Effect of glycerol-induced hyperhydration on thermoregulation and metabolism during exercise in the heat

This study examined the effect of glycerol ingestion on fluid homeostasis, thermoregulation, and metabolism during rest and exercise. Six endurance-trained men ingested either 1 g glycerol in 20 ml H₂O.kg^-1 body weight (bw) (GLY) or 20 ml H₂O.kg^-1bw (CON) in a randomized double-blind fashion, 120 min prior to undertaking 90 min of steady state cycle exercise (SS) at 98 % of lactate threshold in dry heat (35 degrees C, 30 % RH), with ingestion of CHO-electrolyte beverage (6 % CHO) at 15-min intervals. A 15-min cycle, where performance was quantified in kJ, followed (PC). Pre-exercise urine volume was lower in GLY than CON (1119 ± 97 vs. 1503 ± 146 ml· 120 min^-1; p < .05). Heart rate was lower (p < .05) throughout SS in GLY, while forearm blood flow was higher (17.1 ± 1.5 vs. 13.7 ± 3.0 ml.100 g tissue·min^-1; p < .05) and rectal  temperature lower (38.7 ± 0.1 vs. 39.1 ± 0.1 ° C; p < .05) in GLY late in SS. Despite these changes, skin and muscle temperatures and circulating catecholamines were not different between trials. Accordingly, no differences were observed in muscle glycogenolysis, lactate accumulation, adenine nucleotide, and phosphocreatine degradation or inosine 5'-monophosphate accumulation when comparing GLY with CON. Of note, the work performed during PC was 5 % greater in GLY (252 ± 10 vs. 240 ± 9 kJ; p < .05). These results demonstrate that glycerol, when ingested with a bolus of water 2 hours prior to exercise, results in fluid retention, which is capable of reducing cardiovascular strain and enhancing thermoregulation. Furthermore, this practice increases exercise performance in the heat by mechanisms other than alterations in muscle metabolism.

Combination of calcium and magnesium ions prevents substrate inhibition and promotes biomass and lipid production in thraustochytrids under higher glycerol concentration

Effect of calcium and magnesium ions was studied in detail in batch mode in shake flask cultures of two fast growing strains of thraustochytrids (Aurantiochytrium sp. DBTIOC-18 and Schizochytrium sp. DBTIOC-1) for biomass and lipid production. These strains were previously isolated from Indian marine biodiversity. Screening of these two strains on different carbon and nitrogen sources revealed the suitability of glycerol over glucose and sodium nitrate over yeast extract for the cultivation of these strains. The presence of higher concentration of glycerol in the medium inhibited the glycerol utilization by the cell thus resulting in lower biomass and lipid production in both the strains. Supplementing media with calcium and magnesium ions promoted glycerol utilization thus resulted in a substantial rise in volumetric production of biomass (55.12 g L-1, 48.12 g L-1), fatty acid for biodiesel (27.14 g L-1, 22.15 g L-1) and docosahexaenoic acid (14.57 g L-1, 10.12 g L-1) with both strains Aurantiochytrium sp. DBTIOC-18 and Schizochytrium sp. DBTIOC-1, respectively. Growth profile study of these two strains showed further improvement in production of biomass, fatty acid for biodiesel and docosahexaenoic acid when cultures were extended up to 7 days. Finding of this work underlines the importance of calcium and magnesium salts in designing new fermentation strategies to prevent substrate inhibition and achieve high cell density culture under high nutrient concentration especially carbon sources.

Apicoplast-localized lysophosphatidic acid precursor assembly is required for bulk phospholipid synthesis in toxoplasma gondii and relies on an algal/plant-like glycerol 3-phosphate acyltransferase

Most apicomplexan parasites possess a non-photosynthetic plastid (the apicoplast), which harbors enzymes for a number of metabolic pathways, including a prokaryotic type II fatty acid synthesis (FASII) pathway. In Toxoplasma gondii, the causative agent of toxoplasmosis, the FASII pathway is essential for parasite growth and infectivity. However, little is known about the fate of fatty acids synthesized by FASII. In this study, we have investigated the function of a plant-like glycerol 3-phosphate acyltransferase (TgATS1) that localizes to the T. gondii apicoplast. Knock-down of TgATS1 resulted in significantly reduced incorporation of FASII-synthesized fatty acids into phosphatidic acid and downstream phospholipids and a severe defect in intracellular parasite replication and survival. Lipidomic analysis demonstrated that lipid precursors are made in, and exported from, the apicoplast for de novo biosynthesis of bulk phospholipids. This study reveals that the apicoplast-located FASII and ATS1, which are primarily used to generate plastid galactolipids in plants and algae, instead generate bulk phospholipids for membrane biogenesis in T. gondii.

Pre-exercise nutritional strategies: effects on metabolism and performance

The goals of pre-exercise nutritional strategies are to optimise the availability of carbohydrate (CHO) and fluid. Ingestion of CHO 3-4 hr prior to exercise can increase liver and muscle glycogen stores and has been associated with enhanced endurance exercise performance. The metabolic effects of CHO ingestion persist for at least 6 hr. Although an increase in plasma insulin following CHO ingestion in the hour prior to exercise inhibits lipolysis and liver glucose output, and can lead to transient hypoglycemia during subsequent exercise, there is no convincing evidence that this is always associated with impaired exercise performance. Having said that, individual experience should inform individual practice. Interventions to increase plasma FFA availability prior to exercise have been shown to reduce CHO utilisation during exercise, but do not appear to have major ergogenic benefits. It is more difficult to hyperhydrate prior to exercise and although there has been interest in glycerol ingestion, to date research results have been equivocal. At the very least, athletes should ensure euhydration prior to exercise.

Carbohydrate metabolism during exercise in females : effect of reduced fat availability

This study examined the effect of reduced plasma free fatty acid (FFA) availability on carbohydrate metabolism during exercise. Six untrained women cycled for 60 minutes at approximately 58% of maximum oxygen uptake after ingestion of a placebo (CON) or nicotinic acid (NA), 30 minutes before exercise (7.4 ± 0.5 mg·kg⁻¹ body weight), and at 0 minutes (3.7 ± 0.3 mg·kg⁻¹) and 30 minutes (3.7 ± 0.3 mg·kg⁻¹) of exercise. Glucose kinetics were measured using a primed, continuous infusion of [6,6-²H] glucose. Plasma FFA (CON, 0.86 ± 0.12; NA, 0.21 ± 0.11 mmol·L⁻¹ at 60 minutes, P < .05) and glycerol (CON, 0.34 ± 0.05; NA, 0.10 ± 0.04 mmol·L⁻¹ at 60 minutes, P < .05) were suppressed throughout exercise. Mean respiratory exchange ratio (RER) during exercise was higher (P < .05) in NA (0.89 ± 0.02) than CON (0.83 ± 0.02). Plasma glucose and glucose production were similar between trials. Total glucose uptake during exercise was greater (P < .05) in NA (1,876 ± 161 μmol·kg⁻¹) than in CON (1,525 ± 107 μmol·kg⁻¹). Total fat oxidation was reduced (P < .05) by approximately 32% during exercise in NA. Total carbohydrate oxidized was approximately 42% greater (P < .05) in NA (412 ± 40 mmol) than CON (290 ± 37 mmol), of which, approximately 16% (20 ± 10 mmol) could be attributed to glucose. Plasma insulin and glucagon were similar between trials. Catecholamines were higher (P < .05) during exercise in NA. In summary, during prolonged moderate exercise in untrained women, reduced FFA availability results in a compensatory increase in carbohydrate oxidation, which appears to be due predominantly to an increase in glycogen utilization, although there was a small, but significant, increase in whole body glucose uptake.

Regulation of glucose kinetics during intense exercise in humans: effects of α- and β-adrenergic blockade

This study examined the effect of combined α- and β-adrenergic blockade on glucose kinetics during intense exercise. Six endurance-trained men exercised for 20 minutes at approximately 78% of their peak oxygen consumption (V_O 2) following ingestion of a placebo (CON) or combined α- (prazosin hydrochloride) and β- (timolol maleate) adrenoceptor antagonists (BLK). Plasma glucose increased during exercise in CON (0 minutes: 5.5 ± 0.1; 20 minutes: 6.5 ± 0.3 mmol · L⁻¹, P < .05). In BLK, the exercise-induced increase in plasma glucose was abolished (0 minutes: 5.7 ± 0.3; 20 minutes: 5.7 ± 0.1 mmol · L⁻¹). Glucose kinetics were measured using a primed, continuous infusion of [6,6-²H] glucose. Glucose production was not different between trials; on average these values were 25.3 ± 3.9 and 30.9 ± 4.4 μmol · kg⁻¹ · min⁻¹ in CON and BLK, respectively. Glucose uptake during exercise was greater (P < .05) in BLK (30.6 ± 4.6 μmol · kg⁻¹ · min⁻¹) compared with CON (18.4 ± 2.5 μmol · kg⁻¹ · min⁻¹). In BLK, plasma insulin and catecholamines were higher (P < .05), while plasma glucagon was unchanged from CON. Free fatty acids (FFA) and glycerol were lower (P < .05) in BLK. These findings demonstrate that adrenergic blockade during intense exercise results in a blunted plasma glucose response that is due to enhanced glucose uptake, with no significant change in glucose production.

Monitoring a commercial fermentation with proton nuclear magnetic resonance spectroscopy with the aid of chemometrics

Proton nuclear magnetic resonance spectroscopy (NMR) has shown the potential for being a valuable tool in monitoring a commercial fermentation. In this preliminary study, a suite of organic analytes including ethanol, fructose, glucose, methanol, glycerol, malic acid, tartaric acid, succinic acid, acetic acid and lactic acid were simultaneously determined during the fermentation. Data collection and analysis using chemometric algorithms aided the understanding of key processes including the effects of seeding a wine with bacteria for malo-lactic fermentation.

Reduced plasma free fatty acid availability during exercise: effect on gene expression

Endurance exercise transiently increases the mRNA of key regulatory proteins involved in skeletal muscle metabolism. During prolonged exercise and subsequent recovery, circulating plasma fatty acid (FA) concentrations are elevated. The present study therefore aimed to determine the sensitivity of key metabolic genes to FA exposure, assessed in vitro using L6 myocytes and secondly, to measure the expression of these same set of genes in vivo, following a single exercise bout when the post-exercise rise in plasma FA is abolished by acipimox. Initial studies using L6 myotubes demonstrated dose responsive sensitivity for both PDK4 and PGC-1α mRNA to acute FA exposure in vitro. Nine active males performed two trials consisting of 2 h exercise, followed by 2 h of recovery. In one trial, plasma FA availability was reduced by the administration of acipimox (LFA), a pharmacological inhibitor of adipose tissue lipolysis, and in the second trial a placebo was provided (CON). During the exercise bout and during recovery, the rise in plasma FA and glycerol was abolished by acipimox treatment. Following exercise the mRNA abundance of PDK4 and PGC-1α were elevated and unaffected by either acipimox or placebo. Further analysis of skeletal muscle gene expression demonstrated that the CPT I gene was suppressed in both trials, whilst UCP-3 gene was only modestly regulated by exercise alone. Acipimox ingestion did not alter the response for both CPT I and UCP-3. Thus, this study demonstrates that the normal increase in circulating concentrations of FA during the later stages of exercise and subsequent recovery is not required to induce skeletal muscle mRNA expression of several proteins involved in regulating substrate metabolism.

Pyruvate dehydrogenase activation and kinase expression in human skeletal muscle during fasting

Fasting forces adaptive changes in whole body and skeletal muscle metabolism that increase fat oxidation and decrease the oxidation of carbohydrate. We tested the hypothesis that 40 h of fasting would decrease pyruvate dehydrogenase (PDH) activity and increase PDH kinase (PDK) isoform mRNA expression in human skeletal muscle. The putative transcriptional activators of PDK isozymes, peroxisome proliferator-activated receptor-α (PPAR-α) protein, and forkhead homolog in rhabdomyosarcoma (FKHR) mRNA were also measured. Eleven healthy adults fasted after a standard meal (25% fat, 60% carbohydrate, 15% protein) with blood and skeletal muscle samples taken at 3, 15, and 40 h postprandial. Fasting increased plasma free fatty acid, glycerol, and β-hydroxybutyrate concentrations and decreased glucose and insulin concentrations. PDH activity decreased from 0.88 ± 0.11 mmol acetyl-CoA · min^-1 · kg wet muscle wt^-1 at 3 h to 0.62 ± 0.10 (P = not significant) and 0.39 ± 0.06 (P < 0.05) mmol · min^-1 · kg wet mass^-1 after 15 and 40 h of fasting. Although all four PDK isoforms were expressed in human skeletal muscle, PDK^-2 and -4 mRNA were the most abundant. PDK^-1 and ^-3 mRNA abundance was ~1 and 15% of the PDK^-2 and 4^- levels, respectively. The 40-h fast had no effect on PDK^-1, ^-2, and ^-3 mRNA expression. PDK-4 mRNA was significantly increased ~3-fold after 15 h and ~14-fold after 40 h of fasting. Skeletal muscle PPAR-α protein and FKHR mRNA abundance were unaffected by the fast. The results suggest that decreased PDH activation after 40 h of fasting may have been a function of the large increase in PDK-4 mRNA expression and possible subsequent increase in PDK protein and activity. The changes in PDK-4 expression and PDH activity did not coincide with increases in the transcriptional activators PPAR-α and FKHR.

The effects of exercise and adipose tissue lipolysis on plasma adiponectin concentration and adiponectin receptor expression in human skeletal muscle

Objective: It has been suggested that adiponectin regulates plasma free fatty acid (FFA) clearance by stimulating FFA uptake and/or oxidation in muscle. We aimed to determine changes in plasma adiponectin concentration and adiponectin receptor 1 and 2 mRNA expression in skeletal muscle during and after prolonged exercise under normal, fasting conditions (high FFA trial; HFA) and following pharmacological inhibition of adipose tissue lipolysis (low FFA trial; LFA). Furthermore, we aimed to detect and locate adiponectin in skeletal muscle tissue. Methods: Ten subjects performed two exercise trials (120 min at 50% VO2max). Indirect calorimetry was used to determine total fat oxidation rate. Plasma samples were collected at rest, during exercise and during post-exercise recovery to determine adiponectin, FFA and glycerol concentrations. Muscle biopsies were taken to determine adiponectin protein and adiponectin receptor 1 and 2 mRNA expression and to localise intramyocellular adiponectin. Results: Basal plasma adiponectin concentrations averaged 6.57±0.7 and 6.63±0.8 mg/l in the HFA and LFA trials respectively, and did not change significantly during or after exercise. In the LFA trial, plasma FFA concentrations and total fat oxidation rates were substantially reduced. However, plasma adiponectin and muscle adiponectin receptor 1 and 2 mRNA expression did not differ between trials. Immunohistochemical staining of muscle cross-sections showed the presence of adiponectin in the sarcolemma of individual muscle fibres and within the interfibrillar arterioles. Conclusion: Plasma adiponectin concentrations and adiponectin receptor 1 and 2 mRNA expression in muscle are not acutely regulated by changes in adipose tissue lipolysis and/or plasma FFA concentrations. Adiponectin is abundantly expressed in muscle, and, for the first time, it has been shown to be present in/on the sarcolemma of individual muscle fibres.

Regulation of HSL serine phosphorylation in skeletal muscle and adipose tissue

Hormone-sensitive lipase (HSL) is important for the degradation of triacylglycerol in adipose and muscle tissue, but the tissue-specific regulation of this enzyme is not fully understood. We investigated the effects of adrenergic stimulation and AMPK activation in vitro and in circumstances where AMPK activity and catecholamines are physiologically elevated in humans in vivo (during physical exercise) on HSL activity and phosphorylation at Ser⁵⁶³ and Ser⁶⁶⁰, the PKA regulatory sites, and Ser⁵⁶⁵, the AMPK regulatory site. In human experiments, skeletal muscle, subcutaneous adipose and venous blood samples were obtained before, at 15 and 90 min during, and 120 min after exercise. Skeletal muscle HSL activity was increased by ~80% at 15 min compared with rest and returned to resting rates at the cessation of and 120 min after exercise. Consistent with changes in plasma epinephrine, skeletal muscle HSL Ser⁵⁶³ and Ser⁶⁶⁰ phosphorylation were increased by 27% at 15 min (P < 0.05), remained elevated at 90 min, and returned to preexercise values postexercise. Skeletal muscle HSL Ser⁵⁶⁵ phosphorylation and AMPK signaling were increased at 90 min during, and after, exercise. Phosphorylation of adipose tissue HSL paralleled changes in skeletal muscle in vivo, except HSL Ser⁶⁶⁰ was elevated 80% in adipose compared with 35% in skeletal muscle during exercise. Studies in L6 myotubes and 3T3-L1 adipocytes revealed important tissue differences in the regulation of HSL. AMPK inhibited epinephrine-induced HSL activity in L6 myotubes and was associated with reduced HSL Ser660 but not Ser563 phosphorylation. HSL activity was reduced in L6 myotubes expressing constitutively active AMPK, confirming the inhibitory effects of AMPK on HSL activity. Conversely, in 3T3-L1 adipocytes, AMPK activation after epinephrine stimulation did not prevent HSL activity or glycerol release, which coincided with maintenance of HSL Ser660 phosphorylation. Taken together, these data indicate that HSL activity is maintained in the face of AMPK activation as a result of elevated HSL Ser660 phosphorylation in adipose tissue but not skeletal muscle.