Determination of kinin in the rat brain by a sensitive radioimmunoassay

Kinin level in the rat brain was determined using a highly sensitive radioimmunoassay with a purified tracer. Monoiodinated Tyr8-bradykinin (BK) was separated from the non-iodinated peptide by paper chromatography, using 0.2 M ammonium acetate as the developer. This purification method resulted in a ligand with a highly specific radioactivity (2200 muCi/nmol), which raised the radioimmunoassay sensitivity about 5-fold and enabled to determine the brain kinin level in the rat. The brain extract competed with iodinated antigen for an antibody binding site in the same manner as did authentic BK, indicating the immunological identity of them. Brain kinin level was estimated to be 139 +/- 79 fmol BK eq/g (n = 7) in an adult male rat of the Sprague-Dawley strain.