Thromboxane A2/prostaglandin H2 receptor activation mediates angiotensin II-induced postischemic neovascularization

Objective-We analyzed the involvement of thromboxane (TX) A(2)/prostaglandin (PG) H-2 (TP) receptor in ischemia-induced neovascularization in mice. Methods and Results-Unilateral hindlimb ischemia was induced by right femoral artery ligature in male C57BL/6J mice (n = 7 per group). Animals were then treated with or without TP receptor antagonist (S18886, 5 or 10 mg/kg per day; ramatroban, 10 mg/ kg per day) or aspirin ( 30 mg/ kg per day) in drinking water for 21 days. Hindlimb ischemia raised plasma level of TXB2, the stable metabolite of TXA(2), by 4.7-fold. This increase was blocked by aspirin treatment whereas S18886 ( 5 or 10 mg/ kg per day) had no effect. However, neither S 18886 nor aspirin affected postischemic neovascularization. We next assessed the putative involvement of TXA(2) signaling in angiotensin II(Ang II) proangiogenic pathway. Ang II (0.3 mg/ kg per day) enhanced TXB2 plasma levels by 2.6-fold over that of control (P < 0.01). Ang II-induced TXB2 upregulation was reduced by cotreatment with Ang II type I receptor antagonist ( candesartan, 20 mg/ kg per day). Angiographic score, capillary number, and foot perfusion were improved by 1.7-, 1.7-, and 1.4-fold, respectively, in Ang II-treated mice compared with controls (P < 0.05). Ang II proangiogenic effect was associated with a 1.6-fold increase in VEGF-A protein content (P < 0.05) and a 1.4-fold increase in the number of Mac-3-positive cells (ie, macrophages) in ischemic areas (P < 0.05). Interestingly, treatments with TP receptor antagonists or aspirin hampered the proangiogenic effects of Ang II. Conclusion-Endogenous activation of TXA(2) receptor by eicosanoids did not modulate spontaneous neovascularization in the setting of ischemia. Conversely, TXA(2) signaling is involved in Ang II-induced AT1-dependent vessel growth.