OBJECTIVE
We sought to assess the activity of endogenous endothelin-1 (ET-1) in hypercholesterolemic patients using antagonists of ET-1 receptors.
BACKGROUND
Endothelial dysfunction in hypercholesterolemic patients may contribute to their risk of premature atherosclerosis. Endothelin, a peptide released by endothelial cells, may be involved in this process by activating smooth muscle cell mitogenesis and leukocyte adhesion.
METHODS
Forearm blood flow (FBF) responses (strain-gauge plethysmography) to intra-arterial infusion of a selective blocker of ETa receptors (BQ-123) and, on a separate occasion, to ET-1 were measured in 12 hypercholesterolemic patients and 12 normal control subjects. In addition, on a different day, six hypercholesterolemic patients received co-infusion of BQ-123 and BQ-788 (a selective blocker of ETb receptors).
RESULTS
In normal subjects, BQ-123 did not significantly modify FBF from baseline (p = 0.78); however, in hypercholesterolemic patients, BQ-123 administration resulted in a significant vasodilator response (p < 0.001). Administration of exogenous ET-1 resulted in similar vasoconstrictor responses in patients (37%) and control subjects (35%) (p = 0.83). In hypercholesterolemic patients, the vasodilator response to selective ETa blockade was reversed by nonselective blockade of ET-1 receptors obtained by co-infusion of BQ-123 and BQ-788.
CONCLUSIONS
The vascular activity of endogenous ET-1 is enhanced in hypercholesterolemic patients, whereas their sensitivity to exogenous ET-1 is unchanged. These findings suggest increased production of ET-1, which may participate in the pathophysiology of vascular disease characteristic of hypercholesterolemia.
