Inhibitory effects of H-2-receptor antagonists on platelet function in vitro

1 To evaluate in vitro inhibitory effects of four types of histamine H-2-re ceptor antagonist (H-2-receptor antagonists), famotidine, roxatidine, cimet idine and ranitidine, on platelet function, we examined aggregating potency and P-selectin levels with agonist-induced aggregation. Ranitidine and cim etidine inhibited, in concentration of 0.35 mM, the secondary aggregation i nduced by 5 mu M adenosine diphosphate (ADP), the aggregation induced by 1 mu g/mL collagen and 3 mu M arachidonic acid. All of H-2-receptor antagonis ts inhibited, in concentration of 1.4 mM, the aggregation induced by ADP, c ollagen and arachidonic acid. Ranitidine and cimetidine reduced markedly, i n same concentration, P-selectin levels after induction of aggregation by 5 mu M ADP, 1 mu g/mL collagen and 3 mu M 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-2-receptor antagonists on p latelet function are weaker than those of acetylsalicylic acid (ASA), since ASA inhibited platelet aggregation in concentration of 100 mu M. 3 No relationship was observed between inhibitory effects of H-2-receptor a ntagonists on platelet aggregation induced by above agonists and the presen ce or absence of imidazole ring in the chemical structure.