Low platelet MAO activity in psychiatric patients and plasma factors: no evidence for inhibitory influences on MAO in the circulating platelet population.

The influence of plasma and low and high molecular weight plasma fraction on MAO activity in platelets from controls were studied. Plasmas were obtained from patients with decreased platelet MAO activity and suffering from chronic schizophrenia of different syndrome subtypes, unipolar depressions, and alcoholism. Up to 50% inhibition and activation of MAO activity alterations were not different between the plasmas from schizophrenic, depressive, and alcoholic patients. Plasmas from schizophrenic patients without medication or on neuroleptics showed similar inhibition and/or activation of MAO activity in platelets from controls. The results indicate, in accordance with recent findings, that a number of low and high molecular weight substances can trigger platelet MAO activity changes. These plasma factors do not appear to be characteristic of schizophrenic patients with low platelet MAO activity.