Objective: The activity of the renin-angiotensin system may be important in determining the performance of coronary artery bypass grafts. We have examined the activity of tissue angiotensin-converting enzyme and the effects of angiotensin II in vessels used as bypass grafts.
Methods: Organ bath studies were used to determine the vasoactive effect of angiotensin II. The activity of the angiotensin-converting enzyme was assessed by metabolism of a specific synthetic substrate.
Results: The saphenous vein produced greater maximum responses to angiotensin II than did the internal thoracic artery. This response was not modified by inhibition of nitric oxide synthase, cyclooxygenase, or by an endothelin receptor antagonist in either vessel. Losartan, an AT1 receptor antagonist, inhibited the vasoconstrictor response in both blood vessels. Homogenates of saphenous vein and internal thoracic artery displayed tissue angiotensin-converting enzyme activity, which was inhibited by captopril. Enzyme activity was threefold greater in the vein. Both the contractile response to angiotensin II and the enzyme activity were retained in venous grafts removed up to 20 years after coronary bypass surgery.
Conclusions: These data demonstrate that marked differences exist in angiotensin-converting enzyme activity and AT1 receptor responses in the saphenous vein compared with the internal thoracic artery. These findings may have important implications for the performance of the vein when used as a coronary artery bypass graft and may have clinical implications for the use of angiotensin-converting inhibitors and AT1 receptor antagonists in the prevention and treatment of vein graft disease.