Coronary vasomotor response to the selective B1-kinin-receptor agonist Des-Arg9-bradykinin in humans

The aim of the present study was to assess the effects of selective B1-receptor stimulation with des-Arg9-bradykinin on coronary vasomotion in transplanted and non-transplanted patients.

Bradykinin B1-receptors have been identified on endothelial and smooth muscle cells in human coronary arteries in vitro; however, their physiologic role in the coronary circulation is unknown.

Twelve heart transplant patients were compared with 10 control subjects at 3.2 +/- 2.2 months after surgery. Coronary flow velocity was measured using guide-wire Doppler. The diameter of 3 epicardial segments of the left coronary artery and coronary blood flow were assessed at baseline, immediately after infusions of increasing doses of des-arginine(Arg9)-bradykinin at estimated coronary blood concentrations of 5.4 x 10(-9), 5.4 x 10(-8), 5.4 x 10(-7) and 1.6 x 10(-6) mol/liter, and of acetylcholine at 10(-8), 10(-7) and 10(-6) mol/liter).

Des-Arg9-bradykinin induced a similar decrease in all measured epicardial diameters in both groups and no change in coronary blood flow. Vasoconstriction was significant only at the 2 highest concentrations: -6 +/- 9% (p < 0.01) and -7 +/- 11% (p < 0.01) in control subjects, and -8 +/- 8% (p < 0.001) and -9 +/- 11% (p < 0.001) in heart transplant patients. Acetylcholine induced significant epicardial vasodilation in control subjects and vasoconstriction in transplant patients. The presence of allograft rejection did not modify the responses to des-Arg9-bradykinin with regard to both conductance and resistance vessels.

Kinin B1-receptors exist and can be stimulated in humans. The vasoconstrictive action on epicardial coronary arteries of des-Arg(9)-bradykinin in humans argues for a predominant action of B1-receptor stimulation at the level of smooth muscle cells.