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Biomedical subjects

U Borgmann

Publications and source records attributed to U Borgmann.

27 records · Page 2Linked to original sources
PubMed1989

Toxicity test procedures for Hyalella azteca, and chronic toxicity of cadmium and pentachlorophenol to H. azteca, Gammarus fasciatus, and Daphnia magna.

Survival, growth, and reproduction of Hyalella azteca were determined under various test conditions. Reproduction by a cohort begins when the amphipods are 5 to 6 weeks old, peaks at 8 to 12 weeks, and then declines due to continuing adult mortality. Full life-cycle tests can be completed in 12 to 14 weeks at 25 degrees C. Reproduction is poor when only artificial plastic substrate is provided. A substrate of cotton gauze results in dramatic improvements in both reproduction and growth. Better reproduction can be obtained by culturing the amphipods in some sediments, but this makes weekly enumeration difficult. Increased mortality during chronic exposure to cadmium was observed at 1 microgram/L for H. azteca and 3.2 micrograms/L for Gammarus fasciatus. Reproduction during longer exposure was not reduced at concentrations lower than those causing increased mortality within six weeks. Chronic toxicity of pentachlorophenol was observed at 100 micrograms/L for both species. Chronic toxicity to Daphnia magna was similar to that of the amphipods for cadmium, but lower for pentachlorophenol. Amphipods are at least as sensitive as Daphnia to a variety of toxicants during chronic exposure.

Animals↗
PubMed1985

Analytical capillary isotachophoresis: a routine technique for the analysis of lipoproteins and lipoprotein subfractions in whole serum.

A capillary isotachophoretic separation technique was developed for lipoproteins in native serum which, compared with previous electrophoretic techniques, has negligible molecular sieve effects, does not need gel casting, is suitable for whole serum and has a high discriminative power for lipoprotein subfractions. The technique is based on pre-staining whole serum lipoproteins for 30 min at 4 degrees C before separation of 0.5 microliter of the sample in a free-flow capillary system (0.5 mm I.D.) with discontinuous buffer system. In normolipidaemic sera, high-density (HDL) and low-density lipoproteins (VLDL) are separated into two major subpopulations according to their net electric mobility. The identification of these fractions was confirmed by substitution with ultracentrifugally isolated lipoproteins and by their complete absence from Tangier and abetalipoproteinaemic serum. Triglyceride-rich very low-density lipoproteins (VLDL) revealed a defined zone between the HDL and LDL subpopulations. Our preliminary results indicate that the separation of human whole serum lipoproteins by capillary isotachophoresis is a promising method for the determination of lipoprotein subfractions.

Abetalipoproteinemia↗
PubMed1976

Four-and five-step kinetic models of lactate dehydrogenase.

A five-step model for the reaction catalyzed by beef heart lactate dehydrogenase (EC 1.1.1.27) reconciles differences observed in the four-step model if pre-steady-state data in the forward direction are compared with similar data in the reverse direction. The relationship between the four-and five-step models indicates what problems can develop when an incomplete model is proposed. Nevertheless, there are advantages to using the less complicated four-step model when comparing the molecular kinetics of enzymes catalyzing the same reaction but obtained from different sources.

Animals↗
PubMed1975

A comparison of lactate dehydrogenase from an ectothermic and an endothermic animal.

Adaptation to environmental temperature is examined in beef heart, beef muscle, and flounder muscle lactate dehydrogenases (EC 1.1.1.27). Low temperature adaptation in the ectothermic (flounder) enzyme is indicated by a reduced enthalpy of activation for kcat (enzyme turnover number, s-1) and increased catalytic efficiency. Also, the reaction rate at low substrate concentrations has a maximum at a lower temperature than in the endothermic enzymes. This is a result of altered bonding in the enzyme-substrate complexes. Adaptation to higher temperatures in the endothermic (beef) enzymes is suggested by a decreased sensitivity to heat denaturation, especially in the presence of substrates. A direct correlation is found between the degree of bonding in the enzyme-substrate complexes and the decrease in rate of heat denaturation caused by addition of substrates.

Adaptation, Physiological↗
PubMed1975

Kinetics and thermodynamics of lactate dehydrogenases from beef heart, beef muscle, and flounder muscle.

The eight rate constants for a four-step ordered ternary-complex mechanism have been compared for lactate dehydrogenases (EC1.1.1.27) from three sources, beef heart, beef muscle, and flounder muscle. The rate constants were determined at temperatures ranging from 5 degrees C to 50 degrees C, and the corresponding activation parameters deltaG not equal to, deltaH not equal to, and deltaS not equal to were calculated. Significant differences are noted for the values for the three types of enzyme. The relative heights of the activation barriers are much the same in all three cases, differences in kinetic behavior resulting mainly from differences in the stable binary and ternary enzyme-substrate complexes. These complexes are, in general, at lower free-energy and enthalpy levels of the beef-heart and beef-muscle enzymes than for the flounder-muscle enzyme. A high degree of compensation is found between the enthalpies and entropies of activation, resulting in relatively small differences between the free energies (and rates) for homologous steps with different enzymes. Analysis of the results, on the assumption that the compensation effect is due to weak-bonding effects, suggests that there are fewer weak bonds in the stable complexes of the muscle enzymes.

Animals↗
PubMedDate not supplied

Chronic toxicity and bioaccumulation of 2,5,2',5'- and 3,4,3',4'-tetrachlorobiphenyl and Aroclor 1242 in the amphipod Hyalella azteca.

The addition of 100 micrograms/L of Aroclor 1242 (A1242) or 2,5,2',5'-tetrachlorobiphenyl (TeCB) during 10 week chronic toxicity tests with Hyalella azteca resulted in complete mortality. There were no effects on survival, growth, or reproduction after addition of 30 micrograms/L. Toxic effects were observed at tissue levels of between 30 and 180 micrograms/g on a wet weight basis, and tissue levels appear to be a better indicator of toxicity than levels in water. No toxic effects were observed after additions of up to 2,700 micrograms/L of the coplanar congener 3,4,3',4'-TeCB. H. azteca has the ability to avoid accumulating in excess of 140 micrograms/g 3,4,3',4'-TeCB. The amount taken up was proportional to the amount added in water up to 100 micrograms/L, but was constant at higher additions, possibly accounting for its relatively low toxicity. The low toxicity of the coplanar congener, as compared to the non-coplanar 2,5,2',5'-TeCB, is in direct contrast to the high toxicity of coplanar PCB congeners to mammals and may be associated with slower rates of aromatic hydrocarbon metabolism in amphipods. Polychlorinated biphenyl levels measured in amphipods from Lake Ontario are approximately 100-fold below levels associated with toxicity in H. azteca, but are above levels which, through biomagnification up the food chain, lead to salmonid residues in excess of 2 micrograms/g, a tolerance limit for human consumption.

Animals↗
PubMedDate not supplied

[Chorangioma of the placenta].

1. A 26-year-old secondgravida presented at 26 weeks' gestation with severe vaginal bleeding. A caesarean was performed which led to a 880 g female infant with multiple malformations (Wolf-Hirschhorn-Syndrome). It deceased short time later. 2. A 27-year-old second-gravida at 37 weeks' gestation delivered a 1520 g infant by caesarean which was made because of fetal asphyxia. In both cases investigation of the placenta showed capillary chorioangioma. Chorioangiomas are the most common tumors of the placenta. Occasionally they are associated with fetal anomalies and growth retardation. Depending on size complications during delivery must be considered.

Abnormalities, Multiple↗