Inhibition by amlodipine of activity evoked in isolated human coronary arteries by endothelin, prostaglandin F2 alpha and depolarization

Calcium channel blockers in cardiovascular pharmacotherapy

This paper summarizes the pharmacological properties of calcium channel blockers (CCBs), their established therapeutic uses for cardiovascular disorders and the current improvement of their clinical effects through drug combinations. Their identification resulted from study of small molecules including coronary dilators, which were named calcium antagonists. Further experiments showed that they reduced contraction of arteries by inhibiting calcium entry and by interacting with binding sites identified on voltage-dependent calcium channels. This led to the denomination calcium channel blockers. In short-term studies, by decreasing total peripheral resistance, CCBs lower arterial pressure. By unloading the heart and increasing coronary blood flow, CCBs improve myocardial oxygenation. In long-term treatment, the decrease in blood pressure is more pronounced in hypertensive than in normotensive patients. A controversy on the safety of CCBs ended after a large antihypertensive trial (ALLHAT) sponsored by the National Heart, Lung, and Blood Institute. There are two main types of CCBs: dihydopyridine and non-dihydropyridine; the first type is vascular selective. Dihydropyrines are indicated for hypertension, chronic, stable and vasospastic angina. Non-dihydropyridines have the same indications plus antiarrythmic effects in atrial fibrillation or flutter and paroxysmal supraventricular tachycardia. In addition, CCBs reduced newly formed coronary lesions in atherosclerosis. In order to reach recommended blood pressure goals, there is a recent therapeutic move by combination of CCBs with other antihypertensive agents particularly with inhibitors acting at the level of the renin-angiotensin system. They are also combined with statins. Prevention of dementia has been reported in hypertensive patients treated with nitrendipine, opening a way for further studies on CCBs' beneficial effect in cognitive deterioration associated with aging.

Single-dose, randomized, crossover bioequivalence study of amlodipine maleate versus amlodipine besylate in healthy volunteers

Amlodipine, marketed primarily as a besylate salt, is a calcium channel blocker used for treating essential hypertension. Amlodipine maleate is another salt that is considered, in terms of pharmacokinetics and pharmacodynamics, similar to amlodipine besylate. This open, randomized, two-period crossover trial has investigated in 24 healthy volunteers over a 144 h period the bioequivalence of amlodipine maleate tablets 10 mg versus amlodipine besylate tablets (Norvasc 10 mg). Plasma amlodipine concentrations were assessed by ultra performance liquid chromatography interfaced with a double quadrupole mass spectrometer. The area under the curve total (AUC(t)) and the area under the curve to infinity (AUC(inf)) values, peak plasma concentration (C(max)), and time to attain peak (t(max)) were not statistically different between the two drugs. AUC(t) and AUC(inf) values were higher (p < 0.05) in females than in males. The tolerability profile was comparable for the two salts of amlodipine. These findings indicate that amlodipine maleate and besylate are bioequivalent and were well tolerated, which suggests that the plasma kinetics of amlodipine depend on the properties of the molecule itself. Hence, the two salts investigated could be used interchangeably in clinical practice.

Restenosis and clinical outcome in patients treated with amlodipine after angioplasty: results from the Coronary AngioPlasty Amlodipine REStenosis Study (CAPARES)

OBJECTIVES

Our intent was to investigate the effect of the dihydropyridine calcium channel blocker amlodipine on restenosis and clinical outcome in patients undergoing percutaneous transluminal coronary angioplasty (PTCA).

BACKGROUND

Amlodipine has sustained vasodilatory effects and relieves coronary spasm, which may reduce luminal loss and clinical complications after PTCA.

METHODS

In a prospective, double-blind design, 635 patients were randomized to 10 mg of amlodipine or placebo. Pretreatment with the study drug started two weeks before PTCA and continued until four months after PTCA. The primary angiographic end point was loss in minimal lumen diameter (MLD) from post-PTCA to follow-up, as assessed by quantitative coronary angiography (QCA). Clinical end points were death, myocardial infarction, coronary artery bypass graft surgery and repeat PTCA (major adverse clinical events).

RESULTS

Angioplasty was performed in 585 patients (92.1%); 91 patients (15.6%) had coronary stents implanted. Follow-up angiography suitable for QCA analysis was done in 236 patients in the amlodipine group and 215 patients in the placebo group (per-protocol group). The mean loss in MLD was 0.30 +/- 0.45 mm in the amlodipine group versus 0.29 +/- 0.49 mm in the placebo group (p = 0.84). The need for repeat PTCA was significantly lower in the amlodipine versus the placebo group (10 [3.1%] vs. 23 patients [7.3%], p = 0.02, relative risk ratio [RR]: 0.45, 95% confidence interval [CI]: 0.22 to 0.91), and the composite incidence of clinical events (30 [9.4%] vs. 46 patients (14.5%), p = 0.049, RR: 0.65, CI: 0.43 to 0.99) within the four months follow-up period (intention-to-treat analysis).

CONCLUSIONS

Amlodipine therapy starting two weeks before PTCA did not reduce luminal loss, but the incidence of repeat PTCA and the composite major adverse clinical events were significantly reduced during the four-month follow-up period after PTCA with amlodipine as compared with placebo.

Calcium channel blockers in veterinary medicine

Calcium channel blockers are becoming increasingly popular in veterinary medicine for the treatment of systemic hypertension, cardiac arrhythmias, and hypertrophic cardiomyopathy. Calcium is vital to many cellular functions and thus stringent regulation of intracellular calcium concentrations is required. Pharmacologic manipulation of the regulatory mechanisms has the potential to alter cellular function in all body systems. In human medicine, calcium channel blockers are being evaluated for, among other things, use in treating glaucoma, deep vein thrombosis, and pulmonary hypertension, in renal transplantation, and for prevention of reperfusion injury. The potentially beneficial effects of these drugs have often been overshadowed by adverse effects including hypotension, inappetence, bradycardia, conduction abnormalities, and decreased cardiac output. With the introduction of sustained-release formulations (diltiazem) and 2nd generation calcium channel blockers (amlodipine) many of these effects have been attenuated or eliminated. This paper will review the functions of calcium and the calcium channels as well as discussing the classes and current and potential uses of the various calcium channel blockers.

Up-regulation of endothelin-B receptors in atherosclerotic human coronary arteries

Both endothelin-A (ETA) and endothelin-B (ETB) receptors are known to be present in human coronary arteries. However, their absolute and relative amounts, functional roles, and the influence of pathology are uncertain. The goal of the present study was to characterize endothelin receptors mediating constriction in human coronary arteries and to assess the influence of cardiomyopathy (CMP) and coronary artery disease (CAD) on ET receptors in human tissue. For comparison, porcine coronary arteries were evaluated in parallel. Competition binding experiments using [125I]ET-1 and different selective and nonselective ETA- and ETB-receptor agonists or antagonists revealed similar relative densities (relative Bmax) of ETA and ETB receptors in coronary arteries from human cardiomyopathic hearts (83% ETA and 17% ETB; n = 5) and porcine hearts (78% ETA and 22% ETB; n = 5). In marked contrast, the relative Bmax of ETB receptors were significantly higher in coronary arteries from human atherosclerotic hearts (51% ETA and 49% ETB; n = 3). Total receptor density (Bmax; fmol/mg protein) was highest in porcine (385 +/- 29) arteries, followed by human CAD (253 +/- 41) and CMP (174 +/- 20) coronary arteries. The relative and absolute Bmax values for ETA and ETB receptors in coronary arteries from a donor heart were similar to those obtained in CMP hearts. There were no significant differences in affinity constants (KD) values for ET-1, ET-3, Sarafotoxin S6c (SRTX S6c), BQ-123, and bosentan (Ro 47-0203) between tissues. In human coronary arteries from CMP hearts, ET-induced constriction seemed to be solely mediated via ETA receptors. In contrast, in porcine coronary arteries 20% of the maximal effect mediated by ET-1 could be attributed to ETB receptors, in agreement with the binding data. The functional role of ETB receptors in CAD tissue could not be evaluated because of the occurrence of spontaneous phasic contractions. We conclude that ETB receptors are up-regulated in human atherosclerotic coronary arteries. Further studies are needed to determine the pathophysiological importance of these receptors.

Time course of action of amlodipine and felodipine in the rat is most rapid in small arteries

The time course of action of amlodipine was compared to that of felodipine in rat mesenteric resistance arteries and aorta. Both amlodipine and felodipine caused a concentration-dependent relaxation of K(+)-depolarized resistance arteries: with amlodipine 3 x 10(-8) M and felodipine 10(-9) M, complete relaxation was reached after 40 min and 10 min, respectively. Furthermore, in resistance arteries, the time course of action of both drugs was shortest in vessels with the smallest diameter. In aorta, both drugs caused a marked relaxation of K(+)-induced tone, without reaching a maximal effect within 2 h. Recovery of K(+)-induced tone after both drugs was complete in resistance arteries, but not aorta, within 2 h. In resistance arteries exposed to K+ depolarization or noradrenaline, both drugs displayed the characteristics of 1,4-dihydropyridine Ca2+ channel antagonists. The results show that amlodipine was slower to have an effect than felodipine, but that both drugs acted fastest in the smallest arteries.

Calcium antagonists and vasodilatation

Calcium antagonists comprise a diverse group of chemically unrelated agents that interact with voltage-operated calcium channels (L-type) and thereby inhibit smooth muscle contractility. They are used to treat several major cardiovascular disorders, including hypertension and angina pectoris; they are also studied in congestive heart failure and in atherosclerosis. The current view is that their therapeutic action is related to vasodilatation. This view is an oversimplification, as will be shown in this review. It will also be illustrated that all calcium antagonists are not identical pharmacological agents.

Cardioselectivity of calcium antagonists

Calcium antagonists comprise a diverse group of chemically unrelated agents that interact with voltage-operated calcium channels (L-type) and thereby inhibit smooth muscle and cardiac contractility. Although they interact with the alpha 1 subunit of voltage-operated calcium channels, all calcium antagonists are not identical pharmacological agents. They are not only different from a chemical point of view, but also because some of them exhibit tissue selectivity, being more powerful blockers of the contraction of arteries than of cardiac muscle. The current view that their major therapeutic action is related to vasodilation is an oversimplification, as their action is more complex and may be related to factors other than hemodynamic ones.

Evidence for heterogeneity of endothelin receptor distribution in human coronary artery

1. The receptors mediating endothelin-evoked contraction of human coronary artery have been investigated in isolated segments of the left anterior descending coronary artery (LAD). 2. Endothelin-1 (ET-1) was 10 times more potent in distal than in proximal segments but the potency ratio between ET-1 and ET-3 (endothelin-3) was similar and close to 100 in any segment of the artery. 3. BQ-123, an ETA receptor antagonist, competitively antagonized the response to ET-1 of distal segments (pA2 equal to 7.47). In the proximal segments, part of the contractile response was BQ123 sensitive, but the antagonism was non-competitive. In both groups of segments, the response to ET-3 could be completely blocked by BQ-123. 4. These observations indicate that ETA receptors mediate the contractile response to ET-1 in distal, pre-resistant coronary arteries, but that other ET receptors are also involved in the contractile response of proximal segments.

Effects of (+)-S-12967 and (-)-S-12968, two enantiomers of a new slow-acting 1,4-dihydropyridine, on rat coronary resistance arteries

The action of (+)-S-12967 and (-)-S-12968, two isomers of a new 1,4-dihydropyridine molecule (2-(-7-amino-2,5-dioxaheptyl)-3-ethoxycarbonyl-4-(2,3-dichlorop hen yl)-5-methoxycarbonyl-6-methyl 1,4-dihydropyridine), was studied on responses of rat isolated coronary resistance arteries (i.d. about 230 microns) to K+, Ca2+, and 5-hydroxytryptamine (5-HT). Both isomers slowly relaxed coronary arteries contracted with 125 mM K+, reaching a maximal effect in about 2 h. In contrast, the maximal relaxing effect of nifedipine was obtained within 20 min. The response to 125 mM K+ did not recover within the 2-h washout period in vessels exposed to the isomers but returned to pre-drug levels within 40 min in vessels exposed to nifedipine. Nifedipine was 4 times more potent than the (-)-isomer which again was about 200 times more potent that the (+)-isomer. The IC50[M] values were approximately 1 nM, 4 nM and 0.8 microM, respectively. The relaxing effect of the isomers, which has a pKa of 8.6, was dependent on the extracellular pH being greater at high than low pH. Both isomers antagonized the vessel responses to K+ and Ca2+ and 5-HT. Higher concentrations of the isomers were required to antagonize responses to K+ and 5-HT than to Ca2+, probably due to the more depolarized state of the vascular smooth muscle in the latter experiments. In conclusion, the results demonstrate extracellular pH dependence as well as stereoselectivity regarding potency of (+)-S-12967 and (-)-S-12968 in rat coronary arteries.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Endothelin induces a nonselective cation current in vascular smooth muscle cells

The potent vasoconstrictor endothelin leads to smooth muscle cell depolarization and increases in intracellular Ca2+. Although effects of endothelin on calcium channels have been described, it also has been speculated that endothelim may activate additional ion channels. The purpose of the present study was to identify an alternative ion current that could play a role in depolarizing cells in response to vasoconstrictors like endothelin and vasopressin. The effects of endothelin, vasopressin, sarafotoxin S6b, and phenylephrine were assessed using whole-cell patch-clamp recordings from primary dissociated rat aortic or mesenteric arterial smooth muscle cells cultured for 24-72 hours. From the usual resting potentials of these cells of -50 to -60 mV, endothelin (1-100 nM) induced a depolarization via an increase in membrane conductance. This depolarization was phasic, oscillating repeatedly from the resting potential to a relatively depolarized level and back to the resting potential. From a holding potential of -60 mV, endothelin-1, endothelin-3, vasopressin, or sarafotoxin S6b (but not phenylephrine) induced transient inward currents that also could be phasic. In external sodium, lithium, or cesium (but not Tris) and in internal potassium or cesium, these currents reversed near 0 mV. Although nifedipine-insensitive, the inward currents were absent in zero calcium, barium, or strontium, or in the presence of cobalt or nickel. These results represent the first report of a nonselective cation current in primary vascular smooth muscle cells that is calcium dependent and that could be responsible for the depolarizations induced from the resting potential by vasoconstrictors such as endothelin.

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.