T3 increases mitochondrial ATP production in oxidative muscle despite increased
expression of UCP-2 and -3.
Short, Kevin R., Jonas Nygren, Rocco Barazzoni, James Levine, and K. Sreekumaran
Nair.
Endocrinology Research Unit, Mayo Clinic, Rochester, Minnesota 55905
APStracts 8:0026E, 2001.
Triiodothyronine (T3) increases O2 and nutrient flux through mitochondria (Mito) of
many tissues, but it is unclear whether ATP synthesis is increased, particularly in
different types of skeletal muscle, because variable changes in uncoupling proteins (UCP)
and enzymes have been reported. Thus Mito ATP production was measured in oxidative
and glycolytic muscles, as well as in liver and heart, in rats administered T3 for 14 days.
Relative to saline-treated controls, T3 rats had 80, 168, and 62% higher ATP production
in the soleus muscle, liver, and heart, respectively, as well as higher activities of citrate
synthase (CS; 63, 90, 25%) and cytochrome c oxidase (COX; 119, 225, 52%) in the same
tissues (all P < 0.01). In plantaris muscle of T3 rats, CS was only slightly higher (17%,
P < 0.05) than controls, and ATP production and COX were unaffected. mRNA levels
of COX I and III were 33 and 47% higher in soleus of T3 rats (P < 0.01), but there were
no differences in plantaris. In contrast, UCP-2 and UCP-3 mRNAs were 2.5- to 14-fold
higher, and protein levels were 3- to 10-fold higher in both plantaris and soleus of the T3
group. We conclude that T3 increases oxidative enzymes and Mito ATP production and
Mito-encoded transcripts in oxidative but not glycolytic rodent tissues. Despite large
increases in UCP expression, ATP production was enhanced in oxidative tissues and
maintained in glycolytic muscle of hyperthyroid rats.
Received 23 August 2000; accepted in final form 26 January 2001
APS Manuscript Number E396-0.
Article publication pending Am J Physiol Endocrinol Metab
ISSN 1080-4757 Copyright 2001 The American Physiological Society.
Published in APStracts on 27 February 2001