Limited myogenic response to a single bout of weight-lifting exercise in old rats

Abstract

The purpose of the present study was to compare the myogenic response of hindlimb muscles in young (14-20 wk of age) and old (>120 wk of age) rats with a single exhaustive bout of heavy resistance weight lifting. [(3)H]thymidine and [(14)C]leucine labeling were monitored for up to 2 wk after the exercise bout to estimate serial changes in mitotic activity and the level of amino acid uptake and myosin synthesis. Histological, histochemical, and immunohistochemical [anti-5-bromo-2'-deoxyuridine and myogenic determination genes (MyoD)] analyses of whole muscles and analysis of muscle-specific gene expression (MyoD) using Western blotting and RT-PCR were performed. Old rats showed significant muscle atrophy and a lower exercise capacity than young rats. Exercise-induced muscle damage, as assessed in histological sections, and increases in serum creatine kinase activity were evident in both young and old exercised groups. Mitotic activity was increased in young, but not old, rats 2 days after exercise. There was a biphasic increase in [(14)C]leucine uptake during the 14 days postexercise (peaks at 1-4 and 10 days) in young rats: only the first peak was observed in old rats. There was a lower uptake of [(14)C]leucine in the myosin fraction and an impaired expression of MyoD at the protein (immunohistochemistry and Western blotting) and mRNA (RT-PCR) levels in old rats throughout the postexercise period. These results demonstrate a reduced reparative capability of muscle in response to a single bout of exercise in old compared with young rats.

Efficacy of 3 days/wk resistance training on myofiber hypertrophy and myogenic mechanisms in young vs. older adults

“…Although the latter cannot be ruled out based on the current shortage of published findings, we suggest the former explanation has merit. Several animal studies have demonstrated slowed repair/ regeneration in older vs. young adult animals (8,12,21,43,61). If recovery time is rate limiting in older muscle, one might expect a lesser hypertrophy adaptation in older vs. young adults subjected to the same fairly high loading frequency.…”

“…There are several reports of MRF upregulation in response to various muscle perturbations including stretch overload (11,42), ablation (2, 3), denervation (35), myotoxicity (43), and acute resistance loading (9,22,34,53,61). In a number of these studies, MRF responses and/or muscle repair mechanisms were found to be limited by old age (34,(41)(42)(43)61). This may result from heightened basal levels of MRFs in the aging muscle (7,34,35,49) because MRF expression tends to increase as the degree of sarcopenia advances (17).…”

A administração de nandrolona não promove hipertrofia do músculo sóleo em ratos

“…Diante disso, o protocolo de levantamento de peso para ratos, proposto por Tamaki e cols. (43), tem sido utilizado como modelo de exercício resistido de alta intensidade (15), no qual uma sessão do exercício, até a exaustão, é suficiente para desencadear aumento de síntese protéica nos músculos flexores plantares (sóleo, plantar e gastrocnêmio) (15,44). O protocolo de levantamento de peso para ratos em meio líquido é uma variação do modelo proposto por Tamaki e cols.…”

“…A ausência de diferenças estatísticas nas variáveis citadas não estão relacionadas a desajustes no planejamento experimental, já que a utilização de um "n" de seis animais é adequada e suficiente para a reprodução e interpretação dos teores de proteínas e DNA em músculo esquelético (15,45,46). Porém, respostas hipertróficas miofibrilares foram observadas no músculo flexor plantar, com predominância de fibras glicolíticas, em ratos submetidos ao mesmo protocolo experimental por quatro semanas (47).…”

“…Considerando que a metodologia empregada neste estudo está adequada ao objetivo proposto e que o número de animais utilizados por experimento foi suficiente para a determinação de possíveis diferenças com relação aos parâmetros avaliados (15,45,46), os dados obtidos reforçam a necessidade de mais estudos para avaliação da existência de efeitos significativos do uso de EAA sobre a performance, além daqueles desencadeados pelo treinamento físico resistido.…”