Evaluation of Angiotensin II Metabolism in Sheep by Radioimmunoassay

The immunoreactive material detected in sheep arterial blood by the radioimmunoassay procedure was shown to be predominantly the octapeptide angiotensin II and to be the valine-5 form. Levels in venous blood were 60% of arterial. A reasonably proportionate relationship was demonstrated between angiotensin II and sodium loss and renin during the onset of sodium deficiency. Following a single injection of angiotensin II into sheep, the biological half-life of the peptide was found to be less than 1 min. The change in blood pressure after injection of the angiotensin II closely followed the change in angiotensin II concentration determined by the immunoassay. Continuous infusion of angiotensin II until plateaued levels were reached allowed calculation of the blood clearance rate, which was approximately 100 1/hr. Knowledge of the blood clearance rate allowed calculation of angiotensin II production rates during sodium deficiency and following renin infusion. A linear relationship existed between the differen...