AJP - Endocrinology and Metabolism, Vol 265, Issue 2 E252-E258, Copyright © 1993 by American Physiological Society
Regulation of brown adipose tissue lipogenesis by thyroid hormone and the sympathetic nervous system
W. J. Yeh, P. Leahy and H. C. Freake
Department of Nutritional Sciences, University of Connecticut, Storrs 06269-4017.
Thyroid hormone regulates lipogenesis differently in rat liver and brown
adipose tissue (BAT). In the hypothyroid state, lipogenesis is suppressed
in liver but enhanced in BAT. Here we investigated the mechanisms
underlying increased lipogenesis in hypothyroid BAT. Housing the animals at
28 degrees C decreased lipogenesis in hypothyroid BAT to euthyroid levels.
Denervation resulted in a 90% reduction in lipogenesis in hypothyroid BAT
such that levels were lower than in euthyroid tissue. Thyroid hormone
treatment of hypothyroid rats stimulated fatty acid synthesis in denervated
BAT, as in liver, but decreased it in intact BAT. Steady-state levels of
mRNA encoding acetyl-CoA carboxylase, fatty-acid synthase, and spor 14 were
measured in similar animals by Northern analysis. The expression of these
mRNAs mirrored the lipogenic data, showing that both thyroid hormone and
the sympathetic nervous system work at a pretranslational level in this
tissue. These data suggest that the increased BAT lipogenesis found with
hypothyroidism is mediated by the sympathetic nervous system to counter the
reduction in metabolic rate in these animals.
