An early sign of erythroblastic leukemia in rat was nodule formation in the spleen. Hyperplastic foci of stem cells, indistinguishable histologically from leukemic stem cells, were found in the red pulp whereas the malpighian corpuscles were uninvolved.

Anemia is a normal phenomenon in immature rats and the spleen of the prepubertal rat possesses considerable hemopoietic potential. Pulse-doses of 7, 8, 12-trimethylbenz(a)anthracene prevented the physiologic hematological development of maturing rats and was associated with subsequent development of leukemic stem cells in the red pulp of the spleen.

Significant enzyme changes were observed in leukemic spleens. Compared with the spleens of normal littermates, the concentration of lactate dehydrogenase rose while that of malate dehydrogenase fell; the content of alkaline phosphatase rose whereas acid phosphatase fell. Increased alkaline phosphatase activity in leukemic spleen was attributed to nonleukemic foci of myelopoiesis.

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