title: Measurement of plasma renin activity with use of HPLC-electrospray-tandem mass spectrometry.
abstract: BACKGROUND
  The measurement of renin activity is complicated by difficulties in the quantification of angiotensin 1 (Ang1), the product of the renin-catalyzed reaction. We report an HPLC-electrospray-tandem mass spectrometry (HPLC-ESI-MS/MS) method for the quantification of Ang1 as a measure of plasma renin activity (PRA).
  
  
  METHODS
  After incubation (37 degrees C for 3 or 18 h), samples were prepared using C18 solid-phase extraction. [Val]5Ang1 was used as the internal standard (IS). Chromatography was performed on a C18 column, using 200 mL/L ammonium acetate buffer-800 mL/L methanol as the mobile phase. The flow rate was 150 microL/min, with a chromatographic run time of 5 min/sample. Mass spectrometric detection was in the positive ionization mode with selected reaction monitoring (Ang1 m/z 649.0-->784.0; IS m/z 641.9-->770.4).
  
  
  RESULTS
  The assay was linear over the range 2.5-500 ng Ang1/mL, which corresponded to a limit of detection (signal-to-noise ratio of 3:1) of PRA of 0.14 ng Ang1. mL-1. h-1. The imprecision (CV) of the assay at PRA values of 26.1, 13.5, 3.2, and 0.78 ng Ang1. mL-1. h-1 was 7.0%, 7.0%, 15%, and 11%, respectively. Absolute recoveries were 92.3% (Ang1) and 87.4% (IS). Incubation times of 3 h vs 18 h in the PRA assay gave good agreement at PRA <2 ng Ang1. mL-1. h-1, but samples with a PRA of 2-5 ng Ang1. mL-1. h-1 gave lower PRA results after incubation for 18 h than after 3 h. We compared the HPLC-ESI-MS/MS assay and an RIA for the determination of PRA, with PRA incubation times of 3 h and 1.5 h, respectively. The mean PRA based on RIA of Ang1 was higher than that obtained using HPLC-ESI-MS/MS.
  
  
  CONCLUSIONS
  The HPLC-ESI-MS/MS method allows sensitive and specific measurement of PRA. The higher activities measured with the RIA method highlight its potential for overestimation of PRA.
authors.affiliation: Department of Clinical Pharmacology, Princess Alexandra Hospital, Brisbane, Queensland, Australia 4102.
authors.forename: V F
authors.initials: VF
authors.lastname: Fredline
authors.forename: E M
authors.initials: EM
authors.lastname: Kovacs
authors.forename: P J
authors.initials: PJ
authors.lastname: Taylor
authors.forename: A G
authors.initials: AG
authors.lastname: Johnson
mesh_terms: D002851:Chromatography, High Pressure Liquid; D006801:Humans; D013058:Mass Spectrometry; D011863:Radioimmunoassay; D012083:Renin / Q000097:blood*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013997:Time Factors
chemical_list: D012083:Renin