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In the group of 115 endogenous depression patients 84 responded to tricyclic antidepressant medication and 31 remained drug-resistance. The changes of platelet MAO activity and serum DBH activity in the latter group were found. Among drug-resistant patients, 40% showed low MAO/DBH index (.6) and in 36% the index was within the medium range (.6-1.9). The low value of the index is predominantly connected with the increase of DBH and decrease of MAO activity, and it may become the potential predictive factor for the pharmacotherapy in endogenous depression. The results show the influence of the disturbances of catecholamines synthesis and degradation on the phenomenon of drug-resistance to tricyclic antidepressants.

The authors found normal monoamine oxidase (MAO) activity in 40 acute schizophrenic patients, in contrast to previous reports of a genetically linked platelet MAO deficit in chronic schizophrenia. Variations in MAO activity were not significantly associated with the 65 clinical variables analyzed, although there was a tendency for patients in the low-MAO group to have more severely impaired reality testing, more paranoid and grandiose delusions, better prognostic scores, and less restlessness.

A highly significant decrease in platelet monoamine-oxidase activity has been observed in migrainous subjects during a migraine attack compared with activity outside an attack. The effect did not derive from drugs commonly used in migraine therapy.

Platelet-monoamine-oxidase activity predicts treatment response to lithium in manic-depressive illness. In the treatment-responsive group enzyme activity is similar to that in normal controls, whereas in the treatment-refractory group enzyme activity is significantly less than both control and treatment-responsive groups.