An immunoradiometric assay for the measurement of neuropeptide Y in plasma

The development of an immunoradiometric assay (IRMA) for the direct measurement of neuropeptide Y (NPY) concentrations in plasma is reported. The assay employs simultaneous addition of 125I-labelled affinity purified sheep anti-(NPY 31-36) immunoglobulin (IgG) and a rabbit anti-NPY serum to 0.25 ml volumes of standard or unknown. After 16 hr incubation at 4 degrees C NPY-bound labelled IgG is precipitated using sheep anti-(rabbit IgG Fc region) IgG coupled to Dynospheres solid phase. Precipitated counts are proportional to the NPY concentration in samples. Using this methodology it is possible to measure basal levels in normal human subjects (range 1-5 fmol/ml). Technical difficulties encountered in raising "site-specific" antisera to NPY during the establishment of this assay are outlined.