Effect of nimodipine on cerebral blood flow and metabolism in rats during hyperventilation

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.

Role of Pharmacokinetic Effects in the Potentiation of Morphine Analgesia by L-Type Calcium Channel Blockers in Mice

The present study was designed to investigate the pharmacokinetic interaction of morphine with three classes of L-type calcium channel blockers (CCB) and its relationship to morphine-induced mechanical antinociception in mice. The CCB classes were benzothiazepine (diltiazem), dihydropyridine (nimodipine), and phenylalkylamine (verapamil). Each of the three classes of L-type CCB (diltiazem, 40 and 80 mg/kg; nimodipine, 40 mg/kg; verapamil, 40 mg/kg), when administered prior to morphine (4 mg/kg, s.c.), potentiated the analgesic effect of morphine and markedly increased the level of morphine in serum. Pretreatment with diltiazem (40 and 80 mg/kg) and verapamil (40 mg/kg) also increased morphine level in the brain. However, these drugs produced less increase in morphine level in the brain than they produced in serum (i.e., they decreased the brain-to-serum ratio of morphine). Pretreatment with nimodipine (40 mg/kg) did not affect the morphine level in the brain and also decreased the brain-to-serum ratio of morphine. When morphine (3.2-100 mg/kg, s.c.) was injected alone, the brain-to-serum ratio of morphine was constant, regardless of the morphine dose. These results suggest that increases in morphine concentration in peripheral blood may be, at least in part, involved in the ability of L-type CCBs to potentiate the analgesic effect of morphine.

Reduced field response to perforant path stimulation after adrenalectomy: effect of nimodipine treatment

Adrenalectomy enhances apoptosis in the rat dentate gyrus and concurrently decreases the field response of dentate cells to perforant path stimulation. Recent data showed that calcium current amplitude is increased 1 day prior to the appearance of apoptotic cells, pointing to calcium as a risk factor for the onset of apoptosis. We here tested if in vivo administration of nimodipine-thus presumably reducing dentate calcium influx through L type calcium channels-prevents the appearance of apoptotic cells and the change in field responses after adrenalectomy. It was found that nimodipine does not largely alter the number of animals with apoptosis nor the average number of apoptotic cells in the tip of the suprapyramidal blade of the dentate gyrus. After nimodipine treatment, field responses in the dentate gyrus of adrenalectomized rats were comparable to responses in adrenally intact rats. However, this was due to a reduction of the field response in slices from adrenally intact rats, rather than a prevention of synaptic impairment in adrenalectomized rats. The data clearly indicates that in vivo nimodipine treatment is insufficient to prevent apoptosis and synaptic impairment after adrenalectomy.

Nimodipine improves brain energy metabolism and blood rheology during ischemia and reperfusion in the gerbil brain

Whether nimodipine improves cerebral blood flow (CBF) and metabolism in cerebral ischemia remains a controversial issue. We investigated the effect of nimodipine on CBF, brain energy metabolism, using a laser-Doppler flowmeter and in vivo 31phosphorus nuclear magnetic resonance (31P NMR) spectroscopy, and blood rheology during forebrain ischemia and reperfusion in gerbils. Eighty-three adult gerbils received nimodipine (1 micrograms/kg/min), or an equal volume of the vehicle, or saline, over 60 min prior to a transient forebrain ischemia for 60 min. We measured sequential changes in phosphocreatine (PCr) / inorganic phosphate (Pi) ratio, beta-ATP/Pi ratio, and intracellular pH (pHi) during ischemia and reperfusion by 31P NMR spectroscopy, and the measurement of whole blood viscosity (WBV) at 60 min after reperfusion. CBF was measured continuously throughout the study by a laser-Doppler flowmeter. During forebrain ischemia, PCr/Pi and beta-ATP/Pi ratios were higher significantly in the nimodipine-treated group (p < 0.05 and 0.01) than in the vehicle- or saline-treated groups. During reperfusion, PCr/Pi and beta-ATP/Pi ratios recovered significantly only in the nimodipine-treated group (p < 0.05 and 0.01). The WBV at high shear rate (562.5 s-1) lowered significantly in the nimodipine-treated group (p < 0.05) compared with the vehicle- or saline-treated group. CBF was higher significantly only during administration of nimodipine in the nimodipine-treated group (p < 0.01) than other groups. Nimodipine improved brain energy metabolism and blood rheology during forebrain ischemia and reperfusion in the gerbil brain.

The effect of nimodipine on autoregulation of cerebral blood flow after subarachnoid haemorrhage in rat

Disturbance of the autoregulation of the cerebral blood flow (CBF) is frequently seen following subarachnoid haemorrhage (SAH) and is possibly partly caused by cerebral ischaemia. It is well-known, that the calcium channel blocker nimodipine reduces the incidence of cerebral infarction and ischaemic dysfunction after SAH. The aim of the present study was to investigate the effect of nimodipine on autoregulation of CBF in an experimental model of SAH. The autoregulation was investigated in 10 control rats with SAH and in 10 nimodipine treated rats with SAH by serial measurements of CBF using a 133Xenon intracarotid injection method during controlled blood pressure manipulations. In the control rats the autoregulation was severely disturbed, no plateau was found where CBF was independent of changes in the arterial blood pressure (MABP). In rats treated with intravenous nimodipine (0.03 mg/kg body weight/h), CBF was 33.0% higher and MABP 5.3% higher compared with the controls. CBF was found constant in the MABP interval between 60 and 100 mmHg which indicates, that nimodipine improves the autoregulation of CBF after SAH.

A review of brain retraction and recommendations for minimizing intraoperative brain injury

Brain retraction is required for adequate exposure during many intracranial procedures. The incidence of contusion or infarction from overzealous brain retraction is probably 10% in cranial base procedures and 5% in intracranial aneurysm procedures. The literature on brain retraction injury is reviewed, with particular attention to the use of intermittent retraction. Intraoperative monitoring techniques--brain electrical activity, cerebral blood flow, and brain retraction pressure--are evaluated. Various intraoperative interventions--anesthetic agents, positioning, cerebrospinal fluid drainage, operative approaches involving bone resection or osteotomy, hyperventilation, induced hypotension, induced hypertension, mannitol, and nimodipine--are assessed with regard to their effects on brain retraction. Because brain retraction injury, like other forms of focal cerebral ischemia, is multifactorial in its origins, a multifaceted approach probably will be most advantageous in minimizing retraction injury. Recommendations for operative management of cases involving significant brain retraction are made. These recommendations optimize the following goals: anesthesia and metabolic depression, improvement in cerebral blood flow and calcium channel blockade, intraoperative monitoring, and operative exposure and retraction efficacy. Through a combination of judicious retraction, appropriate anesthetic and pharmacological management, and aggressive intraoperative monitoring, brain retraction should become a much less common source of morbidity in the future.

A trial of the effect of nimodipine on outcome after head injury

We performed a randomised prospective double blind trial to study the effect of the calcium antagonist nimodipine on the outcome of head injured patients. The subjects were not obeying commands at the time of entry to the study, within 24 hours of injury. One hundred and seventy-five patients received nimodipine IV, 2 mg per hour for up to 7 days and 176 received placebo. The two groups were well matched for important prognostic features. Six months after injury 93 (53%) of the nimodipine group and 86 (49%) of the control group had a favourable outcome (moderate/good recovery). The relative increase in favourable outcomes (8%) was not significant but is compatible (95% C.I.) with an increase in favourable outcomes in treated patients by 33% or a decrease by 12%. Nimodipine was well tolerated and there were few adverse reactions; means of systolic and diastolic blood pressures and the intracranial pressure did not differ between the groups. It is unlikely that nimodipine has a marked effect on outcome (ie an increase in favourable outcome of greater than 15%) after head injury of this severity but the study does not exclude a modest but clinically useful benefit.

Cerebral blood flow with the indicator fractionation of [14C]iodoantipyrine: effect of PaCO2 on cerebral venous appearance time

The indicator fractionation technique using a diffusible indicator as a tracer for the determination of CBF has been used for numerous investigations of the cerebral circulation and its pathophysiology. The diffusible tracer is "trapped" in the brain based on the proper delay between tracer injection and cessation of the cerebral circulation by decapitation before the appearance of the tracer in the cerebral venous circulation. If this delay is too long, the quantitative assumption of the indicator fractionation technique will not be met, and CBF values will be underestimated. In 13 Sprague-Dawley rats anesthetized with pentobarbital, the appearance of [14C]iodoantipyrine at the torcular was assessed as a function of PaCO2. An inverse linear relationship between PaCO2 (in millimeters of mercury) and cerebral venous appearance, Ta (in seconds), was established with the regression equation Ta = -0.0842.PaCO2 + 12.3 (R2 = 0.70, slope significantly different from zero, p less than 0.001). Ta varied between 5 and 12 s and PaCO2 varied between 84 and 18 mm Hg, respectively. Thus, in low-flow states, the decapitation time may be lengthened to 12 s, whereas in high-flow states, the time must be 5 s to eliminate the possibility of backflux of tracer out of the brain.

Synergistic internal carotid vasodilator effects of human alpha-calcitonin gene-related peptide and nimodipine in conscious rats

1. In a first series of experiments, male Long Evans rats were chronically instrumented for the measurement of internal carotid blood flow and systemic arterial blood pressure; cardiovascular changes were assessed during and after 30 min infusions of human alpha-calcitonin gene-related peptide (CGRP) (0.06 and 0.6 nmol h-1), or nimodipine (60 and 600 nmol h-1) or human alpha-CGRP plus nimodipine. The effects of human alpha-CGRP or nimodipine on internal carotid vasoconstriction induced by endothelin-1 were also measured. 2. Human alpha-CGRP (0.06 nmol h-1) caused a small (+15%), transient increase in internal carotid blood flow and a tachycardia (+33 beats min-1), but no change in mean blood pressure. Nimodipine (60 nmol h-1) caused a brief internal carotid hyperaemia (+16%) but no changes in blood pressure or heart rate. However, concurrent administration of human alpha-CGRP (0.06 nmol h-1) and nimodipine (60 nmol h-1) caused a sustained increase in internal carotid blood flow (+40%) unaccompanied by significant changes in heart rate or blood pressure. 3. Human alpha-CGRP at a dose of 0.6 nmol h-1 or nimodipine at a dose of 600 nmol h-1 caused substantial reductions in internal carotid vascular resistance (-43 and -40%, respectively); concurrent administration of these doses did not have an additive vasodilator effect. 4. Infusion of endothelin-1 (1.2nmolhV1) for 20min caused incremental constriction of the internal carotid vascular bed; human alpha-CGRP infusion (0.6 and 6.0nmolh-1) begun tOmin after the onset of endothelin-1 infusion reversed this effect (dose-dependently); nimodipine (600nmolh-1) also caused a substantial attenuation of the effects of endothelin-1. 5. In a second series of experiments the haemodynamic effects of human alpha-CGRP and/or nimodipine were assessed in rats chronically instrumented for the measurement of renal, superior mesenteric and hindquarters blood flow together with systemic arterial blood pressure. 6. Administration of human alpha-CGRP (0.06 nmol h-') alone or in conjuction with nimodipine (60nmolh-1) had no significant effects on renal or superior mesenteric vascular resistances, although there was a slight hindquarters vasodilatation. Human alpha-CGRP at a dose of 0.6 nmol -1 caused hypotension, tachycardia and reductions in renal and superior mesenteric blood flows, together with a marked (+31% maximum) hindquarters hyperaemia. Nimodipine at a dose of 600 nmol h-1 caused hypotension, tachycardia and a reduction (-34%) in renal blood flow; mesenteric blood flow was unchanged and there was an increase in hindquarters flow (+ 59%). 7. Concurrent administration of human alpha-CGRP (0.6 nmol h 1) and nimodipine (600 nmol h') did not have an additive hypotensive effect or an enhanced hindquarters hyperaemic effect, but was associated with a marked impairment of renal blood flow (-48%). 8. The present results indicate that concurrent administration of low doses of human alpha-CGRP and nimodipine might be particularly helpful in the acute treatment of patients with cerebral vasospasm and impaired renal perfusion, since this intervention improved internal carotid blood flow without compromising blood flow to the kidney.