Effects of procainamide on blood platelet aggregation in rabbits

Platelet aggregation induced by arachidonic acid. thrombin, CaCl2 or clonidine was studied by turbidimetry and radioimmunoassay in rabbit. Procainamide 8.5-8704 vmol/L in vitro or 5 mg/kg iv in vivo inhibited significantly platelet aggregation and the production of thromboxane B2 as well. The inhibition by procainamide was dose-dependent and the inhibition % in vitro were 19-100% (arachidonic acid-induced), 31-87% (thrombin-induced), and - 2-77% (CaCl2 -induced). The inhibition % in vivo at 5, 15, 30 and 60 min after the injection of procainamide were 70, 74, 50. 44% (arachidonic acid-induced) and 30, 27, 24, 28% (thrombin-induced), respectively.