Distribution of 125I‐labeled human growth hormone in immature, hypophysectomized rats pretreated with ACTH or unlabeled human growth hormone

Whole‐body autoradiograms were prepared from intact and hypophysectomized (Hypox) rats after receiving 125I‐HGH iv. In addition, some hypox rats received unlabeled HGH or ACTH six minutes before receiving the 125I‐HGH. Hypox rats had greater concentrations of radioactive material in the renal cortex, adrenal cortex, liver and submandibular gland than was present in blood. Pretreatment with ACTH increased the radioactive material in the inner zones of the adrenal cortex; liver and renal cortex contained more radioactive material than blood; and the submandibular gland contained an amount equal to that in blood. Pretreatment with unlabeled HGH greatly suppressed uptake of radioactivity in liver and adrenal cortex and slightly increased the uptake in the renal cortex. Radioactivity could not be detected in the renal medulla or urine of any of the rats. No concentration of radioactive material greater than that seen in blood was present in any other organ or tissue in any of the groups. In the intact rats, the kidney and the adrenal cortex had the greatest concentrations of radioactivity, while the concentration in the liver was equal to that in blood. Autoradiograms were also prepared from sections from untreated hypox rats that were dipped in 125I‐HGH solutions. These confirmed the presence of binding sites in the adrenal cortex and liver for 125I‐HGH. No binding of radioactive material was seen in the kidney.