Future directions in the use of calcium antagonists

Pharmacological basis of different targets for the treatment of atherosclerosis

The development of atherosclerotic plaque is a highly regulated and complex process which occurs as a result of structural and functional alterations in endothelial cells, smooth muscle cells (SMCs), monocytes/macrophages, T-lymphocytes and platelets. The plaque formation in the coronary arteries or rupture of the plaque in the peripheral vasculature in latter stages of atherosclerosis triggers the onset of acute ischemic events involving myocardium. Although lipid lowering with statins has been established as an important therapy for the treatment of atherosclerosis, partially beneficial effects of statins beyond decreasing lipid levels has shifted the focus to develop newer drugs that can affect directly the process of atherosclerosis. Blockade of renin angiotensin system, augmentation of nitric oxide availability, reduction of Ca(2+) influx, prevention of oxidative stress as well as attenuation of inflammation, platelet activation and SMC proliferation have been recognized as targets for drug treatment to control the development, progression and management of atherosclerosis. A major challenge for future drug development is to formulate a combination therapy affecting different targets to improve the treatment of atherosclerosis.

Evidence that lacidipine at nonsustained antihypertensive doses activates nitrogen monoxide system in the endothelium of salt-loaded Dahl-S rats

Lacidipine is a clinically active, antihypertensive calcium antagonist of the 1,4 dihydropyridine (DHP) class. It is also capable of vascular protection when administered (prophylactically and therapeutically) at nonsustained antihypertensive doses to salt-sensitive Dahl-S rats: useful animal models for studying the vasoprotective effect of calcium antagonists. In our previous work using voltammetry with selective biosensors, we observed that lacidipine implements endothelial nitrogen monoxide (NO) in normal rats. These experiments, performed in aortic rings obtained from Dahl-S rats analyzed with voltammetry and specific biosensors, further demonstrate that lacidipine, given at doses that do not control the development of hypertension (1 mg/kg), enhance endothelial NO activity. Taken together with the observation that 1 mg/kg lacidipine, and not its vehicle, is able to prevent vascular damage and concomitant increases in mortality (accelerated by a salt diet), this voltametric data suggest that NO acts as a component of positive influence of this DHP on vascular structure and function.

Arterial calcification: a review of mechanisms, animal models, and the prospects for therapy

The causes of arterial calcification are beginning to be elucidated. Macrophages, mast cells, and smooth muscle cells are the primary cells implicated in this process. The roles of a variety of bone-related proteins including bone morphogenetic protein-2 (BMP-2), matrix Gla protein (MGP), osteoprotegerin (OPG), osteopontin, and osteonectin in regulating arterial calcification are reviewed. Animals lacking MGP, OPG, smad6, carbonic anhydrase isoenzyme II, fibrillin-1, and klotho gene product develop varying extents of arterial calcification. Hyperlipidemia, vitamin D, nicotine, and warfarin, alone or in various combinations, produce arterial calcification in animal models. MGP has recently been discovered to be an inhibitor of bone morphogenetic protein-2, the principal osteogenic growth factor. Many of the forces that induce arterial calcification may act by disrupting the essential post-translational modification of MGP, allowing BMP-2 to induce mineralization. MGP requires gamma-carboxylation before it is functional, and this process uses vitamin K as an essential cofactor. Vitamin K deficiency, drugs that act as vitamin K antagonists, and oxidant stress are forces that could prevent the formation of GLA residues on MGP. The potential role of arterial apoptosis in calcification is discussed. Potential therapeutic options to limit the rate of arterial calcification are summarized.

Role of transthoracic echocardiography in atrial fibrillation

Atrial fibrillation is a major clinical problem that is predicted to be encountered more frequently as the population ages. The clinical management of atrial fibrillation has become increasingly complex as new therapies and strategies have become available for ventricular rate control, conversion to sinus rhythm, maintenance of sinus rhythm, and prevention of thromboembolism. Clinical and transthoracic echocardiographic features are important in determining etiology and directing therapy for atrial fibrillation. Left atrial size, left ventricular wall thickness, and left ventricular function have independent predictive value for determining the risk of developing atrial fibrillation. Left atrial size may have predictive value in determining the success of cardioversion and maintaining sinus rhythm in selected clinical settings but has less value in the most frequently encountered group, patients with nonvalvular atrial fibrillation, in whom the duration of atrial fibrillation is the most important feature. When selecting pharmacological agents to control ventricular rate, convert to sinus rhythm, and maintain normal sinus rhythm, transthoracic echocardiography (TTE) allows noninvasive evaluation of left ventricular function and hence guides management. The combination of clinical and transthoracic echocardiographic features also allows risk stratification for thromboembolism and hemorrhagic complications in atrial fibrillation. High-risk clinical features for thromboembolism supported by epidemiological observations, results of randomized clinical trials, and meta-analyses include rheumatic valvular heart disease, prior thromboembolism, congestive heart failure, hypertension, older (> 75 years old) women, and diabetes. Small series of cases also suggest those with hyperthyroidism and hypertrophic cardiomyopathy are at high risk. TTE plays a unique role in confirming or discovering high-risk features such as rheumatic valvular disease, hypertrophic cardiomyopathy, and decreased left ventricular function. Validation of the risk stratification scheme used in the Stroke Prevention in Atrial Fibrillation-III trial is welcomed by clinicians who are faced daily with balancing the benefit and risks of anticoagulation to prevent thromboembolism in patients with atrial fibrillation.

Effect of long term isradipine treatment on the morphology of the endothelium in the aorta of spontaneously hypertensive rats

The influence of hypertension and of treatment with the dihydropyridine calcium channel blocker isradipine on the morphology of the thoracic aorta and of the aortic tunica intima were studied. Three experimental groups of male spontaneously hypertensive rats (SHR) of 10 weeks of age were used. Two groups were treated with a daily oral dose of 0.01 mg/kg or of 0.1 mg/Kg of isradipine respectively. A third group of SHR was left untreated and served as control. Age-matched normotensive Wistar-Kyoto (WKY) rats were used as a reference group. Animals were allowed to survive for 12 weeks and were killed at 22 weeks of age. Systolic pressure values which did not change in WKY rats, significantly increased in SHR as a function of age. The dose of 0.1 mg/Kg/day isradipine reduced systolic pressure to normotensive values after the first week of treatment, whereas the lower one was ineffective. The area of the wall, the area of the tunica media and the wall-to-lumen ratio of the aorta significantly increased in SHR and decreased either with the antihypertensive and non-antihypertensive doses of isradipine. Transmission and scanning electron microscope analysis of the tunica intima revealed hypertrophy of the endothelial cells with an increase in sub endothelial space in SHR. An improvement of the endothelial morphology and a decrease in sub endothelial space was noticeable in isradipine-treated SHR. Although the hypotensive dose of the compound was the most effective, the non-hypotensive dose was active was well. The above results suggest that isradipine treatment may counter structural changes of the aorta of SHR and has a protective action on the hypertension-dependent modifications of the endothelium. The endothelial effects are probably dependent only in part by the hypotensive activity of the compound.

Role of calcium antagonists in progression of arteriosclerosis. Evidence from animal experiments and clinical experience. Part I. Preventive effects of calcium antagonists in animal experiments

The quantitative predominance of free and total cholesterol over the amount of mural calcium is a most significant criterion of healthy human coronary arteries during the whole life span (0-90 years). However, this normal ratio increasingly changes as soon as arteriosclerotic alterations of the coronary walls set in. Accordingly, the mural calcium content steadily rises from fatty streaks over severe arteriosclerosis and, lastly, seems to reach a climax in plaques which caused lethal coronary infarction. Furthermore, the severe arteriosclerosis of human art. dorsalis pedis with gangrene (and amputation) is characterized by a tremendous calcium incorporation and absence of any mural cholesterol changes. Only in rare cases of human basilary plaques was a dangerous cholesterol incorporation in brain arterial wall found without significant elevation of serum cholesterol levels. The presented data indicate the existence of two different types of arteriosclerosis in one and the same patient and two basically different types of experimental coronary plaques according to their chemical composition, microscopic aspect and responsiveness to calcium antagonists: 1) the calcium type, developing in vitamin-D3-treated rats, and 2) the cholesterol type, represented by fatty coronary atheromata of cholesterol-fed rabbits. Coronary atheromata of cholesterol-fed New Zealand rabbits may be suitable models for coronary heart disease in rare cases of human familiar hypercholesterolemia. The formation of conventional human coronary artery plaques, however, essentially requires a progressive uptake of calcium, thereby representing a calcium dominated type of arteriosclerosis. Calcium antagonists specifically inhibit progredient mural calcium uptake in all experimental models of arteriosclerosis tested so far. However, neither in atheromatous arteries nor in afflicted organs (myocardium, liver, kidneys) of cholesterol-fed rabbits were we able to find any significant prevention of cholesterol accumulation by calcium antagonist.

Role of calcium in arteriosclerosis--experimental evaluation of antiarteriosclerotic potencies of Ca antagonists. Study Group for Calcium Antagonism

Chemical microanalyses of conventional human coronary artery plaques (stages I-III [WHO]) revealed the correlation between progressive mural Ca overload up to excessive degrees, and the severity of plaque formation, whereas only small amounts of cholesterol were found, even in complicated lesions. The pathogenetic role of Ca was tested in three types of experimental arteriosclerosis and atheromatosis, using Ca antagonists (verapamil, nitrendipine, diltiazem) as research tools: 1) The Ca type, in vitamin D3 plus nicotine-treated rats; 2) the cholesterol type, in cholesterol-fed New Zealand rabbits; 3) mixed types, in SHRs and NaCl-fed Dahl-S rats. Types (1) and (3) were demonstrated to be governed by a progressive arterial Ca uptake that could be established already in early lesions. The increased mural Ca supply promoted cellular necroses, migration, and proliferation, as well as calcification and degradation of elastic fibers. Ca antagonists prevented the increased Ca incorporation into arterial walls and inhibited the development of experimental arterioscleroses of types (1) and (3). Ca antagonists did not protect coronary arteries of cholesterol-fed rabbits (type [2]) from occlusive cholesterol accumulation. The data suggest an important pathogenetic role of Ca and pronounced antiarteriosclerotic potencies of Ca antagonists in Ca-dominated types of experimental arteriosclerosis. The significance of the present results for pathophysiology and therapy of conventional human arteriosclerosis remains to be clarified.

Slowing of mitral valve annular calcium in systemic hypertension by nifedipine and comparisons with enalapril and atenolol

Mitral annular calcium (MAC) is a condition that often occurs in patients with systemic hypertension. To evaluate the effectiveness of nifedipine in preventing MAC, 223 patients with systemic hypertension of recent onset and without MAC were selected and randomly enrolled in 3 groups: group 1 (76 patients) received nifedipine; group 2 (72 patients) received enalapril; and group 3 (75 patients) received atenolol. After 5 years, these treatments significantly reduced systolic (p < 0.001) and diastolic (p < 0.05) blood pressure (BP) in 3 treated groups. M-mode echocardiography revealed MAC only in 2 patients in the nifedipine group (2.6%), in 13 in the enalapril group (18%) and in 15 in the atenolol group (20%). The degree of MAC was mild (< 5 mm) in the 2 patients in group 1, in 5 of the 13 in group 2, and in 6 of the 15 in the group 3, whereas it was severe (> 5 mm) in the remaining 8 in the enalapril group and in the other 9 in the atenolol group. There was also a significant correlation in the degree of MAC, left atrial enlargement and mitral regurgitation. In addition, atrial fibrillation and atrioventricular conduction defects were associated with severe MAC. These results indicate that nifedipine is an effective drug both in the long-term management of systemic hypertension and in preventing or delaying MAC.

Atrial fibrillation: epidemiology and the risk and prevention of stroke

Atrial fibrillation is a common disorder and the incidence increases with each decade of life. Previously, rheumatic mitral valve disease has been the condition most highly associated with atrial fibrillation. However, with the decreasing incidence of rheumatic heart disease, other conditions have assumed greater importance and now congestive cardiac failure, coronary artery disease, and hypertension are the most commonly associated conditions. Nonrheumatic atrial fibrillation is associated with an approximately five-fold increase in the risk of ischemic stroke and a 5% to 7% yearly risk that increases with age. In addition, atrial fibrillation is associated with an increased incidence of silent cerebral infarction and increased mortality. However, whether atrial fibrillation is independently associated with the risk of stroke or is a marker of underlying cardiac disease is contentious. Until recently, the use of preventive therapy has been controversial. However, data from four recently published, prospective randomized studies clearly support the use of warfarin prophylaxis in nonrheumatic atrial fibrillation. Within the diverse group of patients with nonrheumatic atrial fibrillation there are high and low risk subgroups and identification of these may influence decisions regarding antithrombotic prophylaxis. With a few exceptions, however, this remains an area in which there are contradictory findings in the literature. The role of aspirin for prophylaxis in nonrheumatic atrial fibrillation remains unclear and further evaluation awaits the publication of ongoing studies.

Acute hemodynamic effects of intravenous diperdipine, a new dihydropyridine derivative, in coronary heart disease

The acute hemodynamic effects of a new dihydropyridine calcium channel blocker, diperdipine, which is suitable for intravenous administration, were studied by right and left cardiac catheterization in 16 patients with coronary heart disease. Diperdipine markedly reduced systemic vascular resistance and improved stroke index and left ventricular ejection fraction. Mean pulmonary artery and wedge pressures were slightly increased as a possible consequence of enhanced venous return, whereas right atrial and left ventricular end-diastolic pressures were not significantly changed. Nevertheless, an increase in preload was clearly indicated by an augmented left ventricular end-diastolic volume index after administration of diperdipine. Left ventricular contractility, which was estimated by the end-systolic pressure-volume ratio and by dP/dt max was not significantly changed, though analysis of individual data suggests a minimally negative inotropic effect. However, such a minor effect on left ventricular contractility was largely counterbalanced by the marked reduction of afterload, which produced a sharp improvement of stroke index. Enhancement of left ventricular ejection fraction and reduction in systemic vascular resistance were inversely and directly correlated to control values. Overall, diperdipine was well tolerated, but one patient had a major untoward reaction that consisted of an ischemic episode that was possibly related to drug administration. In conclusion, intravenous diperdipine appears to be a potent arteriolar dilating agent that does not affect left ventricular contractility.

Calcium--a neglected key factor in arteriosclerosis. The pathogenic role of arterial calcium overload and its prevention by calcium antagonists

Using specific calcium antagonists as experimental tools, both the physiological messenger and current carrying function of calcium ions as well as their pathogenetic potencies could be elucidated. Notably, excess intracellular calcium signalling and intra- and extracellular calcium overload turned out to be pathogenetic principles of general importance. In this context, progressive calcium overload of arteriosclerotic vascular walls and the antiarteriosclerotic effects of calcium antagonists, deserve particular interest. In fact, with the help of calcium antagonists, arterial calcium overload as decisive component of various types of experimental arteriosclerosis became accessible to a direct therapeutic intervention. According to their responsiveness to calcium antagonists, two pathophysiologically different types of experimental coronary plaques could be characterized: (1) The calcium type, i.e. coronary calcinosis of vitamin D3-intoxicated rats highly sensitive to calcium antagonist treatment, (2) the cholesterol type, represented by coronary atheromata of cholesterol-intoxicated rabbits; this primary coronary cholesterol accumulation could not be inhibited by calcium antagonists. The formation of conventional human coronary artery plaques is characterized from the very early lesion onwards by a progressive local uptake of calcium, finally leading to lethal consequences. Conversely, the analysis of the mural cholesterol does not allow to discriminate arteriosclerotic from normal coronary artery segments. Thereby, conventional human coronary plaques typically represent a calcium-dominated type of human arteriosclerosis and differ widely from plaques produced in cholesterol-fed rabbits. The results indicate the decisive pathophysiological role of calcium and calcium overload in both calcium-dominated types of experimental arteriosclerosis and conventional human coronary artery plaques. Moreover, the antiarteriosclerotic effects of calcium antagonists are demonstrated to be based--in various types of experimental arteriosclerosis--on the inhibition of intra- and extracellular calcium overload of arterial walls evoked by various risk factors (vitamin D3 intoxication, hypertension, nicotine, diabetes).

Calcium and the impairment of contractions to norepinephrine in aorta isolated from the spontaneously hypertensive rat

Helical strip contractility from hypertensive (SHR) and normotensive (WKY) rat aortas assessed in the presence of varying calcium concentrations indicated that SHR strips exhibit a higher intrinsic myogenic tone and contract less to norepinephrine (NE) in a physiological calcium concentration compared to controls. Relatively higher isometric tension was developed in the SHR in low calcium (0-0. 27 mM). While control responses were blunted by LaCl3, EGTA, and nifedipine, the SHR strips were unaffected. Addition of procaine significantly enhanced SHR contractility to NE with no effect on control strips. These data suggest that abnormal cytosolic calcium provokes an increase in myogenic tone and an impaired contractile response of aortic smooth muscle cells to NE.

Progress in cardioprotection: the role of calcium antagonists

Calcium antagonists are now widely used for the treatment of clinical hypertension and angina pectoris. They are efficacious for the treatment of vasospastic, fixed atherosclerotic and mixed angina; they reduce the incidence of silent ischemia; and they have been shown to reduce postmyocardial infarct angina. Experimental data suggest that they may have certain cardioprotective properties in cases of acute myocardial ischemia and infarction, stunned myocardium, diastolic dysfunction, left ventricular hypertrophy and atherosclerosis. Moreover, they have been shown to improve exercise performance, as well as the diastolic abnormalities in patients with hypertrophic cardiomyopathy. In animals, they may delay or reduce the extent of myocardial necrosis after coronary occlusion or coronary occlusion followed by reperfusion, and in low doses that do not alter the hemodynamic profile, they have been shown to enhance the return of ventricular function in animals with stunned myocardium. However, the early first-generation calcium antagonists (nifedipine, verapamil, diltiazem) have not been shown to reduce myocardial infarct size or to enhance survival in patients with acute myocardial infarction. There now are clinical studies that suggest that, unlike beta blockers or nitrates, nifedipine may slow the development of atherosclerotic progression in humans over a 2-year period, and it seems likely that in the 1990s there will be further expansion of the use of calcium antagonists for not only angina and hypertension but also for aspects of cardioprotection. That calcium antagonists may delay, prevent or possibly regress atherosclerotic lesions is an exciting possibility.

Excessive mural calcium overload--a predominant causal factor in the development of stenosing coronary plaques in humans

Healthy human coronary artery walls contain, over their entire lifetime, more free and total cholesterol than calcium. However, as soon as arteriosclerotic alterations set in, the calcium content increases. Thus in coronary fatty streaks (arteriosclerotic plaques of WHO stage I), calcium was increased 13 times, in stage II plaques 25 times, and in fully developed stage III plaques 80 times above normal on average. The most dramatic calcium incrustation was found in coronary stage III plaques that had produced massive fatal coronary infarction. Here, the proportion of calcium salts (particularly hydroxyapatite) may amount to almost 50% of dry weight. Thus the most excessive accumulation of calcium seems to be correlated with the highest fatality. In contrast, there is no correlation between mural coronary free or total cholesterol content, and plaque severity. Accordingly, stenosing coronary stage III plaques contain less cholesterol than do fatty streaks. Moreover, in coronary stage III plaques the proportion of free cholesterol was 1.37%, and of total cholesterol only 2.34% of the whole mass, certainly not enough for directly causing coronary occlusion. Thus the calcium-rich plaques of human coronary arteries considerably differ from the well-known cholesterol-rich plaques (stage I and II) of human aortae. Our findings justify a new prophylactic approach with suitable calcium antagonists to interfere with deleterious calcium uptake in coronary plaque development.

Prevention of arterial disease in experimental renal hypertension

1. This study examined the effect of various antihypertensive agents on the development of polyarteritis nodosa lesions along the mesenteric artery system over a 10 week period after renal artery clipping in uninephrectomized rats (lKlC). 2. Of the agents, only hydralazine, enalapril and diltiazem significantly inhibited systolic blood pressure (SBP) rise over the 10 week period (P less than 0.001). 3. All agents except hydralazine reduced the severity of arteritic lesions compared with lKlC rats, but only with enalapril (P less than 0.001), nifedipine (P less than 0.001), diltiazem (P less than 0.005), propranolol (P less than 0.001) and reserpine (P less than 0.05) was this reduction statistically significant. 4. There was a positive correlation between the degree of arteritic change and SBP, but the correlation coefficient was neither high (r = 0.68) nor highly significant (P = 0.03, d.f. = 9). On examining the data, this was due on the one hand to nifedipine, propranolol and reserpine reducing the severity of lesions without significantly inhibiting SBP, and on the other to hydralazine reducing SBP without significantly affecting the extent of arteritic change. 5. These findings suggest that factors other than mere SBP alone are involved in the pathogenesis of these arteritic lesions.

Calcium antagonists: pharmacologic agents in search of new clinical indications

The broad availability of new pharmacologic agents is usually followed by both the search for similar compounds with more specific and refined actions and the expansion of clinical applicability for these agents. During the last twenty years extensive investigations have revealed that calcium (Ca) antagonists hold a multifaceted pharmacodynamic potential that includes not only the antiarrhythmic and antihypertensive effects of the drug but also the protection against excessive Ca entry into the cells of the cardiovascular system and subsequent cell damage. The physiologic age-dependent Ca accumulation in the arterial wall, which inevitably appears after the second decade, reaches maximal values in the age group of eighty-one to ninety years when the aortic wall exhibits a total Ca content that is 100 times higher than in arteries of infants. In animals we also find age-dependent accumulation of Ca in the arterial wall that is severely aggravated by uncontrolled diabetes or hypertension. Fleckenstein has shown that this arterial calcinosis can be prevented by chronic administration of Ca antagonists. Furthermore, Fleckenstein has demonstrated that excessive Ca overload of myocardial tissue constitutes a basic pathologic process in the development of cardiac necroses--brought about by extreme beta-adrenergic drive (overdoses of catecholamines), high doses of vitamin D3, dihydrotachysterol, alimentary factors such as K or Mg deficiency, or genetic defects (hereditary cardiomyopathy). Even cardiac hypertrophy, either idiopathic or as a consequence of hypertension, can be prevented by the action of Ca antagonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Amlodipine, a new 1,4-dihydropyridine calcium antagonist with a particularly strong antihypertensive profile

The effects of a new 1,4-dihydropyridine derivative amlodipine have been compared with results from our previous work. Application of amlodipine at a concentration of 1.6 X 10(-6) M to isolated guinea-pig papillary muscle for 120 minutes produced a 50% reduction in tension development compared with a concentration of 3.7 X 10(-7) M nifedipine needed to produce the same result under identical conditions. This suggests that amlodipine has even weaker negative inotropic effects than nifedipine. In isolated porcine coronary strips, the K+-induced contractions were approximately 10,000 times more sensitive to the relaxing effects of nisoldipine, nitrendipine and nicardipine than to those of papaverine, whereas nifedipine and amlodipine were 3,000 times more potent than papaverine. However, in comparison with these in vitro actions, the efficacy of amlodipine appears to be greater in vivo: Simultaneous subcutaneous injection of nifedipine (20 mg/kg) and of equimolar doses of nisoldipine and felodipine attenuated the myocardial calcium uptake by rat hearts in situ (stimulated with a single subcutaneous dose of 30 mg/kg isoproterenol) with the same efficacy, whereas the actions of nitrendipine and nimodipine were considerably weaker. In contrast, amlodipine antagonized isoproterenol-stimulated myocardial calcium accumulation more effectively. Furthermore, amlodipine exhibited a high antihypertensive potency combined with rapid onset and long duration of action: Amlodipine (10 mg/kg orally [p.o.]) reduced the blood pressure of spontaneously hypertensive rats almost to the same extent as nifedipine, nitrendipine, verapamil and felodipine administered at the much higher doses of 100 mg/kg p.o. Amlodipine (20 mg/kg/day p.o.) maintained normal blood pressure during the whole life span of Dahl-S rats (5 months), but this dose is considerably lower than that reported for other 1,4-dihydropyridines. The survival of NaCl-loaded Dahl-S rats increased from 20 to 100% after administration of amlodipine (20 mg/kg/day p.o.) over 10 weeks: The effective dose of other calcium antagonists is approximately 5 times higher, but well tolerated as, e.g., demonstrated in long-term studies on Dahl-S rats with nitrendipine over 12 months. Increases in systemic arteriolar tone can be visualized in the ocular fundus of spontaneously hypertensive rats. After amlodipine (10 mg/kg p.o.) arteriolar spasm declines. Prophylaxis with 2 doses of 20 mg/kg amlodipine daily in NaCl-loaded Dahl-S rats abolished the macroscopic and histologic changes that are normally seen in branches of the mesenteric artery. With use of electron microscopy, calcium accumulation in the lamina elastica interna was demonstrated by the potassium-pyr-oantimonate technique.(ABSTRACT TRUNCATED AT 400 WORDS)

Nicardipine in elderly patients with hypertension: a review of experience in France

A double-blind, placebo-controlled clinical trial in France has studied the efficacy and safety of nicardipine in 31 elderly patients, aged 57 to 95 years (mean age 84 years), 16 of whom were actively treated with nicardipine, 10 to 30 mg three times a day (mean dose 69.4 mg/day). After 4 weeks, nicardipine lowered mean blood pressure (186/99 to 150/83 mm Hg; p less than 0.001), and the changes in systolic and diastolic blood pressure were significantly greater in the nicardipine group than in the placebo group. Nicardipine was well tolerated; orthostatic hypotension was not observed and there was no change in heart rate. Plasma renin activity (PRA) was measured in eight patients, but there was no correlation between PRA and the antihypertensive effect of nicardipine. Results of a pharmacokinetic study performed in 15 elderly patients showed a rapid rate of absorption and higher plasma levels than those observed in younger patients with hypertension (mean age 54 years). The results support those of the major French multicenter open study of 29, 104 elderly patients with hypertension (mean age 64 +/- 12 years) treated with nicardipine. The findings of this trial are reviewed and discussed, and recommendations made on the directions for future research in cardiovascular medicine with calcium channel blockers. Results of the trials discussed in this article show that nicardipine is an effective and well-tolerated drug in elderly patients and has wide-ranging effects on the cardiovascular system.

Myocardial properties of the new dihydropyridine calcium antagonist isradipine compared to nifedipine with or without additional beta blockade in coronary artery disease

Isradipine is a new dihydropyridine calcium antagonist with myocardial effects significantly different from those of nifedipine, as shown by in vitro and animal experimental data. Isradipine selectively inhibits the sinus node but not the atrioventricular conduction and its negative inotropic action is much less if administered in a dose of comparable peripheral effects. To study these effects in man, 40 patients with coronary artery disease were divided into 2 groups receiving either a continuous 30-minute intravenous infusion of 2 mg of nifedipine or 0.5 mg of isradipine, doses that resulted in a comparable afterload reduction (decrease of systemic vascular resistance: nifedipine -22.1%, isradipine -25%, p less than 0.001). Ten patients in each group received an additional intravenous bolus of 5 mg of propranolol at the end of the calcium antagonist administration to antagonize its induced adrenergic reflex mechanisms. The heart rate significantly increased after nifedipine only (+9.2%, p less than 0.001), experienced no change after isradipine and the nifedipine and propranolol combination and decreased after the combination of isradipine and propranolol (-9.6%, p less than 0.001). This resulted in a significant decrease of the rate pressure product with isradipine (-12.5%, p less than 0.001) but not with nifedipine. As a result of the afterload-induced adrenergic reflex mechanisms, the maximal derivative of the left ventricular pressure increased after isradipine administration (+13.5%, p less than 0.001) and was unchanged after nifedipine, which demonstrates the significantly less negative inotropic properties of isradipine as compared with nifedipine.

The actions of peppermint oil and menthol on calcium channel dependent processes in intestinal, neuronal and cardiac preparations

The activities of menthol and peppermint oil were determined in guinea-pig ileal smooth muscle, in rat and guinea-pig atrial and papillary muscle, in rat brain synaptosomes and in chick retinal neurones by pharmacological 45Ca2+ uptake and radioligand binding assays. Menthol is a major constituent of peppermint oil and is approximately twice as potent as peppermint oil as an inhibitor of K+ depolarization-induced and electrically stimulated responses in ileum and electrically stimulated atrial and papillary muscles. IC50 values in the ileal preparation ranged from 7.7 to 28.1 micrograms ml-1 and in the cardiac preparations from 10.1 to 68.5 micrograms ml-1. Similar potencies were demonstrated against K+ depolarization-induced 45Ca2+ uptake in synaptosomes and against K+ depolarization and Bay K 8644-induced uptake in chick retinal neurons. IC50 values for menthol inhibition of K+ and Bay K 8644 responses in the retinal neurons were 1.1 x 10(-4) M (17.2 micrograms ml-1) and 1.75 x 10(-4) M (26.6 micrograms ml-1), respectively, and for peppermint oil were 20.3 and 41.7 micrograms ml-1 respectively. Both menthol and peppermint oil inhibited specific [3H]nitrendipine and [3H]PN 200-110 binding to smooth and cardiac muscle and neuronal preparations with potencies comparable to, but slightly lower than, those measured in the pharmacological and 45Ca2+ uptake experiments. Binding of menthol and peppermint oil, studied at 78 micrograms ml-1, was competitive against [3H]nitrendipine in both smooth muscle and synaptosome preparations. The data indicate that both menthol and peppermint oil exert Ca2+ channel blocking properties which may underlie their use in irritable bowel syndrome. Ca2+ channel antagonism may not be the only pharmacological effect of menthol and peppermint oil contributing to intestinal smooth muscle relaxation.

Historical overview. The calcium channel of the heart

The present historical paper concentrates on the roots of the pharmacodynamic concept of Ca++ antagonism, and on the various therapeutic consequences of transmembrane Ca++ entry inhibition, i.e., normalization of hyperkinetic cardiac disorders, suppression of arterial and arteriolar spasms, relief of systemic arterial hypertension, stopping of cardiac dysrhythmias. Obviously in all these cases, medicine makes use of the different manifestations of one and the same fundamental action, that is to say, dose-dependent restriction of transmembrane inward Ca++ movements in active myocardium, vascular smooth muscle, or cardiac pacemaker cells. Interestingly, the origin of the principle of Ca++ antagonism and the discovery of drugs that possess Ca++-antagonistic potencies preceded the detection of the "slow Ca++ channels" by some years. However, the subsequent identification of the "slow channels" (or analogous Ca++ transport systems) as the decisive site of action of specific Ca++ antagonists has to be considered a keystone of the actual concept. The present paper does not treat tissue protection by Ca++ antagonists which is provided against intracellular Ca++ overload and its histopathological sequelae, as for instance Ca++-induced myofibrillar or mitochondrial disintegration. However, the inclusion of morphological topics, such as preservation of myocardial and vascular integrity by Ca++ antagonists, would exceed the limits of this article.

Restriction by nitrendipine of excessive concentration of free intracellular calcium ions in ventricular myocardium of hypertensive rats

In earlier investigations it has been found that high arterial blood pressure of salt-sensitive DAHL rats (DAHL-S) that received a diet containing 8% NaCl could be normalized by chronic treatment with specific calcium antagonists, as for instance, nitrendipine or anipamil. Parallel measurements on heart and arterial vasculature with atomic absorption spectrometry revealed that there was a rise in absolute calcium content upon development of hypertension, whereas under the influence of nitrendipine, not only the blood pressure and heart weight but also myocardial (and arterial) tissue calcium content remained in the physiologic range. In the present study, an additional determination of the free intracellular calcium ion concentration with Ca-sensitive microelectrodes was carried out. For technical reasons, the measurements were restricted to isolated resting rat papillary muscles (stretched to optimal length in a perfusion bath of 1.5 ml at 30 degrees C in normal Tyrode solution). The impalement of the electrodes was considered adequate when the heights of Ca potential and membrane potential were constant for more than twenty minutes. In order to produce severe systemic hypertension, a group of six-week-old DAHL-S rats was fed with an 8% NaCl diet over five weeks. Another group of DAHL-S rats received additionally 150 mg/kg nitrendipine twice a day orally. Salt-resistant DAHL-R rats, also fed with an 8% NaCl diet, served as controls. The findings of this preliminary study are as follows (n = 5 in each group): (table; see text).