[Experimental studies about effect of dexamethasone on diaphragm of normal rats]

The influence of dexamethasone on diaphragm function, its oxidative capacity, fiber cross-sectional areas, the content of glycogen and ultrastructural changes were determined in Wistar rats by receiving dexamethasone (2 mg/kg) muscle injection for two weeks. We noted dexamethasone treatment leads to significant atrophy of the mass of diaphragm, reduction of fiber cross-sectional areas (CSA) of type II a, II b fibers. Under high frequency (100 Hz) stimulation, the tention of the diaphragm muscle strips was decreased and diaphragm fatigue resistance (1/2 RT) was significantly improved. Histochemically, ATPase activity in type I and type II b fibers of the diaphragm was significantly reduced and a significant reduction of succinate dehydrogenase activity in the diaphragm was also observed, but increased glycogen was seen in the diaphragm. Ultrastructural changes including mitochondrial hyperplasia, swelling, myofibillae focus destructure were evident. It is concluded that steroid-induced myopathy may also involve the diaphragm.