The walls of blood vessels are lined by flat cells that are responsible for releasing substance(s) that control the activity of the blood vessel. These cells are referred to as the endothelium of the blood vessel. One of the substances released from the endothelium is called nitric oxide (NO). This substance functions to keep blood vessels relaxed and to prevent blood from clotting inside the vessels.

Studies done by researchers in the Cardiology Branch of the National Heart, Lung and Blood Institute have shown that nitric oxide activity may be lower in patients with hardening of the arteries (atherosclerosis) and risk factors for atherosclerosis.

Another substance released by the cells of the endothelium is called bradykinin. It functions to stimulate the production of nitric oxide. Therefore bradykinin is also responsible for the relaxation and widening of blood vessels.

An enzyme found in the blood called angiotensin-converting enzyme (ACE) inactivates baradykinin and thereby decreases the production of nitric oxide. The activity of ACE is determined by genetics and is different in each person. Medications that block ACE (ACE-inhibitors) may be useful for patients with high levels of ACE activity.

This study is designed to determine;

1. The role of bradkinin in stimulating the production of nitric oxide
2. Whether ACE-inhibitors improve blood vessel relaxation caused by bradykinin
3. Whether ACE-inhibitors improve abnormal blood vessel relaxation
4. Whether ACE-inhibitors and bradykinin affect blood clotting
5. Whether blood vessel response to ACE-inhibitor and bradykinin depends on the patients genetic make-up