Pharmacological basis for the therapeutic applications of slow-channel blocking drugs

Hemodynamic interactions of a new beta blocker, celiprolol, with nifedipine in angina pectoris

The hemodynamic consequences of blockade at both beta-adrenoceptors and slow calcium channels is of therapeutic importance for patients with angina pectoris. The hemodynamic interaction of a new cardioselective beta blocker, celiprolol, and nifedipine was examined in an acute hemodynamic study using three prospectively matched groups with angiographically confirmed coronary artery disease (n = 10/group). Patients were randomly allocated to intravenous celiprolol (8 mg), sublingual nifedipine (20 mg), or their combination. Rest and exercise (supine bicycle) hemodynamics were determined before and following each therapy. At rest, celiprolol did not alter pumping function; nifedipine reduced diastolic blood pressure and systemic vascular resistance index (SVRI), with a small increase in heart rate. Combination therapy reduced systemic arterial pressure and SVRI; heart rate and cardiac stroke volume index increased. During exercise celiprolol tended to reduce heart rate and cardiac index; nifedipine reduced exercise SVR and cardiac stroke work indices. Combination therapy reduced all components of blood pressure; cardiac stroke work and SVR indices fell. These hemodynamic data suggest that beta blockade with celiprolol may result in a slight depression of cardiac pumping during exercise; however, such effects are offset by the vasodilating actions of nifedipine (reflex sympathetic action offsetting cardiodepression). Thus the acute hemodynamic effects of this combination were seemingly safe in these patients; the longer term effects during maintained therapy should be further assessed.

Effect of propionyl-L-carnitine on experimental myocardial infarction in dogs

Limitation on infarct size, using propionyl-L-carnitine (Sigma-Tau) by itself and with the calcium entry blocker, tiapamil (Hoffmann-LaRoche), was evaluated in two groups of ten dogs each, during chronic (9 days) myocardial infarction. There were eight dogs that served as the control group. A closed-chest model was used to produce the thrombus by placing a helically shaped copper wire in the LAD by catheter technique, under x-ray visualization. Necrotic tissue in serial transventricular sections were delineated by triphenyltetrazolium chloride and measured by computer technique, using an IBM PC interfaced with a digitizing pad, 9 days following occlusion. The mean total amount of necrosis in the propionyl-L-carnitine (7.4%) and the propionyl-L-carnitine/tiapamil (6.7%) groups were significantly less (p less than .01) than found in the control (14.1%) group, reflecting a difference of 50 and 58%, respectively, between the treated groups and control. A number of significant between-group comparisons (p less than .05 to p less than .001), under the same conditions, were found for various ischemia, hemodynamic, and hematologic variables followed before and at 30, 60, 90, 120, and 180 minutes after occlusion, as well as on the second and ninth day. The results of this study strongly suggest that propionyl-L-carnitine and propionyl-L-carnitine with tiapamil has a protective effect on myocardial function, following thrombotic occlusion of the LAD, as well as limiting the resulting infarct size.

An exercise hemodynamic comparison of verapamil, diltiazem, and amlodipine in coronary artery disease

A prospective, randomized study compared the effects of equivalent intravenous doses of three slow calcium-channel blockers (verapamil, diltiazem, and amlodipine) on rest and exercise haemodynamics in 30 ischemic heart disease patients. Following a stable control period during which rest and exercise (supine bicycle) hemodynamics were assessed, equivalent hypotensive doses of each compound were administered over 20 minutes and rest/exercise parameters were assessed 10 minutes later. At rest all agents similarly reduced systemic blood pressure; the fall in systemic vascular resistance and the increase in cardiac indices was ranked: amlodipine greater than diltiazem greater than verapamil. The heart rate increase for amlodopine differed from verapamil and diltiazem (+19.4% vs. +1.5% vs. -7%; p less than 0.01). On exercise, similarly greater falls in the systemic vascular resistance index followed amlodipine, compared with verapamil and diltiazem (p less than 0.05). Only amlodipine significantly reduced the exercise pulmonary artery occlusion pressure (PAOP). Exercise cardiac stroke volume improved after diltiazem and amlodipine. In terms of cardiac performance, both amlodipine and diltiazem produced an improvement, whereas verapamil depressed cardiac pumping activity. Thus, hemodynamic differences between slow-calcium-channel blocking drugs may be demonstrated in humans. These differences would be compatible with a predominant peripheral vascular site of action for amlodipine, in contrast with mixed cardiac and peripheral sites for diltiazem and verapamil.

Haemodynamic and radionuclide effects of amlodipine in coronary artery disease

1. The haemodynamic and radionuclide effects of a new long-acting slow-calcium channel blocking agent, amlodipine, were evaluated in 32 patients with coronary artery disease. 2. Haemodynamic measurements in 24 patients were made at rest and 10 to 15 min after 20 mg i.v. amlodipine. Amlodipine significantly reduced systemic arterial blood pressure and vascular resistance index with an increased heart rate and augmented cardiac index. Cardiac stroke volume index rose and stroke work fell without change in pulmonary artery occluded pressure (PAOP). 3. The exercise effects were determined by comparison of measurements during 4 min of supine bicycle exercise at a fixed workload before and after drug treatment. During dynamic exercise, amlodipine reduced systemic arterial pressure and vascular resistance index. Exercise cardiac index, stroke volume index and heart rate were higher. The left ventricular filling pressure was significantly reduced. 4. Radionuclide parameters were studied in 16 patients at rest and on exercise; ejection fraction was unaltered following amlodipine. 5. Pre-therapy haemodynamic values correlated with response following amlodipine for resting mean blood pressure, systemic vascular resistance and exercise PAOP. 6. Thus, the immediate impact of amlodipine in stable coronary artery disease was to reduce left ventricular afterload and thereby improve cardiac pumping performance.

Hemodynamic and electrophysiologic effects of amlodipine, a new calcium channel blocker

The effects of amlodipine (300 micrograms/kg administered intravenously), a new, long-acting, dihydropyridine class, calcium channel blocking drug, were studied in atrially paced (120 beats/min), autonomically blocked dogs. Hemodynamic and electrophysiologic parameters were measured before and up to 3 hours after amlodipine. Coronary blood flow was significantly increased 10 and 30 minutes after drug administration, whereas cardiac output and mean arterial pressure were unaffected. Coronary vascular resistance was decreased but total systemic vascular resistance did not change. Atrioventricular (AV) nodal conduction was slightly prolonged, as reflected by increases in atrial-His bundle and AV conduction times and PR interval, 30 minutes after administration. All parameters returned toward their control values within 3 hours after drug administration. Comparison of coronary vascular resistance and AV conduction changes with those previously reported for other calcium channel blocking drugs where autonomic blockade existed suggests that at equivalent levels of coronary vasodilation, amlodipine's effects more closely resemble the effects of diltiazem or verapamil than other dihydropyridines.

Protection of regional mechanics and mitochondrial oxidative phosphorylation by amlodipine in transiently ischemic myocardium

The effects of amlodipine (0.3 mg/kg administered intravenously, n = 5) and placebo (n = 5) on recovery of myocardial function and respiration of isolated mitochondria were examined in "stunned" myocardium of normotensive pentobarbital-anesthetized dogs. Measures of myocardial wall motion, using sonomicrometers, and tissue blood flow, by radioactive microspheres, were obtained at baseline, 15 minutes after administration of amlodipine or placebo, after 10 minutes of left circumflex artery ligation and at 60 minutes of reperfusion. Mean aortic pressure decreased from 115 +/- 6 to 101 +/- 5 mm Hg after administration of amlodipine and remained decreased throughout the experiment. Heart rate was not significantly affected at any time. Both groups showed similar degrees of ischemia: elevation of ST segment to 4.7 +/- 1.4 vs 6.2 +/- 1.9 mV; reduction of ischemic zone shortening fraction to 0.6 +/- 1.9 vs -3.4 +/- 2.7%; and reduction of epicardial and endocardial blood flows (epicardial = 40 +/- 13 vs 43 +/- 13 ml/100 g/min; endocardial = 7 +/- 4 vs 13 +/- 6 ml/100 g/min [values for amlodipine vs placebo]). Mitochondrial state 3 rate of respiration and respiratory control index indicative of rate of adenosine triphosphate synthesis and membrane integrity in myocardial samples taken after 10 minutes of ischemia were significantly reduced in the placebo but not in the amlodipine group. Myocardial function showed significantly greater improvement in amlodipine vs placebo at 60 minutes of reperfusion as indicated by shortening fraction (17.7 +/- -1.4 vs 5.8 +/- -3.5%, amlodipine vs placebo), which may have been related to increased myocardial blood flow and decreased blood pressure during reperfusion. Thus, amlodipine pretreatment prevented mitochondrial dysfunction during ischemia and accelerated recovery of both myocardial mechanical function and blood flow when compared with placebo.

Hemodynamic assessment of nicardipine alone and with atenolol in coronary artery disease using a modified echo-Doppler device

We have used a modified noninvasive echo-Doppler cardiac output device, based on the principle of attenuated compensation volume flow, to assess the cardiovascular effects of the slow-calcium antagonist nicardipine in coronary disease. The dose-response effects of 2.5, 5.0 and 10.0 mg intravenous nicardipine were determined in 8 patients with angina. Dose-related decreases were seen in systemic mean arterial pressure (p less than 0.01) after administration of nicardipine. Cardiac pumping indexes were improved, as evident from linear increases in cardiac stroke volume (p less than 0.001), stroke length (p less than 0.01) and time-averaged mean velocity (p less than 0.01). The echo-Doppler device was also used to assess beta-blocking/nicardipine combination therapy in patients with angina. When nicardipine was given after the cardioselective beta blocker atenolol the reduction in heart rate and cardiac output after atenolol was reversed compared with a group that received atenolol followed by placebo. Cardiac performance improved and the 35% reduction in systemic vascular resistance was associated with markedly increased cardiac index (p less than 0.01), augmentation of time-averaged mean velocity (p less than 0.01) and cardiac stroke length (p less than 0.05). These data are consistent with previous invasive studies of nicardipine, either alone or when combined with beta blockade in coronary disease. The data also suggest that nicardipine/beta-blocking combination is safe in patients with coronary heart disease and that the echo-Doppler method of cardiovascular monitoring will prove useful in human pharmacodynamic studies.

A haemodynamic and radionuclide assessment of diltiazem in coronary heart disease

To obtain multiple dose-response haemodynamic and radionuclide data on i.v. diltiazem, 12 ischaemic patients were studied during routine catheterization. At rest, following a 20 min stable control period, the effects of four doses (0.0625, 0.0625, 0.125 and 0.25 mg kg-1 diltiazem at 5 min intervals) were measured in the 3-5 min following i.v. injection. The exercise effects of the cumulative 0.5 mg kg-1 dosage were assessed by comparing a control and post drug period of supine bicycle exercise. The increase in plasma diltiazem levels correlated linearly with the administered dose and achieved therapeutic levels. There were significant dose-related reductions in systemic arterial blood pressure and vascular resistance index; the heart rate fell and cardiac stroke index increased. The calculated double-product (heart rate X systolic blood pressure) was significantly reduced. The left ventricular filling pressures, ejection fraction and cardiac volumes were unaltered. During supine bicycle exercise, the systemic diastolic blood pressure, heart rate and calculated double-product were reduced without change in other parameters. Over the dose range 0.0625-0.5 mg kg-1, diltiazem acutely increased cardiac stroke index and reduced resting heart rate. These haemodynamic data, taken together with its described coronary vasodilator activity suggest that its role in acute vasospastic angina and during angiographic procedures ought to be explored further.

A haemodynamic study of the effects of combined slow-calcium channel blockade (nisoldipine) and beta-blockade (metoprolol) in coronary heart disease

The interaction of a new slow-calcium blocker (nisoldipine) and the beta-blocker metoprolol was evaluated in 16 patients with stable angina. Haemodynamic parameters were determined in a control rest and exercise period. Patients were then randomised equally to nisoldipine (4-8 micrograms/kg) or metoprolol (10 mg) and the haemodynamics of monotherapy assessed; finally the second drug was administered and the effects of combination determined. At rest nisoldipine reduced systemic blood pressure and vascular resistance (P less than 0.01); heart rate, cardiac and stroke volume indices increased (P less than 0.01) at an unchanged pulmonary artery occluded pressure. Metoprolol alone reduced heart rate (P less than 0.05) and increased the pulmonary artery occluded pressure (P less than 0.05). Combination therapy reduced systemic blood pressure and vascular resistance (P less than 0.01); cardiac index and pulmonary artery occluded pressure increased (P less than 0.01) at an unchanged heart rate. The effect of combination was influenced by the order of administration; an improvement in cardiac performance was particularly evident when nisoldipine was added to metoprolol. The interaction during dynamic exercise was similar to that at rest. Thus these data indicated the haemodynamic safety of concurrent nisoldipine/metoprolol therapy; the addition of nisoldipine to metoprolol appeared to offset in part the cardiodepressant properties of beta-blockade.

Effect of tiapamil on canine myocardial infarct size

Limitation of infarct size, using the calcium entry blocker, tiapamil (T), was evaluated in a group of eight dogs during acute and chronic (8 days) myocardial infarction. An equal number of dogs served as the control (C) group. A closed-chest model was used to produce the thrombus by placing a helically-shaped copper wire in the left anterior descending artery (LAD) by catheter technique, under x-ray visualization. Necrotic tissue in serial transventricular sections was delineated by triphenyl tetrazolium chloride and was measured by computer technique, using an IBM-PC interfaced with a digitizing pad, 8 days following occlusion. The mean total amount of necrosis in T animals (9.5%) was significantly less (p less than 0.05) than found in C dogs (19.7%), or a difference of 48% between the two groups. A number of significant (p less than 0.05 to p less than 0.001) between-group comparisons, at the same condition, were found for various hemodynamic, creatine phosphokinase (CPK), and precordial ST segment, Q and QS wave variables followed before and at 1, 3, and 6 hours after occlusion, as well as on the second and eighth day. The results of this study strongly suggest that tiapamil has a protective effect on myocardial function, following thrombotic occlusion of the LAD, as well as limiting the resulting infarct size.

Haemodynamic dose-response effects of intravenous nisoldipine in coronary artery disease

The circulatory consequences of slow-calcium channel blockade with a new dihydropyridine nisoldipine were evaluated at rest and during exercise-induced angina in 16 patients with angiographically proven coronary artery disease. In 10 patients resting cardiac stroke output (thermodilution) and pulmonary artery occluded pressure were determined following four intravenous nisoldipine injections (cumulative dosage of 1, 2, 4 and 8 micrograms kg-1). The exercise effects of nisoldipine were evaluated by comparing the effects of the 8 micrograms kg-1 cumulative dosage with a control exercise period at the same workload. At rest nisoldipine reduced systemic vascular resistance and mean arterial pressure, and increased heart rate, cardiac and stroke volume indices. During 4 min supine-bicycle exercise nisoldipine reduced systemic mean arterial pressure and vascular resistance; this resulted in augmented cardiac and stroke volume indices at an unchanged pulmonary artery occluded pressure. In six additional patients rest and exercise ejection fractions were measured using a nonimaging nuclear probe. Nisoldipine (4 micrograms kg-1) resulted in a small trend to increase left ventricular rest and exercise ejection fraction. These data demonstrated improved rest and exercise cardiac performance following nisoldipine in patients with severe coronary artery disease.

Effects of nicardipine on cardiac volume at rest and during exercise-induced angina

The action of nicardipine on cardiac volume, both at rest and during exercise-induced angina, was evaluated in 12 patients with angiographically-proven coronary artery disease. Nicardipine given to patients at rest reduced systemic vascular resistance and mean arterial pressure and increased heart rate and cardiac index. The left ventricular filling pressure, ejection fraction (EF), end-diastolic and end-systolic volumes were unchanged. During supine bicycle exercise, the reduction in systemic arterial blood pressure following nicardipine increased cardiac and stroke index and attenuated the rise in left ventricular filling pressure observed in the control exercise. The effects of nicardipine on EF, end-diastolic and end-systolic cardiac volumes were dependent on the baseline cardiac reserve. In patients with EF less than 50%, nicardipine improved EF and left ventricular exercise volumes.

Verapamil: full spectrum calcium channel blocking agent: an overview

Oral verapamil approved for use in all forms of angina, with its additional heart rate-controlling properties has undergone extensive clinical investigation and use since its initial development and has been demonstrated to be safe, well-tolerated and effective over a broad range of cardiovascular disorders. Further potential therapeutic indications for verapamil use remain to be assessed. Additional research with this exciting drug is ongoing.