The alpha adrenoceptor antagonist properties of idazoxan in normal subjects

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Abstract
The imidazoline derivative idazoxan, which is a potent, selective .alpha.2-adrenoceptor antagonist, was injected i.v. into 8 men with normotension. There was a transient small increase in blood pressure and a decrease in heart rate within 20 min of injection, with a slight increase in plasma norepinephrine levels. These effects were consistent with antagonism of prejunctional .alpha.2-adrenoceptors. In response to infusions of the relatively selective .alpha.2-adrenoceptor agonist .alpha.-methylnorepinephrine, the pressor dose-response curve shifted to the right with idazoxan. These data provide evidence for receptors with .alpha.2-adrenoceptor characteristics on resistance vessels in man. In vitro platelet aggregation studies provided further evidence of selective .alpha.2-adrenoceptor antagonism by idazoxan, with greater potency and affiinity than .alpha.-yohimbine. These observations are consistent with both pre-and postjunctional peripheral .alpha.2-adrenoceptors in man and provide further support that idazoxan is a selective .alpha.2-adrenoceptor antagonist.

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