The pentose cycle in the liver. Estimation under conditions of gluconeogenesis

• 1.1. Two simplified models were developed representing the interaction of the pentose cycle and the gluconeogenic pathway in the liver.
• 2.2. Under conditions of gluconeogenesis, the stoichiometry of the pentose cycle becomes 1 glucose 6-P → 6 CO₂, rather than 1 glucose 6-P → 1 triose P + 3CO₂ as in glycolytic tissues.
• 3.3. The first model to estimate pentose cycle uses the relative ¹⁴C yields in ¹⁴CO₂ and glucose from [1-¹⁴C] galactose, together with an estimation of the rate of glucose 6-phosphatase, obtained from analytical data on the rate of glucose formation, together with isotopic data on the rate of glucose phosphorylation when glucose is initially present.
• 4.4. The second model involves determination of the randomization of ¹⁴C in glucose formed from substrates which introduce ¹⁴C into C-3 (or C-2) of glucose 6-P.
• 5.5. Preliminary degradation data, obtained in experiments with liver cells from starved-refed rats in which lipogenesis was high, are in accord with the classical formulation of the pentose cycle.

     

Ultrastructural study of Kupffer cells in teleost liver under normal and experimental conditions

Summary The Kupffer cells in the liver of the teleost fish, Pimelodus maculatus, are attached by desmosomes to the endothelial cells lining the sinusoids. These provide a strong attachment allowing them to resist the passage of blood. Following perfusion with India ink, both endothelial and Kupffer cells ingest India ink particles by pinocytosis and micropinocytosis. It is suggested that both cell types may represent two different functional states of the same cell.     

Ultrastructural study of the endothelial cells in teleost liver sinusoids under normal and experimental conditions

Summary The ultrastructure of the endothelial cells of liver sinusoids was studied in the teleost, Pimelodus maculatus. These cells have the ability to form pinocytotic vacuoles, starting with the formation of marginal folds. The latter occur in many cells after stimulation by India ink injections and ink particles are ingested by pinocytosis and by micropinocytosis. Desmosomes, structures rarely described between liver sinusoidal endothelial cells, are present in this species.     

Immunohistochemical and electron microscopic study of the rat hypothalamic nuclei and cell clusters under various experimental conditions

Summary In untreated, pregnant and thirsting rats the neurosecretory hypothalamic areas were investigated by means of the immunoperoxidase technique in order to demonstrate vasopressin- and oxytocin containing elements at the light- and electron microscopic level. In addition, chromalum-hematoxylinphloxin (CHP) staining and conventional double staining of ultrathin sections were used. The areas investigated included the anterior and posterior supraoptic nuclei, the paraventricular nuclei, the numerous accessory cell clusters in the region between the tractus opticus and the third ventricle as well as the median eminence. In all nuclei and in the accessory cell clusters, the number of vasopressin-reactive neurons exceeds that of oxytocin-reactive neurons. Compared with the anterior supraoptic nucleus, the posterior supraoptic nucleus and the accessory cell clusters react more heavily to prolonged thirst. In the median eminence the neurosecretory axons display close contacts with the portal vessels not only in its lateral portion but in thirsting animals also around the mid-line. There the internal layer is broadened and vasopressin-positive tanycytic processes reach the external zone. Parasagittally, fine vasopressin-positive material can be traced from the internal layer to small deposits at the portal vessels. In long term thirsting animals the typical feature of swollen axons exhibits a characteristic distribution in the median eminence and renders a distinct positive reaction to anti-vasopressin. The release of peptide hormones from the perikarya and from the axons within the nuclei as well as the mode of release within the median eminence are discussed. The significance of the positive immunostaining of the ependymal tanycytes and of some perikarya of the suprachiasmatic nucleus must be reconsidered by further studies.Supported by the Deutsche Forschungsgemeinschaft (Grant Nr. Kr 569/1) and Stiftung VolkswagenwerkDedicated to Professor Berta Scharrer on the occasion of her 70th birthdayThe author wishes to express her special gratitude to Dr. L.A. Sternberger for supplying the peroxidaseantiper oxidase-complex and to Dr. H. Stein (Pathologisches Institut der Universität Kiel) for supplying Anti-IgG. The skilful technical assistance of Mrs. H. Prien and Mrs. H. Schöning is thankfully acknowledged     

Lipid composition of rat liver microsomes under various experimental conditions

Cholesterol and phospholipid content, and phospholipid composition (sphingomyelin, phosphatidylcholine, phosphatidylserine, phosphatidylinositol, phosphatidylethaolamine) were assayed in rat liver microsomes during regeneration, foetal development and pregnancy. Cholesterol was assayed using Liebermann-Buchard reagent; the phospholipid extract was separated by thin-layer chromatography. While in pregnancy no changes were observed, during foetal development and liver regeneration there was a significative decrease of cholesterol/phospholipid ratio, and of phosphatidylcholine content. Moreover, in developing liver microsomes, there is also a significative increase of sphingomyelin and phosphatidylserine + phosphatidylinositol.     

A scanning electron microscopic study of the rat liver sinusoid

The surface ultrastructure of Kupffer cells in the rat liver has been studied by scanning electron microscopy (SEM). The results demonstrate that Kupffer cells are both significantly different and clearly distinct from endothelial cells. Kupffer cells have neither pores (and/or sieve plates) nor fenestrations, all of which are present in endothelial cells. They possess a stellate shape, and only indirectly, with slender and irregular evaginations, contribute to the lining of the sinusoidal wall. Furthermore, the luminal surface in some areas contains a large population of short microvilli, microphicae and invaginations. These elements form a kind of microlabyrinth which may correpond to the worm-like structures described by transmission electron microscopy (TEM). In the present study, transition forms between endothelial and Kupffer cells were never found. On the contrary, considering the highly fenestrated nature of the endothelial cells, the Kupffer cells may, by ameboid movements, easily cross the overlapping barrier of the sinusoid and protrude into the lumen. Thus, acting as activated macrophages, the Kupffer cells might function to prevent the entrance of foreign material into the tissues of the liver through the fragile and highly fenestrated endothelium. Finally, the topographical reconstruction of the sinusoid by correlated SEM and TEM studies demonstrates the Kupffer cells, with their protruding cytoplasm and ability to extend into the lumen of the sinusoid, may actually change the caliber of the vessel, and thus function as a sphincter which causes a temporary arrest of the blood flow when the diameter of the sinusoidal lumen is reduced.     

Electron microscopic study of experimental infection. II. A study of the dynamics of Shigella infection]

The dynamics of experimental Shigella infection of chick embryo fibroblasts was studied with the use of electron microscopy. The antibiotic-resistant forms of Sh. sonnei 1,188 was found to be incapable of invasion into the fibroblast cytoplasm and intracellular proliferation. The destruction of fibroblasts observed during the infection was seemingly caused by the action of bacterial endotoxins.     

Polyethylene glycol-induced internalization of bacteria into fungal protoplasts: electron microscopic study and optimization of experimental conditions.

We studied the mechanism of internalization of Escherichia coli into Saccharomyces cerevisiae induced by polyethylene glycol (PEG) and optimized the experimental conditions. Transmission electron microscope studies revealed that the principal factor involved in the internalization was the degree of cell aggregation attained. Internalization occurred mainly by an endocytosis-like mechanism and took place during the elimination of PEG. The optimum conditions were to treat a mixed pellet of both microorganisms with 15% PEG and then gradually dilute the polymer. The same conditions were applied to E. coli and Aspergillus nidulans, with similar results.     

Electron microscopic study of experimental infection. 1. A study of the dynamics of staphylococcal infection]

The dynamics of staphylococcus infection was studied in experimental infection of chick embryo fibroblasts with electron microscopy. It was shown that the antibiotic-resistant forms of staphylococci (strain 79) were capable of invading the fibroblast cytoplasm inducing its gradual vacuolization up to complete destruction.     

Comparative characteristics of tRNA-methyltransferases from rabbit liver and myocardium under normal conditions and in experimental ischemia

Comparative studies of the state of aggregation and activity of tRNA-methyltransferases in cytosol (105,000 X g supernatant) from normal and ischemic rabbit liver and myocardium were carried out. The optimal conditions (pH, protein concentration, ionic composition of incubation mixture) for the determination of activity of tRNA-methyltransferases were elaborated. The protein fraction precipitated at 55% saturation of ammonium sulfate was shown to inherit the highest activity of tRNA-methyltransferases. In rabbit liver cytosol, the bulk of the tRNA-methyltransferase activity (approximately 50%) was found to be associated with high molecular weight complexes containing aminoacyl-tRNA-synthetases. The tRNA-methyltransferase activity was increased almost 1.4-fold both in the myocardium cytosol under total ischemia of isolated heart (30 min, 37 degrees C) and in liver cytosol under experimental myocardial infarction (EMI, occlusion of anterior coronary artery for 12 hours). Moreover, the labilization of high molecular weight complexes was observed: up to 80% of the tRNA-methyltransferase activity was localized in the fraction of lower molecular weight complexes and free enzyme fraction. In the total set of eight methylated nucleotides (products of submethylated tRNA methylation by liver enzymes), the decreased m1A content and the increased m7G and m1G contents were observed at EMI. It was assumed that the observed changes in the state of aggregation of tRNA-methyltransferases, in particular, their dissociation from the high molecular weight amino-acyl-tRNA-synthetase complexes are prerequisites for the suppression of protein biosynthesis under ischemic conditions.