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Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo, 05508-900 São Paulo, Brazil
To investigate the role of type II
5'-deiodinase (5'D-II) in the expression of mitochondrial
uncoupling protein (UCP) in brown adipose tissue (BAT), we injected
intact male rats with reverse (r) 3,5,3'-triiodothyronine
(T3; 100 µg · 100 g body
wt
1 · day
1),
an inhibitor of 5'D-II, for 2-5 days. UCP decreased by
~20% in rats kept at 28°C and failed to increase during cold
exposure (4°C). Next, thyroxine treatment (1-10
µg · 100 g body
wt
1 · day
1)
increased nuclear T3 in rats kept
at 28 or 4°C. In these rats, nuclear
T3 correlated positively with UCP.
In addition, T3 (1-50 µg · 100 g body
wt
1 · day
1)
given to intact rats (5-15 days; 28°C) induced an
approximately twofold increase in UCP. In these
T3-treated animals, the
interscapular BAT thermal response to norepinephrine infusion also
correlated positively with T3 dose
and UCP content. Treatment with propranolol or reserpine failed to
block the T3 induction of UCP
(~1.8- and ~2.3-fold). The results emphasize the importance of
local 5'D-II and reveal an independent role of
T3 in the expression of UCP.
thyroid hormones; 5'-deiodinase; norepinephrine; thermogenesis; cold acclimation; uncoupling protein
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