Intra- and extraneuronal formation of the two major noradrenaline metabolites in the cns of rats

The two major noradrenaline metabolites in the rat brain, total 3-methoxy-4-hydroxyphenylglycol (MOPEG) and total 3,4-dihydroxyphenylglycol (DOPEG), were measured by a new analytical procedure after intraventricular (i.v.t.) injection of (3-H) noradrenaline or (3-H) dopamine. I.v.t. injection of (3-H) noradrenaline to rats with a 6-hydroxydopamine-induced destruction of nerve terminals in the central nervous system, resulted in an increased accumulation of 3-H-MOPEG compared to 3-H-DOPEG. On the contrary, reserpine induced a greater increase in 3-H-DOPEG than in 3-H-MOPEG accumulation when these two metabolites were formed from (3-H) noradrenaline synthesized in vivo by i.v.t. injection of (3-H) dopamine. These results indicate that the formation of DOPEG and MOPEG occur with some preference intra- and extraneuronally, respectively. The results, however, also show that these two formations sites should not be considered as specific.