Sensitive radioimmunoassay for somatostatin using N-[125I]-Tyr-somatostatin as labelled antigen

A sensitive radioimmunoassay for somatostatin using N-[125I]-Tyr-somatostatin is described and compared with that using [125I]-Tyr1-somatostatin. The minimum detectable amount of somatostatin using N-[125I]-Tyr-somatostatin as tracer was 0.1 to 0.5 pg, which is approximately 10-fold lower than the lower detection limit of the RIA using [125I]-Tyr1-somatostatin. Moreover, it was found that the shelf-life of N[125I]Tyr-somatostatin was prolonged in comparison with labelled Tyr1-somatostatin. Human pancreatic and gastric extracts displayed immunological similarity to synthetic somatostatin tetradecapeptide.