Metabolic behavior of angiotensins in normotensive human plasma in the supine and upright postures

The effect of activating the renin-angiotensin system on the metabolism of angiotensins (ANGs) in normotensive human plasma was investigated. In normotensive supine human plasma, four peptides with in vitro angiotensin I-converting enzyme (ACE) inhibitory activity which correspond to the sequence of ANG (3-8), ANG (4-8), ANG (5-8), and ANG (3-4) existed at a concentration of > 39 fmol/ml of plasma. When activating the renin activity by keeping upright in posture for 60 min, ANG II and the four peptides significantly increased as compared with the levels in the supine posture, except for ANG I. In particular, Val-Tyr corresponding to ANG (3-4) in the upright posture was about 4-fold more than the value in the supine posture, and was predominantly present (447 fmol/ml of plasma) as well as ANG I. As a result of in vitro degradation tests on ANGs, ANG (3-4) was produced from ANG I, and not from ANG II, III or (3-8), during the 30-min incubation.