Recent research suggests that amino acids, such as leucine and isoleucine, can improve glucose tolerance in vivo and in vitro animal models by accelerating glucose uptake in peripheral tissues and stimulate glycogen synthesis in vitro in the absence of insulin. Our laboratory recently found that gavaging normal Sprague-Dawley rats with an amino acid mixture, composed of isoleucine, leucine, cystine, methionine, and valine, improved blood glucose response during an oral glucose challenge without an increase in the plasma insulin response. The blood glucose-lowering effect of the amino acid mixture was due to an increase in skeletal muscle glucose uptake. These results suggest that this amino acid supplement acutely improves muscle insulin sensitivity and blood glucose homeostasis. However, the effect of this amino acid mixture on glucose tolerance and muscle glycogen synthesis in humans has not been investigated. Some studies have also shown that daily supplementation or acute ingestion of amino acids may prevent muscle damage that occurs as a result of a prolonged, intense endurance exercise or strength training and therefore improves force production and exercise performance. However, the effects of the addition of an amino acid mixture to carbohydrate supplement on muscle damage after a prolonged endurance exercise, as well as on the subsequent anaerobic exercise performance, have not been characterized. Therefore, in this series of two studies, the effects of an amino acid mixture, composed of isoleucine, leucine, cyctine, methionine, and valine, on glucose tolerance, muscle glycogen resynthesis, muscle damage, and anaerobic exercise performance were investigated. Study 1 demonstrated that our amino acid mixture lowered the glucose response to an OGTT in healthy overweight/obese subjects in an insulin-independent manner. Study 2 demonstrated that both high and low dosages of amino acid mixture were effective in lowering blood glucose response to a carbohydrate bolus in athletes postexercise. High dosage of amino acid mixture was more potent in glucose regulation by providing a higher insulin response and amino acid effect. However, our amino acid mixture had no effects on post exercise muscle glycogen synthesis, exercise-induced muscle damage or subsequent anaerobic performance. Taken together, the results of this research series suggest that an amino acid mixture, composed of isoleucine and 4 additional amino acids, attenuates the glucose response to a glucose bolus in an insulin-independent manner, but does not enhance muscle glycogen restoration following exercise or prevent exercise-induced muscle damage. / text

Spinal cord injury (SCI) results in extensive demyelination, leading to deleterious axon degeneration and inability of functional recovery. Remyelination has become a part of the fundamental strategy for SCI repair. Endogenous neural progenitor cells (NPCs) respond to SCI producing progenies and provide a possible source of regenerated oligodedrocytes for remyelination. During development of the central nervous system, glycogen synthase kinase-3 isoform beta (GSK-3β) is involved in multiple pathways that regulate oligodendrocyte differentiation and myelination, and thus may also play an important part in remyelination after SCI. This study aims to investigate (1) the role of GSK-3β in the differentiation of adult spinal cord derived-neural progenitor cells (ASC-NPCs); (2) whether AR-A014418 as a GSK-3β inhibitor, can promote oligodendroglial differentiation of ASC-NPCs; (3) the effect of LiCl, another GSK-3β inhibitor, on functional recovery after SCI; (4) the effects of LiCl on the myelin and axonal preservation after SCI. Neurosphere culture from adult mouse spinal cord was performed to test the effect of GSK-3β inhibitors, LiCl and AR-A014418, on differentiation of ASC-NPCs. Phenotyping of differentiated ASC-NPCs by immunocytochemistry (ICC) was performed to identify oligodendroglia progenitor cells (OPCs) at different stages. It was shown that LiCl (1 mM) and AR-A014418 (5 μM) promoted differentiation of OPCs as labeled by oligodendrocyte lineage-specific markers: PDGFR-α, NG2 and O4, while AR-A014418 was more potent in the OPC differentiation. Moreover, preliminary data from western blot confirmed that ARA014418 (5 μM) treatment increased the expression level of pGSK (inactive form of GSK-3) in differentiated ASC-NPCs. This suggests a possible strategy to modulate endogenous NPC response to SCI: to induce the preferential differentiation of NPCs into oligodendrocyte lineage by inhibiting GSK-3β activity and thus leading to enhanced remyelination by the differentiated oligodendrocytes. Basso Mouse Scale (BMS) open field test was used to evaluate the locomotive function of the spinal cord injured mice. The result showed that LiCl (4 mM, 200 μl) administration delivered locally at the lesion site by osmotic pump for 2 weeks improved functional recovery after SCI. Furthermore, immunohistochemistry (IHC) analyses revealed that LiCl treatment inhibited GSK-3β activity in the 〖Olig2〗^+ OPCs/oligodendrocytes, confirming LiCl as a GSK-3β inhibitor in vivo. Moreover, LiCl treatment better preserved myelin and axons detected by myelin basic protein (MBP) immunostaining and neurofilment-200 (NF-200) immunostaining respectively in the injured spinal cords. All together, the data from our in vitro and in vivo experiments suggested that LiCl treatment after spinal cord injury is beneficial for functional recovery by preventing the loss of myelin and axons after SCI and this effect is mediated via GSK-3β inhibition This study provided evidence for the involvement of GSK-3β in the regulation of OPC differentiation and the subsequent remyelination in the injured adult spinal cord. We propose GSK-3β as an important therapeutic target for SCI repair, LiCl as a potential candidate for SCI clinical treatment and the possibility to manipulate endogenous NPCs after SCI to enhance oligodendrocyte differentiation, remyelination, and ultimately better functional recovery.. / published_or_final_version / Anatomy / Master / Master of Philosophy

The purpose of this study was to examine if the addition of protein to a carbohydrate supplement (CHO+PRO), provided during a simulated soccer match, would reduce fatigue and muscle glycogen utilization in comparison to an isocaloric carbohydrate only supplement (CHO). Two female and eight male (n = 10) trained soccer players performed a modified version of the Loughborough Intermittent Shuttle Test (LIST) on two separate occasions, followed by a run to exhaustion (RTE). Supplements were provided 10 minutes before the simulated match and at the beginning of half-time, but not during exercise in order to create real-match conditions. Supplements were composed of 2.8% protein + 7% carbohydrate (CHO+PRO) or 9.8% carbohydrate (CHO). Muscle biopsies were performed before and at the end of the LIST, after which iv participants ran to exhaustion. No differences were found between treatments for RTE (489 ± 121 sec for CHO and 589 ± 186 sec for CHO+PRO) or glycogen utilization (37.9 ± 7.6 µmol•g wet wt-1 during the CHO and 29.1 ± 6.0 µmol•g wet wt-1 during the CHO+PRO). No differences were found for the other measurements such as sprint times, heart rate, RPE, blood glucose, lactate, and insulin. Blood Creatine kinase (CK), and overall muscle soreness were measured 24 hours after each trial in order to evaluate muscle damage but no differences between treatments were found. In accordance with these findings, the phosphorylation state of the protein FOXO3a was not altered differently by the treatments. These results suggest that the addition of protein to a traditional carbohydrate-only supplement provided immediately prior to and at the half of a simulated soccer match does not further improve the benefits of a CHO supplement. / text

We hypothesize that brain glycogen, a stored form of glucose, may provide fuel for the brain conferring both negative and positive effects throughout the brain. The over accumulation of brain glycogen, or supercompensation, is hypothesized to exacerbate hypoglycemia associated autonomic failure (HAAF), promote memory and learning, and reduce neuron cell death during severe episodes of hypoglycemia. It was determined that brain glycogen supercompensation does occur in the mouse 6 hours following single and recurrent hypoglycemic episodes, but it is not likely a significant mechanism behind HAAF due to the supercompensation subsiding at 27 hours following the hypoglycemic episodes. In regard to memory and learning, brain glycogen is not required for motor skill learning while euglycemic, however, it does enhance motor memory while hypoglycemic as determined using a rotarod treadmill in mouse. In regard to associative learning, brain glycogen is important for contextual, but not cued, memories while both euglycemic and hypoglycemic, as assessed by contextual and cued fear conditioning. Two different genetically engineered models of mice lacking brain glycogen yielded opposing results when assessing whether brain glycogen is neuroprotective during severe and prolonged hypoglycemia. In conclusion, brain glycogen does not appear to play a role in HAAF, is important for learning and memory, and its role in neuronal cell survival during hypoglycemia requires further study. / Department of Biology

This study was undertaken to examine the effects of ingestion of different concentrations of carbohydrate (CHO) (H20, 6, 12, and 18 g/100ml- WP, CHO-6, CH0-12, and CH0--18, respectively) on gastric emptying, muscle glycogen metabolism, and performance. Ten trained male cyclists performed four trials of 105 min of continuous cycling at 70% of VO2max. In a fifth trial the subjects completed seven 15-min rides at 70% of VO2max with three min rest between each ride. In all five trials the submaximal rides were followed by an all-out, self-paced 15-min "performance" ride on an isokinetic ergometer (Fitron) interfaced with a computer which calculated the total work output. Every 15 min the men consumed approximately 150 ml (8.5 ml/kg/hr) of one of the four test solutions (in the intermittent trial the men consumed the CHO-12 solution). Blood samples were taken every 15 min for glucose and insulin determination. Muscle biopsies were obtained from the vastus lateralis at 0 and 105 min in the WP, and the CHO-12 continuous and intermittent trials. Biopsy samples were assayed for glycogen, and sectioned and stained for myosin ATPase and glycogen to determine single fiber depletion patterns. Gastric residue was determined by intubation following the performance ride. The volume of drink emptied in the CHO-12 and CHO-18 trials was significantly less compared to both the WP and CHO-6 trials, and the volume emptied in the CHO-18 trial was less than in the CHO-12. There were no differences in glycogen use between the water and the two CHO-12 trials. Single fiber depletion patterns showed a trend toward a greater depletion of type I fibers but were not influenced by CHO ingestion. Blood glucose was significantly elevated at 105 min in both CHO-12 and the CHO-18 trials compared to the WP trial. CHO oxidation in both CHO-12 and the CHO-18 trials was significantly higher in the performance ride. Work output in both the CHO-12 trials was significantly elevated compared to the WP. These data demonstrate that 12 and 18% CHO solutions retarded gastric emptying, but that adequate CHO was delivered to enable enhanced performance in the CHO-12 trials. The fact that glycogen sparing was not observed suggests that the improved performance may have been due to the maintenance of blood glucose. Single fiber depletion patterns did not explain the performance benefits observed with CHO ingestion. / Human Performance Laboratory

There is no abstract available for this dissertation. / Human Performance Laboratory

To determine whether pre-exercise muscle glycogen levels influence the ergogenic benefits derived from carbohydrate (CHO) feedings during exercise, eight experienced cyclists completed four, 1680 kJ isokinetic cycling trials as quickly as possible. Trials were conducted under the following pre-exercise muscle glycogen (vastus lateralis) and feeding conditions: 1) high glycogen (180.2 ± 9.7 mmol•kg ww-1) with carbohydrate feedings during exercise (HGCHO trial), 2) high glycogen (170.2 ± 10.4 mmol•kg ww-1) with placebo feedings during exercise (HG-PLA trial), 3) low glycogen (99.8 ± 6.0 mmol•kg ww-1) with carbohydrate feedings during exercise (LG-CHO trial), and 4) low glycogen (109.7 ± 5.3 mmol-kg ww-1) with placebo feedings during exercise (LG-PLA trial). The placebo feedings contained no CHO. The CHO feedings provided 116 ± 6 g CHO•trial-1 and prevented the fall in serum glucose that occurred during both placebo trials. Performance times for the HG-CHO, HGPLA, LG-CHO, and LG-PLA trials averaged 117.18 ± 1.44, 118.67 ± 1.84, 121.18 ± 1.88 (P<0.05 vs. HG-CHO), and 122.91 ± 2.46 (P<0.05 vs. HG-CHO, HG-PLA) min, respectively. There were no between trial differences in relative V02 (75 ± 2 % of V02 max) or self-selected pace (8.42 ± 0.14 min-120 kJ-1) during the initial 1200 kJ of exercise. During the remaining 480 kJ, pace was similar under the HG-CHO, HG-PLA, and LG-CHO conditions (8.59 ± 0.14 min-1 20 kJ-1) but was significantly slower over the final 240 kJ of the LG-PLA trial (9.67 ± 0.43 min. 120 kJ-1). In conclusion, when pre-exercise muscle glycogen levels were low, CHO feedings enabled subjects to maintain their optimal pace throughout the exercise bout, but when pre-exercise glycogen levels were elevated, CHO feedings provided no ergogenic benefit. / Human Performance Laboratory

The purpose of this investigation was to determine the influence of post exercise carbohydrate (CHO) intake on the rate of muscle glycogen restorage after high intensity weight resistance exercise in untrained subjects. In a cross over design, eight male subjects performed sets (mean= 8.8) of 6 single leg knee extensions at 70% of one repletion max until 50% of full knee extension was no longer possible. Total force application was equated between trials using a strain gauge interfaced to a computer. Post exercise supplementation was administered at 0 and 1 hrs consisting of either a 23% CHO solution (1.5g•kg-1•hr-1) or an equal volume of water (H20). Total force production, pre-exercise muscle glycogen content, and degree of depletion (-40.6 and -44.3 mmol•kg-1) were not significantly different between H2O and CHO trials, respectively. During the initial 2 hrs recovery, the CHO trial had a significantly greater rate of muscle glycogen resynthesis as compared to the H2O trial. In the final 4 hrs of recovery no difference in repletion rates were observed. The glycogen content (mmol•kg-1 w.w.) and rates of restorage (mmol•kg-1 w.w.) during the recovery period were (mean + SE):TrialPost2 Hr6 HrRate (0-2 hrs)H2O101.3+ 13.1105.1+ 13.1105.5+ 13.01.3+ 2.2CHO91.7+ 11.8117.6+ 16.5123.4+ 15.1 *12.9+ 4.0*significance between trials, p <0.01Only the CHO supplementation trial restored pre-exercise muscle glycogen content after 6 hrs. The spectrophotometric analysis of glycogen stained muscle sections (PAS) indicated no difference between trials in the pre and post glycogen content for Type I and II fibers. The change in absorbance, when these samples were combined demonstrate greater glycogenolysis in the Type II (0.284 + 0.58) as compared to Type I (0.014 ± 0.076). During the recovery period, the change in absorbance supports greater glycogenesis in the Type II ( 0.096 + 0.060) when compared to no observed change in absorbance in the Type I fibers.Supported by a grant from Ross Laboratories. / Human Performance Laboratory

Skeletal muscle glycogenolysis was investigated in eight subjects during both high (HI) (70% 1 RM) and low (LO) intensity (35% 1 RM) leg extension weight-resistance exercise. Total force application to the machine lever arm was determined and equated between trials via a strain gauge and computer interfaced system. After the sixth set, muscle glycogen degradation was similar in the HI and LO trials (46.9 ± 6.6 and 46.6 ± 6.0 mmol•kg-1 wet wt, respectively), with the LO trial characterized by almost double the repetitions (6.0 and 12.7 ± 1.1) and half the peak concentric torque per repetition (24.2 ± 1.0 and 12.4 ± 0.5). After the sixth set, muscle lactate accumulation was also similar (13.8 ± 0.7 and 16.7 ± 4.2 mmol•kg-1 wet wt for HI and LO trials, respectively). After two hours of passive recovery with no feedings, muscle glycogen storage during the HI and LO trials was 22.2 (±6.8) and 14.2 (±2.5) mmol•kg-1 wet wt, respectively These values represented glycogen synthesis rates of 11.1 (±3.4) and 7.1 (±1.3) mmol•kg-1 •hr-1 , and occurred without significant increases in blood glucose relative to resting concentrations. Optical absorbance measurement of PAS stained muscle sections revealed no differences in the glycogen content of fast (FT) and slow twitch (ST) fibers between trials. When data from each trial were combined, declines in absorbance were larger in FT than ST fibers after the sixth set (0.356 ± 0.048) than in slow twitch fibers (0.222 ± 0.039, p < 0.05). The increase in absorbanceduring the two hour recovery was also larger in FT than ST fibers (0.119 ± 0.024 and 0.055 ± 0.024, p < 0.05). When total force application was constant, muscle glycogenolysis was the same regardless of the intensity of resistance exercise. Glycogenolysis was greater in fast twitch fibers, as was glycogen storage during the immediate post-exercise recovery. The relatively high rate of glycogen synthesis after exercise may be evidence of glycogenesis from intramuscular metabolites. / Human Performance Laboratory

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 106-114). Also available via the Internet.