The influence of fasting/refeeding on the lipoprotein lipase activity of adipose tissue and muscle

Lipoprotein lipase activity in adipose tissue and muscle is modulated by changes in the pattern of food intake. We have measured total lipoprotein lipase activity in adipose tissue and muscle of male Wistar rats (N = 6-10), weighing 200-250 g (12 weeks), during the refeeding/fasting state following 24 h of fasting. Lipoprotein lipase activity in tissue homogenates was evaluated using a [³H]-triolein-containing substrate, and released [³H]-free fatty acids were extracted and quantified by liquid scintillation. Adipose tissue lipoprotein lipase activity did not completely recover within 2 h of refeeding (60 percent of refed ad libitum values). Cardiac lipoprotein lipase activity remained increased even 2 h after refeeding (100 percent of refed ad libitum values), whereas no significant changes were observed in the soleus and diaphragm muscles. Adipose tissue lipoprotein lipase activities were consistently higher than the highest skeletal muscle or heart values. It is therefore likely that adipose tissue, rather than muscle makes the major contribution to triacylglycerol clearance. There was concomitant relatively high lipoprotein lipase activity in both adipose tissue and cardiac muscle during the first few hours of refeeding, therefore cardiac muscle may contribute significantly to triacylglycerol clearance during this period. The results suggest that during fasting, increased lipoprotein lipase activity provides a complementary source of free fatty acids from circulating triacylglycerol, allowing the heart to maintain its continuous, high-energy expenditure

Reduced lipogenesis in rats fed a high-protein, carbohydrate-free diet: participateion of liver and four adipose depots

Rates of in vivo fatty acid (FA) synthesis were assessed with 3 H2O in carcass, liver intestines, muscle and four adipose depots from rats fed a high-protein, carbohydrate-free diet (70% casein, 8% fat, w/w) or a balanced diet (66% carbohydrate, 17% casein, 8% fat) for 25-30 days). rats adapted to the high protein (HP) diet showed a marked reduction of total FA synthesis from all carbon sources, which was due to a decreasedsynthesis of triacyglycerols. Rates of phospholipid-fatty acid synthesis in both carcans and liver were not liver were not affected by the diet. Rates of triacyglycerol-fatty acid (TAG-FA) synthesis were markedly reduced in adipose tissue from four different sites: epididymal (79%), retroperitoneal (78%)), subcutaneous (65%) anmd intermuscular (82%). In rats fed the balanced control diet, TAG-FA synthesis in adipose tissue accounted for about 75% of synthesis in whole carcass, whereas it was reduced to 36% in rats under the HP regimen. Although hepatic lipogenesis was also reduced in HP-fed rats, the contribution of the liver to total TAG-FA synthesis was approximately the same in HP (24%) and control (20%) rats, whereas the contribution of adipose tissue was only 26% in HP-fed animals compared to 57% in controls. Force-feeding fed rats with components of their own diets results in a significant (100%) increase of liver TAG-FA synthesis in animals fed the control diet, but did not significantly affect liver lip[ogenesis in HP rats