Iodine-131 metaiodobenzylguanidine intra- and extravesicular accumulation in the rat heart.

In order to establish the appropriate time for [123I]MIBG human myocardial imaging to assess the adrenergic nerve activity, the time courses of metaiodobenzylguanidine (MIBG) intra- and extravesicular accumulation in the rat heart were estimated by using [131I]MIBG and reserpine. In the heart, the intravesicular accumulation was relatively constant, while the extravesicular accumulation decreased rapidly from 5 min to 6 hr. The intravesicular percentage of the total cardiac tissue concentration reached a plateau value of 50% at 4 hr after i.v. injection of [131I]MIBG. In the spleen, similar time courses were observed as those in the heart, both of these organs being richly innervated by adrenergic nerves. Along with the time activity difference previously observed in the human hearts, these results suggest that at 4 hr post i.v. injection, [123I]MIBG myocardial imaging will best express the neuronal accumulation of the tracer and may be useful for the assessment of adrenergic function in various pathological conditions of the human heart.