Modulation of Fatty Acid Synthesis in vivo in Brown Adipose Tissue, Liver and White Adipose Tissue of Cold-Acclimated Rats

Abstract

The present experiment was an appraisal of the relative importance of fatty acid synthesis in brown adipose tissue (BAT) in young 28 or 5 °C adapted rats (9 weeks old). With a low-fat diet in vivo incorporation of ³H₂O into BAT fatty acids was 8 times lower during the day than during the night and was not modified by a 6-hour fast during the day (28 °C). Cold acclimation doubled (night) or increased 8 times (day) BAT lipogenesis. Fasting led to a halving of the diurnal rate. A high-fat diet led to large decrease in synthesis rate during the night but had a weak effect on diurnal synthesis. The specific activity of fatty acids was 3 times lower in phospholipids than in neutral lipids. A comparison between 9- and 15-week-old rats indicated that in older warm-adapted rats BAT lipogenesis decreased by half but that cold stimulation was unaltered. These results were compared with hepatic and epididymal white adipose tissue lipogenesis. In conclusion, we showed that BAT of 5 °C rats is an important but not the major site for the conversion of carbohydrate to fat and that the proportional involvement of each tissue is age-dependent.

In vivo measurement of energy substrate contribution to cold‐induced brown adipose tissue thermogenesis

“…The increased expression of glycolytic enzymes such as Pfkl and Pdha observed in coldadapted rats supports the expected cold-induced activation of glycolysis (43)(44)(45). Cold adaptation also led to a marked increase in the expression of Acacb and Fas,which tends to further support the genuine ability of BAT of coldexposed and cold-adapted rats for de novo fatty acid synthesis (46)(47)(48)(49). In BAT, fatty acids can either be oxidized or serve for TG synthesis.…”