IGF-I and end-to-side nerve repair: A dose-response study

End-to-side nerve repair allows for target-muscle reinnervation, with simul taneous preservation of donor-nerve function. Local administration of insul in-like growth factor-I (IGF-I) has been shown to increase the rate of axon regeneration in crush-injured and freeze-injured rat sciatic nerve. The pu rpose of the current project was to determine the effects of IGF-I in a rat model of end-to-side nerve repair. The left musculocutaneous nerve of 18 a dult male Sprague-Dawley rats was fully transected to induce biceps-muscle paralysis. The distal stump of the musculocutaneous nerve was then coapted by end-to-side neurorrhaphy through a perineurial window to the ipsilateral median nerve. All animals were randomly assigned to three groups: Group A received 100 mug/ml IGF-I; Group B received 50 mug/ml IGF-I; and control Gr oup C received 10 mM acetic acid vehicle solution, Infusions were regulated by the Alzet model 2004 mini-osmotic pump, with an attached catheter direc ted at the coaptation site. Weekly postoperative behavioral evaluations rev ealed significantly increased functional return over control in both experi mental groups as early as 3 weeks. After 28 days, histology evaluations rev ealed statistically significantly higher musculocutaneous nerve axon counts and myelin thickness/axon diameter ratios in both experimental groups vs, controls. The three groups were not significantly different in motor endpla te counts of the biceps muscle. Groups A and B were not significantly diffe rent in all parameters tested. This study suggests that local infusion of I GF-I may expedite the functional recovery of a paralyzed muscle, by increas ing the rate of axon regeneration through an end-to-side nerve graft.