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排序方式: 共有283条查询结果,搜索用时 265 毫秒
1.
Willoughby de Broke Rudyard Kipling Hugh Elliot E. Ray Lankester Leonard Hill Laurence R. Philipps Wm. Arbuthnot Lane James Crichton-Browne H. Bryan Donkin Francis Lloyd R. A. Lyster John MacAlister F. W. Mott William Osler C. W. Saleeby J. H. Sequeira Humphry Rolleston Hugh Wansey Bayly 《BMJ (Clinical research ed.)》1919,2(3074):725
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3.
S K Cunningham S J Sequeira J Chambers A Heffernan T J McKenna 《Journal of steroid biochemistry》1988,31(1):125-130
We have demonstrated that conventional methods for measuring total urinary aldosterone (TUA) may markedly and inconsistently underestimate aldosterone output, since under the conditions usually employed (pH 1.0), the hydrolysis of aldosterone conjugates in urine is incomplete. The use of more acidic hydrolysis conditions (pH 0.2) overcomes this problem. However free aldosterone may be damaged at this pH. Therefore to accurately measure TUA output, it is necessary to isolate the undamaged aldosterone chromatographically and to correct for procedural losses based on the recovery of aldosterone tracer added to the urine prior to hydrolysis. We compared a number of laboratory estimates of aldosterone status (including urinary free aldosterone) with the 24-h urinary sodium output in normal subjects, since this provides a good bioassay of aldosterone. Sodium output correlated best with "optimised" 24 h TUA, i.e. hydrolysed at pH 0.2, (r = -0.589, P less than 0.001), and with plasma aldosterone (r = -0.504, P less than 0.005). Both aldosterone in random urine specimens and plasma renin activity correlated poorly with 24-h sodium output. Therefore, while the measurement of optimised TUA excretion provides the best index of aldosterone activity, assay of aldosterone in random specimens of plasma, which is more convenient for patient and laboratory, may be adequate for many clinical purposes. 相似文献
4.
Summary Adult size (in terms of dry weight; DW) and development time (T
p
) of the solitary parasitoidAphidius ervi varied when reared in different nymphal instars of its host, apterous virginoparae of the pea aphid (Acyrthosiphon pisum). Parasitoid DW increased with an increase in the DW of the host at parasitization, from the first to the third aphid instar. Female wasps gained 1.1 times more in DW than their male counterparts in all four host classes, butT
p
did not significantly differ between the sexes. Parasitoid DW was consistently more variable thanT
p
. The two traits covaried positively with an increase in host size from the first to the third instar, but they varied independently in parasitoids from fourth-instar hosts. The host size (and stage) at the time of parasitization imposes constraints on the growth and development of immatureA. ervi that are reflected in the pattern of covariation between DW andT
p
. When growing in aphids below a certain size threshold, parasitoids can maximize fitness by a trade-off between DW andT
p
. Consequently, the assumption implicit in host-size models of parasitoid oviposition decisions — that females incur a relatively greater reduction in size (used as an index of fecundity) than males when developing in poor quality hosts — can be falsified. 相似文献
5.
A suicide vector was constructed by cloning the transfer genes of the wide-host-range (IncW group) plasmid R388 into the BamHI site of pBR325. This plasmid can deliver Tn5 into Pseudomonas solanacearum at frequencies ranging from 10(-6) to 10(-9) per recipient. 相似文献
6.
7.
Mitochondrial DNA sequence evolution in sharks: rates, patterns, and phylogenetic inferences 总被引:8,自引:0,他引:8
Abundant representation of sharks in the fossil record makes this group a
superb system in which to investigate rates and patterns of molecular
evolution and to explore the strengths and weaknesses of phylogenetic
inferences from molecular data. In this report, the molecular evolution of
the cytochrome b gene in sharks is described and the information related to
results from phylogenetic analysis of the data evaluated in the light of a
phylogeny derived independently of the molecular data. Across divergent
lineages of sharks there is evidence for significant substitution rate
variation, departure from compositional equilibrium, and substantial
homoplasy; nevertheless, the signal of evolutionary history is evident in
patterns of shared transversions and amino acid replacements.
相似文献
8.
There is marked heterogeneity of nucleotide composition in mitochondrial
DNA across divergent animals. Differences in nucleotide composition
presumably reflect differences in directional nucleotide substitution for
A+T or G+C nucleotides. In mitochondrial DNA, there is A+T directional
nucleotide substitution in most (if not all) animals surveyed, and the
magnitude of directional A+T nucleotide substitution differs greatly within
and among groups. Differences in directional nucleotide substitution among
lineages of mammals can be explained by changes in metabolic physiology.
This relationship is thought to be mediated by the effect of oxygen
radicals because these toxic compounds are by-products of aerobic
metabolism and are known mutagens. Association between metabolism and
nucleotide composition provides additional evidence in favor of the
hypothesis that rates and patterns of nucleotide substitution in
mitochondrial DNA can be influenced by factors that impinge on rates of
endogenous DNA damage.
相似文献
9.
Elemental distribution in striated muscle and the effects of hypertonicity: Electron probe analysis of cryo sections 总被引:15,自引:4,他引:11 下载免费PDF全文
A method of rapid freezing in supercooled Freon 22 (monochlorodifluoromethane) followed by cryoultramicrotomy is described and shown to yield ultrathin sections in which both the cellular ultrastructure and the distribution of diffusible ions across the cell membrane are preserved and intracellular compartmentalization of diffusabler ions can be quantitated. Quantitative electron probe analysis (Shuman, H., A.V. Somlyo, and A.P. Somlyo. 1976. Ultramicros. 1:317-339.) of freeze-dried ultrathin cryto sections was found to provide a valid measure of the composition of cells and cellular organelles and was used to determine the ionic composition of the in situ terminal cisternae of the sarcoplasmic reticulum (SR), the distribution of CI in skeletal muscle, and the effects of hypertonic solutions on the subcellular composition if striated muscle. There was no evidence of sequestered CI in the terminal cisternae of resting muscles, although calcium (66mmol/kg dry wt +/- 4.6 SE) was detected. The values of [C1](i) determined with small (50-100 nm) diameter probes over cytoplasm excluding organelles over nuclei or terminal cisternae were not significantly different. Mitochondria partially excluded C1, with a cytoplasmic/ mitochondrial Ci ratio of 2.4 +/- 0.88 SD. The elemental concentrations (mmol/kg dry wt +/- SD) of muscle fibers measured with 0.5-9-μm diameter electron probes in normal frog striated muscle were: P, 302 +/- 4.3; S, 189 +/- 2.9;C1, 24 +/- 1.1;K, 404 +/- 4.3, and Mg, 39 +/- 2.1. It is concluded that: (a) in normal muscle the "excess CI" measured with previous bulk chemical analyses and flux studies is not compartmentalized in the SR or in other cellular organelles, and (b) the cytoplasmic C1 in low [K](0) solutions exceeds that predicted by a passive electrochemical distribution. Hypertonic 2.2 X NaCl, 2.5 X sucrose, or 2.2 X Na isethionate produced: (a) swollen vacuoles, frequently paired, adjacent to the Z lines and containing significantly higher than cytoplasmic concentrations of Na and Cl or S (isethionate), but no detectable Ca, and (b) granules of Ca, Mg, and P = approximately (6 Ca + 1 Mg)/6P in the longitudinal SR. It is concluded that hypertonicity produces compartmentalized domains of extracellular solutes within the muscle fibers and translocates Ca into the longitudinal tubules. 相似文献
10.
A gene cluster required for coordinated biosynthesis of lipopolysaccharide and extracellular polysaccharide also affects virulence of Pseudomonas solanacearum. 下载免费PDF全文
Bacterial cell surface components can be important determinants of virulence. At least three gene clusters important for extracellular polysaccharide (EPS) biosynthesis have been previously identified in the plant pathogen Pseudomonas solanacearum. We have found that one of these gene clusters, named ops, is also required for lipopolysaccharide (LPS) biosynthesis. Mutations in any complementation unit of this cluster decreased EPS production, prevented the binding of an LPS-specific phage, and altered the mobility of purified LPS in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. However, restoration of LPS biosynthesis alone was not sufficient to restore virulence to the wild-type level, suggesting that EPS is important for pathogenesis. 相似文献