Morphometrical changes in the rat thymic lymphoid cells after treatment with two different doses of estradiol benzoate.

In the present study we have evaluated morphometrically the contribution of thymocytes to the thymic involution induced by a single injection either of 100 micrograms or 500 micrograms of estradiol benzoate. Our results demonstrate that changes in the numbers of both cortical and medullary thymocytes contribute to thymic involution although the importance of the first is quantitatively higher. On the other hand, while cortical pyknosis and a decreased mitotic index could be important for explaining the estrogen-dependent thymic changes, the release of lymphocytes from thymus seems to be the main factor inducing the thymic involution as well as the lack of recovery observed at the end of the experimental period.