A comparison of the acute haemodynamic effects of propranolol and pindolol at rest and during supine exercise in man

Effects of sex and exercise training on β-adrenoreceptor-mediated opposition of evoked sympathetic vasoconstriction in resting and contracting muscle of rats

This study investigated the hypothesis that β-adrenoreceptor-mediated inhibition of sympathetic vasoconstriction would be enhanced in female compared with male rats, and that endurance exercise training would augment β-adrenoreceptor-mediated inhibition of sympathetic vasoconstriction in male and female rats. Sprague-Dawley rats were randomized into sedentary (male: n = 7; female: n = 8) and exercise-trained (male: n = 9; female: n = 9) groups. Following 4 wk of exercise training or being sedentary, rats were anesthetized and surgically instrumented for stimulation of the lumbar sympathetic chain, muscle contraction and measurement of arterial blood pressure and femoral artery blood flow (FBF). Femoral vascular conductance (FVC) was calculated as FBF/mean arterial pressure. The percentage change of FVC in response to sympathetic stimulation delivered at 2 and 5 Hz was measured at rest and during contraction of the triceps surae muscles before and after β-adrenoreceptor blockade (propranolol: 0.075 mg·kg^-1 iv). We found that, at rest, β-adrenoreceptor blockade decreased (main effect of drug, 2 Hz: P < 0.001; 5 Hz: P < 0.001) sympathetic vasoconstriction. During contraction, sympathetic vasoconstrictor responsiveness was lower (main effect of sex, 2 Hz: P = 0.001; 5 Hz: P = 0.023) in female compared with male rats, and sympatholysis was enhanced (main effect of sex, 2 Hz: P = 0.001; 5 Hz: P < 0.001) in female rats. β-adrenoreceptor blockade decreased (main effect of drug, 2 Hz: P = 0.049; 5 Hz: P < 0.001) evoked sympathetic vasoconstriction in contracting muscle. The present study demonstrated that β-adrenoreceptors do not blunt sympathetic vasoconstriction in resting or contracting skeletal muscle of male or female rats. Sympatholysis was enhanced in female rats; however, this was not attributable to β-adrenoreceptor-mediated blunting of sympathetic vasoconstriction.NEW & NOTEWORTHY β-adrenoreceptors do not inhibit sympathetic vasoconstriction in resting or contracting muscle of male or female rats, regardless of training status. Sympatholysis was enhanced in female, compared to male rats; however, β-adrenoreceptors were not responsible for the enhanced sympatholysis. These findings indicate that β-adrenoreceptors do not contribute to the regulation of sympathetic vasoconstriction in resting and contracting skeletal muscle and suggest that β-adrenoreceptors do not underlie sex differences in the neural control of the circulation.

β-Adrenoreceptors do not oppose sympathetic vasoconstriction in resting and contracting skeletal muscle of male rats

Sympathetic nervous system (SNS) vasoconstriction is primarily achieved through the binding of norepinephrine (NE) to α-adrenoreceptors. However, NE may also bind to β-adrenoreceptors and cause vasodilation that may oppose/blunt SNS-mediated vasoconstriction. Therefore, this study investigated the hypothesis that β-adrenoreceptor–mediated vasodilation opposes evoked vasoconstriction in resting and contracting skeletal muscle. Male (n = 9) Sprague–Dawley rats were anesthetized and surgically instrumented for stimulation of the lumbar sympathetic chain and measurement of arterial blood pressure and femoral artery blood flow. The percentage change of femoral vascular conductance in response to sympathetic chain stimulation delivered at 2 and 5 Hz was determined at rest and during triceps surae skeletal muscle contraction before (control) and after β-adrenoreceptor blockade (propranolol; 0.075 mg·kg−1, intravenously). β-Adrenoreceptor blockade did not alter (P > 0.05) baseline hemodynamics or the hyperemic response to exercise. At the 2 Hz stimulation frequency, sympathetic vasoconstriction was similar (P > 0.05) in control and β-blockade conditions in resting (control, −34% ± 6%; β-blockade, −33% ± 8%) and contracting (control, −16% ± 6%; β-blockade, −14% ± 7%) muscle. At the 5 Hz stimulation frequency, sympathetic vasoconstrictor responsiveness was reduced (main effect of drug, P < 0.05) following β-blockade (rest: control, −52% ± 7%; β-blockade, −51% ± 9%; contraction: control, −32% ± 11%; β-blockade, −29% ± 13%).

Novelty These data indicate that β-adrenoreceptor blockade did not augment sympathetic vasoconstriction at rest or during exercise. The study demonstrates that β-adrenoreceptors do not oppose evoked sympathetic vasoconstriction in resting or contracting skeletal muscle or contribute to functional sympatholysis.

Cardiovascular effects of topical carteolol hydrochloride and timolol maleate in patients with ocular hypertension and primary open-angle glaucoma. Night Study Group

PURPOSE

To compare the effects of topical timolol maleate 0.5% and carteolol hydrochloride 1% on pulse rate and blood pressure.

METHODS

In a randomized, double-masked, parallel-design, multicenter clinical trial, we compared the effects of timolol and carteolol on pulse rate and blood pressure measured by 24-hour ambulatory blood pressure monitoring in 169 adult patients with either ocular hypertension or primary open-angle glaucoma.

RESULTS

From noon to 8 PM, baseline mean pulse rate of 82 to 83 beats per minute (bpm) had decreased by 4 to 6 bpm in both groups after 4 weeks of therapy with timolol or carteolol. From midnight to 4 AM, the pulse rate in the carteolol group was significantly above baseline (P = .005), while the timolol group was significantly below baseline (P < .001). Four times as many patients became bradycardic (heart rate, < 60 bpm) on timolol (18.4%) as did patients on carteolol (4.5%) from midnight to 4 AM. More than twice as many patients exhibited a resolution of their bradycardia with carteolol (46.7%) as did patients treated with timolol (18.2%) from midnight to 4 AM. Overall cardiovascular adverse effects were reported significantly more frequently in the timolol than the carteolol group (P = .002).

CONCLUSIONS

Timolol causes significantly lower mean heart rate during the nighttime and more nocturnal bradycardia than carteolol does in patients with ocular hypertension and primary open-angle glaucoma. These differences may be because of the intrinsic sympathomimetic activity of carteolol.

Changes in the QRS segment during exercise: effects of acute beta-blockade with propranolol

Changes in the QRS complex during exercise may provide information with respect to ischaemic heart disease. The intention with present investigation was to shed light on mechanisms behind QRS changes and to study the possibly confounding effects of beta-blockade on such alterations with exercise. Placebo or propranolol respectively was infused in randomized and double-blinded order in seven young healthy men before a maximum exercise test. Advanced computerized vectorcardiography and impedance cardiography was recorded continuously together with blood pressures and blood samples. The Y-lead magnitude increased significantly with propranolol infusion (P < 0.05), but it tended to decrease in the Z-lead (P < 0.07). While the serum potassium concentrations increased (P < 0.0005), the spatial QRS magnitude tended to decrease irrespective of treatment (P < 0.07). These changes correlated with changes in QR-duration (adj r2 > 0.58). With exercise, the mean spatial QRS magnitude decreased with similar amounts irrespective of treatment. However, propranolol made the magnitude decrease earlier (P < 0.01). No effect of treatment was detected on the decrease in QRS-duration. Immediately after exercise, the QRS complex continued to change as during exercise in the placebo investigations, but did not with propranolol (P < 0.05). These different patterns were most obvious in the first half of the QRS complex in the Y-lead. It is concluded that acute beta-blockade modifies QRS alterations both during and after exercise in healthy subjects. This indicates that such drugs may have confounding effects in evaluations of the diagnostic value of QRS alterations.

Stroke volume during submaximal exercise in endurance-trained normotensive subjects and in untrained hypertensive subjects with beta blockade (propranolol and pindolol)

The effect of beta-adrenergic blockade on stroke volume (SV) at increasing submaximal exercise intensities was studied in 12 endurance-trained normotensive and 12 untrained hypertensive (diastolic blood pressure greater than 95 mm Hg) men, aged 18 to 34 years. Subjects were assigned to each of 3 treatments in a double-blind, randomized order: placebo, propranolol (80 mg twice daily) and pindolol (10 mg twice daily) for 10 days, with a period of 48 to 60 hours from the initial dose to the first treadmill test and a 4-day washout period between drugs. Cardiac output was measured using the carbon dioxide rebreathing method and SV was calculated from cardiac output and heart rate as follows: SV = cardiac output/heart rate. Cardiac outputs were estimated at rest and while walking on a treadmill at 25, 45, 60 and 75% of the subject's previously determined maximal oxygen uptake (VO2max). No significant differences were found in cardiac output between either of the drugs and placebo at rest, or at any of the 4 rates of work. Propranolol significantly increased SV above placebo values (p less than 0.05) for both trained and untrained groups at the intensities of 45, 60 and 75%. Significant differences in SV were found between pindolol and placebo only at the intensities of 60 and 75% in the trained group. Contrary to expectations, SV showed no indication of a plateau with propranolol in the trained subjects throughout the 4 different exercise intensities, whereas a plateau was established under placebo conditions by 45% of VO2max in both trained and untrained subjects. These results suggest that both trained and untrained hypertensive persons can exercise with beta-adrenergic blockade at submaximal levels without compromised cardiac function.

[Effect of a beta 1-receptor blocker on the plasma level of atrial natriuretic peptide in patients with essential hypertension in the exercise test]

In order to investigate the behaviour of atrial natriuretic peptide (ANP) in untreated mild to moderate essential hypertension and the influence of blood pressure normalisation by a beta 1-receptor blocker a study was conducted in groups of normotensive and hypertensive middle aged subjects. 10 normal subjects and 10 patients with essential hypertension (WHO I-II) without any medication and on betaxolol monotherapy were studied at rest and during graded exercise. In addition the response of ANP, cyclic guanosine monophosphate (cGMP) and the renin-aldosterone-system was investigated. Normal subjects and hypertensive patients did not differ in ANP levels at rest and also responded with a comparable exercise dependent increase at all workload levels. A steady decrease of ANP was noticed during the recovery period in both groups. After beta-blocker treatment in the hypertensive patients ANP concentrations significantly rose, both at rest and more pronounced during exercise. cGMP reacted in a similar way but showed a more inert response. A counter-regulatory behaviour between ANP and PRA or aldosterone, as seen under volume shifts, could not be detected. These findings demonstrate that plasma ANP is not altered in untreated essential hypertension. Increased ANP levels in beta 1-blocker treatment may contribute to its blood lowering effect.

Comparison of the acute haemodynamic effects of bopindolol and propranolol at rest and during supine exercise

The acute cardiovascular effects of two beta-adrenoceptor blocking agents, bopindolol and propranolol, were compared in a randomized study in 16 male patients with coronary heart disease. All patients had had an uncomplicated acute myocardial infarction at least 8 weeks earlier. The two drugs reduced the arterial blood pressure to the same extent, both at rest and during exercise. As heart rate and stroke volume were also decreased, cardiac output was reduced, whereas systemic vascular resistance was increased at rest and during exercise. Left ventricular filling pressure was increased. No statistically significant differences in these variables were seen between the two groups.

Exercise capacity and hemodynamics in persons aged 20 to 50 years with systemic hypertension treated with diltiazem and atenolol

Hemodynamic responses and exercise capacity were studied during maximal exercise in 25 young hypertensive persons (mean age 40 years) taking placebo, diltiazem (mean 216 mg/day) and atenolol (mean 80 mg/day). The study was a crossover, double-blind, randomized trial, each medication period lasting 2 months. Sitting blood pressure (BP) was 160 +/- 19/109 +/- 8 mm Hg after run-in. Both drugs decreased BP significantly, diltiazem by 10/ 11 mm Hg and atenolol by 16/14 mm Hg (difference not significant between drugs). During exercise there were no differences among patients taking placebo, diltiazem and atenolol in peak workload and rating of perceived exertion. Atenolol significantly attenuated the increase in heart rate, BP and heart rate-BP product at each workload. Diastolic BP during exercise was significantly lower (6 to 10 mm Hg) during diltiazem therapy than during placebo at each workload. Thus, both diltiazem and atenolol decrease rest BP significantly without impairing exercise capacity.

Treatment of essential hypertension today. The role of beta blockers, calcium antagonists, and ACE inhibitors

The greater sensitivity of echocardiography than electrocardiography has revealed left ventricular hypertrophy (LVH) to occur in a significant minority of patients with systemic hypertension, with the exact prevalence dependent both on how a population is selected and on the sex. race, and possibly age composition of its members. LVH is more closely related to blood pressure recorded in the patient's natural setting during normal activity or exercise--whether measured by portable recorder or home manometer--than to blood pressure measured by the physician. A subgroup of patients with mild essential hypertension exhibit high cardiac output and evidence of supernormal myocardial contractility in the absence of LVH; whereas amongst patients with more sustained hypertension, LVH may be either concentric (associated with high ejection fractions) or eccentric (associated with abnormal responses to exercise). Recent data indicate that echocardiographic detection of LVH identifies mildly hypertensive patients at significant risk, a finding that may aid identification of patients for drug treatment.

Effect of beta 1-adrenoceptor blockade on plasma levels of atrial natriuretic peptide during exercise in normal man

Increased plasma levels of atrial natriuretic peptide (ANP) during exercise have been reported. To investigate the role of tachycardia as a stimulus for release of ANP during exercise the following study was undertaken. Graded exercise was performed in six healthy volunteers before and after beta 1-adrenoceptor blockade. Plasma levels of ANP were determined at different workloads in both cases. At rest and at all workloads during exercise plasma levels of ANP were higher after beta 1-adrenoceptor blockade than without. Therefore, it is unlikely that tachycardia is a major stimulus for secretion of ANP during exercise. It is suggested that increased right atrial pressure and/or pulmonary arterial blood pressure and increased plasma levels of catecholamines are important secretory stimuli for ANP during exercise.

Comparison of the effects of pindolol and propranolol on exercise performance in patients with angina pectoris

The effects of pindolol (mean dose 17 +/- 8 mg/day), a beta-blocking drug with intrinsic sympathomimetic activity (ISA), and propranolol (130 +/- 40 mg/day) on exercise performance in 11 patients with stable angina pectoris were compared. Doses were titrated to symptoms. The design was a randomized, double-blind, crossover protocol with 8 weeks of treatment with each drug. At the end of each drug period, subjects performed 3 exercise tests: a symptom-limited test on a cycle ergometer with measurement of gas exchange parameters; a steady-state exercise test to measure cardiac output by the CO2 rebreathing method; and a supine exercise test with radionuclide angiography. The ISA effect of pindolol was evident at rest in that the heart rate of 82 +/- 4 beats/min was higher than with propranolol (70 +/- 3). At low levels of exercise heart rate, cardiac output and O2 consumption (VO2) were still higher. However, there was no difference in cardiac output or VO2 at higher levels of exercise and no difference in the VO2 at the anaerobic threshold and peak exercise. Peak VO2 was 1,344 +/- 108 ml/min with propranolol and 1,350 +/- 116 with pindolol therapy. There were also no differences in ejection fraction or cardiac volumes at rest or during exercise. The incidence of side effects was similar with both drugs and there was no significant preference for either medication. In conclusion, patients with angina treated with pindolol had the same peak exercise performance as with an 8:1 equivalent dose of propranolol (clinically equivalent), although at lower levels of exercise, VO2, cardiac output and heart rate were higher from the ISA of pindolol.

Effect of pindolol and propranolol on sinus node recovery time and atrioventricular conduction intervals

In a randomized, observer-blind study, the effect of incremental doses of pindolol 0.001, 0.002, 0.003, and 0.004 mg/kg IV and propranolol 0.01, 0.02, 0.03, and 0.04 mg/kg IV on SA nodal recovery time (SNRT) and atrioventricular conduction interval (AH) was assessed in 20 patients (15 men and 5 women age range thirty to seventy-two, mean age fifty-three). AH and His bundle-to-ventricle (HV) intervals and SNRT were measured at spontaneous heart rate and at incremental atrial pacing rates (80, 100, 120, 140 bpm). Both drugs caused significant beta blockade as estimated by the percentage suppression of heart rate increment induced by 3 mcg isoproterenol administered intravenously (pindolol 67.6 +/- 5.3%, P less than 0.007; propranolol 38.6 +/- 10.6%, P less than 0.001). Propranolol significantly prolonged SNRT (P less than 0.05) and AH interval (P less than 0.05). Pindolol did not significantly affect either SNRT (P = 0.25) or AH intervals (P = 0.78). Significant effects on HV interval were not seen. Thus, in the doses tested that resulted in significant beta blockade, propranolol prolonged SA nodal recovery times and depressed AV nodal conduction while pindolol did not affect these variables.

Immediate haemodynamic effects of a novel partial agonist, beta 1-adrenoceptor blocking drug ICI 141,292 after intravenous administration to healthy young volunteers and patients with ischaemic heart disease

ICI 141,292 is a new beta 1-adrenoceptor blocking drug. The beta 1-adrenoceptor antagonistic effect of ICI 141,292 was examined in a double-blind, randomised crossover study in eight healthy young volunteers and compared with atenolol. Three doses of ICI 141,292 (1, 2 and 4 mg) and atenolol 5 mg were administered intravenously. The attenuation in exercise induced tachycardia varied between 16.0 and 21.2% (P less than 0.01). A significant reduction in blood pressure could be demonstrated following all three doses of ICI 141,292 and atenolol during exercise. At rest in the sitting position HR decreased approximately 8% following all three doses of ICI 141,292 and 14.9% after atenolol 5 mg. No changes in blood pressure were observed under resting conditions after any of the drugs. In six patients with ischaemic heart disease the intrinsic sympathomimetic activity following intravenous administration of four sequential doses (0.5, 0.5, 1.0 and 2.0 mg) of ICI 141,292 was examined. HR decreased 7% (P less than 0.05) following ICI 141,292 1 mg with no further decrease following the succeeding doses. Cardiac output decreased 5.2% (P less than 0.05) following a cumulative dose of 4 mg. No significant changes were observed in mean arterial blood pressure, stroke volume or total peripheral resistance whereas an increase in supine resting mean pulmonary arterial pressure of 3.4 mm Hg (P less than 0.05) could be demonstrated. ICI 141,292 seems to be a potent (at least five times as potent as atenolol) beta 1-adrenoceptor blocking agent possessing moderate intrinsic sympathomimetic activity.

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.

Immediate central hemodynamic effects of five different beta-adrenoceptor-blocking agents, acebutolol, atenolol, pindolol, practolol, and propranolol, in patients with ischemic heart disease

The hemodynamic effects of acebutolol were studied in six patients with ischemic heart disease. The changes in heart rate, cardiac output, and arterial blood pressure were determined after intravenous administration of six increasing doses of acebutolol to a cumulative dose of 0.64 mg/kg. After the sixth dose of acebutolol, cardiac output and heart rate were reduced 15% and 8%, respectively. Pulmonary artery pressure was increased by 4 mm Hg. Arterial blood pressure was not changed significantly. The effects of graded doses of acebutolol on heart rate and cardiac output were compared with earlier obtained results after atenolol (0.19 mg/kg), pindolol (0.025 mg/kg), practolol (0.64 mg/kg), and propranolol (0.19 mg/kg). The effects of increasing doses of acebutolol and practolol were very similar and significantly different from the effects of the other three drugs in spite having been administered at equipotent doses. The hemodynamic effects of acebutolol support the hypothesis that the hemodynamic response to beta-adrenoceptor antagonist drugs at rest is determined primarily by the degree of intrinsic sympathomimetic activity, whereas beta-1 selectivity does not modify the central hemodynamic response.

Effects of beta-adrenoceptor antagonists on the pharmacokinetics of lignocaine

In theory, beta-adrenoceptor antagonists could lower the clearance of free lignocaine in three ways (a) by decreasing hepatic blood flow, (b) by competing for plasma binding sites or (c) by inhibiting the enzymes responsible for metabolising lignocaine. The first mechanism has been demonstrated for propranolol and is probably common to all agents lacking intrinsic sympathomimetic activity. The second mechanism is discounted by data showing that propranolol, one of the more highly bound beta-adrenoceptor antagonists, does not alter the free fraction of lignocaine in plasma. In vitro studies support the third mechanism for the more lipid-soluble beta-adrenoceptor antagonists, as does the fact that observed decreases in the clearance of lignocaine in vivo are generally greater than the anticipated maximum lowering of hepatic blood flow.

Hemodynamic response: decrease in cardiac output vs reduction in vascular resistance

From a hemodynamic point of view, an adequate response to antihypertensive therapy would be restoration of a normal circulatory system. In most patients with mild to moderate essential hypertension considered to need drug therapy, the cardinal hemodynamic disturbance is an increased total peripheral resistance (TPR) and a normal or reduced cardiac output (CO). During a 10- to 17-year follow-up of untreated hypertensives, a gradual increase in TPR, increase in MAP, and a decrease in CO and stroke volume (SV) were seen. Hemodynamic responses to chronic drug therapy were studied at rest and during exercise in 250 men with mild to moderate essential hypertension in WHO Stage I. A significant reduction in TPR was seen on thiazide diuretics, nifedipine and verapamil, but there was no increase of subnormal CO or SV. A greater normalization of central hemodynamics was achieved by prazosin, which induced a reduction in TPR and an increase in CO and SV, particularly during exercise. In contrast, beta-blocker therapy was associated with a chronic reduction in CO and heart rate (HR) and usually no reduction in TPRI below pretreatment values. The chronic CO reduction was associated with an increase in arteriovenous oxygen difference. In 14 patients with therapy-resistant hypertension, a marked increase in TPR was found. Captopril induced a reduction in TPR with rest and exercise, and also a reduction in cardiac output. Prolonged therapy for 5 years with beta-blockers did maintain blood pressure control, but with no further decrease in TPR.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the effect of pindolol and propranolol on heart rate after acute and chronic administration

1 The present study compared the effects in healthy volunteers of the acute and chronic administration of placebo, pindolol and propranolol to see if the partial agonist activity of pindolol was reduced by the beta-adrenoceptor blocking activity of pindolol on chronic administration. 2 Five subjects received in random order for 8 days placebo, propranolol 160 mg and pindolol 10 mg; on days 1 and 8 treatments were given twice at 0 and 2 h. Heart rate in supine position and at end of exercise was recorded before dosing and at 2 and 4 h post-dosing on days 1 and 8. 3 Propranolol and pindolol reduced exercise heart rate to the same extent on days 1 and 8. 4 Propranolol reduced supine heart rate more than pindolol on days 1 and 8 but the difference was only significant on day 8.

Pindolol: a review of its pharmacology, pharmacokinetics, clinical uses, and adverse effects

Pindolol is a new noncardioselective beta adrenergic blocking agent with intrinsic sympathomimetic activity. In the treatment of mild to moderate hypertension, pindolol provides effective control of blood pressure in a large majority of patients when administered alone or, more commonly, when combined with a thiazide diuretic. Pindolol is approximately as effective as propranolol in the therapy of hypertension, but in some crossover trials central nervous system side effects were more frequent with pindolol. A "ceiling effect" may be observed as dosages are titrated upward above approximately 20 to 30 mg per day, such that further blood pressure reductions may not be achievable. Some patients will exhibit a paradoxical increase in blood pressure with an increase in dosage. In patients who respond to modest doses of pindolol, twice or even once daily dosing is often adequate. This prolonged duration of hypotensive activity, while not suggested by the kinetics of this or similar drugs, is probably common to most beta blockers. Investigations in small numbers of patients with angina pectoris have reported variable but generally beneficial results with pindolol.

How intrinsic sympathomimetic activity modulates the haemodynamic responses to beta-adrenoceptor antagonists. A clue to the nature of their antihypertensive mechanism

1 A survey has been made of the literature on acute and long-term haemodynamic effects of ten different β-adrenoceptor antagonists.

The β-adrenoceptor blockers are: pindolol, practolol, alprenolol, oxprenolol, acebutolol, penbutolol, metoprolol, atenolol, propranolol and timolol. The total numbers of patients included in this review are 396 patients in 41 acute studies and 410 patients in 36 long-term studies.

2 The effects of β-adrenoceptor blockers on the concentrations of plasma noradrenaline have also been reviewed. Ten studies including 110 patients on non-ISA-β-adrenoceptor blockers and eight studies including 116 patients on pindolol are presented.

3 In the acute studies (i.e. 15-90 min) arterial pressure was lowered by 1-7% and in the long-term studies (i.e. 3 days-5 years) by 6-17%.

4 The degree of cardio-depression induced by the various β-adrenoceptor blockers was inversely correlated with their pharmacologically defined quantity of intrinsic sympathomimetic activity (ISA) both in acute and in long-term studies.

5 In the acute studies the increments in peripheral vascular resistance were directly correlated with the degree of cardio-depression. This suggests that a fall in arterial pressure immediately after administration of a β-adrenoceptor blocker is prevented by increased vasoconstrictor nerve activity mediated through the arterial baroreflex.

6 The compensatory response of vascular resistance to cardio-depression was similar for β₁-selective and non-selective blockers, thereby indicating that extra-junctional vascular β-receptors are relatively unimportant for maintaining basal vascular tone.

7 In the long-term studies the correlation between changes in cardiac output and changes in vascular resistance was shifted to a lower level of vascular resistance. This means that the onset of blood pressure reduction during β-adrenoceptor blockade was associated with a fall in vascular resistance at any level of cardiac output. Thus vascular resistance was higher during treatment with a non-ISA-β-adrenoceptor blocker than during treatment with an ISA-β-adrenoceptor blocker.

8 The level of vascular resistance ultimately attained during treatment with the various β-adrenoceptor blockers appears to be inversely related to their effects on plasma renin activity.

9 The concentration of noradrenaline in plasma rose by approximately 30% during treatment with non-ISA-β-adrenoceptor blockers and fell by more than 30% after pindolol.

10 There is evidence that under propranolol, which reduces cardiac output and hepatic blood flow, the plasma noradrenaline clearance is diminished. Since noradrenaline is mainly cleared from the circulation by the lungs and by the liver, and since pindolol has no effect on cardiac output and hepatic blood flow, one may expect the plasma noradrenaline clearance not to be diminished by pindolol.

11 The reported effects of β-adrenoceptor blockers on plasma noradrenaline may indicate that the release of neurotransmitter is diminished, but in the case of non-ISA-β-adrenoceptor blockers this effect is not reflected by a decreased concentration of noradrenaline in plasma, because its clearance is also reduced.

12 The hypotensive effect of β-adrenoceptor blockers appears to be independent of blockade of postjunctional cardiac-β-receptors, juxtaglomerular-β-receptors and extrajunctional vascular β-receptors. This indicates that blockade of β-receptors at other sites (i.e. centrally and/or prejunctionally) is more important.

Beta-adrenoceptor blockade and psychic stress in man. A comparison of the acute effects of labetalol, metoprolol, pindolol and propranolol on plasma levels of adrenaline and noradrenaline

1 A random double-blind study was performed in healthy volunteers. The immediate effects of three different beta-adrenoceptor blocking agents, metoprolol, pindolol and propranolol, on the plasma concentrations of adrenaline and noradrenaline were compared in a situation of pleasant psychic stimulation during a television-game of tennis. The immediate effects of labetalol in a group of patients with arterial hypertension were studied in a similar experimental situation. 2 During psychic stress the plasma concentration of noradrenaline rose significantly by 85% after placebo, by 95% after labetalol, by 63% after metoprolol and by 55% after propranolol. After pindolol the noradrenaline concentration remained unchanged. 3 During psychic stress the plasma concentration of adrenaline rose significantly by 135% after labetalol, by 110% after metoprolol and by 83% after propranolol. After pindolol and placebo the adrenaline concentration remained unchanged. 4 The present results are taken to indicate that the intrinsic sympathomimetic activity possessed by pindolol prevents the rise in plasma noradrenaline normally seen during psychic stress. It is suggested that beta-adrenoceptor blockers with strong intrinsic sympathomimetic effect reduce the release of catecholamines during psychic stress.

Relationship of plasma catecholamines to blood pressure in hypertensive patients during beta-adrenoceptor blockade with and without intrinsic sympathomimetic activity

1 This study was designed to follow changes in plasma catecholamine concentrations during β-adrenoceptor blockade using doses of antagonists which decreased the mean arterial pressure (MAP) by about 15 mm Hg. Noradrenaline, adrenaline and dopamine were radioenzymatically determined in 34 patients with moderate essential hypertension during an 8 week course of treatment with either pindolol (with intrinsic sympathomimetic activity, ISA) or propranolol (without ISA). Plasma catecholamines were determined before and 1, 7, 28 and 56 days after commencement of treatment and 1 week after discontinuation of treatment.

2 After one day of pindolol therapy plasma catecholamine concentrations were decreased, but no decrease in MAP was observed. After one day of propranolol therapy, however, MAP was decreased, but except for increased levels of adrenaline, plasma catecholamines showed no changes.

3 On the 56th day of therapy both β-adrenoceptor blockers had decreased the MAP. Pindolol therapy had caused a decrease in all three catecholamines whereas propranolol had caused no change except for decreased dopamine levels.

4 One week after cessation of propranolol therapy catecholamines were decreased but the MAP had begun to return to initial values; after cessation of pindolol therapy however, the MAP remained decreased.

5 The dissimilar relationships between blood pressure and catecholamine concentration during pindolol and propranolol therapy are evidence for multiple and different modes of action for β-adrenoceptor blockers with and without ISA. This study demonstrates that catecholamine concentrations were generally decreased during low-dose β-adrenoceptor blocker therapy, with lower catecholamine levels during pindolol treatment than during propranolol treatment.

Effects of propranolol and pindolol on plasma lignocaine clearance in man

1 Steady state concentrations and clearance of lignocaine were determine in eight healthy volunteers during 360 min continuous lignocaine infusion (2 mg/min). Before the infusion propranolol (0.18 mg/kg i.v.), pindolol (0.023 mg/kg i.v.) or placebo were administered in a random double-blind, cross over design. 2 During the infusion of lignocaine heart rate, cardiac output and arterial blood pressure were measured every 60 min. 3 Propranolol decreased heart rate and cardiac output significantly by 10--20%, while pindolol or lignocaine did not change cardiac output or heart rate significantly. None of the drugs changed the arterial blood pressure. 4 Propranolol pretreatment decreased lignocaine significantly by 14.7% and the steady state concentration was increased by 22.5%. Pindolol produced no significant change in steady state concentration or clearance of lignocaine.

Haemodynamic effects of metoprolol and pindolol: a comparison in hypertensive patients

1 In a double-blind study, 36 patients with essential hypertension were randomly allocated to treatment with either metoprolol, 100--300 mg/day, or pindolol, 5--15 mg/day for 6 months. Haemodynamic investigations were made on three separate occasions. Blood flow in the calves and in the forearm was determined by venous occlusion plethysmography after 6 weeks of placebo, after 6 weeks and again after 6 months of active therapy. 2 Both drugs reduced blood pressure significantly, by 17.1/11.8 mm Hg with metoprolol and 21.9/10.9 mm Hg with pindolol after 6 weeks (P less than 0.005). No further changes were seen after 6 months. 3 Heart rate after 6 weeks was significantly reduced by metoprolol (10.7 +/- 2.4 beats/min, P less than 0.001) but not by pindolol (4.4 +/- 2.3 beats/min, NS). After 6 months a significant reduction was seen also in the pindolol group (5.2 +/- 2.1 beats/min, P less than 0.05). 4 The vascular resistance in the calves at rest was reduced by pindolol (P less than 0.05), whereas resistance tended to increase with metoprolol. 5 Resting vascular resistance in the forearm after 6 months was significantly reduced in the metoprolol group (P less than 0.001) as well as in the pindolol group (P less than 0.02). The increase in forearm vascular resistance seen during leg exercise was not influenced by either drug. 6 Vascular resistance at maximal vasodilatation was unchanged in the calves, but a significant reduction (-17.4 +/- 5.7%, P less than 0.01) in the forearm vascular bed was seen after 6 months of pindolol. No change was observed with metoprolol. 7 It is concluded that pindolol reduces elevated blood pressure partly through peripheral vascular mechanism. Metoprolol, on the other hand, probably acts mainly via central cardiac mechanisms.