The effects of oxmetidine on In vitro platelet aggregation

The authors have studied the effects of oxmetidine (an H sub(2)-receptor antagonist containing an imidazole ring), acetylsalicylic acid (a known inhibitor of cyclo-oxygenase) and imidazole (an inhibitor of thromboxane synthetase) on platelet aggregation, release of beta thromboglobulin (BTG) from platelet alpha granules, and platelet cAMP levels, using an in vitro test system. Platelet aggregation was inhibited by oxmetidine and by acetylsalicylic acid, as shown by a reduced response with ADP, arachidonic acid or collagen. Imidazole had only a slightly inhibitory effect on platelet aggregation induced by ADP and collagen but a moderate effect on arachidonic acid-induced aggregation. The release of (BTG) from platelets induced by 2 mu g collagen/ml was markedly inhibited by oxmetidine and by acetylsalicylic acid, whilst imidazole showed a more variable effect. Reduced release of BTG in the presence of oxmetidine and acetylsalicylic acid paralleled the reduced platelet aggregation responses. The level of cAMP in platelets from 11 subjects was reduced by oxmetidine but that from three subjects was unchanged.