Calcium-antagonist drugs. Receptor interactions that clarify therapeutic effects

Calcium channel blockers for antipsychotic-induced tardive dyskinesia

BACKGROUND

Schizophrenia and related disorders affect a sizable proportion of any population. Antipsychotic medications are the primary treatment for these disorders. Antipsychotic medications are associated with a variety of adverse effects including tardive dyskinesia. Dyskinesia is a disfiguring movement disorder of the orofacial region that can be tardive (having a slow or belated onset). Tardive dyskinesia is difficult to treat, despite experimentation with several treatments. Calcium channel blockers (diltiazem, nifedipine, nimodipine, verapamil, flunarizine) have been among these experimental treatments.

OBJECTIVES

To determine the effects of calcium channel blocker drugs (diltiazem, nifedipine, nimodipine, verapamil) for treatment of neuroleptic-induced tardive dyskinesia in people with schizophrenia, schizoaffective disorder or other chronic mental illnesses.

SEARCH METHODS

We searched the Cochrane Schizophrenia Group Trials Register (July 2015 and April 2017), inspected references of all identified studies for further trials and contacted authors of trials for additional information.

SELECTION CRITERIA

We selected randomised controlled trials comparing calcium channel blockers with placebo, no intervention or any other intervention for people with both tardive dyskinesia and schizophrenia or serious mental illness who remained on their antipsychotic medication.

DATA COLLECTION AND ANALYSIS

We independently extracted data and estimated risk ratios of dichotomous data or mean differences (MD) of continuous data, with 95% confidence intervals (CI). We assumed that people who left the trials early had no improvement. We also created a 'Summary of findings' table using GRADE.

MAIN RESULTS

Previous versions of this review included no trials. From the 2015 search, we identified three cross-over trials that could be included. The 2017 search found no new studies relevant to this review. The included trials randomised 47 inpatients with chronic mental illnesses in the USA and China. Trials were published in the 1990s and were of short duration (six to 10 weeks). Overall, the risk of bias was unclear, mainly due to poor reporting; allocation concealment was not described, generation of the sequence was not explicit, studies were not clearly blinded, and attrition and outcome data were not fully reported. Findings were sparse, no study reported on the primary outcome 'no clinically important improvement in tardive dyskinesia symptoms,' but two small studies (37 participants) found no difference on the tardive dyskinesia symptoms scale Abnormal Involuntary Movement Scale (AIMS) scores between diltiazem or flunarizine and placebo after three to four weeks' treatment (MD -0.71, 95% CI -2.68 to 1.26, very low quality evidence). Only one study randomising 20 participants reported on adverse events, and reported that there were no adverse events with flunarizine or with placebo (very low quality evidence). One study with 18 participants reported no events of deterioration in mental state with diltiazem or with placebo (very low quality evidence). No studies reported on acceptability of treatment or on social confidence, social inclusion, social networks or personalised quality of life outcomes designated important to patients.

AUTHORS' CONCLUSIONS

Available evidence from randomised controlled trials is extremely limited and very low quality, conclusions cannot be drawn. The effects of calcium channel blockers for antipsychotic-induced tardive dyskinesia are unknown. Their use is experimental and should only be given in the context of well-designed randomised trials.

Vasoactivity of Verapamil in the Canine Hindlimb and Sympathetic Nervous System Interaction

Since enhanced sensitivity to verapamil in essential hypertension has been noted, a relationship between verapamil and the sympathetic nervous system has been suggested. It has also been noted that both verapamil and lumbar sympathectomy appear to decrease the vasospasm seen in Raynaud's phenomenon. To further investigate the possible interrelationship between verapamil and the sympathetic nervous system, a unilateral lumbar sympathectomy was performed on eight dogs. Two weeks later the femoral artery blood flow response to intra-arterial verapamil was compared on the sympathectomy limb side and the non-sympathectomy limb side, Blood flow measurements were done without surgical trauma by video dilution technique. Although baseline femoral artery blood flow was unchanged and equal on both sides following sympathectomy (4.6% of cardiac output), there was a significant rise, p<0.05, in the blood flow response to verapamil on the side of sympathectomy. Therefore, sympathectomy appears to enhance the calcium channel blocking properties of verapamil

Calcium channel blockers for neuroleptic-induced tardive dyskinesia

BACKGROUND

Schizophrenia and related disorders affect a sizable proportion of any population. Neuroleptic (antipsychotic) medications are the primary treatment for these disorders. Neuroleptic medications are associated with a variety of side effects including tardive dyskinesia. Dyskinesia is a disfiguring movement disorder of the orofacial region that can be tardive (having a slow or belated onset). Tardive dyskinesia is difficult to treat, despite experimentation with several treatments. Calcium channel blockers (diltiazem, nifedipine, nimodipine, verapamil) have been among these experimental treatments.

OBJECTIVES

To determine the effects of calcium-channel blocker drugs (diltiazem, nifedipine, nimodipine, verapamil) for treatment of neuroleptic-induced tardive dyskinesia in people with schizophrenia, schizoaffective disorder or other chronic mental illnesses.

SEARCH STRATEGY

We updated previous searches in May 2010 by searching the Cochrane Schizophrenia Group Register using the Cochrane Schizophrenia Group search strategy.

SELECTION CRITERIA

Randomised clinical trials comparing calcium-channel blockers with placebo, no intervention or any other intervention for people with both tardive dyskinesia and schizophrenia or serious mental illness.

DATA COLLECTION AND ANALYSIS

We planned to extract and analyse data on an intention-to-treat (ITT) basis. We intended to calculate the relative risk (RR) and 95% confidence intervals (CI) of homogeneous dichotomous data using a random-effects model, and, where possible, calculate the number needed to treat. We planned to calculate mean differences (MD) for continuous data.

MAIN RESULTS

We did not include any trials in this review. We excluded 15 studies; eight were not randomised, one did not use calcium channel blockers, five small, randomised, studies reported no usable data and one did not include people with both tardive dyskinesia and schizophrenia.

AUTHORS' CONCLUSIONS

The effects of calcium-channel blockers for antipsychotic induced tardive dyskinesia are unknown. Their use is experimental and should only be given in the context of well designed randomised clinical trials.

L-type calcium channels and psychiatric disorders: A brief review

Emerging evidence from genome-wide association studies (GWAS) support the association of polymorphisms in the alpha 1C subunit of the L-type voltage-gated calcium channel gene (CACNA1C) with bipolar disorder. These studies extend a rich prior literature implicating dysfunction of L-type calcium channels (LTCCs) in the pathophysiology of neuropsychiatric disorders. Moreover, calcium channel blockers reduce Ca(2+) flux by binding to the α1 subunit of the LTCC and are used extensively for treating hypertension, preventing angina, cardiac arrhythmias and stroke. Calcium channel blockers have also been studied clinically in psychiatric conditions such as mood disorders and substance abuse/dependence, yielding conflicting results. In this review, we begin with a summary of LTCC pharmacology. For each category of disorder, this article then provides a review of animal and human data. In particular, we extensively focus on animal models of depression and clinical trials in mood disorders and substance abuse/dependence. Through examining rationale and study design of published clinical trials, we provide some of the possible reasons why we still do not have definitive evidence of efficacy of calcium-channel antagonists for mood disorders. Refinement of genetic results and target phenotypes, enrollment of adequate sample sizes in clinical trials and progress in physiologic and pharmacologic studies to synthesize tissue and isoform specific calcium channel antagonists, are all future challenges of research in this promising field. © 2010 Wiley-Liss, Inc.

Treatment of alternating hemiplegia of childhood with aripiprazole

We report the pharmacological treatment of a case of alternating hemiplegia of childhood (AHC) in a 14-year-old female with an established diagnosis. Although the patient's symptoms are consistent with those of the condition, she did not respond to treatment with haloperidol, flunarizine, or propranolol. Treatment with aripiprazole resulted in a reduction in the frequency, duration, and severity of episodes of alternating hemiplegia, along with other therapeutic benefits. After treatment with aripiprazole was started, the patient was inadvertently given an inactive drug, resulting in a worsening of her hemiplegic episodes, which improved again on rechallenge. A comparison of the pharmacological actions of successful and unsuccessful treatments for AHC is made. Modulation of both dopamine and histamine systems together appears to be important in the treatment of AHC and further investigation of such pharmacotherapies is suggested.

Effects of valsartan or amlodipine alone or in combination on plasma catecholamine levels at rest and during standing in hypertensive patients

To compare the effects of valsartan and amlodipine alone or in combination on plasma norepinephrine (NE) at rest and standing for 10 minutes in patients with hypertension, 47 patients with a sitting diastolic blood pressure (BP) (DBP)>95 mm Hg and<110 mm Hg were randomized in a double-blind fashion to either valsartan or amlodipine. During the first 4 weeks of treatment, patients received a low dose of either valsartan (80 mg) or amlodipine (5 mg). The patients were force-titrated to the high dose of either drug (160 or 10 mg) for 4 weeks. After 8 weeks of therapy, those who still had a DBP>90 mm Hg (nonresponders) received combination therapy with the other drug, whereas patients with a DBP<90 mm Hg (responders) continued on monotherapy. Decreases in ambulatory BP and clinic systolic BP and DBP were significant (P<.05) after 8 weeks' therapy with no difference between the 2 groups. Amlodipine but not valsartan as monotherapy consistently increased NE levels at rest and enhanced NE levels during standing. Valsartan decreased basal NE in responders. Combination therapy with valsartan and amlodipine did not attenuate the rise in NE levels induced by amlodipine. This study indicates that therapy with amlodipine increases peripheral sympathetic basal tone and reactivity to standing in patients with hypertension, whereas valsartan does not. Combined therapy with amlodipine/valsartan did not attenuate the sympathetic activation induced by amlodipine. The hypotensive action of valsartan may be mediated in part by an inhibition of the sympathetic baroreflex in patients with hypertension.

Effect of the renin–angiotensin system or calcium channel blockade on the circadian variation of heart rate variability, blood pressure and circulating catecholamines in hypertensive patients

OBJECTIVE

To determine the effects of 8 weeks of therapy with amlodipine, ramipril or telmisartan on the autonomic system over 24 h in hypertensives.

METHODS

After a placebo run-in, 57 patients were included in a prospective randomized open-label design protocol for therapy with amlodipine (5 mg for 4 weeks followed by 10 mg for 4 weeks, n = 22), or ramipril (2.5 mg for 1 week, 5.0 mg for 3 weeks and 10 mg for 4 weeks, n = 17) or telmisartan (80 mg for 8 weeks, n = 18). Autonomic functions were assessed by norepinephrine (NE) and epinephrine (E), as well as by the spectral analysis of heart rate variability (HRV).

RESULTS

The 24-h ambulatory blood pressure, plasma NE and HRV demonstrated the characteristic day-night circadian rhythm in hypertensives. Higher values for SBP and DBP and for NE levels, as well as for spectral analysis components - low frequency band (LF) and low frequency/high frequency (LF/HF) ratio - were found during the day, whereas the HF was higher during the night. In patients treated with amlodipine, the HF decreased significantly during the night, while the LF and the LF/HF ratio increased during the day in association with the rise in NE. The therapy with telmisartan did increase the HF during the night and the day, while ramipril did not influence all HRV components during the night but significantly increased the HF, and decreased the LF/HF ratio during the day. No changes were observed in plasma NE with telmisartan or ramipril, but a 50% increase in NE levels throughout the 24-h period was found in amlodipine-treated patients.

CONCLUSION

These data suggest a sympathetic activation during the day and a decrease in parasympathetic activity during the night after therapy with amlodipine, correlated with increases in plasma NE. In contrast, the therapy with telmisartan significantly increased parasympathetic activity without changes in NE during the night and day. The therapy with ramipril increased the parasympathetic activity only during the day.

Calcium channel blocking activity of thioridazine, clomipramine and fluoxetine in isolated rat vas deferens: a relative potency measurement study

PURPOSE

We evaluated the calcium channel blocking activity of thioridazine, clomipramine and fluoxetine in isolated rat vas deferens and determined their relative order of potency.

MATERIALS AND METHODS

Cumulative control concentration-response curves to calcium chloride were obtained in isolated rat vas deferens incubated in depolarizing calcium-free Krebs-Henseleit solution. Tissues were washed to baseline length and equilibrated with a given concentration of test drugs. After a 30-minute period a calcium concentration-response curve was repeated. The resulting rightward displacement of the concentration-response curve to calcium provided a dose ratio. The dose ratio was used in the Schild equation and the antagonism of calcium induced contractions was quantified by Schild analysis.

RESULTS

The calcium channel blocking activity of thioridazine, clomipramine and fluoxetine was compared with nifedipine. All 4 drugs produced parallel rightward displacement of concentration-response curves to calcium. The potency of this effect was quantified by Schild analysis showing pA estimates, namely nifedipine 7, thioridazine 6.2, clomipramine 5.65 and fluoxetine 5.

CONCLUSIONS

A characteristic profile of calcium channel blocking activity on the vas deferens was obtained for all test drugs. The relative order of potency was determined as thioridazine greater than clomipramine greater than fluoxetine. Differences in the potency of calcium entry blockade at peripheral end organs may contribute to differential effects of these drugs on delaying ejaculatory latency in patients with premature ejaculation.

Migraine: preventive treatment

Migraine is a common episodic headache disorder. A comprehensive headache treatment plan includes acute attack treatment to relieve pain and impairment and long-term preventive therapy to reduce attack frequency, severity, and duration. Circumstances that might warrant preventive treatment include: (i) migraine that significantly interferes with the patient's daily routine despite acute treatment; (ii) failure, contraindication to, or troublesome side-effects from acute medications; (iii) overuse of acute medications; (iv) special circumstances, such as hemiplegic migraine; (v) very frequent headaches (more than two a week); or (vi) patient preference. Start the drug at a low dose. Give each treatment an adequate trial. Avoid interfering, overused, and contraindicated drugs. Re-evaluate therapy. Be sure that a woman of childbearing potential is aware of any potential risks. Involve patients in their care to maximize compliance. Consider co-morbidity. Choose a drug based on its proven efficacy, the patient's preferences and headache profile, the drug's side-effects, and the presence or absence of coexisting or co-morbid disease. Drugs that have documented high efficacy and mild to moderate adverse events (AEs) include beta-blockers, amitriptyline, and divalproex. Drugs that have lower documented efficacy and mild to moderate AEs include selective serotonin reuptake inhibitors (SSRIs), calcium channel antagonists, gabapentin, topiramate, riboflavin, and non-steroidal anti-inflammatory drugs.

Differential inhibition of T-type calcium channels by neuroleptics

T-type calcium channels play critical roles in cellular excitability and have been implicated in the pathogenesis of a variety of neurological disorders including epilepsy. Although there have been reports that certain neuroleptics that primarily target D2 dopamine receptors and are used to treat psychoses may also interact with T-type Ca channels, there has been no systematic examination of this phenomenon. In the present paper we provide a detailed analysis of the effects of several widely used neuroleptic agents on a family of exogenously expressed neuronal T-type Ca channels (alpha1G, alpha1H, and alpha1I subtypes). Among the neuroleptics tested, the diphenylbutylpiperidines pimozide and penfluridol were the most potent T-type channel blockers with Kd values (approximately 30-50 nm and approximately 70-100 nm, respectively), in the range of their antagonism of the D2 dopamine receptor. In contrast, the butyrophenone haloperidol was approximately 12- to 20-fold less potent at blocking the various T-type Ca channels. The diphenyldiperazine flunarizine was also less potent compared with the diphenylbutylpiperadines and preferentially blocked alpha1G and alpha1I T-type channels compared with alpha1H. The various neuroleptics did not significantly affect T-type channel activation or kinetic properties, although they shifted steady-state inactivation profiles to more negative values, indicating that these agents preferentially bind to channel inactivated states. Overall, our findings indicate that T-type Ca channels are potently blocked by a subset of neuroleptic agents and suggest that the action of these drugs on T-type Ca channels may significantly contribute to their therapeutic efficacy.

Current concepts of pharmacotherapy in hypertension: combination calcium channel blocker therapy in the treatment of hypertension

Effective control of blood pressure is usually achieved only with the use of two or more antihypertensive medications. The treatment options for hypertension are numerous, and the number of possible combinations large. The selection of a specific combination drug regimen has often been linked to the perceived need for diuretic therapy as first- or second-step therapy; thus, the popularity of such drug combinations as an angiotensin-converting enzyme (ACE) inhibitor/diuretic, an angiotensin-receptor blocker/diuretic, or a beta blocker/diuretic. Rational alternatives exist, including an ACE inhibitor/calcium channel blocker (CCB) or a dihydropyridine CCB/b blocker combination. Traditionally, recommendations have advised against the use of combination therapy with two drugs from the same therapeutic class. However, because of the different binding and pharmacologic characteristics of CCBs, a rationale exists for combining different agents in this class in the management of hypertension and/or symptomatic coronary artery disease. In the treatment of either hypertension or angina, combination CCB therapy can prove uniquely successful.

Clinical outcomes of aneurysmal subarachnoid hemorrhage patients treated with oral diltiazem and limited intensive care management

BACKGROUND

Aneurysmal subarachnoid hemorrhage (SAH) patients are frequently treated with prophylactic nimodipine and undergo invasive monitoring of blood pressure and volume status in an intensive care unit (ICU) setting to decrease the incidence of delayed ischemic neurological deficit (DIND) and improve functional outcomes. The goal of this study was to examine the incidence of DIND and poor functional outcomes in a consecutive series of SAH patients treated with a different regimen of prophylactic oral diltiazem and limited use of intensive care monitoring.

METHODS

The study involved a consecutive series of 123 aneurysmal SAH patients treated by the senior author who were admitted within 72 hours of hemorrhage and who never received nimodipine or nicardipine. Functional outcomes were graded using the Glasgow Outcome Scale (GOS).

RESULTS

Of the 123 patients identified, favorable outcomes (GOS 4 and 5) were achieved in 74.8%. The incidence of DIND was 19.5%. Hypertensive, hypervolemic, hemodilutional (HHH) therapy was used in 10 patients (8.1%) and no patients were treated for DIND by endovascular means. Seven patients (5.7%) had a poor functional outcome or death because of DIND and two of these were related to complications of HHH therapy. These results were compared to contemporary series of SAH patients managed with other treatment protocols.

CONCLUSIONS

Functional outcomes of patients treated with a regimen of oral diltiazem, limited use of ICU monitoring and HHH therapy for DIND compare favorably with other contemporary series of SAH patients.

Magnesium oxide augmentation of verapamil maintenance therapy in mania

The authors compared the antimanic effects of a verapamil-magnesium oxide (V-M) combination with a verapamil-placebo combination (V-P) in patients pretreated with verapamil. BPRS scores and serum magnesium levels were compared. The V-M combination was found to be significantly more effective than V-P in reducing manic symptoms (P=0.015). Serum magnesium levels were significantly higher in the V-M group (P<0.04). These data suggest that magnesium may increase antimanic efficacy of verapamil by mechanisms which may operate at the intracellular level. The magnesium-verapamil combination may have clinical application as an adjunct to verapamil in the maintenance therapy of mania.

Potent vasodilatory with minor cardiodepressant actions of mibefradil in human cardiac tissue

1. The present study compared the cardiovascular effects of mibefradil (MIB), a novel Ca2+-channel antagonist with high selectivity for T-type Ca2+-channels to the effect of the L-type Ca2+-channel-antagonists nifedipine (NIF) and diltiazem (DIL) in left ventricular myocardium and coronary arteries of hearts obtained from patients suffering from dilated cardiomyopathy (NYHA IV). Right atrial myocardium from patients undergoing aortocoronary bypass surgery without signs of cardiac failure was studied as well. 2. NIF and DIL (100 micromol l(-1)) completely depressed force of contraction (FOC) in electrically driven left ventricular myocardium (NIF 6.5+/-1.4% and DIL 7.1+/-1.2% of control), whereas a similar concentration of MIB only reduced force of contraction to 55.1+/-4.0% of the basal FOC. The negative inotropic potency as measured by the concentration needed to reduce basal FOC for 25% was NIF (0.0095 micromol l(-1))>DIL (0.041 micromol l(-1))>MIB (9.47 micromol l(-1)). 3. All three Ca2+-channel antagonists were more potent in human atrial compared to human left ventricular myocardium to reduce FOC. 4. The rank order of Ca+-antagonistic moiety as measured by the decrease of the intracellular Ca2+-transient (fura-2 ratio method) was NIF>DIL>MIB. 5. All Ca2+-channel antagonists completely relaxed human coronary arteries (% of papaverine effect: MIB 81.7+/-5.5%, DIL 91.3+/-0.9%, NIF 96.4+/-3.7%) precontracted with PGF2alpha (0.3 micromol l(-1)). The rank order of vasodilatory potency was NIF (EC50; 0.02 micromol l(-1))>DIL (0.13 micromol l(-1))>MIB (2.05 micromol l(-1)). 6. The vasoselectivity measured by the ratio of the concentration needed to achieve a 25% decrease in force and the concentration needed for 25% vasodilatation was 316 for MIB, 1.5 for NIF and 1.0 for DIL. 7. The present study provides evidence that blockade of T-type Ca2+-channels (e.g. mibefradil) results in potent vasodilatory properties with only minor cardiodepressant effects.

Electrophysiologic assessment of calcium channel blockers in transplanted hearts: an experimental study

The effects of calcium channel blockers on automaticity, conduction, and refractoriness were studied in a model of heterotopic heart transplantation in dogs, which combined an innervated heart (recipient) and a denervated one (donor). Following the surgical procedure, 0.2 mg/kg verapamil (n = 10), 0.15 mg/kg diltiazem (n = 10), or 5 microg/kg + 30 microg/kg/h nifedipine (n = 10) was administered intravenously. In basal situation and after drug administration, each heart was assessed for AV interval, cycle length, sinoatrial conduction time, atrioventricular node antegrade block point, and atrioventricular node and ventricular refractory periods; electrocardiographic PR and QT intervals and QRS complexes; systemic arterial, pulmonary artery, central venous, and pulmonary capillary wedge pressures; and cardiac output. The depressor effects of these calcium channel blockers on automaticity, refractoriness, and conduction were more intense in the transplanted hearts, very possibly because of the absence of adrenergic reflexes mediated by the autonomic nervous system; in particular, verapamil produced a great depression of sinus automaticity in a large number of cases.

Comparative study on the effect of calcium channel blockers on basal and parathyroid hormone-induced bone resorption in vitro

A number of clinical and experimental studies suggest that the effects of calcium channel blockers are not limited to the cardiovascular system but might also involve skeletal calcium metabolism due to the presence of L-type calcium channels in osteoblastic cells. We therefore investigated the influence of calcium channel blockers of the dihydropyridine type (nifedipine, amlodipine) as well as of the phenylalkylamine type (verapamil, gallopamil) on basal and parathyroid hormone-induced bone resorption utilizing organ-cultured neonatal mouse calvaria. Only at 10(-4) M, amlodipine, verapamil and gallopamil reduced basal and parathyroid hormone-induced resorption In contrast, nifedipine, between 10(-5)-10(-4) M, exhibited a dose-dependent inhibitory effect on parathyroid hormone-related bone resorption by up to 50%. When calvariae were cultured for 48 hr in the presence of inhibitory concentrations of the calcium channel blockers and then stimulated with parathyroid hormone, only parietal bones pretreated with nifedipine remained completely responsive to the bone resorbing action of the hormone.

[Effect of changed extracellular K(+) and Mg(2+)-concentration on intracellular Ca(2+) homeostasis, contraction coupling and force-frequency relations in the human myocardium]

The intracellular Ca(2+)-homeostasis may be affected by changes of the extracellular K(+)- and/or Mg(2+)-concentrations. Mg2+ reduces the Ca(2+)-influx via L-type Ca(2+)-channels, facilitates Ca(2+)-uptake into the sarcoplasmic reticulum, modulates the Ca(2+)-induced Ca(2+)-release and the Ca(2+)-binding to troponin C. The extracellular K+ activates the Na+/K(+)-ATPase and changes the membrane potential thereby affecting the mode of action of the Na+/Ca(2+)-exchanger. Especially when intracellular Ca2+ regulation is altered, for example in heart failure, Mg2+ and K+ exert beneficial effects on the frequency-dependent force-generation in human myocardium. Thus, extracellular Mg2+ and K+ influence contraction coupling in the human myocardium.

Influence of certain calcium-channel blockers on some aspects of lorazepam-dependence in mice

The effect of acute and chronic treatments of the calcium-channel blockers, isradipine, diltiazem and flunarizine in protecting against lorazepam dependence has been demonstrated in mice. Dependence was induced by twice-daily administration of lorazepam (1 mg kg-1) for 10 days, doubling the dose during the next 10 days. Withdrawal symptoms and changes in the noradrenaline, dopamine and 5-hydroxytryptamine content of different regions of the brain were observed after either 24-h withdrawal or flumazenil administration. Isradipine inhibited lorazepam withdrawal symptoms, the effect being accompanied in the 24-h withdrawal group by significant decreases in the noradrenaline and dopamine content of the thalamus and hypothalamus and in the noradrenaline content of the mid-brain. In the flumazenil-treated group isradipine produced significant decreases in mid-brain noradrenaline and dopamine levels and in the dopamine content of the thalamus and hypothalamus. Diltiazem did not, on the other hand, afford significant protection against lorazepam withdrawal symptoms and did not induce any significant change in the neurotransmitters studied. Flunarizine significantly inhibited lorazepam withdrawal symptoms, an effect accompanied by significant reduction in noradrenaline and dopamine levels in the thalamus and hypothalamus. Dopamine was also significantly reduced in the cerebral cortex. Similar effects were produced in the flumazenil-treated group, and the noradrenaline content was reduced in the medulla, pons and cerebellum. It was concluded that isradipine and flunarizine might be of value in ameliorating lorazepam withdrawal symptoms.

Dual calcium-channel blocker therapy in the treatment of hypertension

OBJECTIVE

To review the in vitro receptor binding data of calcium-channel blockers (CCBs) and in vivo studies in humans regarding the use of dual calcium-channel blocker therapy, with a focus on the use of this therapy for hypertension.

DATA SOURCE

A MEDLINE search was conducted to identify literature pertaining to CCBs.

STUDY SELECTION

In vitro studies and investigations that evaluated CCB receptor binding and the interactions between subclasses of CCBs were chosen. All studies in humans and clinical trials that evaluated the use of dual CCB therapy in the treatment of cardiovascular diseases were selected for review. Also, case reports describing the use of dual CCB therapy were included in this article.

DATA EXTRACTION

The methodology, results, and conclusions of the selected data were evaluated. Data regarding the in vitro receptor binding kinetics of CCBs, as well as interactions, were reported. Because there is limited information on dual CCB therapy for hypertension, clinical studies using this treatment for ischemic heart disease were also reviewed. They were summarized and compared on the basis of the degree of disease control (e.g., blood pressure, exercise tolerance), adverse effects, and other clinical endpoints of pharmacologic therapy.

DATA SYNTHESIS

In vitro studies have identified binding sites for the dihydropyridine (nifedipine), diphenylalkylamine (verapamil), and benzothiazepine (diltiazem) subclasses of CCBs, and indicate that they are allosterically related to each other within the voltage-sensitive calcium-channel receptor. Dihydropyridine binding affinity is decreased with concomitant verapamil binding, but is enhanced by concomitant diltiazem binding. Dual CCB therapy has been shown to be efficacious in patients with ischemic heart disease. Although this therapy is limited by dose-related adverse effects, it appears to have an important role in patients with ischemia that is refractory to conventional therapy, or for those whose therapeutic options are limited by contraindications. Theoretically, many patients with hypertension may benefit similarly from dual CCB therapy. Because data evaluating this treatment option are sparse, recommendations regarding safety, efficacy, and the role of dual CCB therapy for hypertension would be premature.

CONCLUSIONS

Controlled data evaluating dual CCB therapy for the treatment of hypertension are lacking. This treatment modality may be beneficial in the future, but requires further investigation to determine safety and efficacy.

Comparative effect of ursodeoxycholic acid and calcium antagonists on the binding, uptake and degradation of LDL in isolated hamster hepatocytes

We have shown that ursodeoxycholic acid (UDCA) stimulates low density lipoprotein (LDL) metabolism (Biochem. J. 280 (1991) 589), as well as calcium mobilization (Am. J. Physiol. 264 (1993) G243) in isolated hepatocytes. Therefore, the effect of UDCA and that of different calcium antagonists on hepatic LDL metabolism was compared. Isolated hamster hepatocytes were incubated at 37 degrees C for 60 min in the presence of 125I-labelled hamster LDL, increasing concentrations (25-100 microM) of verapamil, nifedipine, and diltiazem, respectively, and with or without 700 microM ursodeoxycholic acid (UDCA). At concentrations up to 100 microM, neither verapamil nor nifedipine significantly affected cell associated LDL, but both agents decreased LDL degradation in a dose-dependent manner, with almost total inhibition with 100 microM of either agent. In contrast, 25 microM diltiazem stimulated LDL binding and uptake, with a maximum increase of 15-20% of control, while 50 and 100 microM diltiazem stimulated LDL degradation by 50 and 100%, respectively. UDCA increased native LDL binding and uptake by 20%, and degradation by 50%. None of the agents tested had any effect on the binding, uptake and degradation of methylated LDL. The increased hepatic LDL uptake induced by UDCA was not altered in the presence of calcium antagonists, while the increased degradation of LDL by UDCA was abolished by the addition of 50 microM of either verapamil or nifedipine. However, 100 microM diltiazem and 700 microM UDCA stimulated LDL degradation without any additive effect. These studies show that different calcium antagonists have differential effects on hepatic LDL metabolism. The similarities between the effect of diltiazem and UDCA on LDL metabolism and the absence of any additive effect, suggest that these two agents have a similar mechanism of action, which may involve the integration of both agents into the plasma membrane lipid bilayer.

Dopamine receptor antagonists prevent expression, but not development, of morphine sensitization

The present experiments determined the effects of selective dopamine receptor antagonists on the initiation and expression of sensitization to the locomotor-stimulating effects of morphine in rats. Although both the dopamine D1 receptor antagonist R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzaz epine hydrochloride (SCH 23390, 0.25 mg/kg) and the dopamine D2 receptor antagonist eticlopride (0.1 mg/kg) suppressed the ability of morphine (10 mg/kg) to elicit sensitized locomotor activity during the course of a 12 day treatment schedule, subsequent tests with morphine alone revealed significant sensitization. Sensitization in the SCH 23390 + morphine group could not be attributed to dopamine D1 receptor supersensitivity caused by repeated SCH 23390 administration because electrophysiological recordings indicated that nucleus accumbens neurons in SCH 23390-treated rats were not more sensitive to the inhibitory effects of either dopamine or a dopamine D1 receptor-selective agonist. Thus, dopamine receptor stimulation may be involved in expression, but not development, of morphine sensitization.

Stereoselective pharmacokinetics of dihydropyridine calcium antagonists

Many dihydropyridine calcium antagonists are widely used for the treatment of angina and hypertension, and many more are under development. Most of these drugs have one or more chiral centre, and the pharmacological activity between the enantiomers for these drugs is known to be markedly different. First, the stereospecific assay methods for these drugs in plasma or serum are reviewed with emphasis on chiral stationary phase high-performance liquid chromatography for their determination. Next, the stereoselective pharmacokinetics of these drugs (nilvadipine, nitrendipine, felodipine, nimodipine, manidipine, benidipine and nisoldipine) in animals, healthy subjects and patients with hepatic disease is reviewed. Enantiomer-enantiomer interaction, enantiomeric inversion and the stereochemical aspects of pharmacokinetic drug interactions in these drugs are also described.

Dopaminergic function in rat brain after oral administration of calcium-channel blockers or haloperidol. A microdialysis study

Microdialysis technique was used to study the effects of both acute and repeated oral administration of calcium-channel blockers (flunarizine, cinnarizine, verapamil, nifedipine and nicardipine) in dopaminergic function in rat brain and to compare them to the effects of haloperidol. Acute flunarizine, nicardipine or haloperidol increased extracellular levels of dopamine (DA) or metabolites. After repeated (18 days) administration, nicardipine, nifedipine, verapamil or haloperidol increased and flunarizine decreased extracellular striatal levels of dopamine or metabolites. Chronic treatment with calcium-channel blockers or haloperidol failed to block K(+)-evoked release of dopamine. This suggests that the calcium-channel blockers used in this study do not influence calcium entry necessary for DA release. An acute challenge with haloperidol caused either no change or a decrease in extracellular levels of DA or metabolites after repeated administration of calcium-channel blockers or haloperidol. This is considered to be due to the lesser response of dopaminergic neurons because of treatment. A neuroleptic-like mechanism of action together with a decrease in firing activity and/or a reduced dopamine re-uptake of dopaminergic neurons are considered.

Azidobutyryl clentiazem, a new photoactivatable diltiazem analog, labels benzothiazepine binding sites in the alpha 1 subunit of the skeletal muscle calcium channel

[3H]Azidobutyryl clentiazem, a new photoactivable diltiazem derivative, has a higher binding affinity than azidobutyryl diltiazem. It can be covalently incorporated into the alpha 1 subunit of the skeletal muscle calcium channel by UV irradiation, which allows the benzothiazepine binding site to be determined. The photolabeled alpha 1 subunit and its proteolytic fragments were analyzed with a panel of sequence-directed antibodies. The results suggest that the linker region between segment S5 and S6 of domain IV is involved in benzothiazepine binding. This site is different from the dihydropyridine and verapamil binding sites.

Treatment of persistent myoclonic tardive dystonia with verapamil

A dramatic improvement in a patient with tardive dystonia was obtained with verapamil after the failure of other medicines. The use of verapamil or other calcium-channel blockers should be considered when treating drug-induced movement disorders.

Flunarizine inhibits both calcium-dependent and -independent release of glutamate from synaptosomes and cultured neurones

Flunarizine, an established Ca2+ channel antagonist, blocks both exocytotic glutamate release from mammalian cultured cerebellar granule cells and isolated presynaptic nerve endings (synaptosomes) prepared from two distinct areas of the mammalian brain. This blockade of release displays the same flunarizine concentration dependency in synaptosomes in the presence or absence of Ca2+, with total inhibition at a concentration of 10 microM. In cultured neurones, a selective effect on the L-channel-coupled component of the KCl-evoked rise in intracellular Ca2+, [Ca2+]c, can be demonstrated between flunarizine concentrations of 100 nM and 10 microM, while at concentrations above 10 microM, the remaining residual and transient components are affected. In synaptosomes, flunarizine blocks the KCl-evoked elevation in [Ca2+]c in a concentration-dependent manner. Additionally, 10 microM flunarizine directly antagonises ouabain-induced tetrodotoxin (TTX)-sensitive Na+ influx, glutamate, aspartate and GABA release from synaptosomes, whilst inhibiting veratridine-induced Ca(2+)-independent TTX-sensitive Na+ influx and glutamate release at 15 microM and 10 microM in cells and synaptosomes, respectively. In both cultured neurones and synaptosomes, the ability of flunarizine to block both neurotransmitter and cytoplasmic glutamate release is due to a direct antagonism of both voltage dependent Ca2+ channels and tetrodotoxin-sensitive Na+ channels.

Verapamil decreases cyclic load-induced calcium incorporation in ROS 17/2.8 osteosarcoma cell cultures

Bone is a tissue that responds to mechanical load by changing its internal architecture. However, the mode of transmission of mechanical stimuli into biological signals and the effect of load at the cellular level are still not clear. An in vitro system, a Flexercell Strain Unit, was used to apply cyclic load to osteoblast-like cells in culture. In the first series of experiments, ROS 17/2.8 rat osteosarcoma cells, cultured on Flex I, flexible bottomed culture plates, were subjected to a 0.05 Hz, 0.24 STRAIN cyclic load regime for 3 and 7 days, in vitro. One group subjected to load received verapamil, a calcium channel blocker, throughout the experimental period. A second group was exposed to load but received no verapamil. A third group had no drug or load and a fourth group had no load but received verapamil. Cultures were incubated for 24 hours prior to collection with 10 microCi of 45CaCl in the medium, then well bottoms were divided to yield outer (maximum) and inner (minimum) load zones for assay of radioactivity. The effect of verapamil during a 7-day loading period was studied by adding the drug to individual cultures at daily intervals. Results indicated that mechanical loading stimulates calcium incorporation in ROS 17/2.8 cell cultures by day 7 but not by day 3. Only early verapamil addition decreased load-induced calcium incorporation when drug was added prior to day 4. If verapamil was added after 4 days, the channel blocker did not diminish load-induced calcium incorporation.

Demonstration of sodium/calcium exchange in rodent osteoblasts

Based on the inhibition of stimulated Ca release from cultured bone by several different agents that alter Na transport, we proposed that hormonally stimulated bone resorption requires Na/Ca exchange. Calcemic hormones appear to interact primarily directly with the osteoblast, which then mediates the activation of osteoclast activity. In organ culture it is not possible to determine whether Na/Ca exchange is involved in this initiating step in the osteoblast or directly in osteoclast-mediated Ca release, and there have been no prior direct measurements of Na/Ca exchange in bone or bone cells. The purpose of this study was to demonstrate the presence of Na/Ca exchange transport in the osteoblast. Thus, we characterized Na-dependent Ca transport in osteoblast-like rat osteosarcoma cells (UMR-106) and primary bone cells isolated from neonatal mouse calvaria. Cells were loaded with the Ca-sensitive dye fura-2 in the presence of physiologic NaCl and the absence of Ca with or without 0.3 mM ouabain. Changes in free cytosolic Ca after the extracellular addition of 1.5 mM Ca were measured spectrofluorimetrically. An outward Na gradient was generated by decreasing extracellular Na while maintaining isotonicity. UMR-106 cells that were Na loaded by ouabain inhibition of Na,K-ATPase activity exhibited 30% greater Ca uptake than control cells. Similar results were obtained with primary bone cells. This uptake required extracellular Ca, was not inhibited by 200 microM verapamil, and was reversible upon reversal of the Na gradient. These data demonstrate the presence of a Na/Ca exchange transport system in osteoblasts.

Verapamil blocks basal and angiotensin II-induced RNA synthesis of rat aortic vascular smooth muscle cells

We evaluated VER effect on RNA synthesis of quiescent and angiotensin II (AII)- stimulated cultured rat aortic vascular smooth muscle cells (VSMC). In a dose-dependent manner, VER decreased [3H]uridine uptake by quiescent VSMCs (ED50 7 x 10(-6)M), an effect that was shared by other calcium antagonists, but to a variable degree. VER caused a significant effect within 3 hours and attained a maximal effect at 7 hours. In addition VER caused a 22 +/- 2% decrease in [3H]uridine uptake by VSMCs stimulated with 10% fetal bovine serum, while it completely abolished [3H]uridine uptake by VSMCs induced by AII. We conclude that VER decreases basal and inhibits AII-induced increase in mRNA synthesis of VSMCs. These data may explain in part how VER causes a decrease in vascular resistance and alters the vasoconstrictor effect of AII.

Psychopharmacological properties of calcium channel inhibitors

The previous decade has witnessed a major expansion of knowledge of the role played by voltage-sensitive calcium channels in the function of the central nervous system. Significant progress in the field has been made possible with the broadening use of organic calcium channel inhibitors (CCIs, Ca2+ antagonists), until recently considered almost exclusively as peripherally active antianginal and antiarrhythmic drugs. CCIs, however, do penetrate the blood-brain barrier from the periphery. Autoradiographic studies have established a highly heterogeneous distribution of CCI recognition sites within the brain. The existing evidence suggests that CCIs have marked psychotropic properties. The profile of their central activity is unique and spans a wide range of effects. Nevertheless, question regarding potentially confounding potent peripheral effects of these drugs remain. This paper reviews the psychopharmacology of CCIs, concentrating on preclinical data, but including supportive clinical and biochemical evidence as well. It focuses on these drugs' antidepressant, antidopaminergic (neuroleptic-like), anxiolytic and anticonvulsant effects. CCIs may also modify the reinforcing properties of some addictive drugs.

The binding and functional properties of voltage dependent calcium channel receptors in pediatric normal and myelodysplastic bladders

The present study was designed to compare the binding and functional properties of calcium channel receptors in normal and myelodysplastic bladders. Normal bladders were obtained from children with vesicoureteral reflux undergoing ureteral reimplantation. Myelodysplastic bladder specimens were obtained from patients undergoing bladder augmentation. The functional studies included agonist (calcium chloride) dose response experiments and the determination of apparent antagonist dissociation constants for various calcium channel antagonists. The receptor binding studies were performed using the ligand (+)-3H-PN200-110 (specific activity 86.6 Ci./mmol.). The mean maximal response of myelodysplastic bladders to calcium ions was 31% less than normal bladders (p greater than 0.05). The mean EC50 for calcium mediated isometric tension and the mean -log antagonist dissociation constant values of nifedipine, diltiazem and verapamil were similar in normal and myelodysplastic bladders. The radioligand receptor binding studies demonstrated that the equilibrium dissociation constant of (+)-3H-PN200-110 in myelodysplastic bladders was 4-fold greater than in normal bladders. The density of dihydropyridine binding sites in myelodysplastic and normal bladders was similar. Our study demonstrated that the pathophysiology of the poorly compliant hyperreflexic bladder is not related to up regulation of dihydropyridine calcium channel receptors or alterations in the response of detrusor muscle to calcium ions. The relative abundance of calcium channel receptors in the normal and myelodysplastic bladders, and the regulation of detrusor contraction by calcium ions suggest that calcium channel receptors have a meaningful role in detrusor function.

Heterogeneous interference of nicardipine, verapamil, and diltiazem with forearm arteriolar responsiveness to adrenergic stimulation in hypertensive patients

The interference of intraarterial nicardipine, verapamil, and diltiazem with the forearm vascular response to graded exogenous norepinephrine was evaluated in hypertensive patients. Nicardipine antagonized the vasoconstrictor effect of norepinephrine in a dose-dependent manner, whereas verapamil was ineffective, suggesting that functional alpha-adrenergic antagonism may participate in the vasodilatory and possibly the antihypertensive effect. Nicardipine also blunted the vasoconstriction to lower-body negative pressure and the action of angiotensin II administered intraarterially. Despite a comparable increase in basal forearm flow, verapamil was less potent than nicardipine in inhibiting vasoconstriction after both stimuli. Therefore nicardipine suppressed preferentially regional vascular reactivity, probably by blockade of the influx of extracellular calcium in response to receptor activation, because both alpha-adrenergic and angiotensin II receptor-mediated vasoconstrictor responses were attenuated. At variance with both nicardipine and verapamil was potentiation of the responses to norepinephrine after the administration of diltiazem. Because intraarterial propranolol abolished that potentiating action and the local vasodilatation to isoproterenol was clearly reduced, diltiazem probably interfered also with beta-adrenergic receptor-mediated vasorelaxing mechanisms in human forearm arterioles. The data further stress the heterogeneity of calcium channel blockers in humans.

New developments in antihypertensive drugs

New developments in antihypertensive drug treatment include optimizing the use of established drugs, the introduction of novel compounds, and a renewed appreciation that hypertension is but one of various cardiovascular risk factors that must be addressed in managing the patient with raised blood pressure. Thus, the approach used must be tailored to the individual patient both in terms of drug choice and dose as well as preventive measures. New drug development depends very much on improving our understanding of the pathophysiologic mechanisms involved in hypertension and seems likely to be applied at the level of the renin angiotensin system and other local factors governing vascular smooth muscle function.

Nuclear magnetic resonance investigations of calcium antagonist drugs. II: Conformational and dynamic features of verapamil in [2H6]DMSO

Conformational features of verapamil in [2H6]DMSO have been delineated by measuring 13C and 1H NMR parameters. Spin-lattice relaxation rates were interpreted within the frame of an extended alkane chain with segmental motions hampered by the aromatic substituents at both ends. The effective correlation times were all evaluated in the range 0.16-0.22 ns at 293 K. The aromatic rings were found to lie somewhat out-of-plane with the alkane chain. The NMR data were used to construct a Dreiding model of the most probable spatial arrangement and a molecular modeling system was utilized to represent the "preferred" conformation of verapamil in solution.

Changes in dopamine2 and serotonin2 receptors in rat brain after long-term verapamil treatment: comparison of verapamil and lithium

Rat brain 5-HT2 and dopamine2 receptors were assessed following a chronic (3 weeks) administration of verapamil, lithium, and a combination of these two drugs. A significant increase in the number of 5-HT2 receptors was observed in the frontal cortex after the verapamil treatment, but the lithium and combined treatment had no effect on the densities of either binding sites. These data suggest that one or more of the mechanisms of the antimanic effect of verapamil may be involved in the change in 5-HT2 binding sites in a manner that is different from that of lithium.

Elevated platelet intracellular calcium concentration in bipolar depression

Baseline and thrombin-stimulated free intracellular calcium concentrations in blood platelets were significantly higher in untreated depressed bipolar patients than in untreated unipolar depressed patients or controls. Platelet intracellular calcium ion concentrations in euthymic-treated bipolar patients were equivalent to control values, suggesting but not proving a state-dependent change in intracellular calcium ion dynamics in bipolar depression. Unipolar and some subsets of bipolar patients appear not to exhibit this change.

Paradoxical effects of thioridazine on electromechanical coupling in the human and rat vas deferens

The effects of thioridazine on the responses of isolated human and rat vas deferens to high [K+]0, A23187 and caffeine were examined. In the presence of Ca2+ (2.5 mM), thioridazine (1-10 microM) induced spontaneous contractions but caused a dose-related inhibition of the phasic and secondary parts of the response to high [K+]0 (136 mM). The relaxation phase of the high [K+]0 response of the human vas deferens was unaffected by thioridazine (up to 10 microM). In Ca2(+)-free/EGTA (0.5 mM) media, thioridazine caused a dose-related potentiation, shortened the latency and prolonged the duration of high [K+]0 responses. Contractions to caffeine (20 mM) and A23187 (20-50 microM) were relatively unchanged by thioridazine (10 microM). The spontaneous activity caused by thioridazine (10 microM) was sensitive to the Ca2(+)-channel blockers nifedipine (10 microM) or verapamil (10 microM). These results indicate that the action of thioridazine during electromechanical coupling in the human and rat vas deferens may involve more than its blockade of voltage gated Ca2+ channels.

Chronic use of the calcium channel blocker nifedipine has no significant effect on bone metabolism in men

Calcium channel blockers have been reported to have such diverse effects on reduction in protein synthesis, diminished incorporation of proline into new collagen, and decreased hormone release in vitro. The chronic affect of the calcium channel blocker nifedipine was examined in vivo to determine the possible impact of pharmacologic calcium channel blockade on bone metabolism. Eleven Caucasian males treated with an average of 40 mg/d nifedipine for an average of three years were compared to 11 control males matched for age, height, weight, activity level, cardiovascular status, and calcium intake. No significant differences between groups were noted in bone mineral density at the lumbar spine (L2-4), proximal femur (femoral neck, Ward's triangle and trochanter), and proximal and distal radius. There were also no significant differences in parameters of bone turnover (alkaline phosphatase, osteocalcin, urine calcium/creatinine, and hydroxyproline/creatinine ratio), or hormones that might affect calcium metabolism and bone (testosterone, PTH, 25(OH) vitamin D, and calcitonin). In summary, chronic nifedipine use in males is not associated with either a beneficial or adverse effect on bone metabolism.

Effects of nifedipine pretreatment on subjective and cardiovascular responses to intravenous cocaine in humans

The effects of oral nifedipine pretreatment on subjective and cardiovascular responses to intravenous cocaine infusions were studied in cocaine-using volunteers. Nifedipine, 10 mg or placebo, was administered 20-25 min before placebo, 20 mg, or 40 mg cocaine, using a repeated measures randomized double-blind design. The variables measured were self-reported subjective effects, general behavior rated by two observers, blood pressure and heart rate. Cocaine produced the expected dose-related effects on subjective and cardiovascular measures. Nifedipine pretreatment attenuated some subjective effects of cocaine. Nifedipine directly reduced blood pressure but did not antagonize the effects of cocaine on blood pressure. These findings suggest that dihydropyridine calcium channel modulators may be useful compounds in the clinical management of cocaine users.

The use of calcium channel blockers in obstetrics and gynecology; a review

Since their introduction, calcium channel blockers gained wide use in the treatment in various fields of medicine. Calcium channel blockers were shown to inhibit contractions of the pregnant and nonpregnant uterus, and lately their properties have made it, theoretically, an ideal candidate for the use in severe pregnancy-induced hypertension: it is effective in lowering blood pressure, has a fast and long-standing action, may be conveniently administered via the oral route, and it is not associated with serious side effects.