The alpha adrenoceptor antagonist properties of idazoxan in normal subjects

The imidazoline derivative idazoxan, which has been shown to be a potent, selective α 2 ‐adrenoceptor antagonist, was injected intravenously to eight 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 are consistent with antagonism of prejunctional α 2 ‐adrenoceptors. In response to infusions of the relatively selective α 2 ‐adrenoceptor agonist α‐methylnorepinephrine, the pressor dose‐response curve shifted to the right with idazoxan. These data provide evidence for receptors with α 2 ‐adrenoceptor characteristics on resistance vessels in man. In vitro platelet aggregation studies provide further evidence of selective α 2 ‐adrenoceptor antagonism by idazoxan, with greater potency and affinity than α‐yohimbine. These observations are consistent with both pre‐and postjunctional peripheral α 2 ‐adrenoceptors in man and provide further support that idazoxan is a selective α 2 ‐adrenoceptor antagonist. Clinical Pharmacology and Therapeutics (1984) 36, 190–196; doi: 10.1038/clpt.1984.161