The influence of calcium channel blockers on the central action of clonidine.

The influence of verapamil, nifedipine and cinnarizine on clonidine-induced hypothermia, spontaneous and explorative motility was investigated in mice. Verapamil 5 and 15 mg/kg, nifedipine 17.5 and 50 mg/kg and cinnarizine 75 and 200 mg/kg (that is 1/30 and 1/10 of LD50 respectively) were injected intraperitoneally. The drugs were given in single doses (1/10 LD50) and in repeated doses (1/30 LD50) during a 10 days course. In acute experiments the drugs were given 60 min before clonidine administration, while in chronic experiments clonidine was given on the 11th day of the experiment. Nifedipine prevents clonidine-induced hypothermia in both the applied doses, verapamil only in a single dose, and cinnarizine in repeated doses. Only repeated administration of nifedipine and cinnarizine weakens the clonidine-induced sedation in the studies of spontaneous motility, and as for nifedipine also in explorative motility.