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361.
362.
JÖRG THOMAS EPPLEN BRIGITTE KUNZ GERD WIECZOREK-ENGELKEN WOLFGANG ENGEL JÖRG SCHMIDTKE 《Differentiation; research in biological diversity》1981,20(1-3):124-130
Enzymatic digestion of the interstitial tissue of early juvenile and adult rat testes resulted in an enrichment of the Leydig cell population. The cells of the intertubular preparation from adult testes were separated by centrifugal elutriation, according to differences in sedimentation velocity, a counter-flow centrifugation technique leading to 70% Leydig cell purity. Using this approach, it was possible to demonstrate that Leydig cells from adult testes contain only low affinity isoenzymes of cyclic AMP phosphodiesterase (PDE; E.C.: 3.1.4.17), an intracellular regulator of cAMP. Starch gel electrophoresis showed that the isozyme of cAMP PDE of Leydig cells is masked in crude testis homogenates due to the relatively low level of these cells in the total population. In Leydig cells, there are two different electrophoretic forms expressed which resemble two of eleven different molecular forms of cAMP PDE demonstrated for comparison in 21 different organs of the adult rat.
An interstitial cell preparation from early juvenile testes, with a Leydig cell content of up to 20%, was also investigated electrophoretically with regard to molecular forms of cAMP PDE, the properties of which were characterized by kinetic analysis of cAMP hydrolysis. The results presented are discussed in relation to the onset of testosterone synthesis in Leydig cells of prepubertal rats leading to the initiation of male puberty. 相似文献
An interstitial cell preparation from early juvenile testes, with a Leydig cell content of up to 20%, was also investigated electrophoretically with regard to molecular forms of cAMP PDE, the properties of which were characterized by kinetic analysis of cAMP hydrolysis. The results presented are discussed in relation to the onset of testosterone synthesis in Leydig cells of prepubertal rats leading to the initiation of male puberty. 相似文献
363.
364.
R. Broomhead Ian Macpherson J. le Fleming Burrow H. H. Moll J. M. P. Clark Michael C. Oldfield Andrew M. Claye A. B. Pain David W. Currie Leslie N. Pyrah Hugh Garland George Seed F. F. Hellier H. S. Shucksmith Bryan Jeaffreson H. W. Symons A. J. C. Latchmore Maxwell Telling J. M. Lees 《BMJ (Clinical research ed.)》1949,2(4625):484-485
365.
D. G. Oldfield 《Bulletin of mathematical biology》1967,29(1):17-32
A time-dependent DNA histogram is calculated for an irradiated population of cells under the limiting assumption that the
cells cannot pass through prophase due to the effects of the radiation. The population is assumed to increase exponentially
prior to irradiation, but after irradiation to neither gain nor lose cells. Chromosome-number dispersion is taken into account
in the calculation. The qualitative behavior of the calculated and experimental histograms are in reasonable agreement. The
quantitative agreement between the two is relatively good at short post-irradiation times but is poor at long post-irradiation
times (say, greater than half the doubling time). This suggests that recovery phenomena cannot be neglected at long post-irradiation
times. 相似文献
366.
Ronald G. Oldfield 《Journal of applied animal welfare science : JAAWS》2013,16(4):340-360
Many species of fishes are aggressive when placed in small aquaria. Aggression can negatively affect the welfare of those individuals toward whom it is directed. Animals may behave aggressively in order to defend resources such as food, shelter, mates, and offspring. The decision to defend depends on the distribution of resources and on ecological factors such as number of competitors, amount of available space, and amount of habitat complexity. This study tested the effects of these factors on aggression in a common aquarium fish, the Midas cichlid (Amphilophus citrinellus). The study found that time spent behaving aggressively was not associated with small-scale differences in group size or available space. Aggression was significantly lower in a large aquarium with a complex habitat. Aquaria of sizes typically used in the companion animal (pet) hobby did not provide optimal welfare for cichlids housed with aggressive conspecifics. The public should be aware that this and similar species require larger aquaria with complex habitat, which elicit more natural behavior. 相似文献
367.
Josiah Oldfield 《BMJ (Clinical research ed.)》1922,2(3219):491-492
368.
Phospholipid head group conformations in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE), DPPC-cholesterol, and DPPE-cholesterol dispersions, in excess water above the pure lipid gel to liquid-crystal phase transition temperature, have been calculated by using comparisons between experimental 2H and 31 P NMR spectral parameters and theoretical results obtained from a plausible model of head group motions. The new calculations are compared with results obtained in previous studies [Seelig, J., Gally, H. U., & Wohlgemuth, R. (1977) Biochem, Biophys. Acta 467, 109--117; Brown, M. F. & Seelig, J. (1978) Biochemistry 17, 381--384; Seelig, J., & Gally, H. U. (1976) Biochemistry 15, 5199--5204] and are shown to agree qualitatively under certain highly restrictive conditions. Under more general conditions, it is shown that many possible solutions are generated but that these may often be separated into a small number of likely conformations in which the head group torsion angles are restricted to specific ranges rather than to a discrete set of values. There is no NMR evidence, however, to support the notion that there are only single conformational solutions to the NMR measurements for the above phospholipid systems. 相似文献