[Effect of Ca2+ antagonists on experimental cerebral vasospasm (author's transl)]

Slow channel inhibitor effects on brain function: tolerance to severe hypoxia in the rat

1. The protective effects of ten slow channel inhibitor drugs against severe progressive hypoxia were investigated in rats breathing spontaneously during light anaesthesia. Respiration, heart rate, electrocorticogram (ECoG) and/or electroencephalogram (EEG) were recorded. 2. Tolerance times were monitored from hypoxia onset until cessation of respiration, ECoG, EEG synchronization, and 'background-EEG'. Drugs were administered i.v. 5 min before the onset of hypoxia. 3. Verapamil, gallopamil, and nimodipine resulted in a significant increase of tolerance times; fendiline and bepridil showed a small increase (not significant); bencyclan and prenylamine were ineffective; cinnarizine and diltiazem slightly reduced tolerance times as did flunarizine at low doses. 4. At protective doses, verapamil, gallopamil, and nimodipine significantly raised the respiration rate but had little or no cardiac depressor effects. Bencyclan showed ventilatory drive but cardiocirculatory depression. A clear-cut ventilatory drive did not occur with the other ineffective slow channel inhibitors. 5. It is suggested that the protective actions observed were not due to slow channel inhibition per se, nor to spasmolytic potency or increased cerebral blood flow. Ventilatory drive associated with other cardiopulmonary actions which secondarily raise the brain oxygen supply are likely to be responsible for this effect.

Intracarotid slow bolus injection of nimodipine during angiography for treatment of cerebral vasospasm after SAH. A preliminary report

Nimodipine was given as an intracarotid slow bolus injection in six patients with subarachnoid hemorrhage (SAH) due to rupture of a cerebral aneurysm, with angiographically demonstrated vasospasm. The patients were followed by serial angiograms for demonstration of the effect of nimodipine on vasospasm. After angiography, all patients were treated with a constant venous infusion of this new calcium antagonist. Although the therapeutic regimen was started only a few hours after onset of vasospasm, there was no change in cerebral vessel caliber detectable on angiograms following the intracarotid injection. Three patients died, two patients finally recovered with neurological deficits due to cerebral ischemia, and one patient with asymptomatic vasospasm remained symptom-free. Although nimodipine may act to prevent cerebral vasospasm after SAH, the authors believe that the intracarotid application is not effective after vasospasm has occurred.

The pathophysiology of cerebral vasospasm, and pharmacological approaches to its management

Numerous neurotransmitters, autocoids, and blood constituents or breakdown products have been shown to constrict the cerebral vasculature, and have therefore been implicated in the aetiology of cerebral vasospasm. Substances in combination may also act synergistically. Because of the multifactorial causes of vasospasm, the main causative agent may also be different in various subgroups of patients, leading to differential sensitivities to potential treatments. The contraction of vascular smooth muscle is ultimately caused by an increase in the intracellular concentration of free calcium ions. Mechanical, osmotic, or ischaemic trauma may also result in calcium overloading with development of contracture. Many "rational" pharmacological approaches to the treatment of vasospasm have been proposed, but clinical experience has so far been disappointing; agents active against only one possible causative factor may possess too specific a mechanism of action to control spasm caused by several agents simultaneously. A new group of drugs, the calcium antagonists, has selective and potent relaxant actions against the contractions of cerebral vessels produced by a wide range of agonists. They may be of therapeutic use in both the prophylaxis and treatment of cerebral vasospasm.

Calcium ions and calcium antagonists in ischaemia

The effects of a calcium antagonist, nimodipine, were tested on the response of the cerebral circulation to arterial pCO2 and blood pressure changes. The effects of reduced blood flow upon oedema formation and extracellular ion homeostasis under nimodipine preloading were studied. Both open and closed skull primate models were used, with alpha-chloralose anaesthesia. Nimodipine infusion increased basal blood flow in the open skull, but not the closed skull animals. Autoregulation to increased blood pressure was little affected. Responses to arterial pCO2 changes and autoregulation to reduced blood pressure were severely impaired. Residual blood flow after middle cerebral artery occlusion was significantly higher with nimodipine than in controls. The threshold levels of blood flow for the development of cortical oedema and for disturbance of ion homeostasis were, however, increased, suggesting that nimodipine interferes with cellular energy metabolism and increases the susceptibility of tissue to ischaemic damage.