Glucocorticoid-induced cell-size changes and nuclear fragility in rat thymocytes.

The events preceding glucocorticoid-induced lymphocytolysis have been studied in isolated rat thymocytes. Incubation of thymocytes at 37 degrees C in the presence of 1 microM dexamethasone resulted in the progressive appearance of pyknotic cells of modal diameter 4.5 mum, distinct from normal cells of diameter 5.2 mum. The rate of appearance of the pyknotic cells was determined by selective electronic cell counting, and was shown to be accompanied by increased nuclear fragility. The production of pyknotic cells was glucocorticoid-specific, dose-dependent, blocked by cycloheximide, and preceded the loss of cell viability as determined by dye exclusion. The pyknotic cells were separated from the non-pyknotic cells by density gradient centrifugation and shown to be solely responsible for the observed nuclear fragility.