Influence of Cortisol on the Utilization of Precursors of Nucleic Acids and Protein by Lymphoid Cells in Vitro

Abstract

Abstract Effects of cortisol on rat and rabbit lymphoid cells incubated in vitro have been studied. Cells either obtained from cortisol-treated rats or exposed to cortisol in vitro at concentrations of 1 x 10-8 to 1 x 10-5 m showed a diminished degree of incorporation of radioactive precursors into RNA, DNA, and protein. The onset of the effects of cortisol added in vitro was gradual and the effects increased in magnitude with time. Removal of steroid from the cell suspension did not alter the degree of inhibition that already existed. However, with further incubation after removal of steroid there was no further progression or diminution of the inhibitory effect. Cells were not affected when incubated with steroid at 2°. The gradual onset of the effects of cortisol added in vitro was not eliminated by increasing steroid concentration or by varying of several other parameters. In studies with the use of thymocytes with prelabeled RNA, DNA, or protein, incubation with cortisol did not enhance degradation or produce leakage from the cell of the macromolecules. The relative order of sensitivity of lymphoid cells to cortisol added in vitro was as follows: rat thymocytes, rabbit mesenteric node cells, rat mesenteric node cells, and rabbit thymocytes. The steroid inhibitory effects on rabbit node cells also occurred when cells were stimulated in vitro by a thymic fraction containing thymosin, a lymphocytopoietic factor. Thymocytes incubated in vitro after exposure to cortisol in vivo or in vitro exhibited decreased incorporation of precursors into the trichloracetic acid-soluble as well as the trichloracetic acid-insoluble fraction. Medium requirements and the time course for effects on both fractions were the same. Cortisol added in vitro also inhibited α-aminoisobutyric acid and 1-aminocyclopentane-1-carboxylic acid uptake. The data presented indicate a steroid influence on amino acid transport as well as on intracellular accumulation of phosphorylated nucleosides and guanine.