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Biomedical subjects

W Burkart

Publications and source records attributed to W Burkart.

At least 73 records · Page 4Linked to original sources
PubMed1985

Main sources of indoor radon in the Swiss Central Alps.

To estimate the amount of radon gas transferred from the water to the indoor atmosphere of dwellings in the Swiss Central Alps, the radon concentrations of tap water of about 50 public water supplies were analysed. The radon levels of water in alpine communities fit a lognormal distribution with a geometric mean of 26.5 Bq/1 and a geometric standard deviation of 3.15. Radon monitoring in typical homes in the Swiss Midland revealed a significant influence of wind velocity and temperature difference indoor/outdoor on the indoor radon-daughter levels during the winter period.

Environmental Exposure↗
PubMed1985

[Significance of hormones in the amniotic fluid. II. STH and corticoids].

We measured the concentrations of growth hormone and corticosteroids in the amniotic fluid of 50 pregnant diabetic women between the 33rd and 36th week of gestation. These values were compared with normal values obtained by amniocentesis in 275 healthy patients. In the amniotic fluid the concentration of growth hormone decreases during pregnancy. Between the 12th and 16th week we measured 50 ng/ml, whereas in the last four weeks we found 30 ng/ml. In the diabetic patient the amniotic fluid content of STH is lower; however, hyperinsulinaemia of the foetus does not further decrease the concentration of growth hormone. The corticosteroid concentration in the amniotic fluid increases from 10 ng/ml in the 4th month of pregnancy to 35 ng/ml at the end of pregnancy. In diabetic patients we found lower cortisol concentrations; the concentration decreased further in the case of major symptoms of diabetic foetopathy in the newborn. We believe that low corticoid concentration in the amniotic fluid of the diabetic mother may be responsible for the respiratory distress syndrome in the newborn.

Adrenal Cortex Hormones↗
PubMed1984

[Significance of hormones in the amniotic fluid. 1. Insulin and C-peptide].

Samples of amniotic fluid of 275 healthy women were used to establish a standard profile of amniotic fluid insulin and C-peptide concentrations versus gestational age. The reasons for amniocentesis were: exclusion of chromosomal defects, rhesus immunisation, and determination of the L/S ratio. The concentrations of both peptides which were measured in the amniotic fluid in diabetics were compared with the normal profile. We found that long-term blood glucose control as estimated by the concentration of glycosylated haemoglobins in maternal blood is not well correlated with amniotic fluid insulin or C-peptide, respectively. In a few cases with poor metabolic control, we found normal insulin values, and vice versa. Since elevated insulin and C-Peptide levels in amniotic fluid correlate well with diabetic foetopathy, we conclude that measurement of both peptides provides a useful parameter in the management of a diabetic pregnancy.

Amniocentesis↗
PubMed1984

[Children of diabetic mothers].

In the past years several aspects of the diabetogenic fetopathia (e.g. macrosomia, hypoglycemia, cardiomyopathy) have changed. Strict metabolic control of pregnant women approaching normoglycemia and normal fetal insulinemia was followed by a decline in perinatal mortality and morbidity. However, the incidence of congenital malformations (6-8%) remained unchanged. Only normoglycemia before conception and within the first weeks of gestation will reduce this high incidence.

Birth Weight↗
PubMed1983

Curium excretion studies in man and baboon: a predictive animal model.

A major rationale for performing metabolic research in laboratory animals is to obtain useful information which is applicable to man. Since it is usually impossible to determine many of the kinetic parameters which are responsible for the fate of a contaminant in inadvertently-exposed individuals, it is essential that well-controlled laboratory experimentation in animals be performed. In the present case, we will demonstrate how our experimental protocol, i.e. curium in the adult baboon, can provide a model from which to derive important characteristics of curium in man. To accomplish this goal, we have compared the retention and excretion patterns of curium in several men accidentally exposed via inhalation, burns, or puncture wounds with that of 243,244Cm citrate injected i.v. in nine adult baboons. Although many of the exposure conditions are different in considering the two primate species (human and non-human), biokinetic research in the baboon may serve to estimate tissue burdens and dose commitments in man. Comparison of the excretion rates of the nuclide in the urine of man and the baboon gives similar half times between days 10 and 50 post exposure.

Animals↗
PubMed1981

The contribution of the calcium-dependent interaction of aggregation factor molecules to recognition: a system providing additional specificity forces?

Cells from the sponge Microciona prolifera display on their surfaces large but defined proteoglycan complexes (Microciona aggregation factor = MAF) that mediate species-specific cell aggregation by a process requiring high calcium ion concentrations. An analysis of MAF-MAF interactions based on binding studies of MAF to glutaraldehyde-fixed sponge cells and MAF-derivatized beads demonstrates that the requirement for high calcium concentrations can be overcome by extremely small amounts of certain polycations such as polybrene, polylysine, or histones. For measurements of the affinity of these substances of MAF, a method was adopted that partitions 125I-labeled MAF between dextran and polyethyleneglycol in an aqueous two-phase polymer system depending on the net charge of the complex formed. Since only polymers of positive charges affect binding and partitioning at low concentrations, large areas of interaction similar to those found in glycosaminoglycans are proposed for MAF. Through a multitude of appropriately spaced interaction sites, the rather weak selectivity of single charged sites could in such a system still provide strong enough specificities to explain species-specific cell sorting. The biological significance of naturally occurring polycations as well as extracellular calcium includes their role in cell recognition, sorting out as well as the ordered and continual streaming movements of groups of cells seen in the mesohyl of live sponges.

Animals↗
PubMed1980

Hereditary motor endplate disease (med) of the mouse: observations on dissociated myogenic cells and their development in culture.

Myogenic cells from mice homozygous for the lethal mutation "motor endplate disease" (med/med) were grown in culture. Like muscle cells taken from wild type (+/?) litter mates they fused to form myotubes which contracted, developed cross striations, and exposed acetylcholine receptors (AChR) on their surface. However, a decrease of 30% in the number of mononucleated cells per unit fresh weight of muscle was observed as early as 2--3 days postnatal, i.e., at least one week prior to the onset of physiological symptoms. Hence, in addition to influencing the functional maintenance of motor endplates, the med gene seems to control early events in muscle development.

Animals↗
PubMed1980

Fluorescent antibody localization of Microciona prolifera aggregation factor and its baseplate component.

Specific rabbit antisera were prepared against purified aggregation factor and its membrane-associated receptor, baseplate, derived from the marine sponge. Microciona prolifera. They were utilized in conjunction with fluorescent-labeled goat anti-rabbit IgG in an assay to demonstrate the surface localizations of both components. The specificity of antibody preparations for AF and BP was demonstrated through inhibition of the rotation-mediated assay by homotypic antibody. This study confirms the presence of aggregation factor on the surface of disaggregated sponge cells maintained in the presence of the divalent cations, Ca++ and Mg++, and its absence when cells are maintained in Ca++ and Mg++-free seawater. The location of BP could also be demonstrated on the cell surface. Aggregation factors and baseplate appear to be heavily distributed on archeocytes and choanocytes, but are localized less intensely on gray cells. Gray cells are typified by yellowish autofluorescence of their intracellular granules in stained and control preparations. The reaction of anti-Microciona aggregation factor with its homotypic factor appeared to be species specificity judged by immunofluorescence assays and by inhibition of rotation-mediated assay by anti-homotypic AF since antibodies prepared against heterotypic AF preparations were unreactive.

Animals↗
PubMed1979

Choline acetyltransferase induction in cultured neurons: dissociated spinal cord cells are dependent on muscle cells, organotypic explants are not.

The dependence of the induction of choline acetyltransferase (CAT) on the type of tissue culture, monolayer or piece explants, of spinal cord (SC) and muscle (M) was studied. CAT activities of dissociated SC cells were low but were increased by M monolayers. In piece explants of SC, high CAT activities were achieved independently of muscle cells (chick, mouse). It is therefore likely that in tntact SC tissue factors other than the trophic influence of muscle are able to induce cholinergic maturation. M piece explants on SC monolayers did not induce CAT in, and their outgrowth was inhibited by, SC monolayers.

Animals↗
PubMed1977

Calorimetric measurements of the transition enthalpy of DNA in aqueous urea solutions.

The helix-coil equilibrium of DNA is delicately affected by the nature of the solvent. In this investigation the helical secondary structure was destabilized by an increasing concentration of urea. We found a linear dependence of the transition enthalpy deltaH on the urea concentration for calf thymus DNA as well as for salmon sperm DNA.

Animals↗