Renal erythropoietic factor: role of ions and vasoactive agents in erythropoietin formation

Erythropoietin-dependent erythrocytosis associated with hepatic angiosarcoma

Erythropoietin (Ep) dependent erythrocytosis was discovered in a 77-year old man with angiosarcoma involving the liver and spleen. At autopsy, tissue from tumorous and normal sections of liver was obtained and extracts prepared for Ep assay in exhypoxic polycythemic mice. Neither tumor nor normal extracts had Ep activity; however, when the extracts were incubated with normal plasma prior to assay, significant amounts of Ep were generated. The normal liver tissue had three times the activity of the tumorous portion, 0.21 U/ml. These results suggest that the tissue contained an Ep activator, probably erythrogenin. It is proposed that the greater amount of erythrogenin activity in the normal tissue may reflect an attempt at liver regeneration following damage by an invading tumor, as regenerating liver has been identified as a stimulus for extrarenal EP and erythrogenin production.

Demonstration of high levels of erythropoietin in rat kidneys following hypoxic hypoxia

Controversial hypotheses exist as to whether hypoxic kidneys produce biologically active erythropoietin (Ep) or an inactive erythropoietic factor that generates Ep from plasma protein in the blood. To clarify the role of the kidney in Ep production we attempted to extract Ep from kidneys of normal and of hypoxia exposed (6 h at 0.42 atm) Sprague-Dawley rats. Ep was measured in the microsomal fraction of kidney homogenates, using the exhypoxic polycythemic mouse assay for Ep. The Ep content was also determined in kidneys that were flushed free of blood with isotonic phosphate-buffer prior to extirpation. We found 0.04 U Ep/g in blood-depleted kidneys of normal rats. Upon exposure of the animals to hypoxia the Ep level increased to 0.92 U/g kidney. Ep levels were significantly higher in the kidney cortex than in the medulla. The erythropoietic activity in renal extracts was not enhanced after incubation of samples with homologous serum. Ep extracted from hypoxic kidneys behaved identically with plasma-Ep in the following biochemical tests: heat stability, affinity chromatography, with wheat germ lectin, ion exchange chromatography, molecular sieve chromatography, and neuraminidase inactivation. These studies support the hypothesis that kidney cortex cells are capable of producing biologically active Ep.

The in vitro production of erythropoietin and thrombopoietin

In order to determine if there were any relationships between thrombopoietin, erythropoietin and erythrogenin, supernatant fluids from culture lines of foetal mouse liver, foetal and adult bovine kidney, and adult rabbit kidney cells have been assayed for their content of the presumptive humoral regulators of haematopoiesis. Hormone production varied markedly from one culture line to another confirming other studies that the optimal culture conditions for the generation of haematologically-active hormones have not been delineated. The lack of any discernable relationship between the production of thrombopoietin and erythropoietin, thrombopoiet in these and erythrogenin or erythropoietin and erythrogenin suggests that materials represent three distinct entities.