Abstract
The flux of glucose carbon to total body fatty acids was measured in unanesthetized mice either after fasting or 50-80 min after they nibbled a small test meal containing 120 mg of glucose (fasted-refed). Flux was calculated from plasma [(14)C]glucose specific activity curves and from total body (14)C-labeled fatty acid 30 min after intravenous injection of tracer [(14)C]glucose. Mobilization of liver glycogen, changes in the body glucose pool size, and total flux of carbon through the glucose pool during periods of fasting and refeeding were defined. Liver glycogen was almost completely depleted 8 hr after food removal. Body glucose pool size fell during fasting and increased after refeeding the test meal. Irreversible disposal rate of glucose C varied directly with body glucose pool size; but flux of glucose C into fatty acids increased exponentially as body glucose concentration increased. Within an hour after nibbling a small test meal, the flux of glucose C into total body fatty acids increased 700% in mice previously starved for 24 hr. However, flux of glucose C into fatty acids in postabsorptive mice (food removed for 2 hr; livers rich in glycogen) was only about 2% of the value calculated from published studies in which the incorporation of an intubated [(14)C]glucose load into total body fatty acid was measured in mice. A possible explanation for this phenomenon is presented.
Highlights
The fluxofglucose carbon to total body fatty acids was measuredinunanesthetized mice either after fasting or 5&80 min after they nibbled a small test meal containing 120 mg of glucose
From the statement of Yeh and Leveille, Supplementary key words irreversible disposal . fasting . refeeding . control * lipogenesis . liver glycogen . [1*C]glucose . isotope kinetics . mice and from the report of Hollifield and Parson, who showed thattherewasnoappreciablechangein lipogenicrates in vitro before andimmediatelyafteruntrained, fasted rats ate a meal, and that an adaptation period of days was required for lipogenic mechanisms to respond rapidly to dietary carbohydra(t1e3; see 21)
The total body glucose pool decreased by about 30% within 7 hr after removal of food
Summary
Baker and Huebotter [20] reported that negligible vivo in miceand rats[1,2,3,4,5,6,7,8,9,10] These and othesrtudies have [14C]glucosewas recovered as fatty acids 15 min after an intraestablished thatthelipogenicmachinery of thebody varies with dietary state [11,12,13,14,15,16,17,18,19]. Forexfatty acids from glucose was at least 8200% greater than 3 r g of glucose C/min within just 10 min after their mice were given a ample, Jansen and his colleagues [6, 7] have carried out glucose test meal. Ing fatty acids fromglucose become activated at the time that glucose is being actively absorbed from the intestine, Validity of methods for measuring and thathey may become relatively inactive very quickly total body glucose after the dietary carbohydrate has been absorbed
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