Kinetics of Exogenous and Endogenous Acetate Metabolism in Sheep Exposed to Cold Environmet

The contributions of exogenous acetate absorption and endogenous acetate production rate to the total turnover rate of blood acetate were investigated in sheep exposed to thermoneutral(20°C) and cold (0°C) environments. On the 4th day after exposure to the environments, [1, 2-14C]-sodium acetate dissolved in saline was continuously infused at a constant rate through a jugular catheter for 5 hours from 3 hours after feeding. At the same time, indocyanine green dye dissolved in saline was constantly infused into the mesenteric vein for 2.5 hours from 5.5 hours after feeding to measure the portal blood flow. When the steady-state of the blood acetate pool was achieved 6 to 8 hours after feeding, blood samples were taken for measuring parameters of acetate metabolism. The total turnover rate of blood acetate in the cold environment (5.93±0.54 mg/min/kg0.75) was not significantly different from that in the thermoneutral environment (5.61±2.10mg/min/kg0.75). The mean exogenous acetate absorption rate decreased slightly from 4.53±1.18 in the thermoneutral environment to 4.32±0.86mg/min/kg0.75 in the cold environment. The mean endogenous acetate production rate, on the other hand, increased slightly from 1.08±1.00 in the thermoneutral environment to 1.61±1.33 mg/min/kg0.75 in the cold environment. The percentage of exogenous acetate absorption rate to the total turnover rate of blood acetate decreased from 80.7±36.7 in the thermoneutral environment to 72.8±20.4% in the cold environment. The percentage of endogenous acetate production rate to the total turnover rate of blood acetate increased from 19.3±10.0 in the thermoneutral environment to 27.2±20.5% in the cold environment. The mean acetate utilization rate of portal viscera decreased slightly from 1.59±0.62 in the thermoneutral environment to 1.18±0.31 mg/min/kg0.75 in the cold environment. These results suggest that four days, cold exposure does not have significant effects on the rates of exogenous acetate absorption and endogenous acetate production and the contributions of these to the total turnover rate of blood acetate in fed sheep.