Biomedical subjects
Publications and source records attributed to J Neumann.
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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.
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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.
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.
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.
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The currently accepted scheme for photosynthetic electron flow from water to ferredoxin (and subsequently to NADP), known as the Z scheme, envisions a linear electron flow that requires two photosystems joined by several electron carriers. The observation that the extent of photoreduction of ferredoxin depends on whether electrons are provided by water (a donor to photosystem II) or by artificial electron donors to photosystem I led Arnon et al. [Arnon, D. I., Tsujimoto, H. Y. & Tang, G. M.-S. (1980) Proc. Natl. Acad. Sei. USA 77, 2676-2680] to question the validity of the Z scheme for photosynthetic electron transport. Our results show that this difference is not due to any inherent difference in electron transport but to the fact that when electron donors are added to chloroplasts they oxidize (in their oxidized state) reduced ferredoxin. Different electron donors oxidize reduced ferredoxin to a different extent; dehydroascorbate is a more potent oxidant than dithiothreitol. Dichlorophenol-indophenol is also a potent oxidant of reduced ferredoxin. The rate of NADP reduction and the K(m) for NADP with various electron donors reflect the oxidative capacities of the electron donors and mediators. These results also explain the fact that NADP reduction with electron donors to photosystem I is less than that with water, despite the fact that electron flow from donor to artificial dyes can proceed at high rates.
Effective forms of care-giving for psychotic patients after hospitalisation is necessary to ensure that rehabilitation treatment does not cease when they are discharged. The form of combined in-patient and out-patient treatment described by the authors has been developed systematically since 1972 and ensures that the original uniform scheme of treatment is not interrupted. Thr results of examinations on 186 patients are used to describe the benefits of this form of care-giving.
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