Effects of diet and cold acclimation on lipid composition of rat interscapular brown adipose tissue.

The effects of diet and of cold acclimation on lipid composition of interscapular brown adipose tissue (BAT) were studied in rats. Three groups of animals were acclimated for 20 weeks to 28 degrees C (controls), 5 degrees C (CA) or to a daily fluctuating temperature (Cy). They received either normal fat (5 p. 100 lipids) [NF] or high fat (26 p. 100) [HF] diets. Cold acclimation increased the tissue weight and its protein, phospholipid, free fatty acid and cholesterol content. It decreased the total lipid proportion in the tissue. HF diet led to an increase in lipid content and to a decrease in the protein content only in control and Cy groups. The mean chain length of triglyceride or phospholipid fatty acids was increased by HF diet and cold acclimation. The proportion of unsaturated acids was not changed in cold acclimated rats, but the amount of arachidonic acid bound to phospholipid was significantly increased. It is concluded that the total amount of lipid in the diet acts on the synthesis of BAT lipids. The cold dependant changes in lipid composition which are similar but less important in cyclic cold acclimation than in constant cold adaptation seem to be proportional to the increase in the tissue energy metabolism.