Release of angiotensin I-converting enzyme by endothelial cells in vitro.

Bovine fetal aortic endothelial cells cultured in serum-containing medium accumulate angiotensin I-converting enzyme (ACE) activity and also release it into the culture medium. Following subcultivation of a confluent culture using trypsin-EDTA, cellular ACE activity falls 50% within 8 h, but no ACE activity is detected in the medium, suggesting intracellular loss of the enzyme activity. ACE activity reappears in both the cell lysate and culture medium after the culture becomes confluent. The rate of accumulation of ACE activity released into the medium is always greater than that for cellular activity. For example, 21 days following subcultivation 80-85% of the total culture activity is detected in the medium. Both cellular and medium-associated ACE decrease proportionately as the culture progresses through its in vitro lifespan.