In vitro thermogenesis and phospholipid fatty acid composition of brown adipose tissue in fasted and refed rats

Membrane phospholipids are known for their role in the regulation of membrane structures and functions. Membrane phospholipid fatty acid docosahexaenoic acid (DHA) has been recently indicated to be important for the regulation of cellular activities, including metabolic regulation. Our previous studies have indicated the involvement of DHA in the regulation of brown adipose tissue (BAT) thermogenesis. The objective of the present study is to examine the changes in BAT phospholipid fatty acid composition including DHA and thermogenic activity in fasted and refed rats. Phospholipid content per microgram DNA was decreased in rats fasted for 72 h and it was not restored to the control level by refeeding for 72 h. Phospholipid fatty acid composition of BAT, as expressed by mol%, was modified in the fasted rats. Most notably, DHA, which constituted about 89% of the n-3 polyunsaturated fatty acids, was decreased concomitant with the increase in the n-6 polyunsaturated fatty acid arachidonic acid. The monounsaturated to saturated fatty acid ratio, which is an index of Delta(9)-desaturase activity and membrane fluidity, was decreased. Thermogenesis, as measured by the in vitro oxygen consumption of BAT, was suppressed in the fasted rats. All of the above changes were restored to normal levels after refeeding the fasted rats for 72 h. In vitro oxygen consumption correlated with the level of DHA and monounsaturated to saturated fatty acid ratio. These results indicate that the modification of phospholipid fatty acid composition, especially the modification of n-3 polyunsaturated fatty acid DHA, and membrane fluidity are related to BAT thermoregulation in fasted and refed rats.