Effects of hypothyroidism and undernourishment on nuclear-cytoplasmic transport [quot ]in vitro[quot ] of cerebral RNA

Neonatal thyroidectomy impairs, at 10 days of age, the [quot ]in vivo[quot ] specific activity of brain [quot ]rapidly-labeled[quot ] RNA, both in nuclei and microsomes. The labeling of ribosomal RNA, whose nuclear synthesis is not affected by hypothyroidism, appears diminished at the microsomal level, indicating an impairment of transport across the nuclear membranes. [quot ]Rapidly-labeled[quot ] RNA values did not change under the same conditions. Underfeeding causes the same changes as thyroidectomy on the labeling and transport of cerebral RNA, with the only exception of the nuclear mRNA release, which is diminished by undernourishment. The alterations of cytosolic factors cause the impairment of cerebral ribosomal RNA release in hypothyroid rats, while changes in unknown intranuclear mechanisms are responsible for the decreased transport of ribosomal RNA in undernourished rats.