METABOLIC BEHAVIOR OF ANGIOTENSINS IN NORMOTENSIVE HUMAN PLASMA IN THE SUPINE AND UPRIGHT POSTURES

The effect of activating the renin-angiotensin system on the metabolis m of angiotensins (ANGs) in normotensive human plasma was investigated . In normotensive supine human plasma, four peptides with in vitro ang iotensin I-converting enzyme (ACE) inhibitory activity which correspon d to the sequence of ANG (3-8), ANG (4-8), ANG (5-8), and ANG (3-4) ex isted at a concentration of > 39 fmol/ml of plasma. When activating th e renin activity by keeping upright in posture for 60min, ANG II and t he four peptides significantly increased as compared with the levels i n the supine posture, except for ANG I. In particular, Val-Tyr corresp onding 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 fm ol/ml of plasma) as,veil 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.