Determination of endogenous peptides with in vitro ACE inhibitory activity in normotensive human plasma by the fluorometric HPLC method.

An in vitro degradation test of angiotensin (ANG) II or III in normotensive supine human plasma from 9 healthy male subjects confirmed the production of smaller ANG metabolites with angiotensin I-converting enzyme inhibitory activity. These metabolites were identified as ANG (3-8), ANG (5-8), and ANG (3-4), whose respective peptide concentrations were determined by our proposed naphthalene-2,3-dialdehyde (NDA)-HPLC method to be 64 +/- 9, 39 +/- 5, 176 +/- 22, and 197 +/- 35 fmol/ml of plasma.