In rats under either mild stress (= controls) or severe stress (= restraint) gastric secretion (acid; pepsin, volume), mucosal blood flow, serum gastrin and ulcer formation were evaluated without and with additional infusion of a low dose (0.25 mg/kg.h) metiamide over an 8 h experimental period. Calculated constants of dose-response characteristics for acid output in this species are: Km = 1.41 +/- 0.36 mg/kg.h; Vmax = 94.4 +/- 11.0 per cent. Restraint depresses markedly secretion and microcirculation, but stimulates ulcer formation and raises serum gastrin. In controls, metiamide inhibits secretion and ulcer index significantly, but leaves mucosal blood flow and gastrin unaltered. In contrast, with restraint and metiamide, ulcer index was not improved, whereas mucosal blood flow was restored to almost control levels. Therefore, H2-receptor blockers, in addition to inhibition of secretion, may interfere with microcirculation either directly or by secondary release of yet unknown mediator substance(s), depending on the prevailing tissue environment.
The reduction of dose onboard spacecraft and aircraft by appropriate shielding measures plays an essential role in the future development of space exploration and air travel. The design of novel shielding strategies and materials may involve hydrogenous composites, as it is well known that liquid hydrogen is most effective in attenuating charged particle radiation. As precursor for a later flight experiment, the shielding properties of newly developed hydrogen-rich polymers and rare earth-doped high-density rubber were tested in various ground-based neutron and heavy ion fields and compared with aluminium and polyethylene as reference materials. Absorbed dose, average linear energy transfer and gamma-equivalent neutron absorbed dose were determined by means of LiF:Mg,Ti thermoluminescence dosemeters and CR-39 plastic nuclear track detectors. First results for samples of equal aerial density indicate that selected hydrogen-rich plastics and rare-earth-doped rubber may be more effective in attenuating cosmic rays by up to 10% compared with conventional aluminium shielding. The appropriate adaptation of shielding thicknesses may thus allow reducing the biologically relevant dose. Owing to the lower density of the plastic composites, mass savings shall result in a significant reduction of launch costs. The experiment was flown as part of the European Space Agency's Biopan-5 mission in May 2005.
Die faszinierende Umlagerung (1)→(2) verläuft nach theoretischen Untersuchungen nicht über die vorgeschlagenen plausiblen Zwischenstufen. Gegen die direkte Umwandlung von (1) in eine Zwischenstufe mit R2‐substituiertem 1,5‐Cyclooctadien‐3,7‐diin‐Liganden werden keine Argumente angeführt.
The influence of restraint stress on serum calcium (Ca) and phosphate was studied in normal and thyroidectomized rats. In addition the response of gastric stress ulcer index, blood gastrin and glucagon to exogenous Ca was investigated. In intact as well as in thyroidectomized animals serum total, ionised and previously injected radioactive Ca decrease during an 8h stress period, whereas inorganic phosphate increases. Together with a constant specific activity these findings are consistent with hypoparathyroidism and calcitonin independent hypocalcemia during stress. Intragastric infusion of 45 mg/kg Ca-gluconate per 8h proves to be a potent anti-stress ulcer regimen in intact and neck-sham operated, but not in thyroidectomized rats without and with additional adrenal demedullation. Gastrin and glucagon were not correlated with calcemia during either stress alone or stress combined with intragastric Ca infusion. It is suggested that the development of gastric stress ulcerations can be prevented by a Ca-mediated release of endogenous calcitonin.
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