Inhibitory effects of H2-receptor antagonists on platelet function in vitro

1 To evaluate in vitro inhibitory effects of four types of histamine H2-receptor antagonist (H2-receptor antagonists), famotidine, roxatidine, cimetidine and ranitidine, on platelet function, we examined aggregating potency and P-selectin levels with agonist-induced aggregation. Ranitidine and cimetidine inhibited, in concentration of 0.35 mM, the secondary aggregation induced by 5 pM adenosine diphosphate (ADP), the aggregation induced by 1,g/mL collagen and 3 gM arachidonic acid. All of H2-receptor antagonists inhibited, in concentration of 1.4 mm, the aggregation induced by ADP, collagen and arachidonic acid. Ranitidine and cimetidine reduced markedly, in same concentration, P-selectin levels after induction of aggregation by 5 gm ADP, 1 ig/xmL collagen and 3 gM arachidonic acid. When classified by the strength of inhibitory action, ranitidine and cimetidine were strong, followed by famotidine and roxatidine. 2 It is considered that inhibitory effects of H.-receptor antagonists on platelet function are weaker than those of acetylsalicylic acid (ASA), since ASA inhibited platelet aggregation in concentration of 100 MM. 3 No relationship was observed between inhibitory effects of H2-receptor antagonists on platelet aggregation induced by above agonists and the presence or absence of imidazole ring in the chemical structure.