Angiotensin-converting enzyme activity in ocular fluids.

Angiotensin II is a biological active octapeptide that is formed by the action of angiotensin-converting enzyme (ACE) on the inactive precursor, angiotensin I. ACE activity was found in tears and aqueous humor from both rabbit and human eyes. The activity was higher in tears than aqueous humor. Enzyme activity was determined fluorimetrically from the rate of breakdown of the substrate, hippuryl-L-histidyl-L-leucine. The enzyme activity was further characterized by determining the effects of inhibitors. There was a significant difference in ACE levels in human tears when eye color was considered. People with either green or brown eyes had a higher ACE level than did blue-eyed individuals. The presence of this enzyme activity in ocular fluids suggests that angiotensin II may play a role in normal ocular physiology.