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Neural control of biosynthesis and secretion of serum transferrin in perfused rat liver.

ABSTRACT: The effects of sympathetic- and parasympathetic-nerve stimulation on the synthesis of transferrin and other serum proteins from [14C]leucine and their secretion were studied in rat liver perfused in situ. The radioactivities incorporated into perfusate transferrin, albumin and total protein increased with time during 90 min perfusion after an initial lag period of 15-30 min. The increases in the radioactivities of the perfusate proteins were inhibited by electrical stimulation of the hepatic nerve, whereas the increases were enhanced by vagal-nerve stimulation. Measurement of the incorporation of [14C]leucine into transferrin in the microsomal and cytosol fractions of the liver after 90 min perfusion revealed that the synthesis of this serum protein was suppressed by hepatic-nerve stimulation and increased by vagal-nerve stimulation. The results indicate that the biosynthesis and secretion of transferrin, and possibly other serum proteins, are inhibited by sympathetic-nerve stimulation and enhanced by parasympathetic-nerve stimulation.

SUBMITTER: Watanabe Y

PROVIDER: S-EPMC1131325 | biostudies-other | 1990 Apr

REPOSITORIES: biostudies-other

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Activation of integrins by urea in perfused rat liver.

Project description:High concentrations of urea were shown to induce a paradoxical regulatory volume decrease response with K(+) channel opening and subsequent hepatocyte shrinkage (Hallbrucker, C., vom Dahl, S., Ritter, M., Lang, F., and Häussinger, D. (1994) Pflügers Arch. 428, 552-560), although the hepatocyte plasma membrane is thought to be freely permeable to urea. The underlying mechanisms remained unclear. As shown in the present study, urea (100 mmol/liter) induced within 1 min an activation of ?(1) integrins followed by an activation of focal adhesion kinase, c-Src, p38(MAPK), extracellular signal-regulated kinases, and c-Jun N-terminal kinase. Because ?(5)?(1) integrin is known to act as a volume/osmosensor in hepatocytes, which becomes activated in response to hepatocyte swelling, the findings suggest that urea at high concentrations induces a nonosmotic activating perturbation of this osmosensor, thereby triggering a volume regulatory K(+) efflux. In line with this, similar to hypo-osmotic hepatocyte swelling, urea induced an inhibition of hepatic proteolysis, which was sensitive to p38(MAPK) inhibition. Molecular dynamics simulations of a three-dimensional model of the ectodomain of ?(5)?(1) integrin in water, urea, or thiourea solutions revealed significant conformational changes of ?(5)?(1) integrin in urea and thiourea solutions, in contrast to the simulation of ?(5)?(1) in water. These changes lead to an unbending of the integrin structure around the genu, which may suggest activation, whereas the structures of single domains remained essentially unchanged. It is concluded that urea at high concentrations affects hepatic metabolism through direct activation of the ?(5)?(1) integrin system.

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Biosynthesis and secretion of triacylglycerol in rat liver after partial hepatectomy.

Project description:Partially hepatectomized rats were used to investigate the mechanism of fatty-liver development in the regenerating rat liver. After partial hepatectomy the amount of hepatic triacylglycerol increased by almost 4-fold compared with sham-operated rats. The activities of both cytosolic and microsomal phosphatidate phosphohydrolase were enhanced at 12 h after surgery. The activity of diacylglycerol acyltransferase was increased at a later stage of regeneration. Analysis of plasma lipoproteins showed a significant decrease of lipids associated with very-low-density lipoproteins (VLDL). Relative to control, the rate of hepatic triacylglycerol synthesis from [3H]glycerol in vivo was stimulated at 22 h after partial liver resection. However, secretion of glycerol-labelled triacylglycerol in VLDL was the same in control and hepatectomized rats. In cultures of hepatocytes from hepatectomized donor rats, the concentration of triacylglycerol and the biosynthesis of this lipid from [3H]glycerol or from [3H]oleate were enhanced. The secretion of total triacylglycerol into the medium was not affected, resulting in a net accumulation of intracellular triacylglycerol. The rate of secretion of leucine-labelled apolipoproteins B and E associated with VLDL was similar in cell cultures from hepatectomized and sham-operated rats. The results of this study show that the enhancement of the biosynthesis of triacylglycerol in hepatectomized livers is not accompanied by an increase of the secretion of VLDL.

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