Metabolic fate of 3H-noradrenaline released from the mouse hypothalamus

Summary In slices of mouse hypothalamus labelled in vitro with ³H-noradrenaline (³H-NA), the deaminated metabolite ³H-3,4-dihydroxyphenylglycol (³H-DOPEG), represented 40.2±2.6% of the total outflow of radioactivity and was the main fraction in the sponteneous efflux. Inhibition of neuronal monoamine oxidase by exposure to 60 M bretylium, reduced the outflow of ³H-DOPEG to 9.7±0.3%. At the same time, the proportion of ³H-normetanephrine (³H-NMN) was significnatly increased. On the other hand, an increased outflow of ³H-DOPEG and a lower proportion of ³H-NMN was obtained in the presence of 2.9 M of the reserpine like agent Ro 4-1284.It is suggested that in the mouse hypothalamus, the deaminated metabolite, DOPEG, is formed inside the nerve terminals, while the O-methylated metabolite, NMN, might result from the activity of extraneuronal catechol O-methyltransferase.