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961.
Srinath Setty Wei Sun Rodolfo Martinez H Fred Downey Johnathan D Tune 《Journal of applied physiology》2004,97(1):431-438
This study tested whether alpha-adrenoceptor-mediated coronary vasoconstriction is augmented during exercise in diabetes mellitus. Experiments were conducted in dogs instrumented with catheters in the aorta and coronary sinus and with a flow transducer around the circumflex coronary artery. Diabetes was induced with alloxan monohydrate (n = 8, 40 mg/kg i.v.). Arterial plasma glucose concentration increased from 4.7 +/- 0.2 mM in nondiabetic, control dogs (n = 8) to 21.4 +/- 1.9 mM 1 wk after alloxan injection. Coronary blood flow, myocardial oxygen consumption (MVo(2)), aortic pressure, and heart rate were measured at rest and during graded treadmill exercise before and after infusion of the alpha-adrenoceptor antagonist phentolamine (1 mg/kg iv). In untreated diabetic dogs, exercise increased MVo(2) 2.7-fold, coronary blood flow 2.2-fold, and heart rate 2.3-fold. Coronary venous Po(2) fell as MVo(2) increased during exercise. After alpha-adrenoceptor blockade, exercise increased MVo(2) 3.1-fold, coronary blood flow 2.7-fold, and heart rate 2.1-fold. Relative to untreated diabetic dogs, alpha-adrenoceptor blockade significantly decreased the slope of the relationship between coronary venous Po(2) and MVo(2). The difference between the untreated and phentolamine-treated slopes was greater in the diabetic dogs than in the nondiabetic dogs. In addition, the decrease in coronary blood flow to intracoronary norepinephrine infusion was significantly augmented in anesthetized, open-chest, beta-adrenoceptor-blocked diabetic dogs compared with the nondiabetic dogs. These findings demonstrate that alpha-adrenoceptor-mediated coronary vasoconstriction is augmented in alloxan-induced diabetic dogs during physiological increases in MVo(2). 相似文献
962.
963.
The purpose of this research was to investigate the variability of the roller compaction process while monitoring in-line
with near-infrared (NIR) spectroscopy. In this paper, a pragmatic method in determining this variability of in-line NIR monitoring
roller compaction process was developed and the variability limits were established. Fast Fourier Transform (FFT) analysis
was used to study the source of the systematic fluctuations of the NIR spectra. An off-line variability analysis method was
developed as well to simulate the in-line monitoring process in order to determine the variability limits of the roller compaction
process. For this study, a binary formulation was prepared composed of acetaminophen and microcrystalline cellulose. Different
roller compaction parameters such as roll speed and feeding rates were investigated to understand the variability of the process.
The best-fit line slope of NIR spectra exhibited frequency dependence only on the roll speed regardless of the feeding rates.
The eccentricity of the rolling motion of rollers was identified as the major source of variability and correlated with the
fluctuations of the slopes of NIR spectra. The off-line static and dynamic analyses of the compacts defined two different
variability of the roller compaction; the variability limits were established. These findings were proved critical in the
optimization of the experimental setup of the roller compaction process by minimizing the variability of NIR in-line monitoring. 相似文献
964.
Datu BJ Gasser RB Nagaraj SH Ong EK O'Donoghue P McInnes R Ranganathan S Loukas A 《PLoS neglected tropical diseases》2008,2(1):e130
Background
Third-stage larvae (L3) of the canine hookworm, Ancylostoma caninum, undergo arrested development preceding transmission to a host. Many of the mRNAs up-regulated at this stage are likely to encode proteins that facilitate the transition from a free-living to a parasitic larva. The initial phase of mammalian host invasion by A. caninum L3 (herein termed “activation”) can be mimicked in vitro by culturing L3 in serum-containing medium.Methodology/Principal Findings
The mRNAs differentially transcribed between activated and non-activated L3 were identified by suppression subtractive hybridisation (SSH). The analysis of these mRNAs on a custom oligonucleotide microarray printed with the SSH expressed sequence tags (ESTs) and publicly available A. caninum ESTs (non-subtracted) yielded 602 differentially expressed mRNAs, of which the most highly represented sequences encoded members of the pathogenesis-related protein (PRP) superfamily and proteases. Comparison of these A. caninum mRNAs with those of Caenorhabditis elegans larvae exiting from developmental (dauer) arrest demonstrated unexpectedly large differences in gene ontology profiles. C. elegans dauer exiting L3 up-regulated expression of mostly intracellular molecules involved in growth and development. Such mRNAs are virtually absent from activated hookworm larvae, and instead are over-represented by mRNAs encoding extracellular proteins with putative roles in host-parasite interactions.Conclusions/Significance
Although this should not invalidate C. elegans dauer exit as a model for hookworm activation, it highlights the limitations of this free-living nematode as a model organism for the transition of nematode larvae from a free-living to a parasitic state. 相似文献965.
Arlene R. Howe Charles S. Gasser Sherri M. Brown Stephen R. Padgette Jesse Hart Gregory B. Parker Michael E. Fromm Charles L. Armstrong 《Molecular breeding : new strategies in plant improvement》2002,10(3):153-164
Efficient and reproducible selection of transgenic cells is an essential component of a good transformation system. In this paper, we describe the development of glyphosate as a selective agent for the recovery of transgenic embryogenic corn callus and the production of plants tolerant to Roundup® herbicide. Glyphosate, the active ingredient in Roundup® herbicide inhibits the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) and thus prevents the synthesis of chorismate-derived aromatic amino acids and secondary metabolites in plants. A maize EPSPS gene has been cloned, mutated to produce a modified enzyme resistant to inhibition by glyphosate, and engineered into a monocot expression vector. In addition, a bacterial gene which degrades glyphosate (glyphosate oxidoreductase, or GOX) was also cloned into a similar expression vector. Stably transformed callus has been reproducibly recovered following introduction of mutant maize EPSPS and GOX genes into tissue culture cells by particle bombardment and selection on glyphosate-containing medium. Plants have been regenerated both on and off glyphosate selection medium, and are tolerant to normally lethal levels of Roundup®. Excellent seed set has been obtained from both self and outcross pollinations from both sprayed and unsprayed regenerated plants. Progeny tests have demonstrated normal Mendelian transmission and tolerance to the herbicide for some of the transgenic events. 相似文献
966.
Based on resource allocation theory, a negative correlation is predicted between resource availability and plant defense against
herbivore attack. Plants growing in resource-limited environments should display lower growth and higher defense against herbivores
than plants growing where resources are less limited. Interspecific comparisons generally support these predictions. We evaluated
this hypothesis at the intraspecific level, for two sapling populations of the canopy tree Dialium guianense (Caesalpiniaceae) at the Lacandona rain forest in southeast Mexico. The two populations occur in nearby sites, adjacent to
the Chajul Field Station, under the same climatic conditions and within the same vegetation type, but with considerable differences
in soil quality. The Floodplain site, under the influence of the Lacantún River, has favorable conditions for plant growth,
in terms of nutrient and water availability, whereas the Hills site, given its location and soil characteristics, provides
more restricted conditions for plant growth. Plants in the Floodplain site had higher growth and lower concentration of phenolic
compounds than plants in the Hills (a two-fold difference in leaf area production, 1.3 less total phenolics). These differences
were correlated with differences in herbivore attack, as saplings from the Hills, with a higher defensive potential, had lower
average levels of herbivory than Floodplain plants (3.86% ± 0.80 vs. 7.75% ± 1.43 of leaf area loss). The relationship between
the concentration of phenolic compounds and leaf quality for herbivores was consistent with preference assays carried out
under laboratory conditions using two species of generalist herbivores, the army worm Spodoptera fugiperda and the native katydid Orophus sp. In 63.8 and 81.3% of the cases, third-instar larvae of S. fugiperda and adults of Orophus, respectively, preferred leaflets from the Floodplain plants population. Moreover, on average, the adults of Orophus consumed 2.9 times more leaf area from the Floodplain than from the Hills. In addition, a reciprocal transplant experiment
indicated that phenotypic plasticity is likely to be the mechanism by which the plants expressed differential growth and traits
affecting herbivory levels. In this experiment, growth and herbivory levels were 1.6 and 1.7 times higher, respectively, in
plants transplanted into a Floodplain experimental plot than those in a Hills plot. This work contributes to our understanding
of how edaphic heterogeneity can determine intraspecific variation in the relationship of plants with their herbivores and
evaluates the underlying mechanisms promoting such influence.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
967.
968.
969.
Temporal variations in the relationships among plant nutrient concentrations, soil properties and arbuscular-mycorrhizal (AM) fungal dynamics were studied along a topographic and saline gradient in a temperate grassland soil. Soil and plant (Lotus tenuis, Paspalum vaginatum, Stenotaphrum secundatum) samples were collected on four seasonally based occasions. The morphology of AM root colonization had a similar pattern in the plants studied. Maximum arbuscular colonization occurred at the beginning of the growing season in late winter and was minimal in late summer, but maximal vesicular colonization occurred in summer and was minimal in winter, suggesting a preferential production of these morphological phases by the fungus with respect to season. The greatest arbuscular colonization was associated with the highest N and P concentrations in plant tissue, suggesting a correspondence with increases in the rate of nutrient transfer between the symbiotic partners. Water content, salinity and sodicity in soil were positively associated with AM root colonization and arbuscule colonization in L. tenuis, but negatively so in the grasses. There were distinct seasonally related effects with respect to both spore density and AM colonization, which were independent of particular combinations of plant species and soil sites. 相似文献
970.
The dissection of the circadian clock into its molecular components represents the most striking and well-studied example of a gene regulatory network underlying a complex behavioural trait. By contrast, the evolutionary analysis of the clock has developed more slowly. Here we review studies that have surveyed intraspecific clock gene variation over large geographical areas and have discovered latitudinal clines in gene frequencies. Such spatial patterns traditionally suggest that natural selection shapes genetic variation, but it is equally possible that population history, or a mixture of demography and selection, could contribute to the clines. We discuss how population genetics, together with functional assays, can illuminate these possible cases of natural selection in Drosophila clock genes. 相似文献