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Biomedical subjects

R J Elliott

Publications and source records attributed to R J Elliott.

33 records · Page 2Linked to original sources
PubMed1990

Lysine requirements and whole-body protein turnover in growing pigs.

The influence on protein accretion and whole-body protein turnover of changing dietary protein quality while maintaining constant energy intake was studied by varying the degree of lysine supplementation of a lysine-deficient barley-based diet given to growing pigs. Measurements of nitrogen metabolism and whole-body protein turnover, using both classical and 15N end-product methods following a single dose of [15N]glycine, were made in 49-kg male pigs given diets containing 109 g lysine-deficient protein/kg supplemented to make them (1) 'deficient', (2) 'adequate' and (3) 'in excess' with respect to lysine. The 15N dose and protein intake values used to calculate amino N flux from the cumulative urinary excretion of 15N in urea and ammonia were corrected respectively for apparent digestibilities of [15N]glycine and total N determined in a separate experiment in pigs fitted with simple ileal cannulas. N retention and biological value were significantly increased by lysine supplementation of the deficient diet to the 'adequate' level, but were not further increased by the higher level of supplementation. Rates of growth paralleled these changes. The poorer biological value of the unsupplemented diet 1 was shown also in a significantly higher excretion of urea N compared with diets 2 and 3. N digestibility was not markedly influenced by the level of lysine supplementation. Both whole-body protein synthesis and degradation increased markedly on 'adequate' supplementation of the diet with lysine, but did not increase further with an excess of lysine. It is concluded that the increase in protein accretion rate observed on supplementation of the diet with lysine was due to a greater increase in the rate of protein synthesis than of degradation, rather than a decrease in degradation rate.

Animals↗
PubMed1989

Solvent interactions stabilising nucleic acid conformers.

The transition of oligonucleotides from the B to the A conformation has been studied by the use of simple geometric calculations aimed at finding possible hydration sites which could stabilize these conformations. The method involves the classification of equally spaced grid points, surrounding the oligonucleotide, into groups depending on whether a water molecule, so placed, could form single, multiple or nil contacts to polar oligonucleotide atoms. The occurrence of the multiple, and therefore bridging, sites is more extensive for the 'A' than the 'B' conformation. Thus, more general evidence is presented in support of the economy of hydration hypothesis in which phosphate groups, in the low humidity 'A' form, have been seen to be bridged by single water molecules. Similar calculations for the 'Z' DNA conformation show a different preference for multiple bridging sites.

DNA↗
PubMed1989

Solvent bridging sites in A- and B-DNA helices.

Nucleotide hydration is important for the understanding of the stability of and the transitions between the different helical conformations of DNA. We have used energy minimization and geometric criteria in order to look for possible sites for solvent which can bridge more than one polar or charged atomic group on a nucleotide. Such bridging sites between phosphate groups have been seen experimentally and used to explain the A to B transition. We show that these phosphate bridging sites occur at energy minima around A-DNA but do not occur around B-DNA. We also find that there are further low energy bridging sites which depend on sequence and which enable the more economical hydration of the A form.

Base Composition↗
PubMed1987

Ammonium ion representation in Monte Carlo simulations of biomolecular solutions.

Monte Carlo computer simulation techniques may be used to predict structural properties of solvent networks in helical fragments of nucleic acids, provided that suitable potential functions are available to describe the interactions between nucleic acid atoms, water and counterions. Previous studies have shown that simple non-bonded and point charge parameters are adequate for mononuclear ions such as sodium and calcium. In this study a model interaction potential for the polynuclear ammonium ion is evaluated. The parameters used take account of the distribution of charge over the constituent atoms in the ion. Simulations are carried out on the ammonium salt of a small nucleic acid crystal hydrate and a comparison is made between the predicted and experimental results. It is shown that the simulated structure is in reasonable agreement with experiment. It is therefore feasible to use this potential in studies of ammonium-containing bimolecular systems.

Computer Simulation↗
PubMed1987

Monte Carlo simulations of nucleotide crystal hydrates and their counter-ions.

A knowledge of structural and energetic aspects of water- and ion-nucleic acid interactions is essential for the understanding of the role of solvent and counterions in stabilising the various helical forms of nucleic acids. In this study, Monte Carlo computer simulation techniques have been used to predict structural properties of solvent networks in small nucleic acid crystal hydrates containing the ions sodium, ammonium and calcium. Appropriate parameters to describe the interaction potentials of the ions are added to those previously developed for water and nucleic acid atoms. A comparison is made between the predicted and experimental results and it is concluded that the potential functions used lead to simulated solvent structure in reasonable agreement with experimental data, at least in the cases of sodium and calcium. It is now feasible to use these functions in studies of hydration of larger helical fragments of nucleic acids of more direct biological interest.

Calcium↗
PubMed1986

Feeding frequency for lactating cows: effects on rumen fermentation and blood metabolites and hormones.

1. The present paper reports the effects on rumen fermentation and plasma metabolites and hormones of giving fixed rations of hay and high-cereal concentrates at different meal frequencies to lactating cows. In Expt 1 the total ration was given in two and twenty-four meals daily and in Expts 2-4 the concentrates were given in two and five or six meals and the hay in two meals daily. The diets contained 600-920 g concentrates/kg. 2. In Expt 1, minimum rumen pH was higher but mean pH was lower when cows were given their ration in twenty-four meals/d rather than two meals/d. 3. In all the experiments, the effects of increased meal frequency on the molar proportions of rumen volatile fatty acids (VFA) were small and not significant, although there was a general tendency for the proportion of acetic acid to increase and that of propionic acid to fall. Increasing the proportion of concentrates in the diet reduced the proportion of acetic acid and increased the proportions of propionic and n-valeric acids. 4. In Expt 3, more frequent feeding was found to reduce the concentration of non-esterified fatty acids in the blood, but changes in other metabolites were small and not significant. Increasing the proportion of concentrates in the diet reduced the concentrations of acetic acid and 3-hydroxybutyric acid and increased the concentrations of propionic acid and glucose. 5. The mean daily concentration of insulin in the blood was reduced by more frequent feeding of the higher-concentrate diet but not of the lower-concentrate diet. The concentration of glucagon also tended to fall with more frequent feeding. Increasing the proportion of concentrates in the diet increased the concentration of insulin. 6. More frequent feeding reduced the depression in milk-fat concentration caused by feeding the low-roughage diets. About three-quarters of the variation in milk-fat concentration could be related to changes in rumen VFA proportions, but the relations for the two meal frequencies had different intercepts although similar curves. The results suggest that milk-fat depression on low-roughage diets with twice-daily feeding was due to a change in rumen VFA proportions accompanied by elevated plasma insulin concentrations. The improvement in milk-fat concentration due to more frequent feeding could be explained partly by the small change in rumen VFA proportions and partly by a reduction in mean plasma insulin concentrations, but these mechanisms did not fully account for the milk-fat responses observed.

Animals↗
PubMed1985

Gastric emptying of barley-soya-bean diets in the pig: effects of feeding level, supplementary maize oil, sucrose or cellulose, and water intake.

A technique for measuring gastric emptying in growing pigs by complete removal of digesta through a gastric cannula is described. Four pigs were fitted with gastric cannulas and each was used in three trials. The effects of level of feeding (trial 1), cellulose (C), maize-oil (MO) or sucrose (SU) supplementation (trial 2) and the level of water intake (trial 3) on gastric emptying of digesta, dry matter (DM) and nitrogen from a barley-weatings-soya-bean (B) diet were measured during 4 h after the morning feed. In trial 1, pigs were given 0.66, 0.83, 1.00 or 1.17 times their standard level of feeding. As the level of feeding rose, so the weight of digesta, DM and N emptied in the first hour after feeding increased. This trend continued to some extent in the second hour, but no effects of level of feeding were seen in the third and fourth hours. In trial 2, maize-oil addition to the diet significantly reduced the gastric-emptying rate of DM in the second hour after feeding, compared with the rates for diet C. The rate of N emptying was significantly slower for diets MO and SU than for diet C. In trial 3 there were no significant effects of water intake level (1.75, 2.50 and 3.25 times the weight of diet) on the rate of DM or N emptying from the stomach. The rate of digesta (and thus of water) emptying in the first hour after feeding increased significantly as the water intake rose. It was concluded that because the pattern of gastric emptying was very similar despite large differences in nutritional inputs, an important property of the process appeared to be resilience.

Animals↗
PubMed1979

Changes with age in the glycosaminoglycans of human articular cartilage.

Human articular cartilage was obtained post mortem from the lateral femoral condyles of 30 subjects aged from under 1 to 70 years. Cryostat sections taken 0--100 micrometers and 900--100 micrometers deep to the cartilage surface were exhaustively extracted to recover the glycosaminoglycans (GAG). After fractionation by cellulose acetate electrophoresis and enzyme depolymerisation individual GAG were determined by alcian blue -0.05 M MgCl2 and disaccharide microassay procedures. Changes with age were observed in GAG concentration and in the proportion of individual GAG. Large alterations occurred during the period of skeletal growth (0--16y). At birth GAG formed about 50% of the dry weight of cartilage, a value that decreased to about 15% in adult cartilage. Chondroitin sulphates (ChS) formed the principal GAG of articular cartilage and accounted for almost all of the GAG of the infant material. The ChS decreased with age and were partially replaced by keratan sulphate (KS), so the KS eventually comprised 12% of the GAG. Hyaluronic acid (HA) was identified and was found to increase linearly with age to form 6% by weight of the cartilage GAG by 60y.

Adolescent↗
PubMed1977

The micro-assay of the disaccharide isomers of chondroitin sulphate.

Connective tissue extracts containing the 4- and 6-sulphated isomers of chondroitin sulphate can be measured at the microgram level (approximately 10 microgram) using colorimetric assays. The chondroitin sulphates are depolymerised to disaccharides using chondroitin ABC lyase (EC 4.2.2.4). The 4- and 6-sulphated disaccharides after treatment with acid periodate are determined using a thiobarbituric acid procedure. An alkaline borate p-dimethylaminobenzaldehyde reaction is used to measure 6-sulphated disaccharide, the 4-sulphated disaccharide not forming a chromogen. Unsulphated disaccharide causes interference in both assays and if present is separated prior to assay using paper electrophoresis fractionation.

Chondroitin↗