title: Increased extraocular muscle strength with direct injection of insulin-like growth factor-I.
abstract: OBJECTIVE
  Previous work has demonstrated the effectiveness of insulin-like growth factor (IGF)-II in increasing force generation in extraocular muscle (EOM). Studies in the literature have suggested that IGF-I would be even more effective than IGF-II. This study was performed to assess the effects on muscle mass and force generation of IGF-I injection in adult rabbit superior rectus muscle.
  
  
  METHODS
  Adult rabbits received a single injection of IGF-I at one of several doses into one superior rectus muscle. One week after treatment, the rabbits were euthanatized, and the superior rectus muscle from each orbit was removed. Force generation was measured using an in vitro apparatus, and injected muscles were compared with the contralateral control. A second group of animals were injected similarly, and the muscles were examined at 1 week for changes in cross-sectional area of individual myofibers.
  
  
  RESULTS
  EOMs demonstrate significant numbers of cells expressing the IGF receptor. After the EOMs were injected with IGF-I, there were significant increases both in muscle force generation and cross-sectional area at all doses tested in this study. Doses of 10 and 25 microg IGF-I were most effective.
  
  
  CONCLUSIONS
  Direct muscular injection of IGF-I effectively increases EOM force generation without the potential biomechanical hazards of surgery such as permanently altered muscle length or insertional position on the globe.
authors.affiliation: Department of Ophthalmology, University of Minnesota, Minneapolis 55455, USA.
authors.forename: Brian C
authors.initials: BC
authors.lastname: Anderson
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Christiansen
authors.forename: Steven
authors.initials: S
authors.lastname: Grandt
authors.forename: Robert W
authors.initials: RW
authors.lastname: Grange
authors.forename: Linda K
authors.initials: LK
authors.lastname: McLoon
mesh_terms: D000818:Animals; D007273:Injections, Intramuscular; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007797:Laminin / Q000378:metabolism; D009210:Myofibrils / Q000187:drug effects / Q000378:metabolism; D009801:Oculomotor Muscles / Q000187:drug effects* / Q000378:metabolism / Q000503:physiopathology; D011817:Rabbits; D017451:Receptors, Somatomedin / Q000378:metabolism; D013285:Strabismus / Q000188:drug therapy
chemical_list: D007797:Laminin; D017451:Receptors, Somatomedin; D007334:Insulin-Like Growth Factor I