Amine oxidase activities in chemically-induced mammary cancer in the rat

The activities and distributions of monoamine oxidase (MAO) and semicarbazide-sensitive amine oxidase (SSAO) were studied in solid breast tumours induced in rat by treatment with 7,12-dimethylbenz(alpha)anthracene (DMBA). It was observed that increasing degree of malignancy was associated with an increase of MAO-A activity an decrease of MAO-B and SSAO activities. The Km values did not change significantly with malignancy but Vmax values for MAO-A increased whereas Vmax for MAO-B and SSAO diminished with malignancy. It was detected in the more malignant tumours the presence of endogenous reversible inhibitor of SSAO activity not removed by dialysis.