Vasodilatory action of amlodipine on rat aorta, pig coronary artery, human coronary artery, and on isolated Langendorff rat heart preparations

Lipid emulsion attenuates extrinsic apoptosis induced by amlodipine toxicity in rat cardiomyoblasts

Amlodipine-induced toxicity has detrimental effects on cardiac cells. The aim of this study was to examine the effect of lipid emulsion on decreased H9c2 rat cardiomyoblast viability induced by amlodipine toxicity. The effects of amlodipine, lipid emulsion, LY 294002, and glibenclamide, either alone or in combination, on cell viability and count, apoptosis, and expression of cleaved caspase-3 and -8, and Bax were examined. LY 294002 and glibenclamide partially reversed lipid emulsion-mediated attenuation of decreased cell viability and count induced by amlodipine. Amlodipine increased caspase-3 and -8 expression, but it did not alter Bax expression. LY 294002 and glibenclamide reversed lipid emulsion-mediated inhibition of cleaved caspase-3 and -8 expression induced by amlodipine. Lipid emulsion inhibited early and late apoptosis induced by amlodipine. LY 294002 and glibenclamide inhibited lipid emulsion-mediated inhibition of late apoptosis induced by amlodipine, but they did not significantly alter lipid emulsion-mediated inhibition of early apoptosis induced by amlodipine. Lipid emulsion decreased amlodipine-induced TUNEL-positive cells. These results suggest that lipid emulsion inhibits late apoptosis induced by amlodipine at toxic dose via the activation of phosphoinositide-3 kinase and ATP-sensitive potassium channels in the extrinsic apoptotic pathway.

Lipid emulsion inhibits the vasodilation induced by a toxic dose of amlodipine in isolated rat aortae

The goal of this study was to examine the effect of lipid emulsion on the vasodilation induced in isolated endothelium-denuded rat aortae by a toxic dose of amlodipine. We examined the effects of lipid emulsion and verapamil on amlodipine-induced vasodilation. We also examined the effects of a mixture of lipid emulsion and amlodipine, as well as the centrifuged aqueous extract (CAE) obtained by ultracentrifuging such a mixture and then removing the upper lipid layer, on amlodipine-induced vasodilation. The effect of lipid emulsion on the amlodipine concentration was examined. Lipid emulsion attenuated amlodipine-induced vasodilation in isolated aortae. Both CAE and lipid emulsion containing amlodipine inhibited amlodipine-induced vasodilation. However, there was no significant difference in amlodipine-induced vasodilation between aortae treated with CAE and those treated with lipid emulsion containing amlodipine. Verapamil inhibited amlodipine-induced vasodilation. Lipid emulsion decreased the concentration of amlodipine. Lipid emulsion attenuated the vasodilation induced by a toxic amlodipine dose in NaF-precontracted aortae. The data show that lipid emulsion inhibited the vasodilation induced by a toxic amlodipine dose in isolated rat aortae by reducing the concentration of amlodipine. Amlodipine-induced vasodilation seems to be mediated mainly by blockade of L-type calcium channels and partially by inhibition of the Rho-kinase pathway.

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.

Amlodipine inhibits thapsigargin-sensitive CA(2+) stores in thrombin-stimulated vascular smooth muscle cells

Ca(2+) channel blockers, such as amlodipine, inhibit vascular smooth muscle cell (VSMC) growth through interactions with targets other than L-type Ca(2+) channels. The effects of amlodipine on Ca(2+) movements in thrombin- and thapsigargin-stimulated VSMCs were therefore investigated by determining the variations of intracellular free Ca(2+) concentration in fura 2-loaded cultured VSMCs. Results indicated that 10-1,000 nM amlodipine inhibited 1) thrombin-induced Ca(2+) mobilization from a thapsigargin-sensitive pool and 2) thapsigargin-induced Ca(2+) responses, including Ca(2+) mobilization from internal stores and store-operated Ca(2+) entry. These effects of amlodipine do not involve L-type Ca(2+) channels and could not be reproduced with 100 nM isradipine, diltiazem, or verapamil. The inhibition by amlodipine of Ca(2+) mobilization appears therefore to be a specific property of the drug, in addition to its Ca(2+) channel-blocking property. It is suggested that amlodipine acts in this capacity by interacting with Ca(2+)-ATPases of the sarcoplasmic reticulum, thus modulating the enzyme activity. This mechanism might participate in the inhibitory effect of amlodipine on VSMC growth.

Irbesartan reduces QT dispersion in hypertensive individuals

Angiotensin type 1 receptor antagonists have direct effects on the autonomic nervous system and myocardium. Because of this, we hypothesized that irbesartan would reduce QT dispersion to a greater degree than amlodipine, a highly selective vasodilator. To test this, we gathered electrocardiographic (ECG) data from a multinational, multicenter, randomized, double-blind parallel group study that compared the antihypertensive efficacy of irbesartan and amlodipine in elderly subjects with mild to moderate hypertension. Subjects were treated for 6 months with either drug. Hydrochlorothiazide and atenolol were added after 12 weeks if blood pressure (BP) remained uncontrolled. ECGs were obtained before randomization and at 6 months. A total of 188 subjects (118 with baseline ECGs) were randomized. We analyzed 104 subjects who had complete ECGs at baseline and after 6 months of treatment. Baseline characteristics between treatments were similar, apart from a slight imbalance in diastolic BP (irbesartan [n=53] versus amlodipine [n=51], 99.2 [SD 3. 6] versus 100.8 [3.8] mm Hg; P=0.03). There were no significant differences in BP normalization (diastolic BP <90 mm Hg) between treatments at 6 months (irbesartan versus amlodipine, 80% versus 88%; P=0.378). We found a significant reduction in QT indexes in the irbesartan group (QTc dispersion mean, -11.4 [34.5] milliseconds, P=0.02; QTc max, -12.8 [35.5] milliseconds, P=0.01), and QTc dispersion did not correlate with the change in BP. The reduction in QT indexes with amlodipine (QTc dispersion, -9.7 [35.4] milliseconds, P=0.06; QTc max, -8.6 [33.2] milliseconds, P=0.07) did not quite reach statistical significance, but there was a correlation between the change in QT indexes and changes in systolic BP. In conclusion, irbesartan improved QT dispersion, and this effect may be important in preventing sudden cardiac death in at-risk hypertensive subjects.

Human vascular to cardiac tissue selectivity of L- and T-type calcium channel antagonists

1. Voltage-operated calcium channel (VOCC) antagonists are effective antihypertensive and antianginal agents but they also depress myocardial contractility. 2. We compared four L-type calcium channel antagonists, felodipine, nifedipine, amlodipine and verapamil and a relatively T-type selective calcium channel antagonist, mibefradil, on human and rat isolated tissue assays to determine their functional vascular to cardiac tissue selectivity (V/C) ratio. 3. The V/C ratio was calculated as the ratio of the IC50 value of the antagonist that reduced (by 50%) submaximally contracted (K+ 62 mM) human small arteries from the aortic vasa vasorum (vascular, V) mounted in a myograph and the IC50 value of the antagonist that reduced (-)-isoprenaline (6 nM) submaximally stimulated human right atrial trabeculae muscle (cardiac, C) mounted in organ chambers. 4. The average pIC50 values (-log IC50 M) for the human vascular preparations were felodipine 8.30, nifedipine 7.78, amlodipine 6.64, verapamil 6.26 and mibefradil 6.22. The average pIC50 values for the cardiac muscle were felodipine 7.21, nifedipine 6.95, verapamil 6.91, amlodipine 5.94, and mibefradil 4.61. 5. The V/C ratio calculated as antilog [pIC50V-pIC50C] is thus mibefradil 41, felodipine 12, nifedipine 7, amlodipine 5 and verapamil 0.2. 6. In rat small mesenteric arteries the pIC50 values for the five drugs were similar to the values for human vasa vasorum arteries contracted by K+ 62 mM. However for methoxamine (10 microM) contraction in the rat arteries the pIC50 values were lower for felodipine 7.24 and nifedipine 6.23, but similar for verapamil 6.13, amlodipine 6.28 and mibefradil 5.91. 7. In conclusion. in the human tissue assays, the putative T-channel antagonist mibefradil shows the highest vascular to cardiac selectivity ratio; some 3 fold higher than the dihydropyridine, felodipine, and some 200 fold more vascular selective than the phenylalkylamine, verapamil. This favourable vascular to cardiac selectivity for mibefradil, from a new chemical class of VOCC antagonist, may be explained by its putative T-channel selectivity.

Amlodipine dynamic effects and myocardial pharmacokinetics in the isolated and perfused guinea-pig heart

Myocardial dynamic effects and pharmacokinetics of amlodipine were studied in the isolated retrogradely perfused and spontaneously beating guinea-pig heart. Pharmacokinetic analysis of drug accumulation showed one-compartment characteristics with an half-life of 76 min. Whereas disposition exhibited two-compartment characteristics with phasic half-lives of 25 and 174 min., respectively. Myocardial drug accumulation was increased by 600 times at steady-state compared to the perfusion liquid. Dynamic effect parameters were studied during increasing amlodipine concentrations from 0.16 to 220 nM. Dynamic steady-states developed within 20 min. Coronary flow-rate increased with an Emax of 119% and an EC50 of 1.2 x 10(-8) M. Amlodipine produced inhibitory effects on contraction amplitude and velocities of contraction and relaxation. Observed Emax-values and curve-fitted EC50-values were: 97, 97 and 94% and 1.10(-8), 7.7 x 10(-9) and 2.1 x 10(-8) M, respectively. Heart frequency was not changed. Oxygen consumption increased markedly to a maximum of 44% at 3 x 10(-8) M amlodipine and then decreased to nearly initial values. The frequency-corrected QT-interval decreased to a maximal extent of 20% at the three highest concentrations. Myocardial efficiency expressed as the ratio of contraction velocity times frequency to oxygen consumption exhibited a progressive decline to about 2% of initial values. The PQ-interval was not changed and the QRS-interval showed only a small but significant decrease at the highest amlodipine concentration. No arrythmogenic effects were observed. The study demonstrated a very slow accumulation and disposition of amlodipine in the guinea-pig heart with a steady-state myocardial drug concentrating accumulation of 600 times. Marked increase in coronary flow-rate and oxygen consumption accompanied by a progressive negative inotropic effect were observed.

Amlodipine inhibition of serum-, thrombin-, or fibroblast growth factor-induced vascular smooth-muscle cell proliferation

Atherosclerosis, like several other vascular diseases, exhibits structural and functional abnormalities resulting partially from an exaggerated proliferation of vascular smooth-muscle cells (VSMCs). Ca2+ channel blockers, such as amlodipine, have been suggested to retard or even prevent the progression of atherosclerosis. To determine the mechanisms involved in these effects, we investigated the influence of amlodipine on VSMC proliferation by using rat aortic VSMCs in culture. Amlodipine (0.1-10 microM) inhibited serum-, basic fibroblast growth factor (bFGF)-, and thrombin-induced VSMC proliferation and DNA synthesis in a concentration-dependent manner, as demonstrated by cell count and bromodeoxyuridine (BrdU)-incorporation measurements, respectively. Delayed addition of amlodipine after VSMC stimulation showed that the drug exerted its effect early in G1 phase of the cell cycle. This observation was confirmed by the finding that amlodipine did not influence DNA synthesis in VSMCs arrested to the G1/S boundary by hydroxyurea treatment. Consistent with its effects on VSMC growth/proliferation, amlodipine also decreased c-myc, c-fos, and c-jun protooncogene expression induced by serum, thrombin, or bFGF within 1 h after cell activation, as assessed by semiquantitative reverse transcriptase (RT)-polymerase chain reaction (PCR) analysis. The calcium channel agonist Bay K 8644, which counteracted the inhibition by nifedipine of bFGF-, thrombin- or serum-induced DNA synthesis, was ineffective to antagonize the inhibitory effect of amlodipine. The aforementioned effects of amlodipine were of similar amplitude, irrespective of the growth-enhancing agent used. This strongly indicates that amlodipine acts downstream of receptor activation to exert its antiproliferative action, probably early in the G1 phase of the cell cycle. Moreover, the lack of antagonistic effect between amlodipine and Bay K 8644 suggests that, in addition to its L-type Ca2+ channel inhibitory effect, amlodipine inhibits other intracellular signaling pathways. Such an interference of amlodipine with mitogenic signaling pathways might contribute to confer a blood vessel-protecting potential on amlodipine.

Regional differences in the vasorelaxant effects of nicorandil and amlodipine on isolated porcine coronary arteries

The vasorelaxant effects of nicorandil, a K(+)-channel opener, and amlodipine, a dihydropyridine-type Ca(2+)-channel blocker, were investigated on partially and maximally K(+)-depolarized ring preparations from the porcine left anterior descending coronary artery. By comparing vascular responses in the proximal and distal parts of the epicardial segment, the scope of the study was to evaluate regional differences in the action of nicorandil and amlodipine. Nicorandil (10(-7)-10(-4) M) shifted the K+ concentration-response curves to the right and depressed the maximal contractile responses in a concentration-dependent manner, consistent with K(+)-channel opening and secondary non-K(+)-channel opening mechanisms of action. Nicorandil had a significantly more potent relaxant effect in the proximal compared to the distal arterial rings contracted with 85 mM K+. Pretreatment with methylene blue (10(-5) M) did not significantly influence the regional difference in the action of nicorandil. Amlodipine (10(-9)-10(-6) M) had a significantly more potent and effective inhibitory and relaxant effect than nicorandil under the same conditions. In contrast to nicorandil, the effect of amlodipine was more prominent in the distal compared to the proximal vessel rings. The cumulative addition of extracellular Ca2+ exhibited a more potent contractile response in the distal rather than in the proximal rings. Nicorandil totally and amlodipine partly eliminated the contractile responses to the lowest concentration of Ca2+. The inhibitory effect of amlodipine on the contractile responses to higher Ca2+ concentrations was more pronounced than that of nicorandil. The results show that there are regional differences in the responsiveness of porcine coronary arteries to Ca2+, nicorandil and amlodipine. Our findings indicate that the regional difference in nicorandil-induced vasodilation was caused neither by the K(+)-channel opening nor by the nitrate-like mechanism of action, but could be due to a direct Ca(2+)-influx blocking effect of the drug.

In-vitro negative chronotropic and inotropic effects of a novel dihydropyridine derivative, CD-832, in the guinea-pig: comparison with calcium-channel antagonists

The effects of CD-832 (4R-(-)-2-(nicotinoylamino)ethyl-3-nitroxypropyl-1,4-dihydro -2,6-dimethyl-4,3-nitrophenyl, 3,5-pyridine dicarboxylate) , a novel dihydropyridine derivative, on guinea-pig isolated myocardial preparations have been compared with those of Ca2+-channel antagonists. All ten compounds induced concentration-dependent negative chronotropic effects on preparations of isolated right atria and negative inotropic effects on isolated right ventricular papillary muscles. The order of potency for the negative chronotropic effect was CD-832 > nicardipine = gallopamil > clentiazem > nifedipine = efonidipine > amlodipine = semotiadil > verapamil > diltiazem; that for the negative inotropic effect was nicardipine = gallopamil > nifedipine > verapamil > CD-832 > diltiazem > clentiazem > efonidipine = semotiadil > amlodipine. The ratio of the EC50 (the concentration of Ca2+ antagonist having 50% of the maximum effect) for the negative inotropic effect divided by the EC50 for the negative chronotropic effect, considered to be an index of selectivity for negative chronotropic effect, was higher for CD-832, amlodipine, efonidipine and semotiadil than for the other Ca2+ antagonists. The ratio for CD-832, nifedipine, nicardipine, efonidipine, amlodipine, verapamil, gallopamil, diltiazem, clentiazem and semotiadil was 11.4, 0.29, 0.87, 35.4, 37.1, 0.65, 0.87, 0.92, 7.11 and 30.0, respectively. These findings indicate that CD-832 and the newly developed Ca2+ antagonists including amlodipine, efonidipine, semotiadil and clentiazem were selective for a negative chronotropic effect rather than for a negative inotropic effect. This 'chrono-selective' effect of these drugs might be of benefit in the treatment of cardiovascular disorders.

Effects of amlodipine on endothelial function in rats with chronic heart failure after experimental myocardial infarction

In chronic heart failure, the role of endothelial dysfunction is not yet well established. As calcium metabolism plays an important role in the endothelium, it might be suggested that calcium channel blockers influence endothelial function. Although calcium channel blockers are generally contraindicated in chronic heart failure, because they are believed to stimulate neurohumoral mechanisms and to exert negative inotropic effects, recently it has been suggested that amlodipine might have a favorable affect on mortality in patients with heart failure. The mechanism of amlodipine that contributes to this beneficial effect is not known. Therefore we investigated whether 10 weeks of amlodipine treatment could influence endothelial function in rats with congestive heart failure induced by myocardial infarction. The main finding of our study was that amlodipine, when administered for 10 weeks to rats after a myocardial infarction had been induced, had no significant effects on in vitro and in vivo hemodynamics or neurohormones. The effect of amlodipine on endothelium-intact, norepinephrine-precontracted aortic rings appears to differ from the placebo treatment with respect to the endothelium-dependent relaxation, whereas no differences are seen in endothelium-independent relaxation. We conclude that our data do not support a beneficial role of amlodipine on endothelial function in chronic heart failure.

Localization of calcium channels of the L-type in human epicardial arteries: a light microscope autoradiographic study

The anatomical localization of Ca2+ channels of the L-type was analyzed in sections of the human right and anterior interventricular coronary arteries by using in vitro light microscope autoradiography associated with radioligand binding techniques. [3H]Nicardipine was utilised as a ligand. Binding of the radioligand to sections of the two coronary arteries was time-, temperature- and concentration-dependent. Analysis of binding isotherms revealed a dissociation constant value of about 0.5 nM in the two arteries and maximum binding capacities of 139 +/- 6.4 fmol/mg tissue for the right coronary artery and of 173 +/- 9.5 for the anterior interventricular branch. The pharmacological profile of [3H]nicardipine binding to sections of human coronary arteries was consistent with the labelling of Ca2+ channels of the L-type. Dihydropyridine derivatives were the most powerful competitors of [3H]nicardipine binding, whereas phenylalkylamines, benzothiazepine or non-selective channel modulators were weak competitors or ineffective. Light microscope autoradiography revealed the highest density of [3H]nicardipine binding sites in the tunica media of the coronary arteries. In this layer Ca2+ channels of the L-type are located within smooth muscle cells. A lower accumulation of the radioligand occurred in the tunica adventitia, whereas no specific binding was found in the tunica intima. Study of the localization of Ca2+ channels in sections of human coronary arteries may contribute to a better understanding of the mechanism of the marked coronary dilatory activity elicited by Ca2+ antagonists demonstrable in both in vitro preparations and in vivo.

Amlodipine in chronic stable angina: results of a multicenter double-blind crossover trial

The efficacy and safety of amlodipine, 10 mg, a new long-acting calcium antagonist, was compared with placebo in 103 patients with stable angina pectoris in a multicenter double-blind crossover study. The trial consisted of an initial 2-week single-blind placebo period followed by a first period of 4 weeks of double-blind therapy, which was followed by a 1 week washout period and then a second 4-week double-blind period after treatments were crossed over. Twenty-four-hour Holter electrocardiographic monitoring was carried out in 12 patients at three centers. In the first double-blind period amlodipine produced a significantly greater increase in symptom-limited exercise duration (amlodipine 478.5 to 520.6 vs placebo 484.6 to 485.2 seconds; change +8.8% vs +0.1%, respectively; p = 0.0004) and total work (amldipine 2426 to 2984 vs placebo 2505 to 2548 kilopondmeters; change +24% vs +1.7%, respectively; p = 0.0006) and a decrease in angina attack frequency (from 3 to 1 per week; p = 0.016) and nitroglycerin consumption (from 2 to 0.5 tablets/wk; p = 0.01) compared with placebo. Holter monitoring revealed significant reductions in numbers (amlodipine 4.65 to 2.22 vs placebo 1.84 to 1.54; change -52% vs +84%, respectively; p = 0.06), absolute total area (amlodipine 87.66 to 11.43 vs placebo 5.76 to 35.24; change -87% vs +513%, respectively; p = 0.02), and duration (amlodipine 12.29 to 2.95 vs 1.66 to 7.74 seconds; change -76% vs +367%, respectively; p = 0.008) of ST-segment depressions after treatment with amlodipine compared with placebo. After the treatments were crossed over changes continued to favor amlodipine.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

Unique pharmacologic properties of amlodipine

Amlodipine is an intrinsically long-acting, vasoselective calcium antagonist structurally related to nifedipine, but with unique binding and pharmacologic properties that distinguish it from other agents of this class. Pharmacokinetic studies in animal models demonstrate a more prolonged half-life, high volume of distribution, and gradual elimination of amlodipine compared with that of other calcium antagonists. The presence of a basic side chain at the 2-position of the dihydropyridine ring renders the molecule > 90% ionized at physiologic pH and is believed to be primarily responsible for its markedly different pharmacologic and pharmacokinetic properties. Amlodipine has slow receptor binding kinetics that result in a gradual onset of action and may allow for less dependence on instantaneous plasma levels. Although amlodipine appears to bind to additional calcium channel recognition sites blocked by diltiazem and verapamil, it does not significantly depress heart rate nor does it produce significant negative inotropic effects or electrophysiologic disturbances. Preclinical studies indicate that amlodipine is a potent antihypertensive agent with natriuretic and diuretic properties that may enhance its ability to reduce blood pressure without attendant fluid retention.

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)

Long term effects of amlodipine on organ damage, stroke and life span in stroke prone spontaneously hypertensive rats

The long term effects of amlodipine, a new long acting Ca2+ channel antagonist on organ damage, stroke and life span, were examined in stroke prone spontaneously hypertensive rats (SHRSPs). Blood pressure of the SHRSPs increased over the first 16 weeks and reached a stable level of about 250 mmHg in controls and about 200 mmHg in the amlodipine treated group. At 15 weeks after starting amlodipine treatment, all control SHRSPs exhibited varying degrees of myocardial fibrosis, proliferative and/or necrotic vasculitis and glomerular lesions, whereas only a few animals in the amlodipine group showed slight lesions. The average life span of animals was estimated to be 43.3 weeks and 71.1 weeks for control and amlodipine groups, respectively, which suggested a 1.6-fold prolongation of their life span by amlodipine treatment. These results indicate that the long term treatment of amlodipine suppresses the incidence of organ damage and stroke in SHRSPs and prolongs their life span.

CP-96,345 antagonism of NK1 receptors and smoke-induced protein extravasation in relation to its cardiovascular effects

The effects of the non-peptide NK1 receptor antagonist, CP-96,345, on cardiovascular homeostasis were investigated in conscious and anaesthetized rats in vivo and on heart function and muscle tonicity of vessels in vitro. CP-96,345 and its enantiomer, CP-96,344, which does not exhibit NK1 receptor-blocking activity when tested at a concentration of 1 microM, significantly decreased blood pressure in conscious rats at a dose of 0.32 mg/kg i.v. CP-96,345 and CP-96,344 additionally reduced heart rate at doses of 1 and 3.2 mg/kg, respectively. Studies in anaesthetized rats showed that ganglionic blockade did not modify the decreases in blood pressure and heart rate elicited by CP-96,345. In the isolated guinea-pig heart, CP-96,345 and CP-96,344 exerted negative chronotropic effects at 10(-7) M; negative inotropic effects were observed at 10(-6) M. At 10(-5) M, both CP-96,345 and CP-96,344 decreased the amplitude of contraction of the rat portal vein, whereas at 10(-4) M, both compounds increased the frequency of contraction of this vessel. CP-96,345, at 5 x 10(-8) M, caused relaxation of precontracted pig coronary arteries. Since both CP-96,345 and CP-96,344 produced similar changes in haemodynamics and in the contractility of vascular and cardiac tissue, the cardiovascular effects of CP-96,345 are probably not related to NK1 receptor antagonism. As only the enantiomer with NK1 antagonistic activity inhibited cigarette smoke-induced plasma protein extravasation in rat trachea, CP-96,345 remains a useful tool for elucidating NK1 receptor-mediated responses, provided CP-96,344 is included as control.

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.

(+)-S-12967 and (-)-S-12968: 1,4-dihydropyridine stereoisomers with calcium channel agonistic and antagonistic properties in rat resistance arteries

1. The actions of (+)-S-12967 and (-)-S-12968 two isomers of a new 1,4-dihydropyridine (DHP) derivative, were studied on 125 mM K(+)-, Ca(2+)- and noradrenaline-induced contractions in rat isolated mesenteric resistance arteries and compared to those of nifedipine. 2. The action of (+)-S-12967 and (-)-S-12968 was slow in onset in contrast to nifedipine. Both isomers had a dual contractile and relaxant action in arteries contracted with 125 mM K+; however, the (-)-isomer was about 300 times more potent than the (+)-isomer. The response to 125 mM K+, being depressed by 70%, recovered within 20 to 30 min for all DHP derivatives. All vessels were treated with 1 x 10(-6) M phenoxybenzamine thus excluding the possibility that the contraction is mediated by activation of amine-receptors. 3. Both (+)-S-12967 and (-)-S-12968 at low concentrations potentiated responses induced by Ca2+ in arteries activated by 125 mM K+ and inhibited the responses at higher concentrations. (+)-S-12967 and (-)-S-12968 had no contractile action in arteries kept in normal buffer. Nifedipine had only an inhibitory action on vessel responses to 125 mM K+ and Ca2+. 4. Both isomers and nifedipine depressed the maximal vessel response to noradrenaline by about 20% and 44%, respectively. 5. The results confirm that DHP calcium antagonists selectively inhibit vascular smooth muscle responses induced by high potassium and that the potency of 1,4-DHP isomers may vary considerably. Furthermore, since the agonistic/antagonistic properties on the calcium channel were shared by both stereoisomers of the 1,4-DHP molecule and apparently dependent on their concentration and the vascular smooth muscle membrane potential, it suggests that the agonistic action of 1,4-DHPs may be ascribed to functional characteristics of their binding site regulating the Ca2l -channel.

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.

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

Amlodipine, a dihydropyridine calcium antagonist has been examined on the rhythmic activity of isolated human coronary arteries. Amlodipine inhibited both the spontaneous rhythmic activity and the rhythmic activity evoked by prostaglandin F2 alpha and endothelin in isolated human coronary arteries. It also inhibited the contraction evoked by potassium depolarization. The action of amlodipine was characterized by slow onset and voltage dependency.

Relaxation of potassium chloride-induced contractions by amlodipine and its interaction with the 1,4-dihydropyridine-binding site in pig coronary artery

Amlodipine is a light-insensitive and water soluble 1,4-dihydropyridine with prolonged vasodilatory action and plasma half-life. To determine whether the vasodilatory action of amlodipine is due to inhibition of voltage-dependent Ca2+ influx through the calcium channel, its effects on KCl-induced contraction of pig coronary artery rings and its interaction with the 1,4-dihydropyridine binding site in isolated sarcolemmal membranes were studied. The contractile function of artery rings was studied in an organ bath system, and the interaction with the 1,4-dihydropyridine binding site was studied in isolated sarcolemmal membranes of pig coronary artery using [3H](+)PN200-110 as a radioligand. Amlodipine, (+)PN200-110 and (-)PN200-110 inhibited KCl-induced contractions of arterial rings in a dose-dependent manner. The half-maximal inhibition (IC50) was observed at 0.46 +/- 0.02, 36 +/- 8 and 55 +/- 9 nM of (+)PN200-110, (-)PN200-110 and amlodipine, respectively. [3H](+)PN200-110 was found to bind to isolated sarcolemmal membranes with high affinity (KD = 0.04 nM, Bmax = 312 fmoles/mg protein) and stereospecifically, (+)PN200-110 (Ki = 0.05 nM) having about 130-fold higher affinity than (-)PN200-110 (Ki = 6.61 nM). Amlodipine also inhibited [3H](+)PN200-110 binding with high affinity (Ki = 4.41 nM). The inhibition was characterized by an increase in KD of binding of [3H](+)PN200-110 with very little effect on Bmax. The order of relative potency of inhibition of KCl-induced contraction was almost identical to the order of relative affinity for the 1,4-dihydropyridine binding site, as indicated by Ki.(ABSTRACT TRUNCATED AT 250 WORDS)

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

The hemodynamic effects and antianginal efficacy of 10 mg amlodipine administered intravenously were assessed for 45 minutes in 18 subjects with stable angina pectoris. After amlodipine the heart rate was increased from 75 +/- 12 beats/min to 80 +/- 15 beats/min (p less than 0.05) for at least 15 minutes, with a decrease in systemic vascular resistance of 1091 +/- 205 to 815 +/- 390 dynes/sec/cm5 and a decrease in mean arterial pressure at 30 minutes from 99 +/- 11 to 91 +/- 10 (p less than 0.05). There was no change in dp/dt or dp/dt/IP or in cardiac output, wedge pressure, or pulmonary artery pressure. In the parallel placebo group (n = 8) there was no change in any of the hemodynamic parameters. Time to pacing-induced angina was increased in the treated group (n = 12) from 6 +/- 3.2 minutes before the dose to 8.2 +/- 4 minutes after the dose (p less than 0.01) compared to the control subjects who were given saline solution, in whom the time increased from 7 +/- 1.5 minutes before the dose to 7.5 +/- 2.2 minutes after the dose (n = 9). The double product at an equivalent pacing time to the initial onset of angina was reduced after therapy from 15,590 +/- 1490 to 14,100 +/- 1193 with a reduction in ST segment shift from 11.9 +/- 9.4 mm2 to 6.2 +/- 5.6 mm2 (p less than 0.05). Amlodipine after intravenous use has a vasodilator effect and also increases the anginal threshold without deleterious negative inotropic effects.