Regulation of tubulin by triiodothyronine in hypothyroid rat brain

The effect of T₃ (triiodothyronine) on the induction of tubulin in hypothyroid developing rat brain has been examined using organ cultures of brains from late fetal, neonatal and postnatalrats. The neonatal brain displayed maximum sensitivity to T₃. Hypothyroidism resulted in a 26% decline in the level of tubulin in the neonatal brain as opposed to a 5–15% decline in the fetal or postnatal brain. Exposure of the hypothyroi d neonatal brain to T₃ for 2 h in culture led to a 61% rise in the level of tubulin in contrast to a 41% increase seen in the case of normal brain. Total protein synthesis was not significantly affected . The preferential decline of tubulin in the neonatal hypothyroid brain, its enhanced sensitivity to T₃ compared to normal brain, and the coincidence of the period of sensitivity to that of brain maturation indicate that the regulation of the level of tubulin by T₃ in the developing brain is a natural ontogenic phenomenon.