title: Quantitative and qualitative adaptations of muscle fibers to glucocorticoids.
abstract: BACKGROUND
  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 (∼ 13%), whereas both type 1 and type 2A fibers had decreased cross-sectional area (type 1: ∼ 11%, type 2A: ∼ 17%), myosin loss (type 1: ∼ 18%, type 2A: ∼ 32%), and loss of specific force (type 1: ∼ 24%, type 2A: ∼ 33%), which were preferential for fast fibers.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Division of Endocrinology, Diabetology and Metabolism, Department of Medical Sciences, University of Turin, Corso Dogliotti, 14, 10126, Turin, Italy.
authors.forename: Marco Alessandro
authors.initials: MA
authors.lastname: Minetto
authors.affiliation: Department of Molecular Medicine, University of Pavia, Pavia, Italy.
authors.forename: Rizwan
authors.initials: R
authors.lastname: Qaisar
authors.affiliation: Department of Molecular Medicine, University of Pavia, Pavia, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Agoni
authors.affiliation: Division of Endocrinology, Diabetology and Metabolism, Department of Medical Sciences, University of Turin, Corso Dogliotti, 14, 10126, Turin, Italy.
authors.forename: Giovanna
authors.initials: G
authors.lastname: Motta
authors.affiliation: Department of Molecular Medicine, University of Pavia, Pavia, Italy.
authors.forename: Emanuela
authors.initials: E
authors.lastname: Longa
authors.affiliation: Fondazione Salvatore Maugeri, Scientific Institute of Pavia, Pavia, Italy.
authors.forename: Danilo
authors.initials: D
authors.lastname: Miotti
authors.affiliation: Department of Molecular Medicine, University of Pavia, Pavia, Italy.
authors.forename: Maria Antonietta
authors.initials: MA
authors.lastname: Pellegrino
authors.affiliation: Department of Molecular Medicine, University of Pavia, Pavia, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Bottinelli
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects*; D000328:Adult; D003402:Creatine Kinase / Q000097:blood; D003907:Dexamethasone / Q000494:pharmacology*; D005215:Fasting; D005938:Glucocorticoids / Q000494:pharmacology*; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism; D007717:Knee / Q000294:innervation; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D018485:Muscle Fibers, Skeletal / Q000145:classification / Q000187:drug effects* / Q000378:metabolism; D009218:Myosins / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger; D018709:Statistics, Nonparametric; D019415:Torque
chemical_list: D005938:Glucocorticoids; D012333:RNA, Messenger; D003907:Dexamethasone; D003402:Creatine Kinase; D009218:Myosins; D006854:Hydrocortisone
keywords: cross-sectional area; maximal shortening velocity; myosin; specific force; steroid myopathy