314 Platelet Monoamine Oxidase as a Function of Nongenetic Factors

The level of platelet monoamine oxidase (MAO) has been found to be abnormally low in certain types of schizophrenia and in a number of other pathological conditions. It has been suggested that MAO in platelets may be a genetic marker for a subgroup of patients with schizo-phrenia; however, we have demon-strated that several nongenetic fac-tors influence platelet MAO activity by affecting the platelet rather than the MAO enzyme protein. We have observed platelet MAO activities to be heterogeneously distributed in a given subjecf s platelet population, heavy platelet fractions having sig-nificantly higher specific activity than light platelet fractions. We have also found platelet MAO activ-ity to be significantly correlated with mean platelet volume, platelet pro-tein densities, and protein content per platelet. These changes, which might be induced by drugs and stress, could modify production, mobilization, and clearance of platelets and, hence, influence ap-parent MAO activity. The initial report by Murphy and Wyatt (1972) of low platelet monoamine oxidase (MAO) activity in schizophrenic patients has stimu-lated considerable interest because this enzyme appears to be unde