Previous estimates of the half-life of synthetic somatostatin have been based upon the disappearance rate of 125I-labeled Tyr1-somatostatin. In the present study, the half-life of infused synthetic somatostatin was determined by RIA and compared with the duration of its suppressive action upon plasma insulin and glucagon. After the end of a 2-h infusion of somatostatin (500 ng/min), the radioimmunologically measured half-life was 1.82 min. The reappearance half-times for insulin and glucagon were 1.4 and 6.7 min, respectively. These data show that calculations of the half-life of somatostatin-like immunoreactivity in plasma may differ from estimates based on the duration of its biological activities, which may differ from one another.
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