Monoamine oxidase in chronic schizophrenia: Studies of hormonal and other factors affecting enzyme activity.

Reported reductions in the activity of platelet monoamine oxidase (MAO) in chronic schizophrenic patients might be contributed to by alterations in hormones, platelet numbers or other non-specific factors thought to affect enzyme activity. In this study, MAO activity in 27 patients with chronic schizophrenia was measured, using benzylamine as the substrate in an assay based on platelet counts instead of platelet protein, and was found to be markedly lower than mean MAO activity in 375 normal controls. These results were similar to those previously reported with tryptamine as a substrate for the enzyme. Serum testosterone, triiodothyronine, iron and iron-binding capacity were within normal ranges in individuals with reduced MAO activities. Platelet MAO activity remained stable over time in patients and controls.