Functional effects of local thyroid hormone administration after sciatic nerve injury in rats

This study investigates potential functional effects of thyroid hormone (T3) on peripheral nerve regeneration in rats. Forty adult male Lewis rats were included in this study. After complete transection of the right sciatic nerve, the gap between the stumps was bridged with a silicone tube. In the first experimental group (group A, n = 12), T3 solution was used to fill the tube, whereas a sterile buffer solution was used in nontreated rats, (group B, n = 12). Additionally, sham operation with surgical incision and mobilization of the sciatic nerve without any other intervention was performed (group C, n = 10). In a few animals, alpha-segment of the nerve was excised and the stumps were reversed to exclude the possibility of regeneration (group D, n = 6). The process of peripheral nerve regeneration was assessed by functional indices at 3, 6, 9, 13, and 17 weeks postoperatively. Mid-stance angle, at the ankle, measured in degrees, was used as a kinematic index and the withdrawal reflex (measured in grams of applied force) was used to evaluate the return of sensory function. Kinematic indexes were not different between the groups A and B at all time points of the evaluation. Sensory function was significantly different in T3-treated animals compared with buffer-treated control group (x vs. y, P = 0.031) at 9 weeks. Thereafter, sensory function was comparable between groups. In conclusion, T3 seems to accelerate the return of sensory function after complete transection of the sciatic nerves in Lewis rats without a significant effect on motor nerve recovery.