Scintigraphic assessment of MIBG uptake in globally denervated human and canine hearts--implications for clinical studies.

To further characterize the behavior of metaiodobenzylguanidine (MIBG) in the myocardium and to test the hypothesis that the denervated heart would show normal early uptake on MIBG due to non-neuronal localization, we examined the early and late distribution of 123I-labeled MIBG in normal and globally denervated canine and human hearts. Canine hearts were denervated by intravenous injections of 6-hydroxydopamine, while patients were studied a mean of 4.3 mo following cardiac transplantation. Results in denervated hearts were compared to normal controls. Normal hearts showed prominent MIBG uptake on initial 5-min and 3-hr delayed images. Globally denervated canine hearts showed prominent uptake on initial images and absence of localization on delayed images, indicating complete washout of non-neuronally bound radionuclide. The transplanted human hearts showed no localization of MIBG on either early or delayed images. These results suggest that the non-neuronal uptake mechanism (uptake 2) is not significant in human myocardium. This finding has significant implications for interpreting the myocardial behavior of MIBG in various pathologic situations such as dilated cardiomyopathy.