Dual pathway for angiotensin II formation in human internal mammary arteries

Abstract

Angiotensin converting enzyme (ACE) is thought to be the main enzyme to convert antiotensin I to the vasoactive angiotensin II. Recently, in the human heart, it was found that the majority of angiotensin II formation was due to another enzyme, identified as human heart chymase. In the human vasculature however, the predominance of either ACE or non‐ACE conversion of angiotensin I remains unclear. To study the effects of ACE‐ and chymase‐inhibition on angiotensin II formation in human arteries, segments of internal mammary arteries were obtained from 37 patients who underwent coronary bypass surgery. Organ bath experiments showed that 100 μM captopril inhibited slightly the response to angiotensin I (pD₂ from 7.09±0.11–6.79±0.10, P10] angiotensin I, a selective substrate for ACE, and the maximum contraction was reduced from 83±19%–23±17% of the control response (P=0.01). A significant decrease of the pD₂ of angiotensin I similar to captopril was observed in the presence of 50 μM chymostatin (pD₂ from 7.36±0.13–6.99±0.15, PBritish Journal of Pharmacology (1998) 125, 1028–1032; doi:10.1038/sj.bjp.0702150