Effects of triiodothyronine on protein synthesis in regenerating peripheral neurons

Abstract

A combined biochemical and autoradiographic study was made of the incorporation of [ 3H]leucine into protein in the sensory neurons and other tissues of the nodose ganglia and upper vagus nerves of the rat, 2 and 9 days after transection of the left vagus at the thoracic inlet. Half of the animals were treated daily with 1.0 μg/kg of triiodothyronine. The following conclusions were drawn. (i) Transection of one vagus did not affect protein synthesis in neuronal somata or in other tissues on the contralateral side. (ii) Treatment with triiodothyronine caused a transient depression of the rate of protein synthesis in normal sensory neurons. (iii) In untreated rats, the neuronal rate of protein synthesis on the operated side was unchanged at 2 days, but elevated at 9 days, after transection of the nerve. (iv) Treatment with triiodothyronine reversed the above situation, there being an increased rate of synthesis at 2 days, but a normal rate at 9 days. (v) In nonneuronal tissue (including axons) of the operated side, the rate of protein synthesis was increased 2 days and 9 days after operation in the control animals, but only after 2 days in the triiodothyronine-treated rats. We suggest that exogenous triiodothyronine produces an immediate acceleration of the synthesis of protein in the somata of injured neurons, which may account for the acceleration of axonal regeneration which has been found to result from treatment with the hormone.