Angiotensin I conversion and vascular reactivity in pathophysiological states in dogs

To determine if angiotensin converting enzyme activity is altered by acute pathophysiological insults, the authors assessed angiotensin I conversion using a blood pressure response technique in anesthetized dogs studied during acute 100% O₂ breathing and acute acid-base derangements. Also, they determined systemic vascular reactivity to angiotensin II by measuring the magnitude and duration of the arterial blood pressure response to intra-arterial injections of angiotensin II under these same conditions. Angiotensin I conversion found in normoxia [91 ± 7 (SD)%] was unchanged by acute acidosis, alkalosis, and hyperoxia. During acute hyperoxia the mean half time of the hypertensive response increased from 68 ± 25 (SD) s at a PaO₂ of 112 ± 18 (SD) Torr to 100 ± 34 (SD) s at a PaO₂ of 491 ± 47 (SD) Torr (P < 0.01). No other pathophysiological condition studied had any effect on reactivity of systemic vasculature to angiotensin II. The authors conclude that, except during acute hypoxia as previously shown, converting enzyme activity is resistant to other pathophysiological insults and that vascular responsiveness to angiotensin II is enhanced by hyperoxia.