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Biomedical subjects

K Jungermann

Publications and source records attributed to K Jungermann.

At least 181 records · Page 10Linked to original sources
PubMed1982

Activation of glycogenolysis and norepinephrine overflow in the perfused rat liver during repetitive perivascular nerve stimulation.

During in situ perfusion of rat liver stimulation of nerve bundles around hepatic artery and portal vein resulted in an increase of glucose output, a switch from lactate uptake to output and in a decrease of portal flow. These effects remained essentially the same during 3 stimulation periods at 20 min intervals; norepinephrine overflow, however, was strongly decreased during the second and third period. The metabolic and hemodynamic effects were not correlated to norepinephrine overflow during repetitive stimulations and during stimulations in the presence of norepinephrine, phentolamine, propranolol or desipramine.

Animals↗
PubMed1982

The glucose/glucose-6-phosphate cycle in the periportal and perivenous zone of rat liver.

Periportal and perivenous hepatocytes contain different activities (V) of antagonistic key enzymes such as glucokinase and glucose-6-phosphatase. In order to get an insight into the metabolism of the periportal and perivenous area the flux rates (v) of the glucose/glucose-6-phosphate cycle were calculated on the basis of the Michaelis-Menten equation using the measured zonal concentrations of glucose and glucose 6-phosphate, the zonal activities of glucokinase and glucose-6-phosphatase previously reported and the half-saturating substrate concentrations (Km) of the two enzymes found in the literature. The concentrations of glucose were obtained as a first approximation by measuring the concentrations in portal (= periportal) and hepatovenous (= perivenous) blood; those of glucose 6-phosphate were calculated from the levels determined in microdissected periportal and perivenous liver tissue. The calculations showed (a) that the overall cycling rates agreed remarkably well with those reported for intact animals and (b) that during a normal feeding rhythm the periportal zone should catalyze net glucose output and the perivenous zone should mediate net glucose uptake, as proposed by the model of 'metabolic zonation'.

Animals↗
PubMed1982

Direct control of glycogen metabolism in the perfused rat liver by the sympathetic innervation.

The mode of action of hepatic nerves on the metabolism of carbohydrates was studied in the rat liver perfused in situ. 1. Electrical stimulation of the nerve bundles around the hepatic artery and the portal vein resulted in an increase of glucose and lactate output, an enhancement of phosphorylase a activity and a decrease of portal flow. 2. Sodium nitroprusside prevented the hemodynamic changes after nerve stimulation without affecting the metabolic alterations. 3. Phentolamine or an extracellular calcium level below 300 mumol x 1(-1) abolished both hemodynamic and metabolic changes after nerve stimulation, while propranolol or atropine were without effect. 4. Norepinephrine infusion mimicked nerve stimulation only at the highly unphysiological concentration of 0.1 microM; it was not effective at a concentration of 0.01 microM, which might be reached in the sinusoidal blood due to an overflow from intrahepatic synapses. The present results suggest that, in rat liver, glycogen breakdown is regulated by alpha-sympathetic nerves directly rather than indirectly via hemodynamic changes or via norepinephrine overflow.

Animals↗
PubMed1982

Induction in primary culture of 'gluconeogenic' and 'glycolytic' hepatocytes resembling periportal and perivenous cells.

Adult rat hepatocytes were kept in primary culture for 48 h under different hormonal conditions to induce an enzyme pattern which with respect to carbohydrate metabolism approximated that of periportal and perivenous hepatocytes in vivo. 1. Glucagon-treated cells compared with control cells possessed a lower activity of glucokinase, a 4.5-fold higher activity of phosphoenolpyruvate carboxykinase and unchanged levels of glucose-6-phosphatase, phosphofructokinase, fructose-bisphosphatase and pyruvate kinase; they resembled in a first approximation the periportal cell type and are called for simplicity 'periportal'. Inversely, insulin-treated cells compared with control cells contained a 2.2-fold higher activity of glucokinase, a slightly decreased activity of phosphoenolpyruvate carboxykinase, increased activities of phosphofructokinase and pyruvate kinase and unaltered levels of glucose-6-phosphatase and fructose-bisphosphatase; they resembled perivenous cells and are called simply 'perivenous'. Gluconeogenesis and glycolysis were studied under various substrate and hormone concentrations. 2. Physiological concentrations of glucose (5 mM) and lactate (2 mM) gave about 80% saturation of gluconeogenesis from lactate and less than 15% saturation of glycolysis at a simultaneous 40% inhibition of the glycolytic rate by lactate. 3. Comparison of the two cell types showed that under identical assay conditions (5 mM glucose, 2 mM lactate, 0.5 nM insulin, 0.1 muM dexamethasone) gluconeogenesis was 1.5-fold faster in the 'periportal' cells and glycolysis was 2.4-fold faster in the 'perivenous' cells. 4. Metabolic rates were under short-term hormonal control. Insulin increased glycolysis three fold in both cell types with a half-maximal effect at about 0.4 nM, but did not influence the gluconeogenic rate. Glucagon inhibited glycolysis by 70% with a half-maximal effect at about 0.1 nM. Gluconeogenesis was stimulated by glucagon (half-maximal dose: 0.5 nM) 1.8-fold only in 'periportal' cells containing high phosphoenolpyruvate carboxykinase activity, not in the 'perivenous' cells with a low level of this enzyme. 5. A comparison of the two cell types showed that with maximally stimulating hormone concentrations gluconeogenesis was threefold faster in 'periportal' cells and glycolysis was eightfold faster in 'perivenous' cells. The results support the view that periportal and perivenous hepatocytes in vivo catalyse gluconeogenesis and glycolysis at inverse rates.

Animals↗
PubMed1982

Heterogeneous distribution of phosphoenolpyruvate carboxykinase in rat liver parenchyma, isolated, and cultured hepatocytes.

Phosphoenolpyruvate carboxykinase was localized in rat liver parenchyma, as well as isolated and cultured hepatocytes by indirect immunofluorescence microscopy using antibodies against the enzyme raised in rabbits and purified by antigen-affinity-chromatography. 1. In fed and fasted rats the enzyme was heterogeneously distributed over the parenchyma. It was predominantly located in the periportal zone. 2. In hepatocytes shortly after isolation or cultured for 1 h the heterogeneity with respect to the enzyme content was maintained. 3. In hepatocytes cultured for 24 h and treated with glucagon the heterogeneity was lost. The results indicate that the heterogeneity of hepatocytes as to phosphoenolpyruvate carboxykinase content is due to a different expression of the genome.

Animals↗
PubMed1979

The development of functional heterogeneity in the liver parenchyma of the golden hamster.

Prenatal and postnatal stages of the development of golden hamsters were studied histochemically and biochemically. It was shown that, beginning with the 12th gestational day, the fetal liver starts to store glycogen, and that this process reaches its maximum a birth. Glycogen phosphorylase and glucose-6-phosphatase (G6Pase)-activity increased drastically in the last two days before birth, glycogen phosphorylase preceding G6Pase. As a histochemical characteristic, an even distribution of glycogen, glycogen phosphorylase and G6Pase activity is found in the liver parenchyma at birth. During the first two postnatal weeks typical heterogeneous patterns of distribution developed: glycogen depletion could be demonstrated predominantly in zone 1 of the liver acinus, this being at the same time the area of highest glycogen phosphorylase and G6Pase-activity. The periportal zone 1 thus became characterized as the primary site of glycogenolysis (glycogen phosphorylase) and gluco(neo)genesis (G6Pase). "Metabolic Zonation" is interpreted as the chemomorphological equivalent of the regulatory function of the liver as a glucostat.

Animals↗
PubMed1978

Increase of the gluconeogenic and decrease of the glycolytic capacity of rat liver with a change of the metabolic zonation after partial hepatectomy.

During the first 72 h after 67% partial hepatectomy of female Wistar rats (160 g) the specific activities [mumol X min-1 X (g liver)-1] of the glucogenic glucose-6-phosphatase and fructose-bisphosphatase and of the glycolytic hexokinase and 6-phosphofructokinase remained essentially constant. However, the activity of the glycolytic pyruvate kinase (L- plus M2-type) was decreased slightly and that of glucokinase was decreased markedly to below 30%, while the glucogenic phosphoenolpyruvate carboxykinase was increased to over 200%. Between 10 and 40 h after partial hepatectomy, when the proliferation started in the periportal area, a shift of the glucogenic glucose-6-phosphatase-rich zone from its normal periportal to an intermediate or even perivenous position was observed histochemically. After 48 h, when the proliferation was no longer restricted to the periportal zone, the normal glucose-6-phosphatase zonation (as before partial hepatectomy) was restored. Glycogen was degraded rapidly during the first 4 h after operation; it was later repeatedly resynthesized and degraded in correlation with the feeding rhythm of the animals. The zonation of glycogen metabolism was in accord with the observed zonation of glucose-6-phosphatase.

Animals↗
PubMed1976

Properties and function of clostridial membrane ATPase.

ATPase (ATP phosphohydrolase, EC 3.6.1.3) was detected in the membrane fraction of the strict anaerobic bacterium, Clostridium pasteurianum. About 70% of the total activity was found in the particulate fraction. The enzyme was Mg2+ dependent; Co2+ and Mn2+ but not Ca2+ could replace Mg2+ to some extent; the activation by Mg2+ was slightly antagonized by Ca2+. Even in the presence of Mg2+, Na+ or K+ had no stimulatory effect. The ATPase reaction was effectively inhibited by one of its products, ADP, and only slightly by the other product, inorganic phosphate. Of the nucleoside triphosphates tested ATP was hydrolyzed with highest affinity ([S]0.5 v = 1.3 mM) and maximal activity (120 U/g). The ATPase activity could be nearly completely solubilized by treatment of the membranes with 2 M LiCl in the absence of Mg2+. Solubilization, however, led to instability of the enzyme. The clostridial solubilized and membrane-bound ATPase showed different properties similar to the "allotopic" properties of mitochondrial and other bacterial ATPases. The membrane-bound ATPase in contrast to the soluble ATPase was sensitive to the ATPase inhibitor dicyclohexylcarbodiimide (DCCD). DCCD, at 10(-4) M, led to 80% inhibition of the membrane-bound enzyme; oligomycin ouabain, or NaN3 had no effect. The membrane-bound ATPase could not be stimulated by trypsin pretreatment. Since none of the mono- or divalent cations had any truly stimulatory effect, and since a pH gradient (interior alkaline), which was sensitive to the ATPase inhibitor DCCD, was maintained during growth of C. pasteurianum, it was concluded that the function of the clostridial ATPase was the same as that of the rather similar mitochondrial enzyme, namely H+ translocation. A H+-translocating, ATP-consuming ATPase appears to be intrinsic equipment of all prolaryotic cells and as such to be phylogenetically very old; in the course of evolution the enzyme might have been developed to a H+-(re)translocating, ATP-forming ATPase as probably realized in aerobic bacteria, mitochondria and chloroplasts.

2,6-Dichloroindophenol↗