Neuroendocrine responses to carbidopa in primary affective disorders

(1) Measurement of hypothalamic-pituitary function in patients with affective disorders can indicate altered neurotransmitter activity since biogenic amines are involved in the control of these hormones. (2) We studied 18 patients with primary affective disorders, 11 bipolar and 7 unipolar and 10 normal controls for 10 days each. (3) On the first 2 days fasting resting 0900 hr samples were taken for measurement of growth hormone (GH), prolactin, thyroid stimulating hormone (TSH) and cortisol. These measures were repeated on the 9th and 10th days of the study while subjects were on carbidopa. Carbidopa is a peripheral inhibitor of l-aromatic amino acid decarboxylase and therefore inhibits extracerebral synthesis of serotonin and catecholamines. (4) We found bipolar depressed females to show a failure to respond to carbidopa with the normal prolactin elevation and their levels on carbidopa were significantly less than controls. (5) Moreover, bipolar depressed females had higher levels of plasma TSH than controls. (6) No such differences between groups were evident in males. (7) These results support the concept of altered neurotransmitter activity in some groups of patients with primary affective disorder.