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Xylazine‐induced mydriasis in rats and its antagonism by α‐adrenergic blocking agents
Author(s) -
HSU WALTER H.,
LEE PERNG,
BETTS DANIEL M.
Publication year - 1981
Publication title -
journal of veterinary pharmacology and therapeutics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.527
H-Index - 60
eISSN - 1365-2885
pISSN - 0140-7783
DOI - 10.1111/j.1365-2885.1981.tb00717.x
Subject(s) - mydriasis , yohimbine , xylazine , prazosin , atropine , tolazoline , phentolamine , adrenergic receptor , adrenergic , pharmacology , norepinephrine , chemistry , alpha 2 adrenergic receptor , adrenergic antagonist , endocrinology , anesthesia , medicine , antagonist , receptor , propranolol , dopamine , ketamine
Pupillary response to xylazine (10–300 μg/kg, i.v.) norepinephrine (1–30 μg/kg, i.v.) and atropine (3–100 μg/kg, i‐v.) were observed in rats anaesthetized with pentobarbital. Xylazine caused a dose‐dependent mydriasis which was antagonized by a selective α 2 ‐adrenergic blocking agent, yohimbine (2.5 mg/kg, i.v.). A non‐selective adrenergic blocking agent, phentolamine (2.5 mg/kg, i.v.) was less effective in antagonizing this effect of xylazine. A selective α 1 ‐adrenergic blocking agent, prazosin (2.5 mg/kg, i.v.) was ineffective in reducing the xylazine‐induced mydriasis. In contrast, both phentolamine and prazosin blocked the pupillary dilation produced by norepinephrine, while yohimbine was much less effective in antagonizing norepinephrine‐induced mydriasis. Atropine also induced a dose‐dependent mydriasis which was not affected by yohimbine pre‐treatment. The present study suggests that the mydriatic effect of xylazine in the rat is mediated by an adrenergic mechanism, possibly by stimulating the α 2 ‐adrenergic receptors in the iris and CNS.