Evidence indicating trophic importance of IGF-I in regenerating peripheral nerves.

The mechanisms influencing regeneration of peripheral nerves are incompletely known, but growth factors are supposed to play a key role. In the present study, we demonstrate, with the aid of immunohistochemical methods, that somatomedin C (Sm-C/insulin-like growth factor I/IGF-I) rapidly increased from low to high concentrations, reaching peak values in 2 weeks, in regenerating sciatic nerves of adult rats. In addition, IGF-I was demonstrated extracellularly, never observed in the control nerves. Reactive Schwann cells appeared to be the major source for IGF-synthesis. Higher concentrations were seen in tubulated nerves as compared to sutured ones. It is proposed that IGF-I exerts important growth supporting effects on regenerating peripheral nerves.