Serotonin uptake and efflux in blood platelets from untreated and neuroleptic-treated schizophrenics

Earlier studies on platelet serotonin uptake in schizophrenia have given equivocal results. In this study, platelet serotonin uptake in diluted plasma was assessed in 23 drug-free and 19 neuroleptic-treated schizophrenics, compared to 70 controls. The maximal uptake rate, Vmax, was slightly but significantly lower in drug-free schizophrenics than in the controls. In neuroleptic-treated patients there was a nonsignificant trend in the same direction. The "affinity constant" Km was significantly elevated in neuroleptic-treated schizophrenics compared to both controls and drug-free patients. Assessment of serotonin uptake in platelets resuspended in an artificial medium gave no definite answer whether reduced Vmax in plasma is due to a plasmatic or a platelet abnormality. Spontaneous efflux of serotonin from preloaded platelets did not differ significantly between patients and controls.