title: Role of IGF-I and IGF-binding proteins within diaphragm muscle in modulating the effects of nandrolone.
abstract: Recent studies suggest that the anabolic effects of testosterone in muscle may be mediated, in part, by the insulin-like growth factor (IGF) system. The aim of this study was to examine the effects of nandrolone (NAN) on both IGF-I and IGF-binding proteins (IGFBPs) in the diaphragm muscle of 1-yr-old female rats. NAN (6.6 mg. kg(-1) x day(-1)) was infused continuously for 17 days using a subcutaneous Silastic implant, whereas controls (CTL) received blank capsules. Muscle fibers were classified immunohistochemically, and fiber cross-sectional areas (CSA) were determined quantitatively. IGF-I levels in both serum and muscle were determined by RIA. Immunoreactivity to an IGF-I antibody was used to localize IGF-I expression within individual muscle fibers. Muscle IGFBPs were determined by SDS-PAGE and Western ligand blotting and measured by scanning densitometry. Body weight was higher in the NAN group compared with CTL (9.4 +/- 4.5% vs. -0.6 +/- 3.1%). There were no changes in the fiber composition of the diaphragm. NAN increased the CSA of type IIa (20%) and type IIx/b (30%) diaphragm fibers. Levels of IGF-I in the diaphragm muscle were significantly higher (50%) in NAN-treated animals. Immunohistochemistry revealed increased localization of IGF-I within type IIx/b diaphragm fibers. In addition, NAN increased IGFBP-3 within the diaphragm (69%), whereas IGFBP-4 decreased (40%). We conclude that NAN-induced diaphragm muscle fiber hypertrophy is mediated, in part, by influences of the IGF system within the muscle, such that coordinated changes in IGFBPs reflect a direction of change that has been associated with an anabolic response in other test systems.
authors.affiliation: Division of Pulmonary/Critical Care Medicine, The Burns and Allen Research Institute, Cedars-Sinai Medical Center, UCLA School of Medicine, Los Angeles, California 90048, USA. michael.lewis@cshs.org
authors.forename: Michael I
authors.initials: MI
authors.lastname: Lewis
authors.forename: Gail D
authors.initials: GD
authors.lastname: Horvitz
authors.forename: David R
authors.initials: DR
authors.lastname: Clemmons
authors.forename: Mario
authors.initials: M
authors.lastname: Fournier
mesh_terms: D045930:Anabolic Agents / Q000494:pharmacology*; D000818:Animals; D001835:Body Weight / Q000187:drug effects; D003964:Diaphragm; D005260:Female; D007150:Immunohistochemistry; D018969:Insulin-Like Growth Factor Binding Proteins / Q000378:metabolism / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000378:metabolism / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D009277:Nandrolone / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values; D013739:Testosterone / Q000097:blood
chemical_list: D045930:Anabolic Agents; D018969:Insulin-Like Growth Factor Binding Proteins; D013739:Testosterone; D007334:Insulin-Like Growth Factor I; D009277:Nandrolone