The effect of a low-phosphate diet on hematocrit and oxygen transport in uremic rats

Dietary restriction of phosphate was found to prevent the development of anemia in partially nephrectomized rats. In an attempt to examine the reason for this beneficial effect, hematologic and nephrologic studies were carried out on normal and on partially nephrectomized rats fed either a normal or a low-phosphate diet. It was first found that a low-phosphate diet ameliorates the degree of renal impairment found four weeks after partial nephrectomy. Nevertheless, it did not eliminate it, and the degree of uremia actually observed should have been associated with a significant reduction in hemoglobin and red cell mass. However, it did reduce serum phosphate and red cell 2,3-diphosphoglycerate (2,3 DPG) levels and increase hemoglobin affinity for oxygen to a degree that should impair oxygen transport to the tissues. That the low phosphate actually caused tissue hypoxia with increased stimulation of the bone marrow was furthermore suggested by the observation that normal rats fed a low-phosphorous diet developed a significant increase above normal in hemoglobin concentration and red cell mass. It was concluded that the effect of a low-phosphate diet on the anemia of uremia is caused by a combination of reduced renal failure and increased tissue hypoxia.