LOCALIZATION AND PERSISTENCE OF METARAMINOL AND -METHYL-m-TYRAMINE IN RAT AND RABBIT BRAIN

¹ Department of Pharmacology, University of Texas Southwestern Medical School, Dallas, Texas

The localization and persistence of metaraminol (MA) and -methyl-m-tyramine (MMTA) in corpus striatum and hypothalamus of rat and rabbit were examined after parenteral administration of -methyl-m-tyrosine. Effects on striatal dopamine (DA) and hypothalamic norepinephrine were also measured. In both species, the hypothalamus showed a specific and prolonged presence of MA along with persistent norepinephrine lowering. MMTA was highly concentrated in the striatum of both species and was accompanied by DA lowering. In the rat, striatal MMTA levels declined rapidly, and DA levels quickly returned to normal. In the rabbit, on the other hand, MMTA persisted in the striatum for days along with a prolonged DA lowering. Differential centrifugation failed to reveal binding of MMTA to the particulate fraction of striatal homogenates of either rat or rabbit although hypothalamic MA was appreciably particle bound. It is suggested that MMTA may serve as a false transmitter in striatal dopaminergic neurons as does MA in noradrenergic neurons.