title: Clonidine mydriasis in the rat.
abstract: Pupillary responses to clonidine (3--100 micrograms/kg, i.v.) and epinephrine (1--30 micrograms/kg, i.v.) were observed in anesthetized rats. Clonidine caused a dose-dependent mydriasis which was effectively antagonized by pretreatment with yohimbine (1.5 mg/kg, i.v.). Pretreatment with phentolamine (5 mg/kg, i.v.) was less effective in antagonizing this clonidine-induced mydriasis. Phenoxybenzamine (2 mg/kg, i.v.) was almost without effect. In contrast, both phentolamine and phenoxybenzamine blocked the pupillary dilation produced by epinephrine while yohimbine pretreatment resulted in no antagonism of epinephrine-induced mydriasis. These results suggest that clonidine-induced mydriasis in the rat is mediated by a central adrenergic inhibitory mechanism.
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002642:Chick Embryo; D003000:Clonidine / Q000494:pharmacology*; D004347:Drug Interactions; D004837:Epinephrine / Q000494:pharmacology; D008297:Male; D009184:Mydriatics; D051381:Rats
chemical_list: D000317:Adrenergic alpha-Antagonists; D009184:Mydriatics; D003000:Clonidine; D004837:Epinephrine