Endothelin Peptide and Receptors in Human Atherosclerotic Coronary Artery and Aorta

Abstract

The aim of this study was to determine whether there is an alteration in the distribution or quantity of endothelin (ET) peptide or receptor subtypes in human atherosclerotic arteries. Levels of endogenous ET and big ET-1 detectable by radioimmunoassay in human aorta containing raised atherosclerotic plaques were significantly higher than those in histologically normal tissue (Student's t test, P<.01). Immunohistochemistry revealed ET-like immunoreactivity in endothelial cells lining the vessel lumen, neovascularization, recanalization of organized thrombus, and regions rich in macrophages. Little immunoreactivity was associated with vascular smooth muscle cells (VSMCs). Saturation binding assays with [¹²⁵I]ET-1 indicated comparable affinities and maximal densities of receptors in the media of diseased and normal coronary arteries. Quantitative autoradiography with subtype-selective radioligands revealed similar small proportions of ET_B receptors in the diseased and normal arterial media. In arteries with early and late disease, ET_A receptors were localized to medial smooth muscle but were lacking in the VSMCs of the intimal layer, where ET_B receptors were absent. ET_B receptors were detected on perivascular nerves and lymphoid aggregates. In atherosclerotic arteries, microautoradiography localized ET_B receptors to neovascularization and, interestingly, to macrophages. The results of this study indicate that there is an increase in ET and big ET-1 associated with fully developed atherosclerotic plaques. It is likely that this is derived from endothelial cells and macrophages but not VSMCs. ET_A receptors predominate in the media of both normal and diseased arteries. ET receptors are deficient in intimal smooth muscle, and ET_B receptors, where present, are found on endothelial cells and macrophages.