Increased synthesis of nuclear RNA in regenerating rat liver after gamma-irradiation.

Nine hours after partial hepatectomy rats were whole-body, 60Co-gamma-irradiated with exposures of 50, 100, 200, 500, 1000 and 2000 R, respectively. RNA was prepared from isolated nuclei of rat liver 12 hours after partial hepatectomy. Animals were injected with 14C-orotic acid 20 minutes before killing. The isolated labelled nuclear RNA was fractionated by sucrose density gradient centrifugation. The specific radioactivity of RNA was correlated with that of the specific radioactivity of nucleotide pool of the liver homogenates. RNA synthesis was found to increase after each dose applied as compared to the rate of RNA synthesis in 12 hours regenerating liver. The increment depended on the dose delivered: 10% at 50 R, 50% at 500 R and 30% at 2000 R. Nuclear RNA synthesis also increased in the liver of non-hepatectomized rats 3 hours after 500 R gamma-irradiation, but the increment was only 20-30% above the non-hepatectomized and unirradiated control.