Increased level of mRNA for the uncoupling protein in brown adipose tissue of rats during thermogenesis induced by cold exposure or norepinephrine infusion.

We have studied by in vitro translation the mRNA population from rat brown fat in two situations where the thermogenic activity of the tissue is stimulated. Both cold exposure of rats and the presence of pheochromocytoma result in marked alterations among the polypeptides synthesized. Notably, in these two situations there was an increased labeling of polypeptides of the size of the heat-shock proteins and an increased labeling of the 32,000-dalton uncoupling protein of brown fat mitochondria, which is responsible for energy dissipation as heat. Stimulation of the thermogenic activity of brown fat thus results in a high level of mRNA encoding the uncoupling protein. Chronic delivery of norepinephrine mimicked the increase of mRNA for the uncoupling protein observed in animals exposed to cold or bearing pheochromocytoma. Thus, a neuromediator such as norepinephrine is able to trigger the induction of the mRNA encoding the mitochondrial uncoupling protein and is able to stimulate mitochondriogenesis.