Figure 7

Inhibition of platelet aggregation by sildenafil. (a) Sildenafil treatment inhibited the aggregatory effect of thrombin on human platelets. Scale bar = 500 µm. (b) Western blot for VASP phosphorylation (indicates inhibitory activity of platelet aggregation) shows that the increased VASP phosphorylation by sildenafil was reversed by cGK inhibitor in human platelets (n = 3). cGK inh. = cGK inhibitor. pVASP Ser 239 = phospho-VASP at serine239. (c) Immunofluorescence staining for P-selectin(C62P), an activated platelet marker, shows that the aggregation of platelets induced by ADP was inhibited by sildenafil treatment. Moreover, this effect of sildenafil was reversed by cGK inhibitor, suggesting that sildenafil could inhibit platelet aggregation through the cGK pathway (n = 3). (d) Platelet aggregometer with platelet rich-plasma from a human donor showed that cGK activation by sildenafil treatment reduced ADP-induced platelet aggregation. In addition, this reduced platelet aggregation by sildenafil was reversed by cGK inhibitor (n = 5). (e) Quantitative graph of ex vivo aggregation study suing human platelets (n = 5). * indicates P < 0.05. (f) Representative figure of platelet aggregometer with platelet rich-plasma from rat peripheral blood treated with vehicle or sildenafil for 2 weeks (n = 6). (g) The quantitative graph also shows that sildenafil treatment inhibited platelet aggregation in vivo (n = 6). ** indicates P < 0.01.