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Effects of pharmacological and nonpharmacological treatments on thyroid hormone metabolism and concentrations in rat brain.
- Eravci M, Pinna G, Meinhold H, Baumgartner A
Endocrinology. 2000 Mar;141(3):1027-40.
The activities of the 5'I-deiodinase (5'D-I), 5'II deiodinase (5'D-II) and 5III-deiodinase (5D-III) isoenzymes
and tissue concentrations of thyroxine
(T4)
and triiodothyronine
(T3)
were measured in up to 10 regions of the rat brain after acute
and subchronic nonpharmacological (sleep deprivation,
12 h fasting,
14 days' calorie-reduced diet)
and pharmacological (ethanol,
haloperidol,
clozapine,
lithium,
carbamazepine,
desipramine,
fluoxetine,
tranylcypromine,
and mianserin)
treatments. All
of these treatments induced significant and sometimes dramatic changes in 5'D-II activities and tissue concentrations of thyroid hormones
and, to a lesser extent, in 5D-III activity. The activity of 5'D-I remained unaffected. The results revealed a surprising specificity
for each type of treatment in terms of the isoenzyme
and hormone
affected, the direction of the change, the brain region affected and the time of day. The changes in thyroid hormone
concentrations frequently failed to correspond in any way to those in deiodinase activities and unexpected effects such as inhibition
of both 5'D-II and 5D-III were seen, indicating that there may be additional pathways of iodothyronine metabolism
in the CNS.
In conclusion, particularly 5'D-II activity and thyroid hormone
concentrations in the CNS
are highly sensitive to many different kinds of influence that may induce changes in neuronal
activity. However, these changes in deiodinase activities do not ensure stable
tissue concentrations of T3,
but were, on the contrary, in most cases accompanied by marked changes T3
levels in the tissue. The implications of these findings for the physiological role
of thyroid hormones
in the CNS
are discussed.
This abstract at PubMed.