Figure 3.

Effects of receptor antagonists on rates of platelet aggregation. Statistically significant differences are indicated between untreated and 5‐HT/catecholamine‐treated platelets (*) and receptor blocker–pretreated or only 5‐HT/catecholamine‐treated platelets (+). All assays were performed in triplicate (n=10 group). A, Platelets were first pretreated with the receptor blockers propranolol (Prop; β2‐blocker), sarpogrelate (Sarpo; 5‐HT2A blocker), or atipamezole (Atipam; α2‐blocker) for 15 minutes and then treated with 5‐HT/catecholamine for an additional 10 minutes. At the end of the treatments, platelets were stimulated with collagen, and their aggregation profiles were monitored in an aggregometer. B, Approximately 13% of the platelets from Sarpo‐ or Atipam‐treated platelets and 9% of Prop‐treated platelets were aggregated at the end of 10 minutes. The average of 4 measurements is presented in the bar graph. C, Additive effect of 3 blockers on 5‐HT/catecholamine‐treated platelet aggregation. Platelets were processed as describe in panel A then they were stimulated with the mixture of Sarpo, Prop, and Atipam for 15 minutes and then treated with 5‐HT/catecholamine for an additional 10 minutes. At the end of the treatments, platelets were stimulated with collagen, and their aggregation profile was monitored in an aggregometer. D, Approximately 21% of the platelets treated with the mixture of 3 drugs were aggregated at the end of 10 minutes. E, Each receptor blocker reduced the surface level of P‐selectin differently, but the mixture of 3 blockers totally counteracted the 5‐HT/catecholamine‐mediated elevation of P‐selectin level on platelet surfaces. The average of 4 measurements is presented in the bar graph. F, The combined effect of 3 blockers was evaluated by pretreating the platelets first with the mixture of the receptor blockers (Prop, Sarpo, and Atipam) for 15 minutes and then treated with 5‐HT/catecholamine for an additional 10 minutes or vice versa. At the end of the treatments, platelets were stimulated with collagen, and their aggregation profile was monitored in an aggregometer. Only ≈68% of the platelets from blocker mixture–treated platelets were aggregated at the end of 10 minutes; however, if the platelets were first treated with 5‐HT/catecholamine and then with the blocker mixture, this did not reduce the aggregation level. The average of 4 measurements is presented in the bar graph. G, The surface level of P‐selectin showed similar changes with the order of the treatments (blocker mixture and 5‐HT/catecholamine). The average of 4 measurements is presented in the bar graph.