QUANTITATIVE AND QUALITATIVE ADAPTATIONS OF MUSCLE FIBERS TO GLUCOCORTICOIDS

Introduction: The aim of this study was to understand the effects of short-term glucocorticoid administration in healthy subjects. Methods: Five healthy men received dexamethasone (8 mg/day) for 7 days. Vastus lateralis muscle biopsy and knee extension torque measurement were performed before and after administration. A large number of individual muscle fibers were dissected from the biopsy samples (pre-administration: n = 165, post-administration: n = 177). Results: Maximal knee extension torque increased after administration (similar to 13%), whereas both type 1 and type 2A fibers had decreased cross-sectional area (type 1: similar to 11%, type 2A: similar to 17%), myosin loss (type 1: similar to 18%, type 2A: similar to 32%), and loss of specific force (type 1: similar to 24%, type 2A: similar to 33%), which were preferential for fast fibers. Conclusion: Short-term dexamethasone administration in healthy subjects elicits quantitative and qualitative adaptations of muscle fibers that precede (and may predict) the clinical appearance of myopathy in glucocorticoid-treated subjects.