Erythropoietin Production In Rats Research Articles

Cadmium Induces Anemia through Interdependent Progress of Hemolysis, Body Iron Accumulation, and Insufficient Erythropoietin Production in Rats

Cadmium is a toxic heavy metal and distributed widely in the environment. In addition to damaging the liver, kidneys, and bone, cadmium causes anemia through hemolysis, iron deficiency, and insufficient erythropoietin (EPO) production (renal anemia) along with changes in iron metabolism. Here, we investigated the role of iron in the interdependent progress of three types of anemia in cadmium-injected rats fed iron-sufficient or iron-deficient diets for 1 or 3 months. Cadmium injections for 1 month induced renal anemia without renal injury. Injections for 3 months induced hemolysis, iron deficiency, and renal anemia, accompanied by hepatic and renal damage. Iron concentrations in the liver, kidney, and spleen were increased, derived from internally released iron from hemolyzed red blood cells, increased duodenal iron absorption, insufficient erythropoiesis, and hepatic ferritin overproduced by cadmium-induced interleukin-6. Therefore, the iron deficiency anemia was actually apparent. Cadmium suppressed renal EPO production through a direct effect, accumulated iron, and destruction of EPO-producing cells. Increased duodenal iron absorption could be attributed to hypertrophy of the duodenal mucosa derived from anemia. Thus, insufficient EPO production and iron accumulation are the central factors driving anemia in cadmium toxicity.

Effects of Glutathione Depletion on Hypoxia-induced Erythropoietin Production in Rats

In vitro studies have indicated that reactive oxygen species modifying cellular redox status are involved in hypoxia-induced erythropoietin (EPO) production. However, the effects of redox balance on hypoxia-induced EPO production in vivo are still not fully understood. To investigate the effect of the change in cellular redox status on EPO generation, we determined whether glutathione (GSH) depletion has a significant influence on hypoxia-induced EPO production in rats. For the inhibition of GSH synthesis, DL-buthionine-[S,R]-sulfoximine (BSO) was employed by intraperitoneal injection. Twenty male rats were assigned to one of four experimental groups: (1) normoxic placebo, (2) normoxic BSO, (3) hypoxic placebo, and (4) hypoxic BSO. Hypoxic groups were exposed to a simulated normobaric hypoxic condition (4,500 m above sea level) for 12 hours. BSO treatment resulted in a significant depletion of total GSH levels in kidney and plasma in both conditions. However, the hypoxia-induced elevation in serum EPO concentration was not completely affected by the inhibition of GSH synthesis. These data demonstrate that GSH depletion in the kidney is not involved in the increase in serum EPO concentration in response to systemic hypoxia. It is also conceivable that the cellular redox changes could not function as a primary regulator of hypoxia-induced renal erythropoietin formation in vivo.

Erythropoietin gene expression is suppressed after lipopolysaccharide or interleukin-1 beta injections in rats.

Proinflammatory cytokines play an important role in the pathogenesis of anemia in inflammatory diseases. Interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha) have been reported to inhibit the synthesis of erythropoietin (EPO) in vitro. To evaluate the in vivo significance of this observation, we have investigated effects of the administration of bacterial lipopolysaccharide (LPS) and IL-1 beta on renal EPO production in rats. Measurements by competitive reverse-transcription polymerase chain reaction showed that EPO mRNA levels were significantly reduced in the kidneys of normoxic rats 6 h after the injection of LPS (0.1 or 1 mg/kg). In addition, LPS and IL-1 beta (1 microgram/kg) inhibited the increase in EPO mRNA and plasma EPO levels when administered to rats before hypoxia exposure (8% O2 in the inspiratory gas). Evidence for an inflammatory reaction in the kidneys of LPS-treated rats was provided by measurements of greatly elevated renal TNF-alpha mRNA levels. Furthermore, kidneys isolated from LPS-created rats produced less immunoreactive EPO when perfused hypoxically in vitro for 2 h. Thus mediators of the immune response inhibit renal EPO gene expression in vivo, which is relevant with respect to the impaired synthesis of EPO in inflammatory diseases in humans.

Effects of cisplatin on erythropoietin production in rats.

The effects of cisplatin on erythropoietin (EPO) production were investigated in comparison with the effects of phenylhydrazine in rats. Cisplatin (4.5 mg/kg i.p. bolus) decreased red blood cell count (RBC), hematocrit (Hct) and hemoglobin concentration (Hgb) for 14 days after dosing. These decreases were accompanied with increases of blood urea nitrogen (BUN) and serum creatinine (s-CRE). Both serum EPO concentration and kidney EPO mRNA content were significantly decreased in cisplatin-treated rats. On the other hand, phenylhydrazine (10 mg/kg p.o. once a day for 8 days) decreased RBC, Hct and Hgb, and increased serum EPO concentration and kidney EPO mRNA content. Phenylhydrazine had little effect on BUN or s-CRE. These results suggest that a suppression of EPO production is involved in the pathophysiology of cisplatin-induced renal anemia and that measurement of serum EPO concentration and kidney EPO mRNA content is available for distinguishing renal anemia from hemolytic anemia.

Effects of fasting on the hypoxia-induced erythropoietin production in rats.

In order to test the hypothesis that the early cessation of erythropoietin (Ep) production during hypobaric hypoxia is induced by lowered food intake, we have compared the plasma Ep titer of rats after exposure to continuous hypoxia (42.6 kPa = 7000 m altitude) for 4 days with that in fed or fasted rats after exposure to discontinuous hypoxia. We found that plasma Ep was rather low after 4 days of continuous hypoxia. However, the Ep titer significantly rose again, when rats were maintained normoxic for 18 h and then exposed to repeated hypoxia for 6 h. Because this was also found in rats which were deprived of food during the normoxic interval and the second hypoxic period, we conclude that the fall of the Ep titer during continuous hypoxia is not primarily due to reduced food intake. In addition, our findings show that fasting per se lowers the Ep-response to hypoxia in normal rats but not exhypoxic rats.

Effects of partial hepatectomy on extrarenal erythropoietin production in rats

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.

Comparative effects of cyclophosphamide and total body irradiation on erythropoietin production in rats.

Comparative effects of total body irradiation and cyclophosphamide on erythropoietin production in rats are described. The erythropoietin titers in plasma were determined after the rats had been exposed to hypoxia. The rat plasma to be studied was injected into polycythaemic mice. The Fe59 uptake into the red cells of the polycythaemic mice was used as parameter. The results indicate that neither cyclophosphamide nor radiation in sub‐lethal doses suppresses significantly erythropoietin production.