Opposing central autonomic actions of alpha 1- and alpha 2-adrenoceptor antagonists on oculomotor tone.
Electrical stimulation of the afferent sciatic nerve produces reflex mydriasis in anesthetized rats. The alpha 2-antagonist idazoxan (10-100 micrograms/kg i.v.) inhibited this reflex in a dose-dependent fashion. In contrast, the alpha 1-antagonist prazosin (30-300 micrograms/kg i.v.), produced a dose-related enhancement of the reflex. Single dose administration of the alpha 2-antagonists yohimbine (3.0 mg/kg i.v.), rauwolscine (3.0 mg/kg i.v.) and idazoxan (1.0 mg/kg) also blocked the reflex, whereas the alpha 1-antagonists phenoxybenzamine (3.0 mg/kg i.v.), corynanthine (1.0 mg/kg i.v.) and prazosin (1.0 mg/kg i.v.) potentiated this response. These studies demonstrate that alpha 2-antagonists block and alpha 1-adrenoceptor antagonists potentiate alpha 2-adrenoceptor-mediated inhibition of oculomotor tone.
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D001341:Autonomic Nervous System / Q000187:drug effects*; D004146:Dioxanes / Q000494:pharmacology; D004558:Electric Stimulation; D005260:Female; D019329:Idazoxan; D007275:Injections, Intravenous; D008297:Male; D011224:Prazosin / Q000494:pharmacology; D011680:Pupil / Q000187:drug effects*; D051381:Rats; D012584:Sciatic Nerve / Q000502:physiology
D000317:Adrenergic alpha-Antagonists; D004146:Dioxanes; D011224:Prazosin; D019329:Idazoxan