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L.K. McLoon, B. Anderson, S.P. Christiansen; Effect of Basic Fibroblast Growth Factor (FGF2) on Force Generation in Rabbit Extraocular Muscle . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2930.
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While there are drug treatments to weaken overacting muscles in strabismic patients, there are currently no drug treatments in use clinically to strengthen underacting muscles. Our previous work demonstrated that injections of either IGFI or IGFII into extraocular muscles result in increased muscle force generation. Basic fibroblast growth factor (bFGF) is a known myogenic growth factor. We tested the hypothesis that treatment of extraocular muscles with bFGF would result in increased muscle force generation.
One superior rectus muscle of normal adult rabbits was injected with either 1 µg or 5 µg of bFGF (FGF2) in a volume of 100 µl saline. The contralateral muscle was injected with an equal volume of saline. After one and two weeks, the animals were euthanized. Both superior rectus muscles were removed and assayed physiologically using an in vitro apparatus. Muscles were stimulated at 1, 10, 20, 40, 100, 150 and 200 Hz and then subjected to a fatigue protocol.
A single injection of bFGF into the superior rectus muscles resulted in increased force generation at every stimulation frequency tested when compared to controls at one week after treatment. The 1 µg dose resulted in a 25–40% increase in force generation compared to saline–injected control muscles. At the 5 µg dose, increases in force generation of between 15 and 40% over control values were seen. By two weeks after a single injection, there was no difference in muscle force generation between treated and untreated muscles.
Basic fibroblast growth factor results in a significant but short–term increase in extraocular muscle force generation. We are currently testing sustained–release delivery of bFGF to ascertain if such increases can be maintained for longer periods of time. If so, growth factors such as bFGF and IGF could prove to be very useful clinically, either alone or in combination with a weakening agent in the antagonist to treat patients with strabismus.
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