DIRECT, SIMPLIFIED, AND SENSITIVE ASSAY OF ANGIOTENSIN-II IN PLASMA EXTRACTS PERFORMED WITH A HIGH-AFFINITY MONOCLONAL-ANTIBODY

A very simple, fast, and sensitive RIA of angiotensin (Ang) II has been developed, based on a monoclonal antibody with high affinity and specificity, making possible the direct measurement of circulating Ang II in human plasma after solid-phase extraction. The purified monoclonal antibody 4D8 has an association constant of 1.3 x 10(11) L/mol with Ang II and a cross-reactivity of < 1 % for Ang I. The assay can detect as little as 0.8 fmol of Ang II in 2 mL of plasma and is not influenced by the presence of Ang I. Analytical recoveries between 112% and 116% were obtained for Ang II added to human plasma at physiological concentrations. Comparison of the RIA with a reversed-phase, high-performance liquid chromatographic method followed by RIA to measure Ang II in human plasma samples from normal and hypertensive subjects and from normotensive subjects before and after an acute inhibition of angiotensin-converting enzyme with captopril (50 mg)-showed a high degree of correlation (r2= 0.93) between the two methods.