Depressed RNA synthesis in the brains and livers of thyroidectomized, normal and hormone injected rats

Abstract

Depression of rat brain and liver RNA synthesis was seen at 22 and 90 days subsequent to neonatal radiothyroidectomy. Cerebral RNA synthesis (per unit DNA) was depressed by 16% ( P < 0.001) while hepatic RNA synthesis was reduced by 43% ( P < 0.01). Nuclear protein synthesis was not detectably altered. RNA and protein synthesis determinations were conducted, using isolated nuclei in standardized in vitro assay systems which circumvented complications (often seen in vivo approaches) such as pool size changes, cell membrane transport alterations and mediation of blood-brain barrier related effects. Chronic daily administration in vivo of l-thyroxine (10 μg/100 g body weight) restored the depressed cerebral synthesis of RNA to normal levels while daily administration of bovine growth hormone (100 μg per rat) did not.