EXPERIMENTAL HYPER-THYROIDISM FAILS TO EXPEDITE RE-INNERVATION OF MUSCLES DENERVATED BY CRUSHING SCIATIC-NERVES IN RABBITS

The time for initial reinnervation of tibialis anterior muscle after sciatic nerve crushing was measured in rabbits treated with intraperitoneal injections of 3,3′,5-triiodothyronine, 1 μg/kg body weight/day. The sciatic nerve was crushed in the thigh, just above its division into lateral and medial popliteal nerves. The method used to determine the beginning of reinnervation consisted of EMG recordings of (a) muscular potentials evoked by electrical stimulation of the sciatic nerve, below the crushed point, and (b) spontaneous action potentials during activity; the muscle tested was the tibialis anterior. The time for initial reinnervation averaged 43.6 ± 1.15 days in treated rabbits, and 43.2 ± 1.78 days in vehicle-injected animals. The distance from the site of crushing to the point where the anterior tibial nerve enters the tibialis anterior muscle was measured in each animal and the regeneration rate was calculated; this parameter averaged 1.48 ± 0.05 mm/day in treated rabbits, and 1.50 ± 0.04 mm/day in control animals. Therefore, no effect of 3,3′,5-triiodothyronine at the dosage used on the reinnervation process of muscles denervated by a crushed sciatic nerve could be demonstrated. © 1979.