Background-Constitutive bradykinin B 1 receptors have been identified in dogs; however, their physiological implications involving the coronary circulation remain to be determined. This study examined, in conscious dogs, the coronary response to des-Arg 9 -bradykinin (a B 1 receptor agonist) and the mechanisms involved. Methods and Results-Eleven dogs were instrumented with a left ventricular micromanometer, a circumflex coronary catheter, a cuff occluder, a Doppler flow probe, and ultrasonic crystals to measure coronary blood flow velocity (CBFv) and coronary diameter (CD). Intracoronary des-Arg 9 -bradykinin (3 to 100 ng/kg) and bradykinin (0.1 to 10 ng/kg) did not modify systemic hemodynamics but dose-dependently increased CBFv and CD. Des-Arg 9 -bradykinin was less potent than bradykinin. Hoe 140 (a B 2 antagonist, 10 g/kg) abolished the effects of bradykinin but did not influence the effects of des-Arg 9 -bradykinin. When CBFv increase was prevented by the cuff occluder, CD responses to bradykinin and des-Arg 9 -bradykinin were maintained. Intracoronary lisinopril (0.75 mg) increased the CD response to bradykinin, with only minimal effect on CBFv, and extended the duration of the effect. Lisinopril did not alter des-Arg 9 -bradykinin responses. Intracoronary N -nitro-L-arginine (2 mg/kg) decreased the CD effect of bradykinin and prevented the CBFv and CD effects of des-Arg 9 -bradykinin. The relaxing effect of des-Arg 9 -bradykinin on isolated coronary rings was prevented by des-Arg 9 ,[Leu 8 ]-bradykinin. Conclusions-In the conscious dog, B 1 receptors are present in coronary vessels, and their stimulation produces vasodilation in conductance and resistance vessels, which is mediated essentially by NO but not modulated by angiotensin-converting enzyme. However, the coronary vasodilation induced by B 1 receptor stimulation is not as great as that produced by B 2 receptor stimulation.

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