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The comparative hypoxaemic effect of four α 2 adrenoceptor agonists (xylazine, romifidine, detomidine and medetomidine) in sheep
Author(s) -
CELLY C.S.,
McDONELL W.N.,
YOUNG S.S.,
BLACK W.D.
Publication year - 1997
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 - 10.1046/j.1365-2885.1997.00097.x
Subject(s) - detomidine , xylazine , medetomidine , anesthesia , respiratory rate , placebo , saline , chemistry , mean arterial pressure , heart rate , ketamine , blood pressure , medicine , alternative medicine , pathology
In the present study, the hypoxaemic potential of four α 2 agonists possessing different selectivity for α 2 adrenoceptors and of a saline placebo was studied in five clinically healthy sheep using a randomized Latin square design and equipotent sedative doses. Baseline values for heart rate (HR), mean arterial pressure (MAP), arterial oxygen (PaO 2 ) and carbon dioxide (PaCO 2 ) tensions, respiration rate and maximum change in pleural pressure (ΔPpl) were obtained, followed by the intravenous administration of either: xylazine (150 μg/kg); romifidine (50 μg/kg); detomidine (30 μg/kg); medetomidine (10 μg/kg) or placebo. Subsequent recordings were made up to 60 min after drug administration. No significant ( P 0.05) alterations in any variable occurred with placebo. All the α 2 agonists significantly ( P 0.05) decreased PaO 2 levels without a significant ( P 0.05) change in PaCO 2 . The lowest PaO 2 values were 29–42 mm Hg (3.9–5.5 kPa) with no significant difference between drugs. Respiratory rate and ΔPpl increased significantly within 2 min of drug administration; the duration of this effect varied with the α 2 agonist, lasting longest with romifidine. As compared to the saline treated group, a significant increase in MAP was observed up to 10 min after administration of romifidine and detomidine, however, a significant decrease was seen at 10 and 45 min after xylazine and medetomidine, respectively. The α 2 agonists studied induced a similar change in PaO 2 at peak effect, despite their reported variable selectivity for α 2 vs. α 1 adrenoceptors.