Effects of Verapamil on Norepinephrine-, Phenylephrine- and Clonidine-induced Pressor Response in Rabbits and Rats

Shin, Dong-ho; Choi, Soo-hyung

Korean Journal of Veterinary Research 1988;28(1):29-36.

Dong-ho Shin¹, Soo-hyung Choi²

¹College of Veterinary Medicine, Chonnam National University
²College of Pharmacy, Chonnam National University

가토(家兎) 및 Rat에서 Norepinephrine, Phenylephrine 및 Clonidine의 승압반응(昇壓反應)에 대한 Verapamil의 영향(影響)

신동호¹, 최수형²

¹전남대학교 수의과대학
²전남대학교 약학대학

Abstract

To examine the selectivity of verapamil, used in the cardiovascular diseases, on alpha-1 and alpha-2 adrenoceptor-induced pressor rsponses, effects of verapamil on alpha-adrenoceptor agonist-induced pressor responses were investigated in urethane-anesthetized rabbits, spinal rabbits, rats and pithed rats. To evaluate the effects of verapamil on each pressor response induced by norepinephrine, phenylephrine and clonidine, these agonists were previously injected into a ear vein, and then same procedures were performed 1~2 min after treatment with intravenous verapamil. The results are summarized as follows: 1. Intravenous verapamil produced dose-dependent depressor response in rabbits and rats. 2. Pressor responses to intravenous norepinephrine($10{mu}g/kg$) and phenylphrine($30{mu}g/kg$) were inhibited by pretreatment with intravenous verapamil in rabbits and no difference was noted between the degree of both inhibitions of the pressor response by verapamil. 3. Pressor responses to intravenous norepinephrine($3{mu}g/kg$), phenylephrine($20{mu}g/kg$) and clonidine ($300{mu}g/kg$) were inhibited by pretreatment with intravenous verapamil in spinal rabbits. No difference was noted between the inhibition of norepinephrine-induced pressor response and that of phenylephrine-induced pressor response by verapamil. The inhibition of clonidine-induced pressor response by verapamil was more prominent than that of norepinephrine- or phenylephrine-induced pressor response. 4. Pressor responses to intravenous norepinephrine($3{mu}g/kg$) and phenylephrine($10{mu}g/kg$) were inhibited by pretreatment with intravenous verapairlil in rats and no difference was noted between the degree of both inhibitions of the pressor response by verapamil. 5. Pressor responses to intravenous norepinephrine ($3{mu}g/kg$), phenylephrine($30{mu}g/kg$) and clonidine($100{mu}g/kg$) were inhibited by pretreatment with intravenous verapamil in pithed rats. No difference was noted between the inhibition of norepinephrine-induced pressor response and that of phenylephrine-induced pressor response by verapamil. The inhibition of clonidine-induced pressor response by verapamil was more prominent than that of norepinephrine- or phenylephrine-induced pressor response. These results suggest that verapamil significantly inhibits both pressor responses mediated by alpha-1 and alpha-2 adrenoceptors and the inhibition is greater in alpha-2 adrenoceptor-induced response than in alpha-1 adrenoceptor-induced one, and calcium channel takes part in the process of the pressor response mediated by alpha-1 adrenoceptors as well as alpha-2 adrenoceptors.