| Summary: | Lipogenesis from glucose C was previously found to be rapidly activated as soon as mice nibbled a fat-free, glucose-rich diet. We have studied here whether such rapid activation is a specific effect of dietary glucose. The flux of endogenous glucose C to total lipid fatty acids (TLFA) in mice fasted for 1 day was compared with the minimal average flux of exogenous dietary glucose to TLFA during a 40-min period after the ingestion of various glucose-rich test meals by previously fasted mice. The fasted mice were injected intravenously with [U-14C]glucose, and the flux of glucose C to TLFA and to all “end products” was estimated from serial plasma glucose specific activity measurements and 14C incorporation into TLFA 30 min after 14C injection. Only 0.6 to 0.8 μg of glucose C/min/20 g body wt was converted to TLFA, whereas 208 ± 16 μg of glucose C/min/ZO g body wt was converted to all “end products” in the fasted animals. Previously fasted mice were fed [14C]glucose in small test meals as a neat solid, as a 30% aqueous solution, or as a fat-free, 58% glucose diet. During the next 40 min, the average flux of glucose C into TLFA increased at least 50- to 60-fold, regardless of the form in which glucose. was fed; however, when glucose was fed as part of a complete fat-free diet, glucose was utilized at a much lower plasma glucose level than in mice fed either pure solid glucose or an aqueous glucose solution. Rapid activation of lipogenesis from glucose requires only glucose as a dietary constituent.
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