IMAGING THE PRIMATE ADRENAL-MEDULLA WITH [I-123] AND [I-131] METALODOBENZYLGUANIDINE - CONCISE COMMUNICATION

Abstract

An evaluation of radioiodinated M-iodobenzylguanidine (m-IBG) as an adrenomedullary imaging agent is reported in 15 rhesus monkeys. Scintiscans of the monkey adrenal medulla were obtained with [123I]- and [m-131I]IBG 2-6 days after injection. The imaging superiority of m-IBG over its positional isomer, P-iodobenzylguanidine (p-IBG), is documented in both dogs and monkeys. Reserpine administration, a depletor of catecholamine stores, markedly lowers the [m-131I]-IBG content of the dog adrenal medulla, but the adrenergic blocking agents phenoxybenzamine and propranolol have no effect. Subcellular fractionation of the dog adrenal medullae reveals that m-IBG is sequestered mainly in the chromaffin storage granules. These results suggest that radioiodinated m-IBG, previously reported to image the primate myocardium, also merits evaluation as a clinical radiopharmaceutical for the adrenal medulla.