RESUMEN

Skeletal muscles contain several subtypes of myofibers that differ in contractile and metabolic properties. Transcriptional control of fiber-type specification and adaptation has been intensively investigated over the past several decades. Recently, microRNA (miRNA)-mediated posttranscriptional gene regulation has attracted increasing attention. MiR-23a targets key molecules regulating contractile and metabolic properties of skeletal muscle, such as myosin heavy-chains and peroxisome proliferator-activated receptor gamma, coactivator 1 alpha (PGC-1α). In the present study, we analyzed the skeletal muscle phenotype of miR-23a transgenic (miR-23a Tg) mice to explore whether forced expression of miR-23a affects markers of mitochondrial content, muscle fiber composition, and muscle adaptations induced by 4 weeks of voluntary wheel running. When compared with wild-type mice, protein markers of mitochondrial content, including PGC-1α, and cytochrome c oxidase complex IV (COX IV), were significantly decreased in the slow soleus muscle, but not the fast plantaris muscle of miR-23a Tg mice. There was a decrease in type IId/x fibers only in the soleus muscle of the Tg mice. Following 4 weeks of voluntary wheel running, there was no difference in the endurance exercise capacity as well as in several muscle adaptive responses including an increase in muscle mass, capillary density, or the protein content of myosin heavy-chain IIa, PGC-1α, COX IV, and cytochrome c. These results show that miR-23a targets PGC-1α and regulates basal metabolic properties of slow but not fast twitch muscles. Elevated levels of miR-23a did not impact on whole body endurance capacity or exercise-induced muscle adaptations in the fast plantaris muscle.

Asunto(s)

RESUMEN

Regular aerobic exercise accelerates post-exercise cardiovagal reactivation. However, little is known about the potentially favourable modulatory effects of regular aerobic exercise on cardiovagal reactivation in young female. The purpose of this study was to examine effects of regular aerobic exercise on post-exercise vagal reactivation in young female. Our study consisted of 8 female endurance-trained athletes (athlete group) and 10 untrained females (control group). Resting heart rate (HR), HR variability and post-exercise cardiovagal reactivation were measured during the subjects' early follicular (EF) and middle luteal (ML) phases. Post-exercise cardiovagal reactivation was estimated by T30: the time constant of HR decline for the first 30 s after the 4-min cycle ergometer exercise (intensity: 80% of ventilation threshold). In both groups, T30 was more accelerated in the EF phase than in the ML phase (P<0.05). In the EF phase, T30 was lower in the athletes than in the controls (P<0.05). A significant correlation between maximum oxygen uptake (VO2max) and T30 was observed in the EF phase (r=0.545, P<0.05). Our results suggest that regular aerobic exercise accelerates post-exercise cardiovagal reactivation in the EF phase in young female.

Asunto(s)

RESUMEN

Mammalian skeletal muscles undergo adaptation in response to changes in the functional demands upon them, involving mechanical-stress-induced cellular signaling called "mechanotransduction." We hypothesized that p130Cas, which is reported to act as a mechanosensor that transduces mechanical extension into cellular signaling, plays an important role in maintaining and promoting skeletal muscle adaptation in response to mechanical stress via the p38 MAPK signaling pathway. We demonstrate that muscle-specific p130Cas-/- mice express the contractile proteins normally in skeletal muscle. Furthermore, muscle-specific p130Cas-/- mice show normal mechanical-stress-induced muscle adaptation, including exercise-induced IIb-to-IIa muscle fiber type transformation and hypertrophy. Finally, we provide evidence that exercise-induced p38 MAPK signaling is not impaired by the muscle-specific deletion of p130Cas. We conclude that p130Cas plays a limited role in mechanical-stress-induced skeletal muscle adaptation.

Asunto(s)

RESUMEN

BACKGROUND: Dehydroepiandrosterone (DHEA) is precursor of sex steroid hormone. We demonstrated that acute DHEA injection to type 1 diabetes model rats induced improvement of hyperglycemia. However, the effect of the combination of DHEA administration and exercise training on insulin resistance is still unclear. This study was undertaken to determine whether 6-weeks of DHEA administration and/or exercise training improve insulin resistance in obese male rats. METHODS: After 14 weeks of a high-sucrose diet, obese male Wistar rats were assigned randomly to one of four groups: control, DHEA administration, exercise training, and a combination of DHEA administration and exercise training (n = 10 each group). RESULTS: After 6-weeks of DHEA administration and/or exercise training, rats in the combination group weighed significantly less and had lower serum insulin levels than rats in the other groups. Moreover, the rats treated with DHEA alone or DHEA and exercise had significantly lower fasting glucose levels (combination, 84 ± 6.5 mg/dL; DHEA, 102 ± 9.5 mg/dL; control, 148 ± 10.5 mg/dL). In addition, insulin sensitivity check index showed significant improvements in the combination group (combination, 0.347 ± 0.11; exercise, 0.337 ± 0.16%; DHEA, 0.331 ± 0.14; control, 0.308 ± 0.12). Muscular DHEA and 5α-dihydrotestosterone (DHT) concentrations were significantly higher in the combination group, and closely correlated with the quantitative insulin-sensitivity check index (DHEA: r = 0.71, p < 0.01; DHT: r = 0.69, p < 0.01). CONCLUSION: These results showed that a combination of DHEA administration and exercise training effectively improved fasting blood glucose and insulin levels, and insulin sensitivity, which may reflect increased muscular DHEA and DHT concentrations.

RESUMEN

This study examined the effects of amenorrhea on mucosal immune function and susceptibility to upper respiratory tract infection (URTI) in elite female distance runners. Based on their menstrual cycles during the prior year, 21 elite, collegiate, female distance runners were designated as eumenorrheic runners (ERs; n = 8; 19.9 ± 0.8 years) or amenorrheic runners (ARs; n n = 13; 20.0 ± 0.3 years). Resting saliva and blood samples were collected in the morning. The secretory immunoglobulin A (SIgA) concentration was measured using enzyme-linked immunosorbent assay. The SIgA secretion rate was calculated. Serum 17ß-estradiol concentrations and serum progesterone concentrations were measured using radioimmunoassay. Subjects reported the appearance of URTI symptoms (sore throat, headache, runny nose, coughing, or fever), if any, during the prior month. The serum estradiol concentration and salivary SIgA secretion rate were significantly lower for ARs than for ERs (p < 0.05). Serum progesterone concentration was not significantly different between groups. Higher frequencies of headache, runny nose, coughing, and fever were observed in ARs than in ERs. Results show that athletic amenorrhea with low estrogen might accelerate downregulation of mucosal immune function in athletes and enhance susceptibility to infection.

Asunto(s)

RESUMEN

The purpose of this study was to examine the effects of exercise training on age-related impairment of immune parameters related to T-cell activation in elderly individuals. Twenty-four elderly subjects were assigned to an exercise training group (EXC: 3 men, 9 women; age 61-76 years) or a nonexercise control group (CON: 4 men, 8 women; age 62-79 years). Subjects in EXC participated in exercise sessions 2 d·wk(-1) for 12 weeks. The training session included stretching and endurance exercise (10 minutes), resistance training comprised leg extension, leg press, hip abduction, and hip adduction using exercise machine and each subject's body weight. Subjects in CON maintained their normal physical activity levels during the study period. Blood samples were collected before and after the training period. Samples were measured for the numbers of leukocytes, lymphocytes, and monocytes, and for CD3(+), CD4(+), CD8(+), CD28(+)CD4(+), CD28(+)CD8(+), TRL-4(+)CD14(+), and CD80(+)CD14(+) cells. The number of leukocytes, lymphocytes, monocytes, CD3(+), CD4(+), and CD8(+) cells did not change after 12 weeks in either EXC or CON. The number of CD28(+)CD8(+) cells increased significantly after training in EXC (p ≤ 0.05), although CON showed no significant change. In the EXC group, CD80(+)CD14(+) cell counts were significantly higher after training (p ≤ 0.05), but the TLR-4(+)CD14(+) cell counts were unchanged. In the CON group, no significant alteration existed in TLR-4(+)CD14(+) and CD80(+)CD14(+) cell numbers. In conclusion, exercise training in elderly people is associated with increased CD28-expressing Tc cells and CD80-expressing monocytes. Therefore, exercise training might upregulate monocyte and T-cell-mediated immunity in elderly people.

Asunto(s)

RESUMEN

It is not known whether local androgen metabolism is involved in the mechanisms underlying the dehydroepiandrosterone (DHEA) administration-induced improvement of bone mineral density (BMD) in an estrogen-deficiency state. The aim of the present study was to clarify whether DHEA administration would improve local androgen metabolism and BMD in cancellous site of tibia of ovariectomized (OVX) rats. Twenty-two female rats, 6 weeks old, were randomized into three groups: sham-operated rats, OVX control rats, and OVX rats that received DHEA treatment. DHEA was administered intraperitoneally at 20 mg/kg body weight for 8 weeks. The concentrations of free testosterone and dihydrotestosterone (DHT) in cancellous site of tibia did not change as a result of ovariectomy, while the DHT concentration increased following DHEA administration. We revealed that DHEA administration improved the reduction of 17ß- and 3ß-hydroxysteroid dehydrogenases and clearly reversed the reduction of 5α-reductase types 1 and 2 and androgen receptor in the cancellous site of tibia of OVX rats. DHEA administration suppressed estrogen deficiency relative to the decrease in the cancellous BMD, which was positively associated with local DHT concentration. These findings indicate that DHEA administration enhances local bioactive androgen metabolism in the cancellous tibia of young OVX rats, suggesting that local DHT may play a part in the DHEA administration-induced improvement of cancellous BMD.

Asunto(s)

RESUMEN

PURPOSE: Endurance training improves skeletal muscular function including energy metabolism and structure. Sex steroid hormones partly contribute to the exercise-induced muscular adaptations. Recently, we demonstrated that skeletal muscle contains steroidogenic converting enzymes to synthesize sex steroid hormones and an acute endurance exercise activates local steroidogenesis in skeletal muscle. However, whether chronic endurance training leads to enhanced steroidogenesis in skeletal muscle is unknown. Here, we examined changes in steroidogenic enzymes and sex steroid hormones in the skeletal muscle after chronic endurance exercise training. METHODS: Eleven male rats were divided into two groups: sedentary (n = 6) and trained (n = 5). Endurance training was performed on a treadmill (30 m·min(-1), 30 min) for 5 d·wk(-1) for 12 wk. The posttraining harvesting was performed 48 h after the last exercise training. RESULTS: The mRNA expressions of 3ß-HSD, aromatase cytochrome P450, and 5α-reductase in the skeletal muscle of trained rats were significantly higher than those of sedentary rats (P < 0.05). The protein expressions of aromatase cytochrome P450 and 5α-reductase in the skeletal muscle of trained rats were also significantly higher than those of sedentary rats (P < 0.05). The muscular dihydrotestosterone (DHT) concentrations in the skeletal muscle of trained rats were significantly higher than those of sedentary rats (P < 0.01), but there was no change in dehydroepiandrosterone, total testosterone, free testosterone, and estradiol. Furthermore, muscle weight corrected for body weight of trained rats was moderately correlated with the level of muscular DHT concentration in trained rats (r = 0.41, P < 0.05). CONCLUSIONS: Endurance exercise training enhances the muscular DHT concentration through 5α-reductase in the skeletal muscle of rats, suggesting that local bioactive androgen metabolism may participate in exercise training-induced skeletal muscular adaptation.

Asunto(s)

RESUMEN

The purpose of this study was to examine weight loss effects on immune function in judo athletes. Six elite male Japanese judo athletes (20.3 ± 0.4 years) were enrolled in this study. They completed usual weight loss programs during 2 weeks preceding an actual competition. Subjects noted the appearance of upper-respiratory tract infection (URTI) symptoms during the study period. Blood samples were obtained at 40 (baseline period: BL) and 3 (weight loss period: WL) days before and 1 day after the competition (AC). The CD3, CD4, CD8, CD56CD3, CD28CD4, CD28CD8, and Toll-like-receptor-4 (TLR-4) CD14 cells were counted by using flow cytometer analysis. The 6 subjects reported 1 headache, 3 runny nose conditions, and 1 coughing instance during the WL. The CD3, CD4, CD8, and CD28CD4 cell counts were significantly lower at WL than at BL (p ≤ 0.05); they reverted to the baseline value at AC. The TLR-4CD14 cells were significantly fewer at WL (p ≤ 0.05); they remained fewer than they had been at BL, even at AC. These results suggest that 2 weeks of weight loss before a competition can impair cell-mediated immune function and induce high susceptibility to URTI in judo athletes. Coaches, support staff, and athletes should monitor athletes' weight loss, hydration status, appearance of URTI symptoms, and immunocompetence such as lymphocytes and monocytes to prevent the physical condition from becoming worse.

Asunto(s)

RESUMEN

This study was undertaken to assess the effects of dehydroepiandrosterone (DHEA) administration and exercise training on muscular DHEA and 5α-dihydrotestosterone (DHT) levels and hyperglycemia in diet-induced obese and hyperglycemic rats. After 14 wk of a high-sucrose diet, obese male Wistar rats were assigned randomly to one of three 6-wk regimens: control, DHEA treatment, or exercise training (running at 25 m/min for 1 h, 5 days/wk; n = 10 each group). Results indicate that either 6 wk of DHEA treatment or exercise training significantly attenuated serum insulin and fasting glucose levels compared with the control group. Plasma and muscle concentrations of DHEA and DHT and expression levels of 5α-reductase were significantly higher in the DHEA-treated and exercise-training groups. Moreover, both DHEA administration and exercise training upregulated GLUT4 translocation with concomitant increases in protein kinase B and protein kinase Cζ/λ phosphorylation. Muscle DHEA and DHT concentrations closely correlated with blood glucose levels (DHEA treatment: r = -0.68, P < 0.001; exercise training: r = -0.65, P < 0.001), serum insulin levels, and activation of the GLUT4-regulated signaling pathway. Thus, increased levels of muscle sex steroids may contribute to improved fasting glucose levels via upregulation of GLUT4-regulated signaling in diet-induced obesity and hyperglycemia.

Asunto(s)

RESUMEN

PURPOSE: To investigate the effect of menstrual cycle states on ovarian and anabolic hormonal responses to acute resistance exercise in young women. METHODS: Eight healthy women (eumenorrhea; EM) and eight women with menstrual disorders including oligomenorrhea and amenorrhea (OAM) participated in this study. The EM group performed acute resistance exercises during the early follicular (EF) and midluteal (ML) phases, and the OAM group performed the same exercises. All subjects performed three sets each of lat pull-downs, leg curls, bench presses, leg extensions, and squats at 75%-80% of one-repetition maximum with a 1-min rest between sets. Blood samples were obtained before exercise, immediately after, 30 min after, and 60 min after the exercise. RESULTS: In the EM group, resting serum levels of estradiol and progesterone in the ML phase were higher than those in the EF phase and higher than those in the OAM group. Serum estradiol and progesterone in the ML phase increased after the exercise but did not change in the EF phase or in the OAM group. In contrast, resting levels of testosterone in the OAM group were higher than those in both the ML and EF phases of the EM group. After the exercise, serum growth hormone increased in both the ML and EF phases but did not change in the OAM group. CONCLUSIONS: The responses of anabolic hormones to acute resistance exercise are different among the menstrual cycle states in young women. Women with menstrual disturbances with low estradiol and progesterone serum levels have an attenuated anabolic hormone response to acute resistance exercise, suggesting that menstrual disorders accompanying low ovarian hormone levels may affect exercise-induced change in anabolic hormones in women.

Asunto(s)

RESUMEN

Androgens, such as testosterone, play important roles in regulation of diverse physiological process of target tissues. Recently, we reported that steroidogenic enzymes exist in skeletal muscle and regulate local production of testosterone in response to exercise. Testosterone is transformed into a bioactive androgen metabolite, dihydrotestosterone (DHT) by 5alpha-reductase. However, it is unclear whether exercise stimulates local bioactive androgen metabolism in the skeletal muscle in both sexes. In the present study, we examined sex differences in the levels of dehydroepiandrosterone (DHEA), free testosterone, DHT, and steroidogenesis-related enzymes 5alpha-reductase and androgen receptor (AR) in rat's skeletal muscle before and after a single bout of exercise. Basal muscular free testosterone and DHT levels were higher in males than females, whereas the levels of DHEA did not differ between the sexes. Muscular DHEA, free testosterone, and DHT levels were increased in both sexes after the exercise. There were no differences of 5alpha-reductase and AR transcripts and proteins between the sexes, and the expression of 5alpha-reductase was significantly increased in both sexes after the exercise. Finally, the expression of AR was significantly higher in female rats, but not in males after the exercise. These data suggest that acute exercise enhances the local bioactive androgen metabolism in the skeletal muscle of both sexes.

Asunto(s)

RESUMEN

In men, regular aerobic exercise increases central arterial elasticity, but it is decreased by resistance training. We determined the relation between the type of exercise training and arterial elasticity in healthy young women: 26 healthy young women who were sedentary (CO, n = 9), endurance-trained (ET, n = 9), and resistance-trained (RT, n = 8) groups. We determined the carotid arterial compliance and distensibility coefficient (simultaneous ultrasound and applanation tonometry), VO(2max), and 1RM (bench press and leg extension). The VO(2max) in the ET groups was higher than in the CO and RT groups. Both 1RM were higher in the RT groups than in the CO and ET groups. No significant difference was found in the carotid artery compliance and distensibility coefficient among the ET, RT, and CO groups. These results underscore the difficulty in detecting a change in arterial elasticity in young female athletes using the type of exercise training by which it is shown in young men.

Asunto(s)

RESUMEN

Circulating dehydroepiandrosterone (DHEA) is converted to testosterone or estrogen in the target tissues. Recently, we demonstrated that skeletal muscles are capable of locally synthesizing circulating DHEA to testosterone and estrogen. Furthermore, testosterone is converted to 5alpha-dihydrotestosterone (DHT) by 5alpha-reductase and exerts biophysiological actions through binding to androgen receptors. However, it remains unclear whether skeletal muscle can synthesize DHT from testosterone and/or DHEA and whether these hormones affect glucose metabolism-related signaling pathway in skeletal muscles. We hypothesized that locally synthesized DHT from testosterone and/or DHEA activates glucose transporter-4 (GLUT-4)-regulating pathway in skeletal muscles. The aim of the present study was to clarify whether DHT is synthesized from testosterone and/or DHEA in cultured skeletal muscle cells and whether these hormones affect the GLUT-4-related signaling pathway in skeletal muscles. In the present study, the expression of 5alpha-reductase mRNA was detected in rat cultured skeletal muscle cells, and the addition of testosterone or DHEA increased intramuscular DHT concentrations. Addition of testosterone or DHEA increased GLUT-4 protein expression and its translocation. Furthermore, Akt and protein kinase C-zeta/lambda (PKC-zeta/lambda) phosphorylations, which are critical in GLUT-4-regulated signaling pathways, were enhanced by testosterone or DHEA addition. Testosterone- and DHEA-induced increases in both GLUT-4 expression and Akt and PKC-zeta/lambda phosphorylations were blocked by a DHT inhibitor. Finally, the activities of phosphofructokinase and hexokinase, main glycolytic enzymes, were enhanced by testosterone or DHEA addition. These findings suggest that skeletal muscle is capable of synthesizing DHT from testosterone, and that DHT activates the glucose metabolism-related signaling pathway in skeletal muscle cells.

Asunto(s)

RESUMEN

Sex steroid hormones, such as testosterone and estradiol, play important roles in developing both strength and mass of skeletal muscle. Recently, we demonstrated that skeletal muscle can synthesize sex steroid hormones. Whether there are sex differences in basal steroidogenesis or acute exercise-induced alterations of steroidogenesis in the skeletal muscle is unknown. We examined sex differences in the levels of testosterone, estradiol, and steroidogenesis-related enzymes, such as 17beta-hydroxysteroid dehydrogenase (HSD), 3beta-HSD, and aromatase cytochrome P-450 (P450arom), in the skeletal muscle at rest and after exercise. We studied the gastrocnemius muscles of resting rats (10 wk old) and exercised rats (10 wk old, treadmill running, 30 m/min, 30 min). Basal muscular testosterone levels were higher in males than females, whereas estradiol did not differ between sexes. Additionally, 17beta-HSD, 3beta-HSD, and P450arom transcript and protein expression were greater in females. After acute exercise, testosterone levels and 17beta-HSD expression increased in muscle in both sexes. By comparison, muscular estradiol levels increased in males following exercise but were unchanged in females. Expression of P450arom, which regulates estrogen synthesis, increased after acute exercise in males but decreased after exercise in females. Thus a single bout of exercise can influence the steroidogenic system in skeletal muscle, and these alterations differ between sexes. The acute exercise-induced alteration of steroidogenic enzymes may enhance the local steroidogenesis in the skeletal muscle in both sexes.

Asunto(s)

RESUMEN

The functional importance of sex steroid hormones (testosterone and estrogens), derived from extragonadal tissues, has recently gained significant appreciation. Circulating dehydroepiandrosterone (DHEA) is peripherally taken up and converted to testosterone by 3beta-hydroxysteroid dehydrogenase (HSD) and 17beta-HSD, and testosterone in turn is irreversibly converted to estrogens by aromatase cytochrome P-450 (P450arom). Although sex steroid hormones have been implicated in skeletal muscle regulation and adaptation, it is unclear whether skeletal muscles have a local steroidogenic enzymatic machinery capable of metabolizing circulating DHEA. Thus, here, we investigate whether the three key steroidogenic enzymes (3beta-HSD, 17beta-HSD, and P450arom) are present in the skeletal muscle and are capable of generating sex steroid hormones. Consistent with our hypothesis, the present study demonstrates mRNA and protein expression of these enzymes in the skeletal muscle cells of rats both in vivo and in culture (in vitro). Importantly, we also show an intracellular formation of testosterone and estradiol from DHEA or testosterone in cultured muscle cells in a dose-dependent manner. These findings are novel and important in that they provide the first evidence showing that skeletal muscles are capable of locally synthesizing sex steroid hormones from circulating DHEA or testosterone.

Asunto(s)

RESUMEN

This study examined changes among young females of resting serum dehydroepiandrosterone sulfate (DHEAS) concentration after an 8-week period of resistance training. Nineteen healthy untrained young females [training group: age 18.9 (0.3) years, n=10, control group: age 19.3 (1.0) years, n=9; mean (SD)] were recruited in this study. The training group participated in an 8-week resistance training program (2 days per week on nonconsecutive days). The control group did not involve in any resistance training or regular exercise during the study period. Muscular strength, anthropometry, and resting hormonal levels were measured before and after training in both groups. Serum concentrations of DHEAS, dehydroepiandrosterone (DHEA), testosterone and cortisol were measured by radioimmunoassay. Body mass (2.4%) and lean body mass (2.4%) were significantly increased in the training group ( P<0.05), but not in the control group. The training also significantly increased one-repetition maximum (1-RM) values ( P<0.05). In the training group, resting concentration of serum DHEAS significantly increased after training ( P<0.05). Percent change of DHEAS in the training group was greater than that of the control group ( P<0.05). In the training group, the change of DHEAS level was positively correlated with the change of lean body mass during the training ( r=0.61; P<0.05). Serum DHEA, testosterone and cortisol concentrations did not change in either group during the training. The dramatic increase of resting serum DHEAS concentration after training indicates that DHEAS might be an anabolic hormone marker of adaptation to resistance training among young females. Results are presented as mean (SD).

Asunto(s)

RESUMEN

INTRODUCTION: Acupuncture is used to modulate the physical well-being of athletes in Asian countries. However, there is little information on the immediate effects of acupuncture treatment on physiological or psychological responses to exercise. PURPOSE: The purpose of this study was to examine the effect of acupuncture treatment on the physical well-being of elite female soccer players during a competition period. METHODS: Subjects were divided into two groups: those who received acupuncture treatment (18.1 +/- 2.3 yr [+/-SD], N = 9) and a control group (17.7 +/- 2.8 yr, N = 12). In the treatment group, acupuncture stimulus was applied at LI 4 (Goukoku), ST 36 (Ashi-sanri) for 20 min, and ST 6 (Kyosya), LU 6 (Ko-sai) points for 15 min 4 h after the game every night during the competition period. The measured parameters included salivary secretory immunoglobulin A (SIgA) level, cortisol level in saliva, subjective rating of physical well-being, and profile of mood states (POMS). RESULTS: The following were the main results: 1). Exercise-induced decrease of salivary SIgA and increase of salivary cortisol were inhibited by acupuncture. 2). Acupuncture improved subjective rating of muscle tension and fatigue. 3). The POMS score was modulated by acupuncture. CONCLUSION: These results support the effectiveness of acupuncture for physical and mental well-being of athletes.

Asunto(s)