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Biomedical subjects

A M Stephen

Publications and source records attributed to A M Stephen.

At least 37 records · Page 2Linked to original sources
PubMed1987

Effect of changing transit time on colonic microbial metabolism in man.

An investigation was made of the effect of changing mean transit time (MTT) by administration of drugs which affect colonic motility on faecal microbial mass in man. Senokot was used to accelerate and codeine and/or loperamide to prolong transit in subjects maintained on a constant high fibre diet. Doses of Senokot or codeine/loperamide were adjusted to halve or double transit time measured during a three week control period on diet alone. Stools were collected throughout and analysed for bacterial mass by a gravimetric procedure. Transit was measured by a continuous marker method. Senokot decreased mean transit time from 63.9 to 25.0 hours (n = 6), with increased stool weight from 148 to 285 g/day. Bacterial mass increased in all subjects from a mean of 16.5 to 20.3 g/day (dry weight) (p less than 0.025). Codeine/loperamide increased mean transit time from 47.1 to 87.6 hours (n = 5), with decreased stool weight from 182 to 119 g/day. Bacterial mass decreased in all but one subject from a mean of 18.9 to 16.1 g/day (NS). There was a significant correlation between transit time and bacterial mass in all three periods (r = 0.77, p less than 0.001). Changes in transit time are shown to alter microbial growth in the human colon and result in altered stool output, on a constant diet. Factors which affect transit may be as important as diet in determining large bowel function and hence susceptibility to disease.

Adult↗
PubMed1986

The effect of age, sex and level of intake of dietary fibre from wheat on large-bowel function in thirty healthy subjects.

1. To evaluate the effect of age, sex and level of intake on the colonic response to wheat fibre, thirty healthy volunteers aged 17-62 years (nineteen men, eleven women) recruited from a local industry, were divided into four groups and given a controlled diet for two 3-week periods. The diet contained white bread during one period or one of four different amounts of bran-enriched wholemeal bread during the other (30, 60, 110, 170 g/d). 2. Wide variation was observed between subjects in stool weight on the basal diet and in response to wheat fibre. Stepwise regression analysis showed that the variation in stool weight was significantly related to sex (t 4.0, P less than 0.001) but not to age, height, weight or energy:fibre intakes on the basal diet. Stool weight in men (162 (SE 11) g/d) was approximately double that in women (83 (SE 11) g/d). Transit time and stool weight were closely related and the effect of sex on stool weight could be explained entirely by differences in transit. 3. The increase in stool weight with fibre was significantly related to dose (t 4.18, P less than 0.001) with approximately 1 g non-starch polysaccharides (the main component of dietary fibre) increasing stool weight by 5 g/d. Smaller increases in stool weight were seen in females, persons with initially low stool weights and small people. 4. Faecal carbohydrate excretion increased with the addition of bran mainly due to increased amounts of cellulose and pentose (arabinose + xylose), whilst digestibility of dietary non-starch polysaccharide fell from 77.6 (SE 2.3)% on the white bread diet to 65.6 (SE 2.4)% with the added bran (t 7.4, P less than 0.01, n26). 5. Faecal pH was more acid in men than in women and was related to methane production. Methane producers had higher faecal pH than non-producers (7.06 (SE 0.11) v. 6.65 (SE 0.1], lower stool weight (g/d; 93 (SE 12) v. 156 (SE 13] and slower transit times (h; 84.6 (SE 11.7) v. 48.6 (SE 6.6]. 6. These studies show that, when on similar diets, women have much lower stool weights and slower transit times than men. Furthermore, within the range of amounts of wheat fibre used in this and other published work, stool weight increases in linear proportion to the dose of fibre added to the diet. Methane excretion in breath is associated in this group of subjects with slow transit time and high faecal pH.

Adolescent↗
PubMed1983

Passage of carbohydrate into the colon. Direct measurements in humans.

To quantify passage of unabsorbed dietary starch into the colon, 7 healthy volunteers had a multilumen tube positioned close to the ileocecal junction. Marker solution was perfused slowly, 20-40 cm above an aspiration site, to estimate, by marker dilution, flow through the ileum. On consecutive days, subjects ate liquidized meals containing 20 or 60 g starch; ileal aspirates were analyzed for starch and glucose for 5-6 h fasting and 4-7 h postprandially. Volume and carbohydrate concentrations were used to derive total carbohydrate traversing the ileum. In different subjects, unabsorbed carbohydrate was 453-4023 mg (2.3%-20.1%, mean 9.3%) for the smaller meal and 1332-6352 mg (2.2%-10.4%, mean 6.0%) for the larger. In 4 volunteers, hydrogen breath tests were performed on separate occasions after sucrose (50 g), lactulose (26 g), and the 20-g meal. Lactulose increased hydrogen excretion; sucrose and the test meal did not. We conclude that 2%-20% of dietary starch escapes absorption in the small bowel, confirming others' results using breath tests alone. Breath tests, though more convenient than intubation studies, may be a less sensitive index of starch malabsorption.

Adult↗
PubMed1981

Preparation of oligosaccharides by the action of bacteriophage-borne enzymes on Klebsiella capsular polysaccharides.

Depolymerization of bacterial, capsular polysaccharides by viral enzymes provides a convenient method for preparing oligosaccharides that correspond to one or more repeating unit(s) of the polysaccharide. Previous methods used for purifying bacteriophage particles, and also the procedures employed in the isolation and purification of the oligomers generated by the bacteriophage action, have been so modified as to provide a more direct route to the degradation products. Improved techniques, both for the propagation of bacteriophage and for the isolation of the oligosaccharides formed, are reported. These simplified methods make possible the use of bacteriophages as convenient "reagents" for the preparation of oligosaccharides on a gram scale. The acid- and base-labile substituents present in certain of the polysaccharides examined were seemingly unaffected by the conditions used for depolymerization. The methods are illustrated by degradation of the capsular polysaccharides from Klebsiella serotypes K17, K36, K46, K60, K63, and K74

Bacteriophages↗
PubMed1981

Structural investigation of Klebsiella K-type 4 capsular polysaccharide.

The capsular polysaccharide from Klebsiella K4 contains the tetrasaccharide repeating-sequence leads to 3)-alpha-D-Glcp-(1 leads to 2)-alpha-D-Glcp A-(1 leads to 3)-alpha-D-Manp-(1 leads to 3)-beta-D-Glcp-(1 leads to. P.m.r. spectroscopy and the measurement of optical rotation were used to establish the anomeric linkages in the polysaccharide and in the oligosaccharides derived by partial hydrolysis. The repeating unit also contains one 0-acetyl group.

Carbohydrate Conformation↗
PubMed1981

Should we eat more fibre?

Controversy continues over the role of dietary fibre in health, and whether or not a standard fibre intake should be recommended for the UK. In this review an attempt is made to consider the evidence for and against making such a recommendation. In doing so, it is clear that many problems exist in studies examining the role of fibre in disease, such as the inherent inadequacies of epidemiological studies and distrust of such studies by some circles, or the lack of uniformity in definition of dietary fibre and in its chemical analysis. The effect of fibre on faecal bulking is given as an example of experimental verification of epidemiological findings which has led to the widespread use of fibre in treating diverticular disease and constipation. Evidence of beneficial effects for cancer of the colon and ischaemic heart disease are far less convincing. Few harmful effects of fibre have been documented, apart from continuing disagreement regarding fibre and mineral balance, a question which remains to be solved. On weighing the evidence, it is suggested that recommending higher-fibre intakes in the UK is a favourable guideline. The type of fibre to be recommended is discussed, based on new evidence of the mode of action of different types of fibre in the gastrointestinal tract, and the amount of fibre considered, in relation to intakes in other countries and in the past in the UK.

Colonic Neoplasms↗
PubMed1980

The role of dietary fibre in the human colon.

Several effects of dietary fibre on colonic function have been documented by experiment or deduced from epidemiologic observation. The magnitude of these changes depends on the source and the physical and chemical composition of the fibre used, and on the individual response of the subjects. Three theories of the mode of action of fibre are discussed; they relate to the water-holding capacity of fibre, the production of short-chain fatty acids from fibre in the colon and the alteration by fibre of the colonic microflora.

Adult↗
PubMed1980

The molecular structure of the capsular polysaccharide from Klebsiella type 27.

The capsular polysaccharide of Klebsiella serotype K27 had been investigated by techniques involving methylation analysis, autohydrolysis, and graded hydrolysis with acid. The anomeric configurations of the sugar constituents were determined, where possible, on the basis of p.m.r. spectroscopy and optical rotation data. The results of these studies are consistent with a primary structure in which the repeating-unit is the doubly branched hexasaccharide.

Carbohydrate Sequence↗
PubMed1980

Mechanism of action of dietary fibre in the human colon.

Fibre, more than any other dietary component, affects human large bowel function, causing an increase in stool output, dilution of colonic contents, a faster rate of passage through the gut and changes in the colonic metabolism of minerals, nitrogen and bile acids. (Fibre here refers to 'dietary fibre', which comprises plant cell wall polysaccharides and lignin, and not to 'crude fibre'.) It is thought that these changes are brought about by fibre passing through the gut undigested and holding water within its cellular structure. Although the amount of water taken up in vitro varies for different types of fibre, this does not correlate in the expected way with the effects these materials have on colonic function. This is because fibre is extensively degraded in the gut, probably by the colonic microflora. Using a newly developed method modified from ruminant nutrition for isolating bacteria, we have shown that the main component of human faeces is bacteria. We have shown that the main component of human faeces is bacteria. We show here that the way in which two contrasting types of dietary fibre act in the colon depends on the extent to which they are digested. Cabbage fibre, which is extensively broken down, provides a readily usable substrate for the stimulation of microbial growth, whereas wheat fibre remains largely undigested and retains water in the gut lumen.

Body Water↗
PubMed1980

The microbial contribution to human faecal mass.

A method has been developed, based on techniques used for isolating bacteria from the rumen, that enables human faeces to be fractionated into three major components. The method requires repeated, vigorous agitation of a suspension of faecal solids with detergent, the use of a stomacher, and high-speed centrifugation. By this means the faecal microflora are separated from faecal dietary-fibre residues. These two components, with water-soluble material in the stool, comprise 98.3 +/- 0.9% of faecal solids. The purity of the microbial fraction was demonstrated by Gram and plant stains and by scanning electron microscopy. Microscopic counts of the bacteria in each fraction of the stool showed that the microbial fraction contained 95% of the total bacteria. Chemical analysis of the component sugars indicated 6-7% possible contamination by non-bacterial polysaccharides. The bacterial pellet was 6% nitrogen, and accounted for 60% of the total faecal nitrogen. When faeces from nine healthy subjects on a metabolically controlled British-type diet were studied, bacteria comprised 54.7 +/- 1.7% of the total solids, fibre 16.7 +/- 0.8% and soluble material 24.0 +/- 1.3%. Bacteria therefore represent a much larger proportion of the faecal mass than was previously thought.

Adult↗
PubMed1979

Structural studies on the capsular polysaccharide from Klebsiella serotype K64.

Partial hydrolysis with acid, methylation analysis (including uronic acid degradation), Smith degradation, and p.m.r. spectroscopy have been used to determine the primary structure of the capsular polysaccharide of Klebsiella serotype K64. The hexasaccharide repeating-unit, which also contains one O-acetyl substituent, comprises a 4)-alpha-D-GlcpA-(1 leads to 3)-alpha-D-Manp-(1 leads to 3)-beta-D-Glcp-(1 leads to 4)-alpha-D-Manp-(1 leads to chain with a 4,6-O-(1-carboxyethylidene)-beta-D-glucopyranosyl and an L-rhamnosyl group attached to the 4-linked D-mannosyl residue at 0-2 and 0-3, respectively.

Carbohydrate Sequence↗
PubMed1979

Water-holding by dietary fibre in vitro and its relationship to faecal output in man.

The in vitro water-holding properties of 17 dietary fibre preparations, mainly food materials, bulk laxatives, and gel-forming polysaccharides, have been measured. Water uptake was measured by a centrifugation technique and also by a new method using sacs of dialysis tubing containing the material, immersed in simulated gut contents. The centrifugation technique could not be applied to gel-forming polysaccharides but the methods gave broadly similar results for other materials (r=0.85). The gel-forming polysaccharides in general held more water than the food fibres. Studies of matched pairs of materials which differed only slightly in chemical composition suggested that the presence of charged groups on the molecule encouraged water uptake. In the food materials water uptake was related to uronic acid content (r=0.87). Materials ground to a smaller particle size increase their water holding but this effect was small (+28%). The hypothesis that dietary fibre increases faecal bulk by virtue of its ability to hold water was tested by comparing the in vitro water-holding capacity of eight of the fibres with the changes they had produced when fed to human volunteers under controlled conditions. Of these materials pectin had the greatest water-holding capacity (56.2 g water/g material) but produced the smallest change in faecal weight (19%), while bran had the lowest water-holding (4.2 g/g) and the largest faecal weight changes (117%). Overall an inverse relationship (r=0.88) between water-holding and faecal bulking was found, suggesting that dietary fibre does not exert its effect on faecal weight simply by retaining water in the gut.

Cathartics↗
PubMed1973

Proton magnetic resonance spectroscopy of Klebsiella capsular polysaccharides.

The presence of acetate and pyruvate groups in Klebsiella capsular polysaccharides may be demonstrated and estimated quantitatively by running the proton magnetic resonance spectrum of the polysaccharide (as sodium salt) in deuterium oxide at 95 C. Such spectra also permit an assessment to be made of the number of alpha- and beta-linkages in the repeat unit of the polysaccharide structure.

Acetates↗