title: Growth hormone stimulates the collagen synthesis in human tendon and skeletal muscle without affecting myofibrillar protein synthesis.
abstract: In skeletal muscle and tendon the extracellular matrix confers important tensile properties and is crucially important for tissue regeneration after injury. Musculoskeletal tissue adaptation is influenced by mechanical loading, which modulates the availability of growth factors, including growth hormone (GH) and insulin-like growth factor-I (IGF-I), which may be of key importance. To test the hypothesis that GH promotes matrix collagen synthesis in musculotendinous tissue, we investigated the effects of 14 day administration of 33-50 microg kg(-1) day(-1) recombinant human GH (rhGH) in healthy young individuals. rhGH administration caused an increase in serum GH, serum IGF-I, and IGF-I mRNA expression in tendon and muscle. Tendon collagen I mRNA expression and tendon collagen protein synthesis increased by 3.9-fold and 1.3-fold, respectively (P < 0.01 and P = 0.02), and muscle collagen I mRNA expression and muscle collagen protein synthesis increased by 2.3-fold and 5.8-fold, respectively (P < 0.01 and P = 0.06). Myofibrillar protein synthesis was unaffected by elevation of GH and IGF-I. Moderate exercise did not enhance the effects of GH manipulation. Thus, increased GH availability stimulates matrix collagen synthesis in skeletal muscle and tendon, but without any effect upon myofibrillar protein synthesis. The results suggest that GH is more important in strengthening the matrix tissue than for muscle cell hypertrophy in adult human musculotendinous tissue.
authors.affiliation: Institute of Sports Medicine, Bispebjerg Hospital, Center of Healthy Aging, Faculty of Health Sciences, University of Copenhagen, Copenhagen NV, Denmark. simondoessing@gmail.com
authors.forename: Simon
authors.initials: S
authors.lastname: Doessing
authors.forename: Katja M
authors.initials: KM
authors.lastname: Heinemeier
authors.forename: Lars
authors.initials: L
authors.lastname: Holm
authors.forename: Abigail L
authors.initials: AL
authors.lastname: Mackey
authors.forename: Peter
authors.initials: P
authors.lastname: Schjerling
authors.forename: Michael
authors.initials: M
authors.lastname: Rennie
authors.forename: Kenneth
authors.initials: K
authors.lastname: Smith
authors.forename: Søren
authors.initials: S
authors.lastname: Reitelseder
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Kappelgaard
authors.forename: Michael Højby
authors.initials: MH
authors.lastname: Rasmussen
authors.forename: Allan
authors.initials: A
authors.lastname: Flyvbjerg
authors.forename: Michael
authors.initials: M
authors.lastname: Kjaer
mesh_terms: D000328:Adult; D003094:Collagen / Q000096:biosynthesis / Q000187:drug effects* / Q000235:genetics; D018592:Cross-Over Studies; D004311:Double-Blind Method; D015444:Exercise / Q000502:physiology; D015200:Fluoroimmunoassay; D019382:Human Growth Hormone / Q000008:administration & dosage* / Q000097:blood; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism; D008297:Male; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism; D014176:Protein Biosynthesis / Q000187:drug effects / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013710:Tendons / Q000187:drug effects* / Q000378:metabolism; D013997:Time Factors
chemical_list: D009124:Muscle Proteins; D012333:RNA, Messenger; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I; D003094:Collagen