Effect of level of feed intake on lactate and acetate metabolism and lipogenesis in vivo in sheep
Prior, R.L.
Journal of Nutrition 108(6): 926-935
1978
ISSN/ISBN: 0022-3166 PMID: 650294 Document Number: 130043
The relative importance was studied of acetate and lactate as precursors for fatty acid synthesis in sheep fed to appetite to give 3.3 Mcal metabolizable energy (ME) daily, or restricted to 1.7 Mcal. Tritiated water (3H2O) was also used to estimate fatty acid synthesis from all C precursors rather than from a specific C precursor. In experiment 1, 3H incorporated into adipose tissue fatty acids increased with time up to 6 h after intravenous injection of 3H2O in perirenal, mesenteric, omental, shoulder, rump, back fat and abdominal adipose tissue from sheep fed freely. The rate of incorporation did not differ significantly among tissue sites. The 3H2O equilibrated rapidly with body water and plasma 3H2O specific activity did not change significantly for 3 h after injection. Plasma acetate turnover rate was not influenced by free or restricted feeding and was on average 2.99 plus or minus 0.28 mmol/h kg bodyweight. Plasma lactate turnover was significantly slower in restricted than in freely fed sheep, average 0.99 plus or minus 0.01 and 1.76 plus or minus 0.07 mmol/h kg bodyweight. Restriction for 14 days decreased the total weight of perirenal, mesenteric and omental adipose tissue compared to sheep fed freely. Total 3H incorporated into fatty acids in restricted sheep was only 11 to 13% of that in the freely-fed in perirenal and omental adipose tissue; differences in incorporation of 3H 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 freely-fed sheep and only 16 and 21% of the rate for acetate in perirenal and omental adipose tissue. Lactate seems to have been more important as a lipid precursor in freely-fed than in restricted fed sheep.