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Biomedical subjects

J Neumann

Publications and source records attributed to J Neumann.

At least 217 records · Page 12Linked to original sources
PubMed1988

[Extracorporeal blood circulation in the unanesthetized free-moving rabbit--an animal model for biocompatibility studies].

The rabbit is suitable as a basis model for the extracorporal circuit (ECC) in long-term test (20 days). A decrease of the leucocytes and platelets is established already in the blank test qualified by catheter material and pumping influence. This effect can be compensated by the rabbit in long-term test. The typical decrease of the leucocytes and platelets does not show any significant alteration during many test days independent of the number of tests which were carried out in one rabbit (blank test and hemoperfusion). A hemoperfusion across activated carbon--independent of the albumin coating--leads to a significant decrease of the leucocytes in comparison to the blank test. This rabbit model is well-suitable for biocompatibility investigations respectively also for effective investigations of detoxication techniques taken as a basis of our results.

Animals↗
PubMed1987

Comparison of ranitidine 300 mg twice daily, 300 mg at night and placebo on 24-hour intragastric acidity of duodenal ulcer patients.

Continuous measurement of 24-hour intragastric acidity was performed in 12 duodenal ulcer patients in remission during treatment with placebo, ranitidine 300 mg nocte and ranitidine 300 mg b.d. Median 24-hour acidity was 79.4 mmol litre-1 during placebo treatment; it decreased to 28.2 mmol litre-1 during treatment with ranitidine 300 mg nocte and to 3.6 mmol litre-1 during treatment with ranitidine 300 mg b.d. The two regimens decreased intragastric acidity to a similar degree during the night, but significantly greater inhibition of daytime and 24-hour acidity followed use of ranitidine 300 mg b.d.

Adult↗
PubMed1987

Single dose treatment with H2 receptor antagonists: is bedtime administration too late?

Using ambulatory ph-metry, intragastric acidity was measured over three separate 24 hour periods in each of 12 healthy volunteers receiving either (a) placebo (1800 h and 2200 h), (b) 300 mg ranitidine (1800 h) and placebo (2200 h), or (c) placebo (1800 h) and 300 mg ranitidine (2200 h). Ranitidine was significantly more effective in decreasing 24 h median intragastric acidity when the drug was administered at 1800 h rather than at 2200 h. Median pH (and interquartile range) was 1.45 (1.4-1.7) on placebo, 2.55 (2.05-3.2) on ranitidine given at 2200 h and 3.35 (2.5-3.85) on ranitidine given at 1800 h (p less than 0.004). The total duration of highly acidic electrode readings (pH less than 1.5) over a 24 h period was reduced significantly by administering the H2-receptor antagonist at 1800 h compared with the later administration. It is suggested that treatment of duodenal ulcers by single administration of ranitidine in the early evening should be evaluated by clinical trial.

Adult↗
PubMed1986

Role of guanine nucleotide-binding protein in the regulation by adenosine of cardiac potassium conductance and force of contraction. Evaluation with pertussis toxin.

In atrial cardiac preparations adenosine exerts a receptor-mediated negative inotropic effect due to an increased potassium conductance. Pretreatment of guinea pigs with pertussis toxin abolished the negative inotropic and action potential shortening effect of adenosine and the adenosine analogue (-)-N6-phenylisopropyladenosine (PIA). As pertussis toxin specifically inactivates guanine nucleotide-binding proteins involved in the signal transfer from receptor binding to specific cell functions, it is concluded that a guanine nucleotide-binding protein is involved in the regulation of the receptor-mediated change in potassium conductance and force of contraction.

Action Potentials↗
PubMed1986

[Not Available].

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Germany↗
PubMed1986

Experiments with continuous hemofiltration and hemofiltrate regeneration in the rat.

Experimental studies were made with continuous hemofiltration treatment for bilaterally nephrectomized rats and initial observations regarding the effects of such treatment on leukocyte and thrombocyte counts are reported. Hemofiltration of unanesthetized rats able to move freely within their cage could be continued for up to 30 h using a pump-driven ECC system. Blood parameters recorded during this treatment indicate that the detoxification was effective. In another series of experiments the water and electrolyte reabsorption capacity of the colon ascendens of healthy rats was tested by continuously supplying NaCl solution into the colon via a fistula. A large proportion, if not all, of the hemofiltrate can be discharged into the colon without diarrhoea. A final series of experiments showed that the three-stage operation (implantation of permanent catheters, connection of a permanent intestinal fistula and bilateral nephrectomy) is possible with the rat.

Animals↗
PubMed1985

Influence of detergent polar and apolar structure upon the temperature dependence of beef heart cytochrome c oxidase activity.

The temperature dependence of lipid-depleted beef heart cytochrome c oxidase activity was studied in a series of chemically homogeneous detergents. The detergents that were tested included C10 to C18 maltosides, C8 to C12 glucosides, C8 to C16 Zwittergents, and C12 poly(oxyethylene) ethers. The observed rates of electron transport were dependent upon the structure of the polar head group and the length of the hydrocarbon tail. Of the detergents tested, the alkyl maltosides were the best in terms of both high rates of electron transport and superior enzyme stability. With the maltosides, changing the length of the alkyl tail affected the activity of cytochrome c oxidase in a manner quite similar to that reported with synthetic phosphatidylcholines and phosphatidylethanolamines [Vik, S. B., & Capaldi, R. A. (1977) Biochemistry 16, 5755-5759], suggesting that the alkyl maltosides can mimic some of the features of the membrane environment. In each of the detergents, the activation enthalpy (determined from the slope of an Arrhenius plot) was nearly identical, suggesting that the same electron-transfer step within cytochrome c oxidase is rate limiting. This result has been interpreted as evidence for the existence of two or more conformers of cytochrome c oxidase, one of which is significantly more active than the other(s). The enzyme turnover number, which changes by 2 orders of magnitude depending upon the structure of the bound detergent, may reflect the ability of each detergent to alter the equilibrium between the active and nearly inactive conformers.

Animals↗
PubMed1985

[Prognostic significance of perivascular round cell infiltrations in oligodendroglioma].

In 175 cases of oligodendroglioma (all grades, partly operated on several times), histological sections of the surgical material--in all, 226 preparations--were examined with regard to the presence and extent of lymphocytic infiltrates which could be assessed as manifestation of an immune reaction, and correlated with the clinical course. In case of infiltrates, the course was not more favourable than expected. Development of a tumour depends first of all on the inherent dynamics of the tumour itself. Prognosis can be favourably influenced by operation and possibly also by radiation.

Brain↗