The inhibitory effects of ferriprotoporphyrin IX on platelet aggregation and release of serotonin

Abstract

Ferriprotoporphyrin IX (FP) dissolved in 0.025N NaoH in concentrations of 0.01 – 0.04uM/ul platelet suspension competitively inhibited platelet aggregation induced by a low concentration of collagen. 14C-serotonin release was also inhibited. Higher concentrations of collagen overcame the aggregation inhibition. A similar pattern of results was obtained with thrombin-, and arachidonic acid-induced aggregation and release. With ristocetin. there was little inhibition of aggregation although serotonin release was inhibited. ADP-induced aggregation was partially inhibited except at FP concentrations of 0.91 uM/ul. FP caused only platelet shape change and serotonin release of up to 8.1%. These changes were not associated with significant platelet lysis and could also not be attributed to pH or temperature changes. There was no inhibition of collagen-induced aggregation in PRP, but FP precipitates aggregated washed platelets and caused serotonin release. These results show that FP in solution inhibited platelet aggregation induced by the different agents studied. It did not interfere with platelet agglut ination induced by ristocetin. The mechanism(s) of aggregation inhibition remains to be clarified.