The effect of oxygen tension on the in vitro production and release of angiotensin-converting enzyme by bovine pulmonary artery endothelial cells.

Cultured bovine pulmonary artery endothelial cells maintained in airtight chambers were exposed to various oxygen tensions. Exposure to hypoxia (3% O2) for 24 or 48 h resulted in increased cell angiotensin-converting enzyme (ACE) activity compared with cells exposed to normoxia (20% O2), but there was no change in cell supernatant ACE activity. The increase in enzymatic activity could not be attributed to changes in cell protein content or number. The exposure of cells to hyperoxia (80% O2) for 24 or 48 h caused decreased cell and culture supernatant ACE activity compared with cells exposed to normoxia, but the effects of hyperoxia may be attributed to reduced cell growth rates. Cell exposed to 7% O2 and 20% O2 had similar ACE activities. Shorter term (6 h) exposure of cells to 3% O2 showed no difference in cell ACE activity or in conversion of ACE substrate added directly to culture medium compared with cells exposed to normoxia. Our studies show that oxygen tension affects endothelial cell ACE activity.