Muscle glycogen repletion and pre-exercise glycogen content: effect of carbohydrate loading in rats previously fed a high fat diet

We have recently reported that rates of muscle glycogen repletion during the early period of recovery were increased by carbohydrate (CHO) loading in rats previously fed a high fat diet. However, the reason for this remained unanswered. The purpose of this study was to examine whether an increase of glycogen utilization due to an elevated pre-exercise glycogen store would enhance rates of glycogen repletion in muscle. Despite an equal degree of glycogen depletion, the rates of glycogen repletion of soleus, red and white gastrocnemius muscles by postexercise administration of glucose (3.0 g · kg^–1 body mass) and citrate (0.5 g · kg^–1 body mass) were faster in the CHO loaded (3 days) rats than in the nonloaded rats, as a result of elevated pre-exercise glycogen content and consequently the greater glycogen utilization. The higher rate of muscle glycogen repletion may in part be explained by increased postexercise glycogen synthase activity.     

Effect of different types of high carbohydrate diets on glycogen metabolism in liver and skeletal muscle of endurance-trained rats

Male Wistar rats were fed ad libitum four different diets containing fructose, sucrose, maltodextrins or starch as the source of carbohydrate (CH). One group was subjected to moderate physical training on a motor-driven treadmill for 10 weeks (trained rats). A second group received no training and acted as a control (sedentary rats). Glycogen metabolism was studied in the liver and skeletal muscle of these animals. In the sedentary rats, liver glycogen concentrations increased by 60%–90% with the administration of simple CH diets compared with complex CH diets, whereas skeletal muscle glycogen stores were not significantly affected by the diet. Physical training induced a marked decrease in the glycogen content in liver (20%–30% of the sedentary rats) and skeletal muscle (50%–80% of the sedentary rats) in animals fed simple (but not complex) CH diets. In liver this was accompanied by a two-fold increase of triacylglycerol concentrations. Compared with simple CH diets, complex CH feeding increased by 50%–150% glycogen synthase (GS) activity in liver, whereas only a slight increase in GS activity was observed in skeletal muscle. In all the animal groups, a direct relationship existed between tissue glucose 6-phosphate concentration and glycogen content (r = 0.9911 in liver, r = 0.7177 in skeletal muscle). In contrast, no relationship was evident between glycogen concentrations and either glycogen phosphorylase activity or adenosine 5-monophosphate tissue concentration. The results from this study thus suggest that for trained rats diets containing complex CH (compared with diets containing simple CH) improve the glycogenic capacity of liver and skeletal muscle, thus enabling the adequate regeneration of glycogen stores in these two tissues.     

Effects of high fat,protein supplemented diets on maternal behavior in rats

Female albino rats were maintained on either chow, a 25% fat, protein supplemented diet or a 45% fat, protein supplemented diet during breeding, gestation and lactation. Materanal behavior was assessed using observational techniques. Maternal bodyweight of the females on the high fat diets was not different from females on chow. Reproductive success, as indicated by pregnancy and pup survival, was reduced in the females on the 45% fat diet. However, unlike offspring of obese dams, pup growth was enhanced in most of the offspring of the dams on the high fat, protein supplemented diets. The dams on these diets showed more postural nursing, less non-postural nursing, more pup grooming and were observed more frequently with a majority of their pups. These dietary differences in maternal behavior did not appear to be necessarily due to differences in the body weight of the pups.     

Effects of dietary fat feedback on behavioral and psychological variables

This paper reports on the immediate and delayed reactions to dietary fat consumption feedback. Subjects in our study received (1) personalized dietary fat feedback and (2) information about how to alter their fat consumption. Fat consumption was measured using a brief fat assessment instrument. Subjects were categorized into three risk groups: at or below, above, and significantly above the recommended level. Emotional, cognitive, and behavioral reactions were measured immediately after receiving feedback and at 1 month postfeedback. Subjects who received high fat feedback showed greater negative emotional distress in response to the feedback and stated that they knew less about high-fat foods than subjects receiving lower feedback. By the 1-month follow-up, subjects in the highest feedback condition were least likely to report intentions to lower their dietary fat. Interventions designed to alter dietary fat consumption should take into account the emotional and cognitive consequences of risk factor feedback.     

Effect of exercise on glycogen metabolism in muscles of triiodothyronine-treated rats

The aim of the present study was to examine the rate of glycogen mobilization during exercise and the rate of the postexercise glycogen replenishment in different muscle types [white (WG), and red (RG) gastrocnemius, soleus (S) and diaphragm (D)] in rats treated with triiodothyronine (T₃, group T). Rats of the control group (C) were treated with saline. The animals were made to run on a treadmill set at 0° gradient and at a speed of 1200 m·h^–1. The time taken to reach exhaustion in group C was 188 (SD 23) min, whereas in group T, it was only 63 (SD 12) min. The content of glycogen in all muscles of the rats from group T at rest and during exercise was significantly lower than in group C at each corresponding time. At exhaustion, the glycogen content was in WG(C) 34.79 (SD 4.65), (T) 20.10 (SD 4.10); in RG(C) 22.82 (SD 4.66), (T) 16.50 (SD 2.00); in S(C) 14.85 (SD 2.48), (T) 11.90 (SD 2.93); in D(C) 18.18 (SD 3.49), (T) 7.54 (SD 3.36) (mol of glucosyl units·g^–1). The amount of glycogen mobilized during exhausting exercise in RG, S and D was similar in both groups whereas in WG it was much higher in rats of group T than in group C. The concentration of glycogen returned to pre-exercise values in each muscle 3 h after exercise. The net amount of glycogen resynthetized during 3 h of recovery depended on the muscle type. It was in WG(C) 3.30, (T) 18.03; in RG(C) 21.34, (T) 25.88, in S(C) 34.00, (T) 17.68, and in D(C) 17.25, (T) 12.22 mol of glucosyl units·g^–1 (each number represents the difference between the means). It concluded that treatment with T₃ markedly affects this exercise-induced metabolism of glycogen in each muscle type.From our study it is suggested that low muscle glycogen content may contribute to a reduction in exercise performance in hyperthyroidism.     

Effects of pre-exercise carbohydrate feedings on muscle glycogen use during exercise in well-trained runners

Summary The purpose of this study was to examine the effects of pre-exercise glucose and fructose feedings on muscle glycogen utilization during exercise in six well-trained runners ( =68.2±3.4 ml·kg^–1·min^–1). On three separate occasions, the runners performed a 30 min treadmill run at 70% . Thirty minutes prior to exercise each runner ingested 75 g of glucose (trial G), 75 g of fructose (trial F) or 150 ml of a sweetened placebo (trial C). During exercise, no differences were observed between any of the trials for oxygen uptake, heart rate or perceived exertion. Serum glucose levels were elevated as a result of the glucose feeding (P<0.05) reaching peak levels at 30 min post-feeding (7.90±0.24 mmol·l^–1). With the onset of exercise, glucose levels dropped to a low of 5.89±0.85 mmol·l^–1 at 15 min of exercise in trial G. Serum glucose levels in trials F and C averaged 6.21±0.31 mmol·l^–1 and 5.95±0.23 mmol·l^–1 respectively, and were not significantly different (P<0.05). There were also no differences in serum glucose levels between any of the trials at 15 and 30 min of exercise. Muscle glycogen utilization in the first 15 min of exercise was similar in trial C (18.8±8.3 mmol·kg^–1), trial F (16.3±3.8 mmol·kg^–1) and trial G (17.0±1.8 mmol·kg^–1), and total glycogen use was also similar in trial C (25.6±7.9 mmol·kg^–1), trial F (35.4±5.7 mmol·kg^–1) and trial G (24.6±3.2 mmol·kg^–1). In contrast to previous research, these results suggest that pre-exercise feedings of fructose or glucose do not affect the rate of muscle glycogen utilization during 30 min of treadmill running in trained runners.     

The effects of a high carbohydrate diet on postprandial energy expenditure during exercise in rats

Summary Whether or not a high intake of carbohydrate increases postprandial energy expenditure during exercise was studied in rats. The rats were meal-fed regularly twice a day (0800–0900 hours and 1800–1900 hours) on either a high carbohydrate (CHO) (carbohydrate/fat/protein = 70/5/25, % of energy) or high fat (FAT) (35/40/25) diet for 12 days. On the final day of the experiment, all of the rats in each dietary group were fed an evening meal containing equal amounts of energy (420 kJ · kg^–1 body mass). After the meal, they were divided into three subgroups: pre-exercise control (PC), exercise (EX), and resting control (RC). The PC-CHO and PC-FAT groups were sacrificed at 2030 hours. The EX-CHO and EX-FAT groups were given a period of 3-h swimming, and then sacrificed at 2330 hours. The RC-CHO and RC-FAT groups rested after the meal and were sacrificed at 2330 hours. Total energy expenditure during the period 1.5 h from the commencement of exercise was higher in EX-CHO than in EX-FAT. The respiratory exchange ratio was also higher in EX-CHO than in EX-FAT, suggesting enhanced carbohydrate oxidation in the former. Compared with both PC-FAT and RC-FAT, the liver glycogen content of EX-FAT rats was significantly decreased by exercise. On the other hand, the liver glycogen content of both EX-CHO and RC-CHO was higher than that of PC-CHO rats. The glycogen content of soleus muscle of EX-FAT was slightly decreased during exercise, however, that of EX-CHO increased significantly. Thus postprandial energy expenditure during exercise was higher in the rats fed the CHO diet than in those fed the FAT diet, which could have been related to the increase of both liver and muscle glycogen storage during exercise in the former.     

Effects of chronic high fat diets on renal function and cortical structure in rats

Four groups (n = 5) of male Wistar rats were fed with different high-fat diets from 21 days to 18-mo-old: soybean oil (SO), canola oil (CA), lard and egg yolk (LE) or CA+LE. Blood lipids, serum creatinine and proteinuria as well as the cortical stereology were analyzed. The cholesterol, HDL-C and triglycerides were highest in CA group. No significant differences were found among the groups to serum creatinine and proteinuria. The BP was highest in LE group and intermediate in CA+LE group. SO and CA groups showed glomeruli most preserved in number and size. Absolute volume of tubuli was greatest in LE group. Renal cortical interstitium was greatest in SO group and smallest in CA group. Cortical vessels showed smallest indices in LE group and greatest ones in CA group; SO and CA+LE groups were intermediate. Chronic administration of different types of dietetic lipid can significantly alter blood biochemistry, BP and renal cortical structure in rats. Considering these features, canola oil was the more beneficial lipid, while lard and egg yolk mixture was the worst lipid. The addition of canola oil in the LE mixture normally was not efficient to alter the renal damage except in the cortical vessels.     

Effect of short-term exercise training on muscle glycogen in resting conditions in rats fed a high fat diet

Summary It has been reported that exercise training increases muscle glycogen storage in rats fed a high carbohydrate (CHO) diet in resting conditions. The purpose of this study was to examine whether a 3-week swimming training programme would increase muscle glycogen stores in rats fed a high-fat (FAT) diet in resting conditions. Rats were fed either the FAT or CHO diet for 7 days ad libitum, and then were fed regularly twice a day (between 0800 and 0830 hours and 1800 and 1830 hours) for 32 days. During this period of regular feeding, half of the rats in both dietary groups had swimming training for 3 weeks and the other half were sedentary. The rats were not exercised for 48 h before sacrifice. All rats were killed 2 h after their final meal (2030 hours). The glycogen contents in red gastrocnemius muscle, heart and liver were significantly higher in sedentary rats fed the CHO diet than in those fed the FAT diet. Exercise training clearly increased glycogen content in soleus, red gastrocnemius and heart muscle in rats fed the CHO diet. In rats fed the FAT diet, however, training did not increase glycogen content in these muscles or the heart. Exercise training resulted in an 87% increase of total glycogen synthase activity in the gastrocnemius muscle of rats fed the CHO diet. However, this was not observed in rats fed the FAT diet. The total glycogen phosphorylase activity in the gastrocnemius muscle of the rats of both dietary groups was increased approximately twofold by training. These results suggested that muscle glycogen was enhanced in rats fed the CHO diet and that the glycogen content of the muscle of rats fed the FAT diet was not increased by exercise training.     

Effects of age on glycogen synthase and phosphorylase activities in rat liver

Six exopeptidases present in human diploid fibroblasts were identified by separation on polyacrylamide gel electrophoresis and their activity profiles against 17 dipeptides, two tripeptides and L-leucine-p-nitroanilide determined. No differences in relative activity or in the electrophoretic patterns of any of the six exopeptidases were detected with ageing. Aminoacylarylamidase activity assayed spectrophotometrically showed significantly increased activity in the middle age-group cells as opposed to the enzyme isolated from young and old cells. Heat-inactivation studies using the same substrate suggested the possibility of an increased proportion of heat-labile enzyme in the old cells but interpretation of the data was difficult because of the complex nature of the inactivation curves obtained. Overall, the results tended to refute the hypothesis that age-related changes in the free amino acid pool of human diploid fibroblasts were associated with significant alterations in the activities of cellular exopeptidases.     

Effects of dietary sugar and of dietary fat on food intake and body fat content in rats

The long term ingestion of a sugar-rich diet (low fat) caused severe obesity in adult rats. In a separate experiment, the habitual consumption of a fat-rich diet (40% kcal from fat) also caused severe obesity. Severe obesity developed in both groups of animals even though they did not overeat. Voluntary food intake for the sugar-fed rats averaged 28,314 +/- 756 calories/rat per 55 wks which was similar to the value of 28,884 +/- 953 calories/rat per 55 wks for the fat-fed rats. However, both values were lower than that of 32,869 +/- 588 for the control rats eating Purina chow. Despite a lower caloric intake, carcass fat averaged 45 +/- 1% for rats eating the sugar-rich diet and 46 +/- 2% for rats eating the fat-rich diet, but only 33 +/- 2% for rats eating a diet of Purina chow. These results provide evidence that severe obesity can develop in the absence of hyperphagia in animals eating a sugar-rich or fat-rich diet. Finally, a rat model for severe obesity is presented in which carcass fat ranged from 18% (lean) to 61% (severe obesity) using dietary intervention alone at critical stages of the animal's life.     

吡咯烷二硫代氨基甲酸酯对2型糖尿病大鼠肝糖原合成的影响

目的:探讨吡咯烷二硫代氨基甲酸酯(PDTC)对糖尿病大鼠肝糖原合成的影响及其机制。方法:雄性Wistar大鼠,随机分为2组:正常饮食组和高脂饮食组。喂养8周后,高脂饮食组大鼠腹腔注射单剂量链脲佐菌素(STZ)27 mg/kg复制2型糖尿病大鼠模型,2型糖尿病大鼠造模成功后随机分为3组:糖尿病模型组、PDTC治疗组和胰岛素治疗组。PDTC治疗组大鼠每天腹腔注射PDTC(50 mg/kg)1次;其它各组每天同一时间注射相同体积的生理盐水,胰岛素治疗组大鼠在处死前1 h腹腔注射胰岛素(1 U/kg)1次。治疗1周后尾静脉采血测定各组大鼠血糖水平,然后断头处死大鼠,测定肝组织中肝糖原的含量,采用Western blotting分析大鼠肝脏中蛋白激酶B(PKB/Akt)和糖原合成酶激酶-3β(GSK-3β)磷酸化水平的变化。结果:糖尿病模型组与正常饮食组大鼠相比血糖显著升高(P0.01);肝糖原含量明显减少(P0.01);肝脏中Akt及GSK-3β磷酸化水平明显降低(P0.01)。与糖尿病模型组大鼠相比,PDTC治疗组与胰岛素治疗组大鼠肝糖原合成均显著增加(P0.01);血糖均明显降低(P0.01);肝脏中Akt和GSK-3β磷酸化水平均明显增加(P0.01)。结论:PDTC可通过调控Akt/GSK-3β活性,增加肝糖原合成,降低血糖。     

Effects of the administration of angiotensin II on cardiac glycogen metabolism in the rat

Changes in glycogen metabolism after an intravenous injection of angiotensin II were investigated in the left and right ventricles of the rat heart, as a function of location within the ventricular wall. Hearts were cut into 100-m thin sections, all of which were analysed for glycogen content, glucose incorporation into glycogen and 2-deoxyglucose uptake and phosphorylation after the intravenous injection of ¹⁴C-labelled sugar. In control hearts, glycogen levels were uniform across the wall in both ventricles, while the rate of sugar uptake and phosphorylation, and that of glucose incorporation into glycogen, were significantly higher in the subendocardial myocardium of the left ventricular wall. After angiotensin II administration, heart glycogen levels decreased slightly in the left, but not in the right ventricle, while 2-deoxyglucose uptake and phosphorylation, and glucose incorporation into glycogen, increased 2,5- and 5-fold, respectively. With regard to the distribution across the wall of the left ventricle after angiotensin administration, glycogen levels and glucose incorporation into glycogen were uniformly distributed, whereas sugar phosphorylation was still higher in the subendocardium.     

Effect of substrate supply and beta-adrenergic blockade on heart glycogen and triglyceride utilization during exercise in the rat

Summary Exercise-induced heart glycogen and triglyceride mobilization was studied in control rats, in rats with reduced blood glucose supply (fasted rats), in rats with reduced plasma free fatty acids (FFA) supply (nicotinic acid-treated rats), and in rats with blockade of beta-adrenergic receptors (propranolol-treated rats). It was found in the fed control rats that both the heart glycogen and triglyceride levels were reduced at the beginning of the exercise and thereafter they returned to the control level despite the exercise being continued. The triglyceride level was reduced again during the exhaustive exercise. Reduced blood glucose supply increased the heart glycogen and triglyceride utilization during exercise. Partial prevention of the plasma FFA elevation during exercise increased the heart glycogen utilization and had no effect on utilization of the heart triglycerides. Blockade of the beta-adrenergic receptors fully prevented both the heart glycogen and triglyceride mobilization during exercise.This work was supported by the Polish Academy of Sciences, project No. 10.4.2.01.3.2.     

Effects of long-term feeding of high-protein or high-fat diets on the response to exercise in the rat

Summary The aim of this work was to find by which mechanisms an increased availability of plasma free fatty acids (FFA) reduced carbohydrate utilization during exercise. Rats were fed high-protein medium-chain triglycerides (MCT), high-protein long-chain triglycerides (LCT), carbohydrate (CHO) or high-protein low-fat (HP) diets for 5 weeks, and liver and muscle glycogen, gluconeogenesis and FFA oxidation were studied in rested and trained runner rats. In the rested state the hepatic glycogen store was decreased by fat and protein feeding, whereas soleus muscle glycogen concentration was only affected by high-protein diets. The percentage decrease in liver and muscle glycogen stores, after running, was similar in fat-fed, high-protein and CHO-fed rats. The fact that plasma glucose did not drastically change during exercise could be explained by a stimulation of hepatic gluconeogenesis: the activity of phosphoenolpyruvate carboxykinase (PEPCK) and liver phosphoenolpyruvate (PEP) concentration increased as well as cyclic adenosine monophosphate (AMPc) while liver fructose 2,6-bisphosphate decreased and plasma FFA rose. In contrast, the stimulation of gluconeogenesis in rested HP-, MCT- and LCT-fed rats appears to be independent of cyclic AMP.     

Post-exercise ketosis and the glycogen content of liver and muscle in rats on a high carbohydrate diet

Summary Post-exercise ketosis is known to be suppressed by physical training and by a high carbohydrate diet. As a result it has often been presumed, but not proven, that the development of post-exercise ketosis is closely related to the glycogen content of the liver. We therefore studied the effect of 1 h of treadmill running on the blood 3-hydroxybutyrate and liver and muscle glycogen concentrations of carbohydrate-loaded trained (n=72) and untrained rats (n=72). Resting liver and muscle glycogen levels were 25%–30% higher in the trained than in the untrained animals. The resting 3-hydroxybutyrate concentrations of both groups of rats were very low: <0.08 mmol·1⁻¹. Exercise did not significantly influence the blood 3-hydroxybutyrate concentrations of trained rats, but caused a marked post-exercise ketosis (1.40±0.40 mmol·1⁻¹ 1 h after exercise) in the untrained animals, the time-course of which was the approximate inverse of the changes in liver glycogen concentration. Interpreting the results in the light of similar data obtained after a normal and low carbohydrate diet it has been concluded that trained animals probably owe their relative resistance to post-exercise ketosis to their higher liver glycogen concentrations as well as to greater peripheral stores of mobilizable carbohydrate.     

Histocytochemical and immunohistochemical studies related to the role of glycogen in human developing digestive organs

To elucidate the role of glycogen in the epithelium of developing digestive organs, we investigated the appearance of glycogen and glycogen phosphorylase (GP) in these organs. We studied 64 externally normal human embryos at Carnegie stages 13–23 (5.1–28.0 mm in crown-ramp length, 4–8 weeks of gestation) by histocytochemical staining for glycogen and immunohistochemical staining with antibodies against two isoenzymes of GP: brain-type (BGP) and mucle-brain-type (MBGP) GP. At stage 13, glycogen appeared in the epithelium of the digestive tract and the parenchyma of the pancreas. As development advanced, glycogen granules increased in number and size in these tissues, and they became evenly distributed in the epithelium of the digestive tract as either single particles or aggregates, as deduced by electron microscopy at late embryonic stages. Immunoreactivity specific both for BGP and for MBGP was detected in the digestive tract and the pancreas from stage 13. As development advanced, both BGP- and MBGP-immunoreactive cells increased in number and in immunoreactivity, and the number of MBGP-immunoreactive cells became larger than that of BGP-immunoreactive cells. By contrast, in hepatic cells, which serve as a major storage site for glycogen in adults, glycogen was detected only from stage 20, in smaller amounts, without formation of aggregates, and no immunoreactivity specific for BGP or MBGP was apparent throughout the embryonic stages examined. Thus, in the epithelium of the digestive tract and the parenchyma of the pancreas, but not in hepatic cells, the appearance and localization of GP coincided almost exactly with that of glycogen. These observations suggest that glycogen in the epithelium of the digestive tract and the parenchyma of the pancreas has not only been synthesized but also degraded from an early embryonic period and may, thus, be related to active cellular metabolism that is specific for embryonic development, including proliferation of the epithelium and interactions between epithelium and mesenchyme.     

The effect of increased respiratory resistance on glycogen and triglyceride levels in the respiratory muscles of the rat

Summary The effect of increased respiratory resistance (stenosis of the trachea) on glycogen and triglyceride levels in the diaphragm (D) and intercostal (external-IE, internal-II) muscles was studied in the rat. Tracheal stenosis resulted in a reduction of glycogen level in the muscles. For the fed rats the reductions were: D-45 and 79%, IE-14 and 30%, II-14 and 35%, 0.5 and 3 h after stenosis, respectively. For rats fasted for 24 h the reductions were: D-64 and 86%, IE-33 and 71%, II-40 and 82%, after 0.5 and 3 h respectively. The level of triglycerides in the muscles was stable during stenosis in the fed group, whereas in the fasted group it were reduced in the diaphragm by 50% after 0.5 h, and by 52% after 3 h. It is concluded that both endogenous and blood-born energy fuels are utilized by the respiratory muscles during increased resistance breathing. The work was supported by Polish Academy of Sciences (10.4.)