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Biomedical subjects

M K Walker

Publications and source records attributed to M K Walker.

At least 37 records · Page 2Linked to original sources
PubMed1998

Vitamin E analogues reduce the incidence of ventricular fibrillations and scavenge free radicals.

The aim of our study was to analyse the protective effects of different alpha-tocopherol analogues 1) against fibrillations induced by an ischemia-reperfusion sequence, and 2) to further investigate in vitro the radical scavenging properties of these analogues by two sensitive methods. Concerning 1: isolated rat hearts underwent 10 min of coronary ligation followed by reperfusion and the alpha-tocopherol analogues were infused 15 min before occlusion. Functional parameters including heart rate and fibrillations were recorded. Concerning 2: the beta-phycoerythrin assay was utilised to determine the oxygen radical absorbing capacity (ORAC) of these vitamin E analogues against peroxyl radicals. Electron paramagnetic resonance (EPR) was used to measure their scavenger abilities on hydroxyl radical and superoxide anion production. Concerning 1: ventricular fibrillation times were reduced for all analogues treated hearts at concentrations of 1 microM and 5 microM, with Trolox being the most efficacious. Concerning 2: in our experimental conditions of intense production of free radicals, scavenging IC50 values for hydroxyl radical were 1.15, 2.17 and 4.04 mM for Trolox, MDL 74270 and MDL 74366 respectively. Superoxide anion IC50 values were 1.0 and 6.75 mM for Trolox and MDL 74270. Our results show that water-soluble analogues of vitamin E are effective in the prevention of coronary ligation induced reperfusion arrhythmia, under our experimental conditions. Moreover, our data demonstrate that these vitamin E analogues are effective scavengers for a variety of radicals. Our studies support the view that compounds that can either inhibit the formation or scavenge free radicals can protect the heart against arrhythmia associated with ischemia-reperfusion.

Animals↗
PubMed1998

Plasma iron status and lipid peroxidation following thrombolytic therapy for acute myocardial infarction.

Free radical species have been implicated as important agents involved in myocardial ischemic and reperfusion injuries. Superoxide is capable of mobilizing iron from ferritin and the released iron can cause hydroxyl formation from H2O2. The aim of this study was to evaluate the time-dependent increase in lipid peroxidation assessed by plasma thiobarbituric acid reactive substances (TBARS) and the relationship between lipid-peroxidation and the iron status. Peripheral venous blood samples were obtained from 17 men with acute myocardial infarction (AMI) before thrombolytic treatment (T0) and 1, 2, 3, 4, 8, 12, 16, 20, 24 and 48 hours after commencing fibrinolytic treatment. The concentration of TBARS, the parameters of iron metabolism, serum myoglobin, creatine kinase, and creatine kinase-MB were measured. Early reperfusion was judged by regression of sinus tachycardia (ST) elevation and reduction of chest pain. Recanalization of coronary artery was evaluated by a late coronary angiography 24-96 hours after thrombolysis. After thrombolytic therapy, the TBARS level was raised from 2.98 +/- 0.80 (T0) to 4.57 +/- 1.24 (peak), and decreased to 2.96 +/- 0.40 nmol/mL plasma at T48 (T0 vs peak: P < 0.001, peak vs T48: P < 0.001, T0 vs T48: NS). The mean time of the peak was observed at 9.7 +/- 7.5 hours. The iron increased significantly from 0.67 +/- 0.34 (T0) to 1.15 +/- 0.52 mg/L (peak), and returned to the pre-reperfusion to levels: 0.53 +/- 0.28 UI/L at T48 (TO vs peak: P < 0.001, peak vs T48: P < 0.001, T0 vs T48: NS). The mean time of the peak was observed at 9.4 +/- 7.3 hours. In return, no correlation was found between the increase of plasma creatine-kinase activity, myoglobin and iron or between the biochemical markers and time of fibrinolytic therapy. The results confirmed the importance of the temporal relationship between lipid peroxidation and iron status after thrombolytic therapy. Our results are in agreement with the concept that antioxidant agents used in association with thrombolytic therapy might be useful.

Aged↗
PubMed1998

National health policy influence on Medicare home health.

National health policy regulates the delivery of Medicare home health services. These services have grown exponentially over the past several years. Current challenges to service delivery revolve around attempts to contain costs while ensuring quality of and access to care. To meet these challenges, providers must be aware of the societal and ideological influences on national health policies that impact service delivery. This article uses Wong's model of the progression of health care reform to address past health policy influences on Medicare home health delivery, investigate recent sociological trends for relevance to health policy, and propose changes based on current ideology.

Aged↗
PubMed1997

Expression of the aryl hydrocarbon receptor (AhR) and AhR nuclear translocator during chick cardiogenesis is consistent with 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced heart defects.

We examined cardiotoxicity induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the chick embryo and the cardiac expression of transcription factors, the aryl hydrocarbon receptor (AhR) which binds TCDD, and its dimer partner, the AhR nuclear translocator (Arnt). Chicken eggs were injected with control (triolein) or 1.0 pmol TCDD/g egg prior to incubation and collected on Day 10 when cardiomorphogenesis is complete. Relative to controls, TCDD increased heart wet weight (27.2 +/- 0.5 versus 36.6 +/- 1.3 mg, p < 0.001) and dry weight (2.7 +/- 0.1 versus 3.1 +/- 0.1 mg, p < 0.01), and tended to increase heart myosin content (3.5 +/- 0.6 versus 6.3 +/- 2.5 microg, p < 0.07), suggesting an increase in cardiac muscle mass and edema. Histologic and morphometric analyses revealed that 10/13 TCDD-exposed hearts exhibited enlarged right and left ventricles, thickened ventricular septum, and a thinner left ventricular wall with increased trabeculation, and 4/13 exhibited ventricular septal defects compared to controls (0/23). To evaluate AhR and Arnt expression, untreated chick embryos were collected on Days 2.2, 3, 4, 5, and 8 of incubation, preserved in Bouin's fixative, sectioned, and stained with AhR and Arnt antibodies. The AhR was expressed ubiquitously in cardiac myocytes, while Arnt expression was restricted to myocytes overlying developing septa: atrioventricular canal, outflow tract, and atrial and ventricular septa. Both proteins were absent from endocardium and endocardial-derived mesenchyme. In addition, cardiac expression of an AhR/Arnt target, cytochrome P4501A1, was restricted to myocardium coexpressing AhR and Arnt. Thus, the spatial and temporal expression of AhR and Arnt suggests that the developing myocardium and cardiac septa are potential targets of TCDD-induced teratogenicity, and such targets are also consistent with cardiac hypertrophy and septal defects observed following TCDD exposure.

Animals↗
PubMed1997

Recall of the visual body image using a novel boundary detection task.

A new task for eliciting a pictorial mental image of the body or other objects is described. The task involved relating a pair of crosses to the boundary of a mental image 'projected' onto a computer screen. Responses were assessed for accuracy defined as identifying a relationship between a cross and an image that would hold when a photograph (of the same object) was substituted for the mental image. A group of 30 female students achieved between 70 to 80% accuracy when using this task to assess mental images of their own faces, torsos, or a familiar nonbody object. Accuracy was similar for body and nonbody objects. The presence of some kind of quasipictorial representation of the body is confirmed. Its characteristics await further elucidation.

Body Image↗
PubMed1996

Serum insulin and incident coronary heart disease in middle-aged British men.

Earlier studies have not resolved the question of whether elevated circulating insulin levels are independently related to the development of coronary heart disease. Previous studies have not used a specific insulin assay and in all but a minority of studies that have addressed this issue it has not been possible to adjust for possible confounding due to high density lipoprotein (HDL) cholesterol. The authors examined the relation between serum insulin concentration and major coronary disease events (fatal and non-fatal myocardial infarction) in the British Regional Heart Study. The data are based on 5,550 men (aged 40-59 years) in 18 towns whose baseline, non-fasting serum samples were analyzed for insulin using a specific enzyme-linked immunoadsorbent assay (ELISA) method. Known diabetics were excluded. At 11.5 years of follow-up, 521 major coronary disease events had occurred, 261 fatal and 260 non-fatal. A nonlinear relation between serum insulin and coronary disease events was observed with an almost twofold increased relative risk in the 10th decile of the serum insulin distribution (> or = 33.8 mU/liter) relative to the 1st to the 9th deciles combined (age-adjusted relative risk (RR) = 1.9, 95% confidence interval (CI) 1.6-2.4). There was some attenuation of this association on cumulative adjustment for a wide range of biologic and life-style coronary disease risk factors, including HDL cholesterol, though it remained significant in the fully adjusted proportional hazards model (RR = 1.6, 95% CI 1.1-2.3). Similar associations between insulin and coronary disease events were seen in men with and without evidence of coronary disease at screening and in men with baseline serum glucose below the 80th percentile. These data are consistent with the hypothesis that a high level of serum insulin (hyperinsulinemia) is atherogenic, with a threshold effect. However, the markedly nonlinear form of the association and the attenuation in multivariate analysis strongly suggest that elevated insulin levels may only be a marker for common etiologic factors in the development of both coronary disease and non-insulin-dependent diabetes mellitus.

Adult↗
PubMed1996

Low levels of interrater reliability in a standard measure of outcome in eating disorders (the modified Morgan-Russell Assessment Schedule).

OBJECTIVE: The interrater reliability of the modified version of the widely used Morgan-Russell Assessment Schedule was assessed. METHOD: Sixty-six female patients presenting for treatment for the first time in a general hospital and a community health center were assessed by a treating clinician and a researcher during sequential interviews. Two extra items were added to the Schedule to allow for the assessment of bulimic behaviors. Ratings were analyzed using the Cohen's weighted kappa. RESULTS: Poor to very poor levels of agreement were found between rater pairs assessing the 66 separate patients. DISCUSSION: The necessity for a specific, standardized format in using the Morgan-Russell Schedule is discussed. In its current, unstandardized format the Schedule may not be suitable for comparing outcome in eating disorders across different centers.

Adult↗
PubMed1996

Potency of a complex mixture of polychlorinated dibenzo-p-dioxin, dibenzofuran, and biphenyl congeners compared to 2,3,7,8-tetrachlorodibenzo-p-dioxin in causing fish early life stage mortality.

Use of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxicity equivalents concentration (TEC) assumes that polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) act additively and via a common mechanism to cause toxicity. To test these assumptions, 11 TCDD-like congeners and three non-TCDD-like congeners were combined at ratios typically found in Lake Michigan lake trout. The potency of the mixture, expressed as TEC based on fish-specific toxic equivalency factors, was compared to TCDD for producing lake trout and rainbow trout early life stage mortality. Signs of toxicity following exposure of newly fertilized eggs to the mixture or to TCDD were indistinguishable; sac fry mortality associated with blue-sac disease, and slopes of the dose-response curves for percentage sac fry mortality versus egg TEC or versus egg TCDD were parallel. However, the mixture dose-response curves were significantly shifted to the right of the TCDD dose-response curves by 1.3- and 1.8-fold as illustrated by LD50 values. Following exposure to the mixture or TCDD, LD50S for lake trout early life stage mortality were 97 (89-110) pg TE/g egg and 74 (70-80) pg TCDD/g (LD50, 95% fiducial limits) and for rainbow trout were 362 (312-406) pg TE/g egg and 200 (148-237) pg TCDD/g egg. These data suggest that TCDD-like congeners act via a common mechanism to cause toxicity during trout early development, but may not act strictly additively when combined in a mixture of TCDD- and non-TCDD-like congeners at ratios found in Great Lakes fish. The deviation from additivity, however, is less than current safety factors of 10-fold commonly applied in ecological risk assessments, providing support for the continued use of a TE additivity model for assessing risk posed by complex mixtures of PCDDs, PCDFs, and PCBs to fish.

Animals↗
PubMed1995

Prospective study of risk factors for development of non-insulin dependent diabetes in middle aged British men.

OBJECTIVE: To determine the risk factors for noninsulin dependent diabetes in a cohort representative of middle aged British men. DESIGN: Prospective study. SUBJECTS AND SETTINGS: 7735 men aged 40-59, drawn from one group practice in each of 24 towns in Britain. Known and probable cases of diabetes at screening (n = 158) were excluded. MAIN OUTCOME MEASURES: Non-insulin dependent diabetes (doctor diagnosed) over a mean follow up period of 12.8 years. RESULTS: There were 194 new cases of non-insulin dependent diabetes. Body mass index was the dominant risk factor for diabetes, with an age adjusted relative risk (upper fifth to lower fifth) of 11.6; 95% confidence interval 5.4 to 16.8. Men engaged in moderate levels of physical activity had a substantially reduced risk of diabetes, relative to the physically inactive men, after adjustment for age and body mass index (0.4; 0.2 to 0.7), an association which persisted in full multivariate analysis. A nonlinear relation between alcohol intake and diabetes was observed, with the lowest risk among moderate drinkers (16-42 units/week) relative to the baseline group of occasional drinkers (0.6; 0.4 to 1.0). Additional significant predictors of diabetes in multivariate analysis included serum triglyceride concentration, high density lipoprotein cholesterol concentration (inverse association), heart rate, uric acid concentration, and prevalent coronary heart disease. CONCLUSION: These findings emphasise the interrelations between risk factors for non-insulin dependent diabetes and coronary heart disease and the potential value of an integrated approach to the prevention of these conditions based on the prevention of obesity and the promotion of physical activity.

Adult↗
PubMed1995

Pictorial adaptation of Stroop measures of body-related concerns in eating disorders.

Patients with eating disorders were asked to color-name pictures of a variety of body shapes. The time taken to color-name these stimuli was compared with the time taken to color-name a series of neutral visual stimuli. There was a significant delay in naming body shapes in comparison to neutral stimuli, and this delay was greater in anorexic and bulimic patients than in controls. Previous Stroop adaptations have used verbal stimuli to assess the intensity of weight and shape-related concerns. The possible advantages of pictorial stimuli are discussed.

Body Image↗
PubMed1995

Interactions of polychlorinated dibenzo-p-dioxin, dibenzofuran, and biphenyl congeners for producing rainbow trout early life stage mortality.

Fish-specific toxic equivalency factors (TEFs), which relate the toxic potency of polyhalogenated aromatic hydrocarbons (PHAHs) to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) based on the endpoint of early life stage mortality, have been used in assessing the risk to fish early life stage survival of complex mixtures of PHAHs in feral fish eggs. Use of TEFs assumes that PHAH congeners act additively. However, this has not been unequivocally determined. Isobolograms and a probit model were used to assess the validity of the additivity assumption by determining the significance of interactions between pairs of polychlorinated dibenzo-p-dioxin (PCDD), dibenzofuran (PCDF), and biphenyl (PCB) congeners when injected into newly fertilized rainbow trout eggs in ratios bracketing those found in feral lake trout eggs from the Great Lakes. The majority of congener pairs tested acted additively in causing rainbow trout early life stage mortality: [1,2,3,7,8- pentachlorodibenzo-p-dioxin (1,2,3,7,8-PCDD)/TCDD]; [2,3,4,7,8-pentachlorodibenzofuran (2,3,4,7,8-PCDF)/1,2,3,7,8-PCDD]; (2,3,4,7,8-PCDF/TCDD), (2,3,7,8-tetrachlorodibenzofuran/2,3,4,7,8-PCDF); [3,3',4,4'-tetrachlorobiphenyl (PCB 77)/3,3',4,4',5-pentachlorobiphenyl (PCB 126)]; [2,3,3',4,4'-pentachlorobiphenyl (PCB 105)/TCDD]; (2,2',4,4',5,5'-hexachlorobiphenyl/TCDD); (PCB 105/PCB 126); and (2,3',4,4',5-pentachlorobiphenyl/PCB 126). The only pairs showing evidence of a statistically significant interaction that deviated from additivity were (TCDD/PCB 77) and (TCDD/PCB 126). Taken together, these results suggest that the use of fish-specific TEFs to determine TCDD equivalents contributed by individual congeners in a fish egg sample and then adding these TCDD equivalents to determine the total amount contributed by all congeners may not exactly predict the mortality risk posed to fish early life stages by the mixture of TCDD-like congeners in the eggs. However, the relatively small deviations from additivity in the rainbow trout sac fry mortality test (1- to 4-fold) are less than traditional uncertainty factors used in noncancer risk assessments (10-fold/factor) and are not sufficient to warrant a change away from the additivity assumption in assessing the risk to fish early life stage mortality posed by TCDD and related compounds in eggs.

Animals↗
PubMed1995

Body image, disfigurement and disability.

The body-related attitudes of groups of women suffering from physical conditions that are commonly regarded as being disfiguring and/or disabling were studied by means of the Body Attitudes Questionnaire. Despite their conditions, the women did not necessarily disparage their bodies. They also seemed to worry less about small changes in weight and shape than did comparable women without physical difficulties, and to have an enhanced sense of their own robustness. There was an indication that development of negative body attitudes might be linked to emergence of a chronic physical condition during adolescence, rather than from birth or during adulthood. If our results are confirmed, they point to the need to pay special attention to the psychological needs of women whose bodies become dysfunctional at this sensitive time.

Adolescent↗
PubMed1995

Depletion of alpha-tocopherol in human atherosclerotic lesions.

Estimations of alpha-tocopherol content were made on a series of human necropsy samples of normal arterial wall and of atherosclerotic lesions. The results were compared with stage of lesion, shown by histology, and with the amounts of cholesterol and hydroxycholesterols in the same lesions. The ratio of alpha-tocopherol to cholesterol levels varied widely in normal arterial wall but was consistently low in lesions, especially in lesions rich in macrophage foam cells. The results suggested that significant accumulation of hydroxycholesterols, found almost exclusively in lesions, only occurred when alpha-tocopherol levels were low in relation to the cholesterol content. This suggests that oxidative activity in the lesion may lead to significant oxidation of constituents of low-density lipoprotein only after alpha-tocopherol has been depleted.

Adolescent↗
PubMed1994

The influence of age and weight on women's body attitudes as measured by the Body Attitudes Questionnaire (BAQ).

The influence of age and weight on the body-related attitudes of a large sample of South Australian women were measured by the Ben-Tovim-Walker Body Attitudes Questionnaire (BAQ). Attitudes were found not to vary substantially with age, and only the Feeling Fat, Body Disparagement and Lower Body Fatness sub-scales of the BAQ were correlated with BMI. The effect of BMI on attitudes was independent of age. Obese subjects felt significantly less attractive than those with BMIs only slightly above average. However, they did not disparage their bodies more than did less overweight women. Body attitudes appear to be substantially independent of the current physical body.

Adolescent↗
PubMed1994

An insight into the personal and cultural significance of weight and shape in large Samoan women.

The aim of this work was to investigate the personal and cultural significance of body weight and shape for women in Western Samoan culture. A cross cultural study was carried out of Western Samoan and Australian women comparing responses to the Body Attitude Questionnaire (BAQ). The work was carried out in a tertiary education institution and an occupational setting in Apia, Western Samoa, and on community residents in Adelaide, South Australia. The subjects were 70 volunteer female respondents from Western Samoan educational and occupational settings, individually matched for weight and height with 70 respondents from a South Australian random community setting. The psychometric properties of the BAQ, as completed by the Western Samoan respondents, were found to be similar to those for Australian women. Samoan women who were biologically overweight, felt as fat and had similar feelings about lower body fatness as their identical weight Australian counterparts. They, however, showed highly significantly less salience of fatness than the Australian sample, indicating that fatness is not a pre-occupying in Samoans as it is in Australian women. Despite this apparent non-concern over their fatness, Samoan women were significantly more disparaging about their bodies than their Australian counterparts. The other significant finding from this cross-comparative study, was that large Samoan women felt more attractive and much stronger and fitter than their Australian counterparts. It was concluded that Samoan women's body-related attitudes can be studied using techniques and concepts originating in the west, but the specific concerns of Samoan women need to be explored in further detail.

Adult↗
PubMed1993

Measurement of n-alkanals and hydroxyalkenals in biological samples.

A modified method was developed to measure nM levels of a range of n-alkanals and hydroxyalkenals in biological samples such as blood plasma and tissue homogenates and also in Folch lipid extracts of these samples. Butylated hydroxytoluene (BHT) and desferrioxamine (Desferal) were added to samples to prevent artifactual peroxidation. Aldehydes were reacted with 1,3-cyclohexanedione (CHD), cleaned up by solid-phase extraction on a Sep-Pak C18 cartridge and the fluorescent decahydroacridine derivatives resolved by reverse-phase high-performance liquid chromatography (HPLC) with gradient elution. A wider range of aldehydes was detected in lipid extracts of plasma and liver homogenate compared to whole (unextracted) samples. Human plasma contained nM levels of acetaldehyde, propanal, butanal, pentanal, hexanal, and heptanal. 4-Hydroxynonenal (0.93 nmol/g) and alkanals with two to six carbons (up to 7.36 nmol/g) were detected in rat liver. Recovery of aldehydes added to whole plasma or to lipid extracts of plasma was dependent on carbon chain length, varying from 95% for acetaldehyde to 8% for decanal. Recovery from biological samples was significantly less than that of standards taken through the Sep-Pak clean-up procedure, suggesting that aldehydes can bind to plasma protein and lipid components.

Aldehydes↗
PubMed1993

Sporting activity and hyperglycemia in middle-aged men.

OBJECTIVE: To assess the relationship between self-reported frequency of participation in sporting activity and the prevalence of hyperglycemia (nonfasting glucose level > or = 7.8 mM) in middle-aged men. RESEARCH DESIGN AND METHODS: We used a cross-sectional study of 7617 British middle-aged men, drawn from 24 general practices in England, Wales, and Scotland, who were participants in the British Regional Heart Study. The response rate was 78%. Patients with diabetes (physician-diagnosed) were excluded from our analysis. Frequency of participation in sporting activity was determined by the respondents and reported as none (61%), occasionally (12%), or frequently (27%). RESULTS: The age-adjusted prevalence odds ratio for hyperglycemia was 0.86 (95% confidence interval, 0.6-1.2) in those reporting occasional, and 0.62 (95% confidence interval, 0.4-0.85) in those reporting frequent sporting activity, compared with those reporting none. This effect of frequent sporting activity on the prevalence of hyperglycemia was independent of body mass index, occupational status, smoking status, systolic blood pressure, use of antihypertensive therapy, and time of sampling. CONCLUSIONS: Frequent sporting activity in middle-aged men is associated with a reduced prevalence of hyperglycemia and may reduce the risk of NIDDM.

Adult↗