Idazoxan: a novel pharmacological tool for the study of alpha 2-adrenoceptors.

The pharmacological properties of idazoxan, 2-[2-(1,4-benzodioxanyl)]-2-imidazoline, were first described four years ago; since then, this compound has been revealed to be one of the most selective alpha 2-adrenoceptor blocking agent presently available. At peripheral sites, idazoxan antagonized the effects of alpha 2 agonists such as azepexole, B-HT 920, M 7, UK 14,304, alpha-methylnoradrenaline, clonidine but was ineffective against alpha 1 agonists such as cirazoline and phenylephrine. At presynaptic sites idazoxan increased the tachycardia due to the stimulation of the cardioaccelerator nerve of the dog and antagonized the inhibitory effects of alpha 2 agonists in dogs and rats. As compared to the classical alpha 2-adrenoceptor blocking agents, idazoxan was more selective and as potent as yohimbine, rauwolscine, RS 21361, Wy 26703. At central sites, idazoxan has been found to antagonize the sympathoinhibitory effects of alpha 2 agonists. Therefore, idazoxan is a potent and probably the most selective alpha 2-adrenoceptor blocking agent presently available and is now frequently used for the investigation of peripheral and central alpha 2-adrenoceptors.