Pharmacodynamics of amlodipine: hemodynamic effects and antianginal efficacy after atrial pacing

Amlodipine at high dose increases preproendothelin-1 expression in the ventricles and aorta of normotensive rats

BACKGROUND

High doses of dihydropyridine calcium channel blockers can activate the sympathetic nervous system and the renin-angiotensin system. Both noradrenaline and angiotensin II stimulate preproendothelin-1 gene expression, yet the effects of high doses of dihydropyridines on preproendothelin-1 expression in vivo remain unknown.

OBJECTIVES

To investigate the effects of high doses of dihydropyridines on preproendothelin-1 expression in the ventricles and aorta of normotensive rats.

METHODS

Sprague-Dawley rats were treated with amlodipine 5 or 20 mg/kg per day (Amlo 5 or Amlo 20) in drinking water for 5 days or 5 weeks. Systolic blood pressure and heart rate were measured by tail-cuff plethysmography. Gene expression was examined by reverse transcriptase polymerase chain reaction.

RESULTS

Amlo 5 increased heart rate during the first week only and had no effect on blood pressure and ventricular weight and gene expression. Amlo 20 reduced blood pressure transiently and increased heart rate consistently. It did not change relative left ventricular weight (corrected for body weight) after 5 days, but increased it after 5 weeks; it increased relative right ventricular weight at both time points. Aorta weight (mg/mm) was decreased after 5 weeks of treatment with both dosages of amlodipine. Preproendothelin-1 mRNA levels were increased by Amlo 20 in the ventricles and aorta and, concomitantly, renin mRNA was increased in the kidney. Less consistently, interleukin-6 mRNA also increased in ventricles, whereas cardiotrophin-1 mRNA remained unchanged. The sensitivity of isolated aorta to the contractile effect of noradrenaline was decreased by Amlo 5, but not by Amlo 20.

CONCLUSIONS

In Sprague-Dawley rats, high-dose amlodipine, while promoting neurohormonal activation, induced overexpression of preproendothelin-1 mRNA in the ventricles and aorta. Endothelin-1 overexpression could contribute to the lack of inhibitory effect of high-dose amlodipine on ventricular mass in normotensive rats.

Effects of intravenous amlodipine on coronary hemodynamics in subjects with angiographically normal coronary arteries

The aim of the current study was to assess the ability of amlodipine to dilate the coronary vessels in subjects with angiographically normal coronary arteries and normal left ventricular function. Ten patients, six women and four men (mean age 48 +/- 14 years, range 25-67 years) were enrolled. Coronary flow velocity and coronary perfusion pressure were invasively measured at baseline, during intracoronary adenosine (1-mg bolus) and at 5, 15, and 30 min following IV amlodipine (10 or 20 mg). Quantitative coronary angiography was performed at baseline and at 5, 15, and 30 min after amlodipine. Coronary cross-sectional area and mean coronary flow velocity progressively increased after amlodipine administration, resulting in an average increase in coronary flow at 30 min of 76%. On an individual basis, all patients but one showed a consistent trend toward a progressive coronary vasodilator effect of amlodipine over time. The peak effect of amlodipine on baseline mean coronary flow velocity was 43 +/- 12% that of adenosine. This is the first clinical study demonstrating that the IV administration of amlodipine produces a powerful coronary vasodilatation in subjects with angiographically normal coronary arteries and normal ventricular function, besides its known systemic vasodilating effects. The coronary vasodilating properties of amlodipine are particularly expressed at the microcirculatory level.

Electrophysiologic effects of amlodipine vs. diltiazem in patients with coronary artery disease and beta-blocking therapy

This study compares the electrophysiologic effects of amlodipine and diltiazem in patients with coronary artery disease concomitantly treated with background beta-blocking therapy. Thirty patients were included in an open-label parallel study in two phases. During phase 1, patients were screened and placed on maintenance atenolol therapy at 50 or 100 mg/day, while phase 2 consisted of right-sided catheterization and randomization of patients to either amlodipine (10 mg i.v.) or diltiazem (10 mg i.v.). Following treatment with amlodipine, no significant alteration in markers of electrophysiological activity was observed. Treatment with diltiazem resulted in a significant lengthening of sinus cycle length (SCL, p < 0.04), AH interval (p < 0.02), and Wenckebach CL (WCL, p < 0.001), and a trend towards an increase in sinus node recovery time (SNRT, p = 0.057). No effects were observed with regard to HV interval and corrected SNRT. The results of this study indicate that 10 mg intravenous amlodipine has no significant electrophysiological action on sinus or AV node function in patients receiving beta-blocker therapy with atenolol, suggesting that amlodipine can be added to beta-blockers to treat patients with myocardial ischemia and/or hypertension without any significant increase in the risk of bradyarrhythmias.

Antianginal effects of amlodipine at a single dose on exertional angina patients using treadmill exercise testing--a randomized crossover study in comparison with placebo

With eight cases of stable exertional angina as subjects, the antianginal action and sustained effects of single 10 mg oral doses of new calcium antagonists amlodipine were assessed by treadmill exercise tests in randomized crossover trials with respect to a placebo. Exercise tests were conducted before as well as 4, 8, and 24 hours after administration, and plasma amlodipine concentration was investigated at the same times. The maximal exercise time was 299 +/- 43 seconds before as compared with 346 +/- 49 seconds 4 hours after administration and 368 +/- 50 seconds 8 hours after administration, a significant prolongation in each case (p < 0.01). Moreover, the exercise time elapsed until 1 mm of ST-segment depression, as well as the ST-segment depression measured at the same time, were both significantly improved as compared with the placebo results. The plasma amlodipine concentration reached a peak 8 hours after administration and displayed an effective level even 24 hours after administration. The value of delta PRP measured at the same time during the exercise test was also significantly reduced as compared with the placebo results, even 24 hours after administration of amlodipine. These findings supported the conclusion that single 10-mg doses of amlodipine provide stable antianginal action over a 24-hour period.

Amlodipine in patients with stable angina pectoris treated with nitrates and beta-blockers. The influence on exercise tolerance, systolic and diastolic functions of the left ventricle

The effects of 5 and 10 mg of amlodipine and of placebo were compared in 21 patients with stable angina pectoris and multivessel coronary artery disease. The blind comparison was performed by means of bicycle ergometry and stress echocardiography using esophageal stimulation of the left heart atrium. All patients subsequently received placebo, amlodipine 5 mg and 10 mg for 2 weeks. In bicycle ergometry both doses of amlodipine in comparison with placebo significantly lowered the ST segment depression in lead V5 and prolonged the time to onset of angina. The exercise duration was significantly prolonged only after 10 mg of amlodipine. In stress echocardiography 10 mg of amlodipine significantly improved ejection fraction and reduced wall motion score during stimulation and increased peak velocity of relaxation of left ventricular posterior wall at rest and immediately after stimulation. In the patients with left ventricular end-diastolic pressure < or = 20 mmHg, amlodipine reduced the ratio of peak transmitral flow velocity in atrial contraction to that in early diastole (A/E) at rest and shortened deceleration time at rest and immediately after stimulation. Amlodipine in patients with stable angina pectoris significantly improved the exercise tolerance and the function of the left ventricle in a dose-dependent way. Amlodipine was well tolerated.

Effects of amlodipine on myocardial infarction, infarct expansion, and ventricular geometry in the rat

Infarct expansion remains an important sequela of myocardial infarction. Both angiotensin converting enzyme inhibitors and intravenous nitrates reduce early infarct expansion in humans. This is believed to be caused by the reduction in left ventricular systolic wall stress that results from the arteriolar vasodilatation they produce. Patients are frequently already receiving calcium channel blockers at the time of infarction or these drugs are sometimes administered in the perimyocardial infarction period. The calcium blockers of the dihydropyridine class might be expected to modify infarct expansion. However, their effect on this process has not been studied. We therefore evaluated the effect of early treatment with the calcium blocker amlodipine, a potent arteriolar vasodilator with minimal negative inotropic properties, on chronic myocardial infarction in the rat. Permanent left coronary occlusion was created after pretreatment with amlodipine, 0.25 mg/kg (low dose) or 1.0 mg/kg (high dose), or placebo, intravenously twice a day, and continued for 7 days after infarction. Hearts (n = 50) were perfusion fixed 21 days after infarction and analyzed for infarct extent, scar thickness, left ventricular shape and size, and expansion index. Both doses decreased mean blood pressure (119 +/- 3 to 99 +/- 5 mm Hg low dose, p = 0.004; 110 +/- 5 to 84 +/- 4 mm Hg high dose, p = 0.0003), with reflex tachycardia only after the high dose (heart rate 395 +/- 9 to 434 +/- 11, p = 0.001). Infarct extent was equal in the three groups (39 +/- 2%, 41 +/- 2%, and 41 +/- 3% of left ventricular circumference for control, low, and high doses, respectively). The three groups did not differ significantly with regard to left ventricular cavity cross-sectional area (80 +/- 4, 77 +/- 3, and 87 +/- 3 mm2, control, low, and high doses, respectively; p = 0.07 high dose vs control), mean scar thickness (0.74 +/- 0.06, 0.73 +/- 0.05, and 0.65 +/- 0.06 mm, control, low, and high doses, respectively; p = NS), and expansion index (1.52 +/- 0.10, 1.58 +/- 0.12, and 1.95 +/- 0.19, control, low, and high doses, respectively; p = 0.08 high dose vs control). In the subgroup with larger infarcts (infarct extent greater than 0.39 of left ventricle), the expansion index was higher in the high-dose group (2.37 +/- 0.23 vs 1.64 +/- 0.17 control; p = 0.04). In this model, treatment with amlodipine does not limit infarct extent or reduce early infarct expansion and left ventricular dilatation, even when initiated before infarction.(ABSTRACT TRUNCATED AT 400 WORDS)

Amlodipine combined with beta blockade for chronic angina: Results of a multicenter, placebo-controlled, randomized double-blind study

Amlodipine, a potent long-acting dihydropyridine calcium antagonist, was compared with placebo in a parallel, randomized, double-blind study in 134 patients with chronic stable angina pectoris maintained on beta-adrenergic blocking agents. After a single-blind, two-week placebo period, patients were randomized to receive either amlodipine (2.5, 5, and 10 mg) or placebo once daily for four weeks. The effects of amlodipine on maximal exercise time, work, time to angina onset, and subjective indices including angina frequency, nitroglycerin tablet consumption, and patient and investigator ratings were assessed. Each dose of amlodipine produced increases in exercise time and calculated total work accomplished compared to baseline. Improvements at 5 and 10 mg were significantly greater than placebo which produced no significant change (p less than 0.05). Qualitative improvements in the severity of angina were produced by amlodipine at 5 and 10 mg daily assessed by patient-rating questionnaires (p less than 0.05). Reductions in angina frequency attacks per week and weekly nitroglycerin tablet consumption occurred but were not statistically significant when compared with placebo. Adverse effects observed during amlodipine treatment prompted discontinuation of treatment in only 2 out of 100 patients. Three patients discontinued treatment for reported lack of efficacy. No laboratory abnormalities prompted treatment discontinuation and minor side effects of dizziness, nausea, headache, and fatigue were observed infrequently. The results of this controlled, large-scale multicenter trial suggest that amlodipine significantly increased exercise capacity and was well tolerated when added to the antianginal regimen of patients remaining symptomatic while receiving beta-blocking agents.

Amlodipine. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic use in cardiovascular disease

Amlodipine, a basic dihydropyridine derivative, inhibits the calcium influx through 'slow' channels in peripheral vascular and coronary smooth muscle cells, thus producing marked vasodilation in peripheral and coronary vascular beds. Short to medium term clinical trials indicate that amlodipine is effective as both an antianginal agent in patients with stable angina pectoris and an antihypertensive agent in patients with mild to moderate hypertension. In small comparative studies amlodipine was at least as effective as 'standard' agents, including atenolol, verapamil, hydrochlorothiazide or captopril in hypertension, and diltiazem or nadolol in angina pectoris. Amlodipine is well tolerated, and does not appear to cause some of the undesirable effects often associated with other cardiovascular agents (e.g. adverse changes in serum lipid patterns, cardiac conduction disturbances, postural hypotension). The most common adverse effects associated with amlodipine therapy--oedema and flushing--are related to the vasodilatory action of the drug, and are generally mild to moderate in severity. Thus, amlodipine seems to provide a useful alternative to other agents currently available for the treatment of essential hypertension and chronic stable angina pectoris, with certain pharmacodynamic and tolerability properties that should be advantageous in many patients.