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M H Abernethy

Publications and source records attributed to M H Abernethy.

At least 19 recordsLinked to original sources
PubMed1988

Screening for plasma cholinesterase deficiency: an automated succinylcholine based assay.

We describe an automated kinetic method that uses a single aqueous reagent to measure the in vitro hydrolysis of the muscle relaxant succinylcholine. The substrate succinylcholine is hydrolyzed by plasma cholinesterase (EC 3.1.1.8), and the choline produced is oxidized by choline oxidase (EC 11.3.17) in the presence of peroxidase, 4-aminophenazone and phenol, to yield a chromagen with maximum absorbance at 500 nm. The method is reproducible (CV 1.3%), correlates well with a manual procedure using the same substrate (r = 0.994, y = 0.99x - 0.25), and is linear to 150 U/L. The method is well suited to pre-operative screening and detection of "at-risk" individuals, as illustrated by the family of one patient who had a prolonged succinylcholine apnea.

Autoanalysis↗
PubMed1988

An enzymatic method for erythrocyte acetylcholinesterase.

The acetylcholinesterase (EC 3.1.1.7) in 50 microL of a 61-fold dilution of erythrocytes in water hydrolyzes acetylcholine during a timed 20-min reaction at 37 degrees C. The resulting choline is measured by use of choline oxidase coupled to peroxidase, with phenol and aminoantipyrene to give a pink product that absorbs maximally at 500 nm. For calibration, a choline iodide standard is included in each batch of up to 19 samples. Accuracy was assessed by using specific inhibitors and measuring choline in the presence of excess erythrocyte solution. The standard curve for the assay is linear to threefold the normal enzyme activity. Between-batch precision was 0.40 kU/L at a mean of 11.5 kU/L (CV 3.5%), and comparison with an acetylthiocholine procedure (x) gave a good correlation: y = 1.02x - 0.27 kU/L (r = 0.991). Long-term precision (10 months), assessed from three sets of assays of samples from 17 individuals, was 0.71 kU/L at a mean of 11.7 kU/L (CV 6.1%).

Acetylcholine↗
PubMed1987

Effect of daylight on the reaction of thiols with Ellman's reagent, 5,5'-dithiobis(2-nitrobenzoic acid).

The reaction of 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB, Ellman's reagent) with thiols is sensitive to daylight, in particular to ultraviolet radiation at wavelengths around 325 nm. Exposure to light at the absorbance maximum of the yellow product (the thionitrobenzoate ion) at 410 nm had no effect on the reaction. The light-sensitive species is apparently the DTNB, because a spectral-irradiation experiment showed that the wavelength of light that produced the maximum rate of absorbance change coincided with the peak absorbance of DTNB, and it was well separated from the thionitrobenzoate absorbance peak. Ascorbate is ineffective as a stabilizer and can produce an apparent increase in the rate of DTNB destruction. In a practical example we found the light interference to be severe when hydrolysis of propionylthiocholine by plasma cholinesterase (EC 3.1.1.8) was measured after a 20-min incubation. The apparent cholinesterase activity in clear glass or plastic tubes exposed to diffuse daylight could be decreased to 25% of the value obtained for samples in light-excluded tubes. We recommend the reaction be carried out in artificial room light, with total elimination of daylight, because window glass does not sufficiently attenuate 325-nm wavelength irradiation.

Cholinesterases↗
PubMed1986

Plasma cholinesterase phenotyping with use of visible-region spectrophotometry.

A method that overcomes the difficulties of the 240-nm benzoylcholine method for phenotyping plasma cholinesterases has been developed. After a timed reaction, under the same reaction conditions as in the classic procedure, choline is detected at 500 nm by use of choline oxidase coupled with the peroxidase/phenol/aminoantipyrine system. Cholinesterase activity measurements, calibrated by use of choline iodide as standard, are linearly related to results obtained with propionylthiocholine as substrate at 25 degrees C (y = 0.14x + 0.17, n = 30, r = 0.98). Results of differential inhibition with dibucaine and fluoride are virtually identical with those obtained by the ultraviolet method (y = 0.97x + 4.3, r = 0.995, and y = 0.93x - 0.5, r = 0.987, respectively) and give the same classification of homo- and heterozygotes for the usual, atypical, and fluoride-resistant variants. The new method has substantial advantages in that it eliminates the difficulties associated with measuring small changes in high absorbances at a suboptimal wavelength on a steep portion of the absorption curve.

Alcohol Oxidoreductases↗
PubMed1984

Circadian urinary excretory patterns in an Antarctic environment.

Thirteen 24 h urine collections were made by each of the four members of an expedition to Cape Hallett, northern Victoria Land, Antarctica, during five weeks of the 1982/3 summer. Each collection period was divided into the wake (0700 h-2200 h), and the sleep (2200 h-0700 h) times. Three control collections were made in Christchurch prior to the journey to Antarctica. The mean urine volume increased by 500 ml/24 h; the sodium excretion by 50 mmol/24 h. The 24 h potassium, urea, and creatinine excretions showed no significant changes. Daily excretion patterns of water, sodium, potassium, urea and creatinine were observed by comparing the 9 h overnight excretions with the 24 h excretions. Circadian excretion patterns of the pre-Antarctic control period were preserved over the five weeks of continuous daylight. By comparing the 9 h with the same day 24 h results, the ability to predict a 24 h value from the 9 h excretion was tested. Such predictions were shown to be unreliable. Predictions from 9 h sodium creatinine ratios, potassium creatinine ratios, and urea creatinine ratios were no better.

Arctic Regions↗
PubMed1984

A new succinylcholine-based assay of plasma cholinesterase.

We describe a new method for measuring the in vitro rate of hydrolysis of the muscle relaxant succinylcholine. This substrate is hydrolyzed by plasma cholinesterase (EC 3.1.1.8). The resulting choline is determined by measuring the hydrogen peroxide formed on its oxidation by choline oxidase (EC 1.1.3.17). This is done by use of phenol and aminoantipyrine coupled to peroxidase, and yields an intense chromophore, Amax 500 nm. The assay requires 0.1 mL of plasma, and is precise and specific. The CV was 2.7% within run, 7.3% between run. For the usual (U variant) enzyme the Km is 53 mumol/L. Enzyme activity is removed by anticholinesterase antiserum, and is inhibited by dibucaine with a Ki of 2 mumol/L. Ten samples can be assayed in duplicate in an hour. This method is suited to routine use in any laboratory that has a simple spectrophotometer. The mean activity in 11 individuals with the cholinesterase phenotype UU was 105 U/L, for seven UA heterozygotes 61 U/L, and for three AA homozygotes 4 U/L. To the extent allowed by extrapolation from in vitro to in vivo results, this method should increase diagnostic accuracy and may directly predict duration of succinylcholine-induced apnea.

Alcohol Oxidoreductases↗
PubMed1983

Improved Ellman procedure for erythrocyte cholinesterase.

The procedure of Dietz et al. (Clin. Chem. 19: 1309-1313, 1973) for plasma cholinesterase (EC 3.1.1.7) gives a background absorbance of 1.4 A when extended to erythrocyte cholinesterase (EC 3.1.1.8) measurement, because the peak absorbance of the reaction product, 5-thionitrobenzoate, coincides with the hemoglobin Soret band at 410 nm. Consequently, the precision of erythrocyte cholinesterase measurements is poor, and the test is restricted to laboratories with a spectrophotometer having a high signal-to-noise ratio. Use of the detergent benzethonium chloride (Hyamine 1622) instead of quinidine sulfate to stop enzyme action allows readings to be made at 440 nm because the hemoglobin band is shifted to 405 nm and its peak intensity is decreased. Moreover, detergent micelle interactions shift the peak absorbance of the 5-thionitrobenzoate from 410 to 435 nm. Overall, the blank absorbance is decreased to about 0.4 A. This results in an assay that is twice as precise as the previous version and is suited for use in a routine laboratory with a moderate-quality spectrophotometer. Thus erythrocyte cholinesterase measurements can readily be made, to complement plasma cholinesterase in the investigation of exposure to organophosphates.

Benzethonium↗
PubMed1983

Microsampling on the Technicon SMAC system.

The sample volume needed for a Technicon SMAC continuous-flow analyzer has been reduced for routine operation. Two options are available: 141 microL for a 17-test profile, or 224 microL, which allows the direct-sampling assays for creatinine and iron to be included. The sample decrease is achieved by the sequential dialysis of creatinine and iron, an increased sample dilution from sixfold to ninefold, the strict minimization of diluted sample stream wastage, and development of more sensitive methods for glucose and alkaline phosphatase to allow greater use of the diluted sample stream. A glycine-containing diluent increases the sensitivity of the iron method by 25% and prevents the protein precipitation that plagues the continuous-flow analysis for iron in plasma. No deterioration in performance of the analyzer has been detected during nine months of routine operation at the reduced sample size. Added advantages are the decreased consumption of calibration materials and an increased ability to do repeat tests.

Alkaline Phosphatase↗
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

Blood alcohol levels. How accurately can they be guessed?

Volunteers were asked to guess their blood alcohol level immediately before having their venous level measured by gas chromatography. Thirty-one percent were able to guess to within 20 mg per 100ml of the measured amount. There was a tendency for people to over-estimate if the level was low and to under-estimate the higher values. Blood alcohol concentrations ranged from nil to 295mg per 100ml with both high and low being recorded throughout the evening.

Adolescent↗
PubMed1977

A random blood sugar diabetes detection survey.

In a co-operative study undertaken between various groups in the community, 3212 persons were screened at the Agricultural and Pastoral Summer Show in Christchurch. The mean glucose value was 88.4 mg/dl (4.9mmol/l) which roughly equates to 91 mg/dl (5.1mmol/l) plasma value. There was a standard deviation of 19.5mg/dl (1.08mmol/l) the 22.5 percentile was 63mg (3.5mmol/l), the 97.5 percentile was 125 (6.5mmol/l). One hundred and twenty persons of the total of 3212 were advised to contact their family doctors as a result of higher than normal blood sugar levels on the day. Twenty-five probable diabetics were diagnosed.

Adult↗
PubMed1976

What the urine contains following athletic competition.

Forty-two of 369 athletes were found to have a positive Occultest on the first urine sample voided following athletic competition. This positive reaction could be due to the presence of either myoglobin or haemoglobin. The Occultest was most often positive in competitors in the longer duration events such as the marathon. Twenty-six of these 42 specimens with a positive Occultest contained over 10 red cells per mm3. The urine samples were also examined for white cells, casts, bacteriuria and the concentration of urea, creatinine, electrolytes and protein. Proteinuria was a frequent finding and increased with the severity of the exertion.

Bacteriuria↗
PubMed1976

Vitamin C concentration in plasma and leucocytes of men related to age and smoking habit.

Morning plasma and leucocyte vitamin C concentrations were measured in 178 healthy men aged 17-68 years. In the youngest age group (17-29 years), smokers had significantly lower plasma (P less than 0.01) and leucocyte (P less than 0.001) vitamin C levels than non-smokers. With advancing age plasma and leucocyte vitamin C levels of non-smokers appeared to decline. The lower levels in younger smokers did not significantly alter in the later decades. There was no significant difference between the plasma or leucocyte vitamin C levels of smokers and non-smokers in the decade 60-69 years.

Adolescent↗