Increased platelet membrane [3H]‐LSD binding in patients on chronic neuroleptic treatment

Using a [3H]‐lysergic acid diethylamide [(3H]‐LSD) binding technique, platelet 5‐hydroxytryptamine (5‐HT) receptor number and affinity were compared in schizophrenics treated with depot thioxanthenes and phenothiazines and controls. There was an approximately 30% increase in platelet receptor number (Bmax) in the patient group. There was a decrease in affinity (increase in Kd) of about 30% in the patient group. This was probably due to the persistence of the neuroleptic in the platelet membrane preparation. There was a weak positive correlation between receptor number and total neuroleptic dosage. The increased number of 5‐HT receptors is consistent with the previously reported enhancement of 5‐HT‐induced platelet aggregation in patients treated with long‐term phenothiazines and thioxanthenes. Our findings are compatible with 5‐HT up‐regulation in human platelets produced by depot neuroleptic therapy. It is not known whether parallel changes may be occurring in brain 5‐HT receptors.