Carbohydrate Metabolism of the Liver in Normal Man under Varying Dietary Conditions

Abstract

The glucose and urea production and the uptake of gluconeogenic precursors by the liver were measured with the liver vein catheterization technique in two series of healthy subjects after 4 days on a well-defined normo-caloric diet. After a normal mixed diet the net splanchnic glucose production was 0.87 mmol/min. The glucose derived from maximum gluconeogenesis was 0.31 mmol/min. By using a liver biopsy technique in a similar series, the glycogenolysis was found to be 0.54 mmol glucoselmin. After a carbohydratepoor diet the splanchnic glucose production had decreased to 0.30 mmol/min. In this situation the liver was deprived of most of its glycogen, as shown earlier by direct determination of glycogen in liver biopsy specimens. The uptake of gluconeogenic substrates corresponded to the net glucose production. The decreased glucose production during carbohydrate-poor diet did not result in any significant change of the blood glucose level. This indicates a considerable decrease of the peripheral uptake of glucose. Scand J Clin Lab Invest Downloaded from informahealthcare.com by University of Newcastle on 01/02/15 For personal use only. 15. Havel, R. J., Kane, I. P., Balasse, E. O., Segel, N. & Basso, L. V. Splanchnic metabolism of free fatty acids and production of triglycerides of very low density lipoproteins in normotri-Scand J Clin Lab Invest Downloaded from informahealthcare.com by University of Newcastle on 01/02/15 For personal use only.

Hepatic gluconeogenic fluxes and glycogen turnover during fasting in humans. A stable isotope study.

“…Glucagon administration clearly caused mobilization of glycogen (Fig. 6), based on the large increase in [1][2] H 1 ]galactose recovery in plasma glucose, and the composition of the glycogen released either before or after glucagon was very close to the values predicted ‫ف(‬ 50-75% GNG-labeled, ‫ف‬ 25-50% unlabeled or pre-existing).…”

“…Glucagon is generally believed to increase GP primarily by stimulating glycogenolysis and recent NMR spectroscopic measurements in overnight-fasted humans confirmed that net hepatic glycogenolysis accounted for Ͼ 90% of GP after administration of glucagon (38). The previous administration of [1][2] H 1 ]galactose allowed us to quantify the precise extent to which glucagon increased glycogen mobilization. GNG-glucose deposited in, and mobilized from, glycogen could then be compared to direct GNG, or GNG flux that did not pass through glycogen.…”

“…This important and seemingly straightforward metabolic question remains controversial (1)(2)(3)(4)(5)(6)(7)(8). It is well known that the liver can produce glucose from the pathways of gluconeogenesis (GNG) 1 or glycogenolysis, and that the kidney might produce some glucose via GNG (9), but the relative contributions and the precise metabolic pathways traversed remain uncertain after many years of investigation.…”

Influence of a 60-hour fast on insulin-mediated splanchnic and peripheral glucose metabolism in humans.

“…In the postabsorptive overnight fasted state, hepatic glycogenolysis accounts for the major part of glucose production, while only some 25% derives from hepatic gluconeogenesis (1). After 2-3 d of fasting the glycogen depots in the liver are exhausted (2), gluconeogenesis is almost exclusively responsible for glucose production (1,3,4), and the circulating glucose levels in peripheral blood are reduced.…”

“…After 2-3 d of fasting the glycogen depots in the liver are exhausted (2), gluconeogenesis is almost exclusively responsible for glucose production (1,3,4), and the circulating glucose levels in peripheral blood are reduced. The adaptation to this situation is known to include both a reduced insulin secretion (5,6) and a reduced sensitivity to insulin (7), but the site of the latter has not been established.…”