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Biomedical subjects

R Bais

Publications and source records attributed to R Bais.

64 records · Page 4Linked to original sources
PubMed1980

The production of (14C) oxalate during the metabolism of (14C) carbohydrates in isolated rat hepatocytes.

Oxalate (14C) was produced during the metabolism of (U-14C) carbohydrates in hepatocytes isolated from normal rats. At 10 mM, the order of oxalate production was fructose > glycerol > xylitol > sorbitol greater than or equal to glucose in the ratio 10 : 4 : 3 : 1 : 1. This difference between oxalate production from fructose and glucose was reflected in their rates of utilisation, glucose being poorly metabolised in hepatocytes from fasted rats. Fructose was rapidly metabolised, producing glucose, lactate and pyruvate as the major metabolites. Glycerol, xylitol and sorbitol were metabolised at half the rate of fructose, the major metabolites being glucose, lactate and glycerophosphate. The marked similarity in the pattern of intermediary metabolites produced by these polyols was not, however, reflected in the rates of oxalate production. Hepatic polyol metabolism resulted in high levels of cytosolic NADH, as indicated by elevated lactate : pyruvate and glycerophosphate : dihydroxyacetone phosphate ratios. The artificial electron acceptor, phenazine methosulphate (PMS) stimulated oxalate production from the polyols, particularly xylitol. In the presence of PMS, the order of oxalate production was fructose greater than or equal to xylitol > glycerol > sorbitol in the ratio 10 : 10 : 6 : 2. The production of glucose, lactate and pyruvate from the polyols was also stimulated by PMS, whereas the general metabolism of fructose, including oxalate production, was little affected. Oxalate (14C) was produced from (1-14C), (2-14C) and (6-14C) but not (3,4-14C) glucose in hepatocytes isolated from non-fasted, pyridoxine-deficient rats. Whilst this labelling pattern is consistent with oxalate being produced by a number of pathways, it is suggested that metabolism via hydroxypyruvate is a major route for oxalate production from various carbohydrates, with perhaps the exception of xylitol, which appears to have an alternative mechanism for oxalate production. The observation that carbohydrates, particularly fructose, contribute to endogenous oxalate production lends support to the hypothesis that a high sucrose consumption contributes to the formation of renal oxalate stones in man.

Animals↗
PubMed1980

Some biochemical studies on the adaptation associated with xylitol ingestion in rats.

The mechanism of adaptation to dietary carbohydrates was investigated by examining cellular metabolism in the liver and gut lumen. The inclusion of 10% (w/w) glucose, fructose, sucrose, xylose, sorbitol, xylitol or arabitol in the diet of rats for 7 days had essentially no effect on the ability of liver homogenates to produce 14CO2 from labelled glucose, fructose, xylose, sorbitol or xylitol. Moreover, no major changes were observed in the activities of hepatic enzymes. In these studies, diarrhoea and caecal distension were only observed in those rats receiving dietary sugar alcohols. Rats were also fed 0, 2.5, 5, 10, and 20% (w/w) xylitol in their diets for periods ranging from 1 to 14 days. These diets caused no significant changes in 16 of the commonly assessed blood parameters which included liver function tests. Xylitol feeding, however, caused distension, caecal gas production, decreases in the pH of caecal contents, the appearance of a fluffy layer in the centrifuged specimens of caecal contents, and diarrhoea. These changes were directly related to the concentration of xylitol in the caecal contents. After various periods, and depending on the concentration of xylitol in the diet, the rats underwent an adaptation which reduced the incidence of diarrhoea. In the short term, dietary xylitol does not affect the function of the liver or the gut wall, but causes an adaptation within the gut microflora. This adaptation leads to the increased ability of gut microflora to utilise xylitol, followed by a subsequent reduction in the caecal osmotic load and diarrhoea.

Adaptation, Physiological↗
PubMed1980

The effect of dietary xylitol on the ability of rat caecal flora to metabolise xylitol.

The effect of dietary xylitol on the ability of the rat caecal flora to metabolise xylitol was investigated. Xylitol metabolism in micro-organisms has generally been assessed in terms of pH change and acid production which are often insensitive in demonstrating low rates of substrate utilisation. Using a rapid and sensitive radioisotopic assay, in which 14CO2 production from [U-14C] xylitol was measured, it was possible to show that the caecal microflora obtained from rats can metabolise xylitol. This activity was increased 10, 15, 30 and 40-fold in the caecal flora taken from rats fed diets containing 2.5,5,10 and 20% xylitol, respectively. Using the caecal microflora of normally fed rats, the order of 14CO2 production from 14C-labelled sugars and sugar alcohols was glucose greater than fructose greater than xylose greater than sorbitol greater than or equal to xylitol. The feeding of glucose and fructose did not alter the 14CO2 producing activities, whereas xylose feeding increased xylose metabolism, sorbitol feeding increased sorbitol and xylitol metabolism, xylitol feeding increased sorbitol, xylose and its own metabolism and arabitol feeding increased xylose and sorbitol metabolism. Marked changes were also observed in the population of the caecal flora of xylitol-fed rats, with increases in the number of gram-positive bacteria, compared to rats on a normal diet. Possible mechanisms for these effects involve mutation, selection of micro-organisms capable of metabolising sugar alcohols, and the induction of enzymes involved in sugar alcohol metabolism.

Adaptation, Physiological↗
PubMed1980

Increased creatine kinase activities associated with haemolysis.

The effect of haemolysis on creatine kinase activity has been investigated. The presence of adenylate kinase released from erythrocytes increases the apparent creatine kinase activity. This can be overcome by the addition of 10 mumol/l of diadenosine pentaphosphate to the reagents.

Adenine Nucleotides↗
PubMed1979

Oxalate excretion in rats injected with xylitol or glycollate: stimulation by phenobarbitone pre-treatment.

The hypothesis that the prior intake of barbiturates may predispose patients to form increased amounts of oxalate following the intravenous infusion of xylitol was investigated in the rat. Phenobarbitone pre-treatment resulted in a 2-3 fold increase in urinary [14C] oxalate concentration following the intraperitoneal injection of [U-14C] xylitol or [l -14C] glycollate. The absence of any marked changes in urine volumes and creatinine excretion implied that this increase in urinary oxalate excretion was due to the enhanced synthesis of oxalate. The activities of key enzymes in hepatic oxalate synthesis, glycollate oxidase, lactate dehydrogenase, catalase and alanine aminotransferase were not altered by phenobarbitone pre-treatment. It is suggested that the increased activity of the microsomal mixed function oxidases, following phenobarbitone treatment, may facilitate the oxidation of glycollate and possibly xylitol. This communication leads experimental support to the concept that the prior intake of drugs, such as barbiturates, may predispose patients to form increased amounts of oxalate.

Animals↗
PubMed1976

An optimized continuous-monitoring procedure for semiautomated determination of serum acid phosphatase activity.

A continuous-monitoring method for measuring acid phosphatase activity with alpha-naphthyl phosphate as the substrate was critically evaluated and modified. Using partially purified prostatic acid phosphatase, we show that certain conditions for the assay must be satisfied to ensure linearity. These conditions include maintaining the pH between 5.6 and 5.9 and the addition of detergent to sustain linearity. The results obtained with alpha-naphthyl phosphate have been compared with those obtained by using p-nitrophenyl phosphate as substrate. When used with an automatic rate analyzer, the modified method is as sensitive but more reproducible.

Acid Phosphatase↗