RESUMEN
Apoptosis has been implicated in mediating denervation-induced muscle wasting. In this study we determined the effect of interference of apoptosis on muscle wasting during denervation by using mice genetically deficient in pro-apoptotic Bax. After denervation, muscle wasting was evident in both wild-type and Bax(-/-) muscles but reduction of muscle weight was attenuated in Bax(-/-) mice. Apoptotic DNA fragmentation increased in wild-type denervated muscles whereas there was no statistical increase in DNA fragmentation in denervated muscles from Bax(-/-) mice. Mitochondrial AIF and Smac/DIABLO releases and Bcl-2, p53 and HSP27 increased whereas XIAP and MnSOD decreased to a similar extent in muscles from wild-type and Bax(-/-) mice following denervation. Mitochondrial cytochrome c release was elevated in denervated muscles from wild-type mice but the increase was suppressed in muscles from Bax(-/-) mice. Increases in caspase-3 and -9 activities and oxidative stress markers H(2)O(2), MDA/4-HAE and nitrotyrosine were all evident in denervated muscles from wild-type mice but these changes were absent in muscles from Bax(-/-) mice. Moreover, ARC increased exclusively in denervated Bax(-/-) muscle. Our data indicate that under conditions of denervation, pro-apoptotic signalling is suppressed and muscle wasting is attenuated when the Bax gene is lacking. These findings suggest that interventions targeting apoptosis may be valuable in ameliorating denervation-associated pathologic muscle wasting in certain neuromuscular disorders that involve partial or full denervation.
Asunto(s)
Apoptosis/genética , Desnervación , Proteína X Asociada a bcl-2/genética , Animales , Ratones , Ratones Endogámicos C57BL , Proteína X Asociada a bcl-2/deficienciaRESUMEN
Skeletal muscle is a highly plastic tissue. For example, muscle hypertrophies during strength training and increases its oxidative capacity in response to endurance training. Conditions associated with disuse, however, are also accompanied by adaptations, of which atrophy and a slow-to-fast transition are most prominent. Fast and slow muscles respond differently to disuse. The different response of muscle to different models of disuse reveals that loading is most important, but that also activity level, neurotrophic factors, and ageing play a part in determining the mass, morphology, contractile properties, and fatigability of a muscle. Muscle loss during disuse is a result, at least in part, of apoptosis. Finally, skeletal muscle wasting and remodelling during ageing and chronic disorders, such as chronic heart failure and chronic obstructive pulmonary disease, are not entirely attributable to disuse, but are also related to secondary consequences of the disease, most notably inflammation. Besides activating other pathways, we present evidence that inflammation during ageing and chronic disorders causes muscle wasting via alterations in abundance and/or activity of muscle specific transcription factors and induction of apoptosis, and that systemic inflammation rather than disuse is the primary cause of muscle wasting during ageing and chronic disorders.
Asunto(s)
Envejecimiento/fisiología , Músculo Esquelético/anatomía & histología , Músculo Esquelético/patología , Atrofia Muscular/fisiopatología , Anciano , Animales , Apoptosis/fisiología , Modelos Animales de Enfermedad , Fatiga/fisiopatología , Insuficiencia Cardíaca/complicaciones , Humanos , Inmovilización/fisiología , Modelos Biológicos , Atrofia Muscular/etiología , Atrofia Muscular/patología , Tamaño de los Órganos/fisiología , Enfermedad Pulmonar Obstructiva Crónica/complicacionesRESUMEN
Eccentric biased exercise has been reported to elicit more muscle injury than concentric or isometric exercise and potentially generate increased oxidative stress one to two days post exercise. Increased oxidative stress has been shown to up-regulate the expression of UCP3 mRNA. The aim of this study was to investigate the effects of downhill running on skeletal muscle UCP3 mRNA expression. Twenty-four male Sprague Dawley rats were randomly assigned to run continuously for 30 minutes (30-C, n = 6), or run six 5-minute bouts separated by rest periods of 2 minutes (2-R, n = 6), 4 minutes (4-R, n = 6), and 6 minutes (6-R, n = 6) on a 16 degree declined treadmill at a speed of 16 m. min (-1). Sham control animals (n = 8) were placed in a treadmill chamber during the 30-minute run session. Semi-quantitative RT-PCR was conducted to evaluate UCP3 mRNA levels in the plantaris, a muscle used eccentrically during downhill running and tibialis anterior, a muscle which undergoes very little eccentric muscle contraction during this exercise. The level of gene expression was normalized to 18 S ribosomal mRNA expression from the same PCR product. Results are reported as mean +/- standard error. UCP3 of the plantaris muscles from 2-R animals (2.36 +/- 0.13) was significantly greater than UCP3 of the plantaris from control animals (1.72 +/- 0.13), p < 0.05. UCP3 of the tibialis anterior from the continuous group (1.51 +/- 0.17) was significantly less than the UCP3 of the tibialis anterior of the control group (2.09 +/- 1.4), p < 0.05. These data suggest that downhill treadmill running is associated with an increase in UCP3 mRNA expression in the plantaris muscle. These results indicate that exercise which is biased toward eccentric exercise may up-regulate UCP3 mRNA during the period post exercise when muscle damage and repair is elevated.
Asunto(s)
Proteínas Portadoras/genética , ARN Mensajero/metabolismo , Carrera/fisiología , Animales , Prueba de Esfuerzo , Expresión Génica , Canales Iónicos , Masculino , Proteínas Mitocondriales , Músculo Esquelético/metabolismo , ARN Mensajero/genética , Distribución Aleatoria , Ratas , Ratas Sprague-Dawley , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Proteína Desacopladora 3RESUMEN
Embalmed cadaver tissues and organs that are dissected in gross anatomy laboratories lack many characteristics of fresh or living tissues. The purpose of this study was to assess the educational value of allowing first-year medical students to experience first-hand the color, texture, delicacy and other qualities of living porcine tissues and organs that are similar to those of human tissues. Guided by a laboratory protocol, medical students palpated and inspected organs of the opened thorax, abdomen and pelvis of anesthetized pigs on pulmonary ventilators. The learning experience was rated highly by the students as well as by the participating faculty. A further review of the medical students' later experiences at autopsies and in surgical clerkships showed that the living-tissue experience in their gross anatomy course represented a large part of their medical school exposure to unembalmed tissues.
Asunto(s)
Anatomía/educación , Educación de Pregrado en Medicina/métodos , Evaluación Educacional , Enseñanza/métodos , Abdomen/anatomía & histología , Animales , Humanos , Modelos Animales , Pelvis/anatomía & histología , Porcinos , Tórax/anatomía & histologíaRESUMEN
In this study we tested the hypothesis that, compared to young adult rats, senescent rats have a reduced ability to respond to muscle unloading. Unloading of the muscles was induced by hindlimb suspension (HS) of young adult and senescent rats for 21 days. Plantaris muscles from young adult rats had significantly higher levels of myogenin mRNA and protein (890 % and 314 %, respectively, P < 0.05) than plantaris muscles from senescent rats and also a higher MyoD mRNA level (280 %, P < 0.05), but ageing did not increase MyoD protein levels. Although HS did not increase plantaris mRNA or protein levels of myogenin or MyoD in senescent rats (P = 0.22), myogenin mRNA and protein levels increased by 850 % and 580 % respectively, and MyoD mRNA and protein levels by 235 % and 1600 %, respectively in young adult rats (P < 0.05). Soleus muscles from senescent rats had 150 % and 85 % greater myogenin and MyoD mRNA levels, respectively (P < 0.05), than soleus muscles from young adult rats, whereas protein levels of myogenin were similar (P > 0.05) and MyoD protein levels were 60 % lower in the muscle of senescent rats (P < 0.05). In young rats, soleus muscle mRNA levels of myogenin and MyoD were not altered by HS but myogenin protein levels decreased by 57 % (P < 0.05) whereas MyoD protein levels increased by 187 % (P < 0.05). In senescent rats, HS decreased soleus muscle myogenin mRNA and protein levels by 42 % and 26 % respectively (P < 0.05), but MyoD protein and mRNA levels were not changed. MRF4 levels were not affected by ageing in either muscle. These data suggest that ageing reduces the ability of fast muscles to increase myogenin protein levels, and prevents both fast and slow muscles from increasing MyoD protein levels during muscle unloading. Experimental Physiology (2001) 86.4, 509-517.
Asunto(s)
Envejecimiento/metabolismo , Suspensión Trasera/fisiología , Músculo Esquelético/fisiología , Proteína MioD/genética , Miogenina/genética , Animales , Western Blotting , Peso Corporal , Expresión Génica/fisiología , Masculino , Fibras Musculares de Contracción Rápida/química , Fibras Musculares de Contracción Rápida/fisiología , Fibras Musculares de Contracción Lenta/química , Fibras Musculares de Contracción Lenta/fisiología , Músculo Esquelético/citología , Proteína MioD/análisis , Miogenina/análisis , ARN Mensajero/análisis , Ratas , Ratas Endogámicas BN , Ratas Endogámicas F344 , Soporte de Peso/fisiologíaRESUMEN
High levels of clenbuterol have been shown to preserve muscle mass and function during disuse. In this study we report that a low dose of clenbuterol (10 microg/kg per day) lessened the loss of in situ soleus muscle isometric force normalized to wet muscle weight (P(o)/g wet weight) by 8% and reduced isometric fatigue by approximately 30% in senescent rats after 21 days of hindlimb suspension (HS). Clenbuterol did not reduce the loss of relative force in the soleus of adult rats or the plantaris of old or adult rats. Furthermore, clenbuterol failed to improve muscle force or isometric fatigue in the soleus of adult rats or in the plantaris of either age group after HS. We conclude that low levels of clenbuterol reduce muscle fatigue in slow muscles during disuse and this beta-agonist may also have therapeutic value for reducing fatigue in slow muscles (e.g., postural muscles) in the elderly during disuse.
Asunto(s)
Agonistas Adrenérgicos beta/farmacología , Envejecimiento/fisiología , Clenbuterol/farmacología , Fatiga Muscular/efectos de los fármacos , Músculo Esquelético/efectos de los fármacos , Animales , Peso Corporal/efectos de los fármacos , Ingestión de Alimentos/efectos de los fármacos , Contracción Isométrica/efectos de los fármacos , Masculino , Contracción Muscular/efectos de los fármacos , Fibras Musculares de Contracción Rápida/efectos de los fármacos , Tamaño de los Órganos/efectos de los fármacos , Ratas , Ratas Endogámicas F344RESUMEN
Supraphysiological levels of clenbuterol (CL) reduce muscle degradation in both young and old animals; however, these pharmacological levels induce side effects that are unacceptable in the elderly. In this study, we tested the hypothesis that a "physiological" dose of CL (10 microg. kg(-1). day(-1)) would attenuate the loss of in situ isometric force and mass in muscles of senescent rats during hindlimb suspension (HS). Adult (3 mo) and senescent (38 mo) Fischer 344 x Brown Norway rats received CL or a placebo during 21 days of normal-weight-bearing or HS conditions (8 rats/age group). HS reduced soleus muscle weight-to-body weight ratio by 31%, muscle cross-sectional area by 37%, and maximal isometric tetanic force (P(o)) by 76% in senescent rats. CL attenuated the loss of P(o) and muscle weight by 17 and 8%, respectively, in the soleus of senescent rats relative to HS+placebo conditions, but it did not improve muscle weight normalized for body weight. CL did not reduce the decrease in soleus P(o) or mass after HS in adult rats. CL failed to reduce the loss of plantaris weight (-20%) and P(o) (-46%) in senescent rats after HS. Our data support the conclusion that physiological levels of CL do not improve fast muscle atrophy and only modestly reduce slow muscle atrophy, and, therefore, it is largely an ineffective countermeasure for preventing muscle wasting from HS in senescent rats.
Asunto(s)
Agonistas Adrenérgicos beta/farmacología , Envejecimiento/fisiología , Clenbuterol/farmacología , Desarrollo de Músculos , Músculo Esquelético/efectos de los fármacos , Músculo Esquelético/crecimiento & desarrollo , Atrofia Muscular/prevención & control , Animales , Peso Corporal/efectos de los fármacos , Peso Corporal/fisiología , Contracción Isométrica/efectos de los fármacos , Contracción Isométrica/fisiología , Masculino , Contracción Muscular/efectos de los fármacos , Contracción Muscular/fisiología , Proteínas Musculares/metabolismo , Músculo Esquelético/metabolismo , Atrofia Muscular/fisiopatología , Cadenas Pesadas de Miosina/metabolismo , Tamaño de los Órganos/efectos de los fármacos , Tamaño de los Órganos/fisiología , ARN/biosíntesis , Ratas , Ratas Endogámicas BN , Ratas Endogámicas F344RESUMEN
Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA, protein, and enzyme activity levels in hindlimb muscles of adult and senescent Fischer 344 x Brown Norway rats were investigated. Soleus muscles from adult and senescent rats had similar levels of GAPDH. In contrast, muscles containing a large proportion of glycolytic fibers had lower GAPDH levels in senescent rats relative to these muscles in adult rats; this was observed at both the mRNA and protein levels. These data indicate that skeletal muscle glycolytic capacity of fast muscles is diminished with age and that it may be caused by changes at the level of transcription. Also, because GAPDH mRNA levels change with age in several rat muscles, GAPDH mRNA is not always a proper internal control for mRNA analyses of aging skeletal muscle.
Asunto(s)
Envejecimiento/metabolismo , Gliceraldehído-3-Fosfato Deshidrogenasas/genética , Gliceraldehído-3-Fosfato Deshidrogenasas/metabolismo , Glucólisis/fisiología , Animales , Western Blotting , Regulación Enzimológica de la Expresión Génica/fisiología , Gliceraldehído-3-Fosfato Deshidrogenasas/análisis , Masculino , Músculo Esquelético/enzimología , ARN Mensajero/análisis , Ratas , Ratas Endogámicas F344RESUMEN
The objectives of these studies were to determine if (1) hypertrophy-stimulated myogenic regulatory factor (MRF) mRNA increases occur in the absence of proliferating satellite cells, and (2) acute hypertrophy occurs without satellite cell proliferation. Adult and aged quails were exposed to 0 or 2500 Rads gamma irradiation, and then wing muscles were stretch-overloaded for 3 or 7 days. MRF mRNA levels in stretch-overloaded and contralateral anterior latissimus dorsi (ALD) muscles were determined after 3 days; hypertrophy was determined after 7 days. The elimination of proliferating cells in irradiated muscles was verified histologically by bromodeoxyuridine incorporation. Relative levels of MRF4, MyoD, and myogenin mRNA were elevated 100%-400% in stretch-overloaded ALD muscles from irradiated adult quails indicating that satellite cell proliferation was not a prerequisite for MRF mRNA increases. Myogenin was the only MRF that exhibited mRNA increases that were lowered by irradiation. This suggests that satellite cells contribute only to myogenin mRNA increases in non-irradiated adult muscles following 3 days of stretch-overload. Stretch-overloaded ALD muscles from aged quails had a relative increase in myogenin mRNA of approximately 150%. The myogenin increase was the same in non-irradiated and irradiated aged animals and also the same as that in stretch-overloaded muscles from irradiated adult quails. Together, these data indicate that attenuated increases in MRF expression in muscles from aged animals are attributable to lower satellite cell MRF expression. ALD muscle masses and protein contents in adult irradiated quails approximately doubled after 7 days of stretch-overload demonstrating hypertrophy despite the elimination of satellite cell proliferation.
Asunto(s)
Músculo Esquelético/metabolismo , Músculo Esquelético/patología , Proteína MioD/biosíntesis , Factores Reguladores Miogénicos/biosíntesis , Miogenina/biosíntesis , Animales , División Celular , Coturnix , Hipertrofia , Fibras Musculares de Contracción Lenta/metabolismo , Fibras Musculares de Contracción Lenta/patología , ARN Mensajero/análisis , Estrés MecánicoRESUMEN
Twenty-one women aged 60-75 years were examined to determine whether combined endurance and strength training resulted in greater increase in peak oxygen consumption, sub-maximal time to fatigue, cardiac output, stroke volume, and leg extension load when compared to endurance training alone. Subjects in both the endurance training (E) and endurance and strength (E & S) groups trained 3 days a week, for 12 weeks, at an intensity of 70-80% Vo2 peak for 30 min on a cycle ergometer. Subjects in the E & S groups also used resistance equipment to train the knee extensors. The workload for resistance training was based on an initial assessment of 10 repetitions maximum (10 RM), with 80% of that value used for training, three times weekly. Peak oxygen consumption increased to an average of 24.8 and 29.9% in the E and E & S groups, respectively, with no difference between groups. Subjects in the E & S and E groups significantly increased sub-maximal endurance time by 396 and 165%, respectively. Cardiac output, stroke volume, and arteriovenous oxygen difference at 80% peak VO2 were unchanged by either of the training methods. A needle biopsy was taken from the vastus lateralis before and after 12 weeks of training. Chi-square analysis of fibre area data showed an increase in the frequency of larger type I fibres in the post-training data from the E & S group, but an increase in the frequency of smaller fibres in the E group post-training; however, mean fibre area was not significantly changed by training. These data suggest that greater improvements in sub-maximal time to fatigue and strength is achieved when resistance training is added to an aerobic training programme in healthy elderly women.
Asunto(s)
Adaptación Fisiológica/fisiología , Envejecimiento/fisiología , Gasto Cardíaco/fisiología , Tolerancia al Ejercicio/fisiología , Músculo Esquelético/fisiología , Levantamiento de Peso/fisiología , Anciano , Citrato (si)-Sintasa/metabolismo , Prueba de Esfuerzo , Femenino , Humanos , Pierna/fisiología , Persona de Mediana Edad , Fibras Musculares Esqueléticas/enzimología , Fibras Musculares Esqueléticas/patología , Fibras Musculares Esqueléticas/fisiología , Músculo Esquelético/enzimología , Músculo Esquelético/patología , Oximetría , Oxígeno/sangre , Consumo de Oxígeno , Volumen Sistólico/fisiologíaRESUMEN
Myogenic regulatory factors (MRFs) are a family of skeletal muscle-specific transcription factors that regulate the expression of several muscle genes. This study was designed to determine whether MRF transcripts were increased in hypertrophy-stimulated muscle of adult quails and whether equivalent increases occurred in muscles of older quails. Slow-tonic anterior latissimus dorsi and fast-twitch patagialis muscles of adult, middle-aged, aged, and senescent quails were stretch overloaded for 6, 24, or 72 h, with contralateral muscles serving as controls. RNase protection assays showed that MRF4 and MyoD transcript levels were increased and myogenin and Myf5 transcripts were induced in stretch-overloaded muscles. However, MRF4 and MyoD increases were significantly attenuated in patagialis muscles of older quails. RT-PCR analyses of three MRF-regulated genes showed that increases in the transcription of these genes occurred with stretch overload, but the increases were less in muscles of older quails. In summary, attenuated MRF responses in muscles from aged animals may partially explain why muscles from older animals do not hypertrophy to the same extent as muscles from younger animals.
Asunto(s)
Envejecimiento/fisiología , Proteínas de Unión al ADN , Regulación del Desarrollo de la Expresión Génica , Fibras Musculares de Contracción Rápida/fisiología , Proteínas Musculares/biosíntesis , Músculo Esquelético/fisiología , Factores Reguladores Miogénicos/biosíntesis , Transactivadores , Transcripción Genética , Animales , Coturnix , Creatina Quinasa/biosíntesis , Desmina/biosíntesis , Hipertrofia , Isoenzimas , Desarrollo de Músculos , Fibras Musculares de Contracción Rápida/patología , Músculo Esquelético/crecimiento & desarrollo , Músculo Esquelético/patología , Proteína MioD/biosíntesis , Factor 5 Regulador Miogénico , Reacción en Cadena de la Polimerasa , Receptores Colinérgicos/biosíntesis , Factores de Transcripción/biosíntesisRESUMEN
The C-Myc oncoprotein was examined in anterior latissimus dorsi (ALD) muscles of young (6 weeks) and aged (90 weeks) quail after 0.5 hours to 14 days of stretch. Western analyses of nuclear extracts showed an increase in the C-Myc oncoprotein after 1 h of stretch in young adult birds, and C-Myc remained elevated for 3 days of stretch. The onset and total accumulation of the C-Myc oncoprotein was less in muscles from aged quail as compared to muscles from young adult birds. Immunocytochemical analyses showed that C-Myc was localized in nuclei and averaged 0.2 +/- 0.04 nuclei/muscles fiber cross-section (n/f) in control muscles. C-Myc immunopositive nuclei were more numerous in muscles from young adult birds (1.7 +/- 0.2 n/f) compared to aged birds (1.1 +/- 0.1 n/f) after 2-12 h of stretch. C-Myc positive nuclei declined to 0.7 +/- 0.1 n/f after 3 days of stretch, in muscles from young adult birds; however, this was greater than in muscles from aged birds at the same time point (0.3 +/- 0.04 n/f). Many nuclei that were associated with muscle fibers expressed the C-Myc oncoprotein but did not incorporate bromodeoxyuridine, a marker of DNA synthesis and activated satellite cells. These data show a decreased ability of skeletal muscles from aged quails to initiate a program inclusive of early C-Myc oncoprotein accumulation in response to stretch.
Asunto(s)
Envejecimiento/metabolismo , Músculo Esquelético/metabolismo , Proteínas Proto-Oncogénicas c-myc/metabolismo , Animales , Western Blotting , Peso Corporal , Bromodesoxiuridina/metabolismo , Coturnix , Inmunohistoquímica , Músculo Esquelético/anatomía & histología , Tamaño de los Órganos , Estrés Mecánico , Distribución TisularRESUMEN
Hypertrophic responses to stretch are attenuated in slow-tonic muscles from old quail, relative to young birds. It is not known if the age-associated differences would be similar in fast-twitch muscles after stretch. This study compared the effect of 30 days of stretch overload on slow beta fibers and fast-alpha fibers in patagialis (PAT) muscles from young adult (YA) quail aged 12 weeks, old adult (OA) quail aged 52 weeks and the oldest (OO) quail, aged 90 weeks. The PAT muscle was stretched for 7, 14, 21, or 30 days by a sleeve that was attached to one wing. Birds received a subcutaneously implanted 5'-bromo-2'-deoxyuridine (BrdU) pellet that provided a constant release of 0.22mg BrdU/g body wt/day to label nuclei that had undergone DNA synthesis during stretch. Fiber cross-sectional area (CSA) was determined by planimetry from slow beta and fast-alpha fibers after identification by myosin ATPase. Harris hematoxylin was used to identify muscle nuclei. Muscle mass increased by 44.1 +/- 3.1, 32.6 +/- 3.9 and 25.7 +/- 4.3% in YA, OA and OO birds, respectively. Slow-beta fiber hypertrophy was observed at day 7 of stretch in all birds; however, YA birds had greater hypertrophy than the older birds. Fast-alpha fibers were unaffected by stretch. No significant difference was observed between PAT muscles from OA and OO birds. Total fiber number was not significantly elevated in the PAT muscle from any age group after 30 days of stretch. Activated satellite cells were not detected in stretched muscles of either young or old birds. This suggests that the increase in mean slow-beta fiber CSA was potentiated by existing myonuclei rather than by recruiting additional nuclei.
Asunto(s)
Adaptación Fisiológica , Envejecimiento/patología , Núcleo Celular/fisiología , Coturnix/anatomía & histología , Fibras Musculares de Contracción Rápida/patología , Fibras Musculares de Contracción Lenta/patología , Envejecimiento/fisiología , Animales , Peso Corporal/fisiología , Hipertrofia , Fibras Musculares de Contracción Rápida/ultraestructura , Fibras Musculares de Contracción Lenta/ultraestructura , Tamaño de los Órganos/fisiologíaRESUMEN
The purpose of this study was to determine whether 8 wk of progressive resistance exercise training would produce increases in strength and changes in foreleg muscle characteristics indicative of hypertrophy in ponies. Two mature 3- to 6-yr-old, male ponies (188 +/- 16 kg) were taught to carry sheets of lead over their saddle region (wither) while walking on a level treadmill at 1.9 m.s-1. This initial familiarization period was followed by 8 wk of training (3 d per wk), in which the ponies performed a series of progressive sets of weight carrying to fatigue. Each workout started with a 2-min walk at 1.9 m.s-1 followed by sets of weight carrying. The ponies carried 44.5 kg for the first set with increases of 22.3 kg per set until fatigue. Weights were applied and then removed for 60-90 s between sets using a chain hoist and sling apparatus. Measurements of forelimb girth, body weight, and total weight carried were recorded at each workout session. Ultrasound measurement of the diameters of the superdigital flexor muscles and muscle biopsies were performed before and after the 8-wk training period. Eight weeks of resistance training resulted in significant increases in peak weight carried (260%, P < 0.05) and total weight carried (1525%, P < 0.05) during each workout. Forelimb girth increased 12 +/- 1% (P < 0.05) with a corresponding 19 +/- 3% (P < 0.05) increase in muscle cross-sectional diameter. There were no changes (P > 0.05) in Type I muscle fiber area; however, there was a nonsignificant 26% increase in Type IIA+IIB fiber area. These data suggest that 8 wk of progressive resistance exercise training increase strength and cause changes in muscle size and characteristics consistent with hypertrophy.
Asunto(s)
Músculo Esquelético/anatomía & histología , Músculo Esquelético/fisiología , Educación y Entrenamiento Físico/métodos , Animales , Caballos , Hipertrofia , Masculino , Modelos Biológicos , Músculo Esquelético/patología , Levantamiento de PesoRESUMEN
Plantar flexor torque was measured in 24 young (25 +/- 1.4 y) and older (62 +/- 2 y) untrained and endurance-trained men to test the hypothesis that age-associated declines in muscle function would be attenuated in older men who also endurance trained. Endurance-trained subjects averaged 7-9 h/wk of aerobic activity for 10-12 years. These subjects had not engaged in resistance training previously in the past 10 years. Plantar flexor torque was measured at velocities between 0 and 5.23 rads. s-1. In absolute terms, maximal isometric torque was 23% lower in older men compared to young men, regardless of their training status. On the other hand, relative measures of isometric strength (i.e., torque.muscle cross-sectional area-1 and torque.muscle volume-1) were similar in young and older men but were higher in trained than in untrained men. Isokinetic torque.muscle cross-sectional area-1 and torque.muscle volume-1 was greater at contraction velocities of 0.26-2.09 rads.s-1 for trained subjects. These data suggest that endurance training does not attenuate the age-associated loss of muscle mass or absolute strength. However, endurance training might reduce the extent of loss of relative strength because torque-muscle cross-sectional area-1 and torque.muscle volume-1 are greater in endurance-trained older men than in untrained older men.
Asunto(s)
Envejecimiento/fisiología , Músculo Esquelético/fisiología , Resistencia Física , Aptitud Física , Adulto , Humanos , Pierna , Masculino , Persona de Mediana EdadRESUMEN
Stretch overload-induced activation of satellite cells in the anterior latissimus dorsi (ALD) muscle was examined in full-grown adult (12 wk old) and aged (90 wk old) Japanese quail. 5'-Bromo-2'-deoxyuridine (BrdU) constant-release pellets (0.22 mg BrdU.g body wt-1.day-1) were implanted subcutaneously before weighting the left wing of each bird. Nuclei that incorporated BrdU were localized by immunohistochemistry after 1 or 2 wk of stretch overload. Total fiber number was quantified by counting all fibers in a histological cross section from the midbelly of the ALD. Aging reduced increases in ALD mass and fiber number during 2 wk of stretch overload. Fiber proliferation in the ALD of aged birds also demonstrated an altered time course. The percentage of BrdU-positive nuclei associated with muscle fibers and the percentage of fibers associated with BrdU-positive nuclei did not differ between age groups. The altered time course of new fiber formation in the ALD of aged birds during 2 wk of stretch overload does not appear to be related to the capability to activate satellite cells.
Asunto(s)
Envejecimiento/fisiología , Contracción Muscular , Fibras Musculares de Contracción Lenta/fisiología , Músculo Esquelético/fisiología , Animales , Coturnix , Fibras Musculares de Contracción Lenta/ultraestructura , Músculo Esquelético/anatomía & histología , Músculo Esquelético/citología , Alas de AnimalesRESUMEN
The purpose of this study was to determine if aged Japanese quail demonstrated an altered time course of change in the morphology of the anterior latissimus dorsi (ALD) muscle during the first two weeks of hypertrophy induced by stretch overload. The left wing of adult (12 weeks of age) and aged (90 weeks of age) birds were weighted with 10% of their body weight; the right wing served as the intra-animal control. Thirteen to sixteen birds from each age group were killed after 7 and 14 days of stretch overload. Total fiber number was quantified by counting all the fibers in a transverse section from the mid-belly of the ALD muscle. The aged ALD retained the ability to increase the mass and total fiber number of the stretched ALD after 7 (82%, 16%) and 14 (102%, 19%) days of stretch overload. However, there was a main effect of age on the capacity to increase muscle mass and total fiber number after stretch overload. These results suggest that aging diminishes the increase and alters the time course of adaptation in fiber number and myofibrillar mass of the stretch overloaded ALD during the first two weeks of stretch overload.
Asunto(s)
Adaptación Fisiológica , Envejecimiento/fisiología , Coturnix/fisiología , Contracción Muscular , Músculo Esquelético/patología , Músculo Esquelético/fisiología , Animales , Peso Corporal , Coturnix/anatomía & histología , Hipertrofia , Fibras Musculares de Contracción Rápida/ultraestructura , Fibras Musculares de Contracción Lenta/ultraestructura , Tamaño de los Órganos , Factores de Tiempo , Alas de AnimalesRESUMEN
We have previously found alterations in expression of native myosin isoforms during adaptations to 30 d of stretch-induced hypertrophy in the quail anterior latissimus dorsi muscle (ALD). However, myosin heavy and light chain expression have not been studied during adaptations to stretch. In the current study, expression of myosin heavy and light chains and native myosin isoforms were characterized after placing a weight on one wing of Japanese quail for 0, 7, 14, or 21 d (N = 8 birds.d-1). ALD muscle mass was significantly greater at days 14 (67.0 +/- 4.4%) and 21 (70.2 +/- 4.0%) of stretch compared to day 7 (53.6 +/- 2.9%) of stretch. Native slow myosin-2 (SM2) expression increased from 43.1 +/- 17% in control muscles to 55 +/- 1.2% in stretch muscles, relative to the total myosin pool. The increase in native SM2 expression (approximately 12%) was observed at all three time points of stretch. In contrast, native slow myosin-1 (SM1) expression significantly decreased from 34.1% +/- 1.7% in the control muscles to 24.6 +/- 1.2% in the stretch muscles, relative to the total myosin pool. There was an increased expression of slowly heavy chain-two (SHC2) concurrent with a downregulation of the slow heavy chain-1 (shc1). There was no change in the relative percentages of either slow or fast myosin light chains in overloaded muscles at any of the time points following stretch. These results demonstrate that changes in myosin heavy chain expression, but not myosin light chain expression accompany stretch-induced hypertrophy in the quail ALD.
Asunto(s)
Músculo Esquelético/metabolismo , Cadenas Pesadas de Miosina/metabolismo , Cadenas Ligeras de Miosina/metabolismo , Animales , CoturnixRESUMEN
Stretch-induced hypertrophy of the quail anterior latissimus dorsi is associated with decreased slow myosin 1 and increased slow myosin 2 expression and a small increase in expression of fast myosins. Because reduced neural activity has also been shown to accelerate expression from slow myosin 1 to slow myosin 2, we tested whether the increased expression of slow myosin 2 would be maintained when stretch was removed during a time when muscle activity would not be expected to increase. Quail anterior latissimus dorsi muscles were examined after 0-30 days of stretch overload and after 30 or 60 days of unweighting following 30 days of stretch. As expected, slow myosin 2 expression increased and slow myosin 1 expression decreased after 14-30 days of stretch. Novel findings were that slow myosin 1 and slow myosin 2 returned to control levels after unweighting. Furthermore, the expression of developmental and fast myosin heavy chains were evident by day 7, and maintained throughout wing unweighting. These data are consistent with the hypothesis that alterations in fast and developmental myosin expression result from formation and subsequent maintenance of new fibres during hypertrophy and regression. The relative amount and expression of myosin appears dependent upon mechanical stretch in the anterior latissimus dorsi muscle.
Asunto(s)
Adaptación Fisiológica , Isoenzimas/biosíntesis , Músculo Esquelético/fisiología , Miosinas/biosíntesis , Soporte de Peso , Animales , Coturnix , Inducción Enzimática , Hipertrofia , Isoenzimas/genética , Masculino , Fibras Musculares de Contracción Rápida/química , Fibras Musculares de Contracción Rápida/fisiología , Fibras Musculares de Contracción Rápida/ultraestructura , Fibras Musculares de Contracción Lenta/química , Fibras Musculares de Contracción Lenta/fisiología , Fibras Musculares de Contracción Lenta/ultraestructura , Músculo Esquelético/química , Músculo Esquelético/patología , Miosinas/genéticaRESUMEN
The effect of aging on muscle contractile function was examined in the anterior latissimus dorsi (ALD) muscle of Japanese quails aged 8 weeks (young adults), 26 weeks, 60 weeks, or 90 weeks (old birds). In vitro contractile measures of the ALD were made at 25 degrees C (stimulus pulse = 0.1 ms). Twitch contraction time in 90-week-old muscles was significantly greater than 8 to 26-week-old muscles (150 +/- 8 ms vs 168 +/- 18 ms). Similarly, one-half relaxation time of the twitch was increased in the ALD from old birds (221 +/- 17 ms) relative to adult birds 8-26 weeks (173 +/- 11). Aging produced a greater fusing of twitches at stimulation frequencies of 5 and 10 Hz, and this resulted in a leftward shift of the force-frequency curve at these frequencies. Shortening velocity measured by the force-velocity method (Vmax) decreased from 2.6 +/- 0.2 muscle length/s (mL/s) to 1.19 +/- 0.02 mL/s in 8 and 90-week-old muscles, respectively. Maximal velocity of unloaded shortening as measured by the slack test decreased from 3.6 +/- 0.7 mL/s to 2.4 mL/s in 8-week-old and 90-week-old muscles, respectively. Maximal tetanic force (60.6 +/- 3.1 mN) and specific force (11.3 +/- 0.3 N/cm2) were similar in young adult and old muscles. These data indicate that aging induces a slowing of both twitch contractile characteristics and shortening velocity in the ALD, without affecting maximal force capabilities.