Thymus involution, initiated by hydrocortisone treatment, was accompanied by a 90% decrease of thymidine kinase activity per g tissue. The concentration of six other enzymes remained essentially unchanged and that of two increased significantly, indicating that hydrocortisone has a selective effect on the enzymic composition of this organ. Hydrocortisone also decreased the level of thymidine kinase in two erythropoietic organs, fetal liver and neonatal spleen. These results indicate a close connection between thymidine kinase and the effect of glucocorticoids on organs involved in blood cell turnover. The effect of hydrocortisone on thymidine kinase levels does not necessarily coincide with that on cellularity. In spleen of 3-4-day-old rats the hormone did not alter the number of nuclei per g. In fetal liver an injection of hydrocortisone can cause maximal loss of thymidine kinase before there is any detectable loss in the number of hematopoietic cells. These results suggest that intracellular changes in enzyme concentrations precede alterations in cytocomposition.
ASJC Scopus subject areas
- Molecular Biology