Thrittene radioimmunoassay: description and application of a novel method

In the present paper the development and application of a novel thrittene radioimmunoassay (RIA) are described. ¹²⁵I-labeling of Tyr⁽⁰⁾-thrittene was performed by the iodogen-method and the mono-iodinated peptide, as RIA tracer, was separated by reversed-phase high performance liquid chromatography (HPLC). The RIA results show that the antiserum used in the radioimmunoassay turned to be C-terminal specific, without significant affinity to other members of the somatostatin peptide hormone family. Detection limit of the assay was 0.2 fmol/ml. This highly specific and sensitive thrittene RIA was used to investigate the distribution of thrittene in the rat gastrointestinal tract and other tissue samples. Different areas of the gastrointestinal tract and other tissues were removed from rats and after extraction the samples were processed for thrittene radioimmunoassay. Highest concentrations were found in the duodenum samples followed by jejunum and ileum, however, all the examined tissues contained highly enough thrittene for the measurement.