Alterations in the phosphorylation of (3H)uridine and RNA synthesis in rat thymus cells after glucose depletion and treatment with prednisolone.

Abstract

Alterations in the phosphorylation of [3H]uridine and in RNA synthesis resulting from restrictions in the availability of glucose as the only source of energy were studied in rat thymus cells in vitro and compared to the influence of prednisolone injected in vivo on both parameters. The following results were obtained: 1 In the absence of glucose, an impairment in the phosphorylation of [3H]uridine is observed after 15–30 min of incubation. A corresponding decrease in the formation of RNA is not clearly established before 60 min of incubation. 2 Fluctuations in the concentration of glucose in the incubation medium between 1.0 mg and 0.1 mg of glucose/ml produce only modest changes in the capacity of rat thymus cells to synthesize RNA. 3 Phosphorylation of [3H]uridine and RNA synthesis appear to be inhibited in a synchronous rather than a sequential fashion after the administration of prednisolone. 4 The phosphorylation of [3H]uridine is also inhibited in rat thymus cells under the influence of prednisolone when RNA synthesis is completely blocked by actinomycin D or by incubation of thymus cells at 0°. 5 On the other hand, thymus nuclei from prednisolone-treated rats which were depleted of their capacity to phosphorylate [3H]uridine by repeated treatment with a buffer solution containing Triton X-100, still displayed an impairment in their capacity to utilize [3H]ATP for RNA synthesis as compared to corresponding nuclear preparations from normal animals. 6 The steroid-mediated decrease in the phosphorylation of [3H]uridine does not reflect a direct steroid-effect on the kinases but appears to be caused by changes in the structural environment to which these enzymes are normally bound. Our results appear to indicate that prednisolone exerts its catabolic or antianabolic effect on rat thymus cells by at least two distinct mechanisms, one of which involves a decrease in precursor phosphorylation while the other leads to an impairment of RNA synthesis.