Role of endothelial kinins in control of coronary nitric oxide production

The purpose of the present study was to determine whether interventions that promote kinin production or decrease kinin inactivation affect nitric oxide production in isolated canine coronary microvessels. Accordingly, bradykinin (10(-8) to 10(-5) mol/L), ramiprilat (10(-10) to 10(-8) mol/L), A23187 (10(-8) to 10(-6) mol/L), kallikrein (1 to 20 U/mL), and kininogen (0.5 to 10 mu g/mL) were used to stimulate endothelium-dependent nitric oxide production. Receptor antagonists, serine protease inhibitors, and a kinin antibody were used to inactivate local kallikrein-kinin activity. Nitrite, the metabolite of nitric oxide in aqueous solution, was measured using the Griess reaction. All the agonists significantly increased nitrite release. For instance, the highest dose of bradykinin, ramiprilat, A23187, kallikrein, and kininogen markedly increased nitrite production, from 60+/-10 to 156+/-12, 153+/-11, 161+/-15, 176+/-15, and 168+/-16 pmol/mg (all P<.05), respectively. The increased nitrite production caused by these agents was not only blocked by N-omega-nitro-L-arginine methyl ester (L-NAME) and HOE 140 (which blocks B-2 kinin receptor) but by the kinin antibody also. For instance, nitrite production elicited by bradykinin, ramiprilat, A23187, and kininogen was reduced to 95+/-8, 87+/-8, 94+/-11, and 85+/-11 pmol/mg (all P<.05), respectively, by the kinin antibody. Carbachol-induced nitrite production (from 66+/-8 to 144+/-13) was blocked by L-NAME but not by HOE 140 or the kinin antibody. These results suggest that either increasing kininogen to promote endogenous kinin formation or inhibiting angiotensin-converting enzyme to decrease kinin breakdown, increases nitric oxide production in isolated coronary microvessels. These data indicate that a microvessel kallikrein-kinin system has an important role in the control of nitric oxide production in coronary microvessels.