Hormonal Stimulation of Substrate Utilization in Brown Adipose Tissue of Cold Acclimated Rats

Summary A study of glucose, glycerol and free fatty acid (FFA) uptake and release in the interscapular brown adipose tissue (BAT) was done on rats acclimated to constant cold (CA), fluctuating cold (Cy) or a control ambient temperature. At thermal neutrality the arteriovenous differences and the blood flow through the tissue were estimated. The effects of norepinephrine (NE) or dibutyryl cyclic-AMP (DBcAMP) were measured. Before infusions an uptake of plasma FFA by BAT was found in CA and Cy rats, and there was a release in the controls. Plasma glucose was taken up by the BAT of the three groups of rats. DBcAMP infusions did not enhance blood flow and lipid metabolism in BAT but increased glucose uptake in all the groups. By the end of a NE infusion, blood flow was increased 2.4-fold in controls and four- to fivefold in CA and Cy rats. Glucose uptake and glycerol release were greatly increased in all the groups. In controls hydrolyzed fatty acids were released in the venous blood, but in CA and Cy rats most of them were retained in the tissue. Therefore, in the controls BAT seems to be essentially a reserve of lipids which can be mobilized by NE. In the two groups of cold acclimated animals, the fatty acids hydrolyzed by NE, which are retained in the tissue, may be the substrate of the NE dependent increase of tissue energetic metabolism.