Phenylethanolamine N-methyltransferase and other enzymes of catecholamine metabolism in human brain.

The activities of tyrosine hydroxylase (TH), DOPA decarboxylase (DDC), dopamine beta-hydroxylase (DBH), phenylethanolamine N-methyltransferase (PNMT), and monoamine oxidase (MAO) with serotonin and phenylethylamine as substrates were measured in catecholaminergic regions of human brain from 10 controls and 3 patients with Parkinsonism. PNMT activity was detected in hypothalamus, thalamus and cerebellar nucleus of the control human brain, and was reduced in hypothalamus of Parkinsonian cases. Type A (with serotonin as substrate) and type B (with phenylethylamine as substrate) MAO activities were high in all brain regions with little individual variations in controls and Parkinsonian cases. TH activity was high in the controls and was markedly decreased, in substantia nigra, caudate nucleus, putamen and in pallidum, in all three cases of Parkinsonism. DDC activity in these regions was also decreased in 2 patients. However, one Parkinsonian case had only decreased TH and normal DDC activities. DBH activity in hypothalamus was also reduced in the Parkinsonian cases.