Platelet serotonin in subtypes of schizophrenia and unipolar depression.

In subtypes of schizophrenia and unipolar depression, both increased and decreased levels of platelet serotonin were found. Hyperserotonemia was usually observed in patients with psychotic features (i.e., in paranoid schizophrenia and psychotic depression). Hyposerotonemia, although less common than hyperserotonemia, was present in nonparanoid schizophrenia and nonpsychotic depression (i.e., in patients without psychotic symptoms). A sex difference in platelet monoamine oxidase activity was observed among healthy subjects, but not among schizophrenic patients. The activity of platelet monoamine oxidase in paranoid and nonparanoid schizophrenic patients did not differ from that in healthy subjects. The findings in this study suggest that biological differences between subtypes of unipolar depression or schizophrenia might depend upon the presence of psychotic symptoms.