Role of ETB and B2 receptors in the ex vivo platelet inhibitory properties of endothelin and bradykinin in the mouse.
1. We have developed a model to study the inhibitory properties of endogenous autacoids triggered by systemically-administered vasoactive peptides, on platelet aggregation ex vivo in the mouse. 2. Adenosine diphosphate (ADP) (0.5-10 microM) induces a concentration-dependent aggregation of platelet-rich plasma derived from C57BL/6 mice. Intravenously-administered endothelin-1 (0.01-1 nmolx kg(-1)), the selective ETB agonist, IRL-1620 (0.0 -1 nmol x kg(-1)) or bradykinin ( 1-100 nmol x kg(-1)) significantly reduced in a dose-dependent fashion the ADP-induced platelet aggregation. 3. The non-selective cyclo-oxygenase (COX) inhibitor, indomethacin, a selective COX-2 inhibitor NS-398 or the prostacyclin synthase inhibitor, tranylcypromine (10 mg x kg(-1)), markedly reduced the inhibitory properties of endothelin-1, whereas only a combination of both indomethacin, NS-398 or tranylcypromine and L-NAME (10 mg x kg(-1)) were required to abolish the response to bradykinin. 4. An ETB-selective antagonist (BQ-788) or knockout of the B2 receptor gene (in B2 knockout mice) abolishes the platelet inhibitory properties of endothelin-1 and bradykinin, respectively. 5. Our results suggest that intravenously-administered endothelin-1 and bradykinin, through ETB and B2 receptor activation, respectively, inhibit platelet aggregation ex vivo in the mouse. The inhibitory properties of endothelin-1 require the activation of COX-2 and the subsequent generation of prostacyclin. In addition to the two previously mentioned factors, nitric oxide is required for the anti-aggregatory effects of bradykinin.
Labonté
J
J
Department of Pharmacology, Medical School, IPS, Université de Sherbrooke, 3001 12th Avenue North, Sherbrooke, Québec, J1H 5N4 Canada.
Brochu
I
I
Honoré
J C
JC
D'Orléans-Juste
P
P
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D051546:Cyclooxygenase 2; D004305:Dose-Response Relationship, Drug; D019332:Endothelin-1 / Q000494:pharmacology*; D007213:Indomethacin / Q000494:pharmacology; D007527:Isoenzymes / Q000502:physiology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009569:Nitric Oxide / Q000502:physiology; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D011451:Prostaglandin-Endoperoxide Synthases / Q000502:physiology; D043782:Receptor, Bradykinin B2; D044023:Receptor, Endothelin B; D018002:Receptors, Bradykinin / Q000502:physiology*; D017466:Receptors, Endothelin / Q000502:physiology*
D019332:Endothelin-1; D007527:Isoenzymes; D010975:Platelet Aggregation Inhibitors; D043782:Receptor, Bradykinin B2; D044023:Receptor, Endothelin B; D018002:Receptors, Bradykinin; D017466:Receptors, Endothelin; D009569:Nitric Oxide; D000244:Adenosine Diphosphate; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; D001920:Bradykinin; D007213:Indomethacin