Response of Nephrectomized Rats to Erythropoietin

Abstract

Erythropoietic decompensation in renal failure has been attributed to diminished production of erythropoietin(1,2) or decreased marrow sensitivity(3,4) to this substance. The relative significance of diminished stimulation or marrow inhibition remains unknown. In the present experiments erythropoiesis and responsiveness to erythropoietic stimulation were assessed in rats made acutely uremic by bilateral nephrectomy. In addition, the effect of uremic plasma on in vitro reticulocyte iron incorporation was studied. The results suggest that red cell production diminished in part because sensitivity to erythropoietin was decreased. In vitro incorporation of radioiron by reticulocytes was not depressed by the uremic milieu.

Materials and methods. Female Sprague-Dawley rats weighing 200–300 g were maintained on a regular laboratory animal diet† and provided water ad libitum. Erythropoiesis was assessed in normal rats and in nephrectomized rats 48 or 72 hours following removal of the kidneys. Similar assessments were undertaken in normal rats and nephrectomized rats stimulated by injection of exogenous erythropoietin.

The stimulated nephrectomized rats were given injections of active extract of anemic rabbit plasma(5) one, 18, and 24 hours following nephrectomy. Non-operated controls were stimulated in an identical manner and measurements of erythropoiesis were made in both groups at 72 hours. Erythropoiesis was assessed by: determination of microhematocrits, enumeration of reticulocytes(6) and measurement of erythrocyte incorporation of radioiron 24 hours after intravenous injection of 1 μc Fe⁵⁹/1 μg Fe⁵⁶ citrate(5). Radioiron partition in the spleen, liver and bone marrow(7) was also determined. Urea nitrogen content was determined on pooled plasma samples from each group(8).

Additional experiments tested the effect of uremic plasma on in vitro iron incorporation by reticulocytes. Reticulocytosis was produced by serial bleedings each approximating 20% of the rats’ blood volume. One week following the initial bleeding, the rats were exsanguinated.