Lipogenic activation after nibbling and gorging in mice.

Lipogenic activation was studied in mice that had been restricted to a single large meal once a day rather than being allowed to eat at frequent intervals throughout the night. Mice were injected intravenously with [U-(14)C]glucose, and the flux of glucose C to total lipid fatty acids (TLFA) and to all "end products" was estimated from serial plasma glucose specific activities and measurements of incorporation of (14)C into TLFA of hepatic and extrahepatic tissues. Tracer studies were carried out in mice fasted for 1 day and at various times after the mice ate one or two small test meals or a single large test meal. Test meals consisted of a fat-free, 58% glucose diet. The flux of glucose C to TLFA increased by an order of magnitude within an hour after mice nibbled a test meal for several minutes. After ingestion of two small test meals or a single large test meal, the flux of glucose C to TLFA increased from a fasting rate of 0.5 to 35 and 87 micro g of glucose C/min/20 g body wt, respectively. Although trained meal eaters are thought to have abnormally increased lipogenesis, their lipogenic response to a single test meal was the same as that previously reported for untrained nibbling mice. Most of the newly synthesized fatty acids were found in extrahepatic tissues. Ingestion of a first test meal completely prevented the expected hyperglycemic response following ingestion of a second test meal even though the latter contained over 10 times more glucose than that in the total body glucose pool.