1. Lipogenesis was studied in vivo by giving mice 250mg. meals of [U-(14)C]
glucose and measuring the disposition and incorporation of label. About 48% of the (14)C dose was eliminated as (14)CO(2) in the first 2hr. At 60min. after administration, 1.0, 1.9 and 11.9% of the dose was recovered as
liver glycogen,
liver fatty acid and carcass
fatty acid respectively. Of the [(14)C]
glucose converted into fat in the epididymal pads about 90% was present as glyceride
fatty acid and 10% as glyceride
glycerol. 2. Hepatic synthesis of
fatty acid was depressed by
dietary fat to a much greater extent than was synthesis outside the liver. Both feeding with fat and
starvation decreased the proportion of the label taken up by adipose tissue present as fat (
triglyceride) and increased the proportion of
triglyceride label present as glyceride
glycerol. These results are consistent with the hypothesis that the primary action of both these conditions in decreasing fat synthesis is to inhibit synthesis of
fatty acids. 3. Turnover of body fat labelled in vivo from [U-(14)C]
glucose was estimated from the decline in radioactivity measured over the first 24hr. of the experiment. The half-life of liver and extrahepatic
fatty acids (excluding epididymal fat) was 16hr. and 3 days respectively. In contrast, no measurable decrease in radioactivity of the
fatty acids of epididymal fat was observed for 7 days after administration of the [U-(14)C]
glucose.