Increased endothelin release by cultured human smooth muscle cells from atherosclerotic coronary arteries

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Abstract
Objectives Endothelin, a 21-amino acid peptide initially purified from the medium of cultured endothelial cells, is a potent vasoconstrictor exerting its effects predominantly in a paracrine or autocrine manner. Recent data indicate that endothelin is also synthesized by cultured vascular smooth muscle cells and that endothelin is an effective stimulator of smooth muscle cell proliferation. This study aimed to investigate the endothelin release of cultured human smooth muscle cells, isolated from coronary plaques and from normal coronary tunica media, and to determine circulating endothelin concentrations in patients with coronary artery disease compared to control subjects. Methods Coronary plaque material was extracted by thrombendarterectomy during aorto-coronary bypass grafting (n = 19). Segments of normal coronary arteries were obtained at autopsy (n = 33). Cells were isolated by enzymatic disaggregation and identified as smooth muscle cells with antibodies against smooth muscle α-actin. Venous blood samples were drawn from patients with coronary artery disease undergoing cardiac catheterization (n = 32) and from control subjects (n = 38). Endothelin concentrations in culture medium and in plasma samples were measured by radioimmunoassay after Sep Pak C18 extraction. Results Cultured smooth muscle cells, isolated from coronary plaques, released a significantly (P < 0.001) higher amount of immunoreactive endothelin into the culture medium (39.2 ± 3.9 pg/104 cells, mean ± s.e.m., 31 supernatant samples) than smooth muscle cells from normal coronary tunica media (3.9 ± 0.8 pg/104 cells, 28 samples). Circulating endothelin concentrations were slightly elevated (P < 0.01) in patients with coronary artery disease (3.8 ± 0.2 pg/ml) compared to control subjects (3.0 ± 0.2 pg/ml). Conclusions These data suggest that the endothelin production is markedly increased in smooth muscle cells of coronary atherosclerotic plaques. The enhanced endothelin release may stimulate smooth muscle cell proliferation in a paracrine or autocrine manner and thus may contribute to the development or progression of coronary artery disease.

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