DuP 753, the selective angiotensin II receptor blocker, is a competitive antagonist to human platelet thromboxane A2/prostaglandin H2 (TP) receptors.

DuP 753 is a potent, selective angiotensin II type 1 (AT1) receptor antagonist. The possibility was investigated that DuP 753 may crossreact with thromboxane A2/prostaglandin H2 (TP) receptors. DuP 753 inhibited the specific binding of the TP receptor antagonist 3H]SQ 29,548 (5 nM) in human platelets with kd/slope factor values of 9.6 +/- 1.4 microM/1.1 +/- 0.02. The AT2-selective angiotensin receptor ligand, PD 123,177 was a very weak inhibitor of specific 3H]SQ 29,548 binding in platelets (Kd/slope factor:200 microM/0.86). 3H]SQ 29,548 saturation binding in the absence and presence of DuP 753 resulted in an increase in equilibrium affinity constant (Kd: 9.3, 22, 33 nM, respectively) without a concentration-dependent reduction in binding site maxima (Bmax: 3597, 4597, 3109 fmol/mg protein, respectively). Platelet aggregation induced by the TP receptor agonist U 46,619 was concentration-dependently inhibited by DuP 753 (IC50 = 46 microM). These data indicate for the first time that DuP 753 is a weak but competitive antagonist at human platelet TP receptors.