Monoamine oxidase: studies of normal and psychiatric populations in a tropical environment.

The pattern of changes in the platelet and plasma monoamine oxidase (MAO) activities with different substrates was recorded in 75 psychiatric patients compared with 27 normal controls. The results confirm that chronic schizophrenics, manics and manic-depressives have significantly lower platelet MAO activity, while depressives show higher platelet MAO activity than controls, without affecting plasma MAO activity. No significant substrate-related differences were observed, except when tyramine was used as substrate; then acute schizophrenics showed significantly lower platelet MAO activity. The differences persist even during the treatment period. The present finding is consistent with the results previously reported and indicates that biochemically there exist no striking differences between our population and the populations reported on elsewhere in different environments.