Mobilization Of Liver Glycogen Research Articles

Defective liver glycogen autophagy related to hyperinsulinemia in intrauterine growth-restricted newborn wistar rats

Maternal malnutrition plays a critical role in the developmental programming of later metabolic diseases susceptibility in the offspring, such as obesity and type 2 diabetes. Because the liver is the major organ that produces and supplies blood glucose, we aimed at defining the potential role of liver glycogen autophagy in the programming of glucose metabolism disturbances. To this end, newborns were obtained from pregnant Wistar rats fed ad libitum with a standard diet or 65% food-restricted during the last week of gestation. We found that newborns from undernourished mothers showed markedly high basal insulin levels whereas those of glucagon were decreased. This unbalance led to activation of the mTORC1 pathway and inhibition of hepatic autophagy compromising the adequate handling of glycogen in the very early hours of extrauterine life. Restoration of autophagy with rapamycin but not with glucagon, indicated no defect in autophagy machinery per se, but in signals triggered by glucagon. Taken together, these results support the notion that hyperinsulinemia is an important mechanism by which mobilization of liver glycogen by autophagy is defective in food-restricted animals. This early alteration in the hormonal control of liver glycogen autophagy may influence the risk of developing metabolic diseases later in life.

Catecholamine stimulation of hepatic glycogenolysis during anoxia in the turtle Chrysemys picta.

The remarkable tolerance of some species of turtles to anoxia is well documented. The role that hormones play in this anoxia tolerance, however, is poorly understood. This study examined the role of catecholamines in the mobilization of liver glycogen during anoxic submergence in painted turtles (Chrysemys picta). Turtles were subjected to 4 h of submergence anoxia or air (normoxic controls) and received injections of propranolol, a beta-adrenergic receptor antagonist, or saline. The results indicated that the catecholamines function during anoxia to increase blood glucose levels by stimulating hepatic glycogenolysis through an increase in both the total activity of glycogen phosphorylase and the percent a form. Anoxic turtles given propranolol showed a decrease in the percent a form of glycogen phosphorylase compared with control turtles given propranolol, indicating that anoxia per se or a correlate of anoxia may depress hepatic glycogenolysis. Catecholamines may counteract this depressant effect. Hepatic glycogen mobilization during anoxia appeared to be stimulated via beta-adrenergic receptors, as propranolol was effective in blocking the stimulation, whereas phentolamine, an alpha-receptor antagonist, was not.

Alterations of Energy Metabolism Induced by Hexadecane in Mice

Two groups of young male OF-1 mice were fed for 60 days with cafeteria or, as controls, with standard pellet diet respectively. At that time, both groups were daily treated with hexadecane (HDK) on the skin. HDK induced a drastic body weight loss much higher in cafeteria than control mice. White adipose tissue were exhausted after 4 days of treatment in controls but not after 10 days in cafeteria ones. HDK resulted in mobilization of liver glycogen in both groups while muscle glycogen decreased slightly in the end. Hexadecane treatment did not result in massively enhanced nitrogen metabolism, as the actual oxidation of amino acids decreased considerably as indicated by the low levels of plasma urea. The results could be explained by powerful and lasting effects of hexadecane on thermogenesis and metabolic reserve balance. The use of this material for pharmacological manipulation of body weight appeared difficult.

The effect of bovine insulin on [ 14C]glucose and [ 3H]leucine incorporation in fed and fasted rainbow trout ( Salmo gairdneri)

The effect of bovine insulin on tissue incorporation of [ 14C]glucose and [ 3H]leucine was investigated in fed and fasted rainbow trout reared on a control and high-protein diet. Insulin produced marked hypoglycemia and mobilization of liver glycogen in all treatments. Although insulin gave no evidence of glycogenic stimulation it did appear to promote oxidative clearance of [ 14C]glucose. Compared to [ 14C]glucose much greater tissue incorporation of [ 3H]leucine was observed in fasted fish; insulin stimulated the incorporation of [ 3H]leucine into skeletal muscle protein. In plasma, liver, and skeletal muscle of all treatments, the summed specific activities of [ 3H]leucine was considerably greater than that of the summed values of [ 14C]glucose following insulin administration. Four weeks of fasting apparently lowered basal metabolism but no changes were observed in plasma glucose and glycogen stores. There was some evidence of gluconeogenic activity in the high protein-fasted fish and the data indicated in all fasted treatments a stimulation of [ 14C]glucose and [ 3H]leucine metabolism following insulin administration.

Glucose Homeostasis in the Developing Rat

The newborn rat was investigated for the presence of hypoglycaemia during the first hours after birth. Animals were born naturally and were left with the mother until sampled. There was no evidence of hypoglycaemia at birth or over the next 6 h. There was a rise in the blood glucose in the first hour after birth and this was associated with the period of most rapid mobilization of liver glycogen. Plasma immunoreactive insulin (IRI) fell rapidly after birth to values seen in fed adult rats. In contrast to the results obtained from rats born prematurely by Caesarian section, the normal process of birth followed by a normal environment with the mother, allows the newborn rat to maintain its glucose homeostasis.

Endrin Toxicosis in Rainbow Trout (Salmo gairdneri)

In mature rainbow trout (Salmo gairdneri) receiving sublethal doses of endrin (4.3–145 × μg/kg body wt/day in 0.215–7.25 mg/kg of food) for 163 days and then forced to swim for 1 hr, the insecticide affected serum electrolytes, osmolality, total protein, cholesterol, cortisol, lactate, glucose, liver glycogen, and growth. Forced swimming alone altered 9 of 16 serum parameters examined. Apparent increases in serum Na and Cl and significant increases in osmolality and liver glycogen were directly related to dosage. A biphasic distribution of phosphate, total protein, and cholesterol with dosage was apparent. Glucose was increased about 50% by 145 μg/kg but was unaffected by lower doses. Variance analysis of zone electrophoretic patterns disclosed an in teraction between serum protein distribution and dose. Mobilization of liver glycogen was apparently inhibited by low doses and almost totally blocked by high doses. Correspondingly, trout given 14.5 μg/kg or more had lowered serum cortisol levels whereas the lowest dose elevated cortisol. Growth was inhibited appreciably by 145 μg/kg but not by lower doses. Visceral fat accumulated 4.8–8.7 μg endrin/g tissue in the 43 and 145 μg/kg exposures. We conclude that endrin caused dysfunction of physiologic processes critical to survival.

Comparison of the hyperglycaemic and glycogenolytic responses to catecholamines with those to stimulation of the hepatic sympathetic innervation in the dog.

1. The effects of stimulation of the splanchnic innervation to the adrenal medullae, in dogs with cut hepatic nerves, were compared with those obtained previously in response to splanchnic and hepatic nerve stimulation in adrenalectomized dogs.2. Maximal stimulation of both adrenal medullae via the splanchnic innervation (20 c/s for 9 min), in dogs with cut hepatic nerves, produced closely similar hyperglycaemic and glycogenolytic responses to those obtained previously in adrenalectomized dogs with intact hepatic nerves.3. The rise in plasma glucose concentration in response to maximal stimulation of the adrenal medullae in dogs with intact hepatic nerves was found to be comparable to that which occurs in response to maximal stimulation of the hepatic sympathetic innervation alone. In contrast, the rise in haematocrit during maximal stimulation of the entire splanchnic innervation was substantially greater than that observed after removal of both adrenal glands.4. The output of adrenaline and noradrenaline from the left adrenal gland was determined during maximal stimulation of the left splanchnic nerve (20 c/s for 9 min). These results were then used to compute doses of the two amines which would reproduce the output of catecholamines from both glands under such conditions. The extent of the rise in mean plasma glucose concentration in response to these infusions was similar to that produced by maximal stimulation of both adrenal glands, but the duration of hyperglycaemia and depletion of liver glycogen were significantly less.5. Stimulation of the splanchnic innervation was found to produce an initial ;surge' in the release of catecholamines from the adrenal medullae, followed by a rapid decline in output when stimulation was continued for longer than 30 sec. Evidence was obtained which showed that this pattern of release is well suited to produce rapid mobilization of liver glycogen.6. Comparable changes in plasma glucose concentration occurred in response to stimulation of either the adrenal medullae or the sympathetic innervation to the liver at low frequency (2.0 c/s for 5 min). Stimulation of both pathways simultaneously, at the same frequency, produced smaller responses.7. Intramesenteric infusions of noradrenaline at 1.0 mug.kg(-1) min(-1) for 5 min produced comparable changes in plasma glucose concentration to those observed during stimulation of either pathway alone at low frequency. The mean plasma noradrenaline concentration of portal blood was raised by between 92 and 105 ng/ml. during these infusions.8. It is concluded that stimulation of either the splanchnic innervation to the liver, or of both adrenal medullae, at high frequency (20 c/s for 9 min) represents a supramaximal stimulus for hepatic glycogenolysis. Comparison of the responses to stimulation at low frequency (2.0 c/s for 5 min) suggests that the hepatic glycogenolytic mechanism is equally sensitive to stimulation via either route in this species.

Rapid activation and inactivation of fatty acid synthesis from glucose in vivo

The flux of glucose carbon to total body fatty acids was measured in unanesthetized mice either after fasting or 50-80 min after they nibbled a small test meal containing 120 mg of glucose (fasted-refed). Flux was calculated from plasma [(14)C]glucose specific activity curves and from total body (14)C-labeled fatty acid 30 min after intravenous injection of tracer [(14)C]glucose. Mobilization of liver glycogen, changes in the body glucose pool size, and total flux of carbon through the glucose pool during periods of fasting and refeeding were defined. Liver glycogen was almost completely depleted 8 hr after food removal. Body glucose pool size fell during fasting and increased after refeeding the test meal. Irreversible disposal rate of glucose C varied directly with body glucose pool size; but flux of glucose C into fatty acids increased exponentially as body glucose concentration increased. Within an hour after nibbling a small test meal, the flux of glucose C into total body fatty acids increased 700% in mice previously starved for 24 hr. However, flux of glucose C into fatty acids in postabsorptive mice (food removed for 2 hr; livers rich in glycogen) was only about 2% of the value calculated from published studies in which the incorporation of an intubated [(14)C]glucose load into total body fatty acid was measured in mice. A possible explanation for this phenomenon is presented.

The rate of gluconeogenesis from various precursors in the perfused rat liver

1. The rates of gluconeogenesis from many precursors have been measured in the perfused rat liver and, for comparison, in rat liver slices. All livers were from rats starved for 48hr. Under optimum conditions the rates in perfused liver were three to five times those found under optimum conditions in slices. 2. Rapid gluconeogenesis (rates of above 0.5mumole/g./min.) were found with lactate, pyruvate, alanine, serine, proline, fructose, dihydroxyacetone, sorbitol, xylitol. Unexpectedly other amino acids, notably glutamate and aspartate, and the intermediates of the tricarboxylic acid cycle (with the exception of oxaloacetate), reacted very slowly and were not readily removed from the perfusion medium, presumably because of permeability barriers which prevent the passage of highly charged negative ions. Glutamine and asparagine formed glucose more readily than the corresponding amino acids. 3. Glucagon increased the rate of gluconeogenesis from lactate and pyruvate but not from any other precursor tested. This occurred when the liver was virtually completely depleted of glycogen. Two sites of action of glucagon must therefore be postulated: one concerned with mobilization of liver glycogen, the other with the promotion of gluconeogenesis. Sliced liver did not respond to glucagon. 4. Pyruvate and oxaloacetate formed substantial quantities of lactate on perfusion, which indicates that the reducing power provided in the cytoplasm was in excess of the needs of gluconeogenesis. 5. Values for the content of intermediary metabolites of gluconeogenesis in the perfused liver are reported. The values for most intermediates rose on addition of lactate. 6. The rates of gluconeogenesis from lactate and pyruvate were not affected by wide variations of the lactate/pyruvate ratio in the perfusion medium.

Studies on the mechanism of alloxan initial hyperglycemia. I. A role of pituitary and adrenal gland in connection with the effect of alloxan on the blood sugar.

1. The significant reduction of the concentration of ascorbic acid in adrenals in normal rats 2 hours after the exposure to cold stress (O°C, 30 minutes) was observed. Normal rats showed the slight hyperglycemia just after the exposure, but the blood sugar returned soon to initial level and held the normal level during 10 hours. In adrenalectomized rats, the blood sugar fell just after the exposure, then turned to upward during 2 hours but did not return to the initial level even after 10 hours. 2. Although the ascorbic acid concentration in adrenals in rats showed a significant reduction when 1 or 2 mg. of ACTH was given, the fasting blood sugar did not show any changes. So the hyperactivity of pituitary adrenocortical system which is. produced by the alloxan can not be the single cause of the initial hyperglycemia. 3. The diabetogenic action of alloxan disappears within 5 minutes after the time of injection, without any possible involvement of the liver. 4. In normal rabbits which were injected alloxan in dose of, 100mg. per kg. of body weight, the response is the typical triphasic reaction of the blood sugar followed by permanent diabetes. However, when. the liver is stunted from the blood stream for 5 minutes after the injection of alloxan by temporary ligation of hepatic artery and portal vein, the alloxan initial hyperglycemia is completely gone or at least markedly repressed. As the influence of operative procedure can entirely be excluded, it is suggested that alloxan has an action to the liver and produces the mobilization of liver glycogen. 5. These observations and discussions in all lead to a conclusion that the alloxan initial hyperglycemia is probably produced by the hyperactivity of pituitary adrenocortical system on one hand, and by the mobilization of liver glycogen by the effect of alloxan on the liver on the other hand. The author acknowledges with deep appreciation the kind advices and helps given to him by Prof. Shigeo Okinaka and Instructor Nobusada Kuzuya.

Adrenaline and muscular exercise

The mobilization of liver glycogen under the influence of adrenaline has generally been regarded as a factor which may be of importance during muscular exercise, since it may facilitate the transference of glucose to the active muscles. It is, however, by no means clear whether or not this will result in an enhanced use of carbohydrate as a source of energy in the muscles. Dill, Edwards and de Meio (1935) found that a subcutaneous injection of 0·5-1·0 mg. adrenaline during muscular work increases the respiratory quotient and the concentration of glucose and lactic acid in the blood, and concluded that the rise of quotient is mainly due to an increase in the proportion of carbohydrate oxidized. We ourselves (Courtice, Douglas and Priestley 1939), after following in detail the behaviour of the respiratory quotient after the administration of adrenaline and insulin to the resting subject, felt doubtful whether this conclusion was justified, and we have now made a further series of observations on the influence of the subcutaneous injection of adrenaline during muscular exercise. We have followed the same general procedure as in our previous experi­ments, using the same methods for the determination of the respiratory exchange, the concentration of glucose and lactic acid in the blood, and the CO 2 combining power of the blood. The subject was always in the post-absorptive state. After making preliminary determinations of the respiratory exchange and taking blood samples whilst at complete rest reclining in a deck chair, continuous work was done at a steady rate on a Krogh electric brake bicycle ergometer for a period of 2½-3 hr., conditions being kept comfortable by the draught from an electric fan. We restricted our observations to either light or moderate work so that there should be no risk of the added complication of the accumulation of a material excess of lactic acid in the blood as a result of the mere muscular activity, as well as to avoid fatigue since neither of the two subjects, Courtice and Douglas, were in athletic training. We felt, too, that any change in the respiratory quotient caused by adrenaline might become relatively insignificant, and therefore more difficult to interpret, if the total respiratory exchange were greatly exaggerated. Light work was equivalent to 210 kg. m./min., involving an oxygen consumption during the first half hour of about 680 c. c./min. in Courtice and 750 c. c. in Douglas, or rather more than thrice the resting metabolism, and moderate work was equivalent to 700 kg. m./min., involving an oxygen consumption during the first half hour of about 1540 c. c./min. in Courtice, or seven times the resting metabolism. Adrenaline chloride (Parke, Davis and Co., 1 : 1000 solution) was injected subcutaneously into the upper arm after the work had been in progress for half an hour.

Influence of Epinephrine on Blood Sugar Utilization of Functionally Hepatectomized Rats.

Previous experiments1 have led to the conclusion that one of the principal causes for the epinephrine hyperglycemia consists in a decreased utilization of blood sugar in the tissues. It was pointed out that mobilization of liver glycogen alone is an inadequate explanation for the hyperglycemia, because there is not enough liver glycogen present to provide the tissues for hours with sugar at a rate which is greater than their normal ability to utilize sugar. Mobilization of liver glycogen can only lead to a protracted hyperglycemia of the type observed after epinephrine injections, (1) if a new formation of liver glycogen occurs which keeps pace with the conversion of liver glycogen into blood sugar and (2) if utilization of blood sugar itself is diminished. A new formation of liver glycogen exceeding its mobilization was demonstrated during epinephrine action and the source for the newly formed liver glycogen was found to be lactic acid derived from muscle glycogen.1 That blood sugar utilization is low du...