Role of endothelial cells in relaxation of isolated arteries by bradykinin.

Abstract

Bradykinin elicits relaxation of isolated transverse rings of canine coronary, celiac, superior mesenteric, renal, splenic, pulmonary, gastric and femoral arteries. After endothelial cells of the vessel wall are removed by rubbing of the intimal surface, canine arteries fail to relax upon addition of bradykinin. The endothelium-dependent relaxation of canine arteries remains intact after treatment with cyclooxygenase inhibitors (indomethacin and flurbiprofen), and this argues against mediation by prostaglandins. When they are stimulated with bradykinin, endothelial cells of canine arteries appear to release a substance mediating vascular smooth muscle relaxation. In contrast, preparations of arteries of cats (superior mesenteric) and rabbits (superior mesenteric and celiac) may be rubbed on the intimal surface without a consistent loss of sensitivity to the relaxing effects of bradykinin. In addition, relaxation of the cat and rabbit arteries is completely blocked by cyclooxygenase inhibitors. Bradykinin relaxes human arteries in an endothelium-dependent manner and this effect is not mediated by prostaglandins. Arteries of all species tested require the presence of endothelial cells for relaxation in response to acetylcholine and, using the rabbit aorta, this effect was shown to be mediated by the release of an uncharacterized substance from these cells that relaxes vascular smooth muscle. Bradykinin relaxes canine and human arteries via a similar mechanism but it relaxes cat and rabbit arteries by stimulating release of prostaglandins from as yet undefined cell types.