Effect of large doses of 131I-19-iodocholesterol on metapyralone-induced adrenal cortical hyperplasia in dogs.

The potential use of 131I-19-iodocholesterol to treat ACTH excess Cushing's disease was evaluated in the dog. Three normal female dogs were given LD50 radiation doses of 131I-19-iodocholesterol without producing gross or histopathologically demonstrable change of the adrenals at autopsy 3 months later. The adrenal cortices of three dogs were made hyperplastic (to simulate the adrenal cortex in Cushing's disease) with ACTH and three with Metapyralone. In addition these six dogs were given KD50 doses of 131I-19-iodocholesterol. Three months after treatment, the adrenal glands of the ACTH-treated dogs were not enlarged, the cortex was thicker than normal, and there were no changes attributable to irradiation. At 3 months, the Metapyralone-treated dogs had enlarged adrenals, widening of the adrenal cortex, and no necrosis or other changes attributable to irradiation. It is concluded that a therapeutic trial of 131I-19-iodocholesterol in the treatment of Cushing's disease is not indicated.