Protein deficiency impairs erythropoiesis in rats by reducing serum erythropoietin concentration and the population size of erythroid precursor cells.

Erythropoietin (EPO), a glycoprotein produced mainly by the kidney, is the major physiological regulator of erythropoiesis. We developed a sensitive and rapid ELISA for measurement of rat serum EPO with two monoclonal antibodies that recognize different epitopes. To understand the mechanism by which erythropoiesis is impaired in rats deficient in dietary protein, we investigated the levels of the immunoreactive EPO (iEPO) in serums and erythroid precursor cells in hemopoietic tissues during protein deprivation. The iEPO level of 32-d-old rats fed a protein-free diet was lowered to one-third that of rats fed 20% casein at 6 h after protein deprivation began. Protein deprivation decreased the number of EPO-responsive cells in spleen. These results indicate that the impairment of erythropoiesis during protein deficiency is caused by the decrease in serum EPO and the subsequent reduction of the population size of erythroid precursor cells in spleen.