Effect of nifedipine and verapamil on hypotensive action of clonidine in rabbits.

The present study examined the influence of nifedipine and verapamil on clonidine-induced hypotension in the rabbits. Clonidine was given intravenously (i.v.) (0.2 mg/kg) or intracerebroventricularly (icv) (0.03 mg). Nifedipine (0.3 mg/kg and 0.45 mg/kg) and verapamil (0.2 mg/kg and 0.3 mg/kg) were injected i.v. 15 min before clonidine administration or icv (nifedipine 0.03 mg, verapamil 0.1 mg) 10 min before clonidine. It has been shown that nifedipine administered i.v. increases whereas injected icv prevents the hypotensive action of clonidine administered in the same way. Verapamil injected i.v. and icv did not change the hypotensive action of clonidine. It seems that nifedipine has alpha 2-adrenoceptor blocking properties.