Platelet MAO activity, TRH test, and dexamethasone suppression test in depressed patients.

Platelet MAO activity, TRH test and DST results were compared in 23 normal subjects and 13 depressed patients. Patients as a group were older in age, had higher levels of FT4-index and T3-uptake, and lower levels of MAO activity. There was no association between thyroid hormones, including TSH response, and MAO activity. Five patients were DST positive. They showed a higher average age and a higher T3-uptake value than DST negative patients. Serum T4 and MAO activity levels were normal in both groups. These data suggest that MAO activity and TSH are independently regulated in both normal subjects and depressed patients. They also suggest a reduced binding capacity for thyroid hormones in patients with positive DST.