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Biomedical subjects

H Thoma

Publications and source records attributed to H Thoma.

At least 55 records · Page 3Linked to original sources
PubMed1988

Applications of the in vitro aryl hydrocarbon hydroxylase induction assay for determining "2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents": pyrolyzed brominated flame retardants.

The pyrolysis of brominated flame retardants FR 300 BA (decabromobiphenyl) ether, FireMaster BP-6 (polybrominated biphenyls), Bromkal 70-5-DE (primarily pentabromodiphenylether), Bromkal 70-DE (primarily penta and tetrabromodiphenylether) and Bromkal G1 (pentabromodiphenylether) resulted in the formation of relatively high levels of polybrominated dibenzofurans (PBDFs) and dibenzo-p-dioxins (PBDDs as determined by gas chromatography-mass spectrometric analysis. The dose response EC50 values for the induction of aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin O-deethylase (EROD) by the flame retardant pyrolysates was determined in rat hepatoma H-4-II E cells and compared to the relative induction activities of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and the concentrations of "2,3,7,8-TCDD equivalents" were calculated. The range of "2,3,7,8-TCDD equivalents" levels (micrograms/g or ppm) derived from values obtained from the AHH and EROD bioassays for each of the pyrolyzed flame retardant samples was: 174-194, 480-1400, 2140-4680, 6740-8780 and 3920-5260 ppm for FR 300 BA, FireMaster BP-6, Bromkal 70 DE, Bromkal 70-5 DE and Bromkal G1, respectively. The in vivo dose-response effects of 2 pyrolyzed flame retardants were determined in immature male Wistar rats and compared to the dose-response activities of 2,3,7,8-TCDD. The in vivo responses which were measured included hepatic microsomal AHH and EROD induction, body weight loss and thymic atrophy. For the pyrolyzed FireMaster BP-6 and Bromkal 70-5 DE samples, the range of calculated in vivo "2,3,7,8-TCDD equivalents" (ppm in sample) for the 4 in vivo bioassays was 520-1780 ppm and 3860-8960 ppm, respectively. The excellent overlap between the in vivo and in vitro 2,3,7,8-TCDD equivalents for the 2 flame retardant pyrolysate extracts supports the utility of the in vitro induction bioassay for quantitatively determining "2,3,7,8-TCDD equivalents" for mixtures containing toxic halogenated aryl hydrocarbons.

Animals↗
PubMed1986

Influence of long-term low direct current on rat ischiadic nerves.

The effects of a low direct current on peripheral nerves and electrodes on the ischiadic nerve were investigated, and a constant direct current was applied for various time periods. Afterwards clinicophysiological tests and histological evaluations were performed. The muscles of 55 rats could be stimulated by external stimulation during the follow-up examinations, but 90% of all animals showed microscopically visible nerve tissue alterations which might have been caused by mechanical rather than electrolytic factors.

Animals↗
PubMed1986

[Functional electrostimulation of the denervated posticus muscle in an animal experiment: histo- and biochemical results].

Histochemical and biochemical investigations have been carried out in 2 sheep following unilateral recurrent laryngeal nerve paralysis and direct electrical stimulation of the denervated posticus muscles. The stimulation effect was determined histochemically (standard ATP-ase staining) and compared with the fibre pattern of normal posticus muscles. In addition, one-dimensional gel electrophoresis of myosin heavy-chain isoforms was carried out and correlated with the histochemical results. A dramatic increase of type I fibres could be seen after long-term low-frequency direct electrical stimulation of denervated posticus muscles of the sheep. Biochemically the amount of slow myosin heavy-chain isoforms was higher than in normal muscles.

Animals↗
PubMed1985

Testing of biomaterials, accelerated ageing.

The residual elongation is a critical property of materials used for manufacturing diaphragms of artificial hearts. It is therefore important to check goods received or to control manufactured diaphragms, whether their creep properties are within the required limits. Ordinary creep tests take at least several months, while the release of goods received or diaphragms manufactured should be possible within a few days. Acceleration of the creep test by increasing the test temperature permits an estimation whether the creep properties of a material are within the required limits within a week.

Heart, Artificial↗
PubMed1984

Profiles of strongly polar and less polar acids obtained from human blood, plasma and serum by two-step ultrafiltration.

A two-step ultrafiltration method combined with anion-exchange chromatography is described for the separation of lipophilic and strongly lipophobic acids occurring in human blood, serum and plasma. After treatment with diazomethane, the acid fractions are separated further by gas chromatography. The acids were identified by their mass spectra. Profiles obtained from the strongly acidic fraction of blood samples of healthy individuals are characterized by main peaks corresponding to organic phosphoric acid esters. The peaks are absent in plasma and serum.

Acids↗
PubMed1984

The chronically stimulated muscle as an energy source for artificial organs. Preliminary results of a basic study in sheep.

In 5 adult sheep the psoas muscle of one side was electrically stimulated through the muscle nerves with an implantable stimulation unit for more than 5 weeks. In the final experiments the isometric tetanic tension of the stimulated muscles was reduced to 50-70% of the contralateral normal muscle. The use of only 15 Hz as a stimulation frequency led to a transformation of the originally fast muscle into a slow muscle with more resistance to fatigue. Future application of the chronically stimulated psoas muscle for driving artificial organs is discussed.

Animals↗
PubMed1983

Catabolism of fish furan fatty acids to urofuran acids in the rat.

A mixture of long-chain furan fatty acids was prepared as methyl esters from testes lipids of Northern pike (Esox lucius). Upon feeding these esters to rats, dicarboxylic acids, which still contained the furan structure, were found in the urine. The first phase of a rapid but incomplete catabolism is beta-oxidation of the proximal chain of the furan fatty acids. It proceeds to a distance of three carbon atoms from the ring. omega-Oxidation of the terminal alkyl chain, followed by alpha-oxidation gives rise to a second alkylcarboxyl chain with five carbon atoms or less. The ring methyl substituents of the precursor acids seem to be more resistant to oxidation than the alkyl substituent with three or five carbon atoms. The urinary catabolites from furan fatty acids in the rat are similar to furan acids found in human urine, but only one of the structures occurs in both sources.

Animals↗