Binding of iodinated angiotensin congeners to angiotensin II antibodies

Antibodies against angiotensin II (A II) were generated in rabbits by immunization with val5-angiotensin II coupled to albumin. All antisera bound significant amounts of 125I-labelled A II hepta (2-8) and hexapeptide (3-8), but angiotensin I (A I) was not bound. High specificity for A II was found in 3 sera out of 10. The other sera showed above 50% cross-reaction with hepta- or hexapeptide, or both. No sera were found to cross-react with A I. The amino acids in position 1 and 2 may become additional immunological determinants, providing the basis for the generation of antibodies highly specific for A II. Labelling with 125I using the chloramine method may alter the immunoreactivity of angiotensin congeners. Selected antisera against A II may be used for radioimmunoassays of the biologically active angiotensin "III" (2-8 heptapeptide) and the 3-8 hexapeptide fragment of A II.