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Localization of Radiolabeled Enzyme inhibitors in the Adrenal Gland

University of Michigan Medical Center, Ann Arbor, Michigan

Correspondence: For reprints contact: William H. Beierwaltes, Nuclear Medicine Sect., University of Michigan Medical Center, Ann Arbor, MI 48109.

ABSTRACT

Tissue distribution studies were performed in rats and dogs at five time intervals between 10 min and 24 hr after the intravenous injection of one of the following radiolabeled adrenocortical enzyme inhibitors: ³H-amino-glutethimide, ¹²⁵I-3-iodoaminoglutethimide, ³H-SKF-12185, ¹²⁵I-3-SKF-12185, ³H-metyrapone, ³H-metyrapol, ³H-amphenone B, and ³H-SU-10603. In rats, ³H-SKF-12185 showed the highest uptake in the whole adrenal (3.5% kg dose/gm at 1 hr). In dogs, ³H-metyrapol showed the highest uptake in the adrenal cortex (9% kg dose/gm at 1 hr), and the peak cortex-to-liver concentration ratio was 57 at 2 hr. These peak uptakes were comparable to those obtained with the conventional iodocholesterols, but they were reached much earlier, with elimination of most of the adrenal radioactivity by 24 hr. These properties would permit the use of ¹²³I as the label and a higher tracer dose, resulting in a higher photon flux. Thus, the radiolabeled enzyme inhibitors show promise as adrenal-scanning agents, with a markedly shortened scanning procedure, a lower absorbed radiation dose, and better resolution.