Partial agonist behaviour of adenosine 5'-O-(2-thiodiphosphate) on human platelets.

1 The effects of an adenosine diphosphate (ADP) analogue, adenosine 5'-O-(2-thiodiphosphate) (ADP-beta-S), in which a terminal phosphate oxygen has been replaced by sulphur, were studied on human platelets. 2 ADP-beta-S induced platelet aggregation and inhibited prostaglandin E1 (PGE1)-stimulated adenylate cyclase but in both cases was less potent than ADP and did not achieve the same maximal effects. 3 Both actions of ADP could be inhibited by the simultaneous addition of ADP-beta-S (50 microM). 4 Aggregation induced by 11 alpha, 9 alpha-epoxymethano prostaglandin H2 (a stable endoperoxide analogue) was not inhibited by simultaneous addition of ADP-beta-S (50 microM). 5 The behaviour of ADP-beta-S towards human platelets was consistent with it being a partial agonist.