The aim of the present study was to determine the target site cells in the rat thymus after exposure to the synthetic glucocorticoid, dexamethasone, at therapeutic doses. The findings of histology and histochemistry (Feulgen, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling--TUNEL) with quantification by computerized histomorphometry are described.
Material and methods: A quantified investigation of apoptotic and mitotic thymic lymphocytes in 36 young adult Wistar rats was performed at 1-7 days after a 3-day injection of dexamethasone (a total dose of 1.2 mg/rat intraperitoneally).
Results: At the first day after dexamethasone administration the moderate involution and atrophy of thymus histology were observed with simultaneous fall in cortical cellularity and mitotic activity of thymocytes. More rapid fall appeared in the inner cortex. The number of apoptotic (TUNEL-positive) cells was significantly increased. On the days 5 and 7 the expression of apoptosis and the cell proliferation were at almost normal level.
Conclusions: The findings suggest that dexamethasone-induced apoptosis of cortical thymic lymphocytes, mainly correlated with synchronous inhibition of mitosis and cell number fall in thymus. The main target sites of dexamethasone injury were cells in the inner cortex of lobuli thymi.