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Comment la souplesse thoracique augmente-t’elle?

26/05/2019 | Musculation des pectoraux et Etudes Musculation


Effect of intercostal muscle contraction on rib motion in humans studied by finite element analysis
Guangzhi Zhang   japplphysiol.00995.2017

The effect of intercostal muscle contraction on generating rib motion has been investigated for a long time and is still controversial in physiology. This may be because of the complicated structure of the rib cage, making direct prediction of the relationship between intercostal muscle force and rib movement impossible. Finite element analysis is a useful tool that is good at solving complex structural mechanic problems.

In this study, we individually activated the intercostal muscle groups from the dorsal to ventral portions and obtained five different rib motions classified based on rib moving directions. We found that the ribs cannot only rigidly rotate around the spinal joint but also be deformed, particularly around the relatively soft costal cartilages, where the moment of muscle force for the rigid rotation is small. Although the intercostal muscles near the costal cartilages cannot generate a large moment to rotate the ribs, the muscles may still have a potential to deform the costal cartilages and contribute to the expansion and contraction of the rib cage based on the force-length relationship.

Our results also indicated that this potential is matched well with the special shape of the costal cartilages, which become progressively oblique in the caudal direction. Compared with the traditional explanation of rib motion, by additionally considering the effect from the tissue deformation, we found that the special structure of the ventral portion of the human rib cage could be of mechanical benefit to the intercostal muscles, generating inspiratory and expiratory rib motions.

NEW & NOTEWORTHY Compared with the traditional explanation of rib motion, additionally considering the effect from tissue deformation helps us understand the special structure of the ventral portion of the human rib cage, such that the costal cartilages progressively become oblique and the costochondral junction angles gradually change into nearly right angles from the upper to lower ribs, which could be of mechanical benefit to the intercostal muscles in the ventral portion, generating inspiratory and expiratory rib motions.

Regulation Hépatique de la Follistatine pendant l’effort

22/05/2019 | Etudes sur les hormones


Regulation of Hepatic Follistatin Expression at Rest and during Exercise in Mice
PEPPLER, WILLEM T       Medicine & Science in Sports & Exercise: June 2019 - Volume 51 - Issue 6 - p 1116–1125

Introduction Follistatin (FST) is a protein with numerous biological roles and was recently identified as an exercise-inducible hepatokine; however, the signals that regulate this are not well understood. The purpose of this study was to delineate potential endocrine factors that may regulate hepatic FST at rest and during exercise.

Methods This study used four experiments. First, male and female C57BL/6J mice remained sedentary or were subjected to a single bout of exercise at moderate or exhaustive intensity with liver collected immediately post. Second, mice were injected with glucagon (1 mg·kg−1, 60 min), epinephrine (2 mg·kg−1, 30 min), glucagon then epinephrine, or saline. Third, mice were pretreated with propranolol (20–60 mg·kg−1, 30 min) before epinephrine injection. Fourth, glucagon receptor wild type (Gcgr+/+) or knockout (Gcgr−/−) mice were pretreated with saline or propranolol (20 mg·kg−1, 30 min) and were subjected to a single bout of exhaustive exercise with liver collected immediately post or after 2 h recovery. In all experiments liver FST mRNA expression was measured, and in experiment four FST protein content was measured.

Results A single bout of treadmill exercise performed at an exhaustive but not moderate-intensity increased FST expression, as did injection of glucagon or epinephrine alone and when combined. Pretreatment of mice with propranolol attenuated the epinephrine-induced increase in FST expression. The exercise-induced increase in FST expression was attenuated in Gcgr−/− mice, with no effect of propranolol. Gcgr−/− mice had higher protein content of FST, but there was no effect of exercise or propranolol.

Conclusions These data suggest that both glucagon and epinephrine regulate hepatic FST expression at rest; however, only glucagon is required for the exercise-induced increase.

Comment la brûle déclenche l’anabolisme?

09/05/2019 | Etudes sur les hormones et Etudes Musculation et Etudes Compléments alimentaires


IL-6 release from muscles during exercise is stimulated by lactate-dependent protease activity
Pernille Hojman       08 MAY 2019 ajpendo

IL-6 is secreted from muscles to the circulation during high-intensity and long-duration exercise, where muscle-derived IL-6 works as an energy sensor to increase release of energy substrates from liver and adipose tissues. We investigated the mechanism involved in the exercise-mediated surge in IL-6 during exercise. Using interval-based cycling in healthy young men, swimming exercise in mice, and electrical stimulation of primary human muscle cells, we explored the role of lactate production in muscular IL-6 release during exercise. First, we observed a tight correlation between lactate production and IL-6 release during both strenuous bicycling and electrically stimulated muscle cell cultures. In mice, intramuscular injection of lactate mimicked the exercise-dependent release of IL-6, and pH buffering of lactate production during exercise attenuated IL-6 secretion. Next, we used in vivo bioimaging to demonstrate that intrinsic intramuscular proteases were activated in mice during swimming, and that blockade of protease activity blunted swimming-induced IL-6 release in mice. Last, intramuscular injection of the protease hyaluronidase resulted in dramatic increases in serum IL-6 in mice, and immunohistochemical analyses showed that intramuscular lactate and hyaluronidase injections led to release of IL-6-containing intramyocellular vesicles. We identified a pool of IL-6 located within vesicles of skeletal muscle fibers, which could be readily secreted upon protease activity. This protease-dependent release of IL-6 was initiated by lactate production, linking training intensity and lactate production to IL-6 release during strenuous exercise.

La caféine est aussi absorbée par la muqueuse buccale

22/04/2019 | Etudes Compléments alimentaires et Etudes Perte de poids


Caffeine release and absorption from caffeinated gums
Cecile Morris   Food & Function

The objectives of this study were to estimate the impact of chewing time on caffeine release from gum and to understand caffeine pharmacokinetics. Caffeine release increased with chewing time (2 min < 5 min

< 10 min). Furthermore, two plasma caffeine concentration peaks were observed suggesting that

caffeine absorption occurs both through the oral mucosa and gastrointestinal tract. This is of practical relevance to maximise caffeine doses and to synchronise effort with peak caffeine concentration.

Rôle anabolique Inter-Organes du GIP

02/04/2019 | Etudes sur les hormones


A Physiological Role of Inter-Organ Network between Gastrointestine and Skeletal Muscle on the Regulation of Skeletal Muscle Volume
Katsumasa Goto     The FASEB Journal       1 Apr 2019Abstract Number:700.1

Several inter-organ networks have been proposed. In general, gastrointestinal hormone gastric inhibitory polypeptide (GIP), which is synthesized in and secreted from K cells, regulates nutrient absorption via inhibition of gastric contraction and acid secretion. GIP receptor On the other hand, GIPR expresses in not only a gastrointestinal tract but also β cells in the pancreas. Since GIP also modulates glucose metabolism via insulin synthesis and secretion, GIP is also a member of incretin. Recently, the expression of GIP is also confirmed in skeletal muscle. However, there is no evidence for the inter-organ network between gastrointestine and skeletal muscle. In the present study, we investigated a physiological role of the inter-organ network between gastrointestine and skeletal muscle via GIP. GIP stimulates myogenic differentiation of C2C12 cells. Expression of GIPR was observed in C2C12 myoblasts and myotubes. Knockdown of GIPR induced the down-regulation of Pax7 in C2C12 myoblasts. In addition, GIPR-knockdown-associated depression of myotube formation of C2C12 cells were observed. On the other hand, GIPR-knockdown stimulated proliferation of C2C12 myoblasts. Therefore, GIP-GIPR intracellular signal(s) might play a role in the regulation of skeletal muscle volume via the mediation of myogenic differentiative potential.

Effets de la mélatonine sur la régénération nerveuse?

02/04/2019 | Etudes Compléments alimentaires


Effects of melatonin on neural reconstruction after acute spinal cord injury through regulation of endoplasmic reticulum stress response and autophagy
Yunho Jin     The FASEB Journal       1 Apr 2019Abstract Number:662.2

It has been reported that autophagy and endoplasmic reticulum (ER) stress response cause improved hindlimb motor function and reduced damage of axons in spinal cord injured animals, respectively. However, the effects of melatonin on neural reconstruction and motor recovery through regulation of ER stress response and autophagy have not been well described. Therefore, the purpose of this study is to elucidate the effects of melatonin treatment on neural reconstruction and motor recovery through regulation of ER stress response and autophagy.

To verify the effect of melatonin injection on post-SCI alterations regarding neural cells, autophagy, and ER stress response, we analyzed markers at protein level, and morphological changes. At day 3 after SCI, melatonin did not cause behavioral improvement (p<.05). At molecular levels, melatonin suppressed the loss of astrocytes after SCI (p<.05). Beclin-1 expression was decreased by melatonin treatment (p<.05). In other words, autophagy activation in SCI+MT was lower than that of SCI group, indicating melatonin-mediated suppression of autophagic cell death. In addition, GRP78 expression was preserved in SCI+MT group with no difference compared to non-injured groups. Namely, ER stress response was advanced by melatonin. In histological analysis, it was proved that dendritic branches were preserved by melatonin treatment.

In conclusion, exogenous treatment of melatonin may result in neural reconstruction after SCI through regulating autophagy and ER stress response at the injured spinal segments.

Rôles des polyamines dans l’action anabolique des androgènes?

02/04/2019 | Etudes sur les hormones et Etudes Compléments alimentaires


Expression of Genes that Comprise the Core Molecular Clock are Altered in the Atrophied Skeletal Muscle by Androgen Deprivation
Michael L Rossetti     The FASEB Journal       1 Apr 2019Abstract Number:579.1

Skeletal muscle atrophy increases the risk of morbidity and mortality during various pathological conditions. In males, a decrease in the production and/or bioavailability of androgens (termed hypogonadism) directly contributes to muscle atrophy during various pathological conditions. While it is known that androgens prevent muscle atrophy, the mechanism(s) by which androgens mediate this effect are largely undefined. Our laboratory previously showed that mitochondrial turnover is enhanced in the tibialis anterior (TA) muscle of mice by androgen deprivation induced by castration surgery, and the magnitude of turnover was related to the degree of muscle atrophy.

These data suggest that potentially dysfunctional mitochondria contribute to the muscle atrophy observed following androgen deprivation. To gain a better understanding of that factors that might contribute to changes in mitochondrial quality control during androgen deprived conditions, we subjected total RNA from the TA of sham and castrated mice to microarray analysis. This unbiased approach identified significant changes in expression of genes that comprise the core molecular clock. qRT-PCR confirmed that expression of Brain and Muscle Arntl 1 (Bmal1) was decreased, while expression of Period 1, Period 2, and Period 3 (Per1, 2, & 3) were increased in the TA of castrated mice. When measured across a diurnal cycle, the change in expression of Bmal1, Per1, and Per2 exhibited reduced amplitude under androgen-deprived conditions. Interestingly, strong relationships were observed between the castration-mediated changes of core clock components and the measures of mitochondrial turnover. Specifically, Bmal1 expression was directly related to BCL2/adenovirus E1B 19 kDA protein-interacting protein 3 (BNIP3) protein content (R2 = 0.88), and the expression of core clock components were also directly related to the content of various mitochondrial proteins.

Expression of core clock components were also related to the autophagy marker, p62, and the mass of the TA. Ex post facto analysis of the microarray also identified changes in genes regulating polyamine biosynthesis. As polyamines are known to alter core clock function, we determined whether androgen deprivation altered polyamine content. While castration did not alter Spermine content, there was a significant reduction in the content of Spermidine in the TA of castrated mice.

Overall, these data suggest that reduced Spermidine concentrations may contribute to alterations in the core molecular clock in the skeletal muscle under androgen-deprived conditions, which may in turn contribute to reduced mitochondrial quality control and subsequent muscle atrophy

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