123I-tyrosine-(A14)-insulin: preparation and preliminary clinical studies.

Insulin was radioiodinated with 123I (123I-tyrosine-(A14)-insulin) to a specific activity of 1 micrograms/mCi, corresponding to 0.025 I.U. of insulin/mCi. This preparation was used for in vitro binding experiments with adipose tissue, showing active binding to the two subunits of the known insulin receptor. In a preliminary clinical investigation, 5 adipose patients with (n = 2) and without (n = 3) diabetes mellitus Type II, were subject to in vivo injection of the same radiolabeled product using 3 mCi/patient. During the first minutes of dynamic imaging, the liver was the major organ of tracer uptake in all patients. Furthermore, the pancreas, and in one patient the kidneys, were visualised. Further studies on insulin in vivo kinetics and quantification are under way.