title: Effects of testosterone supplementation on skeletal muscle fiber hypertrophy and satellite cells in community-dwelling older men.
abstract: OBJECTIVE
  In this study, we determined the effects of graded doses of testosterone on muscle fiber cross-sectional area (CSA) and satellite cell number and replication in older men.
  
  
  METHODS
  Healthy men, 60-75 yr old, received a long-acting GnRH agonist to suppress endogenous testosterone production and 25, 50, 125, 300, or 600 mg testosterone enanthate im weekly for 20 wk.
  
  
  METHODS
  Immunohistochemistry, light and confocal microscopy, and electron microscopy were used to perform fiber typing and quantitate myonuclear and satellite cell number in vastus lateralis biopsies, obtained before and after 20 wk of treatment.
  
  
  RESULTS
  Testosterone administration in older men was associated with dose-dependent increases in CSA of both types I and II fibers. Satellite cell number increased dose dependently at the three highest doses (3% at baseline vs. 6.2, 9.2, and 13.0% at 125, 300, and 600 mg doses, P < 0.05). Testosterone administration was associated with an increase in the number of proliferating cell nuclear antigen+ satellite cells (1.8% at baseline vs. 3.9, 7.5, and 13% at 125, 300, and 600 mg doses, P < 0.005). The expression of activated Notch, examined only in the 300-mg group (baseline, 2.3 vs. 9.0% after treatment, P < 0.005), increased in satellite cells after testosterone treatment. The expression of myogenin (baseline, 6.2 vs. 20.7% after treatment, P < 0.005), examined only in the 300-mg group, increased significantly in muscle fiber nuclei after testosterone treatment, but Numb expression did not change.
  
  
  CONCLUSIONS
  Older men respond to graded doses of testosterone with a dose-dependent increase in muscle fiber CSA and satellite cell number. Testosterone-induced skeletal muscle hypertrophy in older men is associated with increased satellite cell replication and activation.
authors.affiliation: Division of Endocrinology, Metabolism, and Molecular Medicine, Charles R. Drew University, Los Angeles, CA 90059, USA.
authors.forename: Indrani
authors.initials: I
authors.lastname: Sinha-Hikim
authors.forename: Marcia
authors.initials: M
authors.lastname: Cornford
authors.forename: Hilda
authors.initials: H
authors.lastname: Gaytan
authors.forename: Martin L
authors.initials: ML
authors.lastname: Lee
authors.forename: Shalender
authors.initials: S
authors.lastname: Bhasin
mesh_terms: D000368:Aged; D000375:Aging; D001706:Biopsy; D002452:Cell Count; D002455:Cell Division / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006801:Humans; D006984:Hypertrophy; D007150:Immunohistochemistry; D008297:Male; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D008875:Middle Aged; D018485:Muscle Fibers, Skeletal / Q000473:pathology*; D018482:Muscle, Skeletal / Q000473:pathology*; D018008:Myogenin / Q000032:analysis; D018809:Proliferating Cell Nuclear Antigen / Q000032:analysis; D051880:Receptors, Notch / Q000032:analysis; D032496:Satellite Cells, Skeletal Muscle / Q000737:chemistry / Q000473:pathology*; D013739:Testosterone / Q000008:administration & dosage*
chemical_list: D018008:Myogenin; D018809:Proliferating Cell Nuclear Antigen; D051880:Receptors, Notch; D013739:Testosterone