232 Further Studies on the Endogenous Inhibitor of Monoamine Oxidase in Schizophrenic Plasma

Platelet-free plasma from schizo-phrenic patients satisfying research diagnostic criteria for chronic schiz-ophrenia was obtained and mixed with platelet-rich plasma from nor-mal controls. Decreases in control platelet monoamine oxidase activity were observed, with some control platelets apparently much more sen-sitive than others to the inhibitory activity of the chronic schizophrenic plasma. Experimental conditions and selection from sensitive control individuals seem crucial in demon-strating the presence of endogenous inhibitors in schizophrenics' plasma. We reported in 1978 that platelet-free plasma obtained from chronic schizophrenic patients with low monoamine oxidase (MAO) activity, when mixed with platelets obtained from healthy individuals, could de-crease platelet MAO activity (Berret-tini and Vogel 1978). This decrease did not seem to be caused by the experimental conditions employed, since control platelet-free plasma had no effect on platelet MAO activity (Berrettini and Vogel 1978), or by antipsychotic medication since these drugs have been reported not to af-fect MAO activity (Murphy, Bel