The role of 3,3',5'-triiodothyronine in the regulation of type II iodothyronine 5'-deiodinase in the rat cerebral cortex

Endocrinology
M J ObregonJ E Silva

Abstract

Type II iodothyronine 5'-deiodinase (5'D-II) activity is the source of 75-80% of the cerebral cortex T3 content in euthyroid rats. The activity of this enzyme is increased in hypothyroidism and can be quickly suppressed by T4 and rT3 by mechanisms involving neither protein synthesis nor nuclear T3 receptors. We have examined the possibility that endogenous cerebrocortical rT3 levels play a physiological role in the regulation of this enzyme. Thyroidectomized rats were injected with graded doses of [125I]rT3, and cortex 5'D-II activity and rT3 content were determined at various times thereafter. Enzyme activity was reduced as early as 10 min after the injection of 0.75 microgram rT3/100 g BW, and 18 h after 25 micrograms/100 g BW remained 60% suppressed. Regardless of the time after the injection, 5'D-II activity was inversely related to the rT3 content in the cortex; nearly complete suppression was observed at 0.5 ng rT3/g tissue, 50% at 80 pg/g, and 20-30% at 30 pg/g, the euthyroid level. After the infusion of 0.75 microgram rT3/100 g, maximal inhibition occurred at 10 min, before the rT3 content reached maximum levels, and the 5'D-II activity started to recover after the rT3 level fell below 300 pg/g tissue. After increasing ...Continue Reading

Citations

Sep 1, 2005·Thyroid : Official Journal of the American Thyroid Association·Antonio C Bianco, P Reed Larsen
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Sep 26, 2008·Endocrine Reviews·Balázs GerebenAntonio C Bianco
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