| 17703090 |
Kundu S, Roy S, De J, Biswas A, Pramanik M, Ray AK: Maintenance of homeostasis for thyroid hormone in the adult rat brain: possible involvement of a nuclear-mediated phenomenon. Neuroendocrinology. 2007;86(2):94-103. Epub 2007 Aug 16.
During adult-onset peripheral hypothyroidism, the brain maintains normal levels of thyroid hormone for some time through a mechanism of 'central homeostasis'. Although onset, duration, and termination of such a homeostatic phenomenon have been recently evaluated in rat models, the mechanism behind remains unknown. During our investigation to understand the mechanism further, we injected the protein synthesis blockers actinomycin D and cycloheximide along with propylthiouracil to adult male rats during the days of onset (day 2) and termination (day 20) of the homeostatic mechanism. We evaluated synaptosomal T (3) level and neuronal Na (+)-K (+)-ATPase and acetylcholinesterase activities along with deiodinase II activity and cyclic adenosine monophosphate level in the cerebral cortex. The results indicated prevalence of unchanged or lower levels of synaptosomal T (3) on the 2nd and on the 20th day, respectively. Such a condition has been parallely supported by reflections in cerebrocortical deiodinase II activity and cyclic adenosine monophosphate levels. The activities of cerebrocortical synaptosomal Na (+)-K (+)-ATPase and acetylcholinesterase, which are the two important physiological parameters for neuronal function, have been found to be supportive of the involvement of a neuronal protein-mediated factor in the 'on' and 'off' reactions in central homeostasis during peripheral hypothyroidism. The results of our study indicate that the expression of 'central thyroid hormone homeostasis' is a genomic nuclear-mediated mechanism. |
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