Visualization of nonfunctioning adrenal adenomas with iodocholesterol: possible relationship to subcellular distribution of tracer.

[131I] 19-iodocholesterol (I-131 C) correctly located adrenocortical adenomas in four patients who had no clinical or biochemical evidence of excessive steroid production. Three of the four "nonfunctioning" adenomas showed significant quantities of lipid histologically. To clarify the discordance between uptake and adrenal-steroid excretion, the subcellular location of I-131 C was studied. Normal rats and rats treated with ACTH or aminogluthimide (AG) were injected intravenously with I-131 C or [3H] cholesterol (H-3 C) and killed after three days. The homogenized adrenals were subjected to subcellular fractionation. Treatment with AG increased both the amount and the percentage of both I-131 C and H-3 C contained in the lipid fraction. ACTH treatment decreased H-3 C content but did not change I-131 C content in the lipid layer, suggesting an impairment of I-131 C mobilization from lipid droplets. The data demonstrate that excess steroid production is not necessary for I-131 C uptake and provide an explanation why certain biochemically nonfunctioning adrenocortical adenomas are visualized with I-131 C.