Investigation of the Interaction Between the Vascular Endothelium and Angiotensin-Converting Enzyme

The vascular endothelium tonically releases nitric oxide that produces smooth muscle relaxation, inhibition of platelet aggregation, and inhibition of cellular proliferation. Studies in the Cardiology Branch have demonstrated that nitric oxide activity is reduced in the coronary and peripheral vasculature of patients with atherosclerosis and in those with risk factors for atherosclerosis. Bradykinin, an endothelium-dependent vasodilator, may be an important modulator of vascular tone in vivo because it is tonically produced by the endothelium. Bradykinin is inactivated by angiotensin converting enzyme (ACE) that is found on the endothelial cell surface. The activity of plasma ACE is variable among individuals and is at least partly genetically determined. ACE activity may modulate the local vascular effects of bradykinin, and thus, ACE inhibitors would be expected to improve endothelium-dependent responses in patients with higher tissue ACE activity. This protocol is designed to determine 1) the role of bradykinin in stimulating nitric oxide release in the human coronary and peripheral vasculature; 2) whether ACE inhibitors improve bradykinin-induced vasodilation, and if so, whether this occurs as a result of endothelium-dependent release of nitric oxide; 3) whether ACE inhibitors improve the abnormal shear-induced coronary vasodilation in patients with normal coronary arteries and those with coronary artery disease; 4) whether ACE inhibitors and bradykinin affect platelet function; 5) whether the vascular responses to ACE inhibition and bradykinin depend on the ACE genotype.