Studies on lung N-methyltransferases, a pharmacological approach.

Phenylethanolamine N-methyltransferase (PNMT) was identified as the primary, high affinity N-methylating enzyme for phenylethanolamine (PEA) in rat, dog and Rhesus monkey lung. Human and rabbit lung, however, do not contain this enzyme but possess a more non-specific or general N-methyltransferase with a relatively low affinity for PEA and for which beta-phenethylamine (beta-PE) is also a substrate. The former but not the latter enzyme is markedly inhibited by micromolar concentrations of the PNMT antagonist, SK & F 64139. This evidence indicates that certain species differences exist for the enzyme system(s) available for the N-methylation of phenethylamine-type compounds in pulmonary tissue.