Radiolabeled meta-iodobenzylguanidine and the adrenergic neurons of salivary glands.

The handling of radiolabeled meta-iodobenzylguanidine (MIBG) by salivary glands was evaluated. In the submaxillary glands of rats, the uptake of 125I-MIBG was decreased after 1) nerve injury induced by 6-hydroxydopamine, 2) inhibition of the uptake-1 pathway by desmethylimipramine, and 3) surgical denervation. However, the reduction in 125I-MIGB uptake was less than that of 3H-norepinephrine (3H-NE) and of the endogenous content of NE in the glands. Yet, the sympathomimetic phenylpropanolamine displaced about the same fraction of 125I-MIBG as 3H-NE. These results suggest that 40% or more of 125I-MIBG resides in extraneuronal sites but that at least 30% and possibly more lies in the adrenergic nerve terminals. Fasting and feeding rats produced changes in the rates of disappearance of 125I-MIBG and 3H-NE from the submaxillary gland that were different, and the rates of loss of 125I-MIBG cannot be used as an index of adrenergic nerve activity. In man, the concentrations of 123I-MIBG in the salivary glands, particularly the parotid gland, are readily visible and measureable. Imipramine reduced the uptake of 123I-MIBG into parotid glands little or not at all; some of the 123I-MIBG may enter neurons via an imipramine-insensitive pathway, but a substantial fraction probably arrives in intraneuronal locations. Thus, phenylpropanolamine displacedmore » over 50% of the parotid pool of 123I-MIBG. However, in only the most severe case of generalized autonomic neuropathy was the uptake of 123I-MIBG reduced.« less