Factors affecting determination of platelet monoamine oxidase activity.

Platelet monoamine oxidase (MAO) activity has been reported to be significantly decreased in chronic schizophrenia, but this finding is still quite controversial. Some of the variance between different studies may be due to differences in assay procedures. We have examined the effects of platelet count and platelet pellet protein determinations on assay reliability. The platelet count method was found to be somewhat more reliable than the platelet protein method of determing MAO activity. We also examined the effect of centrifugation conditions on platelet MAO activity. Platelets harvested at 100g had significantly higher MAO activity than platelets harvested at 600g. A significantly greater variation in the 600g platelet MAO activity/100g platelet MAO activity ratio was found in psychiatric patients than in control subjects.