic adaptations to cardiac rehabilitation in the presence of long-term beta-adrenergic blockade.

Beta-adrenoceptor blocking drugs: adverse reactions and drug interactions

Beta adrenoceptor blocking drugs are relatively well tolerated and adverse reactions to them are not common. The ones that do occur are reviewed in this paper under the following headings: Short term adverse reactions, drug interactions, long term adverse reactions, risks in pregnancy and hazards of abrupt withdrawal. Predictable short term effects may be caused either by the actions of these drugs on the beta 1- or beta 2-receptors. The beta 1 adverse effects are hypotension, bradycardia and cardiac failure; these are best avoided by not giving beta-adrenoceptor blocking drugs to susceptible patients with cardiac disease. The beta 2 adverse effects on the bronchi, the peripheral arteries and various metabolic functions may be reduced to some extent by using a relatively cardioselective drug. Unpredictable short term effects such as fatigue, sexual dysfunction and gastrointestinal symptoms may occur but are not common problems with this group of drugs. Similarly, serious drug interactions are infrequent. Under the heading of long term adverse effects the practolol problem and the risk of causing malignant disorders have been considered. There is no evidence that any of the currently available drugs will cause either a practolol syndrome or malignant disease in man. However, the need for careful appraisal by drug regulatory bodies and continued vigilance by all prescribers of beta-adrenoceptor blocking drugs remains. The possible adverse effects of treatment during pregnancy are also considered. It now appears that beta-adrenoceptor drugs can be used safely in pregnancy but since neonatal bradycardia and hypoglycemia may occur, care should be taken to look for these complications. A serious deterioration may occur when beta-adrenoceptor drugs, given to patients with significant ischemic heart disease, are suddenly stopped. This is a rare occurrence but prescribers should be aware of it.

Long-term treatment with slow release oxprenolol alone, or in combination with other drugs: effects on blood pressure, lipoproteins and exercise performance

Twenty-eight patients with mild essential hypertension were treated with placebo for six weeks and then with active medication for a further 32 weeks. Twelve patients were well-controlled with 160-320 mg/day of slow release oxprenolol alone, 12 required oxprenolol and chlorthalidone, and four also required hydrallazine. beta-adrenergic blockade reduced the basal level of plasma free fatty acid (FFA) by 41%. A sub-maximal exercise test reduced the level of FFA by 34% during placebo treatment. The same exercise test during beta-blockade reduced the already lowered basal FFA level by a further 45%. Only female subjects experienced exercise-induced leg fatigue during beta-blockade. They always had higher FFA levels than males, but the relative changes in FFA concentration were similar in both sexes. Exercise testing induced a 52 mmHg rise in systolic blood pressure, but this was reduced to only 14 mmHg during treatment. Patients controlled on oxprenolol alone showed no significant change in plasma lipid and lipoprotein levels. Those patients ultimately requiring combination drug therapy experienced a statistically significant rise in plasma triglycerides and a significant fall in high density lipoprotein cholesterol. The biological importance of these changes is uncertain.

Comparison of beta-adrenoceptor blockers under maximal exercise (pindolol v metoprolol v atenolol)

1 The time-related, comparative beta-adrenoceptor blocking effect of metoprolol 150 mg twice daily, atenolol 100 mg once daily and pindolol 7.5 mg twice daily on heart rate, blood pressure, work performance, blood lactate, free fatty acids and plasma catecholamines was studied in ten males aged 19--25 years by means of repeated maximal bicycle exercise tests. 2 At steady state several differences in effects were noted among the drugs. These could be explained by differences in beta 1-selectivity, potency of the chosen drug-doses and intrinsic sympathomimetic activity (ISA). 3 This study emphasizes the importance of including strong sympathetic stimuli in any model used for comparing beta-adrenoceptor blockers with and without ISA in order not to underrate the effects of beta-adrenoceptor blockers with ISA. 4 In the chosen doses pindolol was more effective, and atenolol less effective than metoprolol in suppressing heart rate and blood pressure responses to maximal exercise.