Role of bradykinin, nitric oxide, and angiotensin II type 2 receptor in imidapril-induced angiogenesis

The angiotensin II ( Ang II)-Ang II type 1 receptor pathway is proangiogenic, whereas studies showed that some angiotensin-converting enzyme inhibitors also stimulate angiogenesis in the setting of tissue ischemia, leaving a controversy of Ang II-mediated angiogenesis. We investigated whether an angiotensin-converting enzyme inhibitor imidapril-induced angiogenesis might be mediated via the tissue bradykinin pathway. To rule out the conventional effects of Ang II on angiogenesis, we used Ang II type 1a receptor knockout ( AT1aKO) mice. We examined the effects of the angiotensin-converting enzyme inhibitor imidapril on angiogenesis in a hindlimb ischemia model using AT1aKO mice. After induction of hindlimb ischemia, AT1aKO mice were treated with or without imidapril ( 1.0 or 0.1 mg/ kg per day for 21 days). Angiogenesis was quantified by laser Doppler blood flowmetry and capillary density. Angiogenesis was reduced in AT1aKO mice compared with wild-type mice. Imidapril with either low or high doses enhanced angiogenesis in AT1aKO mice ( P < 0.01). Ang II type 2 receptor antagonist ( PD123319; 30 mg/ kg per day) and B1 receptor antagonist ( DesArg9-[Leu8]- bradykinin; 50 nmol/ kg per day) suppressed the imidapril-induced angiogenesis in AT1aKO mice to an extent even lower than that of nontreated AT1aKO mice. B2 receptor antagonist ( Hoechst 140; 100 mu g/ kg/ d) and NO synthase inhibitor (N-G-nitro-L-arginine methyl ester; 20 mg/ kg per day) moderately attenuated the imidapril-mediated angiogenesis. RT-PCR revealed that vascular endothelial growth factor receptor 2 mRNA was reduced with PD123319, DesArg9-[ Leu8]- bradykinin, or Hoechst 140, and vascular endothelial growth factor mRNA abundance was suppressed with PD123319 or DesArg9-[ Leu8]- bradykinin. In conclusion, imidapril elicited angiogenesis in the setting of tissue ischemia in AT1aKO mice. This angiogenic effect might involve the Ang II-Ang II type 2 receptor pathway in addition to the bradykinin-B1 and bradykinin-B2 receptor/ NO-dependent pathways.