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Biomedical subjects

M Lever

Publications and source records attributed to M Lever.

At least 37 records · Page 2Linked to original sources
PubMed1994

Glycine betaine and proline betaine in human blood and urine.

In healthy human subjects, glycine betaine concentrations in the blood plasma are normally between 20 and 60 mumol/l, adult males tending to have higher concentrations than females. Proline betaine concentrations are more variable, ranging from undetectable to about 50 mumol/l. Both betaines are present in urine. Whereas the urinary excretion of proline betaine reflects plasma concentrations, with high clearance rates, there is no correlation between plasma and urine glycine betaine concentrations. The apparent clearance rates are low (usually less than 5%). The proline betaine content of human kidney tissue is less than 0.1% of the glycine betaine content, and this is true also of rabbit tissue despite high concentrations of both betaines in rabbit circulation and urine. These data suggest that glycine betaine, but not proline betaine, is important in human and other mammalian biochemistry.

Adolescent↗
PubMed1994

Relationship between osmoprotection and the structure and intracellular accumulation of betaines by Escherichia coli.

Naturally occurring betaines, especially glycine betaine and proline betaine, were accumulated by Escherichia coli from urine. In synthetic hyperosmotic medium, with an homologous series of added betaines, (CH3)3N(+)-(CH2)n-COO-, osmoprotective activity and intracellular accumulation decreased monotonically as n increased from 1 to 5. In contrast, alpha-substituted glycine betaines were accumulated in a similar manner to glycine betaine, but with different osmoprotective activities. Arsenobetaine, with a quaternary arsonium group, was also accumulated but amino acids which can become negatively charged in a chemically basic environment were not.

Betaine↗
PubMed1993

Organic osmolytes in human and other mammalian kidneys.

Osmotically-active organic solutes, or osmolytes, have been found in high concentration in the renal inner medulla of a wide variety of mammalian species, but their existence in human kidneys has not yet been shown. The aim of this study was to demonstrate the presence of osmolytes in the human kidney. Human tissues were obtained from kidneys removed surgically for diseases which involved only one pole of the kidney; in most cases this was a tumor. Animal kidneys analyzed were from dogs, pigs and rabbits. Inner medulla and cortex tissue samples were analyzed and found to contain the organic osmolytes glycine betaine, myo-inositol, sorbitol and glycerophosphorylcholine. The levels were much higher in the medulla than in the cortex. Further dissection of the human kidneys showed that sorbitol, glycerophosphorylcholine and glycine betaine were maximally concentrated at the papillary tip, while myo-inositol was found in highest concentration at the papillary base. Osmolytes were in low concentrations or undetectable in rabbit skeletal muscle, ureter and bladder. The organic osmolytes detected are likely to be physiologically important in humans. Studies in other mammals can be used as models for the investigation of the osmolyte system in human kidney function.

Animals↗
PubMed1992

Same-day batch measurement of glycine betaine, carnitine, and other betaines in biological material.

Glycine betaine, carnitine, carnitine esters, butyrobetaine, and proline betaine (stachydrine) concentrations in biological materials can be reliably measured in 100-microliters samples, with a detection limit below 1 mumol/liter. The procedure is suitable for batches of more than 30 specimens and it is possible to obtain a single result within 2 h. The betaines are extracted into an acetonitrile:methanol mixture, dried with anhydrous disodium hydrogen phosphate containing argentous oxide. The 4-bromophenacyl ester derivatives are formed using 4-bromophenacyl triflate as reagent, in the presence of solid magnesium oxide as base. The derivatives are separated by high-performance chromatography on a silica column, in a mixed partition and ion-exchange mode.

Animals↗
PubMed1988

The quality of performance of the fructosamine test.

The performance of fructosamine assays in 35 laboratories was assessed over a six month period in 1987. While agreement between laboratories was poor in the range expected in diabetic patients, most laboratories were internally consistent. The interlaboratory differences are largely attributed to the calibration methods used for this test. Fructosamine results from any one laboratory must not be interpreted by comparison with data from other laboratories or the literature. Other common biochemical tests were found to suffer from similar problems, but to a less serious extent.

Calibration↗
PubMed1986

Quality assessment of determinations of serum fructosamine in 33 clinical chemistry laboratories.

We investigated the analytical performance of fructosamine measurement in 33 routine clinical chemistry laboratories. We prepared 12 human control sera spanning a range of nondiabetic and diabetic fructosamine concentrations and assigned target values by using commercial reagents and a Cobas Bio centrifugal analyzer. Each control serum was analyzed by participating laboratories on two separate occasions. Averaged results were compared with target values, and systematic error was determined from slope and intercept regression coefficients. Overall, we found no significant (p greater than 0.05) slope or intercept bias, although slight nonlinearity was found with bichromatic instruments. Random error was determined from the standard error of estimate and from duplicate measurements. We found a median interlaboratory CV of 5.36% and similar analytical performance with all automated instruments used. The median random error with manual techniques was 18.1%. We conclude that fructosamine measurement as currently performed in routine laboratories is sufficiently accurate and reliable to function as an index of blood glucose control in diabetic patients.

Blood Glucose↗
PubMed1985

Automated fluorimetric determination of furfurals.

Hydroxymethylfurfural and furfural can be estimated automatically at 60 samples/h in a continuous-flow system. The hydrazone of the furfural with 5-hydroxybenzoylhydrazine is formed in aqueous solution and dialyzed into methanol or other lower alcohols on the recipient side of the dialyzer. The fluorescence of the zinc chelate of the hydrazone is measured. The procedure has applications for estimating the extent of hemoglobin glycosylation and for measuring the levels of hydroxymethylfurfural in some beverages. For more exacting work it can be used in conjunction with corrections from a blank channel or after preliminary specimen purification. Its specificity, though limited, compares favorably with other methods, while having advantages in sensitivity and capacity for high-throughput batch processing.

Acids↗
PubMed1984

Optimal conditions for 4-hydroxybenzoyl- and 2-furoylhydrazine as reagents for the determination of carbohydrates, including ketosamines.

4- Hydroxybenzoylhydrazine ( PAHBAH ) reacts with glucose in hot aqueous solution when alkali exceeds aroylhydrazine concentration. The related 2- furoylhydrazine ( FAH ) reacts at lower alkali concentrations, making this an attractive alternative carbohydrate reagent since it is (unlike PAHBAH ) freely water soluble. FAH reacts with monosaccharides more slowly than does PAHBAH , giving about half the color. Its specificity and behavior with a bismuth catalyst parallel those of PAHBAH . Solutions which contain 0.05 mol/liter PAHBAH with 1.5 mmol/liter bismuth III (as tartrate complex) and 0.5 mol/liter sodium hydroxide, or 0.01 mol/liter FAH with 1.5 mmol/liter bismuth III and 0.1 mol/liter sodium hydroxide are sensitive reagents for quantitative analysis, giving stable colors with many carbohydrates within 10 min at 75 degrees C. Ketosamines react more rapidly than glucose at lower temperatures and undergo similar reactions in less alkaline solutions. At pH less than 8, the reaction is specific for these 1- aminohexoses , and FAH can be used as a reagent for their assay.

Autoanalysis↗
PubMed1984

[Not Available].

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Forensic Medicine↗
PubMed1981

Analytical errors in clinical laboratories as assessed by an interlaboratory survey.

Combined errors ar the commonest systematic errors in laboratory results and occur with most tests studied. In these errors, results are reduced (or, less commonly, increased) by a factor, and this effect is compensated by the addition (or subtraction) of a constant amount. The effect is that results are in error in opposite direction at high and low levels. Inconsistency is predominant and is due mainly to imprecision, although for some tests (iron, cholesterol, calcium, and triglycerides among those studied) other factors such as non-specificity are significant. An interlaboratory survey based upon external method assessment using linear regression analysis provided objective information about analytical error in laboratories which is not usually obtained, while at the same time meeting the usual functions of surveys in the quality audit of performance.

Data Collection↗
PubMed1980

Kober reaction kinetics and their influence on the design of assays for oestrogens in urine during pregnancy.

Rates of reaction of different oestrogens in Kober reagent vary greatly. Rate constants were measured between 100 degrees C and 150 degrees C. Oestradiol, oestrone, 16-oxo-oestradiol, 16 alpha hydroxyoestrone, 16-epioestriol and urine pool show two sequential first order reactions at 100 degrees C; oestriol and its conjugates give a single reaction (slower than the other oestrogens except for the very slow oestretrol). Above 120 degrees C differences decrease, all oestrogens having one rate for Kober product formation: the decay reaction, which is also first order, becomes significant. Oestriol and its conjugates have relatively high apparent activation energies in the Kober reaction (120-138 kJmol-1) compared to other oestrogens studied (105-124 kJmol-1). The apparent activation energy for the decay reaction is the same within experimental error (115 +/- 3 kJmol-1). This is consistent with a common product formed from oestrogen reacting with Kober reagent. Analytical methods must respond similarly to major urinary oestrogens. Appropriate conditions include 100 degrees C for at least 20 min or 135 degrees C for 3 to 4 minutes.

Autoanalysis↗
PubMed1979

Factors in the choice of detergent in automated oestriol estimation.

Detergent must be added to the strongly acidic Kober reagent to obtain reproducible and well separated peaks in continuous flow analytical methods for oestriol in pregnancy urine. Brij 35 and other polyether detergents are not satisfactory because they or their impurities interfere in the reaction causing high blank response in colorimetric reactions and diminished fluorescence responses. In a single phase fluorometric method these detergents also caused turbidity or phase separation in the solution which passed through the fluorometer. Some anionic sulphate and sulphonate detergents were also unsatisfactory being immiscible with Kober reagent. Selected cationic and betaine detergents are shown to be possible alternatives, although one which is satisfactory in the kober reagent may be unsuitable for a dilution reagent. The betaine Empigen BB was found to be suitable for inclusion in both of these reagents.

Autoanalysis↗
PubMed1978

Routine serum lipid analysis in New Zealand.

For two years pairs of serum specimens with a wide range of cholesterol and triglyceride concentrations were regularly dispatched each month to all New Zealand medical laboratories known to measure blood lipids. Four weeks after specimen dispatch each laboratory received a report which displayed all results along with the overall means, standard deviations, and results from "reference laboratories". Six-monthly summaries were prepared for each laboratory in which the previous 12 results were compared with the corresponding "target values" by regression analysis. This allowed classification of inaccuracy into one or more of three categories. Random error (imprecision) explained most of the discrepancies, but systematic errors also contributed strongly to the observed interlaboratory variation. No single class of laboratories performed significantly differently from any others. Approximately 60 percent of the 16000 cholesterol analyses done each month in New Zealand, and 40 percent of the 10000 triglyceride analyses, are performed with precision thought to be adequate for clinical usage.

Cholesterol↗
PubMed1978

Automated continuous flow determination of urine albumin by competition with dye-detergent binding.

A continuous flow automated method for urine albumin was developed based on the ability of albumin to displace bromophenol blue from a bromophenol blue detergent complex. The method is almost specific for albumin, giving a slight response with an alpha-globulin fraction from serum. Results agreed closely with rocket electrophoresis albumin estimates on urine samples, but significantly less closely with "total urine protein" estimates by an acid protein precipitation, followed by biuret colour reaction, procedure. This method is being used to replace the indefinite "total protein" test for most routine purposes.

Albuminuria↗
PubMed1978

Regression analysis in interlaboratory surveys: a case study with cholesterol and triglycerides.

1. A new interlaboratory survey design, that uses regression analysis to compare results from each laboratory with target values, was tested using cholesterol and triglyceride analyses. The fifty New Zealand laboratories involved showed considerable interlaboratory variation (CV = 8% to 27% for cholesterol, 13% to 113% for triglycerides), 30% and 40% of which was associated with systematic differences between laboratories. 2. End-of-period summaries using regression analysis confirmed the presence of systematic errors. These were either simple types caused apparently by incorrect standardisation (regression slope, B not equal to 1.0) or inappropriate blank correction (intercept, A not equal to zero) or complex types presumably due to nonlinearity or nonspecificity. Graphical display of results from each laboratory aided fault diagnosis and allowed the detection of between-run standardisation differences. 3. Method comparison studies were made: the only highly significant result being lower precision achieved by enzymatic cholesterol methods compared with other colorimetric methods.

Blood Chemical Analysis↗