Abstract
An autoradiographic method for studying the retention and distribution of radioactive Zn65 in the rat pancreas was described. Zn65 entered both islet and acinar tissue, but the rates of loss from these two tissues were strikingly different. Although the acinar cells lost the radioisotope quickly, the concentration in islet cells remained high and constant throughout the 92 hours of observation. Islet Zn65 concentration was found to be higher than any organ studied at all periods except those immediately following the injection. Approximately 58% of the injected metal is excreted logarithmically with a biological half-life of about 40 hours. The remainder is retained for a much longer period.