Adult female rats of the Wistar strain were hypophysectomized and divided into 3 groups, the first of which received no treatment for 100 days, the other 2 groups receiving no treatment for 50 days followed by daily subcutaneous injections of 0.6 mg. of cortisone alone or in combination with 0.005 mg. of thyroxin for another 50 days. Another group of rats served as normal unoperated controls.

Hypophysectomy induced a decrease in the number of nucleated cells in the bone marrow, the erythroid elements being the cells responsible for this decrease; the myeloid elements remained normal in number. These marrow changes were reflected in a decrease in reticulocyte percentage and subsequent anemia, while the total white cell count remained normal.

A combined thyroxin-cortisone therapy induced a decrease in myeloid elements in the bone marrow, which resulted in a decrease in the peripheral white cell count. It increased the number of erythroid elements in the bone marrow to a level above that of the hypophysectomized animals with no treatment but not to normal levels. This is undoubtedly due to a very rapid production and release of these cells, for the reticulocyte count was 72 per cent above normal and the anemia in these animals completely eliminated. Blood volume studies showed that these changes in the peripheral blood were not due to a hemoconcentration.

Cortisone therapy alone induced changes in the myeloid elements in the bone marrow similar to that following the dual therapy, and produced a similar decrease in peripheral white cell count. This therapy did not, however, eliminate the post-hypophysectomy anemia as did the combined therapy. Although erythropoiesis in the marrows appeared stimulated and the reticulocyte percentage was elevated, the total cellular volume in these animals was not elevated.

A combined thyroxin and cortisone therapy will not only prevent post-hypophysectomy anemia, as was found previously, but will eliminate the anemia once it has become established.

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