Thyroid hormone state and the incorporation of (14C) leucine by brain microsomes in developing rats.
Cell-free incorporation of (14C) leucine into protein was 38% greater for cerebral cortical microsomes from 22-day old neonatally thyroidectomized rats compared to littermate controls. In contrast, incorporation by liver microsomes of hypothyroid rats was 33% lower compared to controls, confirming their deficient hormonal state. Incubation of cerebral microsomes from either hypothyroid or euthyroid rats with both homologous and heterologous pH 5 enzyme fractions clearly implicated the pH 5 fraction as the source of the apparent increase in protein synthetic capacity in the hypothyroid brain. Daily administration of L-thyroxine (20 microgram/100 g body wt) to hypothyroid animals between 22 and 25 days of age produced an additional increase in (14C) leucine incorporation into protein by cerebral microsomes, whereas the cell-free protein synthesis rate of euthyroid rats was unaffected by similar hormonal treatment. Liver preparations from both hypothyroid and euthyroid rats exhibited the expected increase in cell-free protein synthesis following thyroxine administration. The results support the hypothesis that the young hypothyroid brain exhibits delayed maturation and that thyroid hormones play a regulatory role in cerebral protein synthesis during a defined developmental period.
D000818:Animals; D000831:Animals, Newborn; D001921:Brain / Q000378:metabolism*; D002474:Cell-Free System / Q000187:drug effects; D002540:Cerebral Cortex / Q000378:metabolism; D005260:Female; D006863:Hydrogen-Ion Concentration; D007930:Leucine / Q000378:metabolism*; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000096:biosynthesis; D011247:Pregnancy; D051381:Rats; D013963:Thyroid Hormones / Q000502:physiology*; D013974:Thyroxine / Q000494:pharmacology
D009419:Nerve Tissue Proteins; D013963:Thyroid Hormones; D007930:Leucine; D013974:Thyroxine