An In vitro effect of physiological levels of cortisol and related steroids on the structural integrity of the nucleus in rat thymic lymphocytes as measured by resistance to lysis

Abstract

The ability of rat thymus cell nuclei to survive lysis of cells by hypotonic shock (dilution into 1.5 mM MgCl 2) is decreased by incubation of whole cells with physiological levels of glucocorticoid hormones in vitro. This effect on “nuclear fragility” is first discernible after 0.5–1 h of incubation with hormone as an increase in non-sedimentible DNA in whole cell lysates. It is measureable at 2 h by counting numbers of surviving nuclei, and by changes in the distribution of DNA and protein from lysed cells on sucrose gradients. Evidence is presented to show that the effect is initiated by a series of molecular events characteristically similar to those which initiate the metabolic effects of the hormone, including specific binding of hormone to receptors and events that are sensitive to cycloheximide. The effect differs from effects of the hormone on many transport and biosynthetic processes which occur at the same time (1–3 h) in as much as the nuclear effect does not require the presence of a carbohydrate energy source in order to become apparent. The specificity and time of onset of the decrease in nuclear integrity combined with the fact that it is reflective of changes in nuclear structure, make it quite likely that it is a simple, rapid assay in vitro of the lymphocytolic effects of Cortisol.