Discrepancy between plasma angiotensin converting enzyme activity and in vivo extent of angiotensin I conversion in hypertensive rats.
1. The relationship of plasma angiotensin converting enzyme (ACE) activity to changes in the extent of angiotensin I (ANG I) conversion in vivo in rats with short-term and chronic (8 weeks) hypertension was examined. 2. Plasma ACE activity was measured by a fluorimetric assay and the extent of ANG I conversion was calculated from the equipressor doses of ANG I and ANG II in conscious rats. 3. The extent of ANG I conversion was higher in chronic one-kidney, one clip hypertensive rats than in the normotensive age-matched control rats (64.1 +/- 3.6% vs 34.8 +/- 5.2%), while no difference was found in the ACE activity measured in plasma from both groups. 4. In rats with acute hypertension, produced upon unclamping the renal pedicle occluded for 5 hours, the extent of ANG I conversion was increased when compared to the period prior to renal pedicle occlusion (from 38.8 +/- 4.1% to 68.6 +/- 8.5%), and plasma ACE activity remained unchanged. 5. These results indicate that circulating ACE cannot be used as an index of ANG I conversion in vivo and support the proposal that tissue ACE is responsible for the augmented ANG I conversion observed in vivo in both acute renal hypertension and chronic one-kidney, one clip hypertension.
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Departamento de Farmacologia, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Brasil.
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D000803:Angiotensin I / Q000096:biosynthesis*; D000806:Angiotensin-Converting Enzyme Inhibitors / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D001920:Bradykinin / Q000494:pharmacology; D006973:Hypertension / Q000378:metabolism*; D008297:Male; D007703:Peptidyl-Dipeptidase A / Q000097:blood*; D051381:Rats; D011919:Rats, Inbred Strains; D012044:Regression Analysis; D012084:Renin-Angiotensin System
D000806:Angiotensin-Converting Enzyme Inhibitors; D000803:Angiotensin I; D007703:Peptidyl-Dipeptidase A; D001920:Bradykinin