Depletion of hepatic 3'-phosphoadenosine 5'-phosphosulfate (PAPS) and sulfate in rats by xenobiotics that are sulfated

Sulfation is considered a high-affinity but low-capacity conjugation mechanism that is limited by the availability of 3'-phosphoadenosine 5'-phosphosulfate (PAPS), the cosubstrate for sulfation. Salicylamide, phenol and 1-naphthol are all known substrates for the sulfation reaction. This study was conducted to determine whether the xenobiotics that are sulfated when administered to rats will lower hepatic PAPS and its precursor, sulfate. Urinary sulfate excretion was reduced 85% to 95% by these compounds. Hepatic PAPS was reduced 73%, 39%, and 87% by salicylamide, phenol and naphthol, respectively, 2 hr after administration of 2 mmol/kg. These compounds also decreased serum sulfate concentrations by 45% to 86% and lowered hepatic sulfate concentrations. In summary, these studies demonstrate that salicylamide, phenol and 1-naphthol lower hepatic PAPS and sulfate concentrations, as well as serum sulfate concentrations. These findings imply that increased sulfation, as a result of the sulfation of xenobiotics, results in depletion of hepatic PAPS concentrations, possibly because the utilization of PAPS by the sulfotransferases exceeds its generation via sulfate activation. Thus the capacity-limited sulfation of high dosages of xenobiotics appears to be due to the reduced availability of hepatic PAPS, which in turn is limited by the availability of sulfate.     

Measurement of contribution from intracellular cysteine to sulfate in phosphoadenosine phosphosulfate in rat ovarian granulosa cells

Synthesis of the large dermatan sulfate (DS) proteoglycan by rat ovarian granulosa cells was studied using metabolic radiolabel precursors in culture media with varying concentrations of environmental sulfate (20-800 microM) and cysteine (130 and 650 microM). Experiments using [3H]glucosamine and [35S]sulfate showed that the average size of the DS chains and the rate of DS proteoglycan synthesis were independent of the sulfate and cysteine concentrations in the medium. Experiments with [35S]cysteine were then used to determine the contribution that metabolic conversion of cysteine sulfur to sulfate makes to the 3'-phosphoadenosine 5'-phosphosulfate (PAPS) pool which provides the substrate for sulfoester formation in DS synthesis. When 35S in cysteine is metabolized into [35S]PAPS, the specific activity is reduced from that of the [35S]cysteine pool, by dilution with other sulfur sources such as extracellular sulfate, and this dilution factor directly reflects the contribution of cysteine to the PAPS pool. The decreases of 35S specific activity were measured under various sulfate-depleted and cysteine-supplemented conditions by comparing the specific activity of [35S]sulfate ester in the DS chains with that of [35S]cysteine residues in the core protein of the DS proteoglycan. The contribution of sulfur in cysteine to the intracellular PAPS pool was 0.03% in culture medium with normal sulfate (800 microM). Depleted environmental sulfate (20 microM) and increased cysteine supply (650 microM) only increased the sulfur contribution from cysteine to PAPS up to 0.74 and 1.5%, respectively, even though the DS chains were greatly undersulfated (55 and 82% of the control value). Thus, the source of sulfur in the intracellular pool of PAPS was mainly derived from environmental sulfate, and the contribution from cysteine was minimal in these cells.     

Effects of glucose load on brain extracellular lactate concentration in conscious rats using a microdialysis technique

Changes in the brain lactate concentration in cerebral extracellular fluid (ECF) during intravenous infusion of glucose and local administration of glucose were investigated in adult, conscious, unrestrained rats, with a microdialysis probe in the posterior hippocampus. The rats were infused intravenously with either 25% sucrose solution or 25% glucose solution at a rate of 16.6 microliters.min-1.100 g-1 for three hours. The blood glucose concentration reached 17.0 +/- 2.6 mM at the end of the glucose infusion, and brain ECF glucose showed a parallel change with the blood glucose concentration and increased to 2.37 +/- 0.30 mM. However, blood and brain ECF glucose concentrations did not change in animals infused with the sucrose solution. On the other hand, the blood lactate concentration in the glucose-infused group also increased from 0.93 +/- 0.18 mM to 2.85 +/- 0.39 mM at the end of the glucose infusion, which was significantly higher than that measured in the sucrose-infused group. The blood lactate level in the glucose-infused group returned to the basal level by the end of the experiment. Brain ECF lactate concentrations increased from 1.21 +/- 0.06 mM to 1.69 +/- 0.11 mM in glucose-infused animals, but did not change in the sucrose-infused animals. The brain ECF lactate concentration showed a positive correlation with the brain ECF glucose concentration in glucose-infused animals. Another group of rats was administered glucose locally for 90 min after substitution of artificial cerebrospinal fluid.(ABSTRACT TRUNCATED AT 250 WORDS)     

Methionine and cysteine affect glutathione level, glutathione-related enzyme activities and the expression of glutathione S-transferase isozymes in rat hepatocytes

Methionine and cysteine are constituents of glutathione. To understand the effects of these two sulfur amino acids on the glutathione (GSH)-dependent detoxification defense system, intracellular GSH and GSH-related enzyme activities, including GSH peroxidase, GSH reductase, GSH S-transferase (GST) and gamma-glutamylcysteine synthetase, were determined. In addition, the expression of three GST isozymes and carbonic anhydrase III (CA III) was examined. Hepatocytes isolated from male Sprague-Dawley rats were cultured with 0.1, 0.3, 0.5 or 1.0 mmol/L each of L-methionine and L-cysteine, for up to 7 d. Cells incubated with 0.5 or 1.0 mmol/L methionine and cysteine had increased intracellular GSH. A twofold increase was observed on d 6 compared with freshly isolated hepatocytes (P < 0.05). However, intracellular GSH was lower in cells treated with 0.3 or 0.1 mmol/L each of methionine and cysteine than in cells tested with 0.5 or 1.0 mmol/L. Although the GSH level differed significantly between cells cultured with 0.3 or 1.0 mmol/L of methionine and cysteine, GSH-related enzymes did not differ at these two concentrations. The activity generally remained constant for the first 24 h, then increased up to d 4. Immunodetection analysis revealed no difference in the level of CA III and GST isoforms, Ya, Yb and Yp, with amino acids each at a concentration of at least 0.3 mmol/L. Yp expression steadily increased up to d 7. Most proteins decreased rapidly after 48 h when cultured with 0.1 mmol/L of methionine and cysteine; however, the Yp level increased up to d 6. In conclusion, results indicate that a twofold increase of intracellular GSH is reached by adding methionine and cysteine at a concentration >0.5 mmol/L to the culture medium. The concentrations of methionine and cysteine for maintaining hepatic GSH are higher than for GSH-related enzyme activity and for GST isoform expression.     

Effects of 4 hours magnesium sulfate infusion on fetal heart rate variability and reactivity in a goat model

Effects of magnesium sulfate were investigated on fetal heart rate (FHR) baseline, variability, and reactivity in goats. Six chronically catheterized fetuses of Japanese Saanen goat at 125 to 130 days' gestation (term = 147 days) were used. Magnesium sulfate was directly infused to the fetuses. Short-term variability and long-term variability were obtained according to Huey et al. The baseline, reactivity, short-term variability and long-term variability of the FHR were compared between those receiving magnesium sulfate infusions and those receiving vehicle infusions without magnesium sulfate for 4 hr. Two-way analysis of variance (ANOVA) and Duncan's multiple range test was applied for statistical significance. Four hours magnesium sulfate infusion significantly increased fetal plasma concentration of magnesium from 2.4-6.6 mg/dL, without significant changes in fetal respiratory gases and pH values. The baseline FHR was significantly decreased by magnesium infusion compared with that receiving vehicle infusion. The incidence of acceleration, short-term variability, and long-term variability during the fourth hour of magnesium infusion was also significantly decreased compared to a controlled infusion. The time spent by high amplitude phase of short-term variability and that of long-term variability were also significantly reduced. Significant correlation was obtained between the magnesium concentration and incidence of acceleration at fourth hour of magnesium infusion. Four hours infusion of magnesium sulfate significantly decreases baseline FHR, short-term variability, long-term variability, and reactivity in fetal goats at 0.85 gestation.     

Refractory ascites in cirrhosis: roles of volume expansion and plasma atrial natriuretic factor level elevation

Cirrhotic patients with ascites refractory to diuretics also have blunted response to marked elevations of plasma atrial natriuretic factor levels alone or to moderate intravascular volume expansion by head-out water immersion. However, these patients usually undergo natriuresis after peritoneovenous shunting. To dissect the factors responsible for this response, we studied the effects on separate days of moderate intravascular volume expansion and highly elevated plasma atrial natriuretic factor levels (head-out water immersion and atrial natriuretic factor infusion) or marked volume expansion and moderate plasma atrial natriuretic factor level elevation (head-out water immersion and albumin infusion) in 13 alcoholic cirrhotic patients with massive ascites. Three of these patients, who responded to initial head-out water immersion with a negative sodium balance, served as controls. Unresponsiveness to head-out water immersion was confirmed in the remaining 10 patients on both days on the basis of blunted natriuretic response (urinary sodium excretion < 0.8 mmol/hr after 2 hr). In contrast, these 10 refractory patients were able to achieve negative sodium balance with both combinations. Mean urinary sodium excretion increased from a baseline level of 0.13 +/- 0.10 mmol/hr to a peak level of 2.29 +/- 0.61 mmol/hr after head-out water immersion and atrial natriuretic factor infusion and from 0.10 +/- 0.3 mmol/hr to 1.61 +/- 0.62 mmol/hr after head-out water immersion and albumin infusion. Both maneuvers were associated with suppression of plasma renin activity and serum aldosterone levels. With head-out water immersion and atrial natriuretic factor infusion, we noted a significant increase in 5' cyclic GMP levels, a second messenger of atrial natriuretic factor, indicating possible activation of atrial natriuretic factor receptors at the inner medullary collecting ducts. In contrast, with head-out water immersion and albumin infusion no such increase in levels occurred, indicating that the increase in urinary sodium excretion was mainly due to increased delivery of sodium to the cortical distal nephron, as indicated by a disproportionate increase in urinary potassium excretion. In conclusion, massive (as opposed to moderate) volume expansion or greatly elevated levels of plasma atrial natriuretic factor associated with moderate volume expansion can improve blunted atrial natriuretic factor responsiveness in cirrhotic patients with refractory ascites. This appears to be achieved by way of a marked increase in distal delivery of filtrate in the kidney, with or without activation of distal atrial natriuretic factor receptors in the inner medullary collecting ducts.     

Human hydrometry: comparison of multifrequency bioelectrical impedance with 2H2O and bromine dilution

The renal transport and fractional reabsorption of inorganic sulfate is altered under conditions of sulfate deficiency or excess. The objective of this study was to examine the cellular mechanisms of adaptation of renal sodium/sulfate cotransport after varying dietary intakes of a sulfur containing amino acid, methionine. Female Lewis rats were divided into four groups and fed diets containing various concentrations of methionine (0, 0.3, 0.82 and 2.46%) for 8 days. Urinary excretion rates and renal clearance of sulfate were significantly decreased in the animals fed a 0% methionine diet or a 0.3% methionine diet, and significantly increased in the animals fed a 2.46% methionine diet when evaluated on days 4 and 7. Serum sulfate concentrations were unchanged by diet treatment in all animals. The fractional reabsorption of sulfate was significantly increased in the animals fed the 0% methionine diet and the 0.3% methionine diets, and decreased in the animals fed the 2.46% methionine diet. Increased mRNA and protein levels for the sodium/sulfate transporter (NaSi-1) were found in the kidney cortex following treatment with the 0 and 0.3% methionine diet groups. Sulfate homeostasis by renal reabsorption is maintained by an up-regulation of steady state levels of NaSi-1 mRNA and protein when the diet is low in methionine.     

Estimates of interdialytic sodium and water intake based on the balance principle: differences between nondiabetic and diabetic subjects on hemodialysis

Whether salt or water intake is the primary cause of interdialytic weight gain (deltaW) has important implication for the design of measures to prevent large deltaW. In 17 hemodialysis patients dialyzed against a bath containing 140 mmol/L of sodium, monthly predialysis serum sodium was compared with post dialysis serum sodium. A decrease in serum sodium in the interdialytic period would indicate that primary water consumption accounts for at least part of the deltaW. Interdialytic sodium intake, isotonic fluid gain (deltaW(isotonic)) and net pure water gain (deltaWH2O) were calculated by balance formulae. Serum sodium concentration was corrected in diabetic subjects to the value corresponding to euglycemia (100 mg/dl). Estimated interdialytic sodium intake was compared with the prescribed sodium intake and, in seven subjects, to sodium intake estimated from dietary records. Results for nondiabetic subjects (N = 9): [Na]post 139.3 +/- 1.9 mmol/L, [Na]pre 140.1 +/- 2.1 mmol/L (NS), deltaW 1.15 +/- 0.55 L/24 hr, deltaW(isotonic) 1.33 +/- 0.57 L/24 hr, deltaWH2O -0.20 +/- 0.58 L/24 hr, estimated sodium intake 206 +/- 75 mmol/24 hr, prescribed sodium intake 121 +/- 29 mmol/24 hr (p = 0.028). Results for diabetic subjects (N = 7): [Na]post 140.1 +/- 2.5 mmol/L, [Na]pre 137.7 +/- 3.1 mmol/L (p < 0.01), deltaW 1.26 +/- 0.38 L/24 hr, deltaW(isotonic) 0.59 +/- 0.63 L/24 hr, deltaWH2O 0.66 +/- 0.39 L/24 hr, estimated sodium intake 160 +/- 81 mmol/24 hr, prescribed sodium intake 124 +/- 30 mmol/24 hr (NS), glycosylated hemoglobin 9.7 +/- 2.8% (normal, 4.1-5.7%). In seven subjects, estimates of sodium intake from balance formulae (233 +/- 113 mmol/24 hr) were not different from estimates from dietary records (212 +/- 87 mmol/24 hr). Sodium intake accounted for all the interdialytic weight gain in nondiabetic subjects. In diabetic patients, only approximately half of the interdialytic weight gain was accounted for by sodium intake. The other half was due to pure water gain, probably caused by hyperglycemia.     

Glycated hemoglobin reference limits obtained by high performance liquid chromatography in adults and pregnant women

Pentachlorophenol (PCP) and molybdate have been shown to inhibit the sulfoconjugation of various chemicals in rats and therefore are useful to examine the role of sulfoconjugation on the toxicity of a chemical. PCP inhibits sulfation by competing with substrates for phenol-sulfotransferases, but not hydroxysteroid-sulfotransferases. In contrast, molybdate decreases sulfation by limiting sulfate availability and thereby decreasing the synthesis of 3'-phosphoadenosine 5'-phosphosulfate (PAPS), which is the obligate cosubstrate for sulfation. Therefore, it was of interest to determine whether PCP or molybdate is effective in decreasing the in vivo sulfation of dehydroepiandrosterone (DHEA), which is a substrate for hydroxysteroid-sulfotransferases. PCP (40 micromol/kg ip) or molybdate (7.5 mmol/kg po) was given 45 min and 4 h, respectively, prior to the start of DHEA infusion. The effects of these two sulfation inhibitors on DHEA sulfation were dependent on the rate of DHEA infusion in rats. PCP had different effects on the sulfation of various infusion rates of DHEA in rats. PCP had little effect on the sulfation after the two lowest infusion rates of DHEA (12.5 and 25 mg/kg) and actually increased (233%) DHEA-sulfate serum concentrations with the highest DHEA infusion rate (50 mg/kg). Although molybdate had little affect on the sulfation of the lowest DHEA infusion rate, it significantly decreased (50-85%) DHEA-sulfate serum concentrations with the two higher DHEA infusion rates. These data indicate that molybdate, unlike PCP, decreases the sulfation of DHEA and may be a useful tool to decrease the sulfation of other substrates of hydroxysteroid-sulfotransferases.     

Effects of molybdate on the sulfation of harmol and alpha-naphthol

Sulfation requires the activity of sulfotransferases to transfer the sulfuryl group to the substrate from the activated form of sulfate, 3'-phosphoadenosine 5'-phosphosulfate (PAPS). Inhibition of the sulfate reaction is an important aspect in evaluating the role of sulfation in toxicology. Molybdate decreases hepatic PAPS and its precursor, inorganic sulfate, and could be used as a tool to inhibit the sulfation reaction. The present study was designed to determine the effect of molybdate on the sulfation of two compounds (harmol and alpha-naphthol), for which sulfation is the predominate pathway of biotransformation. Molybdate (7.5 mmol/kg; p.o.) given 4 h prior to the start of harmol infusion (2.5 micromol/kg/min) decreased serum harmol-sulfate concentrations by 32 and 45%, at 45 and 60 min, respectively. This was paralleled by decreases in the cumulative biliary excretion of harmol-sulfate of 37 and 43%, at 45 and 60 min, respectively. Molybdate (5.0 mmol/kg, p.o.) decreased the 24-h cumulative urinary excretion of naphthyl-sulfate by 55% for a 125-micromol/kg i.p. dose of alpha-naphthol, with the greatest decrease (63%) occurring during the first 4 h. These results suggest that molybdate can inhibit the sulfation of compounds that are highly sulfated. Thus, molybdate may prove useful in future studies to examine the pharmacological and toxicological significance of sulfation of xenobiotics.     

Taurine infused intrastriatally elevates, but intranigrally decreases striatal extracellular dopamine concentration in anaesthetised rats

In the present study we infused taurine (50, 150 or 450 mM, 2 microliters/min for 4h) into the dorsal striatum or into the substantia nigra via microdialysis probe and estimated the extracellular concentrations of dopamine and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), in the dorsal striatum of anaesthetised rats. Intrastriatal infusion of taurine elevated striatal dopamine at all concentrations studied. At the 450 mM concentration taurine elevated the extracellular dopamine 10-fold, but only in the first 30 min sample after starting the taurine infusion. At 50 and 150 mM taurine elevated dopamine throughout the 4h infusion maximally up to 3-4-fold the control level. Extracellular DOPAC was increased by 150 and 450 mM taurine (up to about 150-160% of the control level), whereas at all three concentrations taurine decreased HVA to about 85% of the control; however, the decrease caused by 450 mM taurine was short-lasting. At all three concentrations taurine infused into the substantia nigra decreased the extracellular dopamine in the ipsilateral striatum to about 40-50% of the control, and increased extracellular DOPAC and HVA maximally to about 150% and 170% of the control, respectively. These results show that the effects of taurine on the concentrations of extracellular dopamine and its metabolites depend on its administration site on nigrostriatal dopaminergic neurons. It elevates the extracellular dopamine when given into the striatum, but when given into the cell body region of the nigrostriatal dopaminergic pathway it decreases the extracellular dopamine in the ipsilateral striatum.     

Redefining reductive sulfate assimilation in higher plants: a role for APS reductase, a new member of the thioredoxin superfamily?

The reaction steps leading from the intermediate adenosine 5'-phosphosulfate (APS) to sulfide within the higher plant reductive sulfate assimilation pathway are the subject of controversy. Two pathways have been proposed: a 'bound intermediate' pathway in which the sulfo group of APS is first transferred by APS sulfotransferase to a carrier molecule to form a bound sulfite intermediate and is then further reduced by thiosulfonate reductase to bound sulfide; and a 'free intermediate' pathway in which APS is further activated to 3'-phosphoadenosine 5'-phosphosulfate (PAPS) by APS kinase followed by reduction of the sulfo group to free sulfite by PAPS reductase. Sulfite is then reduced to free sulfide by sulfite reductase. Sulfide, either free or bound, is then incorporated into organic form (as cysteine) by the enzyme O-acetylserine (thiol) lyase. In order to better characterize the pathway we attempted to clone PAPS reductase cDNAs by functional complementation of an Escherichia coli cysH mutant to prototrophy. We found no evidence for PAPS reductase cDNAs but did identify cDNAs that encode a small family of novel, chloroplast-localized proteins with APS reductase activity that are new members of the thioredoxin superfamily. We show here that the thioredoxin domain of these proteins is functional. We speculate that rather than proceeding via either of the pathways proposed above, reductive sulfate assimilation proceeds via the reduction of APS to sulfite by APS reductase and the subsequent reduction of sulfite to sulfide by sulfite reductase. In this scheme the product of the APS kinase reaction, PAPS, is not a direct intermediate in the pathway but rather acts as a substrate for sulfotransferase action and perhaps as a store of activated sulfate that can be returned to the pathway as APS via phosphohydrolase action on PAPS. Interactions between enzyme isoforms within the chloroplast stroma may bring about substrate channeling of APS and contribute to the partitioning of APS between sulfotransferase reactions on the one hand and the synthesis of cysteine and related metabolites via the reductive sulfate assimilation pathway on the other.     

Clearance and tissue uptake following 4-hour and 24-hour infusions of pamidronate in rats

Bisphosphonates are clinically useful for the treatment of bone disorders; however, there is some controversy concerning the extent to which the design of the dosage regimen influences the efficacy of these drugs. The effect of different rates of infusion of [14C] pamidronate (APD; 3-amino-1-hydroxy-propylidene-1,1-bisphosphonate) (1 mg/kg infused over 4 or 24 hr) on its pharmacokinetics was investigated in rats by the measurement of tissue disposition and plasma clearance. The pharmacokinetic parameters, including total clearance, renal clearance, and nonrenal clearance, were found to be not significantly affected by the rate of infusion. The concentration of pamidronate in tibia, liver, kidney, and spleen was also unaffected by the two infusion rates. The bone (tibia) contained the highest concentration of all the tissues sampled, and the kidney accumulated the highest concentration among the soft tissues measured; this was in contrast to previous bolus administration studies where the liver and spleen contained higher concentrations than the kidney. The disposition kinetics of pamidronate were found to be essentially multiphasic, with a rapid initial half-life that gradually tails into a very long terminal phase. A terminal half-life could not be reliably estimated as it increased with time. As a consequence a model-independent approach, based on the calculation of the total, renal, and nonrenal clearance, best served to describe the disposition kinetics of pamidronate. For this unmetabolized compound the nonrenal clearance can be ascribed to tissue binding, which appears to be essentially irreversible.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lactate, N-acetylaspartate, choline and creatine concentrations, and spin-spin relaxation in thalamic and occipito-parietal regions of developing human brain

Previous studies of the brains of normal infants demonstrated lower lactate (Lac)/choline (Cho), Lac/creatine (Cr), and Lac/ N-acetylaspartate (Naa) peak-area ratios in the thalamic region (predominantly gray matter) compared with occipitoparietal (mainly unmyelinated white matter) values. In the present study, thalamic Cho, Cr, and Naa concentrations between 32-42 weeks' gestational plus postnatal age were greater than occipito-parietal: 4.6 +/- 0.8 (mean +/- SE), 10.5 +/- 2.0, and 9.0 +/- 0.7 versus 1.8 +/- 0.6, 5.8 +/- 1.5, and 3.4 +/- 1.1 mmol/kg wet weight, respectively: Lac concentrations were similar, 2.7 +/- 0.6 and 3.3 +/- 1.3 mmol/kg wet weight, respectively. In the thalamic region, Cho and Naa T2s increased, and Cho and Lac concentrations decreased, during development. Lower thalamic Lac peak-area ratios are principally due to higher thalamic concentrations of Cho, Cr, and Naa rather than less Lac. The high thalamic Cho concentration may relate to active myelination; the high thalamic Naa concentration may be due to advanced gray-matter development including active myelination. Lac concentration is higher in neonatal than in adult brain.     

Bacq and Alexander Award lecture--chemical radioprotection: past, present, and future prospects

The intracellular magnesium and calcium ion concentrations of in vivo-developed 2-cell hamster embryos were measured using ratiometric fluorometry. Intracellular magnesium and calcium ion concentrations were found to be 0.369 +/- 0.011 mM and 129.3 +/- 7.5 nM respectively. Culture of 1-cell hamster embryos for 24 hr to the 2-cell stage in control medium containing 0.5 mM magnesium and 2.0 mM calcium resulted in approximately a threefold increase to 343.5 +/- 8.0 nM in intracellular calcium ion concentration, while magnesium ion levels were not altered (0.355 +/- 0.007 mM). Increasing medium magnesium concentrations to 2.0 mM significantly increased intracellular magnesium ion concentrations of cultured 2-cell embryos with a concomitant reduction in intracellular calcium ion concentrations. Furthermore, increasing the medium magnesium concentration to 2.0 mM significantly increased development of 1-cell embryos collected at either 3 or 9 hr post-egg activation to the morula/blastocyst and blastocyst stages. Resultant blastocysts had an increased total cell number and increased development of the inner cell mass. Most important, however, culture with 2.0 mM magnesium increased the fetal potential of cultured 1-cells twofold. Therefore, because highest rates of development were observed in a medium that resulted in reduced intracellular calcium ion concentrations, it appears that altered calcium homeostasis is associated with impaired developmental competence of 1-cell embryos in culture.     

Biopharmaceutical studies on drug/conjugated-metabolite interactions. III. Effect of acetaminophen sulfate and its positional isomers on the pharmacokinetics of acetaminophen in rats

The effect of three positional isomers, o-, m- and p-acetylaminophenyl sulfate (AOAPS, AMAPS and APAPS (acetaminophen sulfate), respectively), on the pharmacokinetics of acetaminophen (APAP) was investigated in rats. All of the intravenously administered positional isomers were rapidly eliminated from plasma, and approximately 80% of the dose was excreted in an unchanged form in the urine within 4 h, while biliary excretions represented a small percent of the doses. Following the intravenous bolus injection of APAP, plasma elimination of APAP was accelerated and the distribution volume of APAP was increased under a steady state concentration (about 10 microg APAP eq/ml) of AOAPS or APAPS, but not AMAPS, as compared with saline infusion. Total body clearances of APAP were increased from 18.3 ml/min/kg for the control to 23.9 and 26.9 ml/min/kg for AOAPS and APAPS coadministration, respectively. AOAPS and APAPS competitively displaced the serum protein binding of APAP, while AMAPS had little effect. The distribution volume of unbound APAP was anomalously increased by APAPS, while it was not affected by AOAPS or AMAPS. Tissue-to-plasma concentration ratios of APAP were significantly increased by APAPS in the liver, kidney and brain, while they were only slightly increased by AOAPS. It was suggested that APAPS has not only the displacing activity of serum protein binding but also other specific effectiveness on the distribution of APAP.     

Renal uptake and excretion of homocysteine in rats with acute hyperhomocysteinemia

BACKGROUND: Elevated plasma total homocysteine, an independent risk factor for cardiovascular disease, is commonly observed in renal patients. We have previously shown that the kidney is a major site for the removal of plasma homocysteine in the rat. The present investigation was performed to further characterize the capacity of the kidney to handle acute elevations in plasma homocysteine concentrations. METHODS: Acute hyperhomocysteinemic conditions (4- to 7-fold > controls) in rats were produced by either a primed-continuous infusion of L-homocysteine or exposure to 80:20% nitrous oxide:oxygen, which results in the inhibition of methionine synthase. RESULTS: At physiological homocysteine concentrations, approximately 15% of the arterial plasma homocysteine was removed on passage through the kidney. Renal homocysteine uptake was approximately 85% of the filtered load. The urinary excretion of homocysteine was negligible (<2%). During acute hyperhomocysteinemia produced by the infusion of L-homocysteine, renal homocysteine uptake was increased fourfold and was equivalent to 50% of the infused dose, while urinary excretion remained negligible. Renal homocysteine uptake during nitrous oxide-induced hyperhomocysteinemia increased threefold, with urinary excretion remaining negligible. CONCLUSIONS: These results provide strong evidence that the kidney has a significant capacity for metabolizing acute elevations in plasma homocysteine, and support a very limited role for the re-methylation pathway in renal homocysteine metabolism.     

Evaluation of copper sulfate and a copper lysine complex as growth promoters for weanling swine

Two 5-wk trials using 176 weanling pigs (average initial weight of 8.3 kg and age of 31 d) were conducted to examine the effect of feeding varying levels of dietary Cu from copper sulfate (CuSO4) or a copper lysine complex (CuLys) on performance, mineral stores, serum copper, and serum mitogenic activity. Dietary treatments were 0 (15 mg/kg of Cu in basal diet), 100, 150, or 200 mg/kg of supplemental Cu from CuSO4 or CuLys. Average daily gain and ADFI increased linearly (P < .01) with increasing dietary levels of Cu during wk 1 to 2, 3 to 5, and 1 to 5, with no difference (P > .10) between the Cu sources. Overall gain:feed ratios were not consistently affected by Cu source. Dietary Cu linearly increased liver, kidney (P < .001), and brain (P < .05) concentrations of Cu. In the liver, the linear response to supplemental Cu differed between Cu sources (P < .001); pigs fed 200 mg/kg of Cu from CuLys had the highest concentration of Cu. Serum Cu concentrations increased linearly during wk 1 to 2 (P < .01), 3 to 5, and 1 to 5 (P < .001), with no difference (P > .10) between sources. Serum mitogenic activity increased linearly during wk 1 to 2 and 1 to 5 (P < .05). Growth performance was linearly improved as the dietary level of Cu increased from 15 to 200 mg/kg, with similar responses for both Cu sources. Serum and tissue concentrations of Cu were generally equally affected by the two Cu sources, except liver Cu concentration, which was onefold higher for pigs fed 200 mg/kg of Cu as CuLys.     

Effects of P-glycoprotein modulators on etoposide elimination and central nervous system distribution

In this study, P-glycoprotein modulator effects on pharmacokinetics and central nervous system distribution of the chemotherapeutic agent etoposide were evaluated. The multidrug resistance transporter P-glycoprotein is expressed in normal tissues, and its physiological function is thought to be an excretory and/or protective one. To examine this further, we evaluated etoposide under steady-state and bolus dose conditions. In microdialysis infusion studies, etoposide 15 mg/kg/hr was administered to 12 rats. Rats received sodium cyanide (1 or 100 mM), trifluoperazine (30 mM) or cyclosporine (4.14 mM) via microdialysis probe at 3.5 hr after etoposide infusion initiation. High-dose sodium cyanide (100 mM) increased the etoposide BBR,corr from 0.09 +/- 0.03 to 0.85 +/- 0.35. Similarly, trifluoperazine significantly increased the BBR,corr (0.05 +/- 0.02 vs. 1.30 +/- 0.43), whereas cyclosporine had no effect. In bolus studies, etoposide (10-12 mg/kg) was given alone or concomitant to cyclosporine (5 mg/kg) or tamoxifen (13.5 mg/kg). Control etoposide total systemic clearance (ml/min/kg) was 29.3 +/- 13.0 vs. 16.0 +/- 1.9 and 22.6 +/- 5.3 for cyclosporine and tamoxifen treatments, respectively. Etoposide nonrenal clearance (ml/min/kg) values for cyclosporine (12.0 +/- 1.6) and tamoxifen (18.1 +/- 3.6) treatments was also decreased from controls (23.5 +/- 10.5). Etoposide renal clearance (ml/min/kg) values (5.7 +/- 2.5) were not significantly different from cyclosporine (4.0 +/- 0.7) or tamoxifen (4.6 +/- 1.7) treatments, respectively. In this study, the ability of sodium cyanide and trifluoperazine to alter etoposide BBR,corr, demonstrated that etoposide distribution into brain is partly controlled by an active transport process. Similarly, the results indicate cyclosporine inhibits etoposide transport at the canalicular membrane and/or etoposide P-450 metabolism.     

Effects of hyperinsulinemia under the euglycemic condition on calcium and phosphate metabolism in non-obese normotensive subjects

The effect of acute insulin infusion on the metabolism of calcium (Ca) and phosphate (P) was examined in 17 healthy subjects. They were hospitalized and kept on a constant diet for 5 days, and an euglycemic hyperinsulinemic glucose clamp was applied. Synthetic human insulin was infused at the rate of 40 mU/m2/min for 2 hr, and glucose was also infused to maintain basal glucose levels of each subject. The control study was performed in 8 of the 17 subjects, into whom 10% xylitol was infused for 2 hr at the rate of 100 ml/hr. The plasma insulin concentrations were 7.94 +/- 0.35 and 62.3 +/- 14.3 mU/liter before and after the glucose clamp technique, but serum free Ca ion was increased significantly (p < 0.05), and serum P and serum parathyroid hormone (PTH) were decreased significantly (p < 0.001). Creatinine clearance did not change during the glucose clamp technique. Urinary excretion of Ca (UCaV) was significantly higher after the glucose clamp than the control study. Fractional excretion of Ca (FECa) was increased significantly (p < 0.05), and urinary excretion of P (UPV) and fractional excretion of P (FEP) were decreased significantly (p < 0.05) under the hyperinsulinemic condition. The results suggested that, under the conditions of euglycemic hyperinsulinemia by glucose clamp technique, insulin increased the serum free Ca ion, and as a result, PTH was suppressed. Decreased PTH might induce calciuresis and enhance tubular P reabsorption under hyperinsulinemia. Insulin increased serum free Ca ion might relate to the vasodilating action of insulin by its decrease of intracellular free Ca ion in vascular smooth muscle.