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Estrogen influences myosin phosphorylation and post-tetanic potentiation in murine fast muscle. We tested the hypothesis that this influence is mediated by estrogen effects on skeletal myosin light chain kinase (skMLCK) activity. To this end, extensor digitorum longus muscles from female wildtype and skMLCK-absent ([skMLCK.sup.-/-]) mice were grouped as follows: ovariectomized with estrogen (E+), ovariectomized without estrogen (E-), sham surgery, and intact baseline. At 8 weeks of age, the ovariectomized groups were ovariectomized followed by implantation of either a 0.1 mg 17[beta]-estradiol (E+) or placebo pellet (E-). Two weeks later, muscles were isolated and suspended in vitro (25[degrees]C) for determination of regulatory light chain phosphorylation and post-tetanic potentiation. Regulatory light chain phosphorylation was not different across conditions within either genotype although wildtype values were significantly greater than [skMLCK.sup.-/-] values. Consistent with this, the potentiation of concentric twitch force was similar between E+ and E- groups within each genotype but wildtype values were greater than [skMLCK.sup.-/-] values. However, unaltered estradiol levels following ovariectomy, likely due to previously underappreciated confounds of mouse age, development, and growth during estrogen supplementation, prevented direct testing of the hypothesis. Future studies should note the importance of estrous cycles and continuing physiological developments of young adult mice when working with ovarian hormones. Key words: estrogen, myosin phosphorylation, potentiation, murine, fast twitch. Les restrogenes influencent la phosphorylation et la potentialisation post-tetanique de la myosine dans le muscle rapide de souris. Nous avons tente de verifier l'hypothese selon laquelle cette influence est mediee par les effets des restrogenes sur l'activite de la kinase des chaines legeres de la myosine squelettique (skMLCK pour <>). A cette fin, nous avons reuni des muscles extenseurs communs des orteils de souris femelles de type sauvage et avec absence de skMLCK ([skMLCK.sup.-/-]) dans les groupes suivants: ovariectomie avec restrogenes (E+), ovariectomie sans restrogenes (E-), intervention chirurgicale factice et intact au debut de l'etude. Les souris des groupes avec ovariectomie subissaient une ovariectomie a l'age de 8 semaines, suivie de l'implantation d'une pastille de 0,1 mg de 17[beta]-estradiol (E+) ou de placebo (E-). Deux semaines plus tard, les muscles etaient isoles et suspendus in vitro (25[degrees]C) afin d'etablir la phosphorylation de la chaine legere regulatrice et de la potentialisation post-tetanique. La phosphorylation de la chaine legere regulatrice n'etait pas differente d'un groupe a l'autre pour un meme genotype, mais les valeurs etaient nettement plus elevees pour le type sauvage que chez les [skMLCK.sup.-/-]. En accord avec cela, la potentialisation de la force de contraction concentrique etait semblable dans les groupes E+ et E- pour un meme genotype, mais les valeurs etaient plus elevees pour le type sauvage que chez les [skMLCK.sup.-/-]. Cependant, nous n'avons pas pu verifier l'hypothese directement en raison de l'absence de diminution des taux d'restradiol apres ovariectomie, probablement en raison de facteurs confondants sous-evalues quant a l'age, ainsi qu'au developpement et a la croissance des souris pendant la supplementation en restrogenes. Des etudes futures devraient remarquer l'importance du developpement en continu des cycles restraux et de la physiologie des jeunes souris adultes lors d'etudes portant sur les hormones ovariennes. [Traduit par la Redaction] Mots-cles: restrogenes, phosphorylation de la myosine, potentialisation, murin, contraction rapide., Introduction A muscle contraction is triggered by an influx of intracellular calcium ([Ca.sup.2+]) from the sarcoplasmic reticulum into the sarcoplasm (Ebashi and Endo 1968). In addition to activating the thin [...]

This study examined the effects of a delay in post-ovariectomy replacement of 17β-estradiol (estrogen) on the postexercise proliferation of muscle satellite cells. Nine-week-old, ovariectomized, female Sprague-Dawley rats (n = 64) were distributed among 8 groups based on estrogen status (0.25 mg estrogen pellet or sham), exercise status (90 min run at 17 m x [min.sup.-1] and a grade of -13.5° or unexercised), and estrogen replacement ('proximal', estrogen replacement within 2 weeks; or 'delayed', estrogen replacement at 11 weeks following ovariectomy). Significant increases in satellite cells were found in the soleus and white gastrocnemius muscle (immunofluorescent colocalization of nuclei with Pax7) 72 h following eccentric exercise (p < 0.05) in all exercised groups. Proximal E2 replacement resulted in a further augmentation of muscle satellite cells in exercised rats (p < 0.05) relative to the delayed estrogen replacement group. Expression of PI3K was unaltered and phosphorylation of Akt relative to total Akt increased following estrogen supplementation and exercise. Exercise alone did not alter the expression levels of Akt. An 11 week delay in post-ovariectomy estrogen replacement negated the augmenting influence seen with proximal (2 week delay) post- ovariectomy estrogen replacement on post-exercise muscle satellite cell proliferation. This effect appears to be independent of the PI3K-Akt signaling pathway. Key words: estrogen, satellite cells, muscle, PI3K-Akt, timing hypothesis. La presente visait a etudier les effets du delai de la substitution du 17β-restradiol (restrogene) apres une ovariectomie sur la proliferation des cellules satellites musculaires apres un effort physique. Des rates Sprague- Dawley agees de 9 semaines et ovariectomisees (n = 64) ont ete reparties dans huit groupes selon les criteres suivants : condition restrogenique (pastilles d'restrogene a 0,25 mg ou traitement factice), etat de l'effort physique (course de 90 min a 17 m x [min.sup.-1] sur une pente de -13,5° ou aucun effort physique) et substitution restrogenique (<> : moins de 2 semaines apres l'ovariectomie; ou <> : 11 semaines apres l'ovariectomie). Une augmentation marquee des cellules satellites a ete observee dans le muscle soleaire et le muscle gastrocnemien blanc (colocalisation de l'immunofluorescence des noyaux avec le facteur Pax7) 72 h apres un effort physique excentrique (p < 0,05) dans tous les groupes de rates soumises a un effort physique. La substitution <> avec l'restradiol a entrame davantage d'augmentation du nombre de cellules satellites musculaires chez les rates soumises a un effort physique que dans le groupe de substitution restrogenique <> (p < 0,05). L'expression de la PI3K n'etait pas alteree et la proportion de la proteine Akt phosphorylee par rapport a la proteine Akt totale augmentait apres la supplementation restrogenique et l'effort physique. L'effort physique seul n'a pas altere les taux d'expression de la proteine Akt. Un delai de 11 semaines avant la substitution restrogenique suivant une ovariectomie a annule l'influence accrue de la substitution restrogenique <> (delai de 2 semaines) sur la proliferation des cellules satellites musculaires apres un effort physique. Cet effet semble etre independant de la voie de signalisation PI3K- Akt. [Traduit par la Redaction] Mots-cles: restrogene, cellules satellites, muscle, PI3K-Akt, fenetre d'intervention., Introduction Estrogen (17β-estradiol) has been reported to convey positive protective and regenerative benefits in numerous tissues following various forms of damage. Documented effects of estrogen include protective and (or) regenerative [...]

We examined the influence of estrogen receptor-alpha (ERα) activation on estrogen-mediated regulation of heat shock proteins 70 (Hsp70) and 27 (Hsp27) in soleus. Ovariectomized rats received estrogen (EST), an ERα agonist (propyl pyrazole triol, PPT), both (EST+PPT), or a sham, and they served as either unexercised controls or were subjected to exercise by having to run downhill (17 m/min, -13.5° grade) for 90 min. At 72 h postexercise, soleus muscles were removed and either immunohistochemically stained for Hsp70 and myosin heavy chain or homogenized for Western blotting for Hsp70 and Hsp27. Elevated (p < 0.05) basal Hsp70 in both type I and II fibres in the unexercised EST, PPT, and EST+PPT groups relative to unexercised sham animals was noted. Compared with Hsp70 levels in the unexercised animals, that in exercised animals was elevated (p < 0.05) in both sham and PPT groups but not in EST and EST+PPT groups. Western blot determined that Hsp27 levels were not significantly different between groups. Hence, the ability of estrogen to augment resting type I and type II muscle fibre Hsp70 content is primarily mediated via muscle ERα. However, the blunted Hsp70 response following damaging exercise in estrogensupplemented animals does not appear to be fully accounted for by ERα-mediated effects. Key words: estrogen, heat shock proteins, estrogen receptors, skeletal muscle, exercise, muscle damage. Nous avons examine l'influence de l'activation du recepteur d'oestrogene-alpha (ERα) sur la regulation par l'oestrogene des proteines de choc thermique Hsp70 et Hsp27 dans le soleaire. Des rates ayant subi une ovariectomie ont recu soit de l'oestrogene (EST), un agoniste du ERα (propyl pyrazole triol, PPT), les deux (EST+PPT) ou un faux traitement, et elles ont servi de controles non entraines ou elles ont ete soumises a une course en pente (17 m/min, -13,5° d'inclinaison) pendant 90 min. Soixante-douze heures apres l'exercice, les muscles soleaires ont ete retires et colores par immunohistochimie afin de reveler la Hsp70, la chaine legere de la myosine (MHC), ou homogeneises afin de reveler la Hsp70 et la Hsp27 par buvardage Western. Un niveau de base eleve de Hsp70 (p < 0,05) a ete observe chez les animaux non entraines des groupes EST, PPT et EST+PPT, comparativement aux animaux non entraines du groupe faux traitement et ce, tant dans les fibres de type I que celles de type II. Par rapport aux animaux non entraines, l'exercice accroissait le niveau de Hsp70 (p < 0,05) chez les groupes faux traitement et PPT, contrairement aux groupes EST et EST+PPT. Aucune difference significative des niveaux de Hsp27 determines par buvardage Western n'a ete observee entre les groupes. Donc, la capacite de l'oestrogene a augmenter le contenu en Hsp70 dans les fibres musculaires de type I et II au repos fait d'abord intervenir l'ERα du muscle. Toutefois, la reponse attenuee de la Hsp70 a la suite d'un exercice dommageable chez les animaux supplementes en oestrogene ne semble pas etre totalement expliquee par des effets faisant intervenir l'ERα. [Traduit par la Redaction] Mots-cles: oestrogene, proteines de choc thermique, recepteurs d'oestrogenes, muscle squelettique, exercice, dommage musculaire., Introduction Heat shock proteins (Hsps) can be induced by various forms of stress, including oxidative damage and protein denaturation, which often accompany eccentric exercise in skeletal muscle (Welch 1992). Both [...]

The effects of an eight-week aerobic training program on the activity of human muscle antioxidant enzymes were analyzed in human subjects. Human subjects exhibited elevated levels of maximal oxygen consumption and citrate synthase activities. However, aerobic training did not alter the muscle's positive antioxidant adaptions to superoxide dismutase, catalase, glutathione peroxidase and total gluthathione. However, the muscle's capacity for citric acid cycle-induced flux was enhanced by moderate endurance training.

Responses of vitamin E-depleted female rats to acute exercise and chronic exercise training were tested. Rats were fed either a control diet (+E rats) or a vitamin E-depleted diet (-E rats). After 8 wk, subgroups of the +E and -E rats performed treadmill exercise for 45 min at 28 m/min, 15% grade, and were immediately killed. Vitamin E concentrations were 80-90% lower in liver, heart and muscles in -E rats as determined by HPLC. There was no difference between +E and -E rats in blood lactate concentration, creatine kinase, lipid peroxidation indices, hematocrit or hemoglobin concentration following acute exercise. Remaining rats were either trained for a further 8 wk at 40 m/min, 15% incline for up to 60 min/d or served as untrained controls. No differences in training tolerance were seen between diet groups, with 64% of +E rats and 71% of -E rats consistently completing 60 min of daily training. The training induced similar adaptive elevations in succinate dehydrogenase activity (31-107%) in various hind limb muscles of both +E and -E rats. Trained +E rats had lower vitamin E concentrations in some but not all tissues when compared with untrained +E controls. These results suggest that consumption of a vitamin E-Free diet for 8 wk did not result in differences in blood indices associated with exercise stress or in the ability to perform a submaximal acute exercise test when compared with controls. Additionally, rats fed the vitamin E-free diet for 16 wk and rats fed the control diet for 16 wk did not differ in their ability to complete and adapt to a vigorous endurance running program.

Evaluates the effectiveness of ultrasound treatment and recovery after eccentric-exercise-induced muscle damage. Measurement of concentric and eccentric peak torques, resting elbow angle and subjective muscle soreness; Failure of daily ultrasound to influence recovery.

Examines the effect of ultrasound treatment on postexercise muscle strength recovery or soreness. Application of ultrasound in the treatment of soft tissue; Theoretical benefits of the nonthermal effects of ultrasound; Significant differences between four delayed onset muscle soreness measure in different conditions.