The effect of steroids on the circulating lymphocyte population. I. Changes in the thoracic duct lymphocyte population of the rat after neonatal thymectomy and prednisolone treatment.

The influence of prednisolone on the thoracic duct cells of rats was measured by the cell count in lymph at different times after a single injection and correlated with lymphocytolysis in lymphoid tissues. In both control and neonatally thymectomized animals there was a marked fall in the cell count and flow at 3 hours and the percentage reduction was greater in thymectomized animals. Restitution was rapid in both groups and pretreatment levels were regained in 17 hours. The blood mononuclear cells followed the same pattern. In animals with an intact thymus adrenalectomy causes a significant increase in thoracic duct cell counts but in neonatally thymectomized animals thoracic duct lymph is unchanged after adrenalectomy. It can be concluded that in the rat lymphocyte level in the circulating pool is thymus dependent but restoration of the circulating cell count after steroid induced involution is independent of intact thymic function. Our data support the hypothesis of lymphocyte trapping and redistribution as a major mechanism after a single cortisone dose.