The role of cortisone acetate in liver RNA synthesis of gamma-irradiated rats.

The possible role of induced endogenous glucocorticoid levels stimulated by ionizing radiation and their subsequent effect on rat-liver RNA was investigated in adrenalectomized rats using an intraperitoneal injection of cortisone acetate immediately prior to exposure to gamma-radiation (1800 rad). Adrenalectomized rats were divided into four groups: (1) control rats, (2) irradiated rats, (3) nonirradiated rats treated with cortisone acetate (10 mg/rat), and (4) irradiated rats which received cortisone acetate immediately before irradiation. Newly synthesized RNA was measured by an intraperitoneal injection of 8 muCi (6-14C) orotic acid either immediately after irradiation or 40 min prior to killing. All the rats were killed 6 hours post-irradiation. The results of these investigations indicate that (1) newly synthesized (40 min labelling) RNA increased in irradiated adrenal-intact rats, but not in adrenalectomized animals; (2) cortisone acetate by itself stimulated RNA synthesis whether the radioactive precursor was administered 6 hours of 40 min prior to killing; and (3) irradiation of adrenalectomized rats pre-treated with cortisone acetate induced more RNA synthesis than did cortisone alone. The results of this study support the suggestion that ionizing radiation may induce rat-liver RNA synthesis, at least in part, via stimulated adrenal secretion of glucocorticoids.