Increased extraocular muscle strength with direct injection of insulin-like growth factor-I.
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.
Anderson
Brian C
BC
Department of Ophthalmology, University of Minnesota, Minneapolis 55455, USA.
Christiansen
Stephen P
SP
Grandt
Steven
S
Grange
Robert W
RW
McLoon
Linda K
LK
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
D007797:Laminin; D017451:Receptors, Somatomedin; D007334:Insulin-Like Growth Factor I