The effects of calcium channel blockers on the cardiovascular system of rabbits in vivo.

The effects of i.v. administration of the calcium channel blockers--verapamil (0.045 and 0.45 mg.kg-1) and Mepamil (2-methylphenyl-derivative of verapamil; 0.0445 and 0.445 mg.kg-1) on the cardiovascular system of rabbits in vivo under the paced and non-paced heart conditions were investigated. Verapamil induced--in the dose-dependent manner--a decrease in blood pressure (max. 65.2%), a significant decrease in dP/dtmax. (max. 46.0%), a bradycardia (max. 79.4%), a decrease in minute blood flow (max. 63.9 %) and stroke blood flow (max. 71.5%). The administration of Mepamil did not induce important changes in heart rate; changes in other parameters were--again in the dose-dependent manner--of a similar qualitative character as after verapamil administration, but they were quantitatively less expressed (especially marked in the effect on dP/dtmax, where the maximum decrease was only to 71.5%). The results show a less pronounced cardiodepressive activity of Mepamil compared to verapamil in rabbits.