The α2-adrenoceptor agonists xylazine and guanfacine exert different central nervous system, but comparable peripheral effects in calves |
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| Authors: | Scholtysik Regli Bruckmaier & Blum |
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| Institution: | Institute of Veterinary Pharmacology, Institute of Animal Breeding, University of Berne, Switzerland.; Institute of Veterinary Pharmacology, Institute of Animal Breeding, University of Berne, Switzerland.; Division of Nutrition Pathology, Institute of Animal Breeding, University of Berne, Switzerland.; Division of Nutrition Pathology, Institute of Animal Breeding, University of Berne, Switzerland. |
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| Abstract: | Acute pharmacodynamic effects of the α2-adrenoceptor agonists, xylazine and guanfacine, were investigated in nine healthy calves in an open crossover trial. Xylazine (100 μg/kg body weight intravenously (i.v.)) and guanfacine (20 μg/kg body weight i.v.) were equi-effective in lowering heart rate by 25–30% at 5 min. Under these conditions, xylazine induced strong sedation and increased plasma growth hormone levels, indicating central nervous system mediated actions, whereas guanfacine was not sedative and did not induce release of growth hormone. Oxygen consumption was decreased by both drugs, but respiratory exchange ratio decreased only in response to xylazine. However, in response to both drugs, plasma levels of noradrenaline, adrenaline, insulin and non esterified fatty acids decreased similarly and glucose increased comparably. These results demonstrate marked differences in the central nervous system-mediated effects of the two α2-adrenoceptor agonists, whereas peripheral actions are similar. |
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