Cellular Hemoglobin Concentration Research Articles

Decreased concentration of hemoglobin, accumulation of lipid oxidation products and unchanged skeletal muscle in Atlantic salmon (Salmo salar) fed low dietary vitamin E

Atlantic salmon (Salmo salar) fry, initial weight 0.16 g, were fed a semipurified diet with 0, 15, 30, 60 or 120 mg dl-α-tocopheryl acetate/kg. After 24 weeks, the first two of these groups were extinct, and the fish receiving 30 mg/kg were clearly vitamin E deficient. Vitamin E deficient fish had low hemoglobin levels, characterized by a combination of reduced cellular hemoglobin concentration, red cell volume and red cell number, and an increased number and fraction of immature red blood cells. The hemoglobin concentration decreased over the decreasing range of experimental dl-ga-tocopheryl acetate levels. Therefore, even if 60 mg dl-α-tocopheryl acetate/kg gave good survival, this level was clearly physiologically suboptimal. Ceroid accumulated in the liver of fish fed 30 mg vitamin E/kg, and autofluorescent inclusions were found in the red blood cells of fish fed 30 and 60 mg vitamin E/kg. Degeneration of skeletal muscle was not observed in the present study.

Effects of artificially elevated plasma cortisol levels on blood parameters in the teleost fish Pagrus auratus (sparidae)

1. 1. A treatment protocol involving intraperitoneal injection of cortisol in the fish Pagrus auratus (Sparidae) produced an elevation of plasma cortisol while control snapper maintained stable levels of plasma cortisol. 2. 2. Artificial elevation of cortisol levels led to an increase in blood lactate, and decreases in both blood ATP and MCHC (mean cellular hemoglobin content). 3. 3. Different maintenance techniques of captive snapper led to different resting levels of plasma cortisol. 4. 4. Chronically elevated levels of cortisol led to long term changes in hematological parameters, including decreased MCHC and ATP levels and increased lactic acid when compared to fish sampled directly from the wild.

Stress-Related Changes in the Hematological Profile of the American Eel (Anguilla rostrata)

The authors investigated the impact of environmentally realistic concentrations of cadmium (Cd) on the hematological responses of the eel to acute stress. After 8 weeks of exposure to 150 μg Cd/liter, there was a significant reduction in the total erythrocyte count, hemoglobin (Hb), and hematocrit (Hct). Total leukocyte counts, leukocrit, and large lymphocytes were significantly increased, while the proportion of small lymphocytes fell. After 8 weeks of Cd exposure, acute stress was induced by a 2-min exposure to CO2 bubbles. The untreated control fish responded strongly by erythrocyte swelling, which was evident from a marked increase in the Hct and mean cellular volume, and a decreased mean cellular hemoglobin concentration. Furthermore, there was a marked granulocytosis and a strong drop in the thrombocyte count. After Cd treatment, the erythrocyte changes were attenuated and shorter, granulocytes were increased, and there was no drop in the thrombocyte count. It appears that the Cd exposure decreased the erythrocyte response to adrenergic stress signals. It also decreased the stress-related granulocytosis, and it prevented the drop of the thrombocyte count.

Physiological Response of the Atlantic Cod (Gadus Morhua) to Hypoxia at Various Environmental Salinities

ABSTRACT Atlantic cod (Gadus morhua L.) acclimated to water salinities ranging from 28 ‰ to 7 ‰ were exposed to mild (8.0 kPa) or severe (4.0 kPa) hypoxic conditions for 6h. In each experiment, respiratory, acid–base, ionic, haematological and metabolic disturbances were analyzed. During mild hypoxia, a strong hyperventi-latory response was observed, resulting in a respiratory alkalosis that persisted throughout the 6-h trial. Plasma Cl− and pyruvate levels were the only other variables to display significant changes: they both increased. In more severe hypoxic conditions, although the ventilatory response was the same, a weak metabolic acidosis was superimposed. The haematological response (increased haematocrit and decreased mean cellular haemoglobin content) suggested that catecholamines were released into the blood. Both Na+ and Cl− concentrations increased significantly. Metabolic perturbations occurred: plasma lactate, pyruvate and glucose concentrations increased markedly. Though lactate concen-trations in liver, heart and white muscle increased, the concentrations of pyruvate, glucose and glycogen did not change significantly. Water salinity affected the amplitude of the ionic responses during hypoxia: the amplitude decreased with decreasing salinity. Irrespective of water salinity, 23 of 29 fish survived the severe hypoxic conditions. This relatively good tolerance of low water oxygenation, as compared with other marine bottom-feeders, suggests that this species may face poorly oxygenated waters in the wild. Together with temperature and salinity, water oxygen content may thus be an important variable to take into account in the study of the distribution and migration patterns of Atlantic cod.

Haematological studies on a high-Antarctic fish: Bathydraco marri Norman

This paper presents the first record of the blood parameters of the Antarctic fish Bathydraco marri; the structural and functional characterization of haemoglobin purified from the blood of this species is also reported. One single haemoglobin was detected and the globin chains were purified and subsequently sequenced. The molecular weights of the α- and β-chains were 15552 and 16048, respectively. O 2 binding was measured as a function of pH and a strong Root effect as well as a large, negative, alkaline Bohr effect were observed. The subunit cooperativity was lost at lower pH values, as indicated by the decrease of the Hill coefficient. P 50 was 13.2 mm Hg at 20 °C, pH 7.5. Haematocrit, the number of erythrocytes and the haemoglobin concentration were 14.6, 0.59·10 12·1 −1 and 29.6 g·1 −1, respectively. Mean corpuscular haemoglobin concentration and mean cellular haemoglobin content were 202.7 g·1 −1 and 50.2 pg, respectively. The plasma contribution to the total O 2-carrying capacity was 16.7%. The pH was 7.7; the mean venous pressures of CO 2 and O 2 were 3.8 and 58.5 mm Hg, respectively. For comparison, a summary of the available data from other bathydraconids is also presented. Special attention is given to the mode of life and the evolution of this teleost in relation to its habitat.

Acid-base regulation and blood gas transport following exhaustive exercise in an agnathan, the sea lamprey Petromyzon marinus

Exhaustive exercise in cannulated sea lampreys, Petromyzon marinus, resulted in a marked extracellular acidosis in the arterial blood which had both a respiratory and a metabolic component. Blood CO2 tension (PCO2) returned to control levels within an hour after exercise, but the metabolic acidosis had a somewhat longer time course and the extracellular pH (pHe) did not fully recover until the 4 h recovery sample. The magnitude and duration of the changes in both the plasma lactate concentration and the concentration of metabolic protons were very similar and the maximal proton deficit after exercise was, therefore, only 1.5 mequiv l-1. In contrast to the changes in pHe, there were no significant changes in the erythrocyte pH (pHi) following the exercise period. The regulation of pHi was apparently not adrenergically mediated, however, since addition of catecholamines to lamprey blood in vitro had no significant effect on pHi. In addition, the period of exhaustive exercise in vivo was not associated with any significant changes in the mean cellular hemoglobin concentration. The total carbon dioxide concentration in the arterial whole blood and true plasma were both significantly reduced after exercise, but the total carbon dioxide concentration within the erythrocytes was transiently increased. Finally, there was a marked decrease in the arterial PO2 immediately after exercise, which was associated with a significant reduction in the amount of oxygen bound to hemoglobin; however, within 30 min, these values had both returned to normal. The maintenance of pHi presumably contributes to the regulation of oxygen transport in lampreys and it may be particularly important during the brief period immediately after exercise when oxygen transport is clearly compromised. Although several studies have provided evidence that chloride/bicarbonate exchange limitations may exist in agnathan blood in vitro, the present results demonstrate that the characteristics of carbon dioxide transport and acid-base regulation after exercise in P. marinus are not markedly different from those in other lower vertebrates.

Erythrocyte defense against hydrogen peroxide: preeminent importance of catalase.

To investigate the relative importance of catalase and glutathione in erythrocyte oxidant defense, human and mouse (normal and acatalasemic) erythrocytes were reversibly lysed and resealed in the presence of exogenous catalase or glutathione. This resulted in an increase in intracellular catalase activity or glutathione concentration in the resealed erythrocytes while normal cellular structure, hemoglobin concentration, cell volume, cellular deformability, and adenosine triphosphate concentration were maintained. Resealing alone had no effect on oxidant sensitivity. In human cells, a threefold increase in catalase activity resulted in the maintenance of glutathione levels in response to hydrogen peroxide (H2O2) challenge. Reconstitution of congenitally acatalasemic mouse erythrocytes, which were extremely sensitive to even micromolar concentrations of H2O2 with purified catalase resulted in complete protection against H2O2. Indeed, the catalase-reconstituted acatalasemic cells were less sensitive to H2O2-mediated damage than were normal, catalase-replete mouse cells. In contrast, alteration of the glutathione status of human and mouse (normal and acatalasemic) cells had no significant effect on oxidant sensitivity. Even a five-fold increase in intracellular glutathione concentration (greater than 30 micromoles glutathione per gram of hemoglobin) in normal or catalase-deficient (azide-treated or acatalasemic) red blood cells had no protective effect against H2O2-mediated lipid peroxidation or methemoglobin generation. Similarly, depletion of glutathione by 1-chloro-2,4-dinitrobenzene also had no effect on erythrocyte H2O2 sensitivity. These results suggest an important role for catalase in protection against H2O2-mediated damage at physiologic levels and that catalase is as at least as important as glutathione in cellular defense against H2O2.

Effects of cadmium on anoxic survival, haematology, erythrocytic volume regulation and haemoglobin-oxygen affinity in the marine bivalve Scapharca inaequivalvis

Exposure to 50 ppb Cd for 6 wk reduced survival of Scapharca inaequivalvis in anoxic water (LT 50 decreasing from ≈ 15 to 12 days). The treatment decreased packed erythrocyte volume (haematocrit) and erythrocyte count but increased mean cellular haemoglobin concentration. In vitro Cd administration had no significant effect on O 2 affinity or co-operativity in O 2 binding of the stripped haemolysate. Erythrocyte suspensions exhibited a slight volume regulatory decrease, following swelling in hypotonie media, and no significant capacity for volume regulatory increase under hypertonic stress. Neither pattern was markedly affected by in vivo or in vitro Cd administration, which however, tended to reduce the primary volume changes. The results are discussed as regards Cd toxicity and the cellular and molecular mechanisms implicated in volume regulation and tissue-O 2 supply.

The Influence of Oxygen Tension, Temperature, and Hemoglobin Concentration on the Rheologic Properties of Sickle Erythrocytes

With the use of micromanipulation techniques, the shear modulus or "rigidity" mu, the recovery time tc, and the unfolding time tf for individual sickle cells have been measured at different oxygen tensions, temperatures, and cell densities. In these experiments, the partial pressure of oxygen was varied from 156 to 40 mm Hg and the temperature was controlled at 25 degrees C or 37 degrees C. Three mean cellular hemoglobin concentrations were studied: 29 g/dL, 33 g/dL, and 46 g/dL. The lighter cells (29 and 33 g/dL) exhibited at most a threefold increase in rigidity as the pO2 was decreased from 156 to 40 mm Hg. At 25 degrees C, the densest cells (46 g/dL) also exhibited a threefold increase. However, at 37 degrees C, the rigidity of these cells increased eightfold between 156 to 40 mm Hg. Compared with normal cells, this gives a rigidity that is 18 times larger. In contrast to the values for mu, the values for tc and tf remained essentially unchanged (within the accuracy of the experiments) for the lighter cells and could not be measured for the densest cells.

The influence of oxygen tension, temperature, and hemoglobin concentration on the rheologic properties of sickle erythrocytes

With the use of micromanipulation techniques, the shear modulus or “rigidity” mu, the recovery time tc, and the unfolding time tf for individual sickle cells have been measured at different oxygen tensions, temperatures, and cell densities. In these experiments, the partial pressure of oxygen was varied from 156 to 40 mm Hg and the temperature was controlled at 25 degrees C or 37 degrees C. Three mean cellular hemoglobin concentrations were studied: 29 g/dL, 33 g/dL, and 46 g/dL. The lighter cells (29 and 33 g/dL) exhibited at most a threefold increase in rigidity as the pO2 was decreased from 156 to 40 mm Hg. At 25 degrees C, the densest cells (46 g/dL) also exhibited a threefold increase. However, at 37 degrees C, the rigidity of these cells increased eightfold between 156 to 40 mm Hg. Compared with normal cells, this gives a rigidity that is 18 times larger. In contrast to the values for mu, the values for tc and tf remained essentially unchanged (within the accuracy of the experiments) for the lighter cells and could not be measured for the densest cells.

Dynamics of Erythropoietin Receptor Expression on Erythropoietin-Responsive Murine Cell Lines

We examined erythropoietin receptor expression in two murine cell lines, B6SUtA and DA-1, that respond to erythropoietin in different ways. While B6SUtA cells undergo erythroid differentiation with limited proliferation after addition of erythropoietin, DA-1 cells show only a proliferative response. Equilibrium binding experiments with 125I-erythropoietin revealed that both B6SUtA and DA-1 cells express a single class of erythropoietin receptors. In the absence of erythropoietin, B6SUtA cells exhibited 145 receptors per cell with a dissociation constant (kd) of 380 pmol/L. Six days after induction with erythropoietin, the B6SUtA cells displayed 310 receptors per cell without a change in binding affinity; exposure to erythropoietin also increased cellular hemoglobin content. DA-1 cells adapted to erythropoietin-dependent growth over a period of months and exhibited a progressive increase in erythropoietin receptor expression, from 85 per cell (kd = 540) to 550 per cell (kd = 530), although the cells remained uniformly benzidine-negative. We interpret the data with B6SUtA cells to indicate that early erythroid differentiation stages are attended by an increase in erythropoietin receptor display, coordinate with the initiation of expression of erythroid-specific genes. In contrast, the results with DA-1 cells are most compatible with clonal selection as the mechanism underlying enhanced receptor expression. Thus, display of the erythropoietin receptor is dynamic and can be modulated during the course of erythropoietin-induced differentiation.

Dynamics of erythropoietin receptor expression on erythropoietin- responsive murine cell lines

We examined erythropoietin receptor expression in two murine cell lines, B6SUtA and DA-1, that respond to erythropoietin in different ways. While B6SUtA cells undergo erythroid differentiation with limited proliferation after addition of erythropoietin, DA-1 cells show only a proliferative response. Equilibrium binding experiments with 125I- erythropoietin revealed that both B6SUtA and DA-1 cells express a single class of erythropoietin receptors. In the absence of erythropoietin, B6SUtA cells exhibited 145 receptors per cell with a dissociation constant (kd) of 380 pmol/L. Six days after induction with erythropoietin, the B6SUtA cells displayed 310 receptors per cell without a change in binding affinity; exposure to erythropoietin also increased cellular hemoglobin content. DA-1 cells adapted to erythropoietin-dependent growth over a period of months and exhibited a progressive increase in erythropoietin receptor expression, from 85 per cell (kd = 540) to 550 per cell (kd = 530), although the cells remained uniformly benzidine-negative. We interpret the data with B6SUtA cells to indicate that early erythroid differentiation stages are attended by an increase in erythropoietin receptor display, coordinate with the initiation of expression of erythroid-specific genes. In contrast, the results with DA-1 cells are most compatible with clonal selection as the mechanism underlying enhanced receptor expression. Thus, display of the erythropoietin receptor is dynamic and can be modulated during the course of erythropoietin-induced differentiation.

Correction of spurious haematological results using Technicon H 1-derived data.

Two groups of patients with alert flags on the Technicon H1 analyser, indicating erroneous results for haemoglobin and platelet determinations, were identified. These were due to turbidity from a high WBC affecting haemoglobin or small red cells affecting platelet counts. Data generated by the H1 analyser have been utilized to derive correct Hb and platelet values; for these derivations the haemoglobin utilized the cellular haemoglobin concentration mean and for platelet counts the P COUNT was used. In a prospective study, derived haemoglobin and platelet counts were not significantly different to values obtained by standard haematological techniques. These simplified methods for correcting spurious results have allowed for speedier results and increased laboratory efficiency.

Effect of training on red blood cell parameters and plasma ferritin: a transverse and a longitudinal approach.

In the present study 60 males and 18 females were monitored during an 18- to 20-month training period, during which the training distance was gradually increased. The training period was divided into three periods of 6, 5, and 7 months, respectively. The first, second, and third periods were concluded with a 15-, 25-, and 42-km road race, respectively. The competitive distance always exceeded the maximal distance covered in any previous training session. The effect of training was investigated for erythrocyte count, hematocrit (Ht), hemoglobin (Hb), mean cell volume (MCV), mean cell hemoglobin (MCH), mean cellular hemoglobin content (MCHC), the red cell distribution width (RDW), and ferritin content. The measuring points were the start of the study (used as a reference value) and 1 week before and 1 week after the three contests (15, 25, and 42 km). The results of all measuring points were compared transversely and longitudinally. We found a significant decrease of plasma ferritin content in the first period of the study which further remained constant. Also, other red cell parameters were decreased but remained within the normal range. During the whole training period larger intraindividual variations for most of the red cell parameters were observed compared with non-endurance-trained people.

Intracellular calcium content of human erythrocytes: relation to sodium transport systems.

To study the possible role of intracellular Ca (Cai) in controlling the activities of the Na+-K+ pump, the Na+-K+ cotransport and the Na+/Li+ exchange system of human erythrocytes, a method was developed to measure the amount of Ca embodied within the red cell. For complete removal of Ca associated with the outer aspect of the membrane, it proved to be essential to wash the cells in buffers containing less than 20 nM Ca. Ca was extracted by HClO4 in Teflon vessels boiled in acid to avoid Ca contaminations and quantitated by flameless atomic absorption. Cai of fresh human erythrocytes of apparently healthy donors ranged between 0.9 and 2.8 mumol/liter cells. The mean value found in females was significantly higher than in males. The interindividual different Ca contents remained constant over periods of more than one year. Sixty to 90% of Cai could be removed by incubation of the cells with A23187 and EGTA. The activities of the Na+-K+ pump, of Na+-K+ cotransport and Na+/Li+ exchange and the mean cellular hemoglobin content fell with rising Cai; the red cell Na+ and K+ contents rose with Cai. Ca depletion by A23187 plus EGTA as well as chelation of intracellular Ca2+ by quin-2 did not significantly enhance the transport rates. It is concluded that the large scatter of the values of Cai of normal human erythrocytes reported in the literature mainly results from a widely differing removal of Ca associated with the outer aspect of the membrane.

Inhibition of Hemoglobin Production by Transferrin-Gallium

Abstract Recent clinical trials evaluating gallium nitrate as a chemotherapeutic agent have reported the development of microcytic hypochromic anemia in patients treated with this agent. Because gallium is known to bind avidly to transferrin, we examined the effect of transferrin-gallium (Tf-Ga) on hemoglobin production by Friend erythroleukemia cells in vitro. Cellular hemoglobin production, as assessed by benzidine staining, cellular hemoglobin content, and 59Fe incorporation into heme, was significantly decreased following exposure of cells to Tf-Ga. Tf-Ga led to an early decrease in cellular 59Fe incorporation even before changes in hemoglobin production were detected. A marked increase in cellular transferrin receptor expression occurred following exposure of cells to Tf-Ga. Tf-Ga inhibition of hemoglobin production could be reversed and hemoglobin production could be restored to normal by addition to the media of either transferrin-iron (Tf-Fe) or iron- pyridoxal isonicotinoyl hydrazone, a compound capable of supplying iron directly to reticulocytes for heme synthesis without transferrin as a mediator. These studies provide an explanation for the development of anemia in patients treated with gallium nitrate and suggest that gallium's mechanism of chemotherapeutic action includes inhibition of cellular iron incorporation.

Inhibition of hemoglobin production by transferrin-gallium

Recent clinical trials evaluating gallium nitrate as a chemotherapeutic agent have reported the development of microcytic hypochromic anemia in patients treated with this agent. Because gallium is known to bind avidly to transferrin, we examined the effect of transferrin-gallium (Tf-Ga) on hemoglobin production by Friend erythroleukemia cells in vitro. Cellular hemoglobin production, as assessed by benzidine staining, cellular hemoglobin content, and 59Fe incorporation into heme, was significantly decreased following exposure of cells to Tf-Ga. Tf-Ga led to an early decrease in cellular 59Fe incorporation even before changes in hemoglobin production were detected. A marked increase in cellular transferrin receptor expression occurred following exposure of cells to Tf-Ga. Tf-Ga inhibition of hemoglobin production could be reversed and hemoglobin production could be restored to normal by addition to the media of either transferrin-iron (Tf-Fe) or iron-pyridoxal isonicotinoyl hydrazone, a compound capable of supplying iron directly to reticulocytes for heme synthesis without transferrin as a mediator. These studies provide an explanation for the development of anemia in patients treated with gallium nitrate and suggest that gallium's mechanism of chemotherapeutic action includes inhibition of cellular iron incorporation.

Effects of 2,3-diphosphoglycerate on the mechanical properties of erythrocyte membrane

Investigation by Schindler et al and Sheetz and Casaly have indicated that high (approximately 10 mmol/L) concentrations of 2,3- diphosphoglycerate (2,3-DPG) have a destabilizing effect on erythrocyte membrane and the membrane skeleton. We have investigated changes in the membrane mechanical properties that occur at elevated 2,3-DPG levels in both intact cells and ghosts. The membrane shear modulus, viscoelastic recovery time constant, critical force, “plastic” viscosity, and material relaxation time constant were measured by standard micropipette and flow channel techniques. Intact cells showed no change in properties at physiologic ionic strength and 2,3-DPG concentrations of about 20 mmol/L, except for an increase in membrane viscosity resulting from an increased cellular hemoglobin concentration that occurs when the 2,3-DPG concentration is elevated. At ionic strengths 20% below physiologic and 2,3-DPG concentrations of approximately 20 mmol/L, decreases in membrane shear modulus and membrane viscosity were observed. In ghosts, no changes in these properties were observed at a 2,3-DPG concentration of 10 mmol/L and ionic strengths as low as 25% below physiologic, but a decrease in the force required to form tethers (critical force) was observed at physiologic ionic strength. The decrease in membrane shear modulus and viscosity of intact cells and the reduced critical force in ghosts are consistent with the results of other investigators. However, the difference in the effects of 2,3-DPG on ghosts and intact cells indicates that the effects of 2,3-DPG depend strongly on the conditions of the experiment. It appears unlikely that 2,3-DPG affects erythrocyte membrane material properties under physiologic conditions.

Effects of 2,3-Diphosphoglycerate on the Mechanical Properties of Erythrocyte Membrane

Investigation by Schindler et al and Sheetz and Casaly have indicated that high (approximately 10 mmol/L) concentrations of 2,3-diphosphoglycerate (2,3-DPG) have a destabilizing effect on erythrocyte membrane and the membrane skeleton. We have investigated changes in the membrane mechanical properties that occur at elevated 2,3-DPG levels in both intact cells and ghosts. The membrane shear modulus, viscoelastic recovery time constant, critical force, "plastic" viscosity, and material relaxation time constant were measured by standard micropipette and flow channel techniques. Intact cells showed no change in properties at physiologic ionic strength and 2,3-DPG concentrations of about 20 mmol/L, except for an increase in membrane viscosity resulting from an increased cellular hemoglobin concentration that occurs when the 2,3-DPG concentration is elevated. At ionic strengths 20% below physiologic and 2,3-DPG concentrations of approximately 20 mmol/L, decreases in membrane shear modulus and membrane viscosity were observed. In ghosts, no changes in these properties were observed at a 2,3-DPG concentration of 10 mmol/L and ionic strengths as low as 25% below physiologic, but a decrease in the force required to form tethers (critical force) was observed at physiologic ionic strength. The decrease in membrane shear modulus and viscosity of intact cells and the reduced critical force in ghosts are consistent with the results of other investigators. However, the difference in the effects of 2,3-DPG on ghosts and intact cells indicates that the effects of 2,3-DPG depend strongly on the conditions of the experiment. It appears unlikely that 2,3-DPG affects erythrocyte membrane material properties under physiologic conditions.

Increased monoester lipase activity in red blood cells during hyperthyroidism.

Human red blood cells (RBC) contain a monoester lipase (MEL) activity which is tightly associated with the cell membrane and has its active site externally oriented, as inferred from the ability of the intact cell to hydrolyse an exogenously added lipid substrate. Membrane-bound MEL activity was measured by a radiochemical assay in intact RBC from 29 untreated hyperthyroid patients. The mean (+/- S.D.) MEL level was higher (P less than 0.01) in these patients (1220 +/- 212 mu./10(12) RBC) than in the control group (1010 +/- 120 mu./10(12) RBC). There was no difference between men and women. The increase in MEL values was associated with significantly (P less than 0.001) decreased values of mean cellular volume and mean cellular haemoglobin content. A continued study of 13 patients, who became euthyroid with treatment, showed a normalization of the MEL values in RBC. The increased lipolytic potency of RBC represents a new characteristic of hyperthyroid patients. Further exploration of the possible diagnostic or prognostic implications of this enzymatic change seems warranted.