Chymase-dependent angiotensin II formation in the saphenous vein versus the internal thoracic artery

Objectives: The great saphenous vein graft is known to be less patent than the internal thoracic artery graft. Recently, we reported that chymase-depe ndent angiotensin II formation plays an important role in the development o f intimal hyperplasia in dog grafted veins. In this study we investigated t he levels of angiotensin II-forming enzymes, angiotensin-converting enzyme, and chymase in human saphenous veins and internal thoracic arteries. Methods: The saphenous vein and internal thoracic artery specimens were obt ained from coronary artery bypass grafts of patients during surgical proced ures (saphenous vein, n = 16, internal thoracic artery, n = 16). Activities of angiotensin-converting enzyme and chymase were determined by using the extract from the saphenous vein or internal thoracic artery. Sections of th e saphenous vein or internal thoracic artery were stained with van Gieson's elastin stain and were immunostained with anti-human chymase antibody. Results: The activities of angiotensin-converting enzyme in the saphenous v ein and internal thoracic artery were 0.34 +/- 0.12 and 0.32 +/- 0.17 mU/mg protein, respectively, and the difference was not significant. The chymase activity in the saphenous vein was significantly higher than that in the i nternal thoracic artery (saphenous vein, 10.1 +/- 0.81 mU/mg protein; inter nal thoracic artery, 6.21 +/- 1.86 mU/mg protein). Chymase-positive cells i n the saphenous vein were located in both the media and adventitia, and tho se in the internal thoracic artery were located only in the adventitia. The number of chymase-positive cells in the saphenous vein was about 2.6 times that in the internal thoracic artery. Conclusion: The chymase activity, but not the angiotensin-converting enzyme activity, was significantly higher in the saphenous vein, suggesting that the high levels of chymase activity may be related to the poorer performanc e of the saphenous vein for use as a bypass conduit.