Specificities of Antibodies to Normetanephrine

Antibodies to normetanephrine were produced in rabbits by immunization with conjugates synthesized by linking the amino group of the hapten to the amino groups of the carrier macromolecules using glutaraldehyde. The antibodies are highly specific for the ring structure of the normetanephrine molecule and also recognize substitutions in the side chain. Metanephrine, however, is as effective an inhibitor as the homologous normetanephrine. 3-Methoxytyramine inhibits 5-times and 3-methoxy-4-hydroxyphenylglycol 24-times less effectively than normetanephrine. With this antiserum a radioimmunoassay capable of detecting 10 ng normetanephrine was developed. In this radioimmunoassay, the binding of antibodies to human serum albumin, the immunogenic carrier molecule, to the albumin in the 125I labelled albumin-normetanephrine antigen is effectively eliminated by addition of excess of unlabelled albumin. The specificity of the antibodies allows for normetanephrine determinations, especially in brain and cerebrospinal fluid where the interference by metanephrine is negligible.