Glycogen Formation Research Articles

The incorporation of ingested glycerol-C 14 into the lipids of the rat

Glycerol-C 14 has been shown to provide precursors for the glyceride-glycerol of the rat intestinal tissue lipids when fed under conditions favoring the competition of the ingested material with compounds available from endogenous sources. Glycerol absorption rates maintained nearly constant at each of three feeding levels but enhanced with increase of dose led to C 14 incorporation into the total lipids of the intestine, which was, in general, proportional to the quantities of the tagged alcohol absorbed. Glycerides given simultaneously in 0.5-ml amounts further increased, at each dose level, the incorporation of the isotope into the total fats. Fractionation of these lipids into glycerides and phospholipids showed that increased C 14 incorporation at the medium level was due to a greater isotope content in both fractions. However, at the maximum glycerol-C 14 dose, radioactivity in the phospholipids had reached a plateau, and further increments in the total lipid C 14 inclusion were derived entirely from the greatly enhanced isotopic content of the glycerides. When the fat fed contained deuteriostearic acid, comparisons between the labeling by the C 14 and the deuterium indicated that the glyceride-glycerol of the newly formed phosphatids was derived largely from the exogenous alcohol, while up to 38.5% of that moiety in the glycerides similarly formed could have had an origin in the ingested glycerol-C 14. Some 95% of the C 14 found in the fat was present in the glycerol portion of the molecule. In the liver, glycerol-C 14 incorporation into the lipids was of much greater magnitude than into the intestinal tissue fat, with the radioactivity tending to be somewhat greater in the glyceride than in the phospholipid fraction. Although increased incorporation of C 14 followed augmented glycerol administration, the liver fats from the nonfat-fed rats contained more isotope at each dose level than those from the animals to which fat was given. This may be indicative of a greater substrate competition to provide for immediate glycogen formation under the latter regime.

Mechanism of action of adrenocorticotropic hormone through activation of glucose-6-phosphate dehydrogenase

1. 1. Evidence is presented that the principal mechanism by which adrenocorticotropic hormone (ACTH) stimulates the function of the adrenal cortex is by activation of glucose-6-phosphate dehydrogenase d-glucose 6-phosphate:NADP + oxidoreductase, EC 1.1.1.49). This results in an increased rate of reduction of nicotinamideadenine dinucleotide phosphate (NADP +) by a transfer of H + and electrons from glucose 6-phosphate. Reduced nicotinamide-adenine dinucleotide phosphate (NADPH) is utilized by specific hydroxylases and other enzymes in the formation of all the classes of adrenal steroids from endogenous cholesterol. The specific activity of purified adrenal glucose-6-phosphate dehydrogenase was increased by α s- ACTH and by other preparations of ACTH. Other dehydrogenase enzymes were not activated by ACTH. Other trophic hormones of the anterior pituitary were without effect on adrenal glucose-6-phosphate dehydrogenase. Cyclic adenosine 3′,5′-phosphate did not activate adrenal dehydrogenases. 2. 2. The major source of glucose-6-phosphate in vivo is preformed glycogen, since the rate of phosphorylation of glucose is much slower than the rate of the activated glucose-6-phosphate dehydrogenase to utilize glucose 6-phosphate. Glucose 6-phosphate diverts to glycogen formation in the absence of or with low levels of ACTH. 3. 3. The rate of production of NADPH is the principal rate-limiting mechanism in the synthesis of adrenal steroids. There is an interplay between steroid hormones such as estrogens that inhibit glucose-6-phosphate dehydrogenase and ACTH which activates. The enzyme sites involved in activation by ACTH are probably not the same as those involved in the inhibition to NADP + binding by estrogens. The normal physiological balance between oxidized and reduced nicotinamide-adenine dinucleotide was adequated for maximal rates of generation of corticoids from cholesterol that were stimulated by maximal rates of production of NADPH. 4. 4. ACTH markedly stimulated corticoid synthesis in cell-free preparations of adrenal cortex that were supplemented with glucose 6-phosphate. A plot of rate of NADPH production by glucose-6-phosphate dehydrogenase against rate of corticoid synthesis is a rectangular hyperbola. The steepness of the curve varies with the amount of ACTH activation, the concentration of NADP + and glucose 6-phosphate, and the integrity of the microsomal-mitochondrial components to utilize NADPH for hydroxylations.

GLYCOGEN FORMATION IN THE CYTOTROPHOBLAST OF HUMAN PLACENTA IN EARLY PREGNANCY, AS REVEALED BY ELECTRON MICROSCOPY.

Abstract A description of the ultrastructure of cytotrophoblasts of normal human placentae in early pregnancy is given with special remarks on the glycogen. Glycogen granules in the cytotrophoblast are distinctly revealed by electron microscopy by lead hydroxide staining. Evidence is shown suggesting the intimate relation between the glycogen formation and a degenerative change of the granular endoplasmic reticulum and ribonucleoprotein particles. The glycogen formation mechanism in cytotrophoblast is discussed along with this finding and previous literatures. Evidence suggesting the cytotrophoblast is not the site of chorionic gonadotrophin production is discussed from the view of this glycogen formation pattern and lack of secretion granule.

THE ACTIVITY OF URIDINE DIPHOSPHATE GLUCOSE-GLYCOGEN SYNTHETASE IN SOME EMBRYONIC TISSUES.

Uridine diphosphate glucose (UDPG)-glycogen synthetase has been studied using chemical and histochemical methods. Activity was demonstrated in whole egg and in homogenates of whole 3-day old chick embryos, in the heart and skeletal muscle from the 5th day and in the liver from the 7th day of incubation onwards. The activity increases with age until the 16th day at which time a sharp fall was noted in all tissues studied. Enzyme activity was demonstrated also in heart, liver, skeletal muscle and brain of rat embryos from the 14th day onwards. In these tissues the activity increases with age until birth. The appearance of UDPG-glycogen synthetase in the tissues of the chick embryo coincides with the time at which, according to previously published data, glycogen begins to appear. In the liver of the rat embryo, the enzyme appears before glycogen formation starts. This is contrary to the behavior of phosphorylase which appears later, at least in skeletal muscle. These findings are in agreement with the view that, in vivo, glycogen synthesis occurs via the UDPG, rather than the phosphorylase, pathway.

Effect of Stress from High Protein Diets on Vitamin A Metabolism in Chicks

High protein diets fed to young chicks for 4 weeks produced a stress as evidenced by hypertrophy, hyperactivity and depletion of phospholipid content of the adrenal cortex and at the same time, caused an increased demand on vitamin A nutrition. No adrenal hypertrophy nor hyperactivity occurred in 4-week-old chicks fed high protein diets and simultaneously injected daily with corticosterone. However, daily injections of corticosterone increased the level of vitamin A in the blood plasma and generally caused a decrease in liver vitamin A levels. Although vitamin A deficiency was not found to affect adrenal size or corticoid production the in vitro addition of vitamin A to incubated adrenals from chicks fed high protein diets caused a marked increase in corticosterone production. Liver glycogen formation during the first 4 hours of refeeding high protein-fed chicks after a one-day fast was not impaired by vitamin A deficiency. However, liver glycogen per gram of total feed consumption was significantly decreased in vitamin A-deficient chicks 24 hours after refeeding the high protein diet following the fasting period. These results indicate an important association between vitamin A nutrition and stress produced by high protein feeding.

Action of deoxycorticosterone acetate on glycogen. II. Relationship of muscle glycogen formation to potassium metabolism.

1. Daily administration of DOCA to intact rats resulted in inhibition of muscle glycogen formation, accompanied by an approximately proportional decrease in potassium concentration of both skeletal muscle and blood serum. 2. By forcing an increase in potassium intake of DOCA treated rats, potassium concentrations of both muscle and blood serum were maintained at essentially normal levels, and glycogen production was not significantly inhibited. 3. These data indicated that the DOCA induced inhibition of muscle glycogen formation was secondary to potassium depletion.

Metabolism of glucose-U-C14 in perfused rat heart.

A closed perfusion system was designed to study C14O2 formation during uptake of glucose-U-C14 by the isolated, beating rat heart. An initial period of 5 min of preperfusion with oxygenated buffer allowed stabilization of the heart before 30 min of perfusion in the closed recirculation system. Oxygenation was adequate as judged by cardiac rate and force, the pattern of glucose metabolism, the rate of glycogenolysis, and the perfusate oxygen content. Glucose uptake increased sharply with increasing perfusate glucose concentrations over the range 1.25– 5 mm glucose, with a lesser rise in the 5–10 mm range and very little rise from 10–40 mm. Glucose oxidation, which accounted for 60% of the glucose uptake at 1.25 mm glucose concentration, reached a maximal rate at 5–10 mm. This maximal rate accounted for only 24% of the glucose uptake at 40 mm, indicating the increasing importance of nonoxidative fates of glucose with increasing glucose uptake. Lactate and net glycogen formation, and incorporation of glucose carbon into glycogen, were least at lowest glucose concentrations and increased irregularly as the glucose concentration rose. Uptake and oxidation of fructose-U-C14 (5 mm) was much less than that of glucose.

Regulatory mechanisms of glycogen deposition in liver of normal and tumour-bearing rat, and in Novikoff ascites hepatoma.

THE lowering of glycogen store in normal animal tissues during the growth of a transplanted hepatoma and the absence of glycogen in neoplastic tissues are commonly observed phenomena. The complex processes which result in removal of glycogen from normal tissues during the growth of a transplanted tumour are not fully understood. However, evidence is available for low glycogen formation in tumours and is based mainly on the assumption of a defective system of glycogen synthesis1,2.

Studies on the Mode of Action of Glucocorticoids in Rats: A Comparison of the Effects of Cortisol and Glucose on the Formation of Liver Glycogen

Five rats from a group of adrenalectomized, fasted rats were given a single injection of approximately 1 mg cortisol/100 g body weight, after which blood glucose levels were measured at intervals over a period of 3 hours. Another 5 rats from the same group were given a series of subcutaneous injections of glucose during the 3-hr period, and their levels of blood glucose were measured at similar intervals. At the end of the 3 hours, liver glycogen was determined. Although the average blood glucose levels of the glucose-injected group were higher throughout the experiment than those of the cortisol-injected group, the cortisol-injected rats were found to have considerably more glycogen. The conclusion is drawn that the early changes in liver glycogen resulting from the injection of cortisol in fasted, adrenalectomized rats cannot be accounted for quantitatively by changes in blood glucose levels alone.

Adenosine diphosphate glucose and glucoside biosynthesis.

URIDINE diphosphate glucose (UDPG) has been found to act as glucose donor in a number of enzymatic reactions, such as glucoside formation in plants1 and in locust2, sucrose and starch synthesis in plants3,4 and glycogen formation in mammals5.

A HISTOCHEMICAL STUDY OF THE INCORPORATION OF GLUCOSE C14 INTO GLYCOGEN BY LIVER SLICES IN VITRO

The in vitro formation of glycogen from d-glucose-C14 has been studied by histochemical and autoradiographic techniques. The incorporation of the radioactive glucose into acid soluble glycogen lends support to the suggestion that this is the only glycogen fraction that is demonstrated histochemically. These experiments also confirm the validity of the histochemical tests for glycogen.

The distribution of glycogen in the human developing tooth

The distribution of glycogen in human developing teeth has been investigated. Undecalcified serial sections of tooth germs, fixed in chilled Bouin, chilled Rossman and 10% formol saline, were stained with the periodic acid-Schiff reaction, the lead tetra-acetate-Schiff reaction and by means of the Best's carmine method. Glycogen was found in the oral epithelium, dental lamina, external enamel epithelium, stellate reticulum, stratum intermedium, internal enamel epithelium, dental pulp and dental follicle. Glycogen disappeared from the internal enamel epithelium and stratum intermedium at the onset of amelogenesis. The relationship between glycogen and hard-tissue formation is discussed and it is suggested that the role of glycogen in amelogenesis is as a source of hexosephosphate esters.

THE ROLE OF SEROTONIN IN CARBOHYDRATE METABOLISM. VI. SEROTONIN-STIMULATED GLYCOGEN FORMATION AND ITS RELATION TO INSULIN EFFECT IN ISOLATED RAT DIAPHRAGM

In vitro effect of serotonin on glycogen level of rat diaphragm was investigated. Serotonin stimulated glycogen formation in phosphate-buffered saline, but not in Krebs-Ringer bicarbonate medium.The effect of serotonin disappeared under glycogenolytic condition.Glucose uptake was never augmented by serotonin even in the tissue in which glycogenetic action of serotonin was exhibited.Suppressive action of serotonin on glucose uptake manifested itself in diabetic as well as in glucose-fed non-diabetic rat tissue.The negative interaction was noted between glycogenetic activity of insulin and serotonin.The mechanism involved in in vitro effect of serotonin with respect to stimulation of glycogenesis and inhibition of glucose utilization is discussed along with the comparison to insulin.

CORTISOL STIMULATION OF GLYCOGEN SYNTHESIS IN FASTED RATS1

The acute effects of cortisol that result in an increase in liver glycogen deposition were studied in fasted rats, using C14O2 and glucose-6-C14 as labeled substrates. The incorporation of labeled carbon into blood glucose, liver glycogen and liver dicarboxylic acids was determined. The results of these experiments indicate that cortisol increases the incorporation of label from radioactive bicarbonate into liver glycogen without any significant increase in the activity of either blood glucose or liver dicarboxylic acids. Studies with labeled glucose showed increased deposition of glycogen from this substrate. There was little recycling of C14 from glucose via the Cori cycle. Under these conditions cortisol did not appear to increase hepatic glucose production as measured by changes in specific activity of blood glucose. Evidence is presented that in the fasting adrenalectomized animal there is some specific impairment in glycogen formation apart from the ability of the liver to form glucose. It is sugges...

Electron-microscopic observations on developing chick embryo liver: The Golgi complex and its possible role in the formation of glycogen

Thin sections of livers of chick embryos incubated for 6–8 days have been studied in the electron microscope, and thick (½ to 1 μ ) sections stained according to the periodic acid Schiff method (PAS) have been examined under phase contrast. In livers of embryos about 6½ days old the Golgi complex starts to expand, and granular or homogeneous material forms inside the Golgi vacuoles. In the same livers small areas of cytoplasm appear to be composed of small vacuoles (resembling Golgi vacuoles) and dense small granules lying mostly between the vacuoles. It is believed that these areas correspond to small PAS-positive dots as seen in thick, stained sections, and that they contain glycogen. It appears probable that the Golgi complex is instrumental in the formation of these areas. Hence it seems that the Golgi complex might play a role in the formation of glycogen within these embryonic liver cells.

Electron-microscopic study of glycogen in chick embryo liver

A comparative study of thin and of contiguous thick sections of chick embryo liver was made. Small periodic acid—Schiff (PAS) positive areas as seen with the light microscope in thick sections probably contain glycogen, since previous digestion by means of salivary diastase renders these areas PAS negative. In the electron microscope these areas show a rather typical fine structure. They contain small membrane-bounded vesicles and located between them, small (20–33 m μ ) granules. Infrequently only the vesicular elements are seen, whereas a homogeneous material of low electron density appears in lieu of the granules. These granules and the homogeneous material are considered to represent glycogen. The reason for this variable appearance of the glycogen is not understood at present. The possibility that the Golgi complex plays a role in glycogen formation within these liver cells is discussed. Attempts were made to establish whether the Golgi region is PAS positive. The available evidence, although not conclusive, tends to show that it is not. This would seem to exclude the possibility that small granules seen within Golgi vacuoles are glycogen, but it does not rule out the possible role of the Golgi complex in glycogen formation. It is suggested that within the Golgi vacuoles an accumulation of glycogen precursors or of enzymes necessary for glycogen synthesis occurs and that such substances are subsequently discharged from the vacuoles into the surrounding cytoplasm.

Action of desoxycorticosterone acetate on glycogen. I. Relationship of liver glycogen formation to potassium metabolism.

Summary1. Daily administration of DOCA for short periods caused an increased glycogenic response in liver of rats following intraperitoneal injection of glucose. Daily administration of DOCA for longer periods resulted in decreased glycogenic response. 2. DOCA induced inhibition of glycogen formation was accompanied by decrease in potassium content of both liver and blood serum. 3. By forcing an increase in potassium intake, the potassium content of both liver and blood serum was maintained at essentially normal levels and liver glycogen production was not significantly inhibited in rats that received DOCA. 4. These data indicated that DOCA induced inhibition of glycogen formation was secondary to potassium depletion.

Insulin-stimulated glycogen formation in rat diaphragm. Levels of tissue intermediates in short-time experiments

Studies carried out with rat hemidiaphragms indicated that, under the experimental conditions outlined, over 90% of the increased uptake of glucose in the presence of insulin, on a balance basis, could be accounted for as tissue glycogen. Hexose 6-phosphate content was increased in diaphragms incubated in the presence of insulin, in agreement with an increased conversion of extracellular glucose to intracellular hexose 6-phosphate. Glucose 1-phosphate contents were unchanged, suggesting a rapid removal of glucose 1-phosphate. Glycogen formation in the presence of insulin took place at ratios of inorganic phosphate to glucose 1-phosphate of 305. ADP, ATP, inorganic phosphate, and creatine phosphate were not changed, a finding compatible with the association of the increased glycogen formation to phosphorylative reactions.

Studies on the Delayed Increase of Liver Glycogen by Glucagon

Glu agon is known to cause a transient hyperglycemia by glycogenolysis in the liver. Liver glycogen immediately decreases after glucagon administration. On the contrary, some investigators has recently reported that the liver glycogen increased after more than 24 hours following injection of over medium doses of glucagon. On the other hand, a few studies have been published indicating that a negative balance of nitrogen occured by the administration of a large dose of glucagon. That is, the metabolic action of glucagon is similar to that of glucocorticoid. Therefore, it is reasonable to assume that glucagon causes a certain effect on gluconeogenesis. From the above mentioned stand-point, the mechanism of the delayed liver glycogen increase by glucagon was studied as follows. 1. Liver glycogen production due to intraperitoneal injection of 2g/kg. of alanine to 24 hours fa sting rats definitely increased by the pre-treatment of 300γ/kg. of glucagon (intraperitoneal injection). This fact indicates that glucagon accelerates gluconeogenesis from alanine. 2. The general pattern of metabolism in the acceleating condition of gluconeogenesis was investigated. In this case alloxan diabetic and hydrocortisone given animals were adopted as favourable materials for investigating. At first, alanine (200μM) was added as a substrate to the liver slices of these treated rats. After 1 hour's incubation at 37°C in Warburg flask, the formation of glucose, pyruvate or glycogen from alanine in vitro was found to be increased in the liver slices of treated rats fasted for 24 hours. Secondly, the liver transaminase (glutamic pyruvic- and glutamic oxaloacetic transaminase) was confirmed to be increased 3 to 7 fold, especially a pronounced rise of activity was noted in glutamic-pyruvic transaminase. 3. The experiments were performed in the same may with glucagon and the same trend was confirmed. That is, the delayed increase of liver glycogen is concerned with the enhancement of gluconeogenesis, which is due to a rise of activity in liver transaminase. 4. In order to elucidate whether such an accelerating effect of gluconeogenesis by glucagon depends on the adrenal cortex, 20γ/kg. body weight of glucagon was intravenously administered to human adults, and the urinary excretion of 17-OHCS were measured. Of total 8 cases, increased excretion of 17-OHCS were recognized in 6 cases. On the other hand, in adrenalectomized rats, daily injection of glucagon for 3 days did not promote the liver transaminase activity. Accordingly, it is concluded that glucagon causes the delayed liver glycogen increase mainly by way of the adrenal cortex.

Biosynthesis of glycogen from uridine diphosphate glucose

An enzyme which leads to the formation of glycogen according to the equation: UDPG + primer → UDP + glucosyl α (1 → 4) primer has been studied. The optimal conditions for activity were determined with a partially purified preparation from rat muscle. The reaction requires the presence of a polysaccharide as primer and is strongly activated by hexose 6-phosphates. Using UDPG labeled in the glucose moiety, it was found that the radioactivity was transferred to the glycogen from which it could be removed as maltose with β-amylase or as G-1-P with phosphorylase. Thus it seems that the glucose residue becomes linked α (1 → 4) to the polysaccharide. Several inhibitors were tested as well as the occurrence of the enzyme in different organs.