Determination of chromium in urine by stable isotope dilution gas chromatography/mass spectrometry using lithium bis(trifluoroethyl)dithiocarbamate as a chelating agent

An isotope dilution gas chromatography/mass spectrometry method using lithium bis(trifluoroethyl)dithiocarbamate as a chelating agent is described for the determination of chromium in urine. A wet digestion procedure with HNO3-H2O2 is used for oxidizing the organic matter associated with urine samples. The isotope ratios are measured by selected ion monitoring in a general-purpose mass spectrometer using a 10-m fused silica capillary column. Memory effect, in sequential analyses of samples with different isotope ratios, was evaluated by preparing a series of synthetic mixtures and was found to be negligible. The accuracy of the method was verified by quantitation of chromium in the NIST freeze-dried urine reference material, SRM-2670, with a recommended chromium concentration of 13 micrograms/L in the normal level and certified chromium concentration of 85 +/- 6 micrograms/L in the elevated level.

Normal biochemical and hematological values in New Zealand white rabbits

Animal model systems are used extensively for experimental in vivo studies. When biochemical and hematological measurements are made, reference intervals for the animal species must be determined. Here, the subjects for our study were young adult male New Zealand White rabbits. Blood was sampled from 110 normal healthy rabbits. Biochemical and hematological blood variables were measured by methods available in our routine service laboratory, and we report the ranges.

Normal biochemical and hematological values in New Zealand white rabbits

Animal model systems are used extensively for experimental in vivo studies. When biochemical and hematological measurements are made, reference intervals for the animal species must be determined. Here, the subjects for our study were young adult male New Zealand White rabbits. Blood was sampled from 110 normal healthy rabbits. Biochemical and hematological blood variables were measured by methods available in our routine service laboratory, and we report the ranges.

Ultrastructural localization of aluminium in liver of aluminium maltol-treated rabbits by laser microprobe mass analysis

By means of laser microprobe mass analysis (LAMMA), we have studied the ultrastructural localization of aluminium in livers of aluminium maltol-treated rabbits. This animal model was developed to study long-term aluminium toxicity using systemic (intravenous) administration of aluminium. We could only detect aluminium in electron-dense inclusion bodies found in large, sometimes multinucleated cells. These results prove that the actual observation of aluminium deposits in liver with LAMMA gives more information than bulk analysis and can be very useful to explore mechanisms of toxicity.

Influence of matrix on concentrations of somatotropin measured in serum with commercial immunoradiometric assays

Using immunoradiometric assays (IRMAs) from Hybritech Inc. (H) and Nichols Institute Diagnostics (ND), we measured somatotropin (human growth hormone, hGH) in serum samples obtained every 20 min for 24 h from 10 prepubertal subjects with short stature. Results obtained with the ND reagents were 2.74 times greater than those obtained with the H reagents (P = 0.00001, r = 0.94, SEE = 3.9, n = 720). We therefore compared the IRMAs with the standard hGH RIA from the National Institutes of Health (NIH) National Hormone and Pituitary Program, using the genetically engineered hGH preparations (from Genentech Inc.) 22-kDa hGH and methionated 20-kDa hGH. We also assayed human pituitary hGH (NIH, lot no. AFP-4793B). Each hGH preparation was diluted in three diluent buffer systems: horse serum from H and from ND, and human serum. The RIA and H-IRMA gave superimposable standard curves for all hGH preparations in each diluent. The methionated 20-kDa hGH was not detected in the H-assay. Use of human serum matrix in the ND-IRMA shifted the standard curve as compared with the horse-serum matrix, giving equivalent binding at lower concentrations; i.e., serum hGH was overestimated in samples assayed against standards diluted in horse serum. Quality-control materials (Ciba-Corning) yielded disparate results in all three assays, yet human serum pools containing hGH gave similar results in the H and the NIH assays, and higher values in ND. When a human serum standard was used in the ND assay, both IRMAs gave similar results to the RIA assay for human serum samples. Reference intervals for hGH should be determined by each analytical laboratory, to prevent misdiagnosis of patients. Furthermore, quality-control material should be of human origin, because commercially supplied quality-control material does not react the same as human serum in some hGH assays.

Influence of matrix on concentrations of somatotropin measured in serum with commercial immunoradiometric assays

Using immunoradiometric assays (IRMAs) from Hybritech Inc. (H) and Nichols Institute Diagnostics (ND), we measured somatotropin (human growth hormone, hGH) in serum samples obtained every 20 min for 24 h from 10 prepubertal subjects with short stature. Results obtained with the ND reagents were 2.74 times greater than those obtained with the H reagents (P = 0.00001, r = 0.94, SEE = 3.9, n = 720). We therefore compared the IRMAs with the standard hGH RIA from the National Institutes of Health (NIH) National Hormone and Pituitary Program, using the genetically engineered hGH preparations (from Genentech Inc.) 22-kDa hGH and methionated 20-kDa hGH. We also assayed human pituitary hGH (NIH, lot no. AFP-4793B). Each hGH preparation was diluted in three diluent buffer systems: horse serum from H and from ND, and human serum. The RIA and H-IRMA gave superimposable standard curves for all hGH preparations in each diluent. The methionated 20-kDa hGH was not detected in the H-assay. Use of human serum matrix in the ND-IRMA shifted the standard curve as compared with the horse-serum matrix, giving equivalent binding at lower concentrations; i.e., serum hGH was overestimated in samples assayed against standards diluted in horse serum. Quality-control materials (Ciba-Corning) yielded disparate results in all three assays, yet human serum pools containing hGH gave similar results in the H and the NIH assays, and higher values in ND. When a human serum standard was used in the ND assay, both IRMAs gave similar results to the RIA assay for human serum samples. Reference intervals for hGH should be determined by each analytical laboratory, to prevent misdiagnosis of patients. Furthermore, quality-control material should be of human origin, because commercially supplied quality-control material does not react the same as human serum in some hGH assays.

Isotope dilution gas chromatography/mass spectrometry for the determination of nickel in biological materials

Precise and accurate methods are required to measure nickel in urine and serum samples to identify clinical states of either deficiency or toxicity. This paper presents an isotope dilution gas chromatography/mass spectrometry method for the measurement of nickel in biological samples. The method involves the preparation of a thermally stable and volatile nickel chelate using lithium bis(trifluoroethyl)dithiocarbamate as the chelating agent. Conditions were optimized for the digestion of the sample and quantitative preparation of chelate as well as the precise and accurate measurements of the isotope ratios using a capillary column gas chromatograph with a general purpose mass spectrometer. The memory effect between samples of different isotope ratios was evaluated and was found to be negligible. The quantitative accuracy of isotope dilution was validated by measuring nickel in the NIST freeze-dried urine reference material, SRM 2670, with comparison to the recommended value.

A long-term intravenous model of aluminum maltol toxicity in rabbits: tissue distribution, hepatic, renal, and neuronal cytoskeletal changes associated with systemic exposure

We studied the toxicity of an intravenously injected, water-soluble aluminum complex (aluminum maltol) in 20 young adult male New Zealand white rabbits over a period of 8 to 30 weeks. Sixteen rabbits injected with aluminum-free maltol and 15 untreated rabbits served as controls. Rabbits were injected three times per week with 75 mumol of aluminum maltol per injection, or a molar equivalent amount of maltol alone, through an indwelling jugular catheter. Liver contained the highest concentrations of aluminum among the aluminum maltol-treated rabbits, and aluminum accumulation was correlated with the appearance of periportal multinucleated giant cells in 13 of 20 rabbits. These cells stained positively for aluminum when a fluorescent (Morin) stain was applied to tissue from rabbits with a high concentration of aluminum in the liver. Proximal renal tubular necrosis or atrophy was found in 15 of 20 aluminum maltol-treated rabbits but not in maltol-treated and untreated controls. Renal tubules in rabbits with acute proximal renal necrosis stained positively for aluminum. Neurofibrillary tangles, immunoreactive with a monoclonal antibody to the 200-kDa subunit of neurofibrillary protein, were observed in the oculomotor nucleus of 3 aluminum maltol-treated rabbits (treated for 12, 20, and 29 weeks), but in none of the two groups of controls. These tangles were present in 3 of 10 aluminum-treated rabbits in which the nucleus was located. None of the 17 animals in both control groups in which the nucleus was found demonstrated tangles. A slight increase in brain tissue aluminum concentration was confirmed by an electrothermal atomic absorption spectrophotometric method. There were no specific findings in heart or lung tissue from aluminum-treated rabbits, although the aluminum content of these tissues was 10 to 20 times greater than control values. This model should be useful for investigating the effects of systemic exposure to high concentrations of solubilized aluminum.

Micro-quantity tissue digestion for metal measurements by use of a microwave acid-digestion bomb

We describe a simple and convenient method for processing small amounts of tissue samples for trace-metal measurements by atomic absorption spectrometry, by use of a modified Parr microwave digestion bomb. Digestion proceeds rapidly (less than or equal to 90 s) in a sealed Teflon-lined vessel that eliminates contamination or loss from volatilization. Small quantities of tissue (5-100 mg dry weight) are digested in high-purity nitric acid, yielding concentrations of analyte that can be measured directly without further sample manipulation. We analyzed National Institute of Standards and Technology bovine liver Standard Reference Material to verify the accuracy of the technique. We assessed the applicability of the technique to analysis for aluminum in bone by comparison with a dry ashing procedure.

Micro-quantity tissue digestion for metal measurements by use of a microwave acid-digestion bomb

We describe a simple and convenient method for processing small amounts of tissue samples for trace-metal measurements by atomic absorption spectrometry, by use of a modified Parr microwave digestion bomb. Digestion proceeds rapidly (less than or equal to 90 s) in a sealed Teflon-lined vessel that eliminates contamination or loss from volatilization. Small quantities of tissue (5-100 mg dry weight) are digested in high-purity nitric acid, yielding concentrations of analyte that can be measured directly without further sample manipulation. We analyzed National Institute of Standards and Technology bovine liver Standard Reference Material to verify the accuracy of the technique. We assessed the applicability of the technique to analysis for aluminum in bone by comparison with a dry ashing procedure.

Tumoral calcinosis: seasonal biochemical studies and chemical studies of eyelid lesion

We recently described (Arch Ophthalmol 1988; 106:725-6) the presence of unique calcific lesions in the eyelids of a young woman with a history of hyperphosphatemic tumoral calcinosis. Here we document that no immediate family members showed similar lesions and that none was hyperphosphatemic. Dental roentgenography revealed characteristic abnormalities in the patient that confirmed the clinical diagnosis of tumoral calcinosis. Seasonal biochemical studies demonstrated persistently increased concentrations of phosphorus and 1,25-dihydroxyvitamin D in her serum. A calcific eyelid excrescence removed from the patient, studied by x-ray diffraction, was found to consist of crystals of hydroxyapatite. Microprobe analysis indicated the major elements in the deposit to be Ca, P, S, and Cl, just as in the periarticular deposits found in tumoral calcinosis. The Ca concentration in the patient's tear fluid, measured by atomic absorption spectrometry, was within the range found in tears of healthy volunteers. Phosphorus was undetectable (less than 30 mumol/L) in tears of the patient and the volunteers. These findings suggest that the eyelid lesions represent a new manifestation of the pathological process that produces the characteristic periarticular calcific masses of tumoral calcinosis.

Aluminum and chronic renal failure: sources, absorption, transport, and toxicity

In normal subjects the gastrointestinal tract is a relatively impermeable barrier to aluminum with a low fractional absorption rate for this metal ion. Aluminum absorbed from the gastrointestinal tract is normally excreted by the kidneys; in the presence of impaired renal function aluminum is retained and accumulates in body tissues. Aluminum-containing medications are given, by mouth, to patients with chronic renal failure as phosphate-binding agents for the therapeutic control of hyperphosphatemia. Patients with chronic renal failure are also exposed to aluminum in domestic tap-water supplies used either for drinking or, in those on dialysis treatment, in the preparation of their dialysate. In patients with end-stage chronic renal failure, particularly in those on treatment by hemodialysis, the accumulation of aluminum in bone, brain, and other tissues is associated with toxic sequelae. An increased brain content of aluminum appears to be the major etiological factor in the development of a neurological syndrome called either "dialysis encephalopathy" or "dialysis dementia"; an increased bone content causes a specific form of osteomalacia. An excess of aluminum also appears to be an etiological factor in a microcytic, hypochromic anemia that occurs in some patients with chronic renal failure on long-term treatment with hemodialysis. The various mechanisms involved in the toxic phenomena associated with the accumulation of aluminum in body tissues have not been clearly defined but are the subject of extensive investigations.

Tumoral calcinosis: seasonal biochemical studies and chemical studies of eyelid lesion

We recently described (Arch Ophthalmol 1988; 106:725-6) the presence of unique calcific lesions in the eyelids of a young woman with a history of hyperphosphatemic tumoral calcinosis. Here we document that no immediate family members showed similar lesions and that none was hyperphosphatemic. Dental roentgenography revealed characteristic abnormalities in the patient that confirmed the clinical diagnosis of tumoral calcinosis. Seasonal biochemical studies demonstrated persistently increased concentrations of phosphorus and 1,25-dihydroxyvitamin D in her serum. A calcific eyelid excrescence removed from the patient, studied by x-ray diffraction, was found to consist of crystals of hydroxyapatite. Microprobe analysis indicated the major elements in the deposit to be Ca, P, S, and Cl, just as in the periarticular deposits found in tumoral calcinosis. The Ca concentration in the patient's tear fluid, measured by atomic absorption spectrometry, was within the range found in tears of healthy volunteers. Phosphorus was undetectable (less than 30 mumol/L) in tears of the patient and the volunteers. These findings suggest that the eyelid lesions represent a new manifestation of the pathological process that produces the characteristic periarticular calcific masses of tumoral calcinosis.

Measurement of cholesterol in serum by gas chromatography/mass spectrometry at moderate mass resolution, with a nonendogenous cholesterol isomer as internal standard

We describe a gas chromatography/mass spectrometry method for the quantitative analysis of cholesterol in serum. A structural isomer of cholesterol, 7,(5 alpha)-cholesten-3 beta-ol, is used as an internal standard, its primary advantage being its lesser cost relative to that of a stable-isotope-labeled analog. Analysis of the National Bureau of Standards Certified Reference Serum (SRM 909) was used to validate the method. The results show this method to be highly accurate (bias = -0.6%) and precise (CV = 1.6% between-run, 1.2% within-run). The performance of this method is, therefore, sufficiently good to allow its use as a reference method for determinations of cholesterol in serum.

Measurement of cholesterol in serum by gas chromatography/mass spectrometry at moderate mass resolution, with a nonendogenous cholesterol isomer as internal standard

We describe a gas chromatography/mass spectrometry method for the quantitative analysis of cholesterol in serum. A structural isomer of cholesterol, 7,(5 alpha)-cholesten-3 beta-ol, is used as an internal standard, its primary advantage being its lesser cost relative to that of a stable-isotope-labeled analog. Analysis of the National Bureau of Standards Certified Reference Serum (SRM 909) was used to validate the method. The results show this method to be highly accurate (bias = -0.6%) and precise (CV = 1.6% between-run, 1.2% within-run). The performance of this method is, therefore, sufficiently good to allow its use as a reference method for determinations of cholesterol in serum.

Aluminum metabolism in rats: effects of vitamin D, dihydrotachysterol, 1,25-dihydroxyvitamin D and phosphate binders

In order to study the effects of vitamin D on aluminium balance when different forms of vitamin D and phosphate binders are used simultaneously for therapeutic purposes, 30 Sprague-Dawley weanling rats, weighing 44-66 g, were randomly assigned to 5 groups: (A) control, (B) aluminum hydroxide, (C) dihydrotachysterol at 16 micrograms/kg/day, (D) 1,25-dihydroxyvitamin D at 16 ng/kg/day and (E) vitamin D at 2,000 IU/kg/day. Aluminum hydroxide (60 mg/kg/day) in the feed was provided to all except the control group. The vitamin D or metabolites were fed by stomach tube daily for a period of 10 days. At the end of the study, the mean (+/- SEM) serum aluminum concentration, as determined by flameless atomic absorption spectrophotometry, was 5.0 +/- 2.4 micrograms/l; there were no significant differences in these results between groups. During the last three days of the study, 24-hour urine and stool collections were made with the usual precautions against trace mineral contamination. The means (+/- SEM) of aluminum balances for groups A, B, C, D and E were -388 +/- 261, 1,121 +/- 331; 2,316 +/- 304; 2,387 +/- 245, and 1,968 +/- 337 micrograms/day, respectively. We conclude that at therapeutic doses of aluminum hydroxide and vitamin D or its metabolites, hyperaluminemia was not observed. However, the positive aluminum balances imply retention, and the use of vitamin D, especially its potent metabolites dihydrotachysterol and 1,25-dihydroxyvitamin D, intensified this risk.

Measurement of lipid peroxidation products in rabbit brain and organs (response to aluminum exposure)

A method was developed for measuring the concentration of lipid peroxidation products in rabbit brain, heart, lung, liver, and kidney tissue. Specimens were homogenized in cold buffer, acidified, and heated to near boiling in the presence of thiobarbituric acid in order to form the malondialdehyde-thiobarbiturate adduct. After centrifugation, the supernatant was injected onto a reversed-phase high pressure liquid chromatography (HPLC) column, and the effluent was monitored for absorbance at 532 nm. Absorbances were compared to a standard curve constructed from absorbance data for tetraethoxypropane standards, which yield stoichiometric amounts of the malondialdehyde-thiobarbiturate adduct. Results were expressed as nmol of adduct per gram (dry weight) of tissue. Hippocampus had significantly greater concentrations of lipid peroxidation products (79.0 +/- 15.7 nmol per g) than did brainstem (52.1 +/- 13.8 nmol per g), but there was no significant increase in lipid peroxidation in aluminum treated rabbit brains when compared with controls. Aluminum intoxication appeared, however, to stimulate lipid peroxidation in heart, lung, liver, and kidney. Aluminum accumulation in brain and organ tissue of treated rabbits was confirmed by atomic absorption spectrophotometry of an acid digest of the homogenate. These results are in contrast to previous studies which demonstrated an increase in lipid peroxidation products in rat brains following oral administration of aluminum hydroxide.

Measurement of plasma prostaglandin F2 alpha using capillary gas chromatography negative ion chemical ionization mass spectrometry

A stable isotope dilution gas chromatography/mass spectrometry method for the measurement of prostaglandin F2 alpha (PGF2 alpha) in plasma has been developed. The linearity of the method was 0 to 250 pg per ml, day-to-day precision of five percent at a level of 80 pg per ml, and a limit of detection of one pg per ml. Evaluation of the absolute recovery of PGF2 alpha through the sample clean-up steps using tritium labelled PGF2 alpha gave recoveries of 68 +/- 5 percent. A preliminary reference range estimated a mean plasma PGF2 alpha level of 83 +/- 13 pg per ml (n = 7) with a range of 62 to 103 pg per ml in healthy adults. The major application of this method will be in research protocols studying changes of PGF2 alpha in toxemia of pregnancy.

Limitation of deuterium labelled methoximes as internal standards in the mass spectral analysis of prostaglandins

A reported method for the preparation of d3-methoxime derivatives as internal standards for prostaglandin assays by gas chromatography-mass spectrometry was evaluated. Sample derivatization resulted in 1.5-86% exchange of the d3-methoxime in a series of prostaglandins. Exchange was minimal when the methoxime was on the 5-membered ring; whereas, acyclic methoximes exhibited extensive exchange. Induced strain energy due to the steric interaction of the hydroxyl group and the C13-C20 alkyl side chain with the gem-dimethoxylamine transition state is offered as an explanation for the unusual stability of PGE2. The use of 18O exchange of the carboxylic acid function is presented as an alternative for the preparation of unavailable labelled eicosanoids.

Transferrin binding of Al3+ and Fe3+

An understanding of Al3+-induced diseases requires identification of the blood carrier of Al3+ to the tissues where Al3+ exerts a toxic action. Quantitative studies demonstrate that the protein transferrin (iron-free) is the strongest Al3+ binder in blood plasma. Under plasma conditions of pH 7.4 and [HCO3-]27 mmol/L, the successive stability constant values for Al3+ binding to transferrin are log K1 = 12.9 and log K2 = 12.3. When the concentration of total Al3+ in plasma is 1 mumol/L, the free Al3+ concentration permitted by transferrin is 10(-14.6) mol/L, less than that allowed by insoluble Al(OH)3, by Al(OH)2H2PO4, or by complexing with citrate. Thus transferrin is the ultimate carrier of Al3+ in the blood. We also used intensity changes produced by metal ion binding to determine the stability constants for Fe3+ binding to transferrin: log K1 = 22.7 and log K2 = 22.1. These constants agree closely with a revision of the reported values obtained by equilibrium dialysis. By comparison with Fe3+ binding, the Al3+ stability constants are weaker than expected; this suggests that the significantly smaller Al3+ ions cannot coordinate to all the transferrin donor atoms available to Fe3+.

Transferrin binding of Al3+ and Fe3+

An understanding of Al3+-induced diseases requires identification of the blood carrier of Al3+ to the tissues where Al3+ exerts a toxic action. Quantitative studies demonstrate that the protein transferrin (iron-free) is the strongest Al3+ binder in blood plasma. Under plasma conditions of pH 7.4 and [HCO3-]27 mmol/L, the successive stability constant values for Al3+ binding to transferrin are log K1 = 12.9 and log K2 = 12.3. When the concentration of total Al3+ in plasma is 1 mumol/L, the free Al3+ concentration permitted by transferrin is 10(-14.6) mol/L, less than that allowed by insoluble Al(OH)3, by Al(OH)2H2PO4, or by complexing with citrate. Thus transferrin is the ultimate carrier of Al3+ in the blood. We also used intensity changes produced by metal ion binding to determine the stability constants for Fe3+ binding to transferrin: log K1 = 22.7 and log K2 = 22.1. These constants agree closely with a revision of the reported values obtained by equilibrium dialysis. By comparison with Fe3+ binding, the Al3+ stability constants are weaker than expected; this suggests that the significantly smaller Al3+ ions cannot coordinate to all the transferrin donor atoms available to Fe3+.

Absorption of aluminum from aceglutamide aluminum in healthy adult males

The absorption of aluminum was studied in twelve healthy male volunteers over a period of fourteen days in a placebo-controlled, double blind study. All subjects were institutionalized during the study. Eight subjects (treated group) received ascending doses of aceglutamide aluminum (N-acetyl-L-glutamine aluminum complex) administered in multiple daily doses. The remaining four subjects (untreated group) received placebo. Systemic absorption and excretion of aluminum were evaluated by measuring aluminum concentrations in serum, urine and fecal samples. Aluminum concentrations were determined by electrothermal atomic absorption spectrometry. All serum aluminum concentrations were less than 16 micrograms/L for both groups. The mean urinary and fecal aluminum concentrations in the aluminum-treated group were significantly higher than in the untreated group during the study days the drug was administered. The total amount of aluminum (as aceglutamide aluminum) given to each treated subject during the 14 day study period as 3290 mg. The mean total fecal aluminum concentration was 3318 mg for the treated group and 269 mg for the untreated group during the study period. These findings are consistent with the view that some aluminum absorption from the gastrointestinal tract occurred following the administration of the drug. The absorbed aluminum appears to have been rapidly excreted in the urine and the feces.

Physiological properties of the luteinizing hormone pulse signal: impact of intensive and extended venous sampling paradigms on its characterization in healthy men and women

The pulsatile nature of the gonadotropin signal is a critical determinant of physiological activation of the gonadal axis. Nonetheless, major uncertainties exist regarding the exact patterns of LH secretion that constitute normal physiological profiles in man. To assess possible bases for the discrepancies in the literature, we sampled blood at 5-min intervals for 24 h in eight normal men and eight normal women in the early follicular phase of the menstrual cycle. The constituent 5-, 10-, 15-, and 20-min immunoactive LH series and the consituent 6-, 12-, or 24-h sampling durations provided ranges of sampling intensities and durations for analysis of significant LH pulses. A technique for minimizing the influence of false positive immunoassay errors on peak detection was used to aid in estimating apparent true positive LH pulse frequency. Nonlinear curve fitting of the relationship between sampling intensity and apparent true positive LH pulse frequency revealed a stable pulse frequency estimate at intensive rates of venous sampling, with values of 19.5 +/- 1.9 (+/- SEM) pulses/24 h (periodicity, 73.8 +/- 6.5 min/pulse) in men and 20.6 +/- 3.6 pulses/24 h (periodicity, 70.0 +/- 10 min/pulse) in women. Further analyses indicated that sampling every 3.1 and 2.0 min for 24 h would be required to capture 90% of the LH pulses in men and women, respectively. Moreover, even with a 5-min sampling rate, the statistical counting errors of the LH pulse frequency estimates varied markedly with sampling duration; for example, in men sampled in 6-, 12-, and 24-hr sessions, the values were, respectively, 49%, 35%, and 24% of the observed pulse frequencies. Similar variations were found in women. Counting errors were 30-50% higher for conventional 20-min sampling rates than for 5-min sampling intervals. Measured interpulse intervals varied widely from 10-330 min (median, 60 min; n = 131 LH pulses) in men and from 10-340 min (median, 65 min; n = 125 LH pulses) in women. In addition, absolute LH pulse amplitudes varied from 1-28 mIU/ml (median, 4.1 mIU/ml) in men and from 1-24 mIU/ml (median, 3.6 mIU/ml) in women. These estimates were associated with a median number of points identified within each pulse of 6.0 in men and 4.0 in women. In summary, the present exhaustive sampling studies demonstrate for the first time stable estimates of physiological LH pulsations in normal men and women, and document broad ranges of normal LH pulse amplitudes and interpulse intervals.(ABSTRACT TRUNCATED AT 400 WORDS)

Magnesium and potassium. Inter-relationships in cardiac disorders

Magnesium and potassium are the 2 major intracellular cations. The intracellular concentrations of these 2 ions appear to be closely correlated, but the existence of a relationship between the plasma concentrations of these ions has been controversial. A major function of potassium is to maintain the excitability of nerve and muscle tissue. Alterations in either the intracellular or extracellular potassium concentration affect membrane excitability by alterations in the resting membrane potential. The critical factor is not the actual potassium concentration in either compartment but rather the ratio of the intracellular to the extracellular concentration. The intracellular concentration of potassium is maintained against an electrochemical gradient by active transport involving an ionic pump mechanism. In this metabolically active ion-pump mechanism the inward transport of potassium is balanced by the outward transport of sodium; this active transport mechanism involves magnesium. The plasma concentration of potassium has been reported to be an important factor in the genesis of cardiac arrhythmias. The arrhythmogenic mechanisms of hypokalaemia, particularly in mild degrees, have not been clearly defined. However, evidence has begun to accumulate that magnesium deficiency may be a critical factor in the cardiac arrhythmias associated with hypokalaemia. Diuretic drugs are recognised as primary agents in the treatment of essential hypertension. In patients on antihypertensive treatment evidence has recently been reported that there is a link between the administration of diuretics and sudden death. In addition to their action on the renal tubular handling of sodium and water, diuretic drugs affect the renal tubular handling of other ions. A well-established complication of therapy with diuretic drugs is an increased urinary excretion of potassium resulting in hypokalaemia. Hypokalaemia and hypomagnesaemia can be induced by the same mechanisms and are often clinically correlated with one another. The reported incidence of hypomagnesaemia is greater than that of hypokalaemia; a significant correlation also appears to exist between the plasma concentrations of magnesium and potassium. A significant inter-relationship between the plasma concentrations of magnesium and potassium and the evidence for a critical role of magnesium in the genesis of cardiac arrhythmias would support the proposal that magnesium should be routinely measured in situations, such as diuretic therapy, that are potentially associated with hypokalaemia.(ABSTRACT TRUNCATED AT 400 WORDS)

Water content of aluminum, dialysis dementia, and osteomalacia

In the presence of normal renal function, a high concentration of aluminum in drinking water has been implicated as a factor in the etiology of a neurological syndrome in one specific geographical area. The role of aluminum as a toxic agent in other neurological disorders, where renal function is normal, is controversial. Aluminum is absorbed from the gastrointestinal tract and is normally excreted by the kidneys in the urine. In patients with chronic renal failure, aluminum appears to be of proven toxicological importance. In these patients the accumulation of aluminum in tissues causes an encephalopathy (dialysis encephalopathy or dialysis dementia), a specific form of metabolic bone disease (osteomalacic dialysis osteodystrophy), and an anemia and also plays an etiological role in some of the other complications associated with end-stage chronic renal disease. A failure in the normal renal excretory mechanism accounts for the tissue accumulation in chronic renal failure. The majority of chronic renal failure patients who develop aluminum toxicity are on long-term treatment with either hemo- or peritoneal dialysis; some patients develop toxicity who are only on treatment with aluminum-containing phosphate-binding agents. Aluminum in the dialysate appears to be the major source of the metal in chronic renal failure patients who develop aluminum toxicity. The aluminum content of the dialysate depends primarily on the content of the water with which it is prepared; there may be some contribution from the chemicals used in the concentrate which is added to the water. Some domestic tap-water supplies contain aluminum in high concentration, either naturally or because aluminum has been added as a flocculant in the purification process.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminium toxicity in chronic renal insufficiency

Aluminium is a ubiquitous element in the environment and has been demonstrated to be toxic, especially in individuals with impaired renal function. Not much is known about the biochemistry of aluminium and the mechanisms of its toxic effects. Most of the interest in aluminium has been in the clinical setting of the haemodialysis unit. Here aluminium toxicity occurs due to contamination of dialysis solutions, and treatment of the patients with aluminium-containing phosphate binding gels. Aluminium has been shown to be the major contributor to the dialysis encephalopathy syndrome and an osteomalacic component of dialysis osteodystrophy. Other clinical disturbances associated with aluminium toxicity are a microcytic anaemia and metastatic extraskeletal calcification. Aluminium overload can be treated effectively by chelation therapy with desferrioxamine and haemodialysis. Aluminium is readily transferred from the dialysate to the patient's bloodstream during haemodialysis. Once transferred, the aluminium is tightly bound to non-dialysable plasma constituents. Very low concentrations of dialysate aluminium in the range of 10-15 micrograms/l are recommended to guard against toxic effects. Very few studies have been directed towards the separation of the various plasma species which bind aluminium. Gel filtration chromatography has been used to identify five major fractions, one of which is of low molecular weight and the others appear to be protein-aluminium complexes. Recommendations on aluminium monitoring have been published and provide 'safe' and toxic concentrations. Also, the frequency of monitoring has been addressed. Major problems exist with the analytical methods for measuring aluminium which result from inaccurate techniques and contamination difficulties. The most widely used analytical technique is electrothermal atomic absorption spectrometry which can provide reliable measurements in the hands of a careful analyst.

Serum and lymphocyte, aluminum and nickel in chronic renal failure

In the past decade, aluminum has been recognized as a toxic metal in patients with chronic renal failure. It is, however, possible that other trace metals, such as nickel, may also have toxic actions in these patients. The plasma concentration of a metal, such as aluminum or nickel, may not provide a valid index of either tissue content or total body burden. In the study reported here, the aluminum and nickel content of lymphocytes was measured and compared with plasma concentrations in normal controls and patients with chronic renal failure. The findings suggest that lymphocytes may be of value as a nucleated 'tissue' for the assessment of trace metal status.

Uremic toxins, and their effect on intermediary metabolism

In the late stages of chronic renal damage the functional mass of the kidney is reduced and there is progression to renal insufficiency, usually called uremia, in which all aspects of renal function are affected. The complexity of the biochemical aspects of the syndrome of uremia is a manifestation of the wide variety and nature of the individual disorders that contribute to the pathogenesis of the final clinical syndrome. One major feature is the retention of metabolic end products and their effects, as toxins, on intermediary metabolism. The retained end products, working singly or in combination, probably affect metabolic pathways by some modification of enzymic reactions. They act at the cell membrane level. Although "middle molecules" have been incriminated as uremic toxins, recent attention has also focused on trace elements--especially aluminum, which has been implicated in the pathogenesis of two major disorders, osteomalacic dialysis osteodystrophy and dialysis encephalopathy.

Uremic toxins, and their effect on intermediary metabolism

In the late stages of chronic renal damage the functional mass of the kidney is reduced and there is progression to renal insufficiency, usually called uremia, in which all aspects of renal function are affected. The complexity of the biochemical aspects of the syndrome of uremia is a manifestation of the wide variety and nature of the individual disorders that contribute to the pathogenesis of the final clinical syndrome. One major feature is the retention of metabolic end products and their effects, as toxins, on intermediary metabolism. The retained end products, working singly or in combination, probably affect metabolic pathways by some modification of enzymic reactions. They act at the cell membrane level. Although "middle molecules" have been incriminated as uremic toxins, recent attention has also focused on trace elements--especially aluminum, which has been implicated in the pathogenesis of two major disorders, osteomalacic dialysis osteodystrophy and dialysis encephalopathy.

Quantitative study of aluminum binding to human serum albumin and transferrin by a chelex competitive binding assay

Binding of aluminum to human serum albumin and transferrin was investigated using a competitive binding assay incorporating a cation exchange resin, chelex. Both albumin and transferrin were found to produce linear Scatchard plots of aluminum binding data over the aluminum and protein concentration ranges found in humans. Binding constants measured for albumin and transferrin were 1.96 and 0.515 microM, respectively.

Electrothermal atomic absorption spectrometric determination of aluminum in serum with a new technique for protein precipitation

We have studied the electrothermal atomic absorption measurement of aluminum in serum samples by direct analysis with standard additions and the use of a matrix modifier. We have also measured aluminum by analysis of the supernate after pretreatment of serum with concentrated nitric acid to precipitate proteins, and have compared the results obtained by these two techniques. Both appear to eliminate interferences arising from the serum matrix. We quantified the aluminum by utilizing a stabilized temperature (L'vov) platform. Within-run precision (CV) for the standard-additions method was 16.6% (means = 6.5 micrograms/L) and 6.0% (means = 86.8 micrograms/L) and for the protein precipitation method was 10.1% (means = 10.9 micrograms/L) and 4.2% (means = 88.5 micrograms/L). Linearity of the standard curve extended from 0 to 120 micrograms/L for the standard-additions method and from 0 to 100 micrograms/L for the protein precipitation method. Samples from 38 patients were analyzed by both techniques, and linear regression analysis yielded the equation y (protein precipitation) = 1.02 X (standard additions) + 2.04.

Electrothermal atomic absorption spectrometric determination of aluminum in serum with a new technique for protein precipitation

We have studied the electrothermal atomic absorption measurement of aluminum in serum samples by direct analysis with standard additions and the use of a matrix modifier. We have also measured aluminum by analysis of the supernate after pretreatment of serum with concentrated nitric acid to precipitate proteins, and have compared the results obtained by these two techniques. Both appear to eliminate interferences arising from the serum matrix. We quantified the aluminum by utilizing a stabilized temperature (L'vov) platform. Within-run precision (CV) for the standard-additions method was 16.6% (means = 6.5 micrograms/L) and 6.0% (means = 86.8 micrograms/L) and for the protein precipitation method was 10.1% (means = 10.9 micrograms/L) and 4.2% (means = 88.5 micrograms/L). Linearity of the standard curve extended from 0 to 120 micrograms/L for the standard-additions method and from 0 to 100 micrograms/L for the protein precipitation method. Samples from 38 patients were analyzed by both techniques, and linear regression analysis yielded the equation y (protein precipitation) = 1.02 X (standard additions) + 2.04.

Frequency of calcium binding by monoclonal immunoglobulins in multiple myeloma

Total and ionized calcium and other related parameters were measured in 34 patients with multiple myeloma. Hypercalcemia was not a major feature of the group of patients studied with only three patients exhibiting marked increases in total (Ca total) and ionized (Ca++) calcium concentrations. The Ca++/Ca total ratio was also maintained within relatively narrow limits. No major differences were found in the calcium fractions of patients with different types of multiple myeloma. Serum immunoreactive parathyroid hormone showed no consistent relationship with either the total or ionized calcium concentration. There were no correlations between increased total protein or reduced serum albumin concentrations and changes in total and ionized calcium fractions or Ca++/Ca total ratios. These results imply that in this group of myeloma patients, there was no significant binding of calcium by the monoclonal immunoglobulins.

Relationship of potassium and magnesium concentrations in serum to cardiac arrhythmias

Low concentrations of potassium and magnesium in serum have been implicated in cardiac arrhythmias; the importance of mild hypokalemia or hypomagnesemia is uncertain. To investigate possible associations among use of diuretics, the concentration of these ions in serum, and the onset of clinically important arrhythmias, we reviewed records of 103 patients admitted to our Coronary Care Unit during three months and found mild to moderate hypokalemia and hypo- magnesemia in 18 and 24%, respectively. The significant correlation between the concentrations of magnesium and potassium in serum at admission (r = 0.27, p less than 0.007) remained constant in patients, whether they were receiving diuretics or not. Potassium concentrations were significantly lower (p less than 0.05) in patients receiving diuretics (3.93 mmol/L) than in those who were not (4.21 mmol/L), but the mean concentrations of magnesium did not differ significantly. Except for myocardial infarction, no single variable or combination of variables was highly predictive of cardiac arrhythmias in these patients. We conclude that there is no strong predictive relationship between mildly decreased concentrations of magnesium or potassium in serum and onset of cardiac arrhythmias.

Vitamin D metabolism and chronic liver disease

In recent years, considerable developments have taken place in the understanding of the vitamin D compounds which allows them, or at least their metabolites, to be classified as hormones. The liver has, for many years, entered into any consideration of the normal control of vitamin D status and metabolism in a number of roles. The main importance of the liver in vitamin D metabolism is now recognized to be the critical role it plays in the hydroxylation pathway and consequent formation of biologically active metabolites. Because the liver plays a critical central role in vitamin D metabolism, and possibly determines the overall efficiency of utilization, it may be expected that disorders of vitamin D metabolism, with associated clinical sequelae in the form of metabolic bone disease and hypocalcemia, and clinical features of patients with chronic disorders of liver function. The serum concentration 25-hydroxyvitamin D (25-OHD) is generally accepted as reflecting total body vitamin D status in patients with normal renal function. Low serum 25-OHD concentrations have been reported in patients with a variety of hepatic disorders including: symptomatic primary biliary cirrhosis, alcoholic liver disease, chronic active liver disease, and large bile-duct obstruction owing to carcinoma or stones. The mechanisms for the low circulating serum 25-OHD concentrations in patients with chronic liver disease are complex and multifactorial. The disturbances in vitamin D metabolism in patients with chronic liver disease and biliary disease are associated with disturbances in calcium homeostasis and together they present clinically as hepatic osteodystrophy. The latter consists of osteomalacia, possibly sometimes complicated by secondary hyperparathyroidism, osteoporosis, and periosteal new bone formation.

Relationship of potassium and magnesium concentrations in serum to cardiac arrhythmias

Low concentrations of potassium and magnesium in serum have been implicated in cardiac arrhythmias; the importance of mild hypokalemia or hypomagnesemia is uncertain. To investigate possible associations among use of diuretics, the concentration of these ions in serum, and the onset of clinically important arrhythmias, we reviewed records of 103 patients admitted to our Coronary Care Unit during three months and found mild to moderate hypokalemia and hypo- magnesemia in 18 and 24%, respectively. The significant correlation between the concentrations of magnesium and potassium in serum at admission (r = 0.27, p less than 0.007) remained constant in patients, whether they were receiving diuretics or not. Potassium concentrations were significantly lower (p less than 0.05) in patients receiving diuretics (3.93 mmol/L) than in those who were not (4.21 mmol/L), but the mean concentrations of magnesium did not differ significantly. Except for myocardial infarction, no single variable or combination of variables was highly predictive of cardiac arrhythmias in these patients. We conclude that there is no strong predictive relationship between mildly decreased concentrations of magnesium or potassium in serum and onset of cardiac arrhythmias.

Cerebrospinal fluid polyamines in childhood leukemia

Cerebrospinal fluid (CSF) polyamines were measured in children with acute lymphocytic leukemia or non-Hodgkin's lymphoma in various stages of the disease ranging from complete remission to active central nervous system (CNS) involvement. Polyamines were analyzed by ion exchange chromatography with o- pthalaldehyde fluorimetric detection. Putrescine concentrations in random CSF samples obtained from leukemic patients with and without CNS involvement were not significantly different. Spermidine levels were generally higher in patients without CNS leukemia than in patients with the disease. In serial CSF specimens from an individual patient, spermidine levels correlated well with clinical status, being high in the active stages of the disease and low in remission. Thus, CSF polyamines appear to be of limited value as a screening test for early detection of CNS leukemia; however, they may offer an additional means of evaluating CNS leukemia and its response to therapy.