Dyslipidemia and endothelium-dependent relaxation in internal mammary arteries used for coronary bypass surgery

Objective: Impairment of endothelium-dependent relaxation is related to dyslipidemia and may be an early marker for atherosclerosis in angiographically smooth arteries. The aim of the present study was to relate preoperative serum lipids to endothelium-dependent relaxation in internal mammary arteries of patients undergoing coronary bypass surgery, Methods: The study group consisted of 37 patients, from whom segments of the internal mammary artery were obtained during surgery. Measurements of endothelium-dependent relaxation were performed in organ baths by adding methacholine (10 nM-10 mu M). Results: All internal mammary arteries dilated in response to methacholine, ranging from 4 to 112% of the precontraction to 10 mu mol phenylephrine. In a multiple regression model, increased total serum cholesterol appeared to be the best predictor for impaired endothelium-dependent relaxation. A 1 mmol increase of total cholesterol was associated with a 11.2% decrease of endothelium-dependent relaxation (P = 0.006). When total cholesterol was omitted from the model, LDL-cholesterol became the best predictor of endothelium-dependent relaxation (regression coefficient 10.3%/mmol; P = 0.02). No other variable was significantly associated with endothelium-dependent relaxation, and none of the preoperative variables was associated with endothelium-independent relaxation, expressed as the response to sodium nitrite (10 mM). Conclusion: Our study showed that endothelium-dependent relaxation in apparently non-diseased internal mammary arteries used for coronary bypass surgery was independently related to preoperative (LDL)-cholesterol levels.