Biomedical subjects

E H Morgan

Publications and source records attributed to E H Morgan.

At least 55 records · Page 3Linked to original sources

PubMed1996

Iron and copper interact during their uptake and deposition in the brain and other organs of developing rats exposed to dietary excess of the two metals.

This study examined the effect of iron and copper loading on rat brain, liver, kidney, femur, blood and plasma concentrations of these metals and iron transport into the organs during development. Dams were fed control diets or iron-loaded diets (20 g/kg carbonyl iron) with either distilled water or copper-loaded water (350 mg/L) beginning at d 20 of pregnancy. The weanlings also had access to the diets and water supply and were examined at 15, 21 and 63 d of age. The iron content of the liver was 17- to 30-fold greater in iron-loaded rats than in controls, whereas liver, kidney and plasma copper levels generally were lower. Iron loading alone did not increase brain iron concentrations, suggesting the blood-brain barrier is already developed at birth. However, dual loading of iron and copper resulted in elevated concentrations of brain non-heme iron and copper in 15- and 63-d-old rats compared with animals loaded with iron alone. These results suggest that brain iron uptake mechanisms may be different when excess copper is present. Liver non-heme iron was also greater in copper-loaded rats, irrespective of iron status. However, kidney iron concentrations generally were not affected by dietary copper. In rats fed the copper-containing diet, the uptake of iron into brain and liver was significantly lower than in those fed the control diet, suggesting that copper loading can decrease iron uptake into organs. It is concluded that combined dietary supplementation with iron and copper can alter the metabolism of each metal. These changes are age and organ dependent. Developing rats may be very susceptible to these combined overload states because significant effects are seen in early adulthood.

Animals↗

PubMed1996

Cellular iron processing.

Iron is transported in the blood plasma, mainly bound to transferrin, but in abnormal conditions other iron containing compounds may become important. These include ferritin, haemopexin-haem, haptoglobin-haemoglobin and non-specific non-transferrin-bound iron, all of which are taken up from the circulation by the liver. Transferrin-bound iron can be used by all types of cells in amounts that depend on their complement of transferrin receptors. Immature erythroid cells are the most active in this function. Investigations using reticulocytes as an example of erythroid cells have demonstrated the presence of two mechanisms for the uptake of ferrous iron. One, a high affinity process disappears as reticulocytes mature. It probably represents the mechanism by which iron derived from transferrin is transported into the cytosol after receptor-mediated endocytosis of the iron-transferrin complex. The other mechanism has a lower affinity for iron, is retained when reticulocytes mature and is probably associated with Na+ transport across the cell membrane. The physiological characteristics of the two iron transport processes and the evidence for the above conclusions are summarized in the present paper.

Humans↗

PubMed1996

Defective iron uptake by the duodenum of Belgrade rats fed diets of different iron contents.

Homozygous Belgrade rats have an inherited hypochromic, microcytic anemia that is due to impaired iron transport into immature erythrocytes. There is also evidence for abnormal iron transport in other tissues such as the intestine. This study was aimed at investigating the intestinal defect in rats that had been fed diets for 12 days that are normal, low, or high in iron. The duodenal uptake, transfer, and absorption of Fe(III)-nitrilotriacetate and Fe(II)-ascorbate were studied using in vivo tied-off gut sacs in genetically normal rats and in heterozygous or homozygous Belgrade rats. In normal and heterozygous Belgrade rats, the handling of Fe(III) and Fe(II) was similar; uptake, transfer, and absorption of Fe(III) and Fe(II) changed inversely with the iron content of the diet. In contrast, in homozygous Belgrade rats the uptake of both Fe(III) and Fe(II) was markedly reduced and absorption of Fe(III) did not change when animals were fed an iron-deficient diet. Since absorption of Fe(II) was similar to Fe(III), there is no evidence that the defect in iron absorption is due to failure of a mechanism for reduction of Fe(III). The lowered uptake of Fe(III) and Fe(II) in homozygous Belgrade rats probably involves a defective iron carrier associated with the microvillous membrane of the duodenum.

Absorption↗

PubMed1995

Iron transport mechanisms in reticulocytes and mature erythrocytes.

The mechanism of iron transport into erythroid cells was investigated using rabbit reticulocytes and mature erythrocytes incubated with 59Fe-labelled Fe(II) in isotonic sucrose or in solutions in which the sucrose was replaced with varying amounts of isotonic NaCl or KCl. Iron uptake was inhibited at all concentrations of NaCl, in a concentration-dependent manner, but with KCl inhibition occurred only at concentrations up to 10 mM. Higher KCl concentrations stimulated iron uptake to the cytosol of the cells, but inhibited its incorporation into heme. This effect became more marked as the iron concentration was raised. It was found that KCl inhibits iron incorporation into heme and stimulates iron uptake by mature erythrocytes, as well as by reticulocytes. It is concluded that erythroid cells can take up nontransferrin-bound Fe(II) by two mechanisms. One is a high-affinity mechanism that is limited to reticulocytes, saturates at a low iron concentration, and is inhibited by metabolic inhibitors. The other is a low-affinity process that is found in both reticulocytes and erythrocytes, becomes more prominent at higher iron concentrations, and is stimulated by KCl, as well as RbCl, LiCl, CsCl, and choline Cl. The KCl stimulation is inhibited by amiloride, but not by metabolic inhibitors, and its operation is not dependent on changes in cell volume or membrane potential, but it does require the presence of a permeant extracellular anion. Iron uptake by this process appears to occur by facilitated transport and is possibly associated with exchange of Na+. A further aspect of this study was a comparison of iron uptake by reticulocytes from Fe(II)-sucrose and Fe(II)-ascorbate using a variety of incubation conditions. No major differences were observed.

Amiloride↗

PubMed1994

Role of membrane surface potential and other factors in the uptake of non-transferrin-bound iron by reticulocytes.

Reticulocytes suspended in low ionic strength media such as isotonic sucrose solution efficiently take up non-transferrin-bound iron and utilize it for heme synthesis. The present study was undertaken to determine how such media facilitate iron utilization by the cells. The effects of changes in membrane surface potential, membrane permeability, cell size, transmembrane potential difference, oxidation state of the iron, and lipid peroxidation were investigated. Iron uptake to heme, cytosol, and stromal fractions of cells was measured using rabbit reticulocytes incubated with 59Fe-labelled Fe(II) in 0.27 M sucrose, pH 6.5. Suspension of the cells in sucrose led to increased membrane permeability, loss of intracellular K+, decreased cell size, and increased transmembrane potential difference. However, none of these changes could account for the high efficiency of iron uptake which was observed. The large negative membrane surface potential which occurs in sucrose was modified by the addition of mono-, di-, tri-, and polyvalent cations to the solution. This inhibited iron uptake to a degree which for many cations varied with their valency. Other cations (Mn2+, Co2+, Ni2+, Zn2+) were also very potent inhibitors, probably due to direct action on the transport process. Ferricyanide inhibited iron uptake, while ferrocyanide and ascorbate increased the uptake of Fe(III) but not Fe(II). It is concluded that the high negative surface potential of reticulocytes suspended in sucrose solution facilitates iron uptake by aiding the approach of iron to the transport site on the cell membrane. The iron is probably transported into the cell in the ferrous form.

Animals↗

PubMed1994

Receptor-independent uptake of transferrin-bound iron by reticulocytes.

Under physiological conditions the uptake of transferrin-bound iron by reticulocytes involves transferrin binding to membrane receptors followed by endocytosis, release of iron from the transferrin within endosomes, and recycling of apotransferrin to the cell surface. However, as shown in the present work, iron uptake and incorporation into heme will also occur if the cells are incubated in low-ionic-strength media such as isotonic sucrose. This process has a pH optimum of 5.9, is not inhibited by inactivation of the transferrin receptors, and does not involve transferrin endocytosis, but is inhibited by addition of various salts, ferricyanide, and low concentrations of ferric iron chelators, including apotransferrin, to the incubation medium. Iron uptake is temperature dependent, has a high activation energy and is inhibited by a variety of metabolic inhibitors. It is also saturable with an apparent Km of approximately 0.2 microM transferrin-Fe. It is concluded that under these incubation conditions iron is released from transferrin at the external surface of the cell and is transported into the cell by a facilitated, possibly active, transport process. This may occur via the iron carrier which normally functions in the membrane lining of endosomes. Reduction of the iron to the ferrous state is probably necessary for its transport into the cell.

Animals↗

PubMed1994

Effects of chelators on iron uptake and release by the brain in the rat.

The iron chelators desferrioxamine (DFO), pyridoxal isonicotinoyl hydrazone (PIH), 2,2'-bipyridine, diethylenetriamine penta-acetic acid (DTPA) and 1,2 dimethyl-3-hydroxy pyrid-4-one (CP20) were analysed for their ability to change 59Fe uptake and release from the brain of 15- and 63-day rats either during or after intravenous injection of 59Fe-125I-transferrin. DTPA was the only chelator unable to significantly reduce iron uptake into the brain of 15-day rats. This indicates that iron is not released from transferrin at the luminal surface of brain capillary endothelial cells. CP20 was able to reduce iron uptake in the brain by 85% compared to 28% with DFO. Only CP20 was able to significantly reduce brain iron uptake in 63 day rats. Once 59Fe had entered the brain no chelator used was able to mediate its release. All of the chelators except CP20 had similar effects on femur iron uptake as they did on brain uptake, suggesting similar iron uptake mechanisms. It is concluded that during the passage of transferrin-bound iron into the brain the iron is released from transferrin within endothelial cells after endocytosis of transferrin.

2,2'-Dipyridyl↗

PubMed1992

Iron and transferrin uptake by brain and cerebrospinal fluid in the rat.

Iron and transferrin uptake into the brain, CSF and choroid plexus, and albumin uptake into the CSF and choroid plexus, were determined after the intravenous injection of [59Fe-125I]transferrin and [131I]albumin into control rats aged 15, 21 and 63 days and 21-day iron-deficient rats. Iron uptake by the brain was unidirectional, greatly exceeded that of transferrin and was equivalent to 39 and 36% of the plasma iron pool per day in the 15-day control and 21-day iron-deficient rats. The rate of transferrin catabolism in the rats was only about 20% of the plasma pool per day. Iron and transferrin uptake into the brain and CSF decreased with increasing age and was greater in the iron-deficient than in the control 21-day rats. The quantity of 125I-transferrin recovered in the CSF could account for only a small proportion of the iron taken up by the brain. Albumin transfer to the CSF also decreased with age but was lower than that of transferrin and was not affected by iron deficiency. Similarly, the plasma: CSF concentration ratios of transferrin and albumin, as determined immunologically, decreased with age and were greater for transferrin than albumin. It is concluded that iron uptake by the brain is dependent on iron release from transferrin at the cerebral capillary endothelial cells with recycling of transferrin to the plasma and transfer of the iron into the brain interstitium. Only a small fraction of the transferrin bound by brain capillaries is transcytosed into the brain and CSF, this being one source of CSF transferrin while other sources are local synthesis and transfer from the plasma by the choroid plexuses.

Animals↗

PubMed1992

Changes in the uptake of transferrin-free and transferrin-bound iron during reticulocyte maturation in vivo and in vitro.

The uptake of non-transferrin-bound iron, Fe(II), transferrin-bound iron, Tf-Fe and transferrin was studied in reticulocytes from anaemic rabbits during maturation and then synchronized regeneration in vivo (following injection of actinomycin D) and while maturing during in vitro incubation. The uptake of Fe(II) and Tf-Fe decreased in parallel with each other and with the reticulocyte count and transferrin uptake during maturation in vivo and in vitro. Only during the early phase of reticulocyte regeneration in vivo was there a significant difference between the rates of Fe(II) and Tf-Fe uptake. These results suggest that a membrane carrier for iron and the transferrin receptor are lost at the same rate during reticulocyte maturation, possibly because they are associated with each other in the cell membrane. During reticulocyte maturation the rate of Fe(II) uptake into heme declined more rapidly than uptake into the total cellular cytosol. The loss of transferrin receptors and the uptake of iron from transferrin during reticulocyte maturation was not associated with a change in the affinity of the receptors for transferrin, in the relative distribution of the receptors between the outer cell membrane and intracellular sites or in the ability of the transferrin molecule to donate two iron atoms to the cell with each intracellular cycle, but the average duration of the cycle increased.

Animals↗

PubMed1992

Uptake of transferrin-bound and nontransferrin-bound iron by reticulocytes from the Belgrade laboratory rat: comparison with Wistar rat transferrin and reticulocytes.

The mechanism underlying the impaired uptake of iron from transferrin by reticulocytes from the Belgrade laboratory rat was investigated using 125I- and 59Fe-labeled transferrin isolated from homozygous Belgrade rats and from Wistar rats, nontransferrin-bound Fe(II) in an isotonic sucrose solution, and reticulocytes from Belgrade and Wistar rats. The Belgrade rat transferrin had the same molecular weight and net charge as Wistar rat transferrin, donated iron equally well to both types of reticulocytes, and competed equally for transferrin binding sites on the cells. Hence, the defect in iron uptake by Belgrade rat reticulocytes could not be attributed to an abnormality of the transferrin molecule. The rate of uptake of Fe(II) from sucrose into the cytosolic and stromal fractions of Belgrade rat reticulocytes was only about 35% as great as that by Wistar rat reticulocytes. With both types of cells, the uptake process was saturable, suggesting the presence of a carrier-mediated process. It was therefore concluded that the defect in iron uptake by Belgrade rat erythroid cells is probably the consequence of a deficiency in a membrane carrier for iron.

Animals↗

PubMed1992

Diminished iron acquisition by cells and tissues of Belgrade laboratory rats.

Iron uptake from transferrin by a variety of cells and tissues of homozygous Belgrade laboratory rats was compared with heterozygotes, and normal and iron-deficient Wistar rats. In all cases the results for homozygous Belgrade rats were lower than for the other animals. The maximal rate of iron uptake by fibroblasts cultured in vitro and iron passage to homozygous fetuses in utero was less than 60% of control values. In vivo studies of 15-day-old Belgrade rats revealed a defect in the homozygotes with reduced iron transfer to heart, liver, brain, and femurs. In addition, adult Belgrade laboratory rats had impaired intestinal iron absorption compared with the genetically normal animals. It is concluded that the defect in iron metabolism in the Belgrade laboratory rat is a ubiquitous one that affects transport of iron across membranes of many types of cells, resulting in low intracellular iron levels. This suggests that the genetic defect leads to a widely expressed abnormality in the structure and/or function of a membrane carrier for iron.

Absorption↗

PubMed1992

Iron uptake in relation to transferrin degradation in brain and other tissues of rats.

The possibility that iron uptake by the brain involves transcytosis of the iron-transferrin complex across the brain capillaries, followed by degradation of the transferrin (Tf) within the brain, was investigated using diferric 125I-[59Fe]Tf and [59Fe]Tf coupled to 125I-tyramine cellobiose (TC). The radiolabeled catabolic products of proteins labeled with 125I-TC remain in the cells where degradation occurs. The TCTf complex behaved normally with respect to its ability to donate iron to rat reticulocytes in vitro or to the brain, liver, kidneys, and femurs in vivo. In the brain there was little difference in the uptake of 125I derived from Tf and TCTf, and the amounts were equivalent to only a small fraction of the 59Fe uptake. Hence, the rate of Tf catabolism in the brain was insufficient to account for the rate of accumulation of iron from plasma Tf. It was concluded that Tf recycles to the plasma after delivering its iron to the brain. The uptake of 125I from TCTf by the liver and kidneys accounted for 40-50% of the total rate of Tf catabolism. This indicated that they were important but not the only sites of degradation of this protein.

Aging↗

PubMed1991

Effect of metabolic inhibitors on uptake of non-transferrin-bound iron by reticulocytes.

The relationship between transferrin-free iron uptake and cellular metabolism was investigated using rabbit reticulocytes in which energy metabolism was altered by incubation with metabolic inhibitors (antimycin A, 2,4-dinitrophenol, NaCN, NaN3 and rotenone) or substrates. Measurements were made of cellular ATP concentration and the rate of uptake of Fe(II) from a sucrose solution buffered at pH 6.5. There was a highly significant correlation between the rate of iron uptake into cytosolic and stromal fractions of the cells and ATP levels. Iron transport into the cytosol showed saturation kinetics. The metabolic inhibitors all reduced the Vmax but had no effect on the Km values for this process. It is concluded that the uptake of transferrin-free iron by reticulocytes is dependent on the cellular concentration of ATP and that it crosses the cell membrane by an active, carrier-mediated transport process. Additional studies were performed using transferrin-bound iron. The metabolic inhibitors also reduced the uptake of this form of iron but the inhibition could be accounted for entirely by reduction in the rate of transferrin endocytosis.

2,4-Dinitrophenol↗

PubMed1991

Role of transferrin in iron uptake by the brain: a comparative study.

The role of specific transferrin (Tf) and Tf receptor interaction on brain capillary endothelial cells in iron transport from the plasma to the brain was investigated by using Tf from several species of animals labeled with 59Fe and 125I, and 15-day and adult rats. The rate of iron transfer was much greater in the 15-day rats. It was greatest with Tf from the mammals, rat, rabbit and human, but much lower with chicken ovotransferrin and quokka (a marsupial), toad, lizard, crocodile, and fish Tf. The uptake of Tf by the brain showed a similar pattern, except for a very high uptake of ovotransferrin (ovoTf). Iron uptake by the femurs (a source of bone marrow) was also high with Tf from the mammalian species and low with the other types of Tf, but showed little change with aging of the animals. It is concluded that iron transport into the brain is dependent on the function of Tf receptors, probably on capillary endothelial cells, and that these receptors show the same type of species specificity as the receptors on immature erythroid cells. Also, the decrease in iron uptake by the brain as rats age from 15 days to adulthood is specific for the brain and is not a general effect of the aging process.

Alligators and Crocodiles↗

PubMed1991

Specificity of hepatic iron uptake from plasma transferrin in the rat.

1. The role of specific interaction between transferrin and its receptors in iron uptake by the liver in vivo was investigated using 59Fe-125I-labelled transferrins from several animal species, and adult and 15-day rats. Transferrin-free hepatic uptake of 59Fe was measured 2 or 0.5 hr after intravenous injection of the transferrins. 2. Rat, rabbit and human transferrins gave high and approximately equal levels of hepatic iron uptake while transferrins from a marsupial (Sentonix brachyurus), lizard, crocodile, toad and fish gave very low uptake values. Chicken ovotransferrin resulted in higher uptake than with any other species of transferrin. 3. Iron uptake by the femurs (as a sample of bone marrow erythroid tissue) and, in another group of 19-day pregnant animals by the placentas and fetuses, was also measured, for comparison with the liver results. The pattern of uptake from the different transferrins was found to be similar to that of iron uptake by the liver except that with femurs, placentas and fetuses ovotransferrin gave low values comparable to those of the other non-mammalian species. 4. It is concluded that iron uptake by the liver from plasma transferrin in vivo is largely or completely dependent on specific transferrin-receptor interaction. The high hepatic uptake of iron from ovotransferrin was probably mediated by the asialoglycoprotein receptors on hepatocytes.

Animals↗

PubMed1991

Transferrin and iron uptake by the brain: effects of altered iron status.

Transferrin (Tf) and iron uptake by the brain were measured in rats using 59Fe-125I-Tf and 131I-albumin (to correct for the plasma content of 59Fe and 125I-Tf in the organs). The rats were aged from 15 to 63 days and were fed (a) a low-iron diet (iron-deficient) or, as control, the same diet supplemented with iron, or (b) a chow diet with added carbonyl iron (iron overload), the chow diet alone acting as its control. Iron deficiency was associated with a significant decrease and iron overload with a significant increase in brain nonheme iron concentration relative to the controls. In each dietary treatment group, the uptake of Tf and iron by the brain decreased as the rats aged from 15 to 63 days. Both Tf and iron uptake were significantly greater in the iron-deficient rats than in their controls and lower in the iron-loaded rats than in the corresponding controls. Overall, iron deficiency produced about a doubling and iron overload a halving of the uptake values compared with the controls. In contrast to that in the brain, iron uptake by the femurs did not decrease with age and there was relatively little difference between the different dietary groups. 125I-Tf uptake by the brains of the iron-deficient rats increased very rapidly after injection of the labelled proteins, within 15 min reaching a plateau level which was maintained for at least 6 h. The uptake of 59Fe, however, increased rapidly for 1 h and then more slowly, and in terms of percentage of injected dose reached much higher values than did 125I-Tf uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1990

Effect of lead on the transport of transferrin-free and transferrin-bound iron into rabbit reticulocytes.

The effects of Pb on iron transport into rabbit reticulocytes was investigated using two sources of iron, non-transferrin-bound ferrous iron, Fe(II), and transferrin-bound iron, and fractionating the cells into haem, cytosolic and stromal fractions. Uptake of Fe(II) into all three fractions was inhibited by low concentrations of Pb, 50% inhibition of uptake to the cytosol (IC50) occurring at 1 microM Pb. Fe(II) uptake could be divided into saturable and non-saturable components. The saturable component was inhibited at lower concentrations of Pb than the non-saturable component. Pb reduced the Vmax and increased the Km values for saturable Fe(II) transport. The effects of Pb on Fe(II) transport were reversible and were observed with PbCl2 and Pb (NO3)2 as well as with lead acetate. Pb also inhibited the uptake of transferrin-bound iron but at higher concentrations (IC50, 4 microM) and the inhibition was less readily reversible. The effect was attributable to inhibition of transferrin endocytosis which resulted in a redistribution of transferrin receptors from intracellular to cell surface sites. These results show that Pb can inhibit transferrin endocytosis and iron transport across the cell membrane of reticulocytes and raise the possibility that these effects may contribute to the hypochromic anaemia associated with Pb poisoning, in addition to the previously established inhibition of enzymes of the haem synthesis pathway.

Animals↗

PubMed1990

Developmental changes in transferrin and iron uptake by the brain in the rat.

The uptake of transferrin and iron by the brain, liver and femurs was investigated in rats using 125I-59Fe-transferrin (Tf), and 131I-albumin in order to measure the plasma content of the organs. Measurements in rats ranging in age from birth to 70 days revealed that the rate of iron uptake by the brain increased rapidly over the first 15 days of life, peaking at 15 days and thereafter declining. A similar pattern occurred in the uptake of 125I-Tf. These changes were accompanied by rapid growth of the brain up to 15 days and a decrease in the concentration of non-haem iron. The turnover of 59Fe and 125I-Tf in the brain was also determined by measuring radioactivity in the brain of 15-day rats at various times after injection from 15 min to 13 days. The amount of 59Fe in the brain increased over the first 4 h and thereafter remained constant. By contrast, the 125I-Tf values increased rapidly during the first 15 min to reach a relatively constant level which was maintained for at least 6 h after which it declined. The patterns of uptake by the brain were different from those found in the liver and femurs, indicating that the changes in the brain were specific for that organ.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗