INVESTIGATION OF DECREASED AVAILABILITY OF NITRIC-OXIDE PRECURSOR AS THE MECHANISM RESPONSIBLE FOR IMPAIRED ENDOTHELIUM-DEPENDENT VASODILATION IN HYPERCHOLESTEROLEMIC PATIENTS

Objectives. The purpose of this study was to determine whether the impaired endothelium dependent vasodilation of hypercholesterolemic patients is due to decreased availability of L arginine, the substrate for nitric oxide. Background. Patients with hypercholesterolemia have impaired endothelium dependent vasodilation that is related to a defect in the endothelium derived nitric oxide system. However, the precise location of this abnormality has not been determined. Methods. The study included 12 hypercholesterolemic patients (6 men, 6 women; 52 +/- 9 years old; serum cholesterol >240 mg/dl) and 15 normal volunteers (8 men, 7 women; 50 +/- 6 years old; serum cholesterol <210 mg/dl). The forearm vascular responses to intraarterial infusion of acetylcholine, an endothelium-dependent vasodilator (7.5, 15, 30 mu g/min), and sodium nitroprusside, a direct smooth muscle dilator (0.8, 1.6, 3.2 mu g/min) were studied before and during infusion of L- or D-arginine (a stereoisomer of arginine that is not a nitric oxide precursor). Results. The response to acetylcholine was lower in hypercholesterolemic patients than in control subjects. However, no significant difference was observed with sodium nitroprusside infusion. L-Arginine augmented the response to acetylcholine in normal subjects (maximal blood flow increased from 14.4 +/- 7 to 18.9 +/- 10 ml/min per 100 ml, p < 0.002). In contrast, in the hypercholesterolemic lesterolemic patients, only a mild but not significant improvement in the response to acetylcholine was observed with the infusion of L-arginine (maximal blood flow increased from 6.8 +/- 4 to 8.4 +/- 5 ml/min per 100 mi; p = 0.16); however, a similar mad but not significant change was also observed with D-arginine (maximal blood flow increased from 6.8 +/- 4 to 8.3 +/- 4 ml/min per 100 ml,, p = 0.07). L-Arginine did not modify the response to sodium nitroprusside in either group. Conclusions. The augmentation of endothelium-dependent vasodilation by L arginine, the nitric oxide precursor, is defective in hypercholesterolemic patients. This supports the concept of an abnormal endothelium derived nitric oxide system in hypercholesterolemia and indicates that decreased availability of nitric oxide substrate is not responsible for the impaired endothelial function in this condition.