Diaphragmatic function after resistive breathing in vitamin E-deficient rats.

The effects of vitamin E deficiency on diaphragm function were studied at rest and after resistive breathing (RB) in Sprague-Dawley rats (wt 300-400 g). The animals were pair fed a vitamin E-deficient diet (E-def) or a matched vitamin E-sufficient diet (E-suf). Each diet group was then further subdivided into a group that breathed unimpeded (control) and a second group that breathed through an inspiratory resistor until the animals were unable to sustain 70% of their maximum airway pressure. Diaphragm samples were obtained for analysis of thiobarbituric acid-reactive substances, glutathione (GSH) concentrations, and glutathione disulfide (GSSG) concentrations. In vitro isometric contractile studies were also performed and included twitch (Pt) and maximum tetanic (Po) tensions, force-frequency curves, fatigue index, and recovery index. Pt was significantly reduced in the E-suf RB group as well as both of the E-def groups. Po was also significantly reduced in both E-def groups. The E-def rats subjected to RB showed a significant decrease in tension at both high and low frequencies compared with the E-suf rats. Concentrations of diaphragm thiobarbituric acid-reactive substances were significantly increased in both E-def groups. RB in both E-suf and E-def rats resulted in increases in diaphragm concentrations of GSSG and decreases in the GSH/GSSG ratios. We conclude that reduction of contractile function, lipid peroxidation, and activation of the GSH redox cycle occur with RB and that these effects are significantly increased in the presence of vitamin E deficiency.