The alpha adrenoceptor antagonist properties of idazoxan in normal subjects.
The imidazoline derivative idazoxan, which has been shown to be a potent, selective alpha 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 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 provide further evidence of selective alpha 2-adrenoceptor antagonism by idazoxan, with greater potency and affinity 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.
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000328:Adult; D001786:Blood Glucose / Q000032:analysis; D001794:Blood Pressure / Q000187:drug effects; D002395:Catecholamines / Q000097:blood; D004146:Dioxanes / Q000494:pharmacology*; D004147:Dioxins / Q000494:pharmacology*; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D019329:Idazoxan; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D008297:Male; D008771:Nordefrin / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects; D011188:Potassium / Q000097:blood; D015016:Yohimbine / Q000378:metabolism
D000317:Adrenergic alpha-Antagonists; D001786:Blood Glucose; D002395:Catecholamines; D004146:Dioxanes; D004147:Dioxins; D007328:Insulin; D015016:Yohimbine; D008771:Nordefrin; D011188:Potassium; D019329:Idazoxan