Effect of nimodipine, a calcium antagonist, on cerebral vasospasm after subarachnoid hemorrhage in cats.

Effect of a calcium antagonist, isopropyl-(2-methoxyethyl)-1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5- pyridinedicarboxylate (nimodipine) on the cerebral vasospasm after experimental subarachnoid hemorrhage (SAH) was studied in ten adult cats. The vasospasm was induced by injecting of 0.2-0.3 ml fresh autologous whole blood into the cisterna magna. Diameter of pial vessels was continuously measured by means of the vidicon camera system developed in our laboratory. Intravenous administration of nimodipine (0.1 mg/kg) 20-30 min after SAH resulted in a complete disappearance of the spasm with the reduction of blood pressure. The dilatory response was more marked in the smaller arteries (less than 100 microns) than in the larger ones (greater than or equal to 100 microns). Administration of smaller dose of nimodipine (0.01 mg/kg) also produced dilation of the pial vessels, although the effect was less remarkable in the smaller arteries. These data suggest that nimodipine might be useful in the treatment of the cerebral vasospasm after SAH. The mechanism underlying the action of nimodipine was discussed.