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 membra ne structures and functions. Membrane phospholipid fatty acid docosahexaeno ic acid (DHA) has been recently indicated to be important for the regulatio n of cellular activities, including metabolic regulation. Our previous stud ies have indicated the involvement of DHA in the regulation of brown adipos e tissue (BAT) thermogenesis. The objective of the present study is to exam ine the changes in BAT phospholipid fatty acid composition including DHA an d thermogenic activity in fasted and refed rats. Phospholipid content per m icrogram 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 composi tion of BAT, as expressed by mol%, was modified in the fasted rats, Most no tably, DHA, which constituted about 89% of the n-3 polyunsaturated fatty ac ids, was decreased concomitant with the increase in the n-6 polyunsaturated fatty acid arachidonic acid. The monounsaturated to saturated fatty acid r atio, which is an index of Delta(9)-desaturase activity and membrane fluidi ty, was decreased. Thermogenesis, as measured by the in vitro oxygen consum ption of BAT, was suppressed in the fasted rats. All of the above changes w ere restored to normal levels after refeeding the fasted rats for 72 h, In vitro oxygen consumption correlated with the level of DHA and monounsaturat ed to saturated fatty acid ratio. These results indicate that the modificat ion of phospholipid fatty acid composition, especially the modification of n-3 polyunsaturated fatty acid DHA, and membrane fluidity are related to BA T thermoregulation in fasted and refed rats.