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Biomedical subjects

L Mason

Publications and source records attributed to L Mason.

50 records · Page 3Linked to original sources
PubMed1984

Radioenzymatic assay of catecholamines: real and apparent losses of labelled product.

In the radioenzymatic assay of catecholamines, using catechol-O-methyltransferase, the yield of labelled product is frequently less than the expected value. This has been attributed by some workers to losses during the periodate oxidation of the O-methylated derivatives. Using spectrophotometric methods, we have demonstrated that there is no oxidative demethylation of the methoxycatecholamines during periodate oxidation. In a novel technique designed to determine the specific activity of small quantities of tritiated S-adenosylmethionine, high performance liquid chromatography with electrochemical detection was used to measure the amount of adrenaline formed from unlabelled noradrenaline, in the presence of phenylethanolamine-N-methyltransferase and tritiated S-adenosylmethionine. As well as the real losses occurring during solvent extraction and thin layer chromatography (demonstrated spectrophotometrically), apparent 'loss' of radiolabelled product may be due to the assumption that the value for the specific activity of the tritiated S-adenosylmethionine and the determination of the product's radioactivity are both absolutely accurate, with no allowance being made for the normal and expected experimental errors in such measurements.

Catechol O-Methyltransferase↗
PubMed1984

Kinetics of enzymatic O-methylation: its value in assays for catecholamines in plasma.

The kinetics of enzymatic O-methylation of catecholamines were studied under conditions like those used in the radioenzymatic assay of plasma catecholamines. Inappropriate Michaelis-Menten kinetics and linear approximations of exponential equations were not used. Mathematical analysis indicated the importance of the ratio of methyl donor (S-adenosylmethionine) to substrate (catecholamine) concentration. If the reaction is incomplete, only a large ratio will allow linear approximations between product formed and initial catecholamine concentration. The use of high-concentration internal standards to correct for plasma interference may give erroneous results by reducing this ratio. Accuracy will be improved by ensuring (a) that S-adenosylmethionine is always greatly in excess of catecholamine, (b) that concentrations of added standards are of the same order as for endogenous catecholamine, and (c) that a high activity of enzyme is used, to allow the reaction to reach completion even in the presence of some inhibition.

Catechol O-Methyltransferase↗
PubMed1983

Radioenzymatic assay of catecholamines: reversal of aluminium inhibition of enzymatic O-methylation by desferrioxamine.

Alumina is commonly used for the purification and concentration of catecholamines in biological specimens before analysis. Acid eluates of alumina, found to contain high concentrations of Al3+, interfered with O-methylation but not with N-methylation. The chemistry of the catecholamines, supported by kinetic studies, suggest that complex formation between aluminium and the substrate account for the observed inhibition of O-methylation. The addition of desferrioxamine, a metal-chelating agent, to the reaction mixture reversed this inhibition and, by allowing a preliminary alumina extraction, permits the measurement of low concentrations of catecholamines in biological samples.

Aluminum↗
PubMed1983

Chiari malformation presenting in adults: a surgical experience in 127 cases.

We reviewed 127 patients who were operated upon for adult presentation Chiari malformation and made six conclusions: (a) The clinical examination remains crucial in the diagnosis. (b) The surgical anatomy is highly varied. (c) Syrinxes can be missed on preoperative contrast studies. (d) By a conservative grading system, we determined that 46% of the patients improved during long term follow-up. One-quarter deteriorated over the long run in spite of any treatment. (e) The overall results did not differ whether the treatment was plugging of the central canal plus decompression or decompression alone. (f) In patients with progression, plugging of the central canal obtained superior results. A review of the literature shows that the natural history of this complex disease process has not been established. This history is needed to identify the course of what may be several important factors that lead to the pathological condition in this disease.

Adolescent↗
PubMed1982

Effects of caffeine-free diet on benign breast disease: a randomized trial.

There is considerable interest in the potential effect on benign disease of a diet free of methylxanthines (caffeine, theophylline, and theobromine) found in coffee, tea, colas, and chocolate. We randomly assigned 158 women who presented with a breast concern either to a group encouraged to abstain from methylxanthine-containing foods and beverages or to a group who received no dietary recommendations (controls). At the initial visit each patient's sociomedical history and data on methylxanthine consumption were obtained by interview, and clinically palpable breast findings were graded on a scale of 0 to 4 (no nodularity to confluent hard "dysplasia") for each quadrant of both breasts. On the follow-up visit approximately 4 months later similar information was obtained. Mammograms were taken at both visits for a subset of women in each group. We found a statistically significant reduction in clinically palpable breast findings in the abstaining group as compared with controls, but the absolute change was minor and may be of little clinical significance. Comparison of before-after mammograms offered little support for the methylxanthine hypothesis. There was no relation between clinically palpable breast finding scores at initial examination and caffeine consumption levels reported at that time.

Adult↗
PubMed1981

The marfan skull.

The classic clinical features of Marfan syndrome include ectopic lens, valvular heart disease and dissecting aneurysm, and long, narrow extremeties associated with tall stature. When the classic features are incomplete, diagnosis is uncertain. This study presents some radiographic measurements of the skull in patients with the Marfan syndrome, in an attempt to aid diagnosis by quantitating the features defining the syndrome. Compared with the normal skull, the Marfan skull was found to be longer, taller, thicker, and to have have increased frontal sinus area. The most consistent and therefore diagnostic abnormality ws increased height.

Adolescent↗
PubMed1976

Characteristics of streptolysin S hemolysis.

The characteristics of hemolysis produced by streptolysin S (SLS) were investigated in rabbit erythrocytes. Treatment of erythrocytes with SLS at various temperatures prior to incubation at 37 C revealed an initial temperature-dependent interaction between toxin and the cells. No subsequent hemolysis occurred when erythrocytes were exposed to SLS at 0 to 10 C; exposure to toxin at temperatures above 10 C gradually increased the amount of hemolysis that occurred at 37 C. Very little binding of toxin to erythrocytes or their ghosts, as detected by a decrease of hemolytic activity from toxin preparations, could be demonstrated at any temperature. The release of hemoglobin after the temperature-dependent process occur at virtually the same rate at 0, 22, or 37 C. The loss of intracellular rubidium-86 (Rb) and hemoglobin from SLS-treated erythrocytes was studied. Rb+ release significantly preceded the escape of hemoglobin, suggesting that colloid-osmotic processes play a role in SLS hemolysis.

Adsorption↗
PubMed1976

Effects of fermentation time on in vivo/in vitro relationships.

The effects of six fermentation times, 24 through 84 h at 12 h intervals, were studied on in vivo/in vitro relationships and repeatability and variability of in vitro technique. Three stages of maturity each of bermudagrass, bahiagrass, rye-grass, sorghum-sudan, alfalfa, and orchardgrass were used. For one fermentation time for all types of forages, a 48-h fermentation demonstrated the smallest variation among runs and the least run X forage interaction. However, the optimum fermentation for perennials as a group was 60 h; and for annuals, legumes, and temperate grasses it was 36 h. Further studies in vitro compared a 48-h fermentation for all types of forage with 36 h for annuals and 60 h for perennials. Forty-eight forages, including 20 annuals and 28 perennials, were digested in vitro during three runs. With the 48-h fermentation, forages accounted for 86.43% of the total variation, runs 6.80%, and run X forage interaction 6.44%. Variation due to runs was reduced to .33%, and run X forage interaction to .90%, for a combined 36- and 60-h fermentation for annuals and perennials, respectively. Variation due to forage was increased to 98.53%.

Animal Feed↗
PubMed1975

Association of race, age, menopausal status, and cerumen type with breast fluid secretion in nonlactating women, as determined by nepple aspiration.

Biologic and physiologic factors associated with the availability of breast secretions by a nipple aspiration technique were investigated in 606 normal, non-lactating women. Data obtained on race, age, menstrual status, parity, contraceptive pill use, hormone use, and cerumen type indicated that availability of secretions was related to race, age, and menopause, and to genetic factors associated with apocrine bland function. Fluid aspirates were obtained most often from Caucasians (70.2% success), least often from Chinese (24.1% success). The percentage of successful aspirations declined in women over 50 years of age in all racial groups, but distinctly less so in Caucasians. Chinese and Japanese women with dry-type cerumen had a lower percentage of successful aspirations than those with wet type, which suggested that genetic factors may be associated with breast fluid secretion in nonlactating women.

Age Factors↗
PubMedDate not supplied

The prevalence of challenging behaviors: a total population study.

A total population study was undertaken in two areas of England to identify the situation and characteristics of people reported to exhibit challenging behaviors. We found that: (1) challenging behaviors are shown by 10-15% of people with mental retardation who are in contact with educational, health or social care services for people with mental retardation; (2) the most common forms of challenging behaviors reported were 'other' behavior (shown by 9%-12% of all people screened), aggression (7%), destructive behavior (4%-5%) and self-injury (4%); (3) the majority of people identified showed two or more of these four general forms of challenging behavior; (4) approximately two-thirds of the people identified were boys/men; (5) close to two-thirds of the people identified were adolescents or young adults; (6) approximately 50% of the people identified as showing more demanding challenging behavior were living with their families; (7) people who showed more demanding challenging behavior were more likely to need greater levels of assistance in eating, dressing and washing, be incontinent and have more restricted expressive and receptive communication.

Adolescent↗
PubMedDate not supplied

Predicting the persistence of severe self-injurious behavior.

Information was collected on 95 people with mental retardation who had been identified seven years previously as showing severe self-injurious behavior. At follow up 71% of participants were still showing self-injurious behavior of a severity which presented a management problem for care staff. The occurrence of specific topographies of self-injury was extremely stable among the group showing persistent self-injury. Finally, self-injury status at follow-up was predicted with 76% accuracy by a logistic regression model containing three variables: site of injury (higher persistence being shown by people exhibiting head directed self-injury); reported (greater) stability of self-injury when first identified; and (younger) age.

Adolescent↗
PubMedDate not supplied

Staff stressors and staff outcomes in services for adults with intellectual disabilities: the Staff Stressor Questionnaire.

This paper reports on the development, psychometric properties, and validity of a self-report measure designed to assess potential stressors among staff in services for people with intellectual disabilities, the 33-item Staff Stressor Questionnaire (SSQ). A questionnaire including the SSQ and scales measuring staff outcomes was administered to 512 staff across seven services for people with intellectual disabilities. The SSQ was factor analyzed to produce seven subscales reflecting different potential stressors for staff: user challenging behavior; poor user skills; lack of staff support; lack of resources; low-status job; bureaucracy; and work-home conflict. The SSQ subscales showed adequate internal reliability in terms of Cronbach's alpha and mean inter-item correlations. Associations between SSQ subscale scores and different staff groups, and patterns of associations between SSQ subscales and a range of staff outcomes, provided evidence suggestive of the face-, construct-, and criterion-related validity of the questionnaire. The SSQ shows promise as a measure for assessing potential stressors for staff in services for people with intellectual disabilities. Further studies to examine the reliability, validity, and utility of the SSQ are recommended.

Adult↗
PubMedDate not supplied

Daytime families.

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Activities of Daily Living↗