Studies were performed to determine the effect of injecting repeated doses of erythropoietin (Ep) on the red cell volume of chronically uraemic rats and on that of non-uraemic sham operated ones. After 13 doses of Ep (5 u/dose), started either 5 or 2 I d after removal of five-sixths of the renal mass, the increase in the red cell volume of uraemic rats was as great as that ofnon-uraemic ones. The significance of these results is discussed.The anaemia of chronic renal disease remains a therapeutic problem which is unlikely to be solved until erythropoietin (Ep) becomes available in pure form on a large scale. However, the observation that uraemic plasma contains inhibitors of haem synthesis (Markson & Rennie, 1956; Moriyama et al, 1975) and of erythroid colony forming units (CFU-E) growth in vitro ; and that animals with acute uraemia produced by bilateral nephrectomy (Erslev, 1958;Reissmann et al, 1960;Bozzini et al, 1966) respond poorly to Ep raises serious doubts regarding the value of erythropoietin therapy in patients with chronic renal failure. These doubts are reinforced by the results of studies suggesting that patients with chronic renal failure respond suboptimally to crude Ep-containing preparations (Van Dyke et al, 1963 ; Essers et al, 1973).In 1932 Chanutin & Ferris showed that removal offive-sixths of the renal mass of rats in a two-stage procedure caused them to become uraemic and anaemic, and to remain so for a period of over a month. Recently, Anagnostou et al (1976) showed that rats made uraemic according to the above method have an elevated blood urea and a mild to moderate anaemia, which is associated with a decreased ability to produce Ep for at least 3 weeks post-operatively. When chronically uraemic rats are made plethoric, they respond to a single injection of Ep as briskly as do non-uraemic ones.A definitive test of the effectiveness of Ep in treating the anaemia of patients with chronic renal failure is not yet available but the use of this small animal model for the anaemia of uraemia should provide some information on the effectiveness of Ep in correcting the anaemia of chronic renal disease.In this report we shall describe the results of studies designed to show the effects of repeated injections of Ep on the red cell volume of uraemic rats.Center,

The effects of protein deprivation on erythropoietin (Ep) production were studied. The posthypoxia plasma Ep levels of rats fed a protein- free diet for only 1 day prior to being exposed to 0.5 atmosphere for 7 hr were significantly lower than those of comparably hypoxic rats maintained on a normal diet. The postthypoxia plasma Ep levels were even lower in rats kept on protein-depleted diets for longer periods of time. Rats fed diets with 0.5%, 5% or 12% protein content for 6 days had lower posthypoxia plasma Ep levels than those fed a normal diet (20% protein content). When a single protein meal was force-fed to protein-deprived rats 0–4 hr after initiating the exposure to hypoxia, the posthypoxia plasma Ep levels were significantly higher than in protein-deprived rats that were fed water or dextrose. The posthypoxia plasma Ep titers of protein-deprived rats fed protein 4–8 hr prior to exposure to hypoxia did not differ significantly from those of protein- deprived rats. Although the posthypoxia plasma Ep levels of protein- deprived rats fed a hemolysate containing 0.8 g of hemoglobin 4 hr after beginning hypoxia were greater than those of protein-deprived rats fed only water, the rate of oxygen consumption in these two groups did not differ. We conclude that, in addition to its response to the availability of oxygen, Ep production is infl,enced by the availability of amino acids.

The rates of recovery of colony-forming units (CFU) and of hematopoietic stroma following x-irradiation were compared. Hematopoietic stromal function of femurs and spleens was assessed by assaying the number of CFU in those sites 6 wk after implanting them subcutaneously into isogeneic hosts. Whereas the number of CFU returned to preirradiation levels in 6 wk, the hematopoietic stroma did not recover significantly in 9 wk. The reasons for regeneration of CFU in a defective stroma were next investigated. Two contributing factors were identified: (1) Stromal damage following 950 rads is such as to retard the rate of regeneration of CFU without significantly limiting the eventual number of CFU in the site, and (2) Radiated mice contain factor(s), possibly humoral, which accelerate the rate of regeneration of CFU.

Studies were performed to determine the effects of partial hepatectomy on extra-renal erythropoietin production. Rats were either partially hepatectomized or sham operated. At intervals of from 5 min to 7 days afterward, both kidneys were removed from cohorts of the above two groups of rats and the animals were then exposed to hypoxia for 7.5 hr. Immediately afterward, their plasma was collected and its erythropoietin titer was assayed. Rats which were partially hepatectomized 2–4 days prior to nephrectomy and hypoxia had significantly higher plasma erythropoietin levels than did sham- operated controls, whereas rats hepatectomized 5 min, 1 day, or 7 days prior to nephrectomy and hypoxia did not. These data are consistent with the conclusion that extrarenal erythropoietin production is enhanced in association with rapid regeneration of hepatic cells.