Effect of ionizing radiation on RNA metabolism in rat liver

The effect of whole-body gamma irradiation (1800 rads) and 5-fluoroorotic acid (5-FOA) on RNA metabolism in liver of intact and adrenalectomized rats was studied. The level of incorporation of (6-14C)orotic acid into liver RNA during a 30 minute pulse was determined in whole homogenate, nuclear, polyribosomal and non-sedimentable hepatocyte fractions of control, irradiated, 5-FOA treated rats and rats receiving both irradiation and 5-FOA. In whole liver homogenate of intact rats, (6-14C)orotic acid uptake was elevated between 1-6 hours and was maximally increased 3 hours after either irradiation, 5-FOA treatment or the combination of both. The uptake of the radioactive label in the non-sedimentable fraction reached a maximum 6 hours after irradiation alone or in combination with 5-FOA. However, 5-FOA alone doubled the specific activity 1/2 hour following injection. In contrast, in adrenalectomized rats, the uptake into the whole homogenate, nuclear and the non-sedimentable RNA fractions was not increased above the control 1/2 hour after treatment with either irradiation alone or in combination with 5-FOA. At 6 hours, after pulse labelling, the specific activities of the three RNA fractions and whole homogenate were below the control value.