THE ROLE OF NITRIC-OXIDE IN ENDOTHELIUM-DEPENDENT VASODILATION OF HYPERCHOLESTEROLEMIC PATIENTS

Background. Patients with hypercholesterolemia have a reduced response to endothelium-dependent vasodilators. However, the regulatory function of the endothelium on vascular tone is mediated through the release of several vasoactive substances; therefore, a reduced response to endothelium-dependent agents does not identify which of the factors released by the endothelium is involved in this abnormality. Methods and Results. To investigate the role of nitric oxide in the endothelium-dependent vasodilation in hypercholesterolemia, we studied the effect of N-G-monomethyl-L-arginine (L-NMMA), an inhibitor of endothelial nitric oxide synthesis, on basal vascular tone and on the responses to acetylcholine, an endothelium-dependent vasodilator, and to sodium nitroprusside, a direct smooth muscle dilator. The study included 33 hypercholesterolemic patients (17 men; 51+/8 years; plasma cholesterol, greater than or equal to 240 mg/dL) and 23 normal controls (12 men; 48+/-7 years; plasma cholesterol, <210 mg/dL). Drugs were infused into the brachial artery, and the response of the forearm vasculature was measured by strain-gauge plethysmography. Basal blood flow and vascular resistance were similar in hypercholesterolemic patients and normal controls (3.1+/-1 versus 2.6+/-0.8 mL/min per 100 mL and 32.1+/-13 versus 36.1+/-12 mm Hg/mL(-1).min(-1) 100 mL(-1), respectively). The reduction in basal blood flow and increase in vascular resistance produced by L-NMMA were not significantly different between the two groups. L-NMMA markedly blunted the response to acetylcholine in normals (maximum flow decreased from 16.4+/-8 to 7.0+/-3; P<.005); however, the arginine analogue did not significantly modify the response to acetylcholine in the hypercholesterolemic patients (maximum how, 11.1+/-8 versus 10.0+/-8). L-NMMA did not modify the vasodilator response to sodium nitroprusside in either controls or patients. Conclusions. These findings indicate that hypercholesterolemic patients have a defect in the bioactivity of nitric oxide that may explain their impaired endothelium-dependent vascular relaxation.