Rilmenidine Differs From Clonidine in that it Lacks Histamine‐like Activity

Abstract— Studies were carried out to determine whether rilmenidine, a recently introduced antihypertensive agent with a similar mechanism of action of Clonidine, possesses histamine‐like activity on tissues responding to histamine H₂‐receptor agonists. In guinea‐pig isolated atria, both histamine and Clonidine caused concentration‐dependent positive chronotropic effects which were blocked by the histamine H₂‐receptor antagonist Cimetidine (5 μM);.in contrast, rilmenidine produced a concentration‐dependent negative chronotropic effect which was not altered by Cimetidine. In stilboestrol‐treated rat isolated uterus contracted by KC1, histamine and Clonidine produces concentration‐dependent relaxations which were blocked by Cimetidine (5 μM); rilmenidine also produced relaxation, but this was not affected by Cimetidine (5 μM). These findings suggest that rilmenidine, unlike Clonidine, does not activate histamine H₂‐receptors in either guinea‐pig atria or rat uterus. 1989 Royal Pharmaceutical Society of Great Britain