False transmitters agents

When norepinephrine is substituted in the storage sites by amines of similar structure which are less agonistic, these agents are called "false transmitters." Until its central... 

P450 to alpha-methyl-dopamine and further to alpha-methyl-noradrenaline, a CNS-active hypotensive agent that also may function as a false transmitter (Hoffman et al. 1979). Dougan and colleagues (1986) described the stereoselective neuronal accumulation of hydroxyamphetamine and hydroxynorephedrine in rat striatum and found them to have half-lives of 1.5 and 2.5 days, respectively, at this location. 

The most recent evidence suggests that the false transmitter hypothesis might, after all, furnish the better explanation of the mode of action of a-MMT. a-Methyl [p) tyrosine (a-MT) causes a loss of noradrenaline from the brain and, unlike a-MMT, it produces sedation in a number of animal species. a-MT also inhibits the conditioned avoidance response and this inhibition is correlated, to some extent at least, with a reduction in the noradrenaline content of the brain . It is also clear that the sympathomimetic activities of metaraminol and a-methylnoradrenaline are not so uniformly less than that of noradrenaline as was at first thought the relative potencies of these compounds depend very much on the species and preparation studied. There is also recent evidence that the replacement of noradrenaline by the false transmitters is accompanied by an increased sensitivity of the effector organs . It should, perhaps, be added that these facts, though welcome to the neuropharmacologist, make it even more difficult to explain the efficacy of a-methyldopa as a hypotensive agent. 

---