Myosin heavy chain composition of skeletal muscles in young rats growing under hypobaric hypoxia conditions

Abstract

This study investigated the effects of voluntary wheel running on the myosin heavy chain (MHC) composition of the soleus (Sol) and plantaris muscles (Pla) in rats developing under hypobaric choronic hypoxia (CH) conditions during 4 wk in comparison with those of control rats maintained under local barometric pressure conditions (C) or rats pair-fed an equivalent quantity of food to that consumed by CH animals (PF). Compared with C animals, sedentary rats subjected to CH conditions showed a significant decrease in type I MHC in Sol (-12%, P < 0.01). Although strongly decreased under hypoxia, spontaneous running activity increased the expression of type I MHC (P < 0.01) so that no difference in the MHC profile of Sol was shown between CH active and C active rats. The MHC distribution in Sol of PF rats was not significantly different from that found in C animals. CH resulted in a significant decrease in type I (P < 0.01) and type IIA (P < 0.005) MHC, concomitant with an increase in type IIB MHC in Pla (P < 0.001), compared with C and PF animals. In contrast to results in Sol muscle, this slow-to-fast shift in the MHC profile was unaffected by spontaneous running activity. These results suggest that running exercise suppresses the hypoxia-induced slow-to-fast transition in the MHC expression in Sol muscles only. The hypoxia-induced decrease in food intake has no major influence on MHC expression in developing rats.

Hypoxia transiently affects skeletal muscle hypertrophy in a functional overload model

“…Although largely discussed, the decreased body and muscle growth rate reported during chronic hypoxia exposure have been often explained by the hypoxia-induced hypophagia (7,16). As previously suggested, the putative inhibitory effects of moderate food restriction on the hypertrophic response to functional overload would result from activation of AMPK, REDD1, and/or BNIP-3, three of well-known mTOR inhibitors (33,34,39).…”

“…Muscle atrophy has already been observed in humans after expeditions in high altitude (44), while a reduction in muscle growth has been shown in rodents chronically exposed to hypobaric hypoxia (7,16). In vitro studies showed that the Akt/mTOR pathway could be inhibited by hypoxia exposure (12,27,31), but to our knowledge, only few in vivo studies reported that prolonged hypoxia exposure altered this signaling pathway in skeletal muscles (16).…”

Effects of Pulmonary Rehabilitation on Lung Functions in Patients with COPD

“…It has been suggested that, long standing alveolar hypoventilation and dyspnea in the COPD patients may cause increased work of breathing, hypoxia induced decreased ATP production and increased energy expenditure followed by skeletal muscle wasting in these groups of patients. [27][28][29][30] On the other hand, expiratory airflow limitation due to decrease elastic fibres in the alveolar walls and airways have also been suggested as an important contributory factor for lung hyperinflation in this group of patients. As a consequence, there may be increase in inspiratory airflow resistance followed by derangement of ventilatory variables.…”

O desafio da altitude. Uma perspectiva fisiológica

“…Nos estudos laboratoriais, têm sido utilizadas câma-ras com ambiente interior hermeticamente controlado para simular condições de altitude. Efectivamente, pela capacidade de controlar a pressão barométrica no interior destas câmaras recorrendo à utilização de bombas que aspiram ar para o exterior (10,52,59,74), ou à injecção de uma mistura de gases rica em nitrogénio diminuindo, assim, a pressão parcial de oxigénio no seu interior (28,54,88), é possível simular ambientes de hipóxia hipobá-rica e normobárica, respectivamente. A exposição aguda ou crónica a ambientes de altitude e a prática simultânea de actividades físicas, induzem níveis de stress fisiológico acrescidos, devido às condições de hipotermia, hipohidratação, hipoglicemia e, particularmente, hipóxia hipobárica a que estão associadas (36).…”