Brain extraction of a calcium channel blocker

Brain-penetrant calcium channel blockers are associated with a reduced incidence of neuropsychiatric disorders

Calcium channel blockers (CCBs) differ in their ability to penetrate into the brain. Pharmacoepidemiological studies suggest that CCBs as a class may have beneficial effects on the risks and outcomes of some psychiatric and neurological disorders. It is plausible but unknown whether this effect relates to their brain penetrance. To address this, we used the TriNetX electronic health records network to identify people prescribed a brain-penetrant CCB (BP-CCB), or those given amlodipine, a CCB with low brain penetrability. We created cohorts of patients who, prior to first CCB exposure, either had to have, or could not have had, a recorded ICD-10 diagnosis in any of the following categories: psychotic disorder; affective disorder (including bipolar disorder and major depressive disorder); anxiety disorder; substance use disorder; sleep disorder; delirium; dementia, or movement disorder. Cohort pairs were propensity score matched for age, sex, race, blood pressure, body mass index, and a range of other variables. The outcomes were the incidence of these disorders measured over a two-year exposure period. Matched cohort sizes ranged from 17,896 to 49,987. In people with no prior history of psychiatric or neurodegenerative disorder, there was a significantly lower incidence of most disorders with BP-CCBs compared to amlodipine, with risk ratios ranging from 0.64 to 0.88 and an overall risk ratio of 0.88, i.e. a risk reduction of 12%. In people who did have a prior psychiatric or neurodegenerative diagnosis, differences were much smaller, but again showed lower risks for several disorders with BP-CCBs compared to amlodipine. The differences were somewhat more marked in women and in people less than 60 years old. Results were similar when comparing BP-CCBs with verapamil and diltiazem. We also compared BP-CCBs with angiotensin receptor blockers, and found an overall risk ratio of 0.94 in favour of BP-CCBs, but with differential effects across disorders including a higher risk of psychotic disorder and dementia, but a lower risk for anxiety and sleep disorders. In some analyses, there was evidence of residual confounding even after the extensive matching, in that negative control outcomes showed a reduced incidence with BP-CCBs relative to the comparator cohort. In summary, CCBs that readily penetrate the brain are associated with a lower incidence of neuropsychiatric disorders, especially first diagnoses, compared to CCBs which do not. This may reflect their blockade of neuronal voltage-gated calcium channels. The findings encourage repurposing trials using existing BP-CCBs, and suggest that novel BP-CCBs with enhanced and more selective central actions might have greater therapeutic potential for psychiatric and neurodegenerative disorders.

Calcium Antagonists in the Management of Patients with Aneurysmal Subarachnoid Hemorrhage: A Review

Cerebral arterial vasospasm and infarction is the leading cause of death and disability among patients who reach a major medical center after aneurysmal subarachnoid hemorrhage (SAH). Recent evidence suggests that two calcium antagonists, nimodipine or nicardipine, may be useful in preventing this important complication of SAH. This paper reviews the current status of these two calcium antagonists in the management of SAH.

Analytic Reviews : Potential New Therapies for Acute Ischemic Stroke

Evidence from animal models of acute stroke suggests ischemia may be reversible if blood flow is restored in the first few hours. Studies of human stroke using posi tron emission tomography demonstrate areas with re duced blood flow and relatively preserved metabolism, indicating potentially reversible ischemic brain. Resto ration of blood flow during this reversible phase should improve outcome after stroke.

Many therapeutic strategies for treatment of acute ischemic stroke have been proposed, including increas ing collateral flow, removing vascular obstructions, and interfering with the intracellular cascade of events that lead to neuronal cell death. Hypervolemic hemodilution reduces viscosity and increases cerebral blood flow, and this may hopefully raise blood flow above the critical threshold of irreversible ischemia. Naloxone, calcium channel blockers, and glutamate antagonists alter blood flow and influence intracellular events during and after acute ischemia. Thrombolytic therapy restores blood flow by lysis of obstructing clot. These therapies show promise in preliminary studies, but additional ran domized controlled studies are needed.

Rodent models of global cerebral ischemia

Brain damage after stroke and head injury remains a huge clinical problem. In stroke, the initial cause of the damage is a blockage in a blood vessel (often the middle cerebral artery) and this sets off several pathways that ultimately lead to cell death. Recent studies have demonstrated that several new mechanisms are involved in neuronal death and this has led to an increase in research into novel molecules that might prevent brain damage or improve recuperation post-stroke. There are several models of global cerebral ischemia. Two of the most widely-used models are discussed in detail in UNIT 9.5, the gerbil bilateral carotid artery occlusion (BCAO) model and rat 4-vessel occlusion (4-VO) model. Additionally, several models of focal cerebral ischemia have been developed to mimic the effects of human stroke. The rationale behind the use of animal models, the various types of models and advantage and disadvantages of each model are presented.

Treatment with Nicardipine Protects Brain in an Animal Model of Hypertension‐Induced Damage

Control of blood pressure protects from the development of cerebrovascular lesions and vascular dementia (VaD). This study has assessed the influence of treatment with the dihydropyridine-type Ca2+ antagonist nicardipine on brain microanatomical changes in spontaneously hypertensive rats (SHR). SHR were treated from 16th to 26th week of age with hypotensive (3 mg/Kg/day) or non-hypotensive (0.1 mg/Kg/day) doses of nicardipine, with the non-dihydropyridine-type vasodilator hydralazine (10 mg/kg/day) or with vehicle (control group). Untreated age-matched Wistar Kyoto (WKY) rats were used as a normotensive reference group. Brain volume, number of neurons, glial fibrillary-acidic protein (GFAP)-immunoreactive astrocytes and neurofilament 200 KDa (NFP)-immunoreactivity (IR) were assessed in frontal and occipital cortex, hippocampus and striatum. A decrease of volume and number of nerve cells and a loss of NFP-IR was found in the frontal and occipital cortex and in the CA1 subfield of hippocampus and in the striatum of SHR. Treatment with nicardipine countered microanatomical changes occurring in SHR, whereas hydralazine displayed a less pronounced effect. Comparatively, the non-hypotensive dose of nicardipine was less active than the hypotensive one. The observation that equihypotensive doses of nicardipine or hydralazine did not protect brain in the same way from hypertensive brain damage suggests that lowering blood pressure is per se not enough for affording neuroprotection. The demonstration of neuroprotective effect of nicardipine suggests an use of the compound in situations in which hypertension is accompanied by the risk of brain damage.

Occupancy by oral administration of nicardipine of L-type calcium channels in rat brain

The occupancy of L-type Ca2+ channels by treatment with an oral dose of the dihydropyridine-type Ca2+ antagonist nicardipine (sustained-release formulation) was evaluated in membrane preparations of rat frontal cortex and hippocampus using a radioligand binding assay technique, with [3H]-nicardipine as a ligand. Three hours after nicardipine administration, specific binding was decreased by about 15-20%, both in the frontal cortex and hippocampus. This indicates that oral nicardipine occupied approximately 15-20% of L-type Ca2+ channels. A progressive occupancy of Ca2+ channels was observed between six and 12 h after nicardipine administration. Twelve hours after drug administration, approximately 65-70% of Ca2+ channels were occupied. These findings indicate that oral treatment with 3 mg/kg of nicardipine (sustained-release formulation) occupies L-type Ca2+ channels in rat brain by more than 40% from the 6th to the 24th h after drug administration. This suggests that an oral dose of nicardipine (sustained-release formulation) in duces a significant occupancy of L-type Ca2+ channels in rat frontal cortex and hippocampus for about one day. The possible clinico-therapeutic relevance of this observation is discussed.

The influence of nicardipine and ifenprodil on the brain free arachidonic acid level and behavior in hypoxia-exposed rats

1. The effects of the calcium channel blockers, nicardipine and ifenprodil, on the brain free arachidonic acid level and learning ability in rats exposed to hypoxia were examined. 2. Adult rats were injected with 0.003; 0.01; 0.03; 0.1; 0.3 or 1.0 mg/kg of tested drugs i.p. Thirty min later the learning ability was tested in a passive avoidance task according to the step-through procedure. Immediately after the training trial, the animals were subjected to a period of oxygen deprivation hypoxia until the loss of the righting reflex. The retention trial was carried out 24 hr later. 3. The other groups of animals were pretreated with mentioned substances before hypoxia-exposure. Fifteen min after the loss of the righting reflex they were decapitated and brains were frozen in liquid nitrogen. The brain free arachidonic acid level was quantified by gas chromatography. 4. Both nicardipine and ifenprodil were effective in preventing a memory decline in hypoxia-exposed rats but did not prevent the accumulation of the brain free arachidonic acid in hypoxia-exposed rats. 5. The protective effects of both substances in behavioral studies during acute brain damage caused by hypoxia could not be explained by the prevention of the increase of the brain free arachidonic acid, but by some other mechanism.

Synaptosomal iron-dependent lipid peroxidation inhibition after subarachnoid hemorrhage by lazaroid in vivo treatment

The production of oxygen-free radicals and their subsequent peroxidative action on membrane unsaturated fatty acids could be enhanced after subarachnoid hemorrhage (SAH). We have studied the effects of the in vivo pharmacological treatment with a lazaroid (U78517F) after experimental SAH, on lipid peroxidative patterns in cortical synaptosomal preparations. U78517F is a lipid-soluble antioxidant with a potent action to inhibit iron-dependent lipid peroxidation. Experimental SAH was induced in anesthetized rats by slow injection of 0.3 mL of autologous arterial blood into cisterna magna. The hemorrhagic animals were treated with 5 mg/kg iv of U78517F immediately after surgical operation. The animals were sacrificed 1 d after the hemorrhage and the thiobarbituric acid reactive material (TBAR) was assayed in basal conditions and after 1, 3, 5, 10, and 20 min of incubation at 37 degrees C with a pro-oxidant mixture on three different rat groups: sham-operated (0.3 mL of mock cerebrospinal fluid (CSF) into cisterna magna), hemorrhagic (0.3 mL of autologous arterial blood into cisterna magna), and hemorrhagic-treated. The hemorrhagic event did not influence the membrane lipoperoxidation levels in basal conditions, whereas peroxidative stimulation in vitro caused significant increases in hemorrhagic animals compared to the sham-operated, and in hemorrhagic-treated animals, the synaptosomal TBARs were similar to controls. The pharmacological treatment showed its effectiveness only following incubations with pro-oxidants; therefore, U78517F seems to be protective for membranes in case of severe lipid peroxidative stress.

Nicardipine and MK-801 attenuate platelet-activating factor increases following cerebral ischemia-reperfusion in gerbils

The effects of pretreatment with nicardipine (dihydropyridine Ca2+ channel antagonist), Bay K8644 (dihydropyridine Ca2+ channel agonist), and MK-801 (N-methyl-D-aspartate-receptor antagonist) on changes of platelet-activating factor (PAF) concentrations in transient ischemic brain are reported. The tissue concentration of PAF increases significantly in hippocampus, cortex and thalamus by 210%, 169% and 168% of controls without ischemia-reperfusion, respectively after 1 h of reperfusion. Nicardipine (5 mg/kg) reduces the accumulation of PAF, the remaining increases in hippocampus, cortex and thalamus being 151%, 138% and 145% of the controls, respectively. In contrast, Bay K8644 (2.5 mg/kg) enhances the accumulation of PAF, its concentrations in hippocampus, cortex and thalamus being 376%, 233% and 204% of the controls, respectively. The Bay K8644 enhancement in hippocampus is completely inhibited by pretreatment of nicardipine (5 mg/kg). MK-801 (10 mg/kg) reduces the accumulation of PAF, the remaining increases in hippocampus, cortex and thalamus being 152%, 147% and 144% of the controls, respectively. Moreover, brain tissue from animals subjected to the combined pretreatment with nicardipine (5 mg/kg) and MK-301 (10 mg/kg) indicates there is greater inhibition of ischemia-induced PAF increases than with either drug alone. These results indicate that PAF production in the ischemic brain may be regulated by Ca2+ influx through voltage-sensitive Ca2+ channels which are antagonized and agonized by nicardipine and Bay K8644, respectively and receptor-operated Ca2+ channels which are antagonized by MK-801. Because it is known that increases of intracellular Ca2+ in the brain accompany ischemia and early periods of reperfusion and that PAF exhibits neurotoxicity, the present findings support the role of PAF as a mediator in ischemia-induced brain damage at early stages of reperfusion.

Nicardipine and treatment of cerebrovascular diseases with particular reference to hypertension-related disorders

Nicardipine is a second generation dihydropyridine-type Ca2+ antagonist with high vascular selectivity and strong cerebral and coronary vasodilatory activity. The compound is used in the treatment of hypertension, primarily in the elderly. In this review the main evidence of the cerebrovascular activity of nicardipine in preclinical studies using in vitro and in vivo models is detailed. A particular physico-chemical property of nicardipine is the almost complete protonation in acid environment. This allows its accumulation in ischemic brain regions and makes it a candidate for the treatment of cerebrovascular disorders characterised by impaired brain perfusion. The main clinical data on the use of nicardipine in cerebral ischemia and related disorders, subarachnoid haemorrhage and stroke, are also reviewed. These studies included 5940 patients affected by chronic cerebrovascular insufficiency (cerebral ischemia, cerebral atherosclerosis mainly associated with hypertension, transient ischemic attacks, sequelae of cerebral infarction, thrombosis or embolia, hypertensive encephalopathy), 1540 patients affected by sequelae of subarachnoid haemorrhage and 206 patients affected by stroke. Both preclinical studies and clinical trials have shown that nicardipine is a safe Ca2+ antagonist with powerful cerebrovascular activity. This suggests its possible use in cerebrovascular disorders in which blockade of Ca2+ channels of the L-type and/or selective cerebral vasodilatation is desirable. Further studies are necessary to establish if modulation of neuronal Ca2+ channels of the L-type by nicardipine may have a neuroprotective effect independent by the cerebrovascular activity of the compound.

The effect of deferoxamine on brain lipid peroxide levels and Na-K ATPase activity following experimental subarachnoid hemorrhage

1. In the present study we have studied the effects of deferoxamine treatment on lipid peroxidation and Na-K ATPase activity after experimental induction of subarachnoid haemorrhage (SAH) in guinea pigs. 2. We assessed the extent of lipid peroxidation by measuring the level of malondialdehyde and Na-K ATPase activity in 3 different groups (sham-operated, SAH, SAH + deferoxamine). 3. There was no significant difference in lipid peroxide content between sham-operated and haemorrhagic animals, but Na-K ATPase activity decreased after SAH. 4. Deferoxamine treatment reduced the malondialdehyde content and induced the recovery of Na-K ATPase activity, exerting a brain protective role against the detrimental effects of the haemorrhage.

The effect of lifarizine (RS-87476), a novel sodium and calcium channel modulator, on ischaemic dopamine depletion in the corpus striatum of the gerbil

1. Unilateral ligation of the right common carotid artery in the anaesthetized gerbil for 3 h caused a 62.7% decrease in ipsilateral dopamine in the corpus striatum from 1.40 (+/- 0.13, n = 27) micrograms g-1 in the non-ischaemic hemisphere to 0.47 (+/- 0.07, n = 27) micrograms g-1 in the ischaemic hemisphere (all results are expressed as mean +/- s.e. mean). In sham-operated animals there were no differences in the dopamine levels (1.31 +/- 0.14 micrograms g-1, n = 11, left; 1.27 +/- 0.13 micrograms g-1, n = 11 in the right hemisphere). Animals with intact communicating arteries in the circulus arteriosus were excluded. 2. Lifarizine (RS-87476; 250, 500, but not 50, micrograms kg-1, i.p.) protected against this dopamine depletion showing only a 9.2% decrease at 250 micrograms kg-1, i.p. (P < 0.01) and no decrease at 500 micrograms kg-1, i.p. (P < 0.01). 3. Nicardipine (250 micrograms kg-1, p.o.) was effective when administered chronically once daily for 10 days (26.6% decrease, P < 0.05) but not when administered acutely at 50 micrograms kg-1, i.p.

Nicardipine in the prevention of spasm-induced neurological deficits after subarachnoid hemorrhage: a dose-ranging study

The tolerability of four doses of intravenous nicardipine (0.03, 0.08, 0.11, and 0.15 mg/kg/h) was assessed in this randomized multicenter, parallel-group study. Fifty-two patients with Hunt and Hess grade I-III aneurysmal subarachnoid hemorrhage were treated with intravenous nicardipine beginning within 4 days of bleeding, for a mean duration of 12.6 days; this treatment was followed by administration of oral nicardipine 90-120 mg until day 30. Hypotension was the main side effect, and it occurred only in the two groups that received the highest doses. However, it was possible to continue nicardipine in all cases at lower doses or even without modification, and hypotension was never responsible for any deleterious clinical effect.

Effects of nicardipine treatment on Na(+)-K+ ATPase and lipid peroxidation after experimental subarachnoid haemorrhage

The calcium theory of neuronal damage has been recently adapted to subarachnoid haemorrhage (SAH). It is proposed that haemorrhagic insult to the brain causes free radical-mediated destructive reactions of membrane phospholipids, and the consequent decrease of phospholipid-dependent enzymatic activities, such as Na(+)-K+ ATPase. In the present study we have studied the effects of Nicardipine treatment on lipid peroxidation and Na(+)-K+ ATPase activity after experimental induction of SAH. SAH was induced in anaesthesized rats by slow injection of 0.3 ml of autologous arterial blood into the cisterna magna. We assessed the extent of lipid peroxidation by measuring the level of thiobarbituric acid reactive substances (TBARS) and Na(+)-K+ ATPase activity in 3 different rat brain areas (cerebral cortex, hippocampus and brain stem) of sham-operated (0.3 ml of mock CSF into cisterna magna) and at 1 hour, 6 hours and 48 hours after SAH induction; simultaneously, we investigated the capacity of cerebral lipid peroxidation by measuring the accumulation of TBRAS in homogenates of brain areas incubated under aerobic conditions. Na(+)-K+ ATPase activity decreased in the cerebral cortex at 1 hour and 6 hours and in brain stem at 1 hour after SAH, while the same enzymatic activity did not change in the hippocampus. There was no significant difference in lipid peroxide content between sham-operated and haemorrhagic animals; Nicardipine treatment reduced the TBRAS content and induced the recovery of Na(+)-K+ ATPase activity, exerting a brain protective role against the detrimental effects of the haemorrhage.

Early treatment of ischemic stroke with a calcium antagonist

We performed a feasibility and safety study (phase II) of nicardipine, a calcium antagonist, in 57 patients. The objectives of the study were to begin therapy as early as possible (less than or equal to 12 hours) after the onset of ischemic stroke and to administer as high a dose as possible. All patients received an intravenous infusion of nicardipine for 72 hours, starting with a dose of 3 mg/hr and increasing to a maximum dose of 7 mg/hr. Upward titration of the dose was limited by a 10% decrease in blood pressure or a 20 beats/min increase in pulse. Intravenous therapy was followed by 30 days of oral therapy. The mean +/- SD interval from onset of stroke to commencement of therapy was 9.1 +/- 5.4 hours. Adverse reactions consisted primarily of hypotension requiring discontinuation of therapy in four patients. Score on a graded neurologic examination increased from 41/100 at baseline to 64/100 at 3 months for the 41 patients completing follow-up. There was no correlation between the dose of nicardipine administered and outcome, but the 11 patients starting therapy less than or equal to 6 hours after onset did better than those starting therapy 6-12 hours after onset. Further study of very early therapy with nicardipine is justified.

Central hypotensive effects of nicardipine in conscious freely moving spontaneously hypertensive rat

The central cardiovascular effects of the calcium channel blocker nicardipine was studied in conscious freely moving normotensive Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). Nicardipine was administered in a 1.5 microliters volume into the lateral ventricle of the brain (i.c.v.) or intravenously (i.v.). The injection of vehicle alone did not significantly change mean arterial pressure (MAP) or heart rate (HR). Nicardipine (10, 30, 100 and 300 micrograms/kg) intravenously administered, dose-dependently decreased MAP and increased HR in WKY and SHR. However, when administered i.c.v., nicardipine (10 micrograms/kg) increased MAP and HR in WKY and decreased MAP without any significant change in HR in SHR. These results are consistent with previous work reporting an exaggerated hypotensive response to i.c.v. administration of dihydropyridine calcium channel blockers in anesthetized SHR as compared to WKY. They suggest that a 1,4-dihydropyridine-sensitive pressor system is present in the SHR but not in the WKY.

Inhibition by calcium channel blockers of the binding of platelet-activating factor to human neutrophil granulocytes

The inhibitory action of calcium channel blockers on platelet-activating factor (PAF)-induced activation of human polymorphonuclear granulocytes (PMNL) and on the binding of [3H]PAF to neutrophils was studied. Verapamil and diltiazem inhibited PAF (10(-8)-10(-15) M)-induced degranulation and superoxide production in a dose-dependent manner, with pA2 values of 5.6 and 6.1 for verapamil and 5.9 and 6.2 for diltiazem, respectively. Both channel blockers inhibited the specific binding of [3H]PAF to PMNL in dose-dependent fashion, with Ki values of 3.9 +/- 0.6 X 10(-5) M and 3.2 +/- 0.4 X 10(-5) M for verapamil and diltiazem, respectively. Scatchard analysis of the binding data revealed that both calcium channel blockers decreased the receptor binding affinity and slightly increased the number of high-affinity PAF receptors, whereas they did not affect the binding affinity and number of low-affinity receptors. These results indicate that calcium channel blockers can inhibit neutrophil responses elicited by PAF by a mechanism other than inhibition of calcium influx and suggest that the PAF receptor may be closely associated with calcium channels.

Calcium-calmodulin binding in ischemic rat neurons after calcium channel blocker therapy

Calcium channel blockers such as nicardipine improve outcome after global cerebral ischemia and may attenuate ischemic neuronal injury by preventing calcium influx and binding to calmodulin. We followed the temporal and regional sequence of neuronal calcium-calmodulin binding in normal rats (n = 6), untreated ischemic rats (n = 15), and ischemic rats treated with 0.05 mg/kg/hr s.c. nicardipine (n = 13). After 30 minutes of four-vessel occlusion, 40-microns brain sections were incubated in an anti-calmodulin antibody specific for calmodulin not bound to calcium and brain protein. Light-microscopic sections were examined immediately after ischemia and after 2 and 24 hours of reperfusion. Extensive staining of unbound calmodulin was seen in all hippocampal regions and in the cortex in normal rats. In untreated ischemic control rats, staining was lost, indicating calcium-calmodulin binding immediately after ischemia in all regions. However, after 24 hours, staining returned to normal in the cortex and dentate, and minimal staining returned in CA1 and CA3. Nicardipine-treated animals had significantly less calcium-calmodulin binding in CA1 and in the dentate after 2 hours of reperfusion. This study demonstrates that in clinically relevant doses nicardipine has a limited effect on calcium-calmodulin binding in selectively vulnerable regions after severe ischemia.

Activators and inactivators of calcium channels: effects in the central nervous system

The interactions of calcium antagonists or channel activators with the different classes of calcium channel are reviewed with particular emphasis on interactions with neuronal tissue; reasons for the failure of calcium antagonists to inhibit neurotransmitter release under normal circumstances are outlined. Calcium antagonists may be protective in several pathological situations and the possibilities of protection against ischaemic damage in the central nervous system are evaluated.

Central cardiovascular effects of dihydropyridines in spontaneously hypertensive rats

Intracerebroventricular (i.c.v.) injections of dihydropyridine derivatives calcium channel agonist (BAY K8644) and antagonist (nifedipine, nicardipine, PN 200-110) induced opposite long-lasting changes in blood pressure (BP) in pentobarbital anesthetized spontaneously hypertensive rats (SMR). I.c.v. nifedipine (NIF), nicardipine (NIC), and PN 200-110 decreased mean blood pressure dose-dependently and stereoselectively, (+) NIC and (+) PN being 8 and 3 times more potent than their (-) isomers, respectively. The decrease in BP was due to a withdrawal of the sympathetic tone, since NIF- and NIC-induced falls in BP were suppressed after either hexamethonium (HXM), 6 OHDA or bilateral adrenalectomy. I.c.v. BAY K8644 increased BP dose-dependently. The i.c.v. BAY K8644-induced hypertensive effect was inhibited: a), by NIF and (+) PN but not by (-) PN, therefore probably occurring at central DHP sites; b), by HXM and reserpine, thus probably mediated by an increase in sympathetic tone; c) by i.c.v. methylatropine (MA) while i.v. MA and i.c.v. HXM had no inhibitory effect, thus probably involving central muscarinic sites. In SHR, NIC did not after the K(+)-evoked ACh release but suppressed the BAY K8644-induced increase in ACh release. In anesthetized normotensive control rats (WKY), neither i.c.v. NIF, NIC or BAY increased BP and HR while, in conscious SHR it decreased BP without any change in HR. These data increased BP and HR while, in conscious SHR it decreased BP without any change in HR. These data suggest that central DHP sites may be involved in the cholinergic transmission and may participate in genetic hypertension via sympathetic tone.

In vitro modulation of human neutrophil superoxide anion generation by various calcium channel antagonists used in ischemia-reperfusion resuscitation

Generation of toxic oxygen species by activated polymorphonuclear leukocytes (PMNs) may represent an important mechanism of ischemia-reperfusion injury. Concentration-response data concerning inhibition of superoxide anion (O2-) generation by NADPH oxidoreductase (NADPH OR) from isolated human PMN were generated for five calcium channel antagonists commonly utilized in ischemia-reperfusion investigational therapeutics. Regression analysis derived IC50 values for verapamil, nimodipine, nicardipine and lidoflazine were 45, 20, 12 and 7 microM respectively. Inhibition of the extent of reaction at 5 min paralleled inhibition of initial velocity. No inhibition by flunarizine was noted at concentrations less than or equal to 25 microM (where it did not alter reaction mixture composition). Only nicardipine demonstrated a significant concentration-response effect relative to prolonging lag time preceding O2- synthesis. Inhibition appeared at least partially reversible for all five agents. Neither PMN activation/desensitization, free-radical scavenging, nor PMN cytotoxicity appeared to be involved in the inhibition of PMN O2- synthesis by these agents. Ca2+ antagonist inhibition of PMN NADPH OR appears to involve more than simple inhibition of Ca2+ flux across the PMN plasma membrane. Direct inhibition of the intracellular events involved in the activation and/or activity of NADPH OR may be operative.

A modified four-vessel occlusion model for inducing incomplete forebrain ischemia in rats

The four-vessel occlusion (4VO) model of Pulsinelli and Brierley (Stroke 1979;10:267-272) has been modified for use in halothane-nitrous oxide-anesthetized, physiologically controlled rats that were ventilating spontaneously. Selection criteria for the classification of severity of ischemia were established by correlating changes in the electroencephalogram and the general physiological status with measurements of regional blood flow and regional energy metabolism. In 13% of animals, 4VO did not cause flattening of the electroencephalogram, and such animals were classified as undergoing only "oligemia." In 65% of rats, the electroencephalogram flattened and blood pressure sharply increased with 4VO, whereas spontaneous respiration continued. This group exhibited almost complete ischemia in autoradiographic blood-flow studies, severe acidosis, and depletion of adenosine 5'-triphosphate and glucose in the forebrain and, hence, was classified as the "ischemia" group. The remaining 22% stopped breathing after vascular occlusion and were rejected for further study. Survival experiments of ischemic animals revealed the typical postischemic sequelae, with primary metabolic recovery after 8 hours of recirculation in all brain structures followed after 8-24 hours by severe biochemical deterioration and neuronal death in the striatum and hippocampus. Postischemic seizure activity was rare. The main advantages of the present modification in comparison with the original method are 1) the application of anesthesia without loss of primary selection criteria, 2) the possibility of invasive physiological monitoring, and 3) the absence of postischemic seizures, which eliminates the necessity for secondary selection criteria.

Nicardipine after spinal cord compression in the lamb

To study the effects of the calcium channel blocker nicardipine on spinal cord blood flow and spinal evoked potentials, the following study was undertaken. After cord compression, which was productive of paraparesis, nicardipine was administered intravenously in 10 anesthetized lambs. Ten control animals were subjected to compression but received saline instead. Nicardipine produced a significant decrease in mean arterial pressure when compared to the control group. Thirty minutes after compression, spinal cord blood flow also was lower in the nicardipine group compared with controls. Spinal evoked potentials did not recover after compression in either group.

The potential use of nicardipine in cerebrovascular disease

The efficacy of intravenous nicardipine in the prevention of vasospasm after subarachnoid hemorrhage has been investigated in a dose escalation study in 67 patients admitted within 1 week of subarachnoid hemorrhage. Favorable outcomes were noted in 52 patients (78%). Vasospasm was found by arteriography in 31 patients (46%). A dose-related trend was noted. At the lower dose levels, angiographic spasm was observed in 68% and symptomatic vasospasm in 27% of 34 patients. Only eight of 33 patients (24%) treated at the highest dose level (approximately 10 mg/hr) developed arteriographic evidence of vasospasm. Symptomatic vasospasm was diagnosed in only two of 33 patients (6%) treated with this dose. No deaths from vasospasm occurred. Verification of changes in tissue calcium has been obtained from the rat middle cerebral artery occlusion model, and we concluded that nicardipine administered after permanent occlusion may offer protection against cerebral ischemia in this animal model. Nicardipine uptake was greater at the infarct site than in surrounding tissue, with the highest concentration in the area of maximal ischemia. Nicardipine appears to affect changes in Ca2+ more than other ions: it significantly reduced Ca2+ accumulation in the territory of the middle cerebral artery by 60% at 6 hours, and significantly reduced Na+ and K+ shifts in the same territory by 40% and 50%, respectively, at 6 hours. Although much research remains to be done, a wide role for the dihydropyridines in a number of cerebrovascular conditions is emerging.

Control of epilepsy partialis continuans with intravenous nimodipine. Report of two cases

The authors present two patients with continuous focal epileptic seizures intractable to conventional antiepileptic therapy. Both cases were successfully treated with intravenous nimodipine.

Nicardipine reduces calcium accumulation and electrolyte derangements in regional cerebral ischemia in rats

We studied the effects of the calcium channel blocker nicardipine on regional tissue Ca2+, Na+, K+, and water shifts in the brains of seven Sprague-Dawley rats after permanent occlusions of the middle cerebral artery. We also assessed the entry of [14C]nicardipine into the brains of five rats; the highest concentrations of [14C]nicardipine were in the infarcted area. Nicardipine treatment significantly reduced Ca2+ accumulation in the middle cerebral artery territory by 60% compared with six untreated rats 6 hours after arterial occlusion. Eight 125-micrograms/kg boluses of nicardipine given every 30 minutes starting 5 minutes after arterial occlusion also significantly reduced the Na+ and K+ shifts in the middle cerebral artery territory by 40% and 50%, respectively, 6 hours after arterial occlusion. Nicardipine appears to reduce Ca2+ accumulation more than it reduces Na+ and water accumulation and K+ loss. Our results suggest that a calcium channel blocker can protect brain tissues in a model of focal cerebral infarction by directly reducing Ca2+ entry into ischemic cells.

Effects of calcium channel blockers on neurologic outcome after focal ischemia in rabbits

To determine the efficacy of calcium channel blockers in preserving neurologic function after central nervous system ischemia, we studied three such agents in two animal models. We treated rabbits after inducing ischemia in the brain with intra-arterial microspheres and in the spinal cord using a removable aortic occluding device. We found no benefit, in terms of neurologic functional outcome, from lidoflazine, nimodipine, or nicardipine. All three agents elevated regional blood flow in the spinal cord. We conclude that calcium antagonists are not likely to prove beneficial if used alone in the treatment of focal central nervous system ischemia.

Efficacy and mechanism of action of a calcium channel blocker after global cerebral ischemia in rats

Dihydropyridine calcium channel blockers such as nicardipine are under evaluation for treating acute cerebral ischemia because they may increase cerebral blood flow by causing vasodilation and because they may be cytoprotective in part by limiting production of arachidonic acid metabolites. We demonstrated in a previous study that nicardipine improves postischemic neuronal function, as measured by somatosensory evoked potentials, without reducing the extent of light-microscopic CA-1 hippocampal histologic damage. To characterize further the effect of nicardipine on global ischemic injury, we administered the drug beginning 24 hours before 30 minutes of four-vessel ischemia in Wistar rats. We then measured hippocampal ATP, phosphocreatine, and glucose contents immediately and 2 hours after ischemia, and measured learning ability (working and reference errors) on an eight-arm radial maze beginning 30 days after ischemia. To gain insight into the possible mechanism of action, we measured production of arachidonic acid metabolites (eicosanoids: TXB2 and 6-keto-PGF1 alpha) and hemispheric and hippocampal cerebral blood flow by the [14C]butanol indicator fractionation technique immediately and 2 hours after ischemia. Nicardipine was associated with fewer working errors (p less than 0.02) but no difference in reference errors. The drug had no effect on energy metabolites, cerebral blood flow, or eicosanoids immediately after ischemia, but ATP, phosphocreatine, and cerebral blood flow all returned to normal levels significantly more rapidly during reperfusion in treated rats. Nicardipine improves behavioral, electrophysiologic, and mitochondrial function after ischemia without preventing cellular damage and improves postischemic reperfusion. The drug's positive effect appears to occur during reperfusion.

Dose-escalation study of intravenous nicardipine in patients with aneurysmal subarachnoid hemorrhage

A dose-escalation study of the calcium ion entry blocking drug nicardipine was performed using large dose infusions in 67 patients with recent aneurysmal subarachnoid hemorrhage (SAH). A safe, potentially therapeutic dose of the drug was determined. Patients admitted within 7 days of SAH from a documented cerebral aneurysm were entered into the study if no spasm was present on the initial angiogram. Nicardipine was administered as a continuous intravenous infusion throughout the 14-day period after SAH, regardless of the timing of surgery. To determine the safest possible dose, nicardipine was administered at seven dose levels from 0.01 to 0.15 mg/kg/hr. The total daily doses ranged from 27.7 mg to 375.0 mg. A follow-up angiogram was carried out on all 67 patients 7 to 10 days after SAH. Computerized tomography and neurological examinations were used to determine the presence of cerebral infarction. No major adverse effects, unexpected reactions, or permanent sequelae could be attributed to nicardipine. A decline in blood pressure was noted following administration of the drug. This occurred more frequently among patients given the largest dose but did not produce clinical problems or require discontinuation of the drug. Favorable outcomes were noted in 52 patients (78%). Vasospasm was found by arteriography in 31 patients (46%). A dose-related trend was noted: only eight (24%) of 33 patients treated at the highest dose level (approximately 10 mg/hr) developed arteriographic evidence of vasospasm. Symptomatic vasospasm was diagnosed in only two (6%) of 33 patients treated with this dose. Of the 34 patients receiving the lower dose levels, angiographic spasm was observed in 68% and symptomatic vasospasm in 27%. No deaths due to vasospasm occurred. Nicardipine appears to prevent both vasospasm and cerebral ischemia after SAH. A multicenter randomized double-blind trial to test this hypothesis is planned.

Cerebrovascular and cerebral effects of nimodipine--an update

A survey is given on the vascular and neuronal effects of calcium antagonists under physiological and pathological conditions. Special emphasis is put on vasospasm caused by subarachnoid haemorrhage and on postischaemic cerebral hypoperfusion following different forms of cerebral ischaemia, and on the attempts to influence these phenomena pharmacologically. Regarding its neuronal effects it seems likely that nimodipine potently blocks calcium entry during pathological conditions like cerebral ischaemia and spreading cortical depression. Positive effects also have been seen during epileptic seizures and withdrawal syndromes, whereas calcium entry under normal physiological conditions does not appear to be affected. Possible clinical consequences are discussed.

Combination of aminocaproic acid and nicardipine in treatment of aneurysmal subarachnoid hemorrhage

Antifibrinolytic drugs reduce the risk of rebleeding during the first 2 weeks after aneurysmal subarachnoid hemorrhage. However, they do not lower overall mortality, largely because of an increased incidence of cerebral ischemia. The usefulness of antifibrinolytic drugs might be increased if a method to prevent or control vasospasm in patients were to be developed. We recently completed late Phase I and Phase II studies of the calcium ion blocking drug nicardipine in 67 patients treated within 1 week of subarachnoid hemorrhage. Of these 67 patients, 42 had delayed operations and were treated concomitantly with the antifibrinolytic drug aminocaproic acid (1.5 g/hr) for an average of 6 days before surgery. The outcome of these 42 patients is the subject of this report. Fifteen of 42 patients were treated with the lower dosage levels of nicardipine (0.4-4.5 mg/m2/hr), and 27 patients were treated at the highest dosage level (6.0 mg/m2/hr). Using the World Federation of Neurological Surgeons scale for subarachnoid hemorrhage, at admission 18 patients were Grade I, 15 were Grade II, 6 were Grade III, and 3 were Grade IV. Five patients (12%) developed clinical signs of deterioration suggestive of cerebral ischemia with concomitant evidence of vasospasm on arteriography. These patients were all treated with hypervolemic hypertensive therapy. Only one patient (2%) developed an infarction from vasospasm. Two patients developed symptomatic hydrocephalus requiring ventriculoperitoneal shunting, and a third patient required a temporary ventriculostomy. The 3-month postoperative outcomes were excellent. Three patients (7%) rebled. Three patients died, two from rebleeding of the aneurysm and one who never regained consciousness from the initial hemorrhage.(ABSTRACT TRUNCATED AT 250 WORDS)