Release of angiotensin converting enzyme by the lung after Pseudomonas bacteremia in sheep

We studied release of angiotensin-converting enzyme (ACE) by the lung after acute injury associated with an increase in pulmonary vascular permeability. In eight adult sheep with chronic lung lymph fistulas, we measured lymph flow (QL), and both ACE activity and total protein content in lymph and plasma under base-line conditions and during 24 h after an infusion of live pseudomonas organism. Under base-line conditions, ACE activity in plasma was 4.93 +/- 0.43 U/ml (mean +/- SEM). The [lymph]/[plasma] ([L]/[P]) ratio for ACE was 0.93 +/- 0.18, compared with a ratio of 0.79 +/- 0.08 for albumin (mean +/- SD). We estimated the molecular weight of ovine ACE to be 145,000 by gel chromatography. Predicted [L]/[P] ratio for a molecule this size is 0.51. Thus, a substantial fraction of ACE activity detected lung lymph under base-line conditions (11.1 +/- 6.2 U/h; mean +/- SD) originated in the lung, and did not diffuse passively from plasma. After pseudomonas infusion, endothelial injury was demonstrated by a rise in pulmonary vascular clearance for total protein (Crp = QL X [L]/[P]). Crp = 3.1 +/- 0.6 ml/h before pseudomonas bacteremia, and rose to 6.7 +/- 1.2 ml/h by 2 h after onset of the infusion (means +/- SEM, p less than 0.05). Crp remained significantly elevated for at least 10 h after the infusion. Release of ACE into lung lymph doubled after acute lung injury and equaled 22.3 +/- 13.8 U/h at 4 h after onset of the infusion. ACE secretion into lung lymph had returned to baseline levels by 24 h after bacteremia. We did not observe a significant rise in plasma ACE activity after acute lung injury. Pseudomonas bacteremia in sheep results in acute, reversible lung injury associated with increased pulmonary vascular permeability, and increased release of ACE by the lung. Failure to detect a rise in plasma ACE content might result from dilution in the large vascular pool or rapid catabolism of the enzyme at some site distant from the lung.