Acetaldehyde inhibits angiotensin-converting enzyme activity of bovine lung

The role of ethanol and its primary metabolite, acetaldehyde, were investigated for their effects upon angiotensin-converting enzyme (ACE) (EC 3.4.15.1), since the enzyme plays a key role in the maintenance of blood pressure homeostasis by transforming angiotensin I into angiotensin II and degrading bradykinin. ACE was extracted from a 38 000 × g pellet of bovine lung homogenate with 0.05-M N-(2-hydroxyethyl)piperazine- N′-2-ethanesulfonic acid (HEPES) buffer, pH 7.0/0.4 M NaCl 10 μ M ZnCl 2 0.5% Triton X-100. The solubilized enzyme was preincubated with increasing concentrations of acetaldehyde (0.177–2.213 M) for 30 min at 0°C. Progressive inhibition of 41–84% was observed as enzyme aliquots were assayed with hippuryl-L-histidyl-L-leucine (HHL) as the substrate. The interaction of angiotensin-converting enzyme with acetaldehyde was rapid under these conditions. Ethanol appeared to have no effect upon enzymic activity at comparable concentrations. These results suggest that acetaldehyde-mediated ACE inhibition in vivo may play a contributory role in the development of vasodilation and facial flush reaction consequent to ethanol consumption, thereby accounting for localized hypotension.