[A comparative analysis of the behavior of two labeled ACTH preparations in the body]

Experiments were conducted on male Wistar rats. A study was made of the intensity of incorporation into the liver, kidneys, the thyroid gland, the adrenal glands and the rate of elimination from the blood plasma of two ACTH preparations iodated by Greenwood's method: International Standard for Corticotropin, Mill Hill, London; Hum ACTH--Hid-28, Richter. It appeared that the preparations of natural swine -125-I-ACTH and of synthetic -131-I-ACTH were identical chromatographically and by saturation with iodine-125 and iodine-131, respectively, but differed by their behaviour in the organism. T1/2 for -125-I-ACTH (swine) was 4.7 min; the hormone was not incorporated into hepatic parenchyma, and only very weakly--into the kidneys, but it was intensively accumulated by the adrenal galnds. Radioactivity peak was recorded in the adrenal cortex 6 minutes after the administration of the labeled hormone. -131-I-ACTH (synthetic) disappeared from the blood with a falf-period of 11.2 min, was incorporated into the liver and particularly into the kidneys, and was not accumulated in the adrenal gland.