Effect of growth hormone on ribonucleic acid metabolism. 1. Incorporation of radioactive phosphate into ribonucleic acid fractions of rat liver

Di Stefano & Diermeier (1959) have observed a decrease in liver RNA and protein in hypophy- sectomized rats.Administration of growth hor- mone restored the levels of liver RNA and protein in these animals.Sesso & Valeri (1958) noted that growth hormone increased the DNA and RNA content of the atrophic pancreas in hypophysectomized rats and concluded that the primary effect of growth hormone is to increase cellular multiplica- tion without modifying appreciably the cytoplasmic growth or the per-cell content of the nucleic acids.In this paper we have examined the effects of growth-hormone treatment and of partial hepatectomy on the incorporation of labelled orthophosphate into RNA from several subcellular fractions of rat liver. MATERIALS AND METHODSAnimals.Six-month-old female (plateaued) albino rats (Malaria Institute strain) were used with litter-mates as controls.The rats were deprived of food overnight.Growth hormone.Antuitrin-G (Parke, Davis and Co. Ltd.) was used and diluted in sterilized 0 9 % NaCl, so that each millilitre contained 10 units.The biological potency of the material was confirmed by assay on female plateaued rats (Evans & Simpson, 1931).The weights of the treated rats increased by 16-26 %, whereas those of the controls did not fluctuate beyond 5-7 %.Partial hepatectomy.One lobe of liver was removed under ether anaesthesia.After 26 hr. the rat was killed and the liver removed.Radioactive phosphorus.32P as orthophosphate in sterile 0 9 % NaCl (Atomic Energy Establishment, Trombay) was injected intraperitoneally (100,uc/100 g. of rat).Removal of the tissue.The animals were killed by de- capitation.The liver was perfused through the hepatic vein with cold 0-25M-sucrose; it was weighed and homogenized in a mixture of (a) 8 vol. of 0-25M-sucrose containing 3-3 mM-CaCI2 and (b) 1 vol. of 0 5M-sucrose (final concentra- tion: sucrose 0-28M, CaCl2 2-9 mM).The homogenization was done in a Potter-Elvehjem (Potter, 1955) type of homogenizer fitted with a Teflon pestle.