Effect of acute hypoxia on the pulmonary conversion of angiotensin I to angiotensin II in dogs.

We studied the effect of acute hypoxia on pulmonary conversion of angiotensin I to II in anesthetized dogs. When arterial PO2 was decreased from 86 +/- 14 (SD) to 33 +/- 8 mm Hg without changing pH or PCO2, the single passage conversion of intravenous boluses of radiolabeled angiotensin I in tracer doses fell significantly (P less than 0.005) from 72 +/- 4 to 67 +/- 6%. The effect of comparable levels of hypoxemia on the conversion of continuous intravenous infusions of pharmacological doses (1000 times physiological) of angiotensin I was greater: from 55 +/- 14 to 33 +/- 13% (P less than 0.025). There was prompt return of percent conversion ratios to control levels when hypoxemia was reversed. We conclude that acute hypoxia is associated with a reversible decrease in pulmonary angiotensin converting enzyme availability.