THE EFFECT OF XYLAZINE ON PLASMA THROMBOXANE B-2 CONCENTRATION IN SHEEP

alpha(2)-adrenoceptor agonist drugs can cause respiratory changes lead ing to a short period of hypoxaemia in sheep, It has been suggested th at this is due to transient platelet aggregation and pulmonary microem bolism. If platelet: aggregation were to follow platelet activation in response to the administration of alpha(2) agonists, plasma thromboxa ne levels would be expected to rise. This study was carried out to mea sure plasma thromboxane B-2 concentrations before and after the intrav enous administration of the alpha(2)-agonist drug xylazine at a dose o f 0.1 mg/kg. It. was found that the plasma thromboxane concentration r ose by 320% and, furthermore, the rise was prevented by the prior admi nistration of atipamezole hydrochloride(0.125 mg/kg), an alpha(2)-adre noceptor antagonist.