Nerve regeneration and serum levels of insulin-like growth factor-I in rats with streptozotocin-induced insulin deficiency.

Peripheral nerve regeneration was studied in female Sprague-Dawley rats with streptozotocin-induced insulin deficiency. Nerve regeneration was provoked by a crush lesion on the sciatic nerve 21 days after the streptozotocin injection. The regeneration was assessed by a pinch test at different time-points after injury. The rate of regeneration in insulin-deficient animals, 2.5 mm/day, was significantly lower than in control animals, 2.9 mm/day (P less than 0.05). There was no difference in the initial delay, i.e. the period before regeneration attains a constant velocity. One group of insulin-deficient rats was treated with insulin during the regeneration period by means of implanted osmotic mini-pumps. This treatment prevented the decrease in regeneration. After 6 days the sciatic nerves of insulin-deficient rats had regenerated 12.3 +/- 0.3 mm (mean +/- S.E.M.), while the corresponding value for insulin-treated rats was 15.7 +/- 0.6 mm. (P less than 0.01). The streptozotocin-treated rats were found to have a 39% reduction in the serum level of insulin-like growth factor-I (IGF-I) compared to control rats (0.33 +/- 0.02 micrograms/ml and 0.54 +/- 0.02 micrograms/ml respectively, P less than 0.001). Insulin treatment during the regeneration period completely restored the IGF-I level back to normal.