Binding of thromboxane A2/prostaglandin H2 agonists to human platelets

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Abstract
1 The competition of [125I]-9,11 dimethylmethano-11,12 methano-16-(3-iodo-4- hydroxyphenyl)-13, 14-dihydro-13-aza 15αβ-ω)-tetranor-thromboxane A2 ([125I]-PTA-OH), a thromboxane A2/prostaglan-din H2 receptor antagonist, with a series of thromboxane A2/prostaglandin H2 (TXA2/PGH2) mimetics for binding to the putative TXA2/PGH2 receptor in washed human platelets was studied. 2 The rank order potency for the series of mimetics to compete with [125I]-PTA-OH for binding was compared with their rank order potency for induction of platelet aggregation. The rank order potency for the mimetics to compete with [125I]-PTA-OH for binding was ONO-11113>SQ-26655>U44069>U46619 = 9, 11-azo PGH2>MB28767. This rank order potency was highly correlated with their rank order potency for inducing platelet aggregation (r = 0.992). 3 Changes in the intra or extracellular concentrations of Na+ did not have a significant effect on the competition between U46619 and [125I]-PTA-OH for binding to the putative receptor. 4 In summary, it appears that these TXA2/PGH2 mimetics activate human platelets through the putative TXA2/PGH2 receptor.

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