Effect of sex hormones on the thymus and lymphoid tissue of ovariectomized rats

Abstract

In ovariectomized and ovariectomized adrenalectomized rats, testosterone, estrogen and a combined dose of progesterone estrogen administered over the course of 3 wk caused a marked decrease in relative weight of the thymus, while progesterone by itself had a thymic depressive activity only when given at high dose levels. In contrast, these hormones caused no detectable change in other lymphoid organs. The relative and absolute number of circulating lymphocytes were decreased by treatment with testosterone or estrogen, while the number of circulating neutrophils increased. From the data it was suggested that estrogen may have a dual suppressive action on the thymus, i.e., directly and indirectly by its influence on the adrenal gland, whereas testosterone has only a direct suppressive action. Histologically, testosterone and estrogen caused a preferential depletion and destruction of lymphocytes in the thymic cortex but not in the medulla. Less mitotic activity was observed in the thymic cortex of hormone treated rats. The number and morphology of thymic reticular cells are unaltered by sex hormone treatment.