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The appearance and degradation of specific hepatocellular cytoplasmic inclusion bodies in rat liver due to D-galactosamine. I. The relation between the amount of liver glycogen and the appearance of the atypical dense bodies in the liver cell.

One of the most sensitive and specific signs of the galactosamine effect upon the rat liver cell is the appearance of PAS-positive and diastase-resistant granules within the cytoplasm of hepatocytes. Light-microscopic, histochemical, biochemical, and electron-microscopic findings reveal that the appearance of these ADB (= atypical dense bodies) depends upon a working glycogen metabolism at the time of GalN treatment. The ADB are composed of particles resembling, due to shape and size, ribosomes and beta particles of glycogen. Most of them are surrounded by the rER, but they are never enclosed by a limiting membrane. Due to sequential changes they can be generally classified into three types; the early, the intermediate, and the late type. In seven experiments it can be shown, that the appearance of the ADB depends upon the time and dosage after GalN treatment. They occur even if an additional treatment with galactose or uridine prevents the liver from the features of a hepatitis, as also shown in the livers of newborn animals up to 3 weeks of age. The histochemical response against various glucosidases, hexosaminidases, pronase, and RNAse as well as against various fixatives indicates that ADB are composed of, at least, two different constituents, the former RNAse-sensitive and visible with routine light-microscopic staining procedures, the latter RNA-resistant, PAS-positive, and invisible after staining with H & E or toluidine blue. The latter is diastase-resistant, suggesting that this portion of ADB does not represent the usual glycoproteins but some abnormal metabolite of glycogen. The ADB can be detected with maximal accumulation in the cytoplasm of hepatocytes at that time when the glycogen content determined in the liver homogenate by biochemical methods is greatly reduced.

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Plasma glucose concentration determines direct versus indirect liver glycogen synthesis.

In the present study hepatic glycogenesis by the direct versus indirect pathway was determined as a function of the glucose infusion rate. Glycogen synthesis was examined in catheterized conscious rats that had been fasted 48 h before receiving a 3-h infusion (iv) of glucose. Glucose, containing tracer quantities of [U-14C]- and [6-3H]glucose, was infused at rates ranging from 0 to 230 mumol X min-1 X kg-1. Plasma concentrations of glucose, lactate, and insulin were positively correlated with the glucose infusion rate. Despite large changes in plasma glucose, lactate, and insulin concentrations, the rate of hepatic glycogen deposition (0.46 +/- 0.03 mumol X min-1 X g-1) did not vary significantly between glucose infusion rates of 20 and 230 mumol X min-1 X kg-1. However, the percent contribution of the direct pathway to glycogen repletion gradually increased from 13 +/- 2 to 74 +/- 4% in the lowest to the highest glucose infusion rates, with prevailing plasma glucose concentrations from 9.4 +/- 0.5 to 21.5 +/- 2.1 mM. Endogenous glucose production was depressed (by up to 40%), but not abolished by the glucose infusions. Only a small fraction (7-14%) of the infused glucose load was incorporated into liver glycogen via the direct pathway irrespective of the glucose infusion rate. Our data indicate that the relative contribution of the direct and indirect pathways of hepatic glycogen synthesis are dependent on the glucose load or plasma glucose concentration and emphasize the predominance of the indirect pathway of glycogenesis at plasma glucose concentrations normally observed after feeding.

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