3.   Can either a-methyltyrosine or a-methyldopa act as a false neurotransmitter at the adrenergic nerve terminals? Why or why not?

Ans: Yes, in the peripheral a₁ and b-adrenergic synapses, both a-methyltyrosine and a-methyldopa act like a false neurotransmitter because both of these compounds are converted by the biosynthetic enzymes to give (1R, 2S) a-methylnorepinephrine which is inactive at these receptors. However, in the CNS, the resulting product, (1R, 2S) a-methylnorepinephrine has a high affinity for the a₂ adrenergic receptors and behaves like an a₂-agonist. Thus, in the CNS both a-methyltyrosine and a-methyldopa act as a prodrug.