Citrate tolerance

There is a wide variation among human beings in tolerance to sodium citrate. It is important to those concerned with blood transfusions that the incidence of reactions to citrate is quite low, except in the event of massive transfusing, when the amount of citrate with the blood being given to the patient must be carefully considered.     

Effects of citrate, heparin and cation supplementation on mortality and egg production of laboratory-reared horn flies

Abstract. The effects of the blood anticoagulants sodium citrate and sodium heparin on horn fly, Haematobia irritans L., egg production were tested. Sodium citrate was added to freshly collected bovine blood to give final concentrations of 5-100mM while sodium heparin was used in concentrations of 10–70 USP units/ml blood. Small cages containing five male and ten female newly emerged laboratory-reared horn flies were maintained for 8–10 days on these blood samples, and mortality and egg production recorded daily. Results showed that as blood citrate concentration was increased, egg production decreased logarithmically. At sodium citrate concentrations of 50 mM and above, severe impacts on egg production and adult horn fly survival occurred. Although no dose-related response of egg production to increasing heparin concentrations was noted, the 25 USP units heparin/ml blood treatments gave the largest egg production, yielding approximately 28% more eggs than any other treatment. Since citrate is a known chelator of divalent metal cations, the effects of supplemental cation additions to citrated blood were tested for their ability to reverse the egg production decrease seen at 50 mM sodium citrate. Blood samples containing 50mM sodium citrate were supplemented with CaCl₂, calcium lactate, CuCl₂, cupric acetate, FeCl₃, ferric citrate, MgCl₂, magnesium acetate, MnCl₂, ZnSO₄, EGTA or EGTA plus calcium lactate, each at 1 mM except EGTA which was used at 2.5 mM. The magnesium acetate supplement and the combination of calcium lactate plus EGTA resulted in a statistically significant increase in egg production ( P < 0.05).     

Effect of oral aluminum and aluminum citrate on blood level and short-term tissue distribution of aluminum in the rat

Aluminum (Al) absorption seems to be very low, but many factors can enhance it in animals and humans. In the present study, we investigated the acute effect of Na citrate on Al absorption by monitoring Al levels in blood and several tissues. For this purpose, 18 Wistar male rats were divided into 3 groups: control, Al, and Al + Na citrate. After a 14-h fasting period, animals were dosed orally with deionized water, or 2 mmol Al chloride, or 2 mmol Al chloride plus 2 mmol Na citrate. Blood samples were taken before and 1, 2, 4, and 6 h after the gavage. Al concentrations in blood, liver, tibia, kidney, and intestinal wall were determined by ICP-OES. In the Al and Al + citrate groups, Al blood concentrations peaked at 1 h and 2 h with higher levels in the Al + citrate group. Al gavage resulted in an increase in Al level in intestinal wall, but not in the other investigated tissues. Simultaneous gavage of citrate with Al significantly increased its tissue levels in tibia, kidney, and in intestinal wall. Our data show clearly that Al as chloride can be absorbed, but not well retained by the organism tissues. Furthermore, the model used in the present study is appropriate for acute studies to investigate the effect of various compounds on Al absorption in the rat.     

Citrate binding of Al3+ and Fe3+

Citrate occurs at about 0.1 mM in blood plasma and is the most likely small molecule plasma binder of both Al3+ and Fe3+. This paper assesses published stability constants for citrate binding to each metal ion. From pH 2 to 5 Al3+ forms a neutral complex with citrate that may be absorbed into the body in the upper regions of the gastrointestinal tract. It is especially dangerous to ingest aluminum-containing antacids with citrus fruit or juices. Ignoring the likely occurrence of a competing 2:1 citrate-Fe3+ complex necessitates adjustments in reported stability constants for Fe3+ binding to transferrin. In the blood, plasma transferrin steals both Fe3+ and Al3+ from citrate.     

The Effect on Serum Ionic Magnesium of Exchange Transfusion with Citrated as Opposed to Heparinized Blood

Serum Mg++ levels before, during, and after replacement transfusion were determined in 20 newborn infants. In 10 infants exchanged with acid-citrate-dextrose (ACD) blood, the level fell from 1.75 ± 0.16 mEq./l. to 0.99 ± 0.16 mEq./l. By contrast, levels in 10 infants exchanged with two types of heparinized blood were unchanged: the pre-exchange values were 1.59 ± 0.11, and the postexchange levels were 1.59 ± 0.08 mEq./l. Mean values for donor bloods were 0.42 ± 0.07 mEq./l. with ACD blood, and 1.45 ± 0.03 mEq./l. with heparinized blood. In vitro studies involving the addition of known amounts of citrate to standard Mg++ solutions demonstrated that the citrate caused a reduction of ionic magnesium. It is proposed that the fall in serum Mg++ when ACD blood is used for exchange transfusion is the combined result of Mg++ binding by the citrate, and the dilution effect of the relatively large proportion of anticoagulant to blood (1:3) used with the ACD mixture.     

Human Na+ -coupled citrate transporter: primary structure,genomic organization,and transport function

This paper describes the cloning and functional characterization of the human Na(+)-coupled citrate transporter (NaCT). The cloned human NaCT shows 77% sequence identity with rat NaCT. The nact gene is located on human chromosome 17 at p12-13. NaCT mRNA is expressed most predominantly in the liver, with moderate expression detectable in the brain and testis. When functionally expressed in mammalian cells, human NaCT mediates the Na(+)-coupled transport of citrate. Studies with several monocarboxylates, dicarboxylates, and tricarboxylates show that the transporter is selective for citrate with comparatively several-fold lower affinity for other intermediates of citric acid cycle. The Michelis-Menten constant for citrate is approximately 650 microM. The activation of citrate transport by Na(+) is sigmoidal, suggesting involvement of multiple Na(+) ions in the activation process. The transport process is electrogenic. This represents the first plasma membrane transporter in humans that mediates the preferential entry of citrate into cells. Citrate occupies a pivotal position in many important biochemical pathways. Among various citric acid cycle intermediates, citrate is present at the highest concentrations in human blood. The selectivity of NaCT towards citrate and its predominant expression in the liver suggest that this transporter may facilitate the utilization of circulating citrate for the generation of metabolic energy and for the synthesis of fatty acids and cholesterol.     

枸橼酸转运蛋白mRNA在代谢性酸中毒大鼠肾组织的表达

文章报道了代谢性酸中毒时大鼠肾组织两种钠离子依赖的枸橼酸膜转运蛋白ｍＲＮＡ表达量的变化。给雌性Ｗｉｓｔａｒ大鼠喂含０．２８ｍｏｌ／Ｌ ＮＨ４Ｃｌ饮用水诱导产生代谢性酸中毒。喂酸后分别于１、３、７ｄ处死大鼠,测定血浆ＨＣＯ＾－３浓度的变化。以Ｎｏｒｔｈｅｒｎ杂交方法,用钠离子依赖的枸橼酸膜转运蛋白１（ＳＤＣＴ１）探针及钠离子依赖的枸橼酸膜转运蛋白２（ＳＤＣＴ２）探针,分别检测肾皮质枸橼酸转运蛋白     

THE EFFECT OF ASPARTATE ON CITRATE METABOLISM IN THE CYTOSOLIC FRACTION OF BRAIN UNDER CONDITIONS OF NORMOXIA, HYPOXIA AND ANAESTHESIA

—The utilization of citrate by the cytoplasmic fraction of rat brain is inhibited in hypoxia and remains unaltered in anaesthesia. The addition of exogenous aspartate to the cytosolic fraction isolated from brains of hypoxic animals increases the rate of citrate removal. The level of cytosolic aspartate gradually decreases when the exposure period to low oxygen tension is increased and reaches a minimum after 30 min. The levels of mitochondrial aspartate and of cytoplasmic carbamyl aspartate remain constant. The low level of cytosolic aspartate is accompanied by an increase in the concentration of cytosolic urea and increase in the aspartate level in blood serum. It is suggested that the oxidation of citrate by the cytoplasmic fraction of brain is inhibited in hypoxia owing to the decrease in endogenous aspartate. The decrease in the level of cytoplasmic aspartate is caused by the diversion of this substrate toward urea synthesis and by the increased leakage across the cell/blood barrier to the blood stream. Anaesthesia prevents the changes induced by hypoxia.     

Effect of anticoagulants on farmed giant kokopu,Galaxias argenteus (Gmelin 1789) haematological parameters and erythrocyte fragility

We sought to determine a compatible anticoagulant for routine haematological and physiological assessments with giant kokopu (Galaxias argenteus), an endemic New Zealand fish. We observed that blood treated with lithium heparin (LH) rapidly coagulated and haemolysed, making it unsuitable for G. argenteus. Dipotassium ethylenediaminetetraacetic acid (K₂EDTA) and trisodium citrate (citrate) effectively prevented blood coagulation. K₂EDTA-treated erythrocytes exhibited the least mean haemolysis and mean corpuscular fragility. Further studies into prolonged storage effects of citrate and K₂EDTA are recommended to find a compatible anticoagulant for use with G. argenteus blood.     

Autonomic dysreflexia during sperm retrieval in spinal cord injury: influence of lesion level and sildenafil citrate.

Autonomic dysreflexia (AD) can occur during penile vibratory stimulation in men with spinal cord injury, but this is variable, and the association with lesion level is unclear. The purpose of this study was to characterize the cardiovascular responses to penile vibratory stimulation in men with spinal cord injury. We hypothesized that those with cervical injuries would demonstrate a greater degree of AD compared with men with thoracic injuries. We also questioned whether the rise in blood pressure could be attenuated by sildenafil citrate. Participants were classified as having cervical (n = 8) or thoracic (n = 5) injuries. While in a supine position, subjects were instrumented with an ECG, and arterial blood pressure was determined beat by beat. Subjects reported to the laboratory twice and received an oral dose of sildenafil citrate (25-100 mg) or no medication. Penile vibratory stimulation was performed using a handheld vibrator to the point of ejaculation. At ejaculation during the nonmedicated trials, the cervical group had a significant decrease in heart rate (-5-10 beats/min) and increase in mean arterial blood pressure (+70-90 mmHg) relative to resting conditions, whereas the thoracic group had significant increases in both heart rate (+8-15 beats/min) and mean arterial pressure (+25-30 mmHg). Sildenafil citrate had no effect on the change in heart rate or mean arterial pressure in either group. In summary, men with cervical injuries had more pronounced AD during penile vibratory stimulation than men with thoracic injuries. Administration of sildenafil citrate had no effect on heart rate or blood pressure during penile vibratory stimulation in men with spinal cord injury.     

Comparative studies of radiocitrates in oncological models—I. 99mTc citrate and 67Ga citrate uptake by EMT-6 tumors in mice

⁶⁷Ga citrate and ^99mTc citrate (Solcocitran) were injected sequentially, with an interval of 48 h, into Balb/c mice bearing transplanted EMT-6 tumors. Tissue distributions of ⁶⁷Ga and ^99mTe were measured simultaneously at intervals of 1, 3, 5 and 8 h after injection of the ^99mTc citrate (49, 51, 53 and 56 h after ⁶⁷Ga citrate). Maximal tumor:blood ratios for ^99mGa and ^99mTc were 13.8 ± 3.2 and 4.0 ± 1.0 respectively, both occurring at the final period. The maximum tumor index (T.I. = T:B x % dose/g) for ⁶⁷Ga was 71 ± 23% 56 h after injection, and for Tc was 13 ± 12% 1 h after injection. Liver, kidney and spleen had equal or higher concentrations of radioactivity than tumor for either radiotracer. The somewhat higher tumor:blood ratio for ⁶⁷Ga citrate was offset by the time required for this optimum to be reached. Alternatively, the best ^99mTc citrate tumor:blood ratios were attained within 8 h, with less liver and gut radioactivity. These data fall within the range of results from other clinical and animal model studies of ⁶⁷Ga citrate and Tc citrate. In view of the radiation dose, the inconvenience of the 48–72 h wait, and the cost of ⁶⁷Ga, and because neither radiopharmaceutical is tumor specific, ^99mTc citrate may have a place in early oncological screening. The results are discussed as part of a comprehensive review of the ^99mTc citrate literature.     

Citrate diminishes hypothalamic acetyl-CoA carboxylase phosphorylation and modulates satiety signals and hepatic mechanisms involved in glucose homeostasis in rats

The hypothalamic AMP-activated protein kinase (AMPK)/acetyl-CoA carboxylase (ACC) pathway is known to play an important role in the control of food intake and energy expenditure. Here, we hypothesize that citrate, an intermediate metabolite, activates hypothalamic ACC and is involved in the control of energy mobilization. Initially, we showed that ICV citrate injection decreased food intake and diminished weight gain significantly when compared to control and pair-fed group results. In addition, we showed that intracerebroventricular (ICV) injection of citrate diminished (80% of control) the phosphorylation of ACC, an important AMPK substrate. Furthermore, citrate treatment inhibited (75% of control) hypothalamic AMPK phosphorylation during fasting. In addition to its central effect, ICV citrate injection led to low blood glucose levels during glucose tolerance test (GTT) and high glucose uptake during hyperglycemic-euglycemic clamp. Accordingly, liver glycogen content was higher in animals given citrate (ICV) than in the control group (23.3+/-2.5 vs. 2.7+/-0.5 microg mL(-1) mg(-1), respectively). Interestingly, liver AMPK phosphorylation was reduced (80%) by the citrate treatment. The pharmacological blockade of beta3-adrenergic receptor (SR 59230A) blocked the effect of ICV citrate and citrate plus insulin on liver AMPK phosphorylation. Consistently with these results, rats treated with citrate (ICV) presented improved insulin signal transduction in liver, skeletal muscle, and epididymal fat pad. Similar results were obtained by hypothalamic administration of ARA-A, a competitive inhibitor of AMPK. Our results suggest that the citrate produced by mitochondria may modulate ACC phosphorylation in the hypothalamus, controlling food intake and coordinating a multiorgan network that controls glucose homeostasis and energy uptake through the adrenergic system.     

Effect of anticoagulation with citrate versus heparin on the adsorption of coagulation factors to blood purification resins with different charge

In liver failure, hydrophobic toxins accumulate in the blood circulation. To support hepatic function, extracorporeal blood purification systems have been developed, in which both cationic and neutral adsorbents are used to remove albumin-bound metabolites from blood. An issue of these systems is the additional removal of coagulation factors containing negatively charged γ-carboxyglutamate (Gla) domains, which, in physiological conditions, are shielded by calcium ions. We hypothesized that complexation of calcium ions by citrate leads to exposure of negative Gla domains, resulting in their binding to the positively charged adsorbents. The data presented here confirm that the binding of coagulation factors containing Gla domains to positively charged polymers is enhanced in the presence of citrate as compared to heparin. This effect increased with increasing charge density of the polymer and has important implications for the clinical application of positively charged polymers.     

Structure,function, and expression pattern of a novel sodium-coupled citrate transporter (NaCT) cloned from mammalian brain

Citrate plays a pivotal role not only in the generation of metabolic energy but also in the synthesis of fatty acids, isoprenoids, and cholesterol in mammalian cells. Plasma levels of citrate are the highest ( approximately 135 microm) among the intermediates of the tricarboxylic acid cycle. Here we report on the cloning and functional characterization of a plasma membrane transporter (NaCT for Na+ -coupled citrate transporter) from rat brain that mediates uphill cellular uptake of citrate coupled to an electrochemical Na+ gradient. NaCT consists of 572 amino acids and exhibits structural similarity to the members of the Na+-dicarboxylate cotransporter/Na+ -sulfate cotransporter (NaDC/NaSi) gene family including the recently identified Drosophila Indy. In rat, the expression of NaCT is restricted to liver, testis, and brain. When expressed heterologously in mammalian cells, rat NaCT mediates the transport of citrate with high affinity (Michaelis-Menten constant, approximately 20 microm) and with a Na+:citrate stoichiometry of 4:1. The transporter does interact with other dicarboxylates and tricarboxylates but with considerably lower affinity. In mouse brain, the expression of NaCT mRNA is evident in the cerebral cortex, cerebellum, hippocampus, and olfactory bulb. NaCT represents the first transporter to be identified in mammalian cells that shows preference for citrate over dicarboxylates. This transporter is likely to play an important role in the cellular utilization of citrate in blood for the synthesis of fatty acids and cholesterol (liver) and for the generation of energy (liver and brain). NaCT thus constitutes a potential therapeutic target for the control of body weight, cholesterol levels, and energy homeostasis.     

Inhibition of soluble guanylate cyclase activity by citrate

Soluble guanylate cyclase activity from guinea pig heart is inhibited by increasing concentrations of sodium citrate. The Ki value was found to be 2.83 +/- 0.05 mM in the presence of 3 mM Mn2+ and 0.6 mM GTP. Citrate acts by lowering Vmax and increasing the apparent values of Km for GTP and K0.5 for Mn2+ and Mg2+. The soluble guanylate cyclase, activated by sodium nitroprusside, was also inhibited by citrate. This inhibitory action of citrate was not restricted to soluble guanylate cyclase activity of the heart and has been demonstrated also in the supernatant of lung, liver, diencephalon and in the homogenate of blood platelets. Since citrate is known to be an important intermediate of metabolism, its intracellular concentration may be also of relevance for guanylate cyclase activity.     

Electrophoretic variation of aconitase and phosphoglucomutase detected in Microtus californicus.

Four electrophoretic variants of cytoplasmic aconitase (citrate (isocitrate) hydro-lyase, EC 4.2.1.3) were detected in a population of Microtus californicus when samples were screened by starch gel electrophoresis using Tris/citrate buffers at pH 7.0 and pH 8.7. Variation at what is presumed to be the phosphoglucomutase-3 locus (alpha-D-glucose-1,6-diphosphate:alpha-D-glucose-1-phosphate phosphotransferase, EC 2.7.5.1) was also detected with liver samples but was not detected in kidney samples or red blood cells lysates. This nongenetic variation is due to oxidation of free sulfhydryl groups.     

Haematological, immunological and endocrinological aspects of chronic high frequency blood sampling in rats with replacement by fresh or preserved donor blood

Haematological, immunological and endocrinological aspects of blood transfusions with either freshly collected or preserved donor blood were investigated in chronically cannulated unrestrained rats. Three anticoagulant preservatives were tested: citrate, citrate-dextrose and citrate-phosphate-dextrose-adenine (CPDA-1). Prolactin was used as an indicator of stress in endocrine studies. The repeated collection of 4 ml blood at 2-week intervals did not affect normal blood composition. Whole blood of rats could be stored in citrate, citrate-dextrose or CPDA-1 for 8, 22 or 35 days, respectively. Blood transfusions with fresh or preserved donor blood of F1 (R X U) rats did not affect normal blood composition nor did it induce immunological responses in F1 rats. Frequent blood sampling for several hours at highest rates of 1 sample/min did not affect prolactin secretion when blood volume reduction was replaced by blood transfusions with fresh donor blood. However, compensation with preserved blood affected prolactin secretion significantly. Blood transfusions did not affect health, behaviour, cyclicity or pseudopregnancy. The application of blood transfusion in chronically cannulated rats appeared to be quite simple. Its advantages are the possibility of following individual secretion patterns of blood-bound substances, the repeated use of animals and the reduction of the number of animals.     

Citrate transport and metabolism in mammalian cells

Citrate, an organic trivalent anion, is a major substrate for generation of energy in most cells. It is produced in mitochondria and used either in the Krebs' cycle or released into cytoplasm through a specific mitochondrial carriers. Citrate can also be taken up from blood through different plasma membrane transporters. In the cytoplasm, citrate can be used ultimately for fatty acid synthesis, which is increased in cancer cells. Here, we review the ways in which citrate can be transported and discuss the changes in transport and metabolism that occur in cancer cells. The primary focus is on the prostate gland, which is known to produce and release large amounts of citrate during its normal secretory function. The significant changes that occur in citrate‐related metabolism and transport in prostate cancer are the second focus. This review strives to relate these mechanisms to molecular biology on the one hand and to clinical applications on the other.     

Sodium citrate ingestion and its effects on maximal anaerobic exercise of different durations

The effects of an alkalising agent were studied in ten subjects who participated in anaerobic testing on a cycle ergometer to determine the effectiveness of sodium citrate (0.5 g.kg-1 body mass) as an ergogenic aid during exercise of 10-s, 30-s, 120-s and 240-s duration. Blood was collected prior to, after ingestion of sodium citrate (NaHCO3), and postexercise, from a heated (43-46 degrees C) fingertip and analysed immediately postcollection for pH, partial pressure of oxygen and carbon dioxide, base excess and blood bicarbonate. Total work undertaken (kJ) and peak power (W) achieved during the tests was also obtained via a work monitor unit. The results indicated that a dose of 0.5 g.kg-1 body mass sodium citrate had no ergogenic benefit for exercise of either 10-s or 30-s duration. Blood bicarbonate concentrations, however, were significantly increased (P less than 0.05) following ingestion of the citrate during these trials. Exercise periods of 120 s and 240 s were significantly increased (P less than 0.05) above the control and placebo conditions following sodium citrate ingestion. Blood bicarbonate concentrations were again increased above control and placebo conditions and blood lactate concentrations were also increased following the citrate trials. The pH decreased significantly (P less than 0.05) in all trials below the control and placebo conditions. On the basis of the exercise undertaken in this study we would suggest that a dose of 0.5 g.kg-1 body mass of sodium citrate could improve anaerobic exercise performance of 120-s and 240-s duration.