Responsiveness to Bradykinin in Veins of Hypercholesterolemic Humans

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Abstract

Background.

Hypercholesterolemia impairs endothelium-dependent dilation in arteries. We tested the hypothesis that hypercholesterolemia impairs endothelium-dependent vasodilation by an interaction between elevated plasma lipoproteins and a presumably normal endothelium using human veins in vivo; veins do not generally develop atherosclerosis and are appropriate for testing functional alterations.

Methods and Results.

Full dose-response curves were constructed in 13 hypercholesterolemic and 12 normocholesterolemic subjects by infusing bradykinin (0.25 to 508 ng/min) into hand veins preconstricted with the α-adrenergic agonist phenylephrine. The maximal relaxation induced by bradykinin was 80±38% in the controls and 103±40% in subjects with hypercholesterolemia (P=.08). Responsiveness to bradykinin was also determined after infusion of indomethacin (5.4 μg/min), a cyclooxygenase inhibitor, to block the contribution of prostaglandins; maximal responsiveness was greater in hypercholesterolemic subjects (112±41%) than in controls (81±31%) (P=.03). Hypercholesterolemic subjects were more sensitive to bradykinin, with an ED50 of 4.2 ng/min versus 10.9 ng/min in controls (P=.05); a similarly increased sensitivity was found in the presence of indomethacin. The response to a maximally effective dose of nitroglycerin was greater in hypercholesterolemic subjects (142±31%) versus 106±28% in controls (P=.007). In five hypercholesterolemic subjects, treated with lovastatin to normalize serum cholesterol concentrations, maximal responsiveness to bradykinin decreased from 103±52% to 80±28%.

Conclusions.

These results demonstrate that hypercholesterolemia in humans does not impair endothelium-derived relaxing factor-mediated venodilation. (Circulation.1993;88:2754–2761.)

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