Nuclear ribonucleic acid polymerase activity, rate of ribonucleic acid synthesis and hydrolysis during development. The role of glucocorticoids

Abstract

In the rat liver birth is followed by marked changes in RNA metabolism. The rate of incorporation of pyrimidine precursors into nuclear RNA and the activity of DNA-dependent RNA polymerase of isolated nuclei increase sharply. These data, together with previous reports from the literature, suggest the hypothesis that during the neonatal period a sharp activation of liver RNA synthesis occurs. On the otherhand, the rate of in vitro hydrolysis of endogenous RNA by liver nuclei was found to be somewhat higher in newborn than in adult rats. It seems that adrenal function plays a role in the postnatal activation of RNA synthesis of newborn rat liver. This is suggested by a lower specific activity of nuclear RNA of newborn rats adrenalectomized at birth than in controls. Newborn rat liver behaves in a peculiar way also as far as its response to glucocorticoids is concerned. Differently from what is usually observed in adult animals, after hydrocortisone injection no increase of pyrimidine precursor incorporation into nuclear RNA is observed in animals less than 4 days old and the DNA-dependent RNA polymerase activity does not change before the 13th day of life.