Chronic intermittent hypoxia inhibits proteolysis in juvenile rat skeletal muscle

Abstract

Catecholamines exert anti‐proteolytic effects on rat skeletal muscle in basal conditions. Considering that hypoxia is a powerful stimulus of the sympathetic nervous system, the present study was undertaken to examine in juvenile rat isolated muscles the possible changes in proteolysis that occur after chronic intermittent hypoxia (CIH). For this, 3‐week‐old rats were exposed to 9 days of CIH (6% O2 for 40s at 9 min intervals; 8 h day−1). On the 10th day the weight of CIH was smaller than control rat (83 ± 2 vs 91 ± 2 g). In both soleus and extensor digitorum longus (EDL) muscles, rates of overall proteolysis (nmol Tyr·mg wt−1·2h−1) decreased after CIH. The fall in the rate of protein degradation in soleus and EDL was accompanied by a 50% and 25% decreased activity of Ca2+‐dependent (0,047 ± 0,016 vs 0,100 ± 0,013) and Ubiquitin‐proteasome proteolysis (0,035 ± 0,005 vs 0,047 ± 0,003), respectively. In vitro rates of protein synthesis (nmol Tyr·mg wt−1·2h−1) in soleus from hypoxic rats decreased by 35% (0,371 ± 0,009 vs 0,273 ± 0,016). CIH increased by 75% the content of glycogen (%) in liver (8,9 ± 0,5 vs 5,1 ± 0,3) and soleus (0,71 ± 0,06 vs 0,41 ± 0,02). These data suggest an inhibitory control of intracellular proteolytic systems by adrenergic system and/or insulin in rat muscles exposed to CIH, which may prevent additional loss of body weight during hypoxia on this critical period of the development.Financial support: FAPESP and CNPQ