Erythropoietin

The promotion of mitosis in cultured thymic lymphocytes by acetylcholine and catecholamines

Thymic lymphoblasts possess beta-adrenergic, dopaminergic and nicotinic receptors. When activated by high concentrations of adrenaline, isoprenaline, dopamine and acetylcholine, magnesium-dependent events are initiated, which culminate in mitosis. These events can be blocked by testosterone. The cells also possess muscarinic and alpha-adrenergic receptors which respond to low concentrations of acetylcholine, carbamylcholine and noradrenaline. In these cases calcium-dependent, oestradiol-blockable mechanisms are triggered which eventually lead to cell division.

Inadequate erythroid response to hypoxia in cystic fibrosis

An increase in hemoglobin concentration characterizes the normal compensatory response to chronic tissue hypoxia. We observed no such increase in 42 chronically hypoxic patients with cystic fibrosis, in whom the mean concentration was 12.6 gm/dl; one third of the patients were anemic. Compared with patients with cyanotic heart disease, patients with cystic fibrosis did not have a compensatory increase in P50 or 2,3-diphosphoglycerate. Despite anemia, erythropoietin levels in patients with cystic fibrosis were not significantly different from normal control values. The growth of colony-forming units-erythroid in patients with cystic fibrosis was similar to that in control subjects, and there was no inhibition of growth with the addition of autologous serum. Erythropoietin sensitivity, determined by measuring the CFUe dose response curve, was normal in both patients and controls. Results of iron studies were consistent with iron deficiency in the majority of patients. Impaired absorption of iron was observed in six of 13 iron-deficient patients with cystic fibrosis. An inverse correlation between erythrocyte sedimentation rate and peak serum iron was obtained during the iron absorption study. Eight patients who underwent a therapeutic trial of iron demonstrated a 1.8 gm/dl rise in hemoglobin concentration. Two patients with previously documented iron malabsorption responded to parenteral iron therapy after failure to respond to oral supplementation. These studies demonstrate that patients with cystic fibrosis not only have an impaired erythroid response to hypoxia, but are frequently anemic. Their inadequate erythroid response to hypoxia results in part from disturbances in erythropoietin regulation and iron availability.

The effect of 5 alpha-dihydrotestosterone and 5 beta-dihydrotestosterone on erythropoiesis of the newt, Triturus cristatus carnifex (Laur.)

The erythropoietic effects of 5 alpha-dihydrotestosterone (5 alpha-DHT) and 5 beta-dihydrotestosterone (5 beta-DHT) were compared in the newt, Triturus cristatus carnifex (Laur.). In normal animals, 5 beta-DHT was more active than 5 alpha-DHT in increasing the number of circulating erythrocytes. In animals rendered completely anemic, only 5 beta-DHT was effective. The biochemical parameters of delta-aminolevulinic acid synthase and delta-aminolevulinic acid dehydratase of new basophilic erythroblasts, and incorporation of labeled glycine into heme and globin of new polychromatic erythroblasts were enhanced by 5 beta-DHT. The results are discussed with reference to a direct erythropoietin-independent action of 5 beta-DHT on erythroid stem cells.

Erythrocytosis, glomerulomegaly, mesangial hyperplasia, sialyl hyperplasia, and arteriosclerosis induced in rats by nickel subsulfide

Histopathological examinations were performed upon groups of male Fischer rats killed at intervals from 1 h to 18 weeks after unilateral intrarenal (ir) injection of nickel subsulfide (2.5 or 5 mg of Ni3S2/rat). Consistent with previous findings, erythroid hyperplasia of bone marrow and spleen occurred from 2 to 18 weeks after Ni3S2-treatment, resulting in pronounced erythrocytosis. Hitherto unreported effects of Ni3S2-treatment include: (a) marked glomerulomegaly and hyperplasia of mesangial cells in both kidneys; (b) hyperplasia of submandibular salivary glands, and (c) widespread arteriosclerotic lesions. The present study suggests that mesangial cells of renal glomeruli produce erythropoietin. Discovery that ir injection of Ni3S2 induces arteriosclerotic lesions in rats furnishes a new experimental model to investigate the pathogenesis of arteriosclerosis.

Studies on the liver to kidney switch of erythropoietin production

Although the liver is the major site of erythropoietin (Ep) production in the fetus, this function is assumed by kidneys in the adult. The mechanisms underlying the liver to kidney switch of Ep formation are not understood. We studied the natural progression of this transition in sheep by measuring Ep production in response to anemia in normal and bilaterally nephrectomized fetal and newborn sheep beginning at about 80 d gestation (normal gestation: 140 d). Removal of both kidneys before induction of anemia did not affect Ep formation up to about 120 d of gestation. A significant reduction (29%, P < 0.02) in Ep synthesis was first noted at about 130 d of gestation (initiation of switch). This level of nephrectomy-induced reduction of Ep formation persisted until about 15 d after birth. Thereafter, bilateral nephrectomy caused further significant decreases (P < 0.05) in Ep production, gradually resulting in near total absence of Ep production at about day 40 postpartum (completion of switch). Chronic administration of testosterone (12 mg/wk) or estradiole benzoate (1.5 mg/d, 5 d/wk) to the fetus/newborn beginning at 85-90 d of gestation enhanced or suppressed erythropoiesis, respectively, but failed to affect the time at which the liver to kidney switch was initiated and/or completed. By contrast, a significant delay (P < 0.001) in the onset, but not completion of the switch occurred in animals that were either thyroidectomized or rendered chronically anemic beginning in the second third of the gestation period. Administration of thyroxin (1.2 mg/d, 5 d/wk) to thyroidectomized fetus/newborns not only prevented the delay in the initiation of the switch, but also accelerated the rate at which the switch was completed. These results demonstrate that in sheep (a) the liver to kidney switch of Ep production is initiated in utero during the last third of the gestation period, but is completed after birth, (b) this transition occurs gradually; the assumption of Ep producing capacity by the kidney is not preceded by an abrupt loss of hepatic Ep formation; and (c) the switch is not affected by changes in sex hormone levels during the prenatal-postnatal growth periods, but is profoundly influenced by alterations in thyroid hormone and oxygen supply-demand levels.

Evidence for a sexual variation in production of a hepatic erythropoietic factor by hepatectomized rats

Erythropoietin (Ep) is a glycoprotein hormone that is responsible for mammalian red blood cell production. Adult rat liver regenerating 48-72 h after hepatectomy (hepx) produces elevated levels of Ep in response to hypoxia when compared to sham-operated, anephric hypoxic controls. A factor, termed hepatopoietin (Hp), found in the serum of hepx rats, is capable of stimulating hepatic Ep production when administered to normal rats 18 h prior to hypoxic exposure. Although the hepatic vein is the most potent source of this factor, Hp can also be demonstrated in the systemic arterial circulation. Bilateral nephrectomy (nephrx) of the donor hepx animal 24 h prior to bleeding abolishes this variation, and highest Ep levels are noted when serum from a hepx and nephrx rat is administered to animals immediatley after nephrx and 18 h before hypoxic exposure. Serum derived from hepx male rats displays a greater ability to evoke hepatic Ep production in normal recipients than serum from similarly treated female rats. Regardless of the sex of the hepx donor, Ep elaboration after hypoxia is highest in male recipients. The results indicate that there is a sexual variation in the production of Hp as well as Ep.

Cell-cell interaction in erythropoiesis. Role of human monocytes

Erythroid burst forming units (BFU-E) are proliferative cells present in peripheral blood and bone marrow which may be precursors of the erythroid colony forming cell found in the bone marrow. To examine the possible role of monocyte-macrophages in the modulation of erythropoiesis, the effect of monocytes on peripheral blood BFU-E proliferation in response to erythropoietin was investigated in the plasma clot culture system. Peripheral blood mononuclear cells from normal human donors were separated into four fractions. Fraction-I cells were obtained from the interface of Ficoll-Hypaque gradients (20-30% monocytes; 60-80% lymphocytes); fraction-II cells were fraction-I cells that were nonadherent to plastic (2-10% monocytes; 90-98% lymphocytes); fraction-III cells were obtained by incubation of fraction-II cells with carbonyl iron followed by Ficoll-Hypaque centrifugation (>99% lymphocytes); and fraction-IV cells represented the adherent population of fraction-II cells released from the plastic by lidocaine (>95% monocytes). When cells from these fractions were cultured in the presence of erythropoietin, the number of BFU-E-derived colonies was inversely proportional to the number of monocytes present (r = -0.96, P < 0.001). The suppressive effect of monocytes on BFU-E proliferation was confirmed by admixing autologous purified monocytes (fraction-IV cells) with fraction-III cells. Monocyte concentrations of >/=20% completely suppressed BFU-E activity. Reduction in the number of plated BFU-E by monocyte dilution could not account for these findings: a 15% reduction in the number of fraction-III cells plated resulted in only a 15% reduction in colony formation. These results indicate that monocyte-macrophages may play a significant role in the regulation of erythropoiesis and be involved in the pathogenesis of the hypoproliferative anemias associated with infection and certain neoplasia in which increased monocyte activity and monopoiesis also occur.

Erythropoietin dependent erythropoiesis during the erythroblastic phase of juvenile chronic granulocytic leukaemia

A child aged 3 1/2 years with typical juvenile chronic granulocytic leukaemia whose course terminated in an erythroblastic phase is described. Both in-vivo transfusion studies and in-vitro bone marrow culture studies indicate that red cell production remains erythropoietin dependent in this situation. The relationship of erythropoietin to the reversion to fetal haematopoiesis which characterizes juvenile chronic granulocytic leukaemia is discussed.

A simple test for erythropoietin

In Gelfiltration on Sephadex G-100 crude protein prepared from the urine of anemic patients incubated with 59Fe+++ -ions was separated and a distinct fraction isolated having high erythropoietic activity and a high 59Fe+++ -absorption. Increased amount of erythropoietin resulted in a higher incorporation of 59Fe+++ -ions in this fraction. From this we propose to replace the time consuming and very expensive bioassay for erythropoietin in poly-cythemic mice by gelfiltration of the material under investigation preincubated with 59Fe+++ -ions to test the Fe+++ uptake in the forementioned fraction.

Erythroid colony formation by polycythemia vera bone marrow in vitro. Dependence on erythropoietin

In the plasma clot culture system both normal and polycythemia vera (PV) bone marrow cells respond to erythropoietin (Ep), giving rise to large numbers of colonies of erythroid cells. In PV, but not in normal individuals, the marrow produced endogenous erythroid colonies (EED) in the absence of exogenous Ep. The number of EEC formed varied from patient to patient comprising anywhere from 6 to 29% of the total number of colonies formed in the presence of Ep. Exposure, before use in culture, of fetal calf serum and citrated bovine plasma to the gammaglobulin fraction of rabbit anti-Ep serum followed by treatment with goat anti-rabbit gamma-globulin re sulted in a significant decrease in EEC formation. Addition of anti-Ep directly to the culture medium produced similar results. In addition, the production of EEC in response to added Ep was inhibited in the presence of anti-Ep. Addition of very small doses of highly purified Ep to anti-Ep-treated cultures resulted in the reappearance of a significantnumber of EEC formation in PV may be due to a population of erythroid-committed precursors that are abnormally sensitive to small concentrations of Ep which may be present in fetal calf serum and citrated plasma. Although the mechanism of formation of these cells is not known, it appears that the final steps in the formation of red cells derived from this clone of precursors is subject to the usual Ep control.

125I-labelling = 125I-Labelling

Erythropoietin, the hormone that regulates erythropoiesis in mammals, was 125I-labelled by using the catalytic properties of lactoperoxidase and the H2O2-generating properties of glucose oxidase. This methodology, both rapid and simple, not only produced hormone preparations with high specific radioactivity but also did not substantially alter the biological integrity of erythropoietin when it was assayed in vivo.