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Unidad de Endocrinología Molecular, Instituto de Investigaciones Biomédicas, Centro Mixto "Alberto Sols," Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, 28029 Madrid, Spain
Type II 5'-iodothyronine deiodinase
(D2), produces triiodothyronine (T3) and is
stimulated by cold exposure via norepinephrine (NE) release in brown
adipose tissue. Cultured rat brown adipocytes require T3
for the adrenergic stimulation of D2 activity. D2 mRNA expression in
cultured brown adipocytes is undetectable with the use of basal
conditions or NE without T3. Full D2 expression is achieved
using NE + T3, especially after prolonged
T3 exposure.
3-Adrenergic agonists mimic the
NE action, whereas cAMP analogs do not. Prolonged exposure to
T3 alone increases D2 mRNA. High T3 doses (500 nM) inhibit the adrenergic stimulation of D2 activity while increasing
D2 mRNA. The effects obtained with NE + T3 or T3 alone are suppressed by actinomycin, but not by
cycloheximide, which leads to accumulation of short D2 mRNA
transcripts. Prolonged or short exposure to T3 did not
change D2 mRNA half-life, but T3 seemed to elongate it. In
conclusion, T3 is an absolute requirement for the
adrenergic stimulation of D2 mRNA in brown adipocytes. T3
upregulates D2 mRNA, an effect that might involve stimulation of
factors required for transcription or for stabilization of D2 mRNA.
norepinephrine; uncoupling protein-1
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