Effects of MDL 28,133A, a 5-HT2 receptor antagonist, on platelet aggregation and coronary thrombosis in dogs

We wished to characterize MDL 28,133A (1-(4-fluorophenyl)-2-(4-((4-methanesulfonamidophenyl)carbonyl]-1-piperidinyl-ethanone HCl), a potent 5-HT 2 receptor antagonist, on platelet aggregation and platelet thrombosis and determined its effect on thrombolysis with streptokinase (SK) in dogs with coronary thrombosis. MDL 28,133A and ritanserin, 0.3-1 μM, competitively inhibited 5-HT-induced platelet aggregation in dog platelet-rich plasma (PRP) in vitro. The pA 2 values and slopes were 6.29±0.09, -0.96±0.14, and 6.58±0.09, -1.64±0.34 for MDL 28,133A and ritanserin, respectively, suggesting that both agents are similar in potency to 5-HT 2 receptor antagonists