Calcium channel blockers: a pathophysiologically based antihypertensive treatment concept for the future?

Calcium-channel blockade (nitrendipine) in combination with ACE inhibition (captopril) in the treatment of mild to moderate hypertension

The antihypertensive efficacy of a combination of calcium-channel blockers and angiotensin-converting-enzyme (ACE) inhibitors in severe primary hypertension is well known, but a synergistic action of this drug combination in mild to moderate primary hypertension is still not established. Therefore, the aim of the present study was to evaluate the efficacy and tolerability of monotherapy with nitrendipine (20 mg) or captopril (100 mg), and of their combination (nitrendipine 10 mg plus captopril 50 mg), in patients suffering from mild to moderate primary hypertension, according to a single-blind, randomized, placebo-controlled design. After the first 4-week monotherapy period, both nitrendipine and captopril induced a significant decrease in systolic and diastolic blood pressure (BP) (p less than 0.001). Furthermore, nitrendipine caused a significant increase in heart rate (HR), while no change in HR was observed in patients treated with captopril. Several side effects were observed, both in the nitrendipine-treated patients (facial flushing, headache, malleolar edema) and in the captopril-treated patients (initial hypotension, dizziness, gastrointestinal disorders). However, these side effects were mild and were well tolerated. In the second combined 4-week therapy period, systolic and diastolic BP of patients treated with 10 mg nitrendipine combined with 50 mg captopril continued to decrease to a degree significantly lower (p less than 0.001) than that observed at the end of the monotherapy period. Simultaneously, no change in HR values occurred when compared to basal values. Furthermore, the incidence and intensity of some side effects observed during the combined therapy period were lower than those of the monotherapy period.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet abnormalities and the pathophysiology of essential hypertension

The mechanisms whereby intracellular calcium concentration is controlled are briefly reviewed. With the current knowledge of both calcium homeostasis and the function and properties of cellular Ca2+-target proteins/signal transduction systems, a dysfunction of cellular calcium metabolism is considered in relation to the pathogenesis of hypertension. Although the enhanced peripheral vascular resistance characteristic of hypertension is ultimately a function of Ca2+ availability for smooth muscle cell contraction, the platelet possesses many parallel biochemical and physiological properties. Therefore, we have utilized the platelet as the cell-model for investigating the role of Ca2+ in hypertension disorders. An overview of Ca2+-linked platelet processes altered in essential hypertension is presented, and an attempt is made to integrate these multiple aberrations in a fundamental membrane lesion.

[Increase in liver circulation with nifedipine]

The hepatic hemodynamic effect of 20 mg sublingual nifedipine was evaluated in 15 patients (13 men, 2 women) during heart catheterization. The liver blood flow was measured 10 min after administration of nifedipine by continuous thermodilution (Baim coronary sinus flow analyzer). Nifedipine was associated with a decrease in systolic blood pressure (from 156 +/- 14 to 138 +/-13 mmHg), an increase in heart rate (from 73 +/- 13 to 81 +/- 8.6 beats/min), and increase in cardiac output (from 6.0 +/- 1.6 to 6.5 +/- 1.3 l/min). In 2/15 patients no significant change was derived. The liver blood flow increased in 13/15 patients from 218 +/- 171.7 to 336.7 +/- 247.7 ml/min (22%-194%, P less than 0.01). The study demonstrates that the vasodilation of nifedipine involves the hepatic circulation. If the hepatic clearance of drugs is high and flow dependent, nifedipine-induced increase of hepatic blood flow may impair drug clearance.

The mechanism of action of calcium antagonists relative to their clinical applications

As a class of therapeutic agents calcium antagonists have attracted increasing attention in recent years. Their major indications have been in the treatment of ischaemic myocardial syndromes, certain cardiac arrhythmias, hypertension, obstructive cardiomyopathies, and a number of lesser clinical disorders in which their role is less clearly defined. With the widening spectrum of therapeutic utility and an increasing plethora of newer agents under development, it is of importance to relate the overall pharmacodynamics of individual agents to their clinical effects. Calcium antagonists have a variable specificity for cardiac and peripheral activity. Based on such activity, it is useful to construct a classification of these compounds, new and old, into four categories. Type I agents, typified by verapamil and its congeners (tiapamil and gallopamil) and diltiazem, prolong AV nodal conduction and refractoriness with little effect on ventricular or atrial refractory period. These actions account for their direct antiarrhythmic properties. Type II agents include nifedipine and other dihydropyridines. In vivo, these agents are devoid of electrophysiologic effects in usual doses. They are potent peripheral vasodilators with some selectivity of action for different vascular beds; their overall haemodynamic effects are dominated by this peripheral vasodilatation and reflex augmentation of sympathetic reflexes. Type III agents include flunarizine and cinnarizine (piperazine derivatives), which, in vitro and in vivo, are potent dilators of peripheral vessels, with no corresponding calcium-blocking actions in the heart. Type IV agents are agents with a broader pharmacologic profile (perhexiline, lidoflazine and bepridil); they block calcium fluxes in the heart, in the peripheral vessels, or both. They may inhibit the fast channel in the heart and have other electrophysiologic actions. A clear understanding of the varied pharmacologic properties of the different classes of calcium antagonists is likely to provide a rational basis for the use of these agents in clinical therapeutics.

Rationale for calcium entry-blocking drugs in systemic hypertension complicated by coronary artery disease

There is considerable rationale for the use of the calcium entry-blocking drugs for the treatment of hypertension and prevention of recurrent episodes of angina pectoris in patients with systemic hypertension and significant coronary artery disease--the 2 entities commonly occurring together. Calcium entry-blocking drugs improve myocardial blood flow while decreasing myocardial oxygen demand. These agents can be given to most patients with ischemic heart disease and its complications, and are associated with a relatively low incidence of serious adverse effects and toxicity during long-term therapy. They reduce the frequency of anginal attacks, prolong exercise time to ST-segment depression or angina and improve exercise capacity. With long-term therapy, tolerance does not develop as it does in many patients with the "long-acting" nitrates. Calcium entry-blocking drugs reduce systolic blood pressure in patients with hypertension by a decrease in peripheral vascular resistance and a uniform improvement in blood flow affecting the myocardium, kidney and brain. There are no central nervous system adverse effects and hypokalemia does not occur. Unlike therapy with the beta-blocking drugs, chronic treatment with the calcium entry blockers does not reduce the serum level of high-density lipoprotein cholesterol nor increase serum triglyceride concentration. The calcium blockers decrease the arterial blood pressure without increasing intravascular plasma volume and are associated with only a slight increase in reflex-mediated sympathetic activity and heart rate, the latter occurring predominantly with nifedipine. Calcium entry-blocking drugs provide alternative or preferred therapy to beta-blocking agents in patients with a combination of hypertension and angina pectoris.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic effects of calcium channel blockers at rest and during exercise in essential hypertension

The main hemodynamic disturbance occurring in patients with essential hypertension is an increase in the total peripheral resistance. In young patients with hypertension, this disturbance is clearly seen during muscular exercise, even though the calculated resistance might be normal during rest. This article reports results of studies on the long-term hemodynamic effects of two calcium channel blockers, verapamil and nifedipine, in patients with mild to moderate hypertension. Twenty-five men, aged 20 to 64 years, with diastolic blood pressures between 100 and 120 mm Hg before treatment were studied at rest and during exercise on ergometer bicycles. Blood pressure was recorded intra-arterially, and cardiac output was measured. After this initial study, 10 patients were treated with verapamil (from 40 to 80 mg, three times daily) and 15 patients with nifedipine (long-acting form, from 40 to 80 mg daily). After one year, the hemodynamic study was repeated. Both drugs induced a reduction in blood pressure and in the total peripheral resistance without any reduction in the cardiac index. Verapamil reduced heart rate, particularly during exercise, but this effect was compensated by an increase in the stroke volume. The hemodynamic profile of these two calcium channel blockers clearly differs from the hemodynamic effects of beta blockers.

Does renin determine the blood pressure response to calcium entry blockers?

Male Wistar rats with one-kidney, one clip renal hypertension were maintained on either a regular or a low salt diet for 3 weeks after clipping. At that time mean blood pressure in the unanesthetized rats was equally elevated in sodium-depleted (n = 17) and in sodium-replete rats (n = 19), but plasma renin activity was significantly higher in the former (p less than 0.05). Infusion of the calcium entry blocker verapamil at a rate of 0.05 mg/kg/minute decreased blood pressure within 60 minutes to a similar extent in rats kept on a salt-deficient diet and in rats fed a regular salt diet. In all rats taken as a group, there was a close, direct correlation (r = 0.87, p less than 0.001) between the magnitude of the blood pressure response to verapamil and the pretreatment blood pressure levels. Verapamil markedly accelerated heart rate and stimulated renin release in all rats. In additional groups of sodium-depleted (n = 8) and sodium-replete renal hypertensive rats (n = 7), nifedipine administration (4 micrograms/kg/min i.v.) within a 45-minute observation period caused a blood pressure fall (p less than 0.001) and heart rate acceleration (p less than 0.001) that were comparable in both groups. These findings suggest that in the rat with renal hypertension the short-term blood pressure response to the calcium antagonists verapamil and nifedipine is not influenced by the state of sodium balance and plasma renin activity. In this experimental model of hypertension, the magnitude of the blood pressure lowering effect of calcium entry blockers appears to be proportional to pretreatment blood pressure levels.

Effect of a new calcium antagonist, tiapamil, in hypertension of the elderly

The antihypertensive effect of a single oral dose of tiapamil (450 mg) and placebo were compared in a single blind randomized cross-over study in 10 71-86 year old hypertensive patients. Blood pressure (BP) and heart rate (HR) were recorded every 15 min for 12 h by an automatic device. Tiapamil led to a decrease in mean daytime systolic (SBP) and diastolic (DBP) BP from 171 +/- 12/98 +/- 10 mm Hg to 159 +/- 11/90 +/- 9 mm Hg (P less than 0.001) without significant variation in HR. Thereafter patients received tiapamil 450 twice daily; by the seventh day of treatment mean daytime SBP and DBP were 155 +/- 13/85 +/- 14 mm Hg (P less than 0.001 vs placebo). The hourly mean values of SBP recorded for 8/12 h (first tiapamil day) and 10/12 h (seventh tiapamil day) were significantly lower than the corresponding values after placebo. We conclude that tiapamil in the elderly exerts a sustained antihypertensive effect lasting 12 h or more, with only minor variations in HR. This effect predominates on systolic pressure and is significant from the first dose.