Changes in dietary protein intake fail to prevent decrease in muscle growth induced by severe hypoxia in rats

Muscle growth, fiber size, muscle and liver glycogen, plasma hormones, and muscle glutamine concentration were evaluated in rats chronically exposed (26 days) to a simulated hypobaric altitude (HA; 6,000 m) and fed diets of varying protein concentrations (10, 20, or 40 g protein/100 g of dry matter; LP, MP, and HP, respectively). Values were compared with those measured in animals maintained under normobaric conditions and either fed ad libitum (SL groups) or pair fed equivalent quantities of food consumed by HA animals (PF groups). There was marked anorexia in response to HA exposure for all protein diets (P < 0.001). A specific effect of hypoxia on the decrease in muscle growth has been identified by comparison of the values of the muscle weight-to-body weight ratio between HA and PF groups (P < 0.05 for all dietary protein levels). Plasma insulin concentrations were lower in HA than in SL and PF rats (P < 0.05). Liver glycogen was significantly decreased by exposure to HA (P < 0.001) and high dietary protein content (P < 0.005). Hypoxia per se and decreased food intake had additive effects on soleus muscle glycogen concentrations. An increase in muscle glutamine was observed in rats fed the LP diet in comparison with the MP diet, especially in SL and PF groups (P < 0.05). These results clearly demonstrate that 1) hypobaric hypoxia per se decreases growth rate in rats and 2) increasing the dietary protein intakes in rat had no effect on the depression of muscle growth related to high altitude but had deleterious effects on glycogen deposition in liver and fast muscle.