Effect of Level of Feed Intake on Lactate and Acetate Metabolism and Lipogenesis In Vivo in Sheep

Publisher Website
Google Scholar
Abstract
Experiments were conducted to investigate the relative importance of acetate and lactate as precursors for fatty acid synthesis in vivo in sheep fed ad libitum [3.3 Mcal of metabolizable energy (ME)/day] or a restricted level of feed intake (1.7 Mcal of ME/day). Tritiated water (3H2O) was also used to estimate fatty acid synthesis from all carbon precursors rather than from a specific carbon precursor. In experiment 1, the amount of tritium (3H) incorporated into adipose tissue fatty acids increases with time up to 6 hours after intravenous 3H2O injection in perirenal, mesenteric, omental, shoulder, rump, backfat and abdominal adipose tissue from ad libitum fed sheep. The rate of incorporation did not differ significantly between tissue sites. The 3H2O equilibrated rapidly with body water and the plasma 3H2O specific activity did not change significantly for 3 hours after 3H2O injection. Plasma acetate turnover rate was not influenced by ad libitum versus restricted feeding and averaged 2.99 ± 0.28 mmole/hour/kg of body weight. Plasma lactate turnover was decreased significantly in restricted versus ad libitum fed sheep and averaged 0.99 ± 0.01 and 1.76 ± 0.07 mmoles/hour/kg of body weight, respectively. Restricting feed intake for 14 days decreased the total weight of perirenal, mesenteric, and omental adipose tissue masses compared to ad libitum fed sheep. Total 3H incorporated into fatty acids in restricted fed sheep was only 11% to 13% of that in the ad libitum fed sheep in perirenal and omental adipose tissue; treatment differences in 3H incorporation were much smaller in the total carcass adipose tissue. On the basis of the [14C]lipid relative specific activity, lactate was incorporated into carcass adipose tissue fatty acids at 38% of the rate for acetate in ad libitum fed sheep and only 16% and 21% of the rate for acetate in perirenal and omental adipose tissue. Lactate appears to have been more important as a lipid precursor in ad libitum fed than in restricted fed sheep.