Development of a radioimmunoassay for cyclic somatostatin: antibody production, comparative radioiodination, and dose-response curve.

Since somatostatin lacks a tyrosine residue that can be readily iodinated, three different radiolabeling procedures for synthetic cyclic Tyr^som'atostatin were compared with each other. In addition, cyclic somatostatin was radiolabeled with the Bolton-Hunter reagent. The radiolabeled antigens were purified by G-25 Sephadex adsorption chromatography and thus separated from unreacted components. Maximal yields were achieved when Tyr-somatostatin was iodinated with chloramine-T the largest immunochemical reactivity, however, was obtained by applying the lactoperoxidase-catalysed iodination with I. Iodinated somatostatin-derivatives adsorbed onto an inorganic as well as an organic matrix; the percentage of non-specific binding was 14%.