Increasing muscle strength as a treatment for strabismus: sustained release of insulin-like growth factor-1 in rabbit extraocular muscle.
OBJECTIVE
Currently, no drug treatment is available for strengthening underacting extraocular muscles (EOM) in strabismus. We showed previously that single injections of insulin-like growth factor (IGF-1) result in significant but short-term increases in muscle force generation. This study examined the effects of sustained release of IGF-1 on force generation in rabbit superior rectus muscles.


METHODS
In adult rabbits, slow-release pellets containing IGF-1 were implanted on the global side of one superior rectus muscle. After 1 week, or 1, 2, 3, or 6 months, treated and control muscles were examined for force generation using an in vitro physiology apparatus. All muscles were prepared for histology and mean myofiber cross-sectional areas were determined.


RESULTS
One and 3 months after pellet implantation, treated muscles generated significantly greater force than contralateral control muscles, whereas at 2 months, no significant difference was found. Force per cross-sectional area (mN/cm(2)) at 3 months also increased significantly in the treated muscles. Mean muscle cross-sectional area increased significantly after 1, 2, and 3 months of sustained exposure to IGF-1 compared with controls. After an additional 3 months without IGF-1 exposure, mean cross-sectional areas were significantly greater than controls but significantly reduced compared with areas at 1, 2, and 3 months.


CONCLUSIONS
IGF-1 appears to be highly effective in increasing muscle force generation. Because slow release of IGF-1 results in sustained increases in EOM force generation, it may be a potentially useful alternative to surgical resection procedures because it avoids many of the potential long-term biomechanical hazards of resection surgery.
McLoon
Linda K
LK
Department of Ophthalmology, University of Minnesota, Minneapolis, Minnesota 55455, USA. mcloo001@umn.edu
Anderson
Brian C
BC
Christiansen
Stephen P
SP
D000818:Animals; D003692:Delayed-Action Preparations; D007334:Insulin-Like Growth Factor I / Q000008:administration & dosage*; D053580:Muscle Strength / Q000187:drug effects* / Q000502:physiology; D009801:Oculomotor Muscles / Q000187:drug effects* / Q000503:physiopathology; D011817:Rabbits; D013285:Strabismus / Q000188:drug therapy* / Q000503:physiopathology
D003692:Delayed-Action Preparations; D007334:Insulin-Like Growth Factor I