Background: Bradykinin causes endothelium-dependent vasodilation of isolated human coronary arteries in vitro. However, the effect of bradykinin on vasomotion of human coronary arteries in vivo has not been studied. The aim of this study was to examine whether bradykinin-induced vasodilation is altered at the atherosclerotic or spastic site of human coronary arteries in vivo.
Methods and results: The effect of bradykinin on vasomotion of epicardial coronary arteries was evaluated in 8 patients with normal coronary arteries (control group), 14 patients with organic coronary stenosis (coronary artery disease [CAD] group), and 8 patients with vasospastic angina (VSA group). Changes in the diameter of epicardial coronary artery were assessed by quantitative coronary arteriography. Intracoronary administration of bradykinin at graded doses (60, 200, and 600 ng) dilated epicardial coronary arteries without altering arterial pressure or heart rate in all patients of either group. In the control group, vasomotor responses of the site where acetylcholine caused dilation were compared with the responses of the site where acetylcholine caused constriction. The magnitudes of bradykinin-induced dilation at the site with acetylcholine-induced dilation (mean +/- SD: 6 +/- 6%, 11 +/- 9%, and 15 +/- 9%) were comparable to that (3 +/- 6%, 8 +/- 8%, and 13 +/- 9%) at the site with acetylcholine-induced constriction. In the CAD group, vasomotor responses of the stenotic site (% diameter stenosis, 15% to 50%) and nonstenotic site were examined. The bradykinin-induced dilation at the stenotic site (0 +/- 4%, 3 +/- 8%, and 5 +/- 9%) was significantly less (P < .01) than at the nonstenotic site (3 +/- 4%, 8 +/- 6%, and 16 +/- 11%) and in the control group. Coronary vasodilation with nitrate at the stenotic site (20 +/- 11%) was comparable to that at the nonstenotic site (22 +/- 16%) and in the control group (21 +/- 10%). In the VSA group, vasomotor responses of the site with acetylcholine-induced spasm and the site without spasm were examined. The bradykinin-induced vasodilation at the spastic site (5 +/- 5%, 16 +/- 15%, and 33 +/- 17%) was comparable to that at the nonspastic site (4 +/- 8%, 12 +/- 14%, and 21 +/- 9%). Nitrate-induced dilation was comparable at the spastic site (51 +/- 19%) and the nonspastic site (32 +/- 13%). The ratio of bradykinin-induced vasodilation to nitrate-induced vasodilation at the spastic site was comparable to the control group.
Conclusions: These results suggest that bradykinin causes vasodilation of human epicardial coronary arteries in vivo and that bradykinin-induced endothelium-dependent vasodilation is impaired at the stenotic site but is preserved at the angiographically normal site where endothelium-dependent vasodilation by acetylcholine is impaired and at the spastic site.