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

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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.