RESUMO
A recent study has shown that losartan, an AT-1-receptor antagonist, interacts with thromboxane A2 (TxA2)/prostaglandin H2 (PGH2) receptors in human platelets. The aim of this study was to analyze the ability of different angiotensin II (Ang II) AT-1-receptor antagonists to inhibit TxA2-dependent human platelet activation. Platelets were obtained from healthy volunteers. Platelets were stimulated with the TxA2 analogue, U46619 (10(-6) M). U46619-stimulated platelet activation was significantly reduced by both losartan and irbesartan in a dose-dependent manner. Only maximal doses of valsartan (5 x 10(-6) M) and the main metabolite of losartan, EXP3174 (5 x 10(-6) M), reduced U46619-induced platelet activation. Whereas the active form of candesartan cilexetil (candesartan, CV-11974) failed to modify platelet activation involved by TxA2, telmisartan showed a higher effect than valsartan and EXP3174 but lower than either losartan and irbesartan. Losartan or irbesartan reduced the binding of [3H]-U46619 to platelets, an effect that was observed with lower ability with the other AT-1 antagonists. Although platelets expressed AT-1-type receptors, exogenous Ang II did not modify platelet activation. This effect was not modified by blocking the AT-2 receptor with PD123319. These results suggest that some AT-1-receptor antagonists reduce TxA2-dependent activation independent of Ang II involvement.
Assuntos
Antagonistas de Receptores de Angiotensina , Ativação Plaquetária/efeitos dos fármacos , Ácido 15-Hidroxi-11 alfa,9 alfa-(epoximetano)prosta-5,13-dienoico/metabolismo , Ácido 15-Hidroxi-11 alfa,9 alfa-(epoximetano)prosta-5,13-dienoico/farmacologia , Difosfato de Adenosina/farmacologia , Adulto , Angiotensina II/farmacologia , Anticorpos Monoclonais/farmacologia , Benzimidazóis/farmacologia , Benzoatos/farmacologia , Ligação Competitiva/efeitos dos fármacos , Compostos de Bifenilo/farmacologia , Plaquetas/efeitos dos fármacos , Plaquetas/metabolismo , Relação Dose-Resposta a Droga , Humanos , Imidazóis/farmacologia , Irbesartana , Losartan/farmacologia , Piridinas/farmacologia , Ensaio Radioligante , Receptor Tipo 1 de Angiotensina , Receptor Tipo 2 de Angiotensina , Receptores de Angiotensina/imunologia , Telmisartan , Tetrazóis/farmacologia , Tromboxano A2/farmacologia , Fatores de Tempo , Valina/análogos & derivados , Valina/farmacologia , ValsartanaRESUMO
A recent study has shown that losartan, an AT(1)-receptor antagonist, interacts with thromboxane A(2) (TxA(2))/prostaglandin H(2) (PGH(2)) receptors in human platelets. The aim of the present study was to analyse the ability of different angiotensin II (Ang II) AT(1)-receptor antagonists to inhibit TxA(2)-dependent human platelet activation. Platelets were obtained from healthy volunteers and were stimulated with the thromboxane A(2) analogue, U46619 (10(-6) mol/L). U46619-stimulated platelet activation was significantly reduced by losartan in a dose-dependent manner. Only maximal doses of valsartan (5x10(-6) mol/L), reduced U46619-induced platelet activation. The active form of candesartan cilexetil, candesartan (CV-11974), failed to modify platelet activation. Losartan reduced the binding of [(3)H]-U46619 to platelets, an effect that was observed to a lesser extent with valsartan but not with CV-11974. These results suggest that, whilst some AT(1)-receptor antagonists reduce TxA(2)-dependent human platelet activation, it is not a feature common to all AT(1) antagonists.
