Skeletal muscle MAO activity in the major psychoses. Relationship with platelet and plasma MAO activities.

The skeletal muscle MAO activity of schizophrenics and patients with bipolar and unipolar affective psychoses was lower than that of normal controls. Both platelet and plasma MAO activity was significantly lower in the schizophrenics and patients with undiagnosed psychoses than in the normal controls. Platelet and plasma MAO activities were not correlated with skeletal muscle MAO activity. Both human platelet and skeletal muscle MAO are type B MAO and have similar kinetic constants. The decrease in skeletal muscle MAO activity in various types of psychotic patients is consistent with previous suggestions based on platelet studies that low MAO activity may be a nonspecific factor contributing to the development of different forms of psychopathology. Since total skeletal muscle MAO activity is the largest source of MAO in the body, it is possible that the decrease in muscle MAO activity may lead to excessive quantities of biogenic amines that could adversely affect neural activity.