The hepatocellular uptake of glucose, galactose and fructose in conscious sheep.

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Abstract
Surgical techniques for chronic catheterization of hepatic and portal veins in sheep were described. These catheters remained usable for 2-6 mo. and did not alter hepatic morphology. Hepatocellular uptake of monosaccharides was estimated from their ability to pass the boundaries of the sucrose space in a double indicator dilution procedure in conscious fed sheep. A large proportion (81%) of D-glucose carried in the portal blood was found to enter an hepatic cellular compartment. The radioactive label of D-glucose infused in the portal vein remained associated with D-glucose in hepatic venous blood samples during the experimental period. A large proportion (74%) of an infused trace of D-galactose, a smaller proportion (33%) of D-fructose and negligible amounts of L-glucose were taken up in a single passage through the liver. Raised blood concentrations of sucrose or of methyl-.alpha.-D-glucoside (Me-.alpha.-DG) significantly diminished the proportional uptake of D-glucose. Raised blood concentrations of glucose, galactose or Me-.alpha.-DG diminished the proportional uptake of D-galactose. Raised blood concentrations of fructose diminished the proportional uptake of fructose. Neither total hepatic blood flow changes nor competitive effects within the cell could account for these findings. These monosaccharides seemingly entered the liver cell by facilitated diffusion, and shared at least some of the membrane elements that mediated this process. Only a proportion of the glucose-transporting apparatus was probably accessible to galactose.