Comparison of endothelium-dependent vasoactivity of internal mammary arteries from hypertensive, hypercholesterolemic, and diabetic patients

Background. Endothelium-dependent relaxation is abnormal in a variety of di seased states. Despite the widespread use of the internal mammary artery (I MA) in coronary artery bypass grafting, there is a lack of comparative stud ies on IMA endothelial-dependent function in patients with major cardiovasc ular risk factors. Methods. An IMA segment from 48 selected patients undergoing coronary arter y bypass grafting was harvested intraoperatively and assigned to one of fou r groups (n = 12): diabetics requiring therapy, hypertensives, hypercholest erolemic, and nondiabetic-normotensive-normocholesterolemic patients. Inter nal mammary artery specimens were cut into rings and suspended in organ bat h chambers, and the isometric tension of vascular tissues was recorded. The IMA rings were (1) precontracted with norepinephrine, and the endothelium- derived relaxation was evaluated by cumulative addition of acetylcholine, ( 2) contracted with cumulative concentrations of endothelin-1, and (3) contr acted with the nitric oxide synthase inhibitor, N-G-monomethyl-L-arginine. Furthermore, the release of prostacyclin prostacyclin by the IMA rings was directly measured during basal tone conditions and at the end of the variou s pharmacologic interventions. Histology of IMA rings was randomly performe d. Results. The results obtained in these experiments showed that IMA rings ha rvested from hypertensive patients have the greatest impairment of endothel ium-dependent response to relaxant and contracting stimuli (p < 0.01 versus nondiabetic-normotensive-normocholesterolemic tissues; p < 0.05 versus hyp ercholesterolemic and diabetic tissues) and prostacyclin release in normal and stimulated conditions. To a lesser extent, hypercholesterolemic and dia betic tissues show similar depression (diabetic > hypercholesterolemic) bot h of relaxation and prostacyclin production, with respect to nondiabetic-no rmotensive-normocholesterolemic specimens (p < 0.05). Histology findings (s canning electron microscopy) did not differ in multiple sections from vesse l studies. Conclusions. Major cardiovascular risk factors affect the endothelium-depen dent vasoactive homeostasis of human IMA differently. Depression of relaxat ion is highest in patients with a history of hypertension. These findings m ay be pertinent to early and long-term treatment of patients undergoing cor onary artery bypass grafting. (C) 2001 by The Society of Thoracic Surgeons.