QUANTITATIVE HISTOLOGICAL CHANGES IN THE THYMUS OF NEWBORN RATS TREATED WITH SEX STEROIDS

P. SOBHON, A. ANGSUSINGHA and C. CHIRASATTHUMB

Summary: Exogeneously administered testosterone or estrogen resulted in a decrease of the thymic weight, a reduction of thymic incorporation of ³H-thymidine and a drop in number of circulating lymphocytes in newborn rats. On the other hand, the administration ofprogesterone caused increases of thymic weight and ³H-thymidine incorporation but a decrease in number of circulating lymphocytes. Histologically, the concentration of lymphocytes was lower than normal in the cortex but higher than normal in the medulla of the thymuses of testosterone. extrogen, and progesterone treated rats.

It was suggested that testosterone and estrogen inhibited mitotic activities and induced the death of thymic lymphocytes whereas progesterone stimulated their mitotic activities and their proliferation. Since in all cases the increased concentration of lymphocytes in the medulla occurred concurrently with the drop in number of circulating lymphocytes, it was suggested that sex steroids might reduce the release of lymphocytes from the thymus by interfering with the process of lymphocyte transport through the walls of post-capillary venules in thymic medulla.

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Anatomy Department. Faculty of Science. Mahidol University. Bangkok

Received 22 January 1975