title: Cardiovascular effects of medetomidine, detomidine and xylazine in horses.
abstract: The cardiovascular effects of medetomidine, detomidine, and xylazine in horses were studied. Fifteen horses, whose right carotid arteries had previously been surgically raised to a subcutaneous position during general anesthesia were used. Five horses each were given the following 8 treatments: an intravenous injection of 4 doses of medetomidine (3, 5, 7.5, and 10 microg/kg), 3 doses of detomidine (10, 20, and 40 microg/kg), and one dose of xylazine (1 mg/kg). Heart rate decreased, but not statistically significant. Atrio-ventricular block was observed following all treatments and prolonged with detomidine. Cardiac index (CI) and stroke volume (SV) were decreased with all treatments. The CI decreased to about 50% of baseline values for 5 min after 7.5 and 10 microg/kg medetomidine and 1 mg/kg xylazine, for 20 min after 20 microg/kg detomidine, and for 50 min after 40 microg/kg detomidine. All treatments produced an initial hypertension within 2 min of drug administration followed by a significant decrease in arterial blood pressure (ABP) in horses administered 3 to 7.5 microg/kg medetomidine and 1 mg/kg xylazine. Hypertension was significantly prolonged in 20 and 40 microg/kg detomidine. The hypotensive phase was not observed in 10 microg/kg medetomidine or detomidine. The changes in ABP were associated with an increase in peripheral vascular resistance. Respiratory rate was decreased for 40 to 120 min in 5, 7.5, and 10 microg/kg medetomidine and detomidine. The partial pressure of arterial oxygen decreased significantly in 10 microg/kg medetomidine and detomidine, while the partial pressure of arterial carbon dioxide did not change significantly. Medetomidine induced dose-dependent cardiovascular depression similar to detomidine. The cardiovascular effects of medetomidine and xylazine were not as prolonged as that of detomidine.
authors.affiliation: Department of Veterinary Surgery I, School of Veterinary Medicine, Rakuno Gakuen University, Ebetsu, Hokkaido, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Yamashita
authors.forename: S
authors.initials: S
authors.lastname: Tsubakishita
authors.forename: S
authors.initials: S
authors.lastname: Futaok
authors.forename: I
authors.initials: I
authors.lastname: Ueda
authors.forename: H
authors.initials: H
authors.lastname: Hamaguchi
authors.forename: T
authors.initials: T
authors.lastname: Seno
authors.forename: S
authors.initials: S
authors.lastname: Katoh
authors.forename: Y
authors.initials: Y
authors.lastname: Izumisawa
authors.forename: T
authors.initials: T
authors.lastname: Kotani
authors.forename: W W
authors.initials: WW
authors.lastname: Muir
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D000700:Analgesics / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001784:Blood Gas Analysis / Q000662:veterinary; D001794:Blood Pressure / Q000187:drug effects; D002319:Cardiovascular System / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D006339:Heart Rate / Q000187:drug effects; D006736:Horses / Q000502:physiology*; D007093:Imidazoles / Q000008:administration & dosage / Q000494:pharmacology*; D007275:Injections, Intravenous / Q000662:veterinary; D020926:Medetomidine / Q000008:administration & dosage / Q000494:pharmacology*; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism; D012119:Respiration / Q000187:drug effects; D014991:Xylazine / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D000316:Adrenergic alpha-Agonists; D000700:Analgesics; D007093:Imidazoles; D011942:Receptors, Adrenergic, alpha; D014991:Xylazine; C041255:detomidine; D020926:Medetomidine