METABOLISM OF DOPAMINE AND NORADRENALINE IN NORMAL, ATROPHIED AND POSTGANGLIONICALLY SYMPATHECTOMIZED RAT SALIVARY GLANDS IN VITRO

Slices from normal, atrophied and postganglionically sympathectomized rat salivary glands were incubated with labeled dopamine or noradrenaline. The catabolism of dopamine proceeded at a higher rate than that of noradrenaline. This phenomenon is proposed to be due to the higher affinity of dopamine for monoamine oxidase, the extraneuronal part of which being very important. The major catabolites of dopamine were found to be the phenolic acids dihydroxy‐phenylacetic acid and homovanillic acid. Exogenously added noradrenaline was primarily catabolized to normetanephrine, whereas the major metabolites of newly synthesized noradrenaline from dopamine were the phenolic glycols 3,4‐dihydroxyphenylglycol and 3‐methoxy‐4‐hydroxyphenylglycol, supporting the view that intraneuronally formed noradrenaline initially is metabolized by intraneuronal monoamine oxidase prior to its O‐methylation by catechol‐O‐methyl transferase. Atrophy reduced the levels of all 3‐O‐methylated products, especially those of the methoxylated amines, whereas sympathectomy increased the amounts of these amines and diminished the deaminated products. Thus, catechol‐O‐methyl transferase is localized to the parenchymal cells in the salivary glands. In contrast to the dopamine metabolism, the catabolism of noradrenaline was more affected by postganglionical sympathectomy than by atrophy. The data from the present study demonstrate the importance of the amine concentrating mechanism of the adrenergic nerve cell membranes. © 1969 Scandinavian Physiological Society