The alpha2-adrenoceptor agonists xylazine and guanfacine exert different central nervous system, but comparable peripheral effects in calves.
Acute pharmacodynamic effects of the alpha2-adrenoceptor agonists, xylazine and guanfacine, were investigated in nine healthy calves in an open crossover trial. Xylazine (100 microg/kg body weight intravenously (i.v.)) and guanfacine (20 microg/ 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 alpha2-adrenoceptor agonists, whereas peripheral actions are similar.
Scholtysik
G
G
Institute of Veterinary Pharmacology, University of Berne, Switzerland.
Regli
F
F
Bruckmaier
R M
RM
Blum
J W
JW
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D001786:Blood Glucose / Q000032:analysis; D002395:Catecholamines / Q000097:blood; D002417:Cattle / Q000097:blood / Q000502:physiology*; D002490:Central Nervous System / Q000187:drug effects*; D018592:Cross-Over Studies; D005230:Fatty Acids, Nonesterified / Q000097:blood; D013006:Growth Hormone / Q000097:blood; D016316:Guanfacine / Q000494:pharmacology*; D006339:Heart Rate / Q000187:drug effects; D007275:Injections, Intravenous; D007328:Insulin / Q000097:blood; D008297:Male; D010101:Oxygen Consumption / Q000187:drug effects; D017933:Peripheral Nervous System / Q000187:drug effects*; D011659:Pulmonary Gas Exchange / Q000187:drug effects; D012119:Respiration / Q000187:drug effects; D014991:Xylazine / Q000494:pharmacology*
D000316:Adrenergic alpha-Agonists; D001786:Blood Glucose; D002395:Catecholamines; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D014991:Xylazine; D016316:Guanfacine; D013006:Growth Hormone