Effects of bovine growth hormone on RNA synthesis in brain and liver of neonatal hypothyroid rats.

The action of growth hormone upon RNA synthesis was studied in isolated nuclei from cerebrum and liver of hypothyroid rats. The acute administration of bovine growth hormone (bGH) to cretinoid rats, 10 days after birth, stimulated the endogeneous activity of RNA polymerase I and II in both organs. The transcription of ribosomal RNA in cerebrum and hnRNA in liver increased 40 min. after the injection and continued to be higher than in controls until 14 hrs. An increase in the synthesis of hepatic ribosomal RNA occurred 5 hrs. after treatment, the effect persisting during the whole period studied. The activity of cerebral RNA polymerase II displayed a bimodal curve with an early stimulation at 40 min. and a second one at 14 hrs. The results give evidence in favour of the action of growth hormone during the postnatal development of rat brain.