The proliferative activity of erythropoietic and other tissues has been studied in normal, nephrectomized and bilateral ureter ligated rats.

Forty-eight hours after bilateral nephrectomy, rats showed a significant suppression of DNA synthesis and Fe59 incorporation in the bone marrow and spleen. The administration of erythropoietin prevented this suppression of Fe59 uptake, and produced an increase in splenic DNA synthesis comparable to that noted in the normal, similarly stimulated animal. Bilateral ureter ligation in animals, producing a blood urea nitrogen elevation equal to that induced by nephrectomy, caused no suppression of DNA synthesis in bone marrow or spleen. These latter animals exceeded the normal in their response to erythropoietin administration.

Intestinal DNA synthesis was unaffected in uremia produced by nephrectomy or ureter ligation. Thymic proliferative activity was suppressed in uremia induced by either procedure.

The observations indicate that acute, severe uremia of relatively short duration does not influence the DNA synthetic activity of all tissues in an adverse fashion. What factors may modify tissue responses are unknown. In the case of erythropoietic organs, such factors seem to originate in the kidney.

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