Increased 2,5-adenylate synthetase activity in the spleens of BALB/c mice during hypoxia-stimulated erythropoiesis.

In response to prolonged, intermittent exposure to hypoxia, the spleens of adult BALB/c mice displayed an initial increase and subsequent decrease in erythropoietic activity. The enzyme 2,5-adenylate synthetase was assayed during this period, and a direct relationship was found between the rate of red cell production and enzyme activity; that is, 2,5-adenylate synthetase activity was maximum in the spleen cell populations that contained the largest number of nucleated erythroid cells and minimum in those populations that contained the fewest nucleated erythroid cells. In contrast to this finding, synthetase activity was inversely related to the number of lymphocytes present in these spleen cell populations. On the basis of these observations, it appears that 2,5-adenylate synthetase is present in nucleated erythroid cells. If active in late erythroblasts, 2,5-adenylate synthetase may function as an inhibitor of DNA synthesis and/or hemoglobin synthesis.