Abstract
The aim of this study was to determine the plasma and pericardial levels of endothelin-1 (ET-1) and its precursor big endothelin-1 (Big ET-1) in patients with unstable and stable angina prior to and following coronary bypass surgery. To further investigate the content of ET-1, tissue levels were studied in the internal mammary artery (IMA) in patients with stable and unstable angina pectoris. Finally, the difference in reactivity of the IMA to ET-1 and Big ET-1 in stable and unstable patients was evaluated. Plasma and pericardial levels of ET-1 and Big ET-1 were determined with radioimmunoassay in 81 patients (33 unstable) immediately before coronary bypass surgery, and at 6, 14, 40 and 64 h following the procedure. Specimens of the distal IMA from 12 patients (six unstable) were collected at the beginning of surgery for determination of tissue levels of ET-1. Additionally, distal internal mammary arteries were obtained from another 24 patients (12 unstable). These vessels were mounted in organ baths for functional studies on vascular reactivity to ET-1 and Big ET-1. The peripheral plasma levels of ET-1 in unstable patients were significantly lower in patients with unstable angina compared with patients with stable angina pectoris at all points of measurement. The levels of Big ET-1 were significantly higher pre-operatively in the unstable group, but decreased to similar levels to those of stable patients following coronary bypass grafting. There was no difference in ET-1 tissue content in the IMA between the patients. ET-1 and Big ET-1 caused an endothelin(A) (ET(A))-receptor blocker sensitive, concentration-dependent contraction of the IMA obtained from stable as well as unstable patients. It is concluded that unstable angina pectoris is associated with an increased ET-1 turnover. This increased turnover may participate in the local regulation of coronary vascular tone with subsequent influence of the condition of the patients. The present investigation also implies that ET(A)-blockade may be useful as an additional pharmacological principal in the treatment of unstable angina pectoris prior to revascularization, as well as to prevent post-operative arterial graft spasm.
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