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Cardiopulmonary effects of clonidine, diazepam and the peripheral α 2 adrenoceptor agonist ST‐91 in conscious sheep
Author(s) -
CELLY C.S.,
McDONELL W.N.,
BLACK W.D.,
YOUNG S.S.
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.1365-2885.1997.00098.x
Subject(s) - clonidine , diazepam , sedation , anesthesia , placebo , mean arterial pressure , blood pressure , agonist , medicine , saline , chemistry , heart rate , alternative medicine , receptor , pathology
The cardiopulmonary effects of the intravenous administration of clonidine (15 μg/kg), ST‐91 (30 μg/kg) and diazepam (0.4 mg/kg) were compared in five healthy sheep using a randomized cross‐over design, to determine whether the hypoxaemic effects of α 2 adrenoceptor agonists are due to sedation, or to peripheral α 2 adrenoceptor stimulation. All three drugs significantly lowered arterial oxygen tension (PaO 2 ) levels within 2 min of their administration; however, clonidine and ST‐91 produced long lasting and severe hypoxaemia with mean PaO 2 levels of ≈40 mm Hg and 50 mm Hg (5.3 kPa and 6.6 kPa), respectively. The fall in PaO 2 was considerably less with diazepam (63 mm Hg or 8.4 kPa at 2 min) and by 15 min the values did not differ from placebo treated animals. None of the drugs increased arterial carbon dioxide tension (PaCO 2 ) levels when compared to saline treatment and the acid base variables did not show any significant change. A significant increase was recorded in the packed cell volume of the ST‐91 treated group throughout the study. Within 2 min of their administration, all drugs caused a significant increase in mean arterial pressure (MAP) as compared to the placebo treated group. The MAP remained significantly increased for 5 and 60 min after clonidine and ST‐91 treatment, respectively. The study shows that ST‐91 and clonidine produce a greater degree of hypoxaemia than occurs with diazepam sedation, and that the hypoxaemic effect of α 2 adrenoceptor agonists in sheep are mainly mediated by peripheral α 2 adrenoceptors.