Cocaine-sensitive O-methylation of noradrenaline in dental pulp of the rabbit: comparison with the rabbit ear artery.

Incisor pulp from the rabbit metabolises exogenous noradrenaline in concentrations between 0.12 and 1.2 mumol/l mainly to NMN. Effects of chronic sympathetic denervation indicated that in incisor pulp the NMN is extraneuronal in origin, and that DOPEG and DOMA formation, as well as a major part of the noradrenaline which accumulates in the tissue, are associated with the sympathetic nerves. NMN formation was unaffected by hydrocortisone 210 mumol/l, but was strongly inhibited by cocaine 30 mumol/l. These effects contrasted with those in the rabbit ear artery, where NMN formation was increased by cocaine 30 mumol/l and decreased by hydrocortisone 210 mumol/l. In COMT-inhibited denervated pulp, cocaine inhibited the accumulation of noradrenaline. Monoamine fluorescence histochemistry of pulp exposed to noradrenaline 50 mumol/l indicated that cocaine-sensitive uptake occurred in fibroblasts. It is concluded that O-methylation of noradrenaline in dental pulp involves prior uptake of the amine by a process resembling uptake1 but which is distinguished from uptake1 by its extraneuronal location.