Adrenergic beta receptor blockade: hemodynamic importance of intrinsic sympathomimetic activity at rest

β2-Adrenergic receptor-dependent attenuation of hypoxic pulmonary vasoconstriction prevents progression of pulmonary arterial hypertension in intermittent hypoxic rats

In sleep apnea syndrome (SAS), intermittent hypoxia (IH) induces repeated episodes of hypoxic pulmonary vasoconstriction (HPV) during sleep, which presumably contribute to pulmonary arterial hypertension (PAH). However, the prevalence of PAH was low and severity is mostly mild in SAS patients, and mild or no right ventricular hypertrophy (RVH) was reported in IH-exposed animals. The question then arises as to why PAH is not a universal finding in SAS if repeated hypoxia of sufficient duration causes cycling HPV. In the present study, rats underwent IH at a rate of 3 min cycles of 4-21% O2 for 8 h/d for 6 w. Assessment of diameter changes in small pulmonary arteries in response to acute hypoxia and drugs were performed using synchrotron radiation microangiography on anesthetized rats. In IH-rats, neither PAH nor RVH was observed and HPV was strongly reversed. Nadolol (a hydrophilic β(1, 2)-blocker) augmented the attenuated HPV to almost the same level as that in N-rats, but atenolol (a hydrophilic β1-blocker) had no effect on the HPV in IH. These β-blockers had almost no effect on the HPV in N-rats. Chronic administration of nadolol during 6 weeks of IH exposure induced PAH and RVH in IH-rats, but did not in N-rats. Meanwhile, atenolol had no effect on morphometric and hemodynamic changes in N and IH-rats. Protein expression of the β1-adrenergic receptor (AR) was down-regulated while that of β2AR was preserved in pulmonary arteries of IH-rats. Phosphorylation of p85 (chief component of phosphoinositide 3-kinase (PI3K)), protein kinase B (Akt), and endothelial nitric oxide synthase (eNOS) were abrogated by chronic administration of nadolol in the lung tissue of IH-rats. We conclude that IH-derived activation of β2AR in the pulmonary arteries attenuates the HPV, thereby preventing progression of IH-induced PAH. This protective effect may depend on the β2AR-Gi mediated PI3K/Akt/eNOS signaling pathway.

The possible role of the ancillary properties of beta adrenoceptor antagonists in the management of angina pectoris

Beta adrenoceptor antagonists are effective in the symptomatic management of angina pectoris. This paper examines critically the possible influence of the ancillary properties of beta 1 selectivity, partial agonism and membrane-stabilizing action on the response in anginal patients. The response is categorized according to experimental, pharmacological and clinical endpoints, placing emphasis on the possible errors which may arise from extrapolation from the former to the latter. It is concluded: That selective beta adrenoceptor antagonism confers limited, but tangible advantages over non-selective antagonists in regard to patients with reversible airways obstruction, and also in the metabolic and haemodynamic response to acute hypoglycaemia. Cardioselectivity does not influence the central haemodynamic response to exercise, but lessens adrenaline-mediated hypertensive responses to smoking and hypoglycaemia. Non-selective partial agonists cause less reduction in resting ventricular function, but their effects on cardiac output during exercise are indistinguishable from full antagonists. Membrane stabilizing properties have a marked influence on the tolerability of these agents in terms of unwanted, nonspecific central nervous system symptoms. Unresolved questions relate to the influence of partial agonism on fatigue, metabolic responses, especially blood lipids and glucose, and the possibility of lesser efficacy in angina compared to full antagonists.

Relevance of intrinsic sympathomimetic activity for beta blockers

Intrinsic sympathomimetic activity (ISA) characterizes a group of beta blockers that are able to stimulate beta-adrenergic receptors (agonist effect) and to oppose the stimulating effects of catecholamines (antagonist effect) in a competitive way. Partial agonists are ligands that elicit a submaximal response when bound to beta receptors at maximal occupancy. In the isolated rat atrium, acebutolol produces a maximal stimulatory effect that is only 17 +/- 8% of the maximal effect induced by the full beta agonist isoproterenol. The presence of ISA results in less resting bradycardia and less of a reduction in cardiac output than is observed with beta blockers without ISA. In the long term, partial beta agonists may produce arterial vasodilation and increase arterial compliance, possibly leading to additional beneficial effects in the treatment of hypertension. beta blockers with ISA do not have adverse effects on plasma lipoproteins during long-term treatment; in addition, the presence of ISA could counteract the up-regulation of beta adrenoceptors often observed with beta blockers without ISA. Finally, the presence of ISA has been a conflicting issue for the use of such beta blockers in secondary prevention after myocardial infarction. However, the impressive results of the Acebutolol Prevention of Secondary Infarction trial in high-risk patients after myocardial infarction show that acebutolol, a beta blocker with moderate partial agonist activity, can be effective in decreasing the postinfarction mortality rate. By exhibiting a strikingly different hemodynamic profile from that of beta blockers without ISA, the partial beta agonists form an intriguing pharmacologic class of drugs for which prospective clinical trials should be extensively pursued.

Acute effects of alcohol and food intake on cardiac performance

Alcohol and food intake induce changes in LV performance which can be evaluated by radionuclide cardiographic methods. Alcohol probably exerts its effects by a direct action of ethanol in the blood on the myocardium, while the postprandial hemodynamic changes are related to the effects of food in the intestine. Alcohol intoxication causes a dose-dependent impairment of LV emptying at rest, whereas compensatory mechanisms other than an increased sympathetic nervous activity counterbalance this effect during exercise. In patients with coronary artery disease, alcohol induces only small changes in LV volumes at rest, possibly because of a concomitant vasodilation. Food intake seems to have a considerable influence on central hemodynamics leading to an increase in cardiac output both in healthy subjects and in patients with coronary artery disease. In healthy subjects an increase is recorded in the LVEDV and LVESV after a meal. The autonomic nervous system is probably responsible for most of the hemodynamic changes.

Stable angina pectoris: 3. Medical treatment

The therapeutic goals for the patient with angina pectoris are to minimize the frequency and severity of angina and to improve functional capacity at a reasonable cost and with as few side effects as possible. An integrated approach necessitates attention to conditions that might be aggravating angina, such as anemia or hypertension. Alterations in life-style and personal habits, such as cessation of cigarette smoking, are often necessary and should be continually reinforced by the physician. Certain concomitant diseases, such as chronic obstructive pulmonary disease, may influence the selection of drug therapy. Nitrates, beta-adrenergic blockers, and calcium entry blockers are the major classes of drugs that can be used alone or in combination in a program that is designed for the individual patient.

Hemodynamic and beta-adrenergic receptor adaptations during long-term beta-adrenoceptor blockade. Studies with acebutolol, atenolol, pindolol, and propranolol in hypertensive patients

In an attempt to further clarify the mechanism of the maintenance of the antihypertensive effect of beta-adrenoceptor antagonists, the effects of four antagonists with different ancillary properties (acebutolol, atenolol, pindolol, and propranolol) on systemic and renal hemodynamics, body fluid volumes, hormones, and lymphocyte beta-adrenoceptor density were studied in four groups of 10 hypertensive patients. The patients were observed for 3 weeks during active treatment and for 2 weeks after withdrawal of treatment. At the end of the 3-week treatment period, the four drugs had an equal antihypertensive effect (fall in mean arterial pressure, 10-13%). Although renin activity was suppressed (60-70%) by all four drugs, changes in renin or pretreatment values of renin levels were not correlated with the fall in blood pressure. The drugs had no effect on plasma catecholamine concentrations or body fluid volumes. Despite similar antihypertensive effects among the four drugs, the changes in flow and resistance underlying the fall in blood pressure differed considerably. With pindolol, the fall in blood pressure was associated with a fall in vascular resistance (26 +/- 6%), whereas with propranolol, it was predominantly associated with a fall in cardiac output (11 +/- 7%). No significant changes in vascular resistance or cardiac output occurred with atenolol or acebutolol. The changes in renal blood flow and renal vascular resistance occurred in parallel with the changes in cardiac output and systemic vascular resistance. Plasma epinephrine concentration and pretreatment cardiac chronotropic responsiveness to isoproterenol appeared to be inversely correlated with lymphocyte beta-adrenoceptor density (Bmax) (r = -0.41 and -0.43, respectively). With pindolol, Bmax decreased maximally by 39 +/- 6%, and with propranolol, it increased by 51 +/- 17%. With both drugs, significant changes in Bmax were already present 24 hours after treatment. Furthermore, 1 week after withdrawal of treatment with pindolol, Bmax was still down-regulated, and cardiac chronotropic responsiveness was still decreased, whereas 1 week after withdrawal of propranolol, Bmax was still up-regulated, and cardiac chronotropic responsiveness was still increased. No changes in Bmax occurred with the beta 1-selective antagonists acebutolol and atenolol. Thus, despite an equal antihypertensive effect, the four beta-adrenoceptor antagonists appear to have dissimilar effects on cardiac output, renal blood flow, and lymphocyte beta-adrenoceptors. Changes in cardiac output, the circulating blood volume, or angiotensin-mediated vasoconstriction are factors unlikely to be crucial for the antihypertensive effect of beta-adrenoceptor antagonists. Therefore, interference with vasoconstrictor nerve activity through blockade of either central or peripheral prejunctional beta-adrenoceptors could be an alternative explanation of their blood pressure-lowering potential.

Does alpha 1-adrenergic blockade influence regional blood flow regulation in hearts with coronary artery occlusion?

The effects of selective alpha 1-adrenergic blockade with doxazosin on regional myocardial tissue blood flow was studied in anaesthetized cats with acute coronary artery occlusion. Reflex tachycardia was prevented by selective beta 1-adrenergic blockade with atenolol and coronary perfusion pressure was kept constant by partial stenosis of the descending aorta. Administration of atenolol reduced cardiac mechanical work-load by its negative inotropic and chronotropic effects, and reduced myocardial tissue blood flow in normally perfused myocardium. This reduction was most pronounced in the endocardial half-layer of the myocardium adjacent to the ischaemic region. Administration of doxazosin in this situation clearly reduced peak systolic and coronary perfusion pressure. But when coronary perfusion pressure was raised to pre-administration values, measurements of regional blood flow revealed no changes either in ischaemic or non-ischaemic myocardium. Also, there was no sign of redistribution of blood flow between endocardial and epicardial tissue in any area. This study, therefore, indicates that alpha 1-adrenoceptors play a minor role in the regulation of coronary blood flow in normal myocardium as well as ischaemic myocardium.

Left ventricular function and beta-blockers: does intrinsic sympathomimetic activity have any influence during chronic therapy?

A study comparing the chronic effects of propranolol (n = 21) and pindolol (n = 19) on male patients with stable angina pectoris was performed. Left ventricular function was assessed by serial radionuclide ventriculography. Radionuclide ventriculography was performed at rest and during cold pressor test. Both drugs improved symptoms of angina pectoris by at least one division of the New York Heart Association classification. Cold pressor testing caused increases in heart rate and blood pressure in both groups throughout the study. At rest, pretreatment ejection fraction was similar in both groups. During propranolol treatment this rose sequentially from 49% to 55% at 26 weeks. No change in the resting ejection fraction occurred in those taking pindolol. The difference in response between the groups reached significance at 26 weeks. In those with subnormal left ventricular ejection fraction (less than 50%), resting ejection fraction improved significantly throughout treatment with propranolol rising from a basal value of 39% to 51% at 26 weeks. In comparison, pindolol caused no significant change. There is no apparent advantage to intrinsic sympathomimetic activity in terms of preservation or improvement of left ventricular performance in patients with stable angina pectoris prescribed beta-blockers for extended periods of time.

Hemodynamic and hormonal adaptations to beta-adrenoceptor blockade. A 24-hour study of acebutolol, atenolol, pindolol, and propranolol in hypertensive patients

Comparison of the hemodynamic and hormonal effects of beta-adrenoceptor antagonists with different ancillary properties may help to clarify the antihypertensive mechanism of these drugs. Under strict basal conditions, the effects of acebutolol (400 mg b.i.d.), atenolol (100 mg b.i.d.), pindolol (10 mg b.i.d.), and propranolol (80 mg t.i.d.), were studied for the first 24 hours in 40 hypertensive patients. With pindolol, mean arterial pressure was reduced (p less than 0.05) 1 hour after administration, whereas the cardiac index and the systemic vascular resistance index did not change. With the other three drugs, the fall in mean arterial pressure was delayed 2-3 hours. With these drugs, the fall in mean arterial pressure was preceded by a rise in the resistance index, which compensated for the initial fall in cardiac index. With each drug, the decrements in mean arterial pressure were associated with parallel decrements in the resistance index, and percent changes in mean arterial pressure and the resistance index were always significantly (p less than 0.001) correlated. At the end of the 24-hour period, the four drugs shared an equal antihypertensive effect, which varied 14-17%. This was associated with a return of the cardiac index toward control values by acebutolol, atenolol, and propranolol treatment and a moderately increased cardiac index above pretreatment values (13%, p less than 0.01) with pindolol. The secondary rise in the cardiac index was inversely correlated (p less than 0.001) with the fall in mean arterial pressure with all four drugs. Plasma renin was maximally suppressed 2 hours after treatment, thus before any change in mean arterial pressure had occurred with acebutolol, atenolol, and propranolol. Pretreatment values of active renin and the reduction of mean arterial pressure 24 hours after administration were not correlated in any of the four groups. Despite the "vasodilator" action of the four drugs, plasma norepinephrine did not rise. Our data show that the main hemodynamic change that occurs at the time blood pressure falls after beta-adrenoceptor antagonism is vasodilation. Neither autoregulation of blood flow nor renin suppression can explain this vasodilator action. The absence of an increase in norepinephrine, despite vasodilation, suggests that beta-adrenoceptor antagonism interferes with sympathetic vasoconstrictor nerve activity. This effect may explain the vasodilator and antihypertensive potential of beta-adrenoceptor antagonists.

Preservation of the end-systolic pressure/end-systolic dimension relation following pindolol in congestive heart failure

Beta blockade may adversely affect inotropic state of the ventricle, resulting in exacerbation of congestive heart failure in subjects with reduced ventricular function. In normal subjects, ventricular contractility appears to be preserved following administration of beta blockers with intrinsic sympathomimetic activity (ISA). The inotropic state of the ventricle was assessed in seven subjects with congestive heart failure (mean ejection fraction = 23 +/- 5%) before and after administration of the ISA beta blocker, pindolol, with the use of the noninvasively derived end-systolic pressure/end-systolic dimension (ESP/ESD) relation. The mean slope of the ESP/ESD relation was 36.3 +/- 20.4 mm Hg/cm at baseline and increased to 45.0 +/- 25.2 mm Hg/cm following five consecutive 10 mg oral doses of pindolol (p = ns). Other simultaneously derived inotropic indices that included percent fractional shortening, mean delta P/delta T, velocity of circumferential fiber shortening, and preejection period-to-left ventricular ejection time ratio showed directionally similar changes toward a mild increase in contractility. These results indicate that the slope of the left ventricular ESP/ESD relation is not altered following repeated dosing with pindolol in subjects with congestive heart failure. This reflects a preservation of inotropic state following administration of this ISA beta blocker in a population with severely compromised ventricular function.

Hemodynamic effects of flestolol, a titratable short-acting intravenous beta-adrenergic receptor blocker

The hemodynamic effects of flestolol were evaluated in 30 patients undergoing routine cardiac catheterization. Hemodynamic measurements were obtained during baseline (prior to flestolol), at steady state during IV flestolol infusion (1, 5, and 10 micrograms/kg/min) and at 20 to 30 minutes after discontinuation (postinfusion). Flestolol-induced hemodynamic changes were similar to those induced by other beta blockers without intrinsic sympathomimetic activity. Significant dose-dependent reduction in heart rate, rate pressure product, and increase in peripheral vascular resistance were seen. Flestolol produced clinically insignificant decrease in myocardial contractility as shown by slight decrease in LVdp/dt, CI, and LVEF. Hemodynamic data from patients with paced heart rate, further confirms a direct mild cardiac depressant effect of flestolol, a finding common to other beta blockers. Consistent with the short elimination half-life of flestolol (t1/2 = 6.5 minutes), most of the hemodynamic changes rapidly returned to preinfusion level within 20 to 30 minutes following its discontinuation. Thus flestolol, with its unique pharmacokinetic profile and titrability, may be beneficial in the treatment of critically ill patients.

Evaluation of the antihypertensive effect of celiprolol by ambulatory blood pressure monitoring

The use of ambulatory blood pressure monitoring has gained popularity because it is not subject to those limitations associated with traditional sphygmomanometry (inaccuracy of blood pressure readings, low number of readings, and failure to represent daytime blood pressure readings). In the present study, we provide evidence that the 24-hour mean blood pressure obtained through intraarterial blood pressure measurements in ambulatory patients provides a more accurate diagnosis (and perhaps a prognosis) of hypertension than that provided by cuff-obtained casual blood pressure measurement. Furthermore, despite a reduction in the amount and in the accuracy of the information obtained, blood pressure data provided by noninvasive blood pressure monitoring are also more accurate diagnostically than cuff-obtained casual blood pressure measurements. In 15 essential hypertensive patients in whom celiprolol, 400 mg once daily, was compared with placebo in a randomized double-blind crossover study, the use of noninvasive 24-hour automatic blood pressure monitoring showed that in responsive patients, celiprolol induced a sustained reduction in systolic and diastolic blood pressure throughout the 24 hours. The blood pressure reduction was also apparent during the night, despite the concomitant occurrence of a slight tachycardia. These findings demonstrate that once-daily administration of celiprolol provides an effective lowering of the 24-hour blood pressure profile. This dosing schedule can therefore be regarded as appropriate for antihypertensive therapy.

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.

Haemodynamic dose-response actions of cicloprolol in left ventricular dysfunction due to ischaemic heart disease

Cicloprolol is a cardioselective beta-1 partial agonist; its haemodynamic and radionuclide (nuclear stethoscope) effects were determined in 22 patients with impaired left ventricular function due to coronary artery disease. Following a 20 min stable control period, the effects of four doses of cicloprolol (0.025, 0.025, 0.05 and 0.1 mg/kg at 10 min intervals) were measured at rest 5-10 min after each intravenous injection. The effects of the cumulative 0.2 mg/kg dosage were assessed during supine bicycle exercise and compared with a control exercise period. At rest there were significant increases in systolic arterial without change in mean blood pressure. The heart rate and cardiac index were unchanged. There was a significant increase in left ventricular ejection fraction with a reduction in filling pressure and volume. Patients with resting heart rate below 75 beats/min and with ejection fraction greater than 35% showed the greatest improvement. During supine bicycle exercise, ejection fraction was increased compared to control (31 +/- 2 to 36 +/- 2; P less than 0.01), cardiac volume reduced and exercise tachycardia attenuated. These data suggest that cicloprolol may be of value where beta-blockade is considered in the presence of underlying left ventricular dysfunction due to ischaemic heart disease.

Comparative pharmacokinetics of intravenous propranolol in obese and normal volunteers

Plasma pharmacokinetics of a single IV dl-propranolol dose (8 mg) were investigated in 12 obese subjects (mean +/- SD: 110.3 +/- 20.4 kg; 198.7 +/- 32.5% of ideal body weight) and compared with those of 12 healthy subjects (66.7 +/- 6.8 kg; 94.5 +/- 7.8% of ideal body weight). In obese subjects plasma alpha-1 glycoprotein acid concentrations and propranolol protein binding capacity did not differ significantly from control subjects. When compared with controls, obese subjects showed a significant increase (P less than .01) in AUC (161.0 +/- 67.0 vs 109.6 +/- 23.1 hr.micrograms/L), and significant decreases (P less than .01) in Vss (208.9 +/- 71.9 vs 318.6 +/- 91.8 L), V beta (234.3 +/- 70.4 vs 340.7 +/- 89.1 L), and total clearance (57.5 +/- 18.3 vs 75.9 +/- 15.4 L/hr). Elimination half-life was similar for the two populations (3.5 +/- 0.9 hr in obese subjects vs 3.1 +/- 0.9 hr in controls). Therefore, neither lipophilicity of propranolol nor drug plasma protein binding can explain these data. Altered hepatic function and tissue blood flow in obese subjects are proposed as an explanation for the decrease in total clearance and volume of distribution.

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.

A rest and exercise haemodynamic evaluation of a new cardio-selective beta-adrenoceptor blocker celiprolol alone and in combination with nitroglycerine in ischaemic heart disease

The symptomatic benefits of combining beta-adrenoceptor blockers and nitrates in angina pectoris are well recognised. Their actions on cardiac haemodynamics and volumes when combined have been poorly characterized. Accordingly this study investigated a new cardioselective beta-adrenoceptor blocking agent celiprolol and buccal nitroglycerine in 24 patients with angiographically documented coronary artery disease. Following a control period, with confirmed stable haemodynamics, three groups (n = 8/group) of prospectively matched patients, were studied following intravenous celiprolol (8 mg), buccal nitrate (10 mg) or their combination. Haemodynamics and left ventricular ejection fraction (nuclear probe) were determined following each intervention. The actions of each regimen on the haemodynamics of exercise-induced angina were compared by exercise testing in the control state and following each regimen. At rest, celiprolol did not alter haemodynamic parameters. Nitrate therapy reduced left ventricular filling pressure (pulmonary artery occluded pressure--PAOP) and volumes; the ejection fraction and heart rate increased. Combination therapy resulted in a highly significant reduction in left ventricular preload and afterload (PAOP and mean arterial blood pressure) at an increased left ventricular ejection fraction and reduced cardiac volumes; there was a trend to reduce cardiac double product (HR X SBP). During exercise celiprolol reduced systolic blood pressure, heart rate and cardiac index; systemic vascular resistance index increased. Nitrate therapy reduced blood pressure and PAOP, and increased ejection fraction. Combination therapy reduced all components of the triple product (heart rate, systolic blood pressure and PAOP) without affecting the other haemodynamic or radionuclide parameters. These data suggest improvements in cardiac function from the combination of celiprolol and nitrate therapy which were not achieved by either agent when used as monotherapy; they afford an interesting insight into the manner in which such widely utilised therapeutic modalities interact in coronary artery disease.

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)

Influence of beta blockade and intrinsic sympathomimetic activity on hemodynamics, inotropy and respiration at rest and during exercise

The degree of intrinsic sympathomimetic activity (ISA) is reported to influence the effects of beta blockade at rest, but the effects during exercise are not well documented. Heart rate, blood pressure and left ventricular (LV) function (as assessed by systolic time intervals) were measured at rest and during upright bicycle exercise as well as with flow-volume spirometry at rest in 13 healthy volunteers. The measurements were performed before and 4 and 24 hours after a single oral dose of pindolol (10 mg), nadolol (80 mg) and acebutolol (400 mg) in a double-blind, randomized, crossover manner. All drugs reduced heart rate, but nadolol had the most pronounced and longest bradycardic effect at rest. Diastolic blood pressure was only slightly influenced by the drugs, whereas systolic pressure was significantly lower compared with control values, especially during exercise (p less than 0.001). Neither preejection period (PEP) nor LV ejection time (LVETc) was changed at rest after pindolol, but PEP increased and LVETc decreased significantly after nadolol (p less than 0.05 for PEP and p less than 0.01 for LVETc) and acebutolol (p less than 0.05 for both). During exercise, PEP and LVET were significantly longer after all 3 drugs compared with control values. Only nadolol, which lacks ISA, significantly decreased expiratory flow values (p less than 0.05). Thus, unlike the other beta blockers, pindolol (with strong ISA) did not depress LV function at rest, while during exercise all 3 beta blockers had equal adverse effects. The degree of ISA appears to be important in determining the hemodynamic effects of beta-blocking drugs.

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

Acebutolol is a new hydrophilic, cardioselective beta-adrenergic-blocking agent that possesses partial agonist and membrane-stabilizing activities. In the treatment of mild to moderate essential hypertension, once-daily acebutolol as monotherapy provides effective control in a large majority of patients and produces a further reduction in blood pressure when used concomitantly with diuretics. Acebutolol is as effective as other beta-blocking agents, and in a large, double-blind, parallel study against propranolol was found to cause less reduction in heart rate, and fewer neurologic side effects and patient withdrawals due to adverse effects. Oral acebutolol is also effective in suppressing premature ventricular contractions, and in small numbers of patients generally beneficial results were obtained in supraventricular and ventricular arrhythmias with intravenous administration. These salutary effects are attributable to beta blockade. Controlled clinical trials documented the antianginal actions of oral acebutolol in chronic stable angina pectoris; its efficacy in this regard is comparable to that of other beta-blocking agents. The drug produces smaller decreases in heart rate and cardiac output and alterations in peripheral vascular hemodynamics than beta-blocking drugs without partial agonist activity, and because of its cardioselectivity, it may be used cautiously in patients with bronchospastic disease. Acebutolol has minimal metabolic effects and does not elevate levels of blood lipids during long-term therapy; high-density-lipoprotein cholesterol increased with acebutolol in a small number of patients.

Differences in haemodynamic response to beta-blocking drugs between stable coronary artery disease and acute myocardial infarction

Theoretically the increased sympathoadrenal activity following acute myocardial infarction might augment the haemodynamic impact of beta-adrenoceptor blockade. To evaluate this question 32 haemodynamic studies were performed to compare the effects of equivalent beta-blocking doses of propranolol (8 mg i.v.) and pindolol (0.8 mg i.v.) in patients with a recent acute myocardial infarction (A.M.I.) or stable coronary artery disease (and a presumptive low sympathetic state). In stable coronary artery disease there were clear differences between the haemodynamic impact of propranolol and pindolol. Propranolol decreased both heart rate (delta HR -7 beat/min) and cardiac index (delta CI -0.4 l/min/m2), with an increased pulmonary artery occluded pressure (delta PAOP +4 mmHg) and systemic vascular resistance index (delta SVRI +358 dyn X s X cm-5 m2). However an equivalent beta-blocking dose of pindolol increased PAOP (delta PAOP +3 mmHg) leaving other variables unchanged. These differential actions of propranolol and pindolol have previously been ascribed to the intrinsic sympathomimetic activity (I.S.A.) of pindolol maintaining cardiac pumping function in a low sympathetic state. In contrast following myocardial infarction, both drugs reduced cardiac index to a significantly greater extent compared with stable coronary artery disease (delta CI propranolol -0.81/min/m2; pindolol -0.4 l/min/m2; p less than 0.05); propranolol also reduced the systemic arterial blood pressure (delta systolic -10 mmHg; delta mean -5 mmHg; p less than 0.05). The haemodynamic relevance of the I.S.A. of pindolol appeared attenuated following A.M.I. These data are compatible with experimental evidence of sympathetic nervous activation following coronary occlusion; the resulting hyperadrenergic state appears to condition an augmented haemodynamic response to beta-blocking drugs irrespective of their ancillary pharmacological properties.(ABSTRACT TRUNCATED AT 250 WORDS)

Haemodynamic effects and kinetics of concomitant intravenous disopyramide and atenolol in patients with ischaemic heart disease

The haemodynamic effects of concomitant intravenous administration of disopyramide (Norpace) and atenolol (Tenormin) were studied in a cross-over trial in 7 patients with ischaemic heart disease. Following 150 mg disopyramide i.v. the cardiac index (CI) and stroke volume index (SVI) decreased by 14% and 26%, respectively and the heart rate (HR) and preejection period index (PEPI) increased by 13% and 19%, respectively. A decrease in CI of 14% and HR of 21%, respectively were noted after intravenous administration of 7.5 mg atenolol; PEPI increased by 10% whereas SVI remained unchanged. The cardiac Index (CI) fell by 33% following the administration of both drugs. The effect on CI of the two drugs was additive. The effect of disopyramide and atenolol on HR, SVI and PEPI was not significantly modified by coadministration of the other drug. No change in blood pressure was observed after disopyramide or atenolol. A correlation (rho) of 0.540 and 0.387 was observed between the change in PEPI and the log free and total serum concentrations of disopyramide, respectively. Combined intravenous use of the two drugs in patients with incipient or overt heart failure is not recommended, unless it is due to the arrhythmia to be treated.

Haemodynamic effects of atenolol, pindolol and propranolol during adrenaline infusion in man

In a double blind, cross over study the haemodynamic effects of an i.v. infusion of adrenaline during concomitant administration of atenolol, pindolol, propranolol or placebo were examined in 7 healthy volunteers. During coadministration with placebo, adrenaline caused an increase in systolic blood pressure (SBP) of 26 mm Hg and a decrease in diastolic blood pressure (DBP) of 20 mm Hg. Heart rate (HR) and stroke volume (SV) were increased by about 20-30%. Total peripheral resistance (TPR) fell significantly. When the subjects were pretreated with atenolol, the adrenaline increased SBP by 16 mm Hg, the DBP did not change, HR and SV increased by 19 and 30%, and TPR fell. During concomitant administration of the non-selective betablocker pindolol, which has strong intrinsic sympathomimetic activity (ISA), adrenaline increased SBP by 11 mm Hg and DBP by 17 mm Hg. This pure pressor response led to a significant reduction in HR and SV and an increase in TPR, probably mediated through the baroreceptors. The haemodynamic response to adrenaline during coadministration of propranolol was very similar to that seen after pindolol. It is concluded that a beta1-selective blocker interferes very little with the haemodynamic response to adrenaline, whereas it is changed to a pure pressor response during coadministration of a non-selective betablockers. ISA did not significantly modify the pressor response.

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.

Selection of optimal drug therapy for the patient with angina pectoris

The development of new drugs, especially beta-blocking and calcium entry-blocking agents, has greatly facilitated the medical treatment of angina pectoris. The specific needs of each patient should dictate the appropriate treatment of angina pectoris. Angina may occur in patients who have various concomitant disorders such as hypertension, diabetes mellitus, peripheral vascular disease, chronic obstructive pulmonary disease, or arrhythmias, and the physician must take these factors into account when a drug regimen is prescribed. Individual drugs should be chosen on the basis of specifically desired pharmacologic effects, and the dosages should be gradually adjusted according to the patient's response. Although a therapeutic regimen should be selected primarily on the basis of efficacy, the physician must also attempt to recommend a simple and cost-effective program.

The effects on left ventricular performance of verapamil and metoprolol singly and together in exercise-induced angina pectoris

Concurrent therapy with the calcium channel blocker, verapamil, and the beta-blocking group of compounds is usually felt to be clinically contraindicated due to the former's potent dromotropic and negative inotropic actions. The basis of this assumption was examined in a rest and exercise hemodynamic study of the effects of verapamil and the cardioselective beta-blocking drug, metoprolol, in 22 patients with stable angina pectoris and angiographically confirmed coronary artery disease. In a randomized study, 11 patients were assessed following intravenous verapamil (16 mg) alone, 11 following intravenous metoprolol (10 mg) alone, and all 22 were assessed on combination therapy. The plasma levels achieved at the time of each hemodynamic assessment were in the therapeutic range. At rest, verapamil alone significantly lowered systemic arterial pressure and vascular resistance; metoprolol alone lowered heart rate and increased systemic vascular resistance without change in systemic arterial pressure. Combination therapy reduced systemic arterial pressure and heart rate without change in cardiac output and systemic vascular resistance. During upright bicycle exercise, the changes were directionally similar. Depression of cardiac function (i.e., reduced cardiac output at increased pulmonary artery occluded pressure) occurred following metoprolol but not following verapamil; the addition of verapamil did not accentuate the depression of function induced by metoprolol. These results suggested that in patients with stable coronary artery disease, without manifest conduction system abnormality, the cardiac depressant actions of verapamil were countered by its vasodilator properties.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Ancillary pharmacologic properties of acebutolol: cardioselectivity, partial agonist activity, and membrane-stabilizing activity

Acebutolol, a new beta-blocking agent, possesses the ancillary pharmacologic properties of cardioselectivity and partial agonist and membrane-stabilizing activities. Compared to propranolol at equipotent doses, acebutolol produces less bronchoconstriction and preserves the bronchodilator response to isoprenaline. Similarly, acebutolol has less of an effect on peripheral vascular hemodynamics than does propranolol. Because of partial agonist activity, acebutolol produces a lesser reduction in heart rate and cardiac output than do propranolol and atenolol and has been found to have minimal effects on lipoprotein metabolism. Acebutolol may be the only beta-blocking agent that demonstrates some membrane-stabilizing activity at clinically achievable plasma concentrations. The ancillary pharmacologic properties of cardioselectivity and partial agonist activity are distinct and offer definite advantages to selected patients, particularly patients with respiratory disease, in whom cardioselective acebutolol, particularly at low doses, can minimize patient risk. The ancillary property of membrane-stabilizing activity may also guide therapy in selected patients.

Dynamics of beta-adrenoceptor blockade with cetamolol

Cetamolol is a new beta-adrenoceptor blocking agent shown in animals to have moderate beta 1-adrenoceptor selectivity and partial agonist activity. In healthy normal volunteers, beta 1-adrenoceptor blockade was measured as the reduction of exercise-induced tachycardia, systolic blood pressure, and double product at 2, 8, and 24 h after a single oral dose of 10, 25, and 50 mg cetamolol. beta 1-adrenoceptor blockade was significantly linearly related to log serum cetamolol level, was maximal at 2 h, and was still clinically significant at 24 h. A crossover study of single 0, 10, and 25 mg doses confirmed these findings.

Hypertension and beta-blockers. Are they all the same?

The circadian rhythm of blood pressure derived from continuous recordings of blood pressure in hypertensive subjects, provides an accurate and repeatable method of describing blood pressure on a temporal scale which can be used to evaluate the effects of anti-hypertensive drugs. It has been postulated that the rapid rise of pressure between 0600 and 1000 hr is due to intrinsic sympathetic activity mediated at the peripheral arteriole by alpha-adrenoreceptors. Drugs which block beta-adrenoreceptors do not appear to influence blood pressure at this time, no matter how frequently they are administered or how long-acting they may be. Meteroprolol and sotolol are beta-adrenoreceptor blocking drugs which appear to be different in that they produce a considerable fall in nocturnal blood pressure, which is similar to the effects of alpha-adrenoreceptor blocking agents. The physiological and clinical significance of these findings remains to be defined, but they emphasise the need for full and complete information on blood pressure changes before the most effective method of blood pressure reduction can be defined.

Effect on heart rate over 24 hours of pindolol administered for 14 days

The effect on heart rate of pindolol 5, 15 and 30 mg/day, a beta-adrenoreceptor blocker possessing intrinsic sympathomimetic activity, administered to 8 healthy volunteers for 14 days was studied. Heart rate was continuously recorded over 24 h during placebo treatment before each sequence, every 2 days during treatment, and then on the 15th, 17th and 18th days. Pindolol in the three doses used had no significant effect on mean heart rate over 24 h. It tended to lower mean diurnal heart rate non-significantly between noon and 6 p.m. Pindolol raised nocturnal heart rate between midnight and 6 a.m. to a comparable extent at all the doses used. Sympathetic tone is at its lowest during that period, which makes it possible to detect the intrinsic sympathomimetic activity of pindolol. After cessation of treatment, a rebound effect was observed, cardioacceleration being most marked after 30 mg/day.

Human pharmacokinetic and pharmacodynamic studies on Ro31-1118, a new beta-adrenoceptor antagonist

The pharmacokinetic and pharmacodynamic effects of Ro31-1118 were examined in groups of healthy volunteers. In three subjects given 10 mg of [14C]-Ro31-1118 orally, peak levels of radioactivity (84 +/- 5 ng/ml) were 16 times those of the parent drug (approximately 5 ng/ml). Very little parent drug was recovered in the urine, although recovery of total radioactivity was nearly 80% in the urine by day 5. In five subjects studied after both oral and intravenous administration of 20 mg Ro31-1118 the average bioavailability was 57% (range 41-73%). Following intravenous infusion the apparent volume of distribution for the five subjects averaged 590 1 (range 510-700 1). The elimination half-life averaged 18 h (range 17-26 h). In eight subjects who received 40, 80, 160 and 320 mg of Ro31-1118 orally there was a linear relationship between dose and plasma concentration (r = 0.999) and between dose and AUC (r = 0.996). Ro31-1118 had no effect on resting heart rate whereas atenolol reduced resting heart rate up to 6 h after all doses. The maximum reduction of an exercise tachycardia after Ro31-1118 (320 mg) was 23.13 +/- 0.7% and compared with atenolol (100 mg) was 28.2 +/- 1.25%. At 24 h the percentage reduction after Ro31-1118 was 21.5 +/- 1.7%, while after atenolol the percentage inhibition had decreased to 11.1 +/- 1.6%. In three subjects Ro31-1118 (160 mg) orally had no effect on resting heart rate, forearm blood flow and systolic blood pressure, while atenolol (50 mg) reduced all three parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Improvement in depressed cardiac function in hypertensive patients during pindolol treatment

To assess changes in left ventricular function during antihypertensive treatment using pindolol, a beta-adrenocepter blocking drug with potent intrinsic sympathomimetic activity, serial echocardiographic measurements were obtained in 70 hypertensive patients before and during 15 weeks of treatment with pindolol. For analysis, the patients were separated into three groups on the basis of their baseline left ventricular fractional shortening (Group I, 35 patients with normal fractional shortening of 28 percent or more; Group II, 16 patients with abnormal fractional shortening of 21 to 27 percent; and Group III, 19 patients with markedly abnormal fractional shortening of 20 percent or less). More than half of the patients in Group I and Group II had decreases in mean blood pressure of 10 percent or more in response to pindolol, but only one fourth of Group III patients had similar responses (p less than 0.05). Patients with normal pretreatment fractional shortening had a mild decrease in fractional shortening during pindolol treatment, whereas patients with either abnormal or markedly abnormal fractional shortening had an increase in fractional shortening. This increase in fractional shortening suggests the possibility that the partial agonist or intrinsic sympathomimetic activity of pindolol may play a role in preserving left ventricular function in patients with borderline or impaired function.

Is the intrinsic sympathomimetic activity (ISA) of beta-blocking compounds relevant in acute myocardial infarction?

The relevance of the intrinsic sympathomimetic activity (ISA) of beta-blocking compounds to the clinical therapeutics of acute myocardial infarction was evaluated in 20 patients with an uncomplicated acute myocardial infarction by comparing the haemodynamic effects of equivalent beta-blocking doses of propranolol (non-cardioselective; no ISA) and pindolol (non-cardioselective; 50% ISA). Consecutive eligible male patients admitted to a Coronary Care Unit were randomised following a 1 h control period to two separate studies. In Study 1 the short-term dose-response effects of propranolol (1-8 mg) or pindolol (0.1-0.8 mg) were assessed. In Study 2 comparison of the effects of single i.v. propranolol (8 mg) and pindolol (0.8 mg) doses was undertaken over 6 h. Haemodynamic variables and thermodilution cardiac output were subsequently recorded to compare the effects of each drug on the circulation. The plasma concentrations of propranolol and pindolol were in the recognised therapeutic range. Both drugs were clinically well-tolerated, the changes induced in haemodynamic variables following each drug demonstrated effective beta-blockade. Within the limits of the experimental protocol, these data did not suggest definite haemodynamic advantage for ISA of pindolol in acute myocardial infarction. These findings are perhaps due to sympathetic activation in acute myocardial infarction attenuating the haemodynamic impact of ISA.

Regional myocardial tissue blood flow during sequential beta 1- and beta 2-adrenergic blockade in cat hearts with acute ischaemia

beta-Adrenergic blockade was imposed on cats with ischaemic regions of the left ventricle produced by coronary artery occlusion. Ten animals first received a beta 1-blocking agent (atenolol) followed by a beta 2-blocking agent (IPS 339). In ten more animals this sequence was reversed. Combined blockade, obtained after both agents were administered, showed clear reduction of tissue blood flow in all areas of the ventricle, except for the central ischaemic zone. The flow reduction could be ascribed to bradycardia and reduced coronary perfusion pressure. By analysing the sequential changes it was evident that blockade of beta 1-adrenergic receptors was responsible for the haemodynamic changes, and the coronary vascular resistance rose so as to match the quantity of blood flow to the functional state of the ventricle. Blockade of beta 2-receptors by IPS 339, however, showed no evidence of coronary vasoconstriction but rather maintained vascular resistance at an unchanged level despite a weak beta 1-adrenergic blocking effect.

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.

Haemodynamic dose-response effects of i.v. penbutolol in angina pectoris

The haemodynamic dose-response effects of intravenous penbutolol, a newer beta-adrenoceptor antagonist with intrinsic sympathomimetic activity but without cardioselectivity, were evaluated in 10 patients with angiographically documented coronary artery disease. Following four logarithmetically cumulative i.v. boluses (0.5-4 mg dosage range) there was a log linear increase in plasma penbutolol concentration; the levels achieved (51 +/- 8 to 219 +/- 19 ng/ml) were in the therapeutic range (12 to 250 ng/ml). Penbutolol resulted in a linear decrease in heart rate (maximum delta HR - 4 beats/min; P less than 0.01); there was a small increase in pulmonary artery occluded pressure which reached its maximum at the lower doses (maximum delta PAOP + 1 mm Hg; P less than 0.01). The resting cardiac output, blood pressure and calculated systemic vascular resistance were unchanged. During 4 min steady-state supine bicycle exercise there was attenuation of exercise cardiac output (delta C.I. - 0.6 1 min-1 m-2; P less than 0.01) and systolic pressor response (delta SBP - 13 mm Hg; P less than 0.01) compared with control observations without change in other measured or derived variables. The haemodynamic profile of penbutolol compared favourably with other beta-adrenoceptor antagonists previously evaluated under similar conditions in patients with ischaemic heart disease. Over the i.v. dose-range evaluated penbutolol attenuated exercise-induced angina with a relatively modest depression of cardiac performance; the small change induced in resting haemodynamic variables may, in part, have been contributed to by the intrinsic sympathomimetic activity of penbutolol.

Comparative haemodynamic dose-response effects of intravenous propranolol and pindolol in patients with coronary heart disease

To determine whether the depression of left ventricular pumping activity associated with beta-blockade alone could be offset by a substantial degree of partial agonist activity, the haemodynamic dose-response effects of intravenous propranolol and pindolol were compared in a randomised between-group saline controlled study in twenty patients with angiographically proven coronary artery disease. The intravenous doses of propranolol (2-16 mg) and pindolol (0.2-1.6 mg) used were selected on the basis of published reports of equivalence in terms of exercise blockade of chronotropic beta-adrenoceptors. Following four intravenous boluses of each drug, administered according to a cumulative log-dosage schedule, there was a log-linear increase in the plasma concentrations of each drug. The range of plasma concentrations achieved were those which have been shown to be associated with substantial attenuation of sympathetic stimulation of cardiac beta-adrenoceptors. At rest propranolol resulted in dose-related linear reductions in heart rate and cardiac output and linear increases in left heart filling pressure and systemic vascular resistance compared with saline-controlled measurements. The only statistically significant change at rest after pindolol was a small increase in the left heart filling pressure. The calculated systemic vascular resistance was increased after propranolol but unchanged after pindolol. During supine bicycle exercise the systolic blood pressure increased less after propranolol than after saline or pindolol. The increments in all other measured haemodynamic variables during exercise were equally influenced by the two drugs.(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.