When combined with ketamine, muscle relaxation and visceral analgesia are improved, and emergence from anesthesia is smoother. Major effects develop in approximately 10 to 15 minutes after intramuscular administration of xylazine and within 3 to 5 minutes following intravenous administration. The initial hypertension is caused by xylazine s action at peripheral postsynaptic adrenergic receptors, which produces vascular smooth muscle contraction and vasoconstriction. Eventual reductions in blood pressure are due to decreased sympathetic tone resulting from xylazine s activation of central and presynaptic sympathetic neuronal alpha2 adrenoceptors. Intramuscular administration of the drug does not produce this dramatic initial increase in blood pressure and vascular resistance.
Respiratory rate decreases with the administration of xylazine.
However, arterial pH, PaO2, and PaCO2 remain unchanged or are only minimally altered. Various alterations in gastrointestinal function have been reported following xylazine administration. Xylazine causes transient hypoinsulinemia and hyperglycemia in several species. The magnitude and duration of these actions appear to be dose dependent. In ruminants, xylazine increases myometrial tone and intrauterine pressure.