The effect of xylazine on plasma thromboxane B2 concentration in sheep.

alpha 2-adrenoceptor agonist drugs can cause respiratory changes leading to a short period of hypoxaemia in sheep. It has been suggested that this is due to transient platelet aggregation and pulmonary microembolism. If platelet aggregation were to follow platelet activation in response to the administration of alpha 2 agonists, plasma thromboxane levels would be expected to rise. This study was carried out to measure plasma thromboxane B2 concentrations before and after the intravenous administration of the alpha 2-agonist drug xylazine at a dose of 0.1 mg/kg. It was found that the plasma thromboxane concentration rose by 320% and, furthermore, the rise was prevented by the prior administration of atipamezole hydrochloride (0.125 mg/kg), an alpha 2-adrenoceptor antagonist.