SEROTONIN-MEDIATED INCREASE IN CYTOSOLIC [CA-TREATED SCHIZOPHRENIA-PATIENTS(+] IN PLATELETS OF RISPERIDONE)

Stimulating the platelet 5HT(2) receptor generates the second messenge r IP3, and results in an increase in cytosolic [Ca++] ([Ca++](cyt)). P latelets from risperidone-treated patients would be expected to respon d less effectively, as measured by decreased [Ca++](cyt), after 5HT(2) receptor stimulation, We report the data on 6 risperidone-treated pat ients and 6 normal controls evaluated at our site using the Fura-2 met hod for determining platelet [Ca++](cyt). Data analysis was performed by unpaired two-tailed Student's t-test, No significant differences be tween groups were found for ED(50) 5HT-stimulated [Ca++Icyt (ED(50) 5H T Delta [Ca++](cyt)). Significant differences were found for maximal c hange [Ca++](cyt) (Max Delta [Ca++](cyt)) between risperidone-treated patients and normal controls (p=.03). These preliminary data suggest t hat measurement of 5HT-stimulated changes in platelet cytosolic [Ca++] might be a useful marker for in vivo risperidone inhibition of 5HT(2) function.