Effects of neuroleptics on platelet monoamine oxidase activity.
Platelet MAO activity in schizophrenics was significantly decreased, by about 15%, after 3 weeks of treatment with haloperidol. Treatment with thioridazine or butaperazine also tended to decrease platelet MAO activity. The neuroleptic-induced decrease began to appear within a few days of treatment and did not show tolerance over 1-2 months of treatment with haloperidol. Platelet MAO activity of schizophrenic patients measured during drug-free base-line was not significantly different from that of normal controls, but MAO activity of schizophrenics was significantly lower than normals after 3 weeks of treatment with neuroleptics. The extent of decrease in platelet MAO activity correlated negatively with base-line prolactin and its increase after 24 hr. With PEA as substrate, the decrease in activity correlated positively with steady state plasma haloperidol.