L-NAME-resistant bradykinin-induced relaxation in porcine coronary arteries is NO-dependent: effect of ACE inhibition

1 NO synthase (NOS) inhibitors partially block bradykinin (BK)-mediated vas orelaxation. Here we investigated whether this is due to incomplete NOS inh ibition and/or NO release from storage sites. We also studied the mechanism behind ACE inhibitor-mediated BK potentiation. 2 Porcine coronary arteries (PCAs) were mounted in organ baths, preconstric ted, and exposed to BK or the ACE-resistant BK analogue Hyp(3)-Tyr(Me)(8)-B K (HT-BK) with or without the NOS inhibitor L-NAME (100 mu M), the NO scave nger hydroxocobalamin (200 mu M), the Ca2+-dependent K+-channel blockers ch arybdotoxin+apamin (both 100 nM), or the ACE inhibitor quinaprilat (10 mu M ) 3 BK and HT-BK dose-dependently relaxed preconstricted vessels (pEC(50), 8. 0+/-0.1 and 8.5+/-0.2, respectively), pEC(50)'s were approximate to 10 fold higher with quinaprilat, and approximate to 10 fold lower with L-NAME or c harybdotoxin+apamin. Complete blockade was obtained with hydroxocobalamin o r L-NAMES charybdotoxin+apamin. 4 Repeated exposure to 100 nM BK or HT-BK, to deplete NO storage sites, pro duced progressively smaller vasorelaxant responses. With L-NAME, the decrea se in response occurred much more rapidly. L-Arginine (10 mM) reversed the effect of L-NAME. 5 Adding quinaprilat to the bath following repeated exposure (with or witho ut L-NAME), at the time BK and HT-BK no longer induced relaxation, fully re stored vasorelaxation, while quinaprilat alone had no effect. Quinaprilat a lso relaxed vessels that, due to pretreatment with hydroxocobalamin or L-NA ME+charybdotoxin +apamin, previously had not responded to BK. 6 In conclusion, L-NAME-resistant BK-induced relaxation in PCAs depends on NO from storage sites, and is mediated via stimulation of guanylyl cyclase and/or Ca2+-dependent K+-channels. ACE inhibitors potentiate BK independent of their effect on BK metabolism.