Phenylhydrazine-induced Anemia Research Articles

Heme-Regulated eIF2α Kinase in Erythropoiesis and Oxidative Stress

Abstract SCI-23 Besides serving as a prosthetic group for hemoglobin, heme also regulates translation by inhibiting the kinase activity of heme-regulated translational inhibitor (HRI). HRI is the only known protein kinase that senses the intracellular heme concentration and does so through its two heme-binding domains. HRI is activated in heme deficiency by autophosphorylation, and phosphorylates the α-subunit of eukaryotic initiation factor 2 (eIF2α), which impairs the recycling of eIF2 for further translational initiation and results in cessation of protein synthesis. In this manner, HRI serves as a feedback inhibitor and coordinates the translation of globin mRNAs with the intracellular heme concentration to ensure that globin proteins are not made in excess of the heme available for the formation of hemoglobin. Excess of globin chains or heme is cytotoxic. In the absence of HRI, uncontrolled protein synthesis in heme deficiency results in globin aggregation and precipitation in red blood cells and their precursors. HRI is responsible for the physiological adaptation that produces hypochromic, microcytic erythrocytes in iron deficiency. The expression of HRI was increased during late stages of erythropoiesis with higher expression in Ter119high erythroblasts and reticulocytes, correlating with the active synthesis and regulation of globins at these stages of erythroid differentiation. In addition to inhibiting global protein synthesis, the second important function of eIF2α phosphorylation is to reprogram translation and the subsequent transcription of genes required for stress response. In mammalian cells, translation of the transcription factor ATF4 mRNA is upregulated specifically by eIF2α phosphorylation via upstream open reading frames in the 5’UTR. Activation of the HRI-ATF4 stress response pathway in nucleated erythroid precursors is required for adaptation to acute and chronic oxidative stress. Furthermore, this HRI-dependent ATF4 pathway is also operative and necessary for erythroid differentiation, especially under stress conditions. In chronic iron deficiency, HRI is necessary for adaptive gene expression for erythroid differentiation as well as for iron heme and redox homeostasis. Beyond heme deficiency and oxidative stress, HRI is also activated by osmotic shock and heat shock. HRI deficiency in mice exacerbates erythropoietic protoporphyria and renders β-thalassemia intermedia embryonically lethal. Hri−/− mice also develop ineffective erythropoiesis during iron/heme deficiency and are severely compromised upon phenylhydrazine-induced acute hemolytic anemia. Thus, translational regulation by HRI plays a critical role in the manifestation of red cell diseases in mice and may be a significant modifier of such diseases in humans. Disclosures: No relevant conflicts of interest to declare.

Phenylhydrazine-induced anemia causes nitric-oxide-mediated upregulation of the angiogenic pathway in Notothenia coriiceps

Antarctic icefishes possess several cardiovascular characteristics that enable them to deliver oxygen adequately in the absence of hemoglobin (Hb). To gain insight into mechanisms driving development of these cardiovascular characteristics of icefish, we chemically induced severe anemia in a red-blooded notothenioid, Notothenia coriiceps. After 10 days of treatment with phenylhydrazine HCl, the hematocrit and Hb concentration of N. coriiceps decreased by >90% and >70%, respectively. Anemic fish exhibited a significantly higher concentration of nitric oxide (NO) metabolites in their plasma compared with that of control animals, indicating that corporeal levels of NO are higher in anemic animals than in control fish. The activity of nitric oxide synthase (NOS) was measured in brain, retina, pectoral muscle and ventricle of control and anemic animals. With the exception of retina, no significant differences in NOS activities were observed, indicating that the increase in plasma NO metabolites is due to loss of Hb, which normally plays a major role in the degradation of NO, and not due to an overall increase in the capacity for NO production. To determine whether loss of Hb can stimulate remodeling of the cardiovascular system, we measured expression of HIF-1alpha, PHD2 and VEGF mRNA in retinae of control and anemic fish. Expression of all three genes was higher in anemic animals compared with control N. coriiceps, suggesting a causative relationship between loss of Hb and induction of angiogenesis that probably is mediated through nitric oxide signaling.

Antianaemic potentials of some plant extracts on phenyl hydrazine-induced anaemia in rabbits

The antianaemic potential of three plant extracts on phenyl hydrazine-induced anaemia in rabbits was investigated. Anaemia was induced in rabbits with phenyl hydrazine hydrochloride at a dose of 30 mg kg-1 b.wt by subcutaneous administration. Treatment of anaemia was done with ethanolic extract ofMangifera indica stem bark, aqueous leaves extract of Telfairia occidentalis andAmaranthus hybridus. In vivo investigation showed that oral daily dose of 20 mg kg-1 b.wt of the ethanolic extract of M. indica stem bark and aqueous leaves extract of T. occidentalis produced a significant (P < 0.05) antianaemic effect. The aqueous leaves extract of A. hybridus only produced a minimal antianaemic effect, reflected by a significant increase (P < 0.05) in haemogloin concentration. Phytochemical analysis of the plant extracts detected saponins, tannins, cardiac glycosides, flavonoids and alkaloids in the 3 extracts. This study therefore, shows that M. indica and T. occidentalis extracts have antianaemic potential. Key words: Anaemia, phenyl hydrazine, Mangifera indica, Telfairia occidentalis, Amaranthus hybridus.

Structural and biological properties of erythropoietin in Xenopus laevis

Erythropoietin (EPO) and its receptor (EPOR) are key regulators of red blood cell production in mammals and fish. We aimed to investigate the structural and functional conservation of the EPO-EPOR system in amphibian erythropoiesis, using Xenopus laevis as a model. X. laevis epo (xlepo) complementary DNA was identified by referring to the Xenopus tropicalis genome database. Biological activity of recombinant xlEPO expressed in COS-1 cells was evaluated using xlEPOR-expressing murine FDC/P2 cells and human EPO-dependent UT-7/EPO cells. Expression of xlepo messenger RNA in adult X. laevis tissues in the normal state and under the condition of phenylhydrazine-induced anemia was evaluated by real-time reverse transcription polymerase chain reaction. In the encoded protein, the positions of four cysteine residues were conserved; however, xlEPO had only 38% identity with human EPO. N-glycosylation sites were absent. Recombinant xlEPO induced proliferation of cell lines expressing xlEPOR and UT-7/EPO, confirming biological activity and cross-species reactivity. Despite little primary amino acid sequence similarity, the evolutionary highly conserved sequence NFLRGK was identified in the EPOR-binding site 1 region as in the human EPO protein. Strong expression of xlepo messenger RNA was detected in the lung and liver, especially in fractionated hepatocytes. No marked increase in xlepo expression was seen in the lung and liver of phenylhydrazine-induced anemic X. laevis. We confirmed that xlEPO is the ligand to the previously reported xlEPOR in X. laevis. xlEPO shares structural and functional similarities and differences with mammalian counterparts, and regulation of xlepo expression and its influence on the erythropoietic system appears to be unique.

In Vitro and in Vivo Inhibition of JAK2 Signaling by Potent and Selective JAK2 Inhibitor

Recent advances in understanding the role of JAK2 V617F mutation in Bcr-Abl negative myeloproliferative (MPD) diseases pathogenesis opened up a possibility to develop highly targeted therapies against these debilitating ailments. We used a Ba/F3 cell line expressing the V617F mutant of JAK2 to screen a focused small molecule library for potential inhibitors of JAK2 V617F-dependent proliferation. Further extensive SAR of initial hits resulted in identification of R723, a potent and selective JAK2 inhibitor. This molecule is strongly antiproliferative (IC50 130–200 nM) against mouse BaF3 cells used for initial screening as well as against human UKE1 and SET2 cell lines harboring the same mutation. On the other hand, R723 has only weak activity in IL2-dependent (i.e. JAK1/JAK3-dependent) proliferation assays performed with human primary T (IC50 1300 nM) and mouse T-cell leukaemia CTLL2 cells (IC50 600 nM). A 10 to 20 fold cell-based selectivity of R723 was further confirmed by measuring inhibition of constitutive STAT5 phosphorylation in SET2 and BaF3 cells versus inhibition of IL-2 inducible STAT5 phosphorylation in human primary T and mouse CTLL2 cells using FACS-based approach. Compound R723 has low nonspecific antiproliferative activity against JAK2-independent MOLT4, A549 and H1299 cell lines with an IC50 ranging from 4 to 6 uM. The molecule has been also proven to be potent (IC50 of 2 nM against JAK2 in biochemical assay) and highly selective (window of more than 500 fold over JAK1 and 10 fold over JAK3) inhibitor of JAK2 kinase in vitro. Moreover, when tested in biochemical assay against a panel of more than 200 kinases at a concentration of 20 nM (IC90 for JAK2), R723 inhibited none of them. The selectivity of R723 was further confirmed using a variety of cell-based assays probing T-, B- and mast cell activation. Compound R723 was further evaluated in a stress-induced erythropoiesis mouse model, where kinetics of EPO-dependent hematocrit recovery from phenylhydrazine-induced anemia was assessed. Significant delay in recovery was observed at doses of 75 and 100 mg/kg bid indicating strong compound effect on EPOR signaling in vivo. The result could not be attributed to general toxicity effects as 14 day toxicology study did not identify any abnormalities at doses tested. As a result, R723 could become the basis for next generation of potent and selective compounds targeting JAK2-dependent myeloproliferative diseases.

Effect of Tectona grandis on phenylhydrazine-induced anaemia in rats

Traditional oral report indicates that Tectona grandis is used in the treatment of anaemia in Togo. For this purpose, the extract of T. grandis leaves is evaluated on anaemia model of rat induced by intraperitoneal injection of phenylhydrazine at 40 mg/kg for 2 days. Oral administration of T. grandis extract at 1 g/kg/day and 2 g/kg/day, to the rats previously treated with phenylhydrazine, increased the concentration of haemoglobin, red blood cells number, haematocrit and reticulocytes rate. Moreover, the extract of T. grandis enhanced the osmotic resistance of the red blood cells that confirm the important presence of young red blood cells. These results support partially the traditional use of T. grandis in the treatment of anaemia.

Enhanced Erythroblast Mobilization in Nix-Deficient Mice Confers Resistance to Phenylhydrazine-Induced Anemia Despite Accelerated Erythrocyte Turnover.

Steady-state and dynamic regulation of erythrocyte production occurs by altering the balance of cell-survival versus apoptosis signaling in maturing erythroblasts. Previously, the pro-apoptotic factor Nix was identified as a critical death signal in normal erythropoietic homeostasis, acting in opposition to erythroblast-survival signaling by erythropoietin and Bcl-xl. However, the role of Nix in stress-erythropoiesis is not known. Here, by comparing the consequences of erythropoietin administration, acute phenylhydrazine-induced anemia, and aging in wild-type and Nix-deficient mice, we show that complete absence of Nix, or its genetic ablation specifically in hematopoietic cells, mimics the effects of erythropoietin (Epo). Both Nix ablation and Epo treatment increase early erythroblasts in spleen and bone marrow and increase the number of circulating reticulocytes, while maintaining a pool of mature erythroblasts as an “erythropoietic reserve”. As compared with WT, Nix null mice develop polycythemia more rapidly after Epo treatment, consistent with enhanced sensitivity to erythropoietin observed in vitro. After phenylhydrazine administration, anemia in Nix-deficient mice is less severe and recovers more rapidly than in WT mice, despite lower endogenous Epo levels. Anemic stress depletes mature erythroblasts in both WT and Nix null mice, but Nix null mice with basal erythroblastosis are resistant to anemic stress. These findings show that Nix null mice have greatly expanded erythroblast reserve and respond normally to Epo- and anemia-stimulated induction of erythropoiesis. However, the hematocrits of young adult Nix null mice are not elevated, and these mice paradoxically develop anemia as they age with decreased hemoglobin content (10g/dl) and hematocrit (36%; at 80±3 weeks of age) compared to WT mice (13g/dl and 46%; 82±5 weeks of age), inspite of persistent erythoblastosis observed in the bone marrow and spleen. Nix null erythrocytes, which are macrocytic and exhibit membrane abnormalities typically seen in immature cells or with accelerated erythropoiesis, demonstrate shorter life span with a half life of 5.2±0.6 days in the peripheral circulation by in vivo biotin labeling (as compared with a half life of 11.7±0.9 days in WT), and increased osmotic fragility as compared with normal erythrocytes. This suggests that production and release of large numbers of reticulocytes in Nix null mice can decrease erythrocyte survival. To rule out a non-hematopoietic consequence of Nix ablation that contributes to or causes increased erythrocyte fragility and in vivo consumption, such as primary hypersplenism, we undertook Tie2-Cre mediated conditional Nix gene ablation. Nixfl/fl + Tie2-Cre mice (hematopoietic-cell specific Nix null) develop erythroblastosis with splenomegaly, reticulocytosis, absence of polycythemia and increased erythrocyte fragility; suggesting that erythroblastosis and accelerated erythrocyte turnover are a primary consequence of Nix ablation in hematopoietic cells. Hence, dis-inhibition of erythropoietin-mediated erythroblast survival pathways by Nix ablation enhances steady-state and stress-mediated erythropoiesis.

Cardiac remodelling in rainbow troutOncorhynchus mykissWalbaum in response to phenylhydrazine-induced anaemia

We examined the nature, extent and timing of cardiac ventricular remodelling in response to chronic, chemically induced anaemia in warm- and cold-acclimated rainbow trout Oncorhynchus mykiss. Chronic anaemia was induced by bi-weekly injections of phenylhydrazine hydrochloride (PHZ) and resulted in transient but large decreases in haematocrit (Hct) and haemoglobin concentration. After 2 weeks of anaemia, relative ventricular mass (rM(V)) in warm-acclimated rainbow trout had already increased significantly and, by the eighth week of anaemia, rM(V) was 58% greater than in the sham-injected control fish. Temperature modulated the anaemia-induced ventricular remodelling and erythropoietic responses, as indicated by cold-acclimation reducing the extent of the cardiac remodelling and slowing erythropoietic recovery. For example, in cold-acclimated fish, PHZ reduced Hct to 8.8+/-1.9% (ranging from 4-16%) and increased rM(V) by 15% over a 4-week period, whereas the same treatment in warm-acclimated fish reduced Hct to only 17.4+/-2.1% (ranging from 6-29%) and yet increased rM(V) by 28%. Cold-acclimated fish also recovered more slowly from anaemia. In addition, warm-acclimated fish maintained compact myocardium between 32% and 37% during anaemia, while cold-acclimated fish responded with an increase in compact myocardium (from 29% to 37%). Routine cardiac output (Q) was continuously monitored following a single PHZ injection to examine the initial cardiac response to anaemia. Contrary to expectations, acute anaemia did not produce an immediate, proportionate increase in routine Q. In fact, Q did not increase significantly until Hct had decreased to 10%, suggesting that rainbow trout may initially rely on venous oxygen stores to compensate for a reduced arterial oxygen-carrying capacity. Thus, we conclude that myocardial oxygenation, acclimation temperature and cardiac work load could all influence anaemia-induced cardiac remodelling in rainbow trout.

PBI-1402: A Non-Toxic Immunorestorative Small Molecule for the Treatment of Anemia.

Erythropoiesis is regulated by an intricated network of transcription factors and other molecules that mediate differentiation of stem cell progenitors into erythroid lineage. PBI-1402 is a non-toxic, well-defined chemo- and radio-protective orally active small molecule which stimulates erythropoiesis. In vivo studies demonstrate that PBI-1402 has an immunorestorative effect in anemia induced by phenylhydrazine or lethal irradiation. In phenylhydrazine-induced anemia, PBI-1402 treated mice had an increased number of hematopoietic progenitor cells compared to the control mice. This increase was more pronounced in the erythroid lineage (BFU-E and CFU-E). In myeloablated mice that received a syngeneic bone marrow transplant, oral treatment with PBI-1402 resulted in a significant increase in peripheral erythrocyte count and hemoglobin concentration. In conclusion, these results indicate that PBI-1402 plays an important role in the formation of red blood cells. Therefore, PBI-1402 may be useful for the treatment of anemia associated with chemotherapy, radiotherapy, bone marrow transplantation and cancer.

Adult murine hematopoiesis can proceed without β1 and β7 integrins

AbstractThe function of α4β1 and α4β7 integrins in hematopoiesis is controversial. While some experimental evidence suggests a crucial role for these integrins in retention and expansion of progenitor cells and lymphopoiesis, others report a less important role in hematopoiesis. Using mice with a deletion of the β1 and the β7 integrin genes restricted to the hematopoietic system we show here that α4β1 and α4β7 integrins are not essential for differentiation of lymphocytes or myelocytes. However, β1β7 mutant mice displayed a transient increase of colony-forming unit (CFU-C) progenitors in the bone marrow and, after phenylhydrazine-induced anemia, a decreased number of splenic erythroid colony-forming units in culture (CFUe's). Array gene expression analysis of CD4+CD8+ double-positive (DP) and CD4–CD8– double-negative (DN) thymocytes and CD19+ and CD4+ splenocytes did not provide any evidence for a compensatory mechanism explaining the mild phenotype. These data show that α4β1 and α4β7 are not required for blood cell differentiation, although in their absence alterations in numbers and distribution of progenitor cells were observed.

Effect of Oral Administration of Aqueous Extract of Khaya senegalensis Stem Bark on Phenylhydrazine-induced Anaemia in Rats

Effect of Oral Administration of Aqueous Extract of Khaya senegalensis Stem Bark on Phenylhydrazine-induced Anaemia in Rats

Mechanisms of regulation of erythropoiesis during hemolytic anemia

We studied changes in the erythroid hemopoietic stem during phenylhydrazine-induced hemolytic anemia. Stimulation of erythropoiesis was associated with increased functional activity of erythroid precursors, which resulted from changes in feeder capacity of hemopoiesis-inducing microenvironmental cells and erythropoietic activity of the plasma. The development of encephalopathy induced by a hemolytic poison was accompanied by a decrease in hyperplasia of bone marrow erythropoiesis. It was related to a decrease in the number of proliferating erythroid precursor cells. These changes accompanied the increase in the secretory function of adherent myelokaryocytes, rise in erythropoietic activity of the plasma, enhanced formation of erythroid hemopoietic islets, and accelerated maturation of hemopoietic cells.

Attenuated signaling by a phosphotyrosine-null Epo receptor form in primary erythroid progenitor cells

AbstractSignals provided by the erythropoieitin receptor (EpoR) are required for erythroid development beyond the erythroid colony-forming unit (CFU-e) stage and are propagated via the EpoR-tethered Janus kinase, JAK2. JAK2 functions, in part, to phosphorylate 8 conserved EpoR phosphotyrosine (PY) sites for the binding of a diverse set of signaling factors. However, recent studies in transgenic and knock-in mice have demonstrated substantial bioactivity for PY-null EpoR forms. Presently, the activities of a PY-null EpoR-HM form in primary progenitor cells from knock-in mice were further assessed using optimized Epo dose-dependent proliferation, survival, and differentiation assays. As compared with the wild-type (wt)–EpoR, EpoR-HM activity was compromised several-fold in each context when Epo was limited to physiologic concentrations. Possible compensatory increases in serum growth factor levels also were investigated, and as assayed using embryonic stem (ES) cell–derived erythroid G1E2 cells, activities in serum from EpoR-HM mice were substantially elevated. In addition, when challenged with phenylhydrazine-induced anemia, EpoR-HM mice failed to respond with efficient splenic stress erythropoiesis. Thus, the function of this JAK2-coupled but minimal PY-null EpoR-HM form appears to be attenuated in several contexts and to be assisted in vivo by compensatory mechanisms. Roles normally played by EpoR PY sites and distal domains therefore should receive continued attention.

Interaction between FOG-1 and the corepressor C-terminal binding protein is dispensable for normal erythropoiesis in vivo.

The hematopoietic, zinc-finger protein FOG-1 is essential for the development of the erythroid and megakaryocytic lineages. FOG-1's function in hematopoiesis is dependent on its ability to interact with the transcription factor GATA-1. FOG-1 has also been observed to interact with the corepressor molecule C-terminal binding protein (CtBP) through a peptide motif shared by all FOG family members. In this study, we confirmed that FOG-1 and CtBP interact by coimmunoprecipitation. We further demonstrate that a FOG-1 mutant unable to interact with CtBP has increased erythropoietic (but not megakaryocytic) rescue (relative to the wild type) of a FOG-1(-/-) cell line. To analyze further the physiological role of the FOG-1-CtBP interaction, we generated knock-in mice that express a FOG-1 variant unable to bind CtBP. Surprisingly, these mice are normal and fertile. Furthermore, erythropoiesis at all stages of development is normal in these mice. Erythrocyte production is similar in mutant and wild-type mice even under conditions of erythropoietic stress stimulated by either exogenously added erythropoietin or phenylhydrazine-induced anemia. Thus, despite conservation of the FOG-CtBP interaction site, the in vivo function of FOG-1 in erythroid development is not affected by its inability to interact with the corepressor CtBP.

Microrheological characteristics of reticulocyte in vivo

Using the method of phenylhydrazine-induced anemia in rabbits, a mass of new reticulocytes, which synchronously grow, were got in vivo. The measurements of deformation index, orientation index, electrophoresis mobility etc. were performed for more than 72 h in the process of reticulocytes turning into red blood cells in vivo. There were obvious changes in the microrheological characteristics of reticulocytes in the course of turning into erythrocytes. The present study is significant in clinic for studying erythrocytes' microrheological characteristics when there are a lot of reticulocytes in blood, and also important in basic theorem for studying reticulocytes microrheological characteristics. It makes up a deficiency in the study on microrheological characteristics of reticulocytes turning into new RBCs from reticulocytes during reticulocytes life span.

Reduced progression of atherosclerosis in apolipoprotein E-deficient mice with phenylhydrazine-induced anemia

Epidemiological and experimental studies suggest that circulating erythrocytes play a role in the incidence of coronary heart disease. We investigated the influence of phenylhydrazine (PHZ)-induced anemia on the formation of atherosclerotic lesions in apo E-deficient mice on regular chow and on a high-fat, high-cholesterol diet during 10 weeks. The repeated doses of PHZ caused sustained anemia throughout the study, changes in the physical characteristics of erythrocytes and increased retyculocyte count. The lesions of the anemic animals were smaller than in the controls and this was even more evident in mice fed with the atherogenic diet. A positive correlation was found between circulating red blood cells at the end of the experiment and the area of aortic lesion. There was also a negative association between the lesion and the retyculocyte count. This reduced progression of atherosclerotic lesions is independent of nutritional status or the lipoprotein cholesterol distribution. The results suggest that mechanisms related to the number of circulating red blood cells may have a significant influence on the development of atherosclerosis.

Changes of serum hemolytic activity and the number of reticulocytes in canine Babesia gibsoni-infection.

When the serum hemolytic activity in Babesia gibsoni-infected dogs was determined with self red blood cells from the infected animals, the decrease in the activity is paralleled with the increase in the number of reticulocytes. The activity determined with red blood cells from phenylhydrazine-induced anemia also decreased parallel with the increase in the number of reticulocytes. These results suggest that the rapid decrease in the serum hemolytic activity after reaching the peak is due to the increase in reticulocytes, which are probably unsusceptible to the hemolytic factor(s).

Dexamethasone suppresses the generation of phenylhydrazine-induced anemia in the rat.

The immunoactive steroid dexamethasone (DXM) was administered to rats injected with a dose of phenylhydrazine (PHZ) known to induce anemia. PHZ treatment alone resulted in a hemolytic anemia that was most pronounced on Days 1-7 after injection. This anemia was accompanied by a leukocytosis that was greatest on Days 2-7 following PHZ treatment. Lymphocytes accounted for greater than 75% of this incremental increase. In contrast, rats treated with PHZ as well as with DXM displayed erythrocyte counts and hematocrits within the normal range. Although the reticulocyte counts of these rats were higher than those of controls, they were significantly lower than those of animals receiving PHZ alone. In addition, DXM suppressed the leukocytosis and splenomegaly resulting from PHZ administration and inhibited the rise in plasma IgG titers induced by PHZ exposure. DXM also altered the ratio of peripheral blood T and B lymphocytes of PHZ-treated rats. DXM suppression of PHZ-induced anemia is further confirmation that this anemia is associated with immune activation.

The effect of macrocytosis on rat erythrocyte deformability during recovery from phenylhydrazine-induced anemia

To investigate the role of red blood cell (RBC) geometry in determining the filterability of stress-induced macrocytes, measurements of RBC volume, diameter, and passage time through 3 micron and 5 micron filters were made on RBCs from control rats and from phenylhydrazine-treated rats during a 28-day recovery period following the peak hemolytic response to the anemia induced by phenylhydrazine (PHZ). Mean cell volumes (MCV) were calculated from volume distribution curves; RBC diameters were obtained from peripheral blood smears; surface area (SA) and mean cylindrical diameter (MCD) were calculated using a biconcave erythrocyte model. At the time of the peak macroreticulocyte response to PHZ, MCD and MCV were significantly increased compared to controls (3.07 vs 2.57 microns, and 102.1 vs 59.7 cubic microns, respectively), the ratio SA/MCV was significantly reduced (1.405 vs 1.670), and RBC filterability through both 3 and 5 micron cylindrical pores was significantly reduced. During the 28-day recovery period, MCV, MCD, SA/MCV, and filterability all returned toward the control values, MCD was inversely correlated with filterability through both 3 micron (r = -0.861, p less than .01) and 5 micron (r = -0.767, p less than .01) pores, and MCD fell below 3.6 microns in 97.5% of the animals despite the persistence of large macrocytic subpopulations. These results emphasize the correlation between RBC geometry and filterability, and demonstrate that macrocytes with favorable geometry can persist in the circulation for extended periods without remodeling or reduction in size.

Evidence for the appearance of a reticulocyte population low in lipoxygenase mRNA during the recovery from a phenylhydrazine-induced anemia in rabbits

It is shown that during recovery from a phenylhydrazine-induced anemia in rabbits a selective decrease in lipoxygenase mRNA takes place with a corresponding shut-off of the synthesis of the enzyme. It is suggested that a new population, ‘recovery’-reticulocytes, makes its appearance in the peripheral blood. Their cells are more mature than the stress macroreticulocytes. A cell-free system prepared from the recovery-reticulocytes exhibits low endogenous synthesis of non-globin polypeptides, even without nuclease treatment, but retains full capacity to be stimulated by exogenous mRNA.