Influence of the Thymus on Thyroxin‐induced Changes in Blood Lymphocytes of Young Guinea‐pigs

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Abstract
Ernström, U. and B. Larsson. Influence of the thymus on thyroxin‐induced changes in blood lymphocytes of young guinea‐pigs. Acta physiol. scand. 1965. 64. 426–433. – Young male guinea‐pigs were thymectomized or sham‐operated, and treated with thyroxin or saline shortly after operation or one month after it. The influence of thyroxin on the total number of blood lymphocytes, and on blood lymphocytes with different mitochondrial content, was compared in thymectomized and sham‐operated animals. The average mitochondrial content of the blood lymphocytes was not influenced by thymectomy, but was highly increased by thyroxin treatment in both sham‐operated and thymectomized animals. Thyroxin treatment decreased the number of lymphocytes/mm3 of blood in the thymectomized animals, but not in the sham‐operated ones. This reduction was due exclusively to a decreased number of lymphocytes with low mitochondrial content; it was highly significant one month after thymectomy but not significant shortly after it. Thyroxin treatment increased the absolute number of blood lymphocytes with a high mitochondrial content, significantly in the sham‐operated and almost significantly in the thymectomized animals. It is concluded that an intact thymus is not necessary for a thyroxininduced increase in the number of blood lymphocytes with high mitochondrial content. In addition, the results suggest that thymectomy of young guinea‐pigs causes a failure of the thymo‐lymphatic system to maintain an unchanged number of small lymphocytes/mm3 of blood during thyroxin treatment. This failure is not manifested immediately after thymectomy, but is significantly established one month after it.