An effect of corticosteroids on thymocytes not mediated by macromolecule synthesis.

Rat thymocytes were incubated for 2 min at 37 degrees C and the cells then broken by osmotic shock in 1.5 mM MgCl2 and the nuclei harvested. Treatment with 50 nM dexamethasone for 2 min resulted in about one third of nuclei showing abnormalities in appearance, in shape and density. This was not prevented by prior incubation for 10 min with actinomycin D and cycloheximide, but was when nuclei were isolated in the presence of anions larger than F- and Cl-, including I-, Br-, SO = 4 and citrate identical to. Subsequent addition of Cl- ion, however, resulted in development of abnormalities in steroid-treated nuclei. It is concluded that the steroid induces a mechanism resulting in influx of chloride ion leading to nuclear edema, which is not mediated by processes involving synthesis of macromolecules.