Altered platelet serotonin uptake kinetics in schizophrenia and depression

Platelet uptake of serotonin (5-HT) was studied in drug-free groups of normal controls, depressives and schizophrenics. The Michaelis constant was significantly higher in both the schizophrenics and the depressives than in the controls. The Vmax did not differ significantly between the three groups. Uptake velocity at low substrate concentrations was significantly lower in the schizophrenic group and showed a similar trend in the depressives. There were no significant differences in Km or Vmax when depressives wee subclassified as unipolar and bipolar. There were no significant correlations between 5-HT uptake kinetics and severity of illness. These findings raise the possibility of a structural defect inthe 5-HT reuptake system in the major psychoses that reduces the affinity of the carrier for the amine. This alteration, if present in central serotonergic neurons, may play a role in the etiology and pathogenesis of depression and schizophrenia.