125I-labelled iodothyronines: useful tools for studies of effects of an antidepressant drug fluoxetine in the rat

Abstract

Thyroid hormones (TH) are supposed to control the activity of some neurotransmitters (e.g., serotonin), which are hypothetically involved in the pathogenesis of depressive illness. A new group of non-tricyclic antidepressant drugs includes selective serotonine re-uptake inhibitors. The most frequently used representative of this group is fluoxetine (Fluox). We followed in the present paper the effects of Fluox, administered subchronicaly (for 25 days) to Wistar rats by itself, or in combination with 3,3′,5-triiodo-l-thyronine (T3). In studies of the interaction of Fluox with the metabolism of TH, we applied adapted radiometric enzyme assays for iodothyronine sulfotransferases (ST) and uridine 5′-diphospho-glucuronyltransferase (UDP-GT), as well as our newly developed radiometric assays for iodothyronine deiodinases (IDs) of types 1, 2 and 3 (D1, D2 and D3), using 125I-labelled iodothyronines of high specific radioactivity as substrates. We found about two-fold higher UDP-GT enzyme activities in samples of liver microsomes of rats treated with Fluox, in comparison with control rats. In contrast, the radiometric determination of ST activities in liver and kidney cytosolic fractions did not demonstrate any significant effects of the administration of Fluox, alone or together with T3, on the induction of these enzymes. However, profound changes in enzyme activities were determined in case of IDs, especially in the pituitary and cerebellum of treated rats. The adapted and newly elaborated radiometric enzyme assays proved to be very sensitive and rapid and, at the same time, reliable and robust.