Inflammation-induced synthesis of proteoheparan sulfate: a novel acute-phase reactant in rat hepatocytes.

The synthesis of proteoheparan sulfate in hepatocytes is positively regulated under acute-phase conditions produced either by turpentine or deep back incision. In both cases the incorporation of [35S]sulfate and [14C]glucosamine is doubled during a 4-h incubation period if compared with control rat hepatocytes. Neither the fractional secretion rate of heparan sulfate into the medium (less than 0.1 of cell-associated glycosaminoglycans) nor the composition of newly formed proteoglycans in hepatocytes are affected during acute phase reaction.

Endocytosis via galactose receptors in vivo. Ligand size directs uptake by hepatocytes and/or liver macrophages.

We followed the intrahepatic binding and uptake of variously sized ligands with terminal galactosyl residues in rat livers. The ligands were administered to prefixed livers in binding studies and in vivo and in situ (serum-free perfused livers) in uptake studies. Gold sols with different particle diameters were prepared: 5 nm (Au5), 17 nm (Au17), 50 nm (Au50) and coated with galactose exposing glycoproteins (asialofetuin (ASF) or lactosylated BSA (LacBSA)). Electron microscopy of mildly prefixed livers perfused with LacBSA-Au5 in serum-free medium showed ligand binding to liver macrophages, hepatocytes and endothelial cells. Ligands bound to prefixed cell surfaces reflect the initial distribution of receptor activity: pre-aggregated clusters of ligands are found on liver macrophages, single particles statistically distributed on hepatocytes and pre-aggregated clusters of particles restricted to coated pits on endothelial cells. Ligand binding is prevented in the presence of 80 mM N-acetylgalactosamine (GalNAc), while N-acetylglucosamine (GlcNAc) is without effect. Electron microscopy of livers after ligand injection into the tail vein shows that in vivo uptake of electron-dense galactose particles by liver cells is size-dependent. Using a LacBSA-Au preparation with heterogeneous particle diameter (2.2-11.7 nm) we found that hepatocytes take up only ligands up to the size of 7.8 nm, whereas particles of all sizes available in this experiment are found in liver macrophages and endothelial cells. ASF-Au17 and LacBSA-Au17 are endocytosed by liver macrophages and endothelial cells, but not by hepatocytes. ASF-Au50 is taken up by liver macrophages only. In vivo uptake by liver macrophages is mediated by galactose-specific recognition as shown by inhibition with GalNAc. Some 52-65% inhibition was measured in in vivo experiments and 78% inhibition in in situ experiments. GlNAc showed no inhibitory effect. Furthermore, we measured uptake of [125J]ASF and of [125J]ASF adsorbed to Au17 by the different cell populations of rat livers in vivo. While the bulk of the molecular ligand is found in the hepatocyte fraction, the particulate ligand is located in the sinusoidal fraction.

Glycogen synthesis from serine in isolated perfused hindquarters of acutely uraemic rats.

Isolated hindquarters of bilaterally nephrectomized and sham-operated rats were perfused in the presence and absence of 14C-labelled serine, respectively. After a perfusion period of 30 min 14C-serine was 4,074 +/- 270 dpm/ml in the perfusion medium of sham-operated animals and decreased to 2,800 +/- 190 dpm/ml in the medium of acutely uraemic rats. Muscle glycogen concentration in sham-operated animals was 1.10 +/- 0.04 mg/g wet weight in the absence and 1.03 +/- 0.11 mg/g in the presence of serine. In contrast, in acutely uraemic rats there was a glycogen concentration of 0.57 +/- 0.09 mg/g in the absence of serine. Glycogen was increased in the presence of serine in the perfusion medium, the value being 1.50 +/- 0.13 mg glycogen/g wet weight. Incorporation of labelled serine into skeletal muscle glycogen was significantly higher in acutely uraemic animals (15 +/- 0.5 mumol/g glycogen) than in sham-operated animals (10 +/- 0.4 mumol/g). The results are compatible with the hypothesis that serine increases muscle glycogen synthesis in acute uraemia.