The effects of a calcium antagonist (nimodipine) on basal cerebral blood flow and reactivity to various agonists

Nimodipine augments cerebrovascular reactivity in aging but runs the risk of local perfusion reduction in acute cerebral ischemia

Introduction

The efficacy of cerebrovascular reactivity (CVR) is taken as an indicator of cerebrovascular health.

Methods and Results

We found that CVR tested with the inhalation of 10 % CO₂ declined in the parietal cortex of 18-20-month-old rats. The CVR deficit in old rats was coincident with cerebrovascular smooth muscle cell and astrocyte senescence, revealed by the immuno-labeling of the cellular senescence marker p16 in these cells. In a next series of experiments, CVR was severely impaired in the acute phase of incomplete global forebrain ischemia produced by the bilateral occlusion of the common carotid arteries in young adult rats. In acute ischemia, CVR impairment often manifested as a perfusion drop rather than blood flow elevation in response to hypercapnia. Next, nimodipine, an L-type voltage-gated calcium channel antagonist was administered topically to rescue CVR in both aging, and cerebra ischemia. Nimodipine augmented CVR in the aged brain, but worsened CVR impairment in acute cerebral ischemia.

Discussion

A careful evaluation of benefits and side effects of nimodipine is recommended, especially in acute ischemic stroke.

Calcium channel blockade with nimodipine reverses MRI evidence of cerebral oedema following acute hypoxia

Acute cerebral hypoxia causes rapid calcium shifts leading to neuronal damage and death. Calcium channel antagonists improve outcomes in some clinical conditions, but mechanisms remain unclear. In 18 healthy participants we: (i) quantified with multiparametric MRI the effect of hypoxia on the thalamus, a region particularly sensitive to hypoxia, and on the whole brain in general; (ii) investigated how calcium channel antagonism with the drug nimodipine affects the brain response to hypoxia. Hypoxia resulted in a significant decrease in apparent diffusion coefficient (ADC), a measure particularly sensitive to cell swelling, in a widespread network of regions across the brain, and the thalamus in particular. In hypoxia, nimodipine significantly increased ADC in the same brain regions, normalizing ADC towards normoxia baseline. There was positive correlation between blood nimodipine levels and ADC change. In the thalamus, there was a significant decrease in the amplitude of low frequency fluctuations (ALFF) in resting state functional MRI and an apparent increase of grey matter volume in hypoxia, with the ALFF partially normalized towards normoxia baseline with nimodipine. This study provides further evidence that the brain response to acute hypoxia is mediated by calcium, and importantly that manipulation of intracellular calcium flux following hypoxia may reduce cerebral cytotoxic oedema.

Impact of Early Versus Late Intravenous Followed by Oral Nimodipine Treatment on the Occurrence of Delayed Cerebral Ischemia Among Patients With Aneurysm Subarachnoid Hemorrhage

BACKGROUND

Guidelines for aneurysm subarachnoid hemorrhage (aSAH) management recommend treatment with nimodipine to all patients to reduce delayed cerebral ischemia (DCI) and poor clinical outcome. However, it did not give the most beneficial time to start therapy and route of administration.

OBJECTIVES

To compare the DCI occurrence and clinical outcome among aSAH patients who received nimodipine treatment at different times.

METHODS

A retrospective cohort study was conducted by collecting data from medical chart reviews between August 30, 2010, and October 31, 2015, at Prasart Neurological Institute, Thailand. Patients were classified into 2 groups by time to receive nimodipine: early group and late group (<96 and >96 hours, respectively). All patients received intravenous (IV) followed by oral nimodipine to complete treatment course. Clinical outcome was graded using the Glasgow Outcome Scale at 21 days. The factors related to DCI were analyzed using multivariate logistic regression.

RESULTS

A total of 149 patients were recruited: early (n = 97) and late (n = 52). No difference in baseline characteristics between groups was observed. The occurrence of DCI was not statistically significantly different between groups (early group, 18.60%, vs late group, 20.80%; P = 0.74). The World Federation of Neurosurgical Societies IV to V was associated with DCI occurrence. The proportion of patients with good outcome, poor outcome, or death did not show any difference between groups.

CONCLUSIONS AND RELEVANCE

Receiving IV nimodipine 3 to 7 days following oral therapy after bleeding can be the alternative regimen in patients who did not start nimodipine within 96 hours.

Mechanisms, treatment and prevention of cellular injury and death from delayed events after aneurysmal subarachnoid hemorrhage

INTRODUCTION

Subarachnoid hemorrhage (SAH) patients often develop brain injury as a result of a number of delayed complications, resulting in significant morbidity and mortality. Many of these complications arise due to delayed cerebral ischemia, which occurs secondary to the hemorrhage.

AREAS COVERED

The mechanisms of the delayed injury are reviewed, including angiographic vasospasm, cortical spreading ischemia, small arteriolar constriction, microthromboemboli, free radical injury and inflammation. Some current and prospective therapies for SAH are discussed, in the context of these complications. Statins have been particularly promising in experimental studies.

EXPERT OPINION

Multiple mechanisms are involved in the pathogenesis of the delayed insult after SAH. New drugs may need to target multiple pathways to injury. Trials aiming to treat complications after SAH could benefit from taking into account the multifactorial pathogenesis of delayed insults.

Hypothermic cardiopulmonary bypass for minimally invasive mitral valve plasty in adult moyamoya disease

A 43-year-old man underwent minimally invasive mitral valve plasty of a flail mitral valve. Four years previously, he had been diagnosed with moyamoya disease (MMD) by cerebral magnetic resonance imaging/angiography findings. In MMD, risk factors for cerebral stroke include changes in arterial carbon dioxide partial pressure, blood pressure, and body temperature. And during cardiopulmonary bypass (CPB), these hemodynamic changes can be challenging. However, hypothermia during CPB can decrease cerebral oxygen consumption and have a cerebral protective effect. We performed a minimally invasive mitral valve plasty, using hypothermic CPB, in a patient with MMD, without any neurological deficits.

Cerebral oxygen saturation monitoring for off-pump coronary bypass graft surgery with Moyamoya disease: A case report

We report a case using cerebral oxygen saturation (rCbO2) for off-pump coronary artery bypass graft (OPCAB) surgery in a patient with co-existing Moyamoya disease. The rCbO2 with the routine monitoring for OPCAB surgery were monitored intraoperatively. In spite of infusing nimodipine (0.2 microgram/kg/min) and maintaining the end-tidal CO2 tension at 35-40 mmHg, a sudden reduction in the right-side rCbO2 from the base line value of 70-80%/78-83% (Left/Right) to 70-72%/65-70% was developed during the harvesting of the vascular graft. We increased the rate of phenylephrine infusion to increase systemic and cerebral perfusion pressure, and both rCbO2 values were elevated to 80%/70% within 3 minutes. However, the preferential reduction in the right-side rCbO2 compared with the left-side value was not corrected. While suspecting cerebral ischemia due to cerebral vascular spasm, we administered nimodipine 2 mg bolus and increased infusion rate to 0.5 microgram/kg/min. Finally, the preferential rCbO2 reduction in the right-side was corrected and both rCbO2 reached 84%/91%. We concluded rCbO2 monitoring is useful for detecting an intraoperative episode of cerebral ischemia and maintaining the optimal cerebral perfusion during OPCAB surgery with Moyamoya disease.

Behavioural and anti-psychotic effects of Ca2+ channel blockers in rhesus monkey

The potential utility of Ca2+ channel blockers in the treatment of various psychiatric disorders has been recently suggested. In the present study, the behavioural and anti-psychotic effects of Ca2+ channel blockers were investigated in unrestrained rhesus monkeys (Macaca mulatta) living together in a colony. The different behaviours categorised as social, solitary and abnormal were video recorded and analysed. Graded doses of verapamil (5-20 mg/kg, i.m.) and nimodipine (7.5-30 mg/kg, p.o.) produced a mild decrease in social and solitary behaviour without producing any cataleptic posture in the tested monkeys. In order to determine potential antipsychotic effects, Ca2+ channel blockers were studied in the model of amphetamine-induced psychosis. Amphetamine, at the dose of 2 mg/kg, i.m., induced suppression of approach, contact, grooming, and feeding, whilst vigilance (checking), stereotyped behaviour and oral hyperkinesia were increased in the monkeys. Pre-treatment with verapamil (10 and 20 mg/kg, i.m.) significantly suppressed amphetamine-induced hypervigilance, stereotypy, oral hyperkinesia and tachypnoea but was unable to reverse other amphetamine-induced behavioural effects. Nimodipine showed insignificant anti-psychotic effects at both 15 and 30 mg/kg doses. These results suggest that verapamil has a definite antipsychotic effect without any extrapyramidal side effects and thus may be of clinical significance in the treatment of psychosis.

Chronic administration of the Ca(2+) channel blocker amlodipine facilitates learning and memory in mice

Acute administration of the Ca(2+) channel antagonist amlodipine has been shown to facilitate memory for several types of learning in adult animals and to improve retention in aging mice. This study reports three experiments investigating the effect of chronic amlodipine treatment on retention in mice. In the first experiment, groups of mice were treated with either amlodipine or vehicle once a day for 14 days prior to training on a spatial discrimination task. Immediately after training, animals were given a single dose of amlodipine or the vehicle and tested for retention 24 h later. Both groups showed facilitated retention, thereby demonstrating that chronic amlodipine treatment did not produce desensitization to the facilitating effects of a post training treatment. In the second experiment, chronic treatments were administered once daily for 14 days beginning 24 h after training on one-way active avoidance and retention was tested on day 15. Results showed that chronic amlodipine attenuated spontaneous forgetting, but surprisingly, a similar enhancement could be achieved by a single treatment administered 1 day after training. In the third experiment, amlodipine was given either before or immediately after 10 daily training sessions in the one-way active avoidance task. Results showed that chronic treatment accelerated rate of learning. These findings confirm the memory facilitating properties of amlodipine under conditions of chronic drug administration.

Amlodipine, a Ca2+ channel antagonist, modifies cerebral blood flow autoregulation in hypertensive rats

We measured the cerebral blood flow at rest and during hemorrhagic hypotension in 7 rats of each group using laser-Doppler flowmetry. Simultaneously, the absolute baseline cerebral blood flow values in the parietal cortex were quantified with the hydrogen clearance method. Baseline mean arterial pressure was significantly lowered, by 29 mm Hg, in the amlodipine-treated group, while the baseline cerebral blood flow was 36 +/- 4 ml/100 g/min (mean +/- S.D.) which was almost the same as the 40 +/- 5 in the control group. The lower limits of the cerebral blood flow autoregulation, defined as the mean arterial pressure at which the cerebral blood flow decreased by 10% of the baseline value, were shifted to a lower level of 107 +/- 9 mm Hg in the treated group compared with 133 +/- 5 mm Hg in the control (P < 0.001). The results demonstrated that, in hypertensive rats with amlodipine treatment, cerebral perfusion was preserved at a lower blood pressure level, which is advantageous under hypotensive conditions.

Calcium channels in cerebral arteries

Electrophysiological evidence shows the existence of voltage-operated Ca2+ channels of the L- and, in some cases, T- and B-, type in the smooth muscle cells of major cerebral arteries and arterioles. Current intensity through L-type Ca2+ channels is higher in cerebral than in peripheral arteries, which points to a greater dependence on extracellular Ca2+ of contractile responses in cerebral arteries. The increase in cytosolic Ca2+ concentration is the key event leading both to maintenance of basal cerebrovascular tone and to contraction of cerebral arteries in response to depolarization and agonist-receptor interaction. Such an increase results from increased transmembrane influx of Ca2+ through L-type Ca2+ channels, as well as from the release of Ca2+ from intracellular Ca2+ stores. Ca2+ entry modulators (dihydropyridines, phenylalkylamines, benzothiazepines, and diphenylpiperazines) bind to allosterically coupled sites in the Ca2+ channel, thus inhibiting (Ca2+ entry blockers) or stimulating (Ca2+ entry activators) Ca2+ influx and, therefore, contractile responses of the cerebral arteries. In vivo, Ca2+ entry blockers increase pial vascular caliber and cerebral blood flow by their direct action on the cerebroarterial wall. However, such an action also takes place on several peripheral vascular beds, which leads to hypotension. Therefore, the brain cannot be considered a "privileged" organ when the vasodilatatory action of Ca2+ entry blockers is considered. Since increased cytosolic Ca2+ concentration (and, therefore, activation of Ca2+ channels) plays a crucial role in the pathogenesis of ischemic brain damage (e.g., acute stroke and subarachnoid hemorrhage), Ca2+ entry blockers could be useful cytoprotective drugs. However, with the exception of nimodipine in the management of subarachnoid hemorrhage, clinical trials have yielded results that are not so promising as one could expect from those obtained in experimental research.

Evaluation of the calcium channel antagonist nimodipine after experimental spinal cord injury

The cortical somatosensory evoked potentials (CSEPs) were recorded to determine if the administration of nimodipine improves axonal function after spinal cord injury. Animals receiving a 52 g compression injury (a moderately severe injury) for 5 minutes were randomly allocated to one of five treatment groups. Each group was given an infusion of one of the following nimodipine regiments over 2 hours, commencing 1 hour before compression: placebo (n = 20), 0.5 micrograms/kg (n = 10), 0.25 micrograms/kg (n = 20), 0.125 micrograms/kg (n = 10), and 0.25 micrograms/kg + Hetstarch (n = 10). In the control group, 65% of animals lost the CSEPs immediately after the injury with almost all (95%) of these regaining the CSEPs within 15 minutes after decompression of the spinal cord. In the treated groups, the rate of the CSEP loss was highest in the 0.5 micrograms/kg group. This group also had the lowest CSEP recovery. The proportion of the CSEP loss was essentially the same for the other nimodipine-treated groups, although it seemed that there was an increasing number of nonresponses with increasing the nimodipine dose. Our data indicate lack of any beneficial effects of nimodipine on axonal function as measured by evoked activities in experimental spinal cord injury.

In vivo and in vitro effects of magnesium sulfate in the cerebrovascular bed of the goat

The effects of magnesium sulfate in the cerebrovascular bed were studied both in vivo, by measuring cerebral blood flow in conscious nonpregnant goats, and in vitro, by recording isometric tension in isolated goat middle cerebral arteries. Injections of increasing doses (10 to 300 mg) of magnesium sulfate directly into the cerebral circulation elicited transient and dose-dependent increases in cerebral blood flow and decreases in cerebral vascular resistance. Similar results were obtained when increasing doses (0.3 to 3 gm/15 min) of magnesium sulfate were infused intravenously, although the vasodilatations reached a stable plateau that remained when the infusions finished. Cumulative addition of magnesium sulfate (10(-5) to 3 x 10(-2) mol/L) did not change the isometric tension of isolated arterial segments at resting tone, but relaxed in a concentration-dependent manner the arterial segments preconstricted with 10(-5) mol/L prostaglandin F2 alpha. These results demonstrate that magnesium sulfate acts as a dilator in the cerebral circulation by acting directly on the cerebral arteries. This could explain, at least in part, its beneficial effects on preeclampsia-eclampsia.

New calcium antagonists: relevance of vasoselectivity

The calcium antagonists are a heterogeneous class of drugs used to treat a number of cardiovascular disorders. A new generation of calcium antagonists under development have a higher degree of selectivity for vascular smooth muscle and coronary vasculature compared with verapamil, nifedipine, and diltiazem. The clinical relevance of vasoselectivity and its impact on drug selection are discussed. The newer calcium antagonists are important alternatives to older agents and may be associated with improved tolerance and a reduced incidence of adverse effects. Their place in therapy has yet to be defined by comparative studies of efficacy and safety.

Protective effect of nimodipine against ischemic neuronal damage in rat hippocampus without changing postischemic cerebral blood flow

The purpose of the present study was to investigate the neuroprotective action of nimodipine. Furthermore, the influence of nimodipine on postischemic local CBF (LCBF) was examined. Forebrain ischemia of the rat was performed for 10 min by bilateral carotid clamping, administration of trimethaphan, and blood withdrawal to obtain an MABP of 40 mm Hg. LCBF was measured after 10 min of postischemic recirculation by injecting [14C]iodoantipyrine in saline solution. Nimodipine (0.1, 0.3, and 1.0 mg/kg) was suspended in miglyol oil and applied orally 60 min prior to ischemia. Histological evaluation was performed 7 days after ischemia. Hippocampal neuronal damage was determined as the percentage of necrotic neurons. After preischemic application of nimodipine, neuronal damage was significantly reduced in the hippocampal CA1 subfield. Postischemic LCBF was not affected by treatment with nimodipine. These findings show that nimodipine is able to protect neurons against ischemic damage. The neuroprotective effect of nimodipine was not mediated by a postischemic cerebral vasodilation, but by a direct action on the neurons.

Delayed brainstem ischemia following rupture of a basilar artery aneurysm and its reversal by nimodipine

A patient with delayed onset of deteriorating consciousness and episodes of opisthotonos, following rupture of an aneurysm of the basilar artery is described. The condition was reversed by intravenous nimodipine and the final outcome was excellent.

The use of a calcium-channel blocker, nicardipine, for severely asphyxiated newborn infants

A continuous infusion of nicardipine was given to four severely asphyxiated fullterm infants who were at high risk for adverse outcome and had abnormal cerebral Doppler haemodynamic studies. The heart rate increased in all four infants and mean arterial blood pressure (MAP) fell in three. Two infants had a sudden and marked fall in MAP, together with severe impairment of skin blood-flow and a concurrent fall in cerebral blood-flow velocity. The serum level of nicardipine was less than 40ng/mL in all cases. The use of nicardipine, and possibly other calcium-channel blockers, may be associated with marked hypotension, and if there is no cerebral autoregulation, may cause further cerebral hypoperfusion, so use of these drugs in asphyxiated newborn infants should only be attempted if blood pressure is carefully monitored.

Nimodipine has no effect on the cerebral circulation in conscious pigs, despite an increase in cardiac output

1. We studied the effects of four doses of nimodipine (0.5, 1, 2 and 4 micrograms kg-1 min-1) on systemic haemodynamics and on regional vascular beds, in particular the cerebral circulation, in conscious pigs. 2. Nimodipine caused dose-dependent, probably reflex-mediated, increases in heart rate (42% with the highest dose) and cardiac output (54%), while arterial blood pressure was only minimally affected. Left ventricular end-diastolic pressure and systemic vascular resistance decreased dose-dependently (35-40% at the highest dose) while stroke volume remained unchanged. 3. Total brain blood flow was not affected by the drug. Furthermore, we could not demonstrate any regional cerebral differences, as blood flows to both cerebral hemispheres as well as the diencephalon, cerebellum and brain stem remained unchanged. 4. Blood flow to the kidneys, liver, small intestine and skin also did not change. Nimodipine caused dose-dependent increases in blood flow to the stomach (95%), myocardium (97%) and adrenal glands (102%), while blood flow to skeletal muscles (267%) increased most. 5. It is concluded that in the conscious pig, nimodipine is an arterial vasodilator which shows some selectivity for the skeletal muscle vasculature but does not increase total or regional cerebral blood flow.

The effect of nimodipine and dextran on axonal function and blood flow following experimental spinal cord injury

There is evidence that posttraumatic ischemia is important in the pathogenesis of acute spinal cord injury (SCI). In the present study spinal cord blood flow (SCBF), measured by the hydrogen clearance technique, and motor and somatosensory evoked potentials (MEP and SSEP) were recorded to evaluate whether the administration of nimodipine and dextran 40, alone or in combination, could increase posttraumatic SCBF and improve axonal function in the cord after acute SCI. Thirty rats received a 53-gm clip compression injury on the cord at T-1 and were then randomly and blindly allocated to one of six treatment groups (five rats in each). Each group was given an intravenous infusion of one of the following over 1 hour, commencing 1 hour after SCI: placebo and saline; placebo and dextran 40; nimodipine 0.02 mg/kg and saline; nimodipine 0.02 mg/kg and dextran 40; nimodipine 0.05 mg/kg and saline; and nimodipine 0.05 mg/kg and dextran 40. The preinjury physiological parameters, including the SCBF at T-1 (mean +/- standard error of the mean: 56.84 +/- 4.51 ml/100 gm/min), were not significantly different (p greater than 0.05) among the treatment groups. Following SCI, there was a significant decrease in the SCBF at T-1 (24.55 +/- 2.99 ml/100 gm/min; p less than 0.0001) as well as significant changes in the MEP recorded from the spinal cord (MEP-C) (p less than 0.0001), the MEP recorded from the sciatic nerve (MEP-N) (p less than 0.0001), and the SSEP (p less than 0.002). Only the combination of nimodipine 0.02 mg/kg and dextran 40 increased the SCBF at T-1 (43.69 +/- 6.09 ml/100 gm/min; p less than 0.003) and improved the MEP-C (p less than 0.0001), MEP-N (p less than 0.04), and SSEP (p less than 0.002) following SCI. With this combination, the changes in SCBF were significantly related to improvement in axonal function in the motor tracts (p less than 0.0001) and somatosensory tracts (p less than 0.0001) of the cord. This study provides quantitative evidence that an increase in posttraumatic SCBF can significantly improve the function of injured spinal cord axons, and strongly implicates posttraumatic ischemia in the pathogenesis of acute SCI.

The effect of nimodipine on the evolution of human cerebral infarction studied by PET

Fourteen patients were studied by positron emission tomography (PET) within 48 h of onset of a hemispheric ischemic stroke and again 7 days later. After the first set of PET scans, the patients were randomized to receive either nimodipine (n = 7) or a carrier solution (n = 7) by intravenous infusion. The infusions were maintained until the end of the second PET studies. CBF, cerebral blood volume (CBV), oxygen extraction ratio (OER), CMRO2, and CMRglc were measured each time. These metabolic and perfusion measurements were performed by standard methods. A surface map of each metabolic and perfusion measurement in the cortical mantle was generated by interpolating between the available slices. The various surface maps representing the physiological characteristics determined in the same or subsequent studies were aligned so that all data sets could be analyzed identically using an array of square regions of interest (ROIs). The functional status of each ROI was recorded at the two intervals following the cerebrovascular accident to characterize the evolution of the infarct, penumbra, and normal brain regions. We presumed the ischemic penumbra to be cortical regions in the proximity of the infarct and perfused at CBF values between 12 and 18 ml/100 g/min on the first PET scan, while densely ischemic regions had CBF of less than 12 nl/100 g/min and normally perfused brain greater than 18 ml/100 g/min. In the densely ischemic zone, CBF increased more in the nimodipine-treated group than in the carrier group. As well, in this region nimodipine reversed the decline in CMRO2 noted in the carrier group, the difference in the changes being significant. In the penumbra zone, comparable trends were noted in OER and CMRO2 but the difference in the changes between the two groups did not reach statistical significance. Changes in CMRglc and CBV were comparable between the two groups in both cortical regions.

Cerebrovascular autoregulation is resistant to calcium channel blockade with nimodipine

In normal baboons cerebrovascular resistance changed along with blood pressure to maintain blood flow constant. This 'autoregulation' was not significantly altered in animals treated with a dose of the calcium channel blocker nimodipine causing selective cerebral vasodilation.

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.

Nimodipine prevents hyperglycemia-induced cerebral acidosis in middle cerebral artery occluded rats

The effects of acute moderate hyperglycemia on local cerebral pH (LCpH) and local cerebral blood flow (LCBF) were studied in rats infused with glucose before middle cerebral artery (MCA) occlusion, and compared with findings in MCA occlusion alone. The effects of nimodipine infusion on LCBF and LCpH in MCA-occluded hyperglycemic rats were also studied. LCpH and LCBF were determined simultaneously by a double-label autoradiographic technique. Hyperglycemia was induced by an intraperitoneal injection of 2 g/kg D-glucose before MCA occlusion. Nimodipine-treated rats received the drug as an intravenous infusion of 0.5 micrograms/kg/min starting 15 min after occlusion, and ending at decapitation 4 h postocclusion. Cortical LCpH of five structures in the MCA territory of hyperglycemic rats varied between 6.64 +/- 0.04 and 6.72 +/- 0.02 (mean +/- SEM). These values were significantly lower than LCpH in the same ischemic structures in the control rats, which varied between 6.76 +/- 0.04 and 6.82 +/- 0.03 (p less than 0.05 for four of five structures). Cortical LCpH of hyperglycemic nimodipine-treated rats ranged between 6.94 +/- 0.02 and 7.05 +/- 0.02, indicating significant elevations in LCpH (p less than 0.001) compared with the untreated ischemic hyperglycemic animals. LCBF in the ischemic structures was not modified by hyperglycemia or nimodipine treatment. This suggests that nimodipine, by mechanisms other than improvement in blood flow, can prevent the enhanced cerebral tissue acidosis produced by hyperglycemia before incomplete focal ischemia.

Effect of nimodipine-associated hypotension on recovery from acute spinal cord injury in cats

The effect of nimodipine on acute spinal cord trauma was studied in cats. Spinal evoked responses (SERs) were abolished after weight drop injury of 100 g-cm. All control animals showed spontaneous recovery of spinal cord function as measured by SERs. Treatment with a moderate intravenous dose of nimodipine resulted in a 32% drop in systemic blood pressure and delay in or failure of spinal cord recovery. We concluded that in this model, nimodipine treatment had deleterious effect on the spinal cord recovery due to the significant associated hypotension. It is likely that marked hypotension in the case of traumatic loss of autoregulation overrides the expected nimodipine-related increase in spinal cord blood flow with resultant additional ischemic damage.

Pharmacology of nimodipine. A review

The major pharmacological findings with nimodipine reviewed in this chapter are summarized in TABLE 3. On the basis of these findings, the following conclusions appear to be justified: 1. Nimodipine is a 1,4-dihydropyridine with Ca2+ channel antagonist properties. It is more lipophilic than nifedipine and its distribution volume in the brain of rats is higher than that of nifedipine. 2. Nimodipine dilates cerebral vessels at considerably lower concentrations than required for dilatation of peripheral blood vessels. It can, therefore, improve cerebral blood flow at doses that do not reduce systemic arterial pressure. 3. Nimodipine inhibits 45Ca uptake into vascular smooth muscle and neuronal cells. 4. Nimodipine antagonized postischemic cerebral hypoperfusion in cats and prolonged life of stroke-prone spontaneously hypertensive (SH) rats at doses that have little if any effect on arterial blood pressure. 5. Nimodipine reduced neurological deficits in dogs and monkeys with global cerebral ischemia. In focal ischemia (MCA occlusion) nimodipine reduced infarct size and neurological deficits and normalized intracellular brain pH. 6. In addition to its cerebral vasodilator effect, nimodipine appears to have a direct neuronal action. The suggested evidence for the neuronal site of action of nimodipine includes: a. Presence of nimodipine binding sites in brain. b. Blockade by nimodipine of Ca2+ channels in single nerve cells and in endocrine cells under conditions of sustained depolarization. c. Interactions with centrally acting drugs. d. Effects on release of various neurotransmitters from neuronal tissue or endocrine cells. e. Demonstration of anticonvulsant action of nimodipine. f. Blockade of behavioral effects of Ca2+ channel agonists by calcium channel antagonists.

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.

Effects of the calcium antagonist NB-818 on cerebral blood flow

The effects of intravenous injection of NB-818, isopropyl methyl 2-carbamoyloxymethyl-6-methyl-4-(2,3-dichlorophenyl)-1,4-dihydropyridine-3,5- dicarboxylate, on regional cerebral blood flow were studied in rabbits and Rhesus monkeys, using the hydrogen clearance technique. The above effects were compared with those of nicardipine and nimodipine. In rabbits, NB-818 (10 micrograms/kg i.v.) increased both cerebral cortical blood flow (rCBF) and cerebellar cortical blood flow by about 80% of the predrug level with a moderate decrease in mean arterial blood pressure, and no increase in skeletal muscle blood flow. The increase in cerebral blood flow with NB-818 was as great as that with nicardipine or nimodipine. In Rhesus monkeys, NB-818 (10-20 micrograms/kg i.v.) increased rCBF by about 30% of the predrug level, and its effect continued 30-60 min after dosing. The increase in rCBF with NB-818 was greater than that with nicardipine. The results from the present study indicate that NB-818 predominantly increases rCBF with a concomitant moderate hypotension, and its action is greater than that of nicardipine or nimodipine.

The effect of nimodipine on intracranial pressure. Volume-pressure studies in a primate model

Nimodipine was administered by intravenous infusion to six male baboons before, during, and after 6 hours of middle cerebral artery occlusion. Intracranial pressure (ICP) and systemic blood pressure were monitored continuously. An epidural balloon was inflated at regular intervals at three levels of arterial CO2 tension (25, 35, and 50 mm Hg) before and after the administration of nimodipine, and volume-pressure curves were generated. In every case, curves generated after intravenous nimodipine infusion were lower and shifted more to the right than the same set of curves generated before nimodipine administration, regardless of the baseline ICP. The reduction in ICP following nimodipine infusion was not due to a reduction in mean arterial blood pressure and was statistically significant at all three levels of pCO2 (p less than 0.01). These results suggest that, in the presence of elevated ICP due to cerebral infarction, there is no increased risk of exacerbating intracranial hypertension with the addition of nimodipine.

Effects of calcium entry blocker emopamil on postischemic energy metabolism of the isolated perfused rat brain

The effects of emopamil on postischemic energy metabolism and electroencephalographic (EEG) recovery were investigated in the isolated rat brain perfused at either constant pressure or, alternatively, at constant flow rate. Flow rate and perfusion pressure were monitored continuously. The brains were perfused with a fluorocarbon emulsion for 30 min, and after 30 min of ischemia, perfusion was reinstituted for 5, 30, or 60 min. Global cerebral perfusion rate was increased by emopamil throughout the perfusion period and, accordingly, in brains perfused at a constant flow rate, perfusion pressure was reduced by the drug. At constant pressure perfusion, after 5 min after ischemia, cortical levels of creatine-phosphate, adenosine triphosphate (ATR), glucose, glucose-6-phosphate, and fructose-6-phosphate were higher in emopamil-treated brains than in controls, although the levels of adenosine diphosphate (ADP) and adenosine monophosphate (AMP) were reduced. When brains were perfused at constant flow rate, however, emopamil exhibited no effect on brain energy metabolism in the early reperfusion period. Postischemic restoration of high-energy phosphates proved to depend on the flow rate used. After 30 min of postischemic reperfusion, cortical levels of lactate were lower in emopamil-treated brains compared to controls at both constant pressure and constant volume perfusion. Postischemic lactate levels were independent of flow rate and were also reduced when emopamil was only present during reperfusion. The postischemic restoration of cortical EEG activity was improved by the calcium entry blocker.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypercholesterolemia and the baboon cerebral circulation

We investigated cerebrovascular vasodilator responses to increased arterial CO2 and the cerebrovascular response to infused 5-hydroxytryptamine (5-HT) in normal and hypercholesterolemic baboons. After 6-8 weeks of feeding an atherogenic diet the plasma cholesterol levels were increased without change in the triglycerides. The hypercholesterolemic animals showed a higher basal systemic arterial blood pressure than the normal controls without significant decrease in cerebrovascular prostacyclin production, altered basal cerebral blood flow or altered cerebrovascular response to infused 5-HT. However, the vasodilator response to hypercapnia was significantly decreased from the control value of 2.78 ml/min per mmHg increase in PCO2, to 1.62 ml/min per mmHg. Thus functional impairment of cerebral hemodynamics occurred before atherosclerotic alteration in the cerebral vessels could have been present.

Effect of a calcium channel blocker on posttraumatic spinal cord blood flow

The normal rat spinal cord blood flow (SCBF) has been shown to increase after administration of nimodipine, a calcium channel blocker. The present study investigates the capability of nimodipine to improve SCBF, as measured by the hydrogen clearance technique, after a 53.0-gm clip compression injury to the T-1 segment of the rat spinal cord. The profound drop in mean systemic arterial blood pressure (MSAP) after cervical cord injury precluded any improvement in posttraumatic SCBF by nimodipine alone. Hence, in a randomized controlled study with five rats per group, pressor agents (whole blood, angiotensin, or adrenaline) were infused to maintain MSAP between 100 and 120 mm Hg after injury. Control animals received only a saline infusion. Nimodipine at the optimal dose found in normal animals (1.5 microgram/kg/min) was added to the pressor agents. The MSAP and other physiological parameters were measured in rats receiving the pressor agents only and in those receiving pressor agents combined with nimodipine. In rats receiving whole blood, angiotensin, or adrenaline the posttraumatic MSAP improved to between 100 and 120 mm Hg, but there was no improvement in SCBF compared to the saline group. The addition of nimodipine decreased MSAP and SCBF in all groups except those animals also receiving adrenaline, where the MSAP was maintained at 109 +/- 5 mm Hg. In these animals a significant increase in posttraumatic SCBF from 16.5 +/- 2.1 to 20.2 +/- 2.3 ml/100 gm/min (mean +/- standard error of the mean) occurred at the site of injury with the addition of nimodipine. The maintenance of an adequate MSAP by a pressor agent was crucial for nimodipine to improve posttraumatic SCBF by its ability to dilate the spinal vascular bed. Adrenaline was the only pressor agent that could fulfill the above criteria, although other pressor agents need to be investigated. Experiments are underway with the combination of adrenaline and nimodipine to further verify these encouraging results demonstrating an improvement in posttraumatic ischemia of the spinal cord.

Cerebrovascular and metabolic changes during the delayed vasospasm following experimental subarachnoid hemorrhage in baboons, and treatment with a calcium antagonist

A model has been designed in baboons for simulating the clinical situation during the late phase of vasospasm in patients with subarachnoid hemorrhage (SAH). A total amount of 14-33 ml autologous blood was injected into the cisternal system on 3 occasions in the course of 4 days. Neurological symptoms were seen, and the mortality rate was 29%. Angiography 3 days after the last injection showed arterial vasoconstriction amounting to 23% in the vertebro-basilar system, and 11% (right) and 18% (left) in the carotid system. Cerebral blood flow (CBF) measured by the intra-arterial 133Xe technique and the cerebral metabolic rate of oxygen (CMRO2) were reduced by 18% and 11%, respectively. The hypercapnic CBF response was significantly impaired, from a mean of 3.90 ml/100 g/min to 1.72 ml/100 g/min of flow increase for each mm Hg elevation of paCO2. Autoregulation, tested by administration of angiotensin II, was also significantly affected as evidenced by a pressure-dependent increment of CBF during hypertension in 5 out of 7 animals tested. The impaired autoregulation was reflected in the autoregulatory index, which in the whole group increased from 0.06 ml/100 g/min for each mm Hg increase in MABP in the pre-SAH animals to 0.29 ml/100 g/min per mm Hg post-SAH. Treatment with the calcium antagonist, nimodipine (0.5 microgram/kg/min i.v. during 45 min), enhanced CBF significantly by 17% before experimental SAH, whereas after SAH the effect was slight and did not reach statistical significance; CMRO2 was not significantly affected in either group. Intravenous nimodipine combined with hypertension resulted in a marked increase in the autoregulatory index to 1.58 ml/100 g/min per mm Hg in pre-SAH animals and a less pronounced increment to 0.58 ml/100 g/min per mm Hg following experimental SAH. The beneficial effect of nimodipine reported in SAH patients is therefore, in view of our findings, more likely due primarily to a protective mechanism at the cellular level than to an influence on the vascular bed.

The effects of nimodipine on cerebral blood flow and metabolism

Nimodipine, a calcium entry blocker, was administered in increasing doses of 0.1-3.0 micrograms kg-1 min-1 to six dogs after they had recovered consciousness from a surgical preparation that was conducted under general anesthesia and while they were under the influence of total spinal anesthesia. CBF was measured with a sagittal sinus outflow technique and CMRO2 was calculated as the product of CBF and the arteriovenous O2 difference. Nimodipine did not influence either CBF or CMRO2. There was a decrease in the cortical pyruvate level at the end of the study, but no significant change in phosphocreatine, ATP, lactate, or energy charge when compared with six control dogs. It has previously been reported that nimodipine increases the CBF in global ischemia with a potentially beneficial effect on the neurological outcome. With no effect on normal CBF or metabolism, this suggests that nimodipine may be useful in a variety of ischemic situations without fear of either a steal phenomenon or untoward effects on intracranial pressure.

Cerebral acidosis in focal ischemia: II. Nimodipine and verapamil normalize cerebral pH following middle cerebral artery occlusion in the rat

The effects of prostacyclin, nimodipine, and verapamil on local cerebral pH (LCpH) and CBF (LCBF) in middle cerebral artery (MCA)-occluded rats were compared with those in controls and others receiving nimodipine carrier. LCpH and LCBF were determined simultaneously by a double-label autoradiographic technique. The infusions were intravenous, started 15 min following the occlusion, and ended at decapitation 4 h postocclusion. The dosages were 0.5 micrograms/kg/min for nimodipine, 40 micrograms/kg/min for verapamil, and 5 ng/kg/min for prostacyclin. Cortical LCpH in the MCA territory of control and carrier-infused rats varied between 6.72 +/- 0.05 and 6.76 +/- 0.05 (means +/- SEM). These values were significantly lower than the LCpH in the same structures in the contralateral hemisphere (7.09 +/- 0.06; p less than 0.05). LCBF on the side of occlusion varied between 54 +/- 5 ml/100 g/min for the parietal and 57 +/- 7 ml/100 g/min for the sensorimotor cortex, while on the contralateral side, LCBF in these same structures was 190 +/- 18 and 191 +/- 4 ml/100 g/min, respectively. LCpH was not modified by prostacyclin treatment following MCA occlusion, but the pH in the structures that were acidotic in the controls became indistinguishable from contralateral values in nimodipine- and verapamil-treated animals. In contrast, LCBF was statistically higher than controls in many structures only in rats treated with prostacyclin. This suggested that the correction of LCpH produced by calcium blockers was not related to an effect they had on blood flow. Animals receiving calcium blockers tended to have smaller areas of infarction. These results may have therapeutic implications in cerebral ischemia.

Effects of two dihydropyridine calcium channel blockers on cerebral metabolism and blood flow in traumatized rat brain

The effect of two dihydropyridine calcium (Ca) channel blocking drugs on cerebral glucose metabolism (LCGU), blood flow (LCBF), and blood flow-metabolism coupling were studied in thermally injured rat brain using quantitative radioautographic techniques. No reversal of the previously noted LCGU depression caused by the freezing lesion (Pappius, 1981) was detected following treatment with either PY-108-068 (PY) or nimodipine (NIM). These results therefore provided no support for the role of Ca in the mechanism of functional disturbances induced by cold injury (Pappius and Wolfe, 1983b), though they do not rule out its involvement. Treatment with PY, but not NIM, reestablished the normal LCBF-LCGU relationship in cortical areas, which has been shown to be disturbed by the freezing lesion and in subcortical and brainstem structures, in which the alteration caused by the injury was not as pronounced. The results suggest that the mechanism that apparently uncouples LCBF from LCGU in injured brain is altered in the presence of PY. However, since NIM did not have the same effect on LCBF, it is not clear whether the effects of PY relate to blockade of Ca channels or some other effect of PY.

Nimodipine-induced changes in the distribution of carotid blood flow and cardiac output in pentobarbitone-anaesthetized pigs

In view of the claimed effectiveness of nimodipine in migraine and its possible selectivity for cerebral vessels, we investigated the effects of nimodipine in anaesthetized pigs on the fractionation of carotid arterial blood flow into non-nutrient (arteriovenous anastomoses; AVAs) and nutrient (capillary) parts, and on regional tissue blood flows and vascular conductances. Intracarotid infusions of nimodipine (0.05-1.25 microgram kg-1 min-1) redistributed carotid blood flow in favour of its nutrient compartment, particularly to the skeletal muscles and tongue. Vascular conductance in the non-nutrient (AVAs) compartment decreased (40%), most likely, as a result of 'steal' following profound (5.5 fold) arteriolar dilatation. Intravenous infusions of nimodipine (0.05-6.25 micrograms kg-1 min-1) caused hypotension, bradycardia, a decrease in conduction in the non-nutrient fraction, and an increase in conduction in the nutrient fraction (mostly in the skeletal muscles, but also in the gastrointestinal tract, cerebral hemispheres, heart and adrenals). Probably due to the hypotensive effect, only skeletal muscle blood flow increased. The nimodipine-induced increase in vascular conductance in the skeletal muscles showed regional variation; the effect was most pronounced in the cheek muscles, followed by the muscles of the chest, abdominal, trunk and gluteal regions. We conclude that: AVA flow seems to represent a 'reserve' perfusion which can be readily diverted to tissues in the case of increased metabolism and/or vasodilatation, though the overall response to nimodipine of carotid blood flow distribution qualitatively resembles that to some antimigraine drugs, the relevance of such acute effects in the prophylactic usefulness of nimodipine in migraine remains to be ascertained, and nimodipine lacks a selective cerebral vasodilator action in the anaesthetized pig.

Nimodipine and early aneurysm operation in good condition SAH patients

A prospective open multicenter study on the preventive effect of nimodipine on symptomatic vascular spasm was performed in 120 (consecutive) patients with aneurysmal subarachnoid haemorrhage (SAH). All patients underwent early surgery (i.e. within 72 hours post SAH) and were in neurological grades I-III in Hunt and Hess. Grade IV and V as well as patients with significant intracerebral haematoma are not included. On preoperative CT, SAH was mild in 28 cases, moderate in 56 and severe in 36 cases. 25 patients (21%) were in grade I, 63 patients (53%) in grade II and 32 patients (26%) in grade III. The ruptured aneurysm was located on the anterior cerebral artery complex in 57 patients, on the internal carotid artery complex in 35, on the middle cerebral artery in 24 patients and on the basilar artery in 4 patients. After occlusion of the ruptured aneurysm, the lipophilic calcium channel blocker nimodipine was administered in the following manner: Intraoperative, topical irrigation of the exposed arteries. Intravenous infusion until day 7-14 after SAH followed by peroral medication for another week. Nimodipine was well tolerated and neither significant hypotension nor any other adverse reaction attributable to the drug was observed. Ischaemic cerebral dysfunction of delayed onset with permanent neurological deficit occurred in 2 patients (2%). Another 8 patients showed transient ischaemic symptoms. At 6 months follow-up, 93% of the patients were classified as having made a full recovery, 16% as being minimally disabled, 5% as being moderately disabled and 3% as being severely disabled. Three patients had died. The present study supports the concept that preventive nimodipine treatment may reduce delayed ischaemic deficit in early aneurysm surgery.

Increase in rat spinal cord blood flow with the calcium channel blocker, nimodipine

Nimodipine, a calcium channel blocker, is known to increase cerebral blood flow. In the present study, the authors investigated the effect of nimodipine on spinal cord blood flow in normal rats. Cardiovascular parameters, including mean systemic arterial blood pressure, cardiac output, and heart rate, were recorded during infusion of nimodipine in a dose-response fashion. The experiment was a randomized blind study in which four groups of five rats received different doses of nimodipine (0.001, 0.01, 0.05, and 0.10 mg/kg) intravenously over 30 minutes, and a control group of five rats received only the diluent. The hydrogen clearance and thermodilution techniques were used to measure spinal cord blood flow and cardiac output, respectively. The 0.05-mg/kg dose of nimodipine caused the largest increase in spinal cord blood flow, with a 40% increase over the preinfusion level, although there was a 25% reduction in mean arterial pressure. The 0.10-mg/kg dose did not increase spinal cord blood flow more than the 0.05-mg/kg dose, most likely due to the concomitant 37% reduction in mean arterial pressure. Cardiac output was significantly increased by the 0.05- and 0.10-mg/kg doses secondary to the drop in total peripheral resistance. The increase in spinal cord blood flow produced by nimodipine lasted approximately 20 minutes after the termination of the infusion. Thus, nimodipine at a dose of 0.05 mg/kg markedly increased blood flow in the normal spinal cord even though there were major changes in mean systemic arterial pressure and cardiac output. Further research is required to determine whether this drug might be beneficial in treating ischemic states of the spinal cord, such as posttraumatic ischemia.

Evaluation of the efficacy of intrathecal nimodipine in canine models of chronic cerebral vasospasm

Previous studies have examined whether calcium antagonists given sublingually, intravenously, or orally affect an experimentally induced vasospasm. This study was designed primarily to determine the efficacy of nimodipine given intracisternally in reversing the cerebral vasospasm produced in dogs by the injection of 4 ml of autogenous blood into the cisterna magna. The magnitude of the vasospasm and the vascular response to nimodipine were determined arteriographically. One group of animals was studied acutely to determine the dose and pharmacodynamic effects of intrathecal nimodipine, a second group was studied 1 to 4 days after the intrathecal injection of blood, and a third group was studied 3 to 6 days after successive injections of cisternal blood given 48 hours apart. Some animals were studied further 24 hours after the nimodipine treatment. Intrathecal administration of 4 ml of 10(-3) M nimodipine promptly and completely reversed the cerebral vasospasm in all groups. This effect lasted at least 4 hours but had disappeared by 24 hours. The intrathecal administration of nimodipine produced a transient drop in blood pressure. In contrast, nimodipine given sublingually (0.28 to 0.58 mg/kg) or intravenously (0.1 mg/kg) produced a persistent hypotensive effect without affecting the vasospasm. The results show that the presence of nimodipine in the cerebrospinal fluid will reverse the blood-induced vasospasm, and suggest that this calcium antagonist administered intrathecally would be an effective emergency treatment of cerebral arterial spasm.