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A very reliable isocratic reverse phase high performance liquid chromatography (HPLC) system has been developed to separate angiotensins, which combined with a very sensitive radioimmunoassay, provided precise measurements of the endogenous angiotensin II (AII) concentration in the rat plasma in different experimental circumstances. The overall recoveries of AII were 95.2 +/- 15.8% (means +/- SD) when 10 pg of this peptide was added to 1 ml of human plasma. The coefficient of variation for within-assay precision was 10% (n = 6). The plasma AII, measured by this method, of normal male pentobarbital-anesthetized rats was 53.0-141.6 pg/ml (mean: 103.9 +/- 29.7 pg/ml). The plasma AII of rats fed a sodium deficient diet was 300.0 +/- 100.6 pg/ml, while that of rats given oral Enalapril, an angiotensin converting enzyme (ACE) inhibitor, for 1 week was 35.7 +/- 28.0 pg/ml. The plasma AII of bilaterally nephrectomized rats was 2.7 +/- 2.9 pg/ml 24 hours after nephrectomy and below the detection limit 48 hr after nephrectomy. This method, therefore, can be used to study AII in different pathophysiological states or after treatment with renin-angiotensin system inhibitors.
Huang et al. (1989) studied this question.