Dietary whey protein increases liver and skeletal muscle glycogen levels in exercise-trained rats

We investigated the effect of different types of dietary protein on glycogen content in liver and skeletal muscle of exercise-trained rats. Twenty-four male Sprague-Dawley rats (approximately 100 g; n 6 per group) were divided into sedentary or exercise-trained groups with each group being fed either casein or whey protein as the source of dietary protein. Rats in the exercised groups were trained during 2 weeks using swimming exercise for 120 min/d, 6 d/week. Exercise training resulted in an increase in the skeletal muscle glycogen content. Furthermore, the whey protein group significantly increased the skeletal muscle glycogen content compared with the casein group. The increase in glycogen content in liver was significantly greater in rats fed the whey protein diet compared with those fed the casein diet. We also found that the whey protein diet increased the activity of liver glucokinase, whereas it decreased the activities of 6-phosphofructokinase and pyruvate kinase compared with the casein diet. However, hepatic total glycogen synthase activity and mRNA expression were similar with the two diets. In the skeletal muscle, whey protein decreased only 6-phosphofructokinase activity compared with casein. Total glycogen synthase activity in the skeletal muscle in the whey protein group was significantly higher than that in the casein group. The present study is the first to demonstrate that a diet based on whey protein may increase glycogen content in liver and skeletal muscle of exercise-trained rats. We also observed that whey protein regulated glycogen metabolism in these two tissues by different mechanisms.     

Suppression of glycogen consumption during acute exercise by dietary branched-chain amino acids in rats

The effects of a diet supplemented with branched-chain amino acids (BCAA; 4.8% or 6.2%) on BCAA catabolism and glycogen metabolism in rats were examined. Rats were fed a BCAA diet or control diet for 4 wk and part of the rats were subjected to exercise training during the experimental period. Feeding the BCAA diet increased serum BCAA concentrations and activity of the hepatic branched-chain alpha-keto acid dehydrogenase complex, the rate-limiting enzyme in the catabolism of BCAA, suggesting that dietary BCAA promotes BCAA catabolism. Although the serum glucose concentration and glycogen contents in the liver and gastrocnemius muscle of rested rats were not significantly affected by feeding of the BCAA diet, those in rats exhausted by acute exercise were 2-4-fold higher in rats fed the BCAA diet than in rats fed the control diet. The activity of pyruvate dehydrogenase complex in the liver and gastrocnemius muscle after acute exercise showed reverse trends; the complex activities (especially in liver) tended to be less in the BCAA diet group than in the control diet group. These results suggest that dietary BCAA spares glycogen stores in liver and skeletal muscle during exercise and that the decrease in pyruvate dehydrogenase complex activity in these tissues by dietary BCAA is involved in the mechanisms.     

Effect of vitamin B6 deficiency on glycogen metabolism in the skeletal muscle, heart, and liver of rats.

The effect of vitamin B6 deficiency was studied on glycogen metabolism in the gastrocnemius muscle, heart, and liver of rats. The glycogen phosphorylase activities in the gastrocnemius muscle and heart but not in the liver of vitamin B6-deficient rats were significantly decreased. The decrease in the enzyme activity in the gastrocnemius muscle was due to decrease in the amount of enzyme. The glycogen content of the muscle of vitamin B6-deficient rats was higher than that of the controls, but the glycogen content of the liver was similar in the two groups. These data suggest that glycogen degradation was impaired in the muscle but not the liver of vitamin B6-deficient rats.     

Schedule of protein ingestion and circadian variations of glycogen phosphorylase, glycogen synthetase and phosphoenolpyruvate carboxykinase in rat liver.

The circadian rhythms of liver glycogen and hepatic activity of glycogen synthetase (GS), glycogen phosphorylase (GP) and phosphoenolpyruvate carboxykinase (PEPCK) were studied in adult male rats. The rats either received a mixed diet ad libitum (10% protein) or a protein meal (1.85 g protein) given at 09:00 or 21:00 hours, with free access to a protein-free diet (separately-fed). When the protein meal was ingested at 09:00 hours it was followed by a drop in liver glycogen and a persistent daylight increase in GP and PEPCK activities, this phenomenon being attenuated when proteins were ingested during darkness (21:00 hours). Moreover in the latter case, the circadian rhythm of liver glycogen was modified (glycogen accumulation occurring later) and the protein meal ingestion was followed after a transient decrease by a high and sustained GS activity during a long period (12 hours). The drop in the hepatic glycogen level and the unusually long daylight period of sustained GP and PEPCK activities in separately-fed rats consuming the protein meal at 09:00 hours suggests that, in this case, part of the ingested nitrogen could have been catabolized and used for gluconeogenesis, thus explaining our previous observation of lower nitrogen retention observed in this group of rats.     

Dietary whey protein downregulates fatty acid synthesis in the liver, but upregulates it in skeletal muscle of exercise-trained rats

OBJECTIVE: This study compared the effects of casein and whey protein as the source of dietary protein on the activity of lipogenic enzymes and mRNA levels in the liver and skeletal muscle of exercise-trained rats. METHODS: Twenty-eight male Sprague-Dawley rats were randomly assigned to one of four groups (n = 7/group). Rats were assigned to sedentary or exercise-trained groups and were fed the casein or whey protein diet. Rats in the exercise groups were trained for 2 wk using a swimming exercise for 120 min/d and 6 d/wk. RESULTS: A significant decrease in the activity of the hepatic lipogenic enzymes, glucose-6-phosphate dehydrogenase, malic enzyme, adenosine triphosphate citrate lyase, acetyl-coenzyme A carboxylase, and fatty acid synthase (FASN) was observed in rats fed whey protein compared with animals fed casein. Compared with the casein diet, the whey protein diet also lowered mRNA expression of these enzymes, except for FASN. In contrast to the findings in liver, whey protein, as compared with casein, increased skeletal muscle FASN activity and mRNA. Further, exercise training resulted in increased skeletal muscle glucose-6-phosphate dehydrogenase and FASN activity and adenosine triphosphate citrate lyase, acetyl-coenzyme A carboxylase-1, and FASN mRNA expression. CONCLUSIONS: Exercise training or whey protein may play an important role in suppressing hepatic fatty acid synthesis, thereby decreasing accumulation of body fat and stimulating the skeletal muscle to increase energy substrate as fat during prolonged exercise.     

Effect of exercise on riboflavin status of rats

The effect of exercise on the riboflavin status of male rats was studied after 6 or 8 wk of treadmill running. Sedentary and exercised rats were pair fed diets marginal in riboflavin (2.0 or 2.5 mg/kg), and their tissue riboflavin concentrations and erythrocyte glutathione reductase activity coefficients (EGRAC) were compared. The rats exercised for 8 wk had similar body weights but significantly greater weights for heart, gastrocnemius and soleus muscles, less epididymal fat and more total muscle nitrogen and riboflavin than their sedentary controls. Similar changes were evident after 6 wk of exercise, but some were not statistically significant. The EGRAC values of both exercised and sedentary rats responded to changes in dietary riboflavin but were not different from each other. The specific activity of mitochondrial acyl-CoA dehydrogenase (per milligram protein) of the soleus muscle was unaffected by exercise; however, when expressed per gram of tissue or per muscle, the activities in exercised rats were 25% (P less than 0.05) and 60% (P less than 0.01) higher, respectively, than in sedentary rats. On the basis of the riboflavin-dependent parameters measured in this study, exercise did not increase the dietary riboflavin requirement of growing rats but did increase total riboflavin retention in gastrocnemius and soleus muscles.     

Influence of exercise training on tissue chromium concentrations in the rat

This study reports on the effects of exercise training on the chromium concentrations in the heart, liver, kidney, and gastrocnemius muscle of normal Sprague-Dawley rats. A pair-fed (to the trained rats' intake) and a preexperimental group were also studied in order to control food intake and to ascertain any age-related influence on tissue chromium levels, respectively. Four groups of animals were examined: exercise-trained, pair-fed, preexperimental, and sedentary control. Chromium determination was performed by flameless atomic absorption spectrophotometry. The results from this study show that exercise training increases while pair-feeding and normal aging both decrease chromium levels in tissues. It is suggested that the male Sprague-Dawley rat adapts to exercise training by enhancing tissue levels of chromium or by simply maintaining the high levels of the element found at a younger age.     

Dietary whey hydrolysate with exercise alters the plasma protein profile: a comprehensive protein analysis

Objective

It has been shown that dietary whey protein accelerates glucose uptake by altering glycoregulatory enzyme activity in skeletal muscle. In the present study, we investigated the effect of dietary whey protein on endurance and glycogen resynthesis and attempted to identify plasma proteins that reflected the physical condition by a comprehensive proteomics approach.

Methods

Male c57BL/6 mice were divided into four groups: sedentary, sedentary with whey protein hydrolysate, exercise, and exercise with whey protein hydrolysate. The mice in the exercise groups performed treadmill running exercise five times per week for 4 wk. Protein profiling of plasma sample obtained from individuals was performed, as were measurements of endurance performance and the glycogen content of gastrocnemius muscle.

Results

After the training period, the endurance of mice fed the whey diet was improved compared with that of mice fed the control diet. Muscle glycogen content was significantly increased after 4 wk of exercise, and intake of whey protein led to a further increase in glycogen. Apolipoproteins A-II and C-I and β₂-glycoprotein-1 were found to be altered by training combined with the intake of whey protein, without significant changes induced by exercise or whey protein alone.

Conclusion

Results of the present study suggest that these three proteins may be potential biomarkers of improved endurance and glycogen resynthesis and part of the mechanism that mediates the benefits of whey protein.     

Effects of high doses of leucine and ketoleucine on glycogen and protein metabolism in acute uremia

Binephrectomized rats treated with high doses of ketoleucine (0.5 g/rat per 20 hr) expired after about 45 hr. In contrast, survival time was 100% 60 hr after ureteral ligation. In comparison to animals receiving low-protein diets, addition of leucine to the diet almost doubled muscle and liver protein content whereas ketoleucine increased liver protein during the first 40 hr after operation about 1.5-fold. Skeletal muscle protein content was enhanced in the ureter-ligated rats with administration of ketoleucine. There was also about a 10-fold elevation in liver glycogen and total carbohydrate content between the 20th and 60th hr in binephrectomized rats fed leucine at 5-hr intervals. In skeletal muscle glycogen, there were no significant differences among the acutely uremic rats fed at 10-hr intervals low-protein diets alone or supplemented with leucine or ketoleucine. Leucine inhibits glycogenolysis by lowering phosphorylase alpha activity in muscle and liver, whereas ketoleucine enhances glycogenolysis in acute uremia. In rats supplemented with letoleucine, there is a progressive inactivation of glycogen synthetase I which occurs in parallel with increasing phosphorylase alpha activity. In binephrectomized rats receiving leucine supplements at 5-hr feeding intervals, the activity of liver glycogen synthetase I increases up to a maximum of 90% of total enzyme activity.     

Effect of diet supplementation with glutamine, dihydroxyacetone, and leucine on food intake, weight gain, and postprandial glycogen metabolism of rats

OBJECTIVE: We tested the hypothesis that increasing the rate of postprandial hepatic glycogen synthesis would decrease food intake and growth rate in normal rats. METHODS: Diets supplemented with glutamine, glutamine plus dihydroxyacetone, and glutamine plus dihydroxyacetone plus leucine were administered to male Sprague-Dawley rats for 1 wk. These are combinations that have been shown to stimulate hepatic glycogen synthesis in vitro. Food intake and body weight were monitored throughout the experiment. At the end of the feeding period, rats were fed a test meal and injected with 3H2O to measure in vivo rates of glycogen and lipid synthesis. Positional analysis of the 3H incorporated into glycogen was used to determine the proportion of glycogen synthesized via pyruvate. Final levels of plasma glucose and triacylglycerol and hepatic glycogen were also measured. RESULTS: Dietary glutamine increased hepatic glycogen synthesis. Addition of dihydroxyacetone, with or without additional leucine, caused an additional increase in hepatic glycogen synthesis and increased the proportion of glycogen synthesized via pyruvate. Lipogenesis was not altered in the liver or adipose tissue. None of the dietary treatments had any effect on food intake, but the diets that contained dihydroxyacetone decreased the rate of weight gain. CONCLUSIONS: Increasing glycogen synthesis had no effect on food intake. Increasing the proportion of glycogen synthesized by the indirect pathway through pyruvate was associated with a decrease in weight gain.     

Long-term Leucine Supplementation Improves Metabolic But Not Molecular Responses in the Skeletal Muscle of Trained Rats Submitted to Exhaustive Exercise

Aim: Although there is some evidence of an ergogenic effect of leucine supplementation on acute response to exercise, there is a paucity of information on whether long-term leucine supplementation influences the adaptive response to chronic endurance training and performance. The main aim of our study was to assess the role of long-term leucine supplementation on molecular and metabolic response in skeletal muscle of trained rats after an exhaustion test.

Methods: Twenty-four male Wistar rats were randomly allocated into 4 groups. Two of them (control and trained groups) received a balanced control diet (18% protein) and the other 2 (control leucine and trained leucine groups) received a leucine-rich diet (15% protein with 3% leucine) for 6 weeks. The trained groups were submitted to 1 hour of swimming exercise, 5 d/wk for 6 weeks. Three days after the exercise training period, trained groups were submitted to swimming exercise until exhaustion and muscle metabolic and molecular parameters were assessed.

Results: Endurance training increased citrate synthase activity significantly, whereas exercise until exhaustion increased cytokine levels and led to a lack of activation of phosphorylation of the signaling intermediates assessed. Long-term leucine supplementation enhanced muscle glycogen level in trained rats and citrate synthase activity in sedentary ones. However, it failed to enhance endurance performance of trained rats submitted to an exhaustion test and did not prevent exercise-induced reduction in Akt and mTOR activation.

Conclusion: Long-term leucine supplementation can enhance citrate synthase activity by itself in sedentary individuals and glycogen content when combined with exercise; however, it does not improve endurance performance or prevent Akt and mTOR exercise-induced inhibition.     

Contributions of dietary carbohydrate and ethanol to alterations in liver glycogen levels and glycolytic activity.

Hepatic glycogen levels are decreased in rats as a consequence of chronic ethanol consumption. In earlier studies ethanol (36% of total calories consumed) replaced carbohydrate in the ethanol-containing diet, thus leading to the possibility that the decreases in liver glycogen were a result of limited dietary carbohydrate. In the present study, rats were administered ethanol in low-carbohydrate (LC) or high-carbohydrate (HC) diets to determine if lowered dietary carbohydrate contributes to the decrease in glycogen levels associated with ethanol consumption. The glycogen content of isolated hepatocytes was not different between rats fed LC or HC in control or ethanol-containing diets. Lactate and pyruvate were measured to determine the effects of dietary carbohydrate and ethanol on glycolytic activity, and were not significantly altered by changes in the levels of dietary carbohydrate. However, ethanol-containing diets resulted in decreased concentrations of hepatic glycogen, lactate, and pyruvate as compared with controls in both LC and HC diets. These observations demonstrate that decreases in glycogen content and lactate + pyruvate concentrations are due to chronic ethanol consumption rather than a carbohydrate deficiency, when carbohydrate is maintained above 10% of total calories.     

Restoration of the glycogen-forming function of hepatocytes in rats with liver cirrhosis is facilitated by a high-carbohydrate diet

Using cytofluorimetric and biochemical methods, the content of glycogen and its labile and stable fractions, as well as activities of glucose-6-phosphatase (EC 3.1.3.9), glycogen phosphorylase (EC 2.4.1.1) and glycogen synthase (EC 2.4.1.11) were determined in the rat liver for 6 months after chronic poisoning of the animals with CCl4 and then at 1, 3, and 6 months after the end of the poisoning. One group of rats was given a standard diet, the other, a high-carbohydrate diet. The 6-month long chronic intoxication with CCl4 was shown to produce development of typical liver cirrhosis characterized by a 2.8-fold increase in the total glycogen content in hepatocytes as compared with normal cells, by a fall in the glycogen labile fraction (from 85 to 53% of the total glycogen) as well as by decreases in the activities of glycogen phosphorylase and glucose-6-phosphatase by 25 and 82% respectively. The structural rehabilitation occurred faster and more completely at the cellular level than at the tissue level. Functional variables of the cirrhotic liver tissue also recovered, after cessation of poisoning, faster and more completely than the liver structure at the tissue level: glycogen levels in hepatocytes fell dramatically, the labile: stable glycogen fraction ratio recovered completely, and the activity of glycogen phosphorylase rose to the level characteristic of the normal liver. Use of the high-carbohydrate diet promoted a somewhat faster and more complete recovery of hepatic structure and function.     

Effect of insulin administration on cardiac glycogen synthase and synthase phosphatase activity in rats fed diets high in protein, fat or carbohydrate

Rats were fed a 70% carbohydrate, 70% protein, 70% fat, or a standard purified diet for 7 d to determine the effect of the diet on heart glycogen synthase response to an acute insulin challenge. Rats fed the high protein or the high fat diets, i.e., the carbohydrate-free diets, exhibited insulin resistance as evidenced by higher plasma glucose levels following insulin administration when compared to rats fed high carbohydrate or standard diet. The diets had no effect on the initial proportion of synthase in the active or I form. Insulin injection resulted in an increase in the proportion of synthase in the active form in rats fed the standard, high carbohydrate or high protein diets, but not in rats fed the high fat diet. Synthase phosphatase activity was similar in rats fed one of the four diets compared to rats fed a nonpurified diet. Thus the lack of synthase response to insulin in fat-fed rats was not due to diminished synthase phosphatase activity. Neither the diets nor insulin administration had any effect on the proportion of phosphorylase in the active or a form. Cardiac glycogen was significantly lower in rats fed the high fat diet than in those fed the standard diet. The latter was a surprising observation since the high fat diet was used to simulate a starved state and cardiac glycogen concentrations increase with starvation.     

The paradoxical response of cardiac glycogen to oral casein hydrolysate in rats

In fasted rats, casein hydrolysate administration resulted in a marked increase in glycogen synthase I activity, no change in phosphorylase a and a marked decrease in glycogen concentration. This occurred with doses as small as 0.5 g/kg body weight. The major reason for an increase in synthase I appeared to be the reduced glycogen concentration, although insulin may play a role early in the time course. The decrease in glycogen in the absence of a change in phosphorylase a most likely is due to a decrease in an allosteric inhibitor. The nature of this inhibitor is unknown.     

Toxicity of the pyrethroid insecticide fenvalerate to a fresh water fish, Tilapia mossambica (Peters): changes in glycogen metabolism of muscle

Toxic effects of a pyrethroid insecticide, fenvalerate, on fish muscle glycogen metabolism were investigated. Estimations were made after 10 and 20 days of exposure, and altered muscle glycogen metabolism was observed. The changes included a significant (P less than 0.001) decrease in the levels of glycogen, pyruvate, maleate dehydrogenase (MDH), succinate dehydrogenase (SDH), and phosphorylase a, b, and ab activities, while elevated levels of lactic acid, aldolase, and lactate dehydrogenase (LDH) activity were observed under fenvalerate intoxication. There was a decrease in opercular movement and oxygen consumption with an increase in concentration of fenvalerate.     

Effect of the combination of voluntary exercise and dietary protein levels on the deposition of glycogen, liver and serum lipids in mice.

The effects of voluntary exercise on the growth, glycogen of muscle and lipid contents of the liver and serum of mice fed different levels of dietary protein were investigated. In both the exercise and non-exercise groups, body weight gains were significantly greater in the 20% and 30% protein diet groups than in the 6% and 4% protein diet groups. After 6 weeks of age, it was shown that the amount of voluntary exercise by the 6% and 4% protein diet groups was greater than that by the 20% and 30% protein diet groups. As for hematological status, the raising of hemoglobin levels due to increasing dietary protein levels was further exaggerated by voluntary exercise. Hematocrit values rose with the increase in dietary protein levels. However the effect of exercise on hematocrit values was not clear. Liver glycogen levels, which were elevated with the increase in dietary protein levels, rose further due to exercise, though no changes were observed in muscle glycogen due to dietary protein levels and exercise. The lipid contents of the liver in all groups tended to be lower in exercise groups compared with non-exercise groups and it was observed that the high levels of dietary protein depressed the increase in liver lipids. Liver triglyceride levels of all groups fed the dietary protein levels except for the 20% casein diet group decreased due to voluntary exercise, and liver triglyceride levels were also lowered as dietary protein levels increased. The levels of serum triglyceride of all groups decreased due to voluntary exercise. This phenomenon was most remarkable in rats fed a 6% casein diet. The tendency for serum cholesterol levels to decrease due to exercise. However it was not further influenced by voluntary exercise in the 4% casein diet group.     

Muscle lipid metabolism and insulin secretion are altered in insulin-resistant rats fed a high sucrose diet

Feeding rats a sucrose rich diet (SRD) induces hypertriglyceridemia and insulin resistance. The purposes of this study were to determine the time course of changes in lipid and glucose metabolism in the gastrocnemius muscle, both in the basal state and after the euglycemic hyperinsulinemic clamp, in rats fed a SRD for 3, 15 or 30 wk, and to analyze the changes in glucose-stimulated insulin secretion from perifused isolated islets from SRD-fed rats and their relationships to peripheral insulin insensitivity. A control group of rats was fed a control diet (CD) for the same period of time. After 3 wk of consuming the SRD, long-chain acyl CoA (LCACoA) levels in muscle were greater than in rats fed the CD, an early indication of the disturbance of lipid metabolism. Neither glycogen storage nor glucose oxidation were impaired at this time. Moreover, the biphasic patterns of glucose-stimulated insulin secretion showed a marked increase in the first peak, which helped maintain normoglycemia in SRD-fed rats. After 15 or 30 wk of consuming the SRD, triglyceride and LCACoA levels in muscles were greater than in rats fed the CD. Glucose oxidation as well as insulin-stimulated glycogen synthase activity and glycogen storage were lower than in rats fed the CD. Moreover, the altered pattern of insulin secretion further deteriorated. This was accompanied by peripheral insulin resistance and moderate hyperglycemia. Our results indicate that the dyslipemia present in rats chronically fed a SRD may play an important role in the progressive deterioration of insulin secretion and sensitivity in this animal model.     

The effects of exercise on milk yield, milk composition, and offspring growth in rats

This study examined effects of exercise training throughout pregnancy and lactation upon selected indicators of lactational performance in Wistar rats. During the 7 wk prior to mating, experimental female rats were gradually trained to swim for 2 h/day, 5 days/wk with a 3% tail weight; they continued swimming until the 19th day of pregnancy. Control animals remained sedentary. Swimming resumed during days 2-14 of lactation. Food intake was greater in exercised rats during the lactation period. Body weights of the two groups were comparable. Mild yield (day 10), energy content (day 15), and protein and fat concentrations did not differ, but milk of exercised rats had a lower lactose concentration. The exercise regimen had no statistically significant effect on litter size or on offspring weight to day 15. This study indicates that moderate-intensity, aerobic exercise does not markedly affect the lactational performance of ad libitum-fed rats.     

Oxidative stress and antioxidant status in rat blood, liver and muscle: effect of dietary lipid, carnitine and exercise

The purpose of this study was to determine the effect of dietary fat, carnitine supplementation, and exercise on oxidative damage and antioxidant status. Male Wistar rats (60 days old) were fed diets containing either hydrogenated fat (HF) or peanut oil (PO) with or without 0.5 mg % (of dry diet) carnitine. The rats were given exercise, i.e. swimming for 60 minutes, for 6 days/week for 6 months under each dietary condition. The blood malondialdehyde (MDA) level was higher in PO-fed rats, more so in exercising ones, while the same was not altered in carnitine-supplemented rats irrespective of the dietary fat or physical activity. The MDA level was significantly decreased in muscle, while increased in liver, of carnitine-fed rats. The blood glutathione (GSH) level also significantly increased in exercising rats as compared to sedentary ones, while carnitine supplementation elevated it in all the groups. Exercise and carnitine supplementation significantly lowered GSH levels in liver while increasing it in muscle. The glutathione peroxidase (GPX) activity was significantly increased in blood and muscle from PO-fed exercising rats as compared to sedentary ones, while carnitine supplementation elevated GPX activity in all the groups. The liver and muscle catalase (CAT) activities were significantly increased in PO-fed exercising rats, while carnitine did not have any effect. The pro-oxidative effect of the monounsaturated fatty acid (MUFA)-rich PO diet and prolonged regular exercise was less pronounced due to augmented antioxidant enzymes, GPX and CAT, induced by training to protect against the oxidative stress, while carnitine supplementation could help to counter lipid peroxidation due to exercise through redistribution of GSH from liver to blood and muscle.