Multiple forms of amine oxidase in perfused rabbit lung

The biogenic monoamines, phenylethylamine and 5-hydroxytryptamine are rapidly and extensively deaminated when perfused in Krebs' solution through rabbit lung. Deamination of phenylethylamine is inhibited approximately 70% by 10(-5) M pargyline and 30% by 10(-3) M semicarbazide. Deamination of this monoamine is unaffected by 10(-6) M harmaline whereas deamination of 5-hydroxytryptamine is inhibited about 75%. These data indicate that the intact perfused rabbit lung contains three forms of amine oxidase two of which are analogous to the A and B forms of the mitochondrial enzyme, monoamine oxidase described previously only in broken cell preparations of lung and other tissues. The third form of amine oxidase is similar to the enzyme found in plasma and several large arteries. Since uptake and metabolism of these amines, as well as loss of their deaminated metabolites, occurs very rapidly, it is suggested that all these forms of monoamine oxidase are associated with vascular endothelium.