Effects of selenium deficiency on diaphragmatic function after resistive loading.

Diaphragmatic fatigue has been associated with increased production of reactive oxygen species. Among the defenses against reactive oxygen species is the glutathione redox system. The selenium-dependent enzyme glutathione peroxidase is an important component of this system. Thus, we hypothesized that selenium deficiency would lower glutathione peroxidase activity and render the diaphragm more susceptible to a mild exertional protocol. Sprague-Dawley rats were fed a selenium-deficient or control diet for 12 weeks then divided into four experimental groups: (1) unloaded, basic diet with selenium supplementation (control); (2) unloaded, selenium-deficient diet; (3) loaded, basic diet with selenium supplementation; and (4) loaded, selenium-deficient diet. Diaphragmatic in vitro contractile properties, glutathione peroxidase activity and glutathione content were measured. During inspiratory resistive loading, the animals breathed against an inspiratory resistor at 70% of maximal airway pressure until the target pressure was not achieved for five consecutive breaths. Selenium deficiency resulted in a significant decrease in diaphragmatic glutathione peroxidase activity, without changes in total glutathione content. Neither selenium deficiency nor inspiratory resistive loading alone impaired diaphragmatic contractility. Selenium deficiency in conjunction with inspiratory resistive loading resulted in a significant decrease in diaphragmatic twitch and tetanic force, with a downward shift in the force/frequency curve. These data suggest that selenium deficiency lowers diaphragmatic glutathione peroxidase activity, and when these animals are subjected to the oxidative stress of resistive loading, there is an impairment in muscle function. We conclude that a functional glutathione peroxidase is necessary to protect the diaphragm against the effects of resistive loading.