MYOCARDIAL IMAGING WITH A RADIOIODINATED NOREPINEPHRINE STORAGE ANALOG

Abstract

M-Iodobenzylguanidine (M-IBG), an iodinated aromatic analog of the hypotensive drug guanethidine, localizes in the heart of the rat, dog and rhesus monkey. A comparative study of tissue distribution in the dog was performed with 5 myocardiophilic agents: 201Tl, 125I 16-iodohexadecanoic acid, H-3 norepinephrine, 14C guanethidine and 125I M-IBG [M-Iodobenzyl-guanidine]. The last 2 compounds give heart concentrations and heart-to-blood concentration ratios similar to those of 201Tl. Planar and tomographic images of the hearts of the dog and rhesus monkey were obtained using 131I or 125I labeled M-IBG. Blocking studies with reserpine suggest that a major component of myocardial retention of M-IBG is sequestration within the norepinephrine storage vesicles of the adrenergic nerves. The localization of M-IBG in other organs with rich sympathetic innervation and the relative insensitivity of myocardial uptake to a wide range of loading doses lend additional support for a neuronal mode of retention.