EFFECTS OF ACUTE STEROID-ADMINISTRATION ON VENTILATORY AND PERIPHERALMUSCLES IN RATS

Occasional case reports have shown that acute myopathy may occur in pa tients treated with massive doses of corticosteroids. The mechanism of this myopathy is poorly understood. Therefore, 60 male rats were rand omly assigned to receive daily injection of saline (C), methylpredniso lone (M), or triamcinolone (T) 80 mg/kg/d for 5 d. Nutritional intake, measured daily in 15 animals, showed a significant reduction of food intake in the steroid-treated groups (-50 and -79% in M and T, respect ively). This was associated with a similar loss in body weight. In the 45 remaining animals, diaphragm contractility and histopathologic fea tures of several muscles were studied. Weights of respiratory and peri pheral muscles were similarly decreased after steroid treatment. Maxim al twitches of the diaphragm were lower in the C group (653 +/- 174 g/ cm(2)) than in the M group (837 +/- 171 g/cm(2); p < 0.05) and the T g roup (765 +/- 145 g/cm(2), NS). Half-relaxation time was prolonged in both steroid groups, and time to peak tension was longer with M, where as tetanic tensions were similar. Steroid treatment also induced a lef tward shift of the force-frequency curve at 25 and 50 Hz when compared with saline treatment (p < 0.05). ATPase staining of the diaphragm, s calenus medius, and gastrocnemius showed type IIb fiber atrophy in the steroid groups and also diaphragmatic type IIa atrophy with T, wherea s histologic examinations revealed a normal muscular pattern with abse nce of necrosis. Finally, a pair-fed (PF) study, performed in 18 rats (C, T, and PF), showed that muscle atrophy was considerably less prono unced in PF animals than in T-treated animals. We conclude that (1) sh ort-term treatment with massive doses of steroids induced severe respi ratory and limb muscle wasting; (2) both types of steroids induced pre dominantly type IIb atrophy, resulting in the expected alterations in diaphragm contractile properties; (3) neither steroid caused muscle ne crosis; (4) type IIb atrophy was not caused by acute nutritional depri vation alone.