title: Growth hormone restores aged diaphragm myosin composition and performance after chronic undernutrition.
abstract: The effects of growth hormone (GH) on diaphragm muscle myosin heavy chain (MHC) composition and mechanical performance were investigated in Fischer 344 male rats aged to senescence (24.5 mo of age). Chronic undernutrition (UN), refeeding (RF), and RF+GH were compared with ad libitum feeding by using a model of UN that produced a 50% decrease in body weight over a 12-mo period. The effect of aging was assessed by comparing MHC composition of ad libitum-fed rats at 12 and 24.5 mo of age. At senescence, significant decreases in slow type I (-23%) and fast type IIA (-31%) MHC had occurred with aging. Conversely, UN over this aging period increased types I (32-73%) and IIA (22-23%) MHC and decreased fast types IIB (32-54%) and IIX (30-31%) MHC. RF and RF+GH reversed these shifts back toward control values. At senescence, maximal specific force, maximal velocity, and specific power capacity were not different across treatment groups. During repetitive isotonic contraction trials, the diaphragms of UN rats maintained power production over time (54% of initial power at 60 s), whereas the power production of diaphragms of ad libitum-fed rats fell to 0% (P < 0.05). In comparison with UN rats, the diaphragms of RF and RF+GH rats produced 23 (not significant) and 11% (P < 0.05) of initial power, respectively, suggesting that RF+GH treatment restored performance characteristics after UN. We conclude that RF+GH can reverse alterations in MHC composition and mechanical performance produced by chronic UN in the aged rat diaphragm.
authors.affiliation: Department of Cell Biology and Physiology, Allergy, and Critical Care Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA. ameredes@pop.pitt.edu
authors.forename: B T
authors.initials: BT
authors.lastname: Ameredes
authors.forename: J F
authors.initials: JF
authors.lastname: Watchko
authors.forename: M J
authors.initials: MJ
authors.lastname: Daood
authors.forename: J F
authors.initials: JF
authors.lastname: Rosas
authors.forename: M P
authors.initials: MP
authors.lastname: Donahoe
authors.forename: R M
authors.initials: RM
authors.lastname: Rogers
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002908:Chronic Disease; D003964:Diaphragm / Q000187:drug effects* / Q000378:metabolism / Q000503:physiopathology*; D013006:Growth Hormone / Q000494:pharmacology*; D008297:Male; D018763:Muscle Fatigue; D018995:Myosin Heavy Chains / Q000378:metabolism; D009218:Myosins / Q000378:metabolism*; D009748:Nutrition Disorders / Q000503:physiopathology*; D051381:Rats; D011916:Rats, Inbred F344
chemical_list: D013006:Growth Hormone; D018995:Myosin Heavy Chains; D009218:Myosins