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Central and peripheral α‐adrenoceptor actions of amitraz in the dog
Author(s) -
CULLEN L. K.,
REYNOLDSON J. A.
Publication year - 1990
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.1365-2885.1990.tb00752.x
Subject(s) - amitraz , yohimbine , prazosin , bradycardia , chronotropic , endocrinology , anesthesia , medicine , chemistry , pharmacology , heart rate , blood pressure , antagonist , receptor , acaricide , organic chemistry
The aim of this study was to determine the contribution of α 2 ‐and α 1 adrenoceptor agonist activity of the formamidine, amitraz, on peripheral circulation in the dog. Intra‐arterial injections of amitraz (0.25‐5.0 μg/kg) produced a dose‐dependent increase in perfusion pressure in the autoperfused hind limbs of methoxyflurane‐anaesthetized dogs. A constant blood flow to the hind limbs was maintained using a peristaltic pump. Intravenous phentolamine (0.5 mg/kg), prazosin (35 μg/kg) and yohimbine (10 μg/kg) in separate experiments antagonized the vasoconstrictor actions of amitraz and produced a parallel shift to the right of the amitraz dose‐response curve. Cumulative doses of amitraz (0.5‐15 μg/kg) given by intracisterna magna (i.c.m.) injections reduced mean arterial pressure and heart rate in a dose‐dependent manner. Similar responses were produced by intravenous amitraz but at much higher doses. In separate experiments amitraz‐induced hypotension (doses up to 25 μg/kg i.c.m.) was prevented by pre‐treatment with yohimbine (30 μg/kg i.c.m.) but not prazosin (20 μg/kg i.c.m.). Both antagonists partially inhibited the bradycardia produced by amitraz. It is concluded that amitraz stimulates α 1 ‐and α 2 ‐adrenoceptors to produce vascular constriction. The central hypotensive action of amitraz appears to be mediated by α 2 ‐adrenoceptors; however, both receptor subtypes appear to be stimulated to produce bradycardia.