ULTRASTRUCTURAL-CHANGES IN THE ADULT-RAT THYMUS AFTER ESTRADIOL BENZOATE TREATMENT

Although numerous authors have correlated high levels of circulating e strogens with thymic involution, a systematic analysis to date on the histological changes affecting the thymus gland in that situation is l acking. In the present study we report both histological and ultrastru ctural changes occurring in the thymus of adult Wistar rats which rece ived a single dose either of 100 mu g or 500 mu g of estradiol benzoat e. Both doses induced thymic involution which correlated well with his tological changes observed in the lymphoid populations but also with p rofound modifications in the thymic epithelial component. Moreover, in trathymic erythro-and granulopoiesis, increased numbers of both macrop hages and plasma cells, and important variations in the thymic vascula r permeability occurred in estradiol benzoate treated rats. These resu lts are discussed from the perspective that changes in both the non-ly mphoid cell components of thymic microenvironments and vascular permea bility are essential to understand the general effects of sex steroids on the immune system.