A sensitive method for precise measurement of endogenous angiotensins I, II&III in human plasma

We measured endogenous angiotensins (ANGs) I, II&III using a system of extraction by Sep-Pak column followed by high performance liquid chromatography (HPLC) combined with radioimmunoassay (RIA). An excellent separation of ANGs was obtained by HPLC. The recovery of ANGs I, II&III was 80-84%, when these authentic peptides were added to 6 ml of plasma. The coefficient of variation of the ANGs was 0.04-0.09 for intra-assay and 0.08-0.13 for inter-assay, thereby indicating a good reproducibility. Plasma ANGs I, II&III measured by this method in 5 normal volunteers were 51,4.5 and 1.2 pg/ml. In the presence of captopril, ANGs II&III decreased by 84% and 77%, respectively, while ANG I increased 5.1 times. This method is therefore useful to assess the precise levels of plasma ANGs.