RESUMO
Despite of Glucocorticoids have a well known immunosuppressive action, a little is known about its induction of lymphoid cell death through activation of programmed-cell death known as apoptosis. This work was undertaken with the aim of studying the histological and genetic changes in the thymus gland of albino rats following dexamethasone administration and withdrawal using different doses. Thirty-six adult male albino rats weighting 180-200 gm were used in the present study. The rats were divided into three equal groups [12 animals for each]. Group I [control], injected daily intraperitoneally [IP] with 1ml distilled water. Group H, injected daily [IP] with low dose of dexamathazone [1 gm / Kg b.w.] for seven days and group III, injected daily [IP] with high dose of dexamathazon [2 gm / Kg b.w.] for seven days. Specimens were taken one day after the 1st, 3[rd] and 7[th] injection and three animals from each group were left for recovery and sacrificed seven days after stoppage of treatment. From each specimen, a part was taken for histological, and immunohistochemical studies under light microscopy and the other part was processed for gel electrophoresis. Histological results demonstrated apoptotic changes in thymocytes after a single dose of dexamethasone, more pronounced with the high dose. Aggregation of apoptotic lymphocytes and many large macrophages engulfing apoptotic materials were seen in the cortex. The apoptotic changes were confirmed with positive reaction for Fas-ligand immune activity after a single dose of dexamethasone injection. Severe atrophy of the gland was seen more with high dose where the cortex appeared depleted from lymphocytes. Withdrawal of the drug revealed considerable degree of resolution. The lymphocytes appeared morphologically normal with dispersion of their nuclear chromatin. Our results were confirmed by the results obtained by gel electrophoresis which showed DNA ladders after one day of injection in both low and high doses and complete disappearance of ladders after seven days of medication and in recovered animals. From this study, it was concluded that dexamethasone induced apoptotic changes in thymocytes early after a short period of adminestratione and these changes were timed and dose-dependant with recovery periods proportional to the dose