EFFECTS OF 6-HYDROXYDOPAMINE ON NORADRENALINE METABOLISM LINKED TO NEURONAL UPTAKE(1) AND EXTRANEURONAL UPTAKE(1) IN DENTAL-PULP IN-VITRO

The study was undertaken to determine the relative roles of neuronal a nd extraneuronal uptake(1) in the metabolism of H-3-noradrenaline in h uman dental pulp. Rabbit dental pulp was used as a reference since it was already known that normetanephrine (NMN) formation in this tissue utilised extraneuronal uptake(1). Slices of pulp were preincubated in the absence and presence of 6-hydroxydopamine (1.6 mmol/l, for 10 or 2 0 min at pH 4.5) and subsequently incubated with H-3-noradrenaline (0. 18 mu mol/l for 30 min at pH 7.4). The principal metabolites formed we re normetanephrine in rabbit pulp and deaminated catechols (dihydroxym andelic acid and dihydroxyphenylglycol) in human pulp. In both tissues 6-hydroxydopamine strongly inhibited formation of the deaminated cate chols, but was without effect on normetanephrine formation. It is conc luded that: i) in vitro 6-hydroxydopamine does not influence the metab olic process which is dependent on extraneuronal uptake(1), namely nor metanephrine formation in rabbit dental pulp, and ii) the deaminated c atechols are largely neuronal in origin in human pulp. Attention is dr awn to an unusual feature of the neuronal metabolism in human pulp, na mely the appearance of dihydroxymandelic acid as the principal metabol ite.