Angiotensin II and Its Heptapeptide (2-), Hexapeptide (3dash;) and Pentapeptide (4-) Metabolites in Arterial and Venous Blood of Man

• Published in: Circulation research Vol. 39; no. 5; pp. 671 - 677
• Main Authors: Semple, Peter F., Boyd, Alistair S., Dawes, Paul M., Morton, James J.
• Format: Journal Article
• Language: English
• Published: United States American Heart Association, Inc 01.11.1976
• Subjects: Adult; Aged; Amino Acid Sequence; Angiotensin II - analogs & derivatives; Angiotensin II - blood; Angiotensin II - isolation & purification; Arteries; Chromatography, Paper; Female; Half-Life; Heparin - pharmacology; Humans; Hydrolysis; Male; Middle Aged; Peptides - blood; Peptides - isolation & purification; Pregnancy; Radioimmunoassay; Renin - blood; Veins
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.RES.39.5.671

We made separate measurements of angiotensin II (A II) and of its immunoreactire metabolites (2–8 heptapeptide, 3–8 bexapeptide, and 4–8 pentapeptide) in arterial and venous plasma from subjects with widely different plasma levels of the peptides. A II and its three metabolites were extracted from blood, separated by paper chromatography, and measured by radioimmunoassay using an A II antisemm which had a 100% cross-reaction with each metabolite. In contrast to results of previous studies, A II was found to predominate in both arterial (60–100%) and venous (55–100%) blood. The biologically active 2–8 beptapeptide metabolite accounted for only 10% of the activity in arterial plasma. Radioimmunoassay of venous plasma extracts using an A II antisemm which had a low cross-reaction with the 3–8 hexapeptide and the 4–8 pentapeptide confirmed the results obtained using the antisemm which had a 100% cross-reaction with the metabolites. We conclude that radioimmunoassay methods for measuring A II in venous blood may be more accurate and relevant than has previously been recognized. The small difference between A II concentrations in arterial and venous plasma suggests further that there may be significant conversion of angiotensin I (A I) to A II in the limb vasculature.