Specific measurement of angiotensin metabolites and in vitro generated angiotensin II in plasma

Hypertension. 1986 Jun;8(6):476-82. doi: 10.1161/01.hyp.8.6.476.

Abstract

Combining high-performance liquid chromatography with radioimmunoassay enabled the precise measurement of different angiotensins and their metabolites in plasma. Peptides were extracted from 2 ml of plasma by reversible adsorption to phenylsilyl-silica, separated by isocratic high-performance liquid chromatography, and quantitated by radioimmunoassay using a sensitive but suitably cross-reacting angiotensin II antiserum. For the C-terminal angiotensin II metabolites (2-8)heptapeptide, (3-8)hexapeptide, and (4-8)pentapeptide, overall recoveries of 10 fmol peptide added to 1 ml of plasma were (mean +/- SD), 74 +/- 6, 68 +/- 8, and 67 +/- 11%, respectively. The detection limit for these peptides in plasma was 0.2 fmol/ml. Blanks were below the detection limits. In eight seated normal subjects treated for 4 days with enalapril, 20 mg p.o., q.d., angiotensin II metabolites tended to decrease during the 4 postdrug hours. However, their cumulated concentration in relation to octapeptide increased from 54 to 163% on Day 1 and from 62 to 103% on Day 4. After 4 hours of converting enzyme inhibition with enalapril there was still a close correlation between plasma renin activity and angiotensin-(1-8)octapeptide level (r = 0.83, p less than 0.05) and between blood angiotensin I and angiotensin-(1-8)octapeptide levels (r = 0.86, p less than 0.01). Adding angiotensin I in vitro raised the angiotensin-(1-8)octapeptide levels after incubation at 4 degrees C for 4 hours. Thus, immunoreactive "angiotensin II" does not disappear after converting enzyme inhibition largely because of the cumulated contribution of cross-reacting metabolites and partly because of in vitro generation of true angiotensin II.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Angiotensin I / blood
  • Angiotensin II / blood*
  • Angiotensin III / blood
  • Angiotensin-Converting Enzyme Inhibitors
  • Angiotensins / blood*
  • Angiotensins / immunology
  • Chromatography, High Pressure Liquid
  • Cross Reactions
  • Enalapril / pharmacology
  • Humans
  • In Vitro Techniques
  • Male
  • Radioimmunoassay

Substances

  • Angiotensin-Converting Enzyme Inhibitors
  • Angiotensins
  • Angiotensin II
  • Angiotensin III
  • Enalapril
  • Angiotensin I