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Biomedical subjects

I T Johnson

Publications and source records attributed to I T Johnson.

At least 91 records · Page 5Linked to original sources
PubMed1988

Intestinal microflora and gastrointestinal adaptation in the rat in response to non-digestible dietary polysaccharides.

1. A comparison was made of the effect of a fibre-free diet and diets containing non-digestible polysaccharides on rat caecal and colonic physiology and microflora. 2. All polysaccharide-containing diets led to enlargement of the caecum and colon, associated with increased weight of contents, and of tissue. Carboxymethylcellulose (CMC) had the most marked effect and animals given this also had watery faeces. 3. The density of bacteria in the caecum and colon varied significantly with diet and the proportion of aerobic bacteria in the flora was increased by the CMC diet. 4. In vitro, CMC and hydroxypropylmethylcellulose were poorly fermented. 5. There was a high correlation (caecum r 0.93; colon r 0.94) between tissue weight and wet weight of organ contents but no correlation with bacterial density, number of bacteria per organ, moisture content or short-chain fatty acid content. 6. It is concluded that caecal and colonic enlargement is due to tissue hypertrophy in response to increased bulk of contents, irrespective of the nature of that bulk which varies with diet; it is unlikely that short-chain fatty acids or other microbial metabolites are the stimulus for the trophic response seen when non-digestible dietary polysaccharides are fed to rats.

Adaptation, Physiological↗
PubMed1988

Plasma enteroglucagon and small bowel cytokinetics in rats fed soluble nonstarch polysaccharides.

The influence of dietary fiber on plasma glucagon and enteroglucagon (EG) and on ileal crypt cell production rate (CCPR) was assessed in the rat. A fiber-free semisynthetic diet and diets containing insoluble cellulose, Na-carboxymethylcellulose (CMC), guar gum, pectin, gum arabic, methylcellulose (MC), and hydroxypropylmethylcellulose (HPMC) at 10 g/100 g were fed for 14 d. Animals given soluble polysaccharides had plasma EG levels significantly higher than animals given insoluble cellulose, but only those fed the most viscous gums showed evidence of increased mucosal cell proliferation in the distal ileum. It was concluded that viscous nonfermentable polysaccharide gums stimulate the release of EG in the rat by slowing the absorption of nutrient, whereas the nonviscous polysaccharide gum arabic, or its breakdown products, probably directly stimulate mucosal endocrine cells. The failure of gum arabic to stimulate CCPR despite increased plasma EG indicated that EG alone is not a sufficient stimulus for increased mucosal cell proliferation.

Animals↗
PubMed1988

Interactions between hemolytic saponins, bile salts and small intestinal mucosa in the rat.

The interaction between bile salts and saponins from Gypsophylla was investigated in vitro, using changes in transmural potential difference across isolated lengths of rat jejunum as an index of the capacity of the saponin to affect the permeability of intestinal mucosal cells. The addition of saponin (ca. 5 mM) to taurocholic acid in buffered saline (pH 7.4) led to a significant increase in viscosity, indicating the formation of a polymer. The viscosity of the solution was highest at low molar ratios of bile salt to saponin (0.5-2.0). Under these conditions there was an inhibition of the permeating effect of saponins on the gut, as judged by the rate of decline in transmural PD. There was no evidence of inflammation or functional damage to the jejunal mucosa of rats fed a diet containing Gypsophylla saponin (ca. 1.5% w/w) for 7 d but changes in villus morphology were observed. There was also evidence of an increased rate of mucosal cell proliferation. Serum cholesterol levels were significantly lower in saponin-fed rats than in controls, while the cholesterol content of the cecal contents was increased. These results suggest that despite the protective effect of bile salts, Gypsophylla saponins interact with the mucosa of the proximal small intestine in vivo, but at the dietary level used in this study the mucosa was protected by an enhanced rate of cell replacement. The loss of cholesterol via exfoliated mucosal cells may contribute to the hypocholesterolemic effect of saponins in rats.

Animals↗
PubMed1988

Do viscous polysaccharides slow absorption by inhibiting diffusion or convection?

Viscous polysaccharides such as guar gum delay absorption probably by impairing the access of luminal contents to the absorptive epithelium. Measurements of the electrical resistivity of saline solutions were carried out to determine if guar gum (0.5, 0.75 and 1 per cent w/v), in concentrations which impaired absorption in vitro, delayed diffusion of solutes or inhibited convection of luminal contents. Our results indicated that guar had no effect on the mobility of ions in a completely unstirred solution but delayed the time taken for saline solutions of different resistivity to achieve complete mixing, when they were brought into contact inside a vessel, which was rotated at a constant speed. The time taken to achieve complete mixing was directly related to the viscosity of the guar solutions. The effect of intestinal contraction on the absorption of glucose was simulated in an in vitro model, consisting of a length of dialysis tubing, alternately contracted at each end. Movement of glucose out of the dialysis tubing was increased by increasing the rate of contraction. The incorporation of guar gum into the solution prevented the rise in glucose uptake produced by increasing the rate of contraction. These effects suggest that guar probably reduces absorption by resisting the convective effects of intestinal contractions.

Dietary Fiber↗
PubMed1987

In vitro estimation of iron availability from a range of plant foods: influence of phytate, ascorbate and citrate.

Plant foods were digested in vitro and the proportion of iron which diffused across a semi-permeable membrane was used as an index of Fe availability. The mean (with SEM) Fe diffusibility from a group of eighteen cereals, legumes and nuts was very low, 2.1 (0.25)%, whereas from a group of sixteen fruits and vegetables it was high, 31.7 (1.09)%. The difference between the two food groups was highly significant (P less than 0.001). The results for Fe diffusibility correlated well with literature values for the in vivo absorption of Fe from similar foods (r0.84, P less than 0.01). When phytate, citrate and ascorbate were added to selected foods in amounts corresponding to endogenous levels, only phytate and citrate gave the expected effects on Fe diffusibility. Ascorbate only enhanced Fe diffusibility to the expected extent when it was added in much larger amounts, not normally found in foods. When added to cereal foods, orange juice was found to enhance greatly Fe diffusibility even when its content of ascorbate was completely destroyed by boiling followed by prolonged storage. When citrate and ascorbate were added to cereal foods in amounts equivalent to those found in fresh orange juice, both enhanced Fe diffusibility but citrate was far more effective. It is concluded that phytate is a major inhibitor of Fe diffusibility in cereals, legumes and nuts. However, citrate rather than ascorbate would appear to be the major enhancer of Fe diffusibility from many fruits and vegetables. The implications of the present results are discussed in relation to the relative influence of phytate, citrate and ascorbate on dietary Fe availability.

Ascorbic Acid↗
PubMed1987

The effect of prolonged dietary supplementation with guar gum on subsequent iron absorption and retention in rats.

The effect of prolonged consumption of guar gum on iron absorption and Fe status was investigated in rats. Experiments with closed loops of duodenum, isolated in situ, were designed to reveal changes in the short-term regulation of duodenal Fe uptake, induced by challenge with low- and high-Fe meals. In separate experiments, the effect of guar gum on the capacity of intact rats to maintain Fe status and to absorb Fe from a test-meal was investigated. Male Wistar rats were given either a control, semi-synthetic diet (C) for 21 d or a similar diet containing 100 g guar gum (G)/kg for 27 d. Both diets contained 36 mg Fe/kg. Two subgroups were then challenged with meals containing low-Fe (8 mg/kg) or high-Fe (566 mg/kg), while a third subgroup received a meal of the control diet (36 mg Fe/kg). At intervals of 12, 36, 60 and 84 h after the dietary challenge, the uptake of [59Fe]ferric citrate was measured using closed duodenal loops in situ. All G-supplemented animals absorbed less Fe than their C-fed counterparts. Within group C, animals given the high-Fe challenge had lower absorptions 12, 36 and 60 h later, compared with those given the maintenance diet, whilst those given the low-Fe meal showed much increased uptake 12 and 36 h later. The latter effect was virtually abolished by guar gum. In the second experiment, male Wistar rats were fed on the C or G diets containing 8, 15, 20, 26 or 36 mg Fe/kg for approximately 10 weeks ad lib.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

The effect of dietary protein source and guar gum on gastrointestinal growth and enteroglucagon secretion in the rat.

1. Male Wistar rats (approximately 100 g) were given fibre-free semi-synthetic diets containing either casein or albumin (168 g/kg diet) as the protein source with or without guar gum (75 g/kg diet) (casein, albumin, casein guar gum and albumin-guar gum groups). 2. Small intestinal length, weights of caecal tissue and contents and plasma enteroglucagon concentration were significantly increased in guar-gum-fed animals compared with the fibre-free groups. 3. Total caecal weight and plasma enteroglucagon concentration were higher in the albumin-guar gum group compared with the casein-guar gum group. The weights of caecal tissue and contents were significantly increased in rats given the fibre-free albumin diet compared with those consuming a similar diet with casein as the protein source, although daily food intake tended to be lower. 4. It is concluded that the effect of materials classed as dietary fibre may be significantly influenced by the non-polysaccharide component of the diet, and that such interactions may influence both the growth and endocrine activity of the gastrointestinal tract.

Albumins↗
PubMed1987

The chemistry and biological significance of saponins in foods and feedingstuffs.

Saponins occur widely in plant species and exhibit a range of biological properties, both beneficial and deleterious. This review, which covers the literature to mid 1986, is concerned with their occurrence in plants and their effects when consumed by animals and man. After a short discussion on the nature, occurrence, and biosynthesis of saponins, during which the distinction between steroidal and triterpenoid saponins is made, the structures of saponins which have been identified in a variety of plants used as human foods, animal feedingstuffs, herbs, and flavorings are described. Many of these compounds have been characterized only during the last 2 decades, and modern techniques of isolation, purification, and structural elucidation are discussed. Particular consideration is given to mild chemical and enzymatic methods of hydrolysis and to recent developments in the application of NMR and soft ionization MS techniques to structural elucidation. Methods currently used for the quantitative analysis of saponins, sapogenols, and glycoalkaloids are critically considered; advances in the use of newer methods being emphasized. The levels of saponins in a variety of foods and food plants are discussed in the context of the methods used and factors affecting these levels, including genetic origin, agronomic, and processing variables, are indicated. Critical consideration is given to the biological effects of saponins in food which are very varied and dependent upon both the amount and chemical structure of the individual compounds. The properties considered include membranolytic effects, toxic and fungitoxic effects, adverse effects on animal growth and performance, and the important hypocholesterolemic effect. A final section deals briefly with the pharmacological effects of saponins from ginseng, since use of this plant is increasing in certain sections of western society as well as being traditional in the Orient.

Animals↗
PubMed1987

Viscosity of food gums determined in vitro related to their hypoglycemic actions.

Experiments were carried out in vitro and in normal human subjects to evaluate alternative food-grade viscous polysaccharides as agents for reducing postprandial hyperglycemia and to assess the relationship between the in vitro and in vivo performance of the polysaccharides. A 1:1 mixture of xanthan and locust bean gum (X/LBG) had the greatest viscosity at equivalent concentrations and shear rates and was more effective than guar gum, xanthan, or locust-bean gum at inhibiting glucose movement in vitro. It was not, however, more efficient in lowering postprandial blood glucose and plasma insulin in human subjects when incorporated in a drink containing 50 g glucose. When the different gums were acidified and reneutralized to mimic conditions in the gut, there was a better correlation between viscosity and blood glucose and plasma insulin levels. This effect may explain why X/LBG was no more effective than the other gums in reducing postprandial hyperglycemia in man.

Adolescent↗
PubMed1987

Food energy values of dietary fibre components and decreased deposition of body fat.

The effects of guar gum (GG) and solka floc cellulose (SF) on food intake, stomach emptying and body fat deposition in rats were assessed together with their food energy values. Voluntary food intake in meal-fed rats (ca 100 g, male Wistar kept at 21C) was depressed initially by 40 per cent on adding 10 g GG to 100 g fibre free (FF) semisynthetic diet. This effect was not sustained, intake doubling within 15 d. Similar effects were not observed with SF. In pair-fed animals neither GG nor SF affected the rate of stomach emptying after 28 days. Digestible energy (DE) intake per rat over the 28 days was GG diet = 4616, SF diet = 4410, FF diet = 4373 kJ but body fat was lower in GG (25%) and SF (16%) fed rats than in FF fed rats. The calculated DE values of the fibre components were 10.1 kJ/g GG and 1.5 kJ/g SF (sem 1 kJ/g). After including body fat into the equations for metabolizable energy, the energy values were -7.1 kJ/g GG and -4.8 kJ/g SF (sem 2 kJ/g). This is equivalent to an increased energy expenditure of 17.2 kJ/g GG and 6.3 kJ/g SF. For GG an increased intestinal mucosal mass and cell turnover explains part of the apparent increase in energy demand. Our overall conclusion is that under certain circumstances and with regard to fat deposition some fibre components can be attributed negative energy values.

Adipose Tissue↗
PubMed1986

Hexose absorption from jejunal loops in situ in zinc-deficient and Zn-supplemented rats.

1. Immature, male Wistar rats were given a low-zinc semi-synthetic diet (2 mg Zn/kg) for 22-28 d. Control groups received a similar diet supplemented with 58 mg Zn/kg either ad lib., or in amounts matched to the consumption of the Zn-deficient group. There was a rapid onset of reduced food consumption and growth retardation in the Zn-depleted animals. 2. Serosal surface area of small intestines taken from Zn-deficient rats was significantly reduced compared with that of control animals. Villi, dissected from samples of proximal jejunum, were markedly smaller than those of control rats and were present in greater numbers per unit area of serosa. 3. Luminal loss of galactose from jejunal loops in situ was significantly greater in the Zn-deficient rats compared with controls when expressed in terms of unit dry weight of intestine and serosal or villous surface area. Since only a small proportion of the total galactose remained in the mucosal tissue and associated extracellular space, this loss could only be accounted for by an increased efficiency of net trans-epithelial transport. Differences in total galactose absorption per unit length of jejunum were not so marked. 4. This intestinal adaptation to Zn-deficiency allows the maintenance of normal, and possibly increased, rates of hexose transfer into the body of animals exhibiting severe growth retardation, reduced food utilization and abnormal glucose metabolism.

Animals↗
PubMed1986

Gastrointestinal adaptation in response to soluble non-available polysaccharides in the rat.

1. Rats were fed on a control semi-synthetic diet containing insoluble cellulose (Solkafloc; 100 g/kg; control group) as the only source of dietary fibre, or on one of two test diets containing the same quantity of either guar gum or carboxymethylcellulose (CMC). Animals in the test groups showed similar growth rates and food intakes, which were significantly lower than those of the control group. The CMC group produced frequent poorly formed faeces throughout the 21 d feeding period. 2. The small intestines of animals in both test groups were significantly longer than those of the control group at the end of the study. The caeca were also enlarged and heavier, particularly in the CMC-fed group. 3. The rate of production of mucosal cells was increased in the small and large intestines of both test groups. The CMC-fed group exhibited a particularly high rate in the distal ileum, where the rate of cell divisions per crypt was over three times greater than at the same site in the control group. The increased proliferation was associated with a significant lengthening of the crypts and an approximately 25% increase in the basal width of the villi. 4. Mucosal alkaline phosphatase (EC 3.1.3.1) and lactase (EC 3.2.1.23) levels were lower than those of the control group at proximal and distal sites in the small intestines of both CMC- and guar-gum-fed groups. Altered spatial distributions of maltase (EC 3.2.1.20) and sucrase (EC 3.2.1.48) activities were also observed in these animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1986

Intestinal microflora, morphology and enzyme activity in zinc-deficient and Zn-supplemented rats.

1. Immature, male Wistar rats were given a low-zinc diet (2 mg/kg) for 22-24 d. Control groups received a similar diet supplemented with 58 mg Zn/kg either ad lib., or in amounts matched to the consumption of the Zn-deficient group. Food consumption, rate of growth and food conversion efficiency were markedly lower in the Zn-deficient group of rats compared with controls. Appetite, growth rate and food utilization improved dramatically over a subsequent 4 d period of Zn supplementation. 2. Morphological examination of samples of jejunum and ileum confirmed that Zn deficiency in the rat is accompanied by a reduction in villous dimensions and increase in villous density. After a short period of Zn supplementation, villous density and the basal width and maximum height of individual villi in the jejunum returned to normal. Similar changes occurred in the ileum but to a lesser extent. 3. Mucosal alkaline phosphatase (EC 3.1.3.1) activity was significantly lower in the small intestine of Zn-deficient rats compared with Zn-supplemented rats. Disaccharidase activities were lower in the Zn-deficient group, compared with their feed-restricted counterparts, but were similar to values for ad lib.-fed controls. Tissue alkaline phosphatase and disaccharidase activities were consistently higher after a 4 d period of Zn supplementation, compared with non-supplemented animals, but this increase was only significant for alkaline phosphatase. 4. Although there were striking similarities in the mucosal characteristics of gnotobiotic and Zn-deficient rats, there was no indication that even severe dietary Zn depletion reduced the numbers of viable bacteria present in either the small or large intestine.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkaline Phosphatase↗
PubMed1986

Influence of saponins on gut permeability and active nutrient transport in vitro.

The influence of four saponins, three triterpenoid glycosides and one steroidal amine glycoside, upon intestinal transport was investigated in vitro. In the presence of Gypsophylla saponin, carrier-mediated galactose transport was inhibited, although the uptake of the passively transported L-isomer of glucose increased. The uptake of the extracellular space marker, polyethylene glycol 4000, was also higher, indicating that the saponin inhibited active transport by increasing the general permeability of the enterocytes. Gypsophylla saponin, in contact only with the mucosal surface of everted jejunal sacs, induced a rapid decline in glucose-stimulated transmural potential difference. The rate of decline increased as the saponin concentration was raised over the approximate range of 0.3 to 8 mM. Saponaria saponin and alpha-tomatine also reduced transmural potential difference, but soya saponins were much less effective. The results indicate that some saponins readily increase the permeability of the small intestinal mucosal cells, thereby inhibiting active nutrient transport, and facilitating the uptake of materials to which the gut would normally be impermeable.

Animals↗
PubMed1985

Differences in intestinal protein synthesis and cellular proliferation in well-nourished rats consuming conventional laboratory diets.

Male Wistar rats (100 g) were given a commercial pellet feed or a semi-synthetic diet ad lib. Although the pellet-fed group grew slightly faster than the other group during the early part of the feeding period, there was no significantly difference between the final weights of the groups. The fractional rates of protein synthesis in jejunum, proximal ileum and liver were measured by a technique based on the determination of L-[4-3H]phenylalanine incorporation over a short time period. Protein synthesis was higher in both jejunum and ileum of the pellet-fed rats compared with those eating the semi-synthetic diet, but there was no difference between the rates of protein synthesis measured in the livers of the groups. The rate of mucosal cell division was significantly faster in the ileal mucosa of the pellet-fed group compared with the other group, and there were significant differences in some aspects of mucosal morphology. The maintenance of higher rates of cell turnover and protein synthesis in animals given a commercial pellet feed is unexplained, but it may be related to the presence of non-absorbable polysaccharides or other complex plant materials in the pellet feed.

Animal Feed↗
PubMed1985

Intestinal cellular proliferation and protein synthesis in zinc-deficient rats.

Immature male Wistar rats were given a low-zinc semi-synthetic diet (2 mg Zn/kg) for 28 d. Control groups received a similar diet supplemented with 58 mg Zn/kg either ad lib. or in amounts matched to the consumption of the Zn-deficient group. Rates of growth, food consumption and small intestinal length were significantly reduced in the Zn-depleted rats. Zn deficiency in the rat was associated with a reduction in the ratio, crypt: villus and a lower rate of crypt cell division in the jejunum. This resulted in a substantial decrease in the net influx of new cells into the villi of the Zn-deficient animals compared with controls. The fractional rates of protein synthesis in jejunal mucosa were measured by a technique based on the determination of L-[4-3H]phenylalanine incorporation. There was no evidence of a decline in the protein synthetic rate in total mucosa from Zn-deficient rats. It is suggested that a reduction in cell influx into the villi may be responsible for the morphological and functional changes observed in the small intestine of rats fed on a low-Zn diet.

Animals↗