In vitro uptake of 3-methoxytyramine by rat brain tissue slices

The means by which the brain handles the dopamine (DA) metabolite, 3-methoxytyramine (3-MT), has not been characterized. This study has examined one aspect by utilizing tritiated 3-MT in synaptosomes from rat striatum and slices of both striatum and cerebellum. No accumulation of 3-MT could be demonstrated in synaptosomes but DA (0.1 muM) uptake was inhibited by 3-MT (IC50 = 1.3 X 10(-5)M). Studies in brain tissue slices showed: 1) 3-MT accumulation was greater than could be expected from diffusion at a high concentration (10 muM) of amine; 2) the accumulated amine was easily washed out of the tissue slice; 3) the uptake appeared to be saturable with high estimated values for Km and Vmax; and 4) agents, such as metanephrine, which inhibit peripheral extraneuronal amine uptake had similar effectiveness against 3-MT uptake. It was concluded that: 1) the mechanism for the accumulation of 3-MT is similar in structurally different areas of the brain; 2) 3-MT is accumulated by a mechanism which is not a part of the nerve terminal; and 3) 3-MT accumulation in the brain is similar to the extraneuronal accumulation of amines in the periphery.