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W Tiemeyer

Publications and source records attributed to W Tiemeyer.

11 recordsLinked to original sources
PubMed1990

[Effect of purine-rich nutrients on weight gain, catabolites in blood plasma and the uric acid transport of erythrocytes--a model study in dogs].

In a nutritional tolerance study 36 young dogs were fed over 52 weeks high or low purine diets at an average paired feeding intake of 0.6 and 80 mg purine-N/MJ per day. The high purine diet resulted in a significant decrease of growth rate by -23% (Beagles) and -38% (Dalmatians) and of feed efficiency (-29 and -42%). The fasting levels of allantoin, uric acid and uracil in blood plasma were significantly increased. During the experiment a metabolic adaptation to the high purine diet decreased the plasma concentrations of uric acid, uracil and in part of allantoin. The high purine diet effected a significant increase of Km (2.5-fold) and of Vmax (1.6-fold) of uric transport through the erythrocyte membrane. The results documented disadvantageous effects of high purine nutrition during juvenile development.

Allantoin↗
PubMed1986

Uric acid uptake in erythrocytes of beagle and dalmatian dogs.

Uric acid uptake by erythrocytes of Beagle and Dalmatian dogs has been measured, using (2-14C) uric acid. Uptake was characterized by a fast and a slow component. Urate uptake was inhibited by certain purine and pyrimidine derivatives and by anion transport inhibitors. It was dependent on intraerythrocyte glycolysis. Temperature only influenced uptake by the slow component (Q10 = 2.6). Urate uptake by the slow component is apparently due to the transport into the erythrocytes by facilitated diffusion (Km = 6.6 mmol/l, Vmax = 390 mumol/l/min), whereas the fast component exhibits an adsorption of urate on erythrocyte surface. No difference of urate uptake by erythrocytes of Beagle and Dalmatian dogs has been observed.

Animals↗
PubMed1985

[Why Dalmatians excrete uric acid. Causes and consequences of a classical metabolic disorder].

After introducing into developmental aspects of "Dalmatian dog research" uric acid excretion is explained on the basis of new results by the loss of a specific transport system in liver cell membranes. Therefore, uricase which is present in normal activities is supplied only to a limited extent with uric acid for the transformation into the easily soluble allantoin. As indicated by feeding experiments, the plasma urate level is increased from about 32 mumol/l (no purine intake) up to 150-200 mumol/l at very high levels of purine intake. Thus, the influence of nutrition on plasma urate level is extraordinary. The diseases urate-urolithiasis and "bronze syndrome" associated with dalmatian urate metabolism are characterized in view of the typical pattern of the diseases and of the therapeutical and prophylactical measures to be taken.

Allantoin↗
PubMed1984

Defect of uric acid uptake in Dalmatian dog liver.

The uptake rate of uric acid into liver slices of the Dalmatian dog was found to be significantly lower compared with that in the beagle. Since there was no difference in the hepatic uricase activity between the two breeds, the abnormality of uric acid metabolism in the Dalmatian dog is considered to result from a defective hepatic transport system for uric acid.

Animals↗
PubMed1984

Active pyrimidine absorption by chicken colon.

Pyrimidine absorption by chicken large intestine was investigated employing the everted sac and flux chamber techniques. 3H-labelled uracil was used as substrate. The small intestine and the colon unlike the caecum, transported uracil from the mucosal to the serosal surface against a concentration gradient in the everted sac experiments. Furthermore, there was a net transport of uracil from the mucosal to the serosal side of the colon and jejunum in the flux chamber experiments. Uracil transport by the everted colon sacs against a concentration gradient was inhibited when the purine hypoxanthine was present in the incubation medium. Uracil transport by the everted colon sacs was also inhibited under anaerobic conditions and when 2,4-dinitrophenol was present in the incubation medium. Replacing the Na+ ions of the incubation medium by Li+ ions also caused an inhibition of uracil transport. It is concluded from these results that uracil (and probably other pyrimidines) are absorbed from the chicken colon by a Na+ ion-dependent active transport process having also an affinity for purines.

2,4-Dinitrophenol↗
PubMed1984

Metabolites of nucleic acids in bovine milk.

To investigate metabolites of nucleic acids in milk as by-products of protein biosynthesis, a method for determination of pyrimidine and purine compounds by reversed-phase high-pressure liquid chromatography was developed. Reproducibility of the measured compounds was 2%. Recovery of the main constituents averaged about 99%. In addition to orotic acid, allantoin, and uric acid, the free bases hypoxanthine, xanthine, and guanine, the ribonucleosides uridine, cytidine, and pseudouridine, and the ribonucleotides, guanosine 5'-monophosphate and cytidine 5'-monophosphate, were quantified in milk samples of Holstein-Friesian cows. Milk production from days 45 to 65 of lactation influenced concentrations of individual metabolites differently. Concentrations of orotic acid, allantoin, and uric acid decreased with increasing milk production, whereas concentrations of uridine, cytidine, pseudouridine, hypoxanthine, xanthine, and guanine remained unchanged. The results allowed conclusions on rate limiting steps of catabolic pathways of pyrimidines and purines and indicated relationships with protein biosynthesis. A possible role of metabolites of nucleic acids as taste factors and as substrates for milk microbes is suggested.

Allantoin↗
PubMed1982

Purine availability and metabolism in dogs fed single-cell protein or RNA.

For the evaluation of single-cell protein (SCP) the proportion of dietary purines made available by digestion and absorption was estimated with dogs (Dalmatian) in total urine collection experiments. The animals received a low purine control diet with 25% casein, diets with 25-100% replacement of casein by a bacterial SCP grown on methanol, and the control diet plus yeast RNA purine equivalent to SCP diet. Nucleic acids, bases, and purine metabolites were determined by reversed-phase high-pressure liquid chromatography. The quantitative influence of dietary purines (x) on renal purine excretion (y) was described by the equation (millimoles per day) y = 0.57x + 3.52 (r = 0.955) indicating the endogenous excretion rate of 3.5 mmol/day and the metabolic availability of 57% of ingested purines. As the ratio of urate to allantoin increased with purine intake, individual equations were established for both metabolites. On the control diet + RNA and SCP diet (100% replacement for casein), purine intakes of 20.0 and 18.2 mmol/day resulted in purine excretion values of 7.3 and 11.4 mmol/day (P less than 0.05). The proportion of free bases in the latter diet appeared as the main reason for this differences. Other influences are discussed.

Allantoin↗
PubMed1981

Active absorption of hypoxanthine by lamb jejunum in vitro.

The kinetics of [3H]hypoxanthine entry into lamb mid-jejunum were measured using 2-min mucosal exposures. Mucosal hypoxanthine uptake occurred by a Na+- and energy-dependent saturable mechanism indicating that a carrier-mediated active transport process is involved. Inhibitory measurements indicate that hypoxanthine, adenosine, uracil and thymine complete for a common entry mechanism. Adenine, uric acid, allantoin and thymidine produced no significant inhibition of hypoxanthine entry. In additional experiments hypoxanthine was transported against a high concentration gradient from the mucosal to the serosal side of everted sacs of mid-jejunum. Therefore hypoxanthine appears to be absorbed by active transport from the lamb jejunum.

Animals↗