The effects of increased endurance training load on biomarkers of heat intolerance during intense exercise in the heat

The effects of increased training (IT) load on plasma concentrations of lipopolysaccharides (LPS), proinflammatory cytokines, and anti-LPS antibodies during exercise in the heat were investigated in 18 male runners, who performed 14 days of normal training (NT) or 14 days of 20% IT load in 2 equal groups. Before (trial 1) and after (trial 2) the training intervention, all subjects ran at 70% maximum oxygen uptake on a treadmill under hot (35 degrees C) and humid (similar to 40%) conditions, until core temperature reached 39.5 degrees C or volitional exhaustion. Venous blood samples were drawn before, after, and 1.5 h after exercise. Plasma LPS concentration after exercise increased by 71% (trial 1, p < 0.05) and 21% (trial 2) in the NT group and by 92% (trial 1, p < 0.01) and 199% (trial 2, p < 0.01) in the IT group. Postintervention plasma LPS concentration was 35% lower before exercise (p < 0.05) and 47% lower during recovery (p < 0.01) in the IT than in the NT group. Anti-LPS IgM concentration during recovery was 35% lower in the IT than in the NT group (p < 0.05). Plasma interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha concentrations after exercise (IL-6, 3-7 times, p < 0.01, and TNF-alpha, 33%, p < 0.01) and during recovery (IL-6, 2-4 times, p < 0.05, and TNF-alpha, 30%, p < 0.01) were higher than at rest within each group. These data suggest that a short-term tolerable increase in training load may protect against developing endotoxemia during exercise in the heat.

Influence of timing of milk consumption coupled with endurance training on body composition and endurance training adaptations in humans.

Consumption of low-fat milk (LFM) after resistance training has been shown to have positive influences on body composition and training adaptations; however, little research has examined the effects of LFM consumption following endurance training. The purpose of the study was to look at the effects of combining additional servings of LFM following endurance exercise on body composition, bone health, and training adaptations. 40 healthy males were recruited. Individuals were randomized into 4 groups – DEI (750mL LFM immediately post exercise), DEA (750mL LFM 4 hrs prior to or 6 hrs post exercise), CEI (750mL carbohydrate beverage immediately post-exercise), and CEA (750mL carbohydrate beverage immediately post-exercise). Participants took part in a 12-week endurance training intervention (1 h/day, 3 d/wk, ~60% max HR). 22 participants completed the study. Analysis showed significant increases in lean mass, spinal bone mineral content, relative VO2peak, and a decrease in Trap 5β across all groups (p < 0.05).

Changes in mitochondrial PLIN3 and PLIN5 protein content in rat skeletal muscle following acute contraction and endurance training

Surrounding lipid droplets in skeletal muscle are the perilipin (PLIN2-5) family of proteins, regulating lipid droplet metabolism. During exercise lipid droplets provide fatty acids to the mitochondria for oxidation while increasing their proximity to each other. Whether PLIN3 and PLIN5 associate with mitochondria following contraction has not been examined. To determine whether contraction altered mitochondrial PLIN3 and PLIN5 content, sedentary and endurance trained rats underwent acute contraction. The main outcomes are; 1) mitochondrial PLIN3 content is unaltered while mitochondrial PLIN5 content is increased following an acute contraction 2) mitochondrial PLIN3 content is higher in endurance trained rats when compared to sedentary and mitochondrial PLIN5 content is similar in both conditions 3) only PLIN5 mitochondrial content is increased similarly in both groups following acute contraction. This work highlights the dynamics of these two PLIN proteins, which may have roles not only on the lipid droplet but also on the mitochondria.

Skeletal muscle protein content of lipolytic inhibitor G(0)/G(1) switch gene-2 protein: the effect of endurance training

The first and rate-limiting step of lipolysis is the removal of the first fatty acid from a triglyceride molecule; it is catalyzed by adipose triglyceride lipase (ATGL). ATGL is co-activated by comparative gene identification-58 (CGI-58) and inhibited by the G(0)/G(1) switch gene-2 protein (G0S2). G0S2 has also recently been identified as a positive regulator of oxidative phosphorylation within the mitochondria. Previous research has demonstrated in cell culture, a dose dependent mechanism for inhibition by G0S2 on ATGL. However our data is not consistent with this hypothesis. There was no change in G0S2 protein content during an acute lipolytic inducing set of contractions in both whole muscle, and isolated mitochondria yet both ATGL and G0S2 increase following endurance training, in spite of the fact that there should be increased reliance on intramuscular lipolysis. Therefore, inhibition of ATGL by G0S2 appears to be regulated through more complicated intracellular or post-translation regulation.

EFFECT OF ENDURANCE TRAINING ON HYPOTHALAMIC SEROTONIN CONCENTRATION AND PERFORMANCE

Serotonin is a neurotransmitter that modulates several functions, such as food intake, energy expenditure, motor activity, mood and sleep. Acute exhaustive endurance exercise increases the synthesis, concentration and metabolism of serotonin in the brain. This phenomenon could be responsible for central fatigue after prolonged and exhaustive exercise. However, the effect of chronic exhaustive training on serotonin is not known. The present study was conducted to examine the effect of exhaustive endurance training on performance and serotonin concentrations in the hypothalamus of trained rats. Rats were divided into three groups: sedentary rats (SED), moderately trained rats (MOD) and exhaustively trained rats (EXT), with an increase of 200% in the load carried during the final week of training. Hypothalamic serotonin concentrations were similar between the SED and MOD groups, but were higher in the EXT group (P < 0.05). Performance was lower in the EXT group compared with the MOD group (P < 0.05). Thus, the present study demonstrates that exhaustive training increases serotonin concentrations in the hypothalamus, together with decreased endurance performance after inadequate recovery time. However, the mechanism underlying these changes remains unknown.

Endurance training modulates lymphocyte function in rats with post-MI CHF

Purpose: Exercise training restores innate immune system cell function in post-myocardial infarction (post-MI) rats. However, studies of the involvement of lymphocyte (Ly) in the setting of the congestive heart failure (CHF) are few. To address this issue, we investigated the function of Ly obtained from cervical lymph nodes from post-MI CHF rats submitted to treadmill running training. Methods: Twenty-five male Wistar rats were randomly assigned to the following groups: rats submitted to ligation of the left coronary artery, which were sedentary (MI-S, N= 7, only limited activity) or trained (MI-T, N= 6, on a treadmill (0% grade at 13-20 m.m(-1)) for 60 min.d(-1), 5 d.wk(-1), for 8-10 wk); or sham-operated rats, which were sedentary (sham-S, N = 6) or trained (sham-T, N = 6). The incorporation of [2-C-14]-thymidine by Ly cultivated in the presence of concanavalin A (Con A) and lipopolysaccharide (LPS), cytokine production by Ly cultivated in the presence of phytohemagglutinin (PHA), and plasma concentration of glutamine were assessed in all groups, 48 h after the last exercise session. Results: Proliferative capacity was increased, following incubation with Con-A in the MI groups, when compared with the sham counterparts. When incubated in the presence of PHA, MI-S produced more IL-4 (96%) than sham-S (P < 0.001). The training protocol induced a 2.2-fold increase in the production of interleukin-2 (P < 0.001) of the cells obtained from the cervical lymph nodes of MI-T, compared with MI-S. Conclusion: The moderate endurance training protocol caused an increase in IL-2 production, and a trend toward the reversion of the Th-1/Th-2 imbalance associated with IL-4 production increased in the post-MI CHF animal model.

Endurance training induces depot-specific changes in IL-10/TNF-alpha ratio in rat adipose tissue

White adipose tissue (WAT) is the source of pro- and anti-inflammatory cytokines and recently, it has been recognized as an important source of interleukin 10 (IL-10). Acute physical exercise is known to induce an anti-inflammatory cytokine profile, however, the effect of chronic physical exercise on the production of IL-10 by WAT has never been examined. We assessed IL-10 and TNF-alpha concentration in WAT of rats engaged in endurance training. Animals were randomly assigned to either a sedentary control group (S, n = 7) or an endurance trained group (T, n = 8). Trained rats ran on a treadmill 5 days/wk for 8 wk (55-65% VO(2max). Detection of IL-10 and TNF-alpha protein and mRNA expression, as well as the gene expression of PPAR-gamma, and immunocytochemistry to detect mononuclear phagocytes were carried out. A reduction in absolute retroperitoneal adipose tissue (RPAT) weight in T (44%; p < 0.01), when compared with S was observed. IL-10 concentration was increased (1.5-fold, p < 0.05), to a higher extent than that of TNF-alpha (66%. p < 0.05) in the mesenteric adipose tissue (MEAT) of the trained group, while no change related to training was observed in RPAT. In MEAT, IL-10/TNF-alpha ratio was increased in T, when compared with S (30%; p < 0.05). PPAR-gamma gene expression was increased in T (1.1-fold; p < 0.01), when compared with S in the same adipose depot. No monocyte infiltration was found. In conclusion, exercise training induced increased IL-10 expression in the mesenteric depot, resulting in a modified IL-10/TNF-alpha ratio. We also conclude that WAT presents a depot-specific response to endurance training regarding the studied aspects. (C) 2008 Elsevier Ltd. All rights reserved.

Effect of endurance training upon lipid metabolism in the liver of cachectic tumour-bearing rats

The syndrome of cancer cachexia is accompanied by several alterations in lipid metabolism, and the liver is markedly affected. Previous Studies showed that moderate exercise training may prevent liver fill accumulation through diminished delivery of lipids to the liver, increased hepatic oxidation and increased incorporation of triacylglycerol (TAG) into very low density lipoprotein (VLDL). Our aim was to examine the influence of moderate intensity training (8 weeks) upon TAG content, VLDL assembly and secretion, apolipoprotein B (apoB) and microsomal transfer protein (MTP) gene expression in the liver of cachectic tumour-bearing rats. Animals were randomly assigned to a sedentary control (SC), sedentary tumour-bearing (ST) or exercise-trained control (EC) or to all exercise trained tumour-bearing (ET) group. Trained rats ran on a treadmill (60% VO2max) for 60 min day(-1), 5 day week(-1), for 8 weeks. TAG content and the rate of VLDL secretion (followed for 3 h), its well its mRNA expression of apoB and MTP, and total cholesterol, VLDL-TAG, VLDL-cholesterol, high density lipoprotein cholesterol (HDL-cholesterol) and tumor weight were evaluated. VLDL-cholesterol showed a decrease in ST (p < 0.05) in relation to SC. Serum TAG, VLDL-TAG and tissue TAG content were all increased in ST (p < 0.01), when compared with SC. ST showed a lower rate of VLDL secretion (p < 0.05) and reduced expression of apoB (p < 0.001) and MTP (p < 0.001), when compared with SC. These parameters were restored to control values (p < 0.05) when the animals were submitted to the exercise training protocol. Tumour weight decreased 10-fold after training (p < 0.001). It is possible to affirm, therefore, that endurance training promoted the re-establishment of lipid metabolism in cachectic tumour-bearing animals, especially in relation to VLDL secretion and assembly. Copyright (C) 2008 John Wiley & Sons, Ltd.

Endurance training activates AMP-activated protein kinase, increases expression of uncoupling protein 2 and reduces insulin secretion from rat pancreatic islets

Endurance exercise is known to enhance peripheral insulin sensitivity and reduce insulin secretion. However, it is unknown whether the latter effect is due to the reduction in plasma substrate availability or alterations in beta-cell secretory machinery. Here, we tested the hypothesis that endurance exercise reduces insulin secretion by altering the intracellular energy-sensitive AMP-activated kinase (AMPK) signaling pathway. Male Wistar rats were submitted to endurance protocol training one, three, or five times per week, over 8 weeks. After that, pancreatic islets were isolated, and glucose-induced insulin secretion (GIIS), glucose transporter 2 (GLUT2) protein content, total and phosphorylated calmodulin kinase kinase (CaMKII), and AMPK levels as well as peroxisome proliferator-activated receptor-gamma coactivator-1-alpha (PGC-1 alpha) and uncoupling protein 2 (UCP2) content were measured. After 8 weeks, chronic endurance exercise reduced GIIS in a dose-response manner proportionally to weekly exercise frequency. Contrariwise, increases in GLUT2 protein content, CaMKII and AMPK phosphorylation levels were observed. These alterations were accompanied by an increase in UCP2 content, probably mediated by an enhancement in PGC-1 alpha protein expression. In conclusion, chronic endurance exercise induces adaptations in beta-cells leading to a reduction in GIIS, probably by activating the AMPK signaling pathway. Journal of Endocrinology (2011) 208, 257-264

Endurance training in humans leads to fiber type-specific increases in levels of peroxisome proliferator-activated receptor-[gamma] coactivator-1 and peroxisome proliferator-activated receptor-[alpha] in skeletal muscle

The peroxisome proliferator-activated receptor (PPAR)-γ coactivator-1 (PGC-1) can induce mitochondria biogenesis and has been implicated in the development of oxidative type I muscle fibers. The PPAR isoforms α, β/δ, and γ control the transcription of genes involved in fatty acid and glucose metabolism. As endurance training increases skeletal muscle mitochondria and type I fiber content and fatty acid oxidative capacity, our aim was to determine whether these increases could be mediated by possible effects on PGC-1 or PPAR-α, -β/δ, and -γ. Seven healthy men performed 6 weeks of endurance training and the expression levels of PGC-1 and PPAR-α, -β/δ, and -γ mRNA as well as the fiber type distribution of the PGC-1 and PPAR-α proteins were measured in biopsies from their vastus lateralis muscle. PGC-1 and PPAR-α mRNA expression increased by 2.7- and 2.2-fold (P < 0.01), respectively, after endurance training. PGC-1 expression was 2.2- and 6-fold greater in the type IIa than in the type I and IIx fibers, respectively. It increased by 2.8-fold in the type IIa fibers and by 1.5-fold in both the type I and IIx fibers after endurance training (P < 0.015). PPAR-α was 1.9-fold greater in type I than in the II fibers and increased by 3.0-fold and 1.5-fold in these respective fibers after endurance training (P < 0.001). The increases in PGC-1 and PPAR-α levels reported in this study may play an important role in the changes in muscle mitochondria content, oxidative phenotype, and sensitivity to insulin known to be induced by endurance training.

Effects of endurance training status and sex difference on Na+, K+-pump mRNA expression, content and maximal activity in human skeletal muscle

Aim: This study investigated the effects of endurance training status and sex differences on skeletal muscle Na⁺,K⁺-pump mRNA expression, content and activity. Methods: Forty-five endurance-trained males (ETM), 11 recreationally active males (RAM), and nine recreationally active females (RAF) underwent a vastus lateralis muscle biopsy. Muscle was analysed for Na⁺,K⁺-pump α1, α2, α3, β1, β2 and β3 isoform mRNA expression (real-time reverse transcription-polymerase chain reaction), content ([³H]-ouabain-binding site) and maximal activity (3-O-methylfluorescein phosphatase, 3-O-MFPase). Results: ETM demonstrated lower α1, α3, β2 and β3 mRNA expression by 74%, 62%, 70% and 82%, respectively, than RAM (P < 0.04). In contrast, [³H]-ouabain binding and 3-O-MFPase activity were each higher in ETM than in RAM, by 16% (P < 0.03). RAM demonstrated a 230% and 364% higher α3 and b3 mRNA expression than RAF, respectively (P < 0.05), but no significant sex differences were found for α1, α2, β1 or β2 mRNA, [³H]-ouabain binding  or 3-O-MFPase activity. No significant correlation was found between years of endurance training and either [³H]-ouabain binding or 3-O-MFPase activity. Significant but weak correlations were found between the number of training hours per week and 3-O-MFPase activity (r = 0.31, P < 0.02) and between incremental exercise V O_2(peak) and both   [³H]-ouabain binding (r = 0.33, P < 0.01) and 3-O-MFPase activity (r = 0.28, P < 0.03). Conclusions: Isoform-specific differences in Na⁺,K⁺-pump mRNA expression were found with both training status and sex differences, but only training status influenced Na⁺,K⁺-pump content and maximal activity in human skeletal muscle.

Effect of 2 weeks of endurance training on uncoupling protein3 content in untrained human subjects

Aim: The mitochondrial uncoupling protein-3 (UCP3) is able to lower the proton gradient across the inner mitochondrial membrane, thereby uncoupling substrate oxidation from ATP production and dissipating energy as heat. What the effect of endurance training on UCP3 is, is still  controversial. Endurance-trained athletes are characterized by lower levels of UCP3, but longitudinal studies in rodents reported no effect of endurance training on muscular UCP3 levels. Here, we examined the effect of a 2-week training programme on skeletal muscle UCP3 protein content in untrained human subjects, and hypothesized that UCP3 will be reduced after the training programme. Methods: Nine untrained men [age: 23.3±3.2 years; BMI: 22.6±2.6 kg m^-2; maximal power output (^Wmax): 3.8±0.6 W kg^-1 body weight] trained for 2 weeks. Before and at least 72 h after the training period, muscle biopsies were taken for determination of UCP3 protein content. Results: UCP3 protein content tended to be lower after the training programme [95±10 vs. 109±12 arbitrary units (AU), P= 0.08]. Cytochrome c content tended to increase with 33% in response to endurance training (52± 6 vs. 39± 6 AU, P = 0.08). The ratio UCP3 relative to cytochrome c tended to decrease significantly upon endurance training (2.0±0.4 vs. 3.2±0.6 AU, P = 0.01). Conclusion: A short-term (2-week) endurance training programme decreased UCP3 protein levels and significantly reduced the ratio of UCP3 to cytochrome c.

Endurance training adaptations modulate the redox–force relationship of rat isolated slow-twitch skeletal muscles

1. Studies have shown that, in isolated skeletal muscles, maximum isometric force production (Po) is dependent on muscle redox state. Endurance training increases the antioxidant capacity of skeletal muscles, a factor that could impact on the force-producing capacity following exogenous exposure to an oxidant. We tested the hypothesis that 12 weeks treadmill training would increase anti-oxidant capacity in rat skeletal muscles and alter their response to exogenous oxidant exposure.

2. At the conclusion of the 12 week endurance-training programme, soleus (slow-twitch) muscles from trained rats had greater citrate synthase (CS) and catalase (CAT) activity compared with soleus muscles from untrained rats (P < 0.05).
In contrast, CAT activity of extensor digitorum longus (EDL; fast-twitch) muscles from trained rats was not different to EDL muscles of untrained rats. The CS activity was lower in EDL muscles from trained compared with untrained rats (P < 0.05).

3. Equilibration with exogenous hydrogen peroxide (H2O2, 5 mmol/L) increased the Po of soleus muscles from untrained rats for the duration of treatment (30 min), whereas the Po of EDL muscles was affected biphasically, with a small increase initially (after 5 min), followed by a more marked decrease in Po (after 30 min). The H2O2-induced increase in Po of soleus muscles from trained rats was less than that in untrained rats (P < 0.05), but no differences were observed in the Po of EDL muscles following training.

4. The results indicate that 12 weeks endurance running training conferred adaptations in soleus but not EDL muscles. These adaptations were associated with an attenuation of the oxidant-induced increase in Po of soleus muscles from trained compared with untrained rats. We conclude that endurance training-adapted soleus muscles have a slightly altered redox - force relationship.