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Biomedical subjects

J Mann

Publications and source records attributed to J Mann.

At least 217 records · Page 12Linked to original sources
PubMed1992

Influence of dietary factors on the renal renin-angiotensin system.

Protein meals and infusion of amino acids cause an increase of glomerular filtration rate in humans and animals with normal renal function despite the circulating renin concentration remaining unchanged. The renal hemodynamic response is not altered by angiotensin converting enzyme inhibitors, but it is obliterated by cyclooxygenase inhibitors. By contrast, chronic exposure to high protein diets raises circulating renin and increases messenger RNA of renin (but not of angiotensinogen) in kidney tissue. Chronically high protein intake raises the glomerular filtration rate and reduces glomerular permselectivity; the reverse is seen with low protein intake. In patients with renal failure, acute amino acid infusion or protein meals cause a paradoxical drop in glomerular filtration rate which is not influenced by converting enzyme inhibitors.

Amino Acids↗
PubMed1992

Should mono- or poly-unsaturated fats replace saturated fat in the diet?

The effects of diets differing in saturated, monounsaturated and polyunsaturated fatty acid composition (SAFA, MUFA and PUFA, respectively) on plasma lipoproteins and factor VIIc were investigated in 28 middle-aged men and women with mild to moderate hyperlipidaemia. The subjects were stabilized on a diet with a total fat content fairly typical of New Zealand, containing approximately 40% energy as fat, before entering a randomized cross-over trial of diets high in PUFA (20% energy; SAFA and MUFA 10% each) or a high MUFA diet (20% energy; SAFA and PUFA 10% each). After 6-week periods on each diet the subjects returned to a high SAFA diet. Body weight and blood pressure remained unchanged during the study. Total and LDL cholesterol, HDL cholesterol and the HDL2 subfraction were significantly lower on both the MUFA and the PUFA diet than on SAFA. However, there were no statistically significant differences in lipoprotein concentrations on the MUFA and PUFA diet. Factor VIIc concentrations were similar on the three diets. The proportion of PUFA in a MUFA diet appears to be a major determinant of the relative lipoprotein response to such a diet. In order to avoid a reduction in HDL-C when replacing SAFA with MUFA it may be necessary to ensure that PUFA does not provide more than about 8% total energy. Thus careful planning is needed to identify the most appropriate foods to replace those rich in SAFA in diets designed to reduce the lipoprotein-mediated risk of coronary heart disease.

Aged↗
PubMed1991

Fibrinogen and lipid concentrations as risk factors for transient ischaemic attacks and minor ischaemic strokes.

OBJECTIVES: To determine whether fibrinogen and lipid concentrations are risk factors for ischaemic stroke. DESIGN: Case-control study with a population based comparison within the overall study. SETTING: Oxfordshire community stroke project and a neurology clinic. SUBJECTS: 105 patients who had a transient ischaemic attack or minor ischaemic stroke and 352 randomly chosen controls matched for age and sex from the same general practitioners as the incident cases. 52 controls were ineligible or refused interview. 104 cases and 241 controls gave blood samples for analysis. MAIN OUTCOME MEASURES: Response to structured questionnaire, height, weight, blood pressure, and serum concentrations of fibrinogen and lipids. RESULTS: Adjusted for other variables, odds ratios of ischaemic stroke were 1.78 (95% confidence interval 0.91 to 3.48; p = 0.09) [corrected] for fibrinogen concentrations greater than 3.6 g/l; 1.73 (0.90 to 3.29; p = 0.09) [corrected] for total cholesterol concentrations greater than 6.0 mmol/l; 1.34 (0.69 to 2.61; p greater than 0.4) for low density lipoprotein cholesterol concentrations greater than 3.5 mmol/l; and 0.32 (0.15 to 0.69; p = 0.002) for high density lipoprotein cholesterol concentration greater than 1.2 mmol/l. Similar results emerged comparing only community derived cases with transient ischaemic attacks and controls. The effects of fibrinogen, total cholesterol, and high density lipoprotein cholesterol were significant in a test of trend after adjusting for all other variables in the study (chi 2 = 4.14, p less than 0.05; chi 2 = 4.31, p less than 0.05, and chi 2 = 12.15, p greater than 0.001, respectively). History of ischaemic heart disease and hypertension were the only other variables that showed significance, though both lost significance after adjustment (2.06, p = 0.08 and 1.53, p = 0.2, respectively). CONCLUSIONS: Fibrinogen and lipids are important risk factors for ischaemic stroke. The pattern of changes mirrors that found in ischaemic heart disease.

Adult↗
PubMed1991

Psychiatric morbidity in young adults with insulin-dependent diabetes mellitus.

Psychiatric disorder and sub-threshold psychological distress were more common in 113 young men and women with insulin-dependent diabetes living in a defined area than in comparable general population samples. Twelve per cent of men and 19% of women were classified by the PSE as psychiatric 'cases'. Forty per cent of women and 47% of men reported at least one major social problem; effects of diabetes on everyday activities were common. There were associations between medical and social variables. The clinical implications are discussed.

Adolescent↗
PubMed1991

Is oral contraceptive use still associated with an increased risk of fatal myocardial infarction? Report of a case-control study.

OBJECTIVE: To investigate the association between fatal myocardial infarction and use of modern low-dose oral contraceptives. DESIGN: A case-control study. SETTING: General practices throughout England and Wales. SUBJECTS: 161 women aged under 40 dying from myocardial infarction during 1986-1988. Living controls (2 per case), matched for age and marital status, were chosen from general practice lists. Information was collected during structured interviews with general practitioners, and from postal questionnaires sent to surviving partners of the cases and to control women. MAIN OUTCOME MEASURES: Mortality from myocardial infarction in relation to many risk factors, notably oral contraception, as measured by relative risk. RESULTS: After allowing for the confounding effects of medical risk factors and for surgical sterilization, the overall relative risk associated with both current and past use of oral contraceptives was estimated to be 1.9 (95% CI 0.7 to 4.9, and 1.0 to 3.5 respectively). The relative risk associated with current use of preparations containing 50 micrograms of oestrogen, however, was estimated to be 4.2 (0.5 to 39.2). At least some of the relative risk associated with oral contraceptive use is likely to be attributable to the confounding effect of cigarette smoking, but it is impossible to estimate how much from the available data. CONCLUSIONS: If there was an increased risk of fatal myocardial infarction associated with oral contraceptive use in 1986-1988 it is likely to have been less than two-fold; in this study risks were slightly, but not significantly, elevated with both current and previous use. It may be that any increase in risk is associated solely with the older combined preparations containing 50 micrograms of oestrogen.

Adult↗
PubMed1991

A study of inter- and intra-examiner reliability of pocket depth and attachment level.

Factors affecting inter- and intra-examiner variability for probing pocket depth and periodontal attachment level were studied on a sample of 20 patients, each given six full-month examinations, two by each of 3 examiners. The major determinant of both dimensions of variability was the degree of periodontal destruction, measured as either pocket depth or level of attachment: the greater the degree of destruction, the greater the disagreements within and between examiners. Differences in variability were generally minor between sites on anterior and sites on posterior teeth, between midsites and proximal sites, and between sites on the facial and sites on the lingual surface. When differences were found between the average variances for different kinds of sites, they may have been due to corresponding differences between the average depths, and not to any inherently greater difficulty in measuring one kind of site than another.

Adolescent↗
PubMed1991

Mechanisms by which endothelin 1 induces pulmonary vasoconstriction in the rabbit.

To investigate the mechanisms by which endothelin 1 (ET-1) causes pulmonary vasoconstriction, we studied the effect of synthetic ET-1 on pulmonary vascular tone in the buffer-perfused isolated rabbit lung. In nanomolar concentrations (1.2-8 nM), ET-1 causes a dose-dependent increase in pulmonary arterial pressure that persists for greater than or equal to 1 h (increase in pressure 19 +/- 2 mmHg with ET-1 vs. 2 +/- 1 with vehicle, P less than 0.0001). Reduction of calcium availability with verapamil, cadmium, or a calcium-free buffer significantly blunts the increase in pressure caused by ET-1. Pretreatment with a calcium-free buffer plus the chelator ethylene glycol-bis(beta-aminoethyl ether)-N,N,N', N'-tetraacetic acid (EGTA) completely eliminates the vasoconstriction. Three different inhibitors of protein kinase C, phloretin, staurosporine, and dihydrosphingosine, significantly diminish the response to ET-1. Indomethacin and a thromboxane synthase inhibitor partially decrease the response to the highest concentration of ET-1. Isoproterenol and dibutyryl adenosine 3',5'-cyclic monophosphate (cAMP) are significantly more effective in preventing the vasoconstriction caused by ET-1 than are nitroprusside and guanosine 5'-cyclic monophosphate (cGMP) analogues. ET-1 in doses of 1.2-8 nM is a potent pulmonary vasoconstrictor in the isolated rabbit lung. ET-1 appears to cause pulmonary vasoconstriction by increasing calcium entry and by activating protein kinase C. Vasodilators that increase cAMP are substantially more effective in preventing the increase in pressure than are drugs that increase cGMP.

Animals↗
PubMed1991

Time sampling: a methodological critique.

Numerous developmental studies of social behavior employ an observational technique called time sampling. This technique is used to estimate the frequencies and proportions of time that actual behaviors occur and to measure group or individual differences. By contrasting time sampling to continuous sampling, we demonstrate that (a) time sampling is inaccurate for estimating actual durations or frequencies of behavior, and (b) resulting individual and/or group differences can change depending on whether time sampling or continuous sampling is used. Error rates are particularly high when the total bout lengths of the actual behaviors are short (as in mother-infant interactions) and/or when interval length is long. Because the majority of mother and infant behaviors are short in bout length (less than 60 sec), when percent error is the greatest, we suggest that alternative sampling methods that have proven validity be used in future studies (e.g., scan, point, or continuous sampling).

Behavior↗
PubMed1990

Synthesis of 2',3'-dideoxy-2',3'-alpha-methanocytidine.

A six-stage synthesis of 2',3'-dideoxy-2',3'-alpha-methanocytidine (3) from (5S)-5-benzoyloxymethyl-(5H)-furan-2-one (5) is described. The key step involved the stereoselective formation of (1R,4S,5S)-4-benzoyloxymethyl-3-oxabicyclo[3.1.0]hexan-2-one (7) via 1,3-dipolar cycloaddition of diazomethane to 5 followed by photoinduced elimination of nitrogen. Reduction of 7 to the corresponding lactol followed by acetylation yielded primarily 1-O-acetyl-5-O-benzoyl-2,3-dideoxy-beta-D-ribofuranose (8). Reaction of 8 with 2,4-bis(trimethylsilyl)cytosine and EtAlCl2 followed by deprotection and chromatography gave 3, which exhibited only weak activity against the human immunodeficiency virus (HIV).

Antiviral Agents↗
PubMed1990

Dietary intake and plasma lipid levels: lessons from a study of the diet of health conscious groups.

AIM: To re-examine the contentious relation between diet and plasma lipids within a population. DESIGN: Cross sectional sample from a large prospective cohort study of people eating different diets in Britain. Blood samples and diet records collected from subjects. SUBJECTS: Volunteers eating one of four distinct diets--namely, vegans, vegetarians, fish eaters who do not eat meat, and meat eaters. 52 Subjects selected from each group. METHODS: Examination of the relation between nutritional intake recorded in a four day dietary record and plasma lipid concentrations of subjects measured in blood samples collected previously. RESULTS: After controlling for age, sex, and body mass index, the correlation between plasma total cholesterol and the Keys score (which includes dietary cholesterol and saturated and polyunsaturated fat) was 0.37 (p less than 0.001). The mean saturated fat intake in all groups was low (6-14% of energy), but polyunsaturated fat intake was high, so mean total fat intake was generally above that recommended. A high dietary fibre intake was not associated with high carbohydrate intake. Plasma high density lipoprotein values were not associated with any measure of fat intake, but there was a significant correlation of 0.24 between high density lipoprotein values and alcohol intake. CONCLUSIONS: The nature rather than quantity of dietary fat is an important determinant of cholesterol concentrations. Health conscious individuals select a fat modified, rather than a low fat--high carbohydrate diet. National cholesterol lowering dietary advice should be reconsidered.

Adult↗