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At least 631 records · Page 35Linked to original sources
PubMed1978

Effects of triiodothyronine on the anemia of chronic renal failure.

The present study was done in order to determine whether treatment with triiodothyronine (T3) would improve the anemia of chronic renal insufficiency. Four patients with stable renal failure and anemia were treated with 75 microgram/day of T3 for a period of four weeks. The patients were not in chronic dialysis, had normochromic normocytic anemia and hypocellular bone marrow, and showed no evidence of external blood loss during the study. They had received no iron, folic acid, or androgenic steroids for at least six months prior to the study. The administered dose of T3 was adequate to depress the serum levels of thyroid-stimulating hormone (TSH); however, there was no detectable improvement in the levels of hemoglobin, hematocrit, bone marrow cellularity, serum and erythrocyte folate determinations, serum iron (Fe), 59Fe half-life, plasma iron turnover rate, percentage Fe incorporated into red blood cells, or in the ratio of surface radioactive counting over bone marrow/liver and spleen. It is concluded that the experimental observations concerning direct bone marrow stimulation by T3 in anephric rats are probably not clinically applicable for the treatment of the anemia associated with uremia.

Adult↗
PubMed1969

Measurement of blood and iron loss in colitis with a whole-body counter.

Estimation with a whole-body counter of the fall in total body radioactivity due to loss of parenterally administered (59)Fe has been used to measure blood loss in 17 patients with ulcerative colitis. It was shown that blood loss was related to the activity of disease as judged by sigmoidoscopic changes and less obviously to the extent of involvement of the colon. Blood losses of 50 to 150 ml per week were observed when the patient saw no blood in the stools and the rectal mucosa did not appear haemorrhagic. Some patients lost more than 0.5 g iron during the few weeks following an exacerbation of ulcerative colitis suggesting that repeated replacement of the body's iron stores is often necessary in this disease.

Adult↗
PubMed1983

Identification of the serum binding proteins for iron, zinc, cadmium, nickel, and calcium.

The binding of five biologically important metals to serum proteins has been studied. After suitable radioactive isotopes were added to serum proteins separated and precipitated by two-dimensional immunoelectrophoresis, the sample plates were exposed to roentgenogram film. 59Fe bound to transferrin alone; 65Zn bound mostly to albumin, but also to another 12 proteins; 109Cd was mostly associated with alpha 2-macroglobulin, but was also present on albumin, immunoglobulins G and A, and prealbumin; 63Ni, added in high concentration, was associated with an alpha 2-mobility protein and albumin; and, finally, 45Ca was mostly bound to albumin, but seven other binding proteins were also identified, with transferrin predominant. The results are not quantitative, but the technique is simple and specific, and the information gained can direct further studies on isolated proteins.

Autoradiography↗
PubMed1989

An experimental study on the pathway of iron transfer from macrophages to erythrocytes in rat liver.

In order to reveal the pathway of iron release from macrophages, a 59Fe-labelled ferric hydroxide-potassium polyvinyl sulfate complex (Fe-PVS) was injected intravenously into anemic rats and the level of radioactivity in the liver, spleen, bone marrow, blood plasma and red blood cells (RBC) was estimated at various time intervals after the injection. Histochemical observation of ferric iron and ferritin in the liver was also made on anemic rats treated using unlabelled Fe-PVS. Fe-PVS injection promoted the recovery of anemia causing a rapid increase in the RBC number, with activated erythropoiesis occurring in the spleen and bone marrow. Soon after the injection, most of the radio iron was found in the liver with a small amount in the circulating erythrocytes, bone marrow and spleen. The iron level in the liver decreased gradually with a rapid increase in the iron level of the erythrocytes which reached a very high level 6 days after the 59Fe-PVS injection. Histochemical observations showed a heavy deposition of ferritin in the Kupffer cells 3 days after Fe-PVS injection. This deposition was minimized after 6 days with an increase in the level of ferritin in the parenchymal cells in the central area of acini. The level of radioferritin estimated biochemically in the nonparenchymal cell fractions of the liver revealed that the level dropped by about one third approximately 3.5 days after the Fe-PVS injection, showing the stimulated ferritin release at this stage. Results indicate that Kupffer cells in the liver play an important role in ferritin synthesis from the phagocytized iron compounds and that the iron is supplied for erythroid cell proliferation.

Animals↗
PubMed1978

Nonexistence of N-acetylseryl-tRNA in rat liver.

Reports of the existence of N-acetylseryl-tRNA in rat liver were reinvestigated. Methods were developed to permit recovery of N-acetylserine in a yield of 30--40% from N-acetylseryl-tRNA added to liver homogenates and cell-free incubations. [14C]Serine and [3H]acetate were injected into rats pretreated with iron and into rats after partial hepatectomy, and aminoacyl-tRNA was isolated from their livers. The amount of radioactivity associated with N-acetylserine in the amino acids released by hydrolysis from the aminoacyl-tRNA was negligible. No formation of N-acetylseryl-tRNA could be observed in incubations of acetyl CoA and seryl-tRNA or tRNA with enzyme fractions from liver of rats pretreated with iron. It is concluded that previous reports of the existence of N-acetylseryl-tRNA in rat liver are erroneous.

Animals↗
PubMed1995

Uptake of iron from N-terminal half-transferrin by isolated rat hepatocytes. Evidence of transferrin-receptor-independent iron uptake.

The aim of the present study was to determine if human N-terminal half-transferrin (N- fragment), prepared by thermolysin cleavage of diferric transferrin, would bind to the rat hepatocyte transferrin receptor and donate iron to the cell. Competition experiments between 125I-labelled N-fragment and diferric transferrin revealed no receptor binding of the half-transferrin. Still, the N-fragment delivered iron to the cells in amounts approximately 30-fold above what could be accounted for by uptake of the fragment itself. The rate of cellular iron uptake from the fragment was comparable to what is seen with the intact transferrin. The uptake of 125I-labelled N-fragment was not inhibited by excess non-radioactive diferric transferrin. By comparison, the uptake of 59Fe from the N-fragment was inhibited 70% by excess nonradioactive diferric transferrin. This suggests that iron derived from diferric transferrin competes with the iron derived from the N-fragment for a common transport pathway. Although some cellular degradation of the N-fragment occurred, the extent of degradation was too low to explain the amount of iron accumulated by the cells. The results show that the hepatocyte has an effective transferrin-receptor-independent mechanism for accumulation of iron from transferrin.

Animals↗
PubMed2001

Aluminium toxicity and iron homeostasis.

In an animal model of aluminum overload, (aluminium gluconate), the increases in tissue aluminium content were paralleled by elevations of tissue iron in the kidney, liver heart and spleen as well as in various brain regions, frontal, temporal and parietal cortex and hippocampus. Despite such increases in iron content there were no significant changes in the activities of a wide range of cytoprotective enzymes apart from an increase in superoxide dismutase in the frontal cortex of the aluminium loaded rats. Such increases in tissue iron content may be attributed to the stabilisation of IRP-2 by aluminium thereby promoting transferrin receptor synthesis while blocking ferritin synthesis. Using the radioactive tracer (26)Al less than 1% of the injected dose was recovered in isolated ferritin, supporting previous studies which also found little evidence for aluminium storage within ferritin. The increases in brain iron may well be contributory to neurodegeneration, although the pathogenesis by which iron exerts such an effect is unclear.

Aluminum↗
PubMed1975

Ethanol inhibition of reticulocyte protein synthesis: the role of haem.

Ethanol, in concentrations of 0.05-0.8 M, inhibited intact human and rabbit reticulocyte protein synthesis in the presence of iron-transferrin for endogenous haem synthesis. Associated with this effect there was a conversion of polyribosomes to monoribosomes and a decreased incorporation of radioactive leucine into nascent globin chains. When physiological levels of ethanol (0.05-0.1 M) were used, these effects were prevented by incubation with 50 muM haemin and reversed by removing the alcohol and reincubating with iron-transferrin or haemin. The polyribosomal disaggregation was also prevented by stopping ribosomal movement with 5 mM cycloheximide. Neither ATP nor GSH levels were altered in the presence of ethanol. When non-physiological levels of 0.8 M ethanol were used, haemin did not prevent the inhibition of protein synthesis. Likewise, in the rabbit reticulocyte cell-free lysate system containing haemin inhibition was noted at concentrations greater than 0.05 M ethanol. The polyribosomal disaggregation in reticulocytes incubated with 0.8 M ethanol was associated with decreased dissociation of monoribosomes into subunits. Similarly, when ribosomes were directly suspended cell-free in 0.1 or 0.8 M ethanol there was a decreased percentage of subunits. These results indicate that physiological concentrations of ethanol inhibit initiation of reticulocyte protein synthesis secondary to a block in haem synthesis. When intact cells are exposed to high non-physiological concentrations of ethanol the inhibition is secondary to decreased ribosomal dissociation. The cell-free lysate inhibition is also through this effect on ribosomal dissociation. This study supports the view that alcohol is a direct toxin to developing red cell precursors via its effect on mitochondrial haem synthesis. The physiological role of the decreased dissociation of monoribosomes into subunits is not yet clear.

Acetaldehyde↗
PubMed1999

Kinetic analysis of 52Fe-labelled iron(III) hydroxide-sucrose complex following bolus administration using positron emission tomography.

Kinetic analysis of a single intravenous injection of 100 mg iron(III) hydroxide-sucrose complex (Venofer) mixed with 52Fe(III) hydroxide-sucrose as a tracer was followed for 3-6 h in four generally anaesthetized, artificially ventilated minipigs using positron emission tomography (PET). The amount of injected radioactivity ranged from 30 to 200 MBq. Blood radioactivity, measured by PET in the left ventricle of the heart, displayed a fast clearance phase followed by a slow one. In the liver and bone marrow a fast radioactivity uptake occurred during the first 30 min, followed by a slower steady increase. In the liver a slight decrease in radioactivity uptake was noted by the end of the study. A kinetic analysis using a three-compartment (namely blood pool, reversible and irreversible tissue pools) model showed a fairly high distribution volume in the liver as compared with the bone marrow. In conclusion, the pharmacokinetics of the injected complex was clearly visualized with the PET technique. The organs of particular interest, namely the heart (for blood kinetics), liver and bone marrow could all be viewed by a single setting of a PET tomograph with an axial field of view of 10 cm. The half-life (T1/2) of 52Fe (8.3 h) enables a detailed kinetic study up to 24 h. A novel method was introduced to verify the actual 52Fe contribution to the PET images by removing the interfering radioactive daughter 52mMn positron emissions. The kinetic data fitted the three-compartment model, from which rate constants could be obtained for iron transfer from the blood to a pool of iron in bone marrow or liver to which it was bound during the study period. In addition, there was a reversible tissue pool of iron, which in the liver slowly equilibrated with the blood, to give a net efflux from the liver some hours after i.v. administration. The liver uptake showed a relatively long distribution phase, whereas the injected iron was immediately incorporated into the bone marrow. Various transport mechanisms seem to be involved in the handling of the injected iron complex.

Bone Marrow↗
PubMed1986

Formation of the iron-sulfur cluster of ferredoxin in isolated chloroplasts.

The formation of the iron-sulfur cluster of ferredoxin was examined in vitro by incubating isolated chloroplasts with [(35)S]cysteine. The ferredoxin molecule was radioactively labeled in chloroplasts without synthesis of its polypeptide and comigrated with holoferredoxin during polyacrylamide gel electrophoresis under nondenaturing conditions. When the labeled ferredoxin was denatured by the addition of trichloroacetic acid, radioactive acid-labile sulfide in the cluster was released from the polypeptide as a gas and trapped in a 0.1 M NaOH solution. These results indicate that the sulfur atom derived from cysteine was incorporated into ferredoxin through formation of the iron-sulfur cluster. This process was stimulated by light and inhibited by the electron transport inhibitor, dichlorophenyldimethylurea, and the uncouplers, atebrin and gramicidin, but not by the protein synthesis inhibitor, chloramphenicol. These inhibitory effects were reversed by the addition of ATP to the incubation mixture. Formation of the iron-sulfur cluster of ferredoxin in chloroplasts is thus dependent on ATP.

Journal Article↗
PubMed1979

Subcellular distribution of radio-labelled iron during intestinal absorption in guinea-pig enterocytes with special reference to the mitochondrial localization of the iron.

1. 59Fe-labelled ferric chloride was introduced into tied loops of guinea-pig jejunum. 2. After 5--30 min the loop was removed, the enterocytes were isolated, homogenized and subjected to analytical subcellular fractionation. 3. Uptake of 59Fe was extremely rapid and after 5 min 45% of the radioactivity sedimented in the mitochondrial fraction. 4. Density gradient centrifugation indicated that approximately 80% of this radioactivity was associated with the mitochondria themselves; the remainder was in brush-border fragments. 5. Selective disruption of the mitochondria demonstrates that the iron is localized to the matrix and the inner membrane, indicating transport of the absorbed iron into the organelle. 6. It is suggested that mitochondria are actively implicated at an early stage in the intestinal transport of iron.

Animals↗