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At least 811 records · Page 45Linked to original sources
PubMed1988

The effect of Escherichia coli STa enterotoxin and other secretagogues on mucosal surface pH of rat small intestine in vivo.

The mucosal surface pH of rat small intestine was measured in vivo. The surface pH in the normal jejunum was 6.20 +/- 0.02 (67) and 7.00 +/- 0.05 (5) in the ileum. Escherichia coli STa toxin induced a rapid and reversible alkalinization of both jejunal and ileal mucosae to a pH of 6.91 +/- 0.08 (10) and 7.67 +/- 0.06 (5) respectively. The synthetic ST analogue, STh-(6-19), had an effect identical to native STa toxin on jejunal surface pH. Theophylline (20 mM) maintained the STa-elevated jejunal surface pH after toxin removal but had no effect on untreated tissue. 8-Bromo cyclic GMP resembled STa by causing similar mucosal alkalinization in the jejunum; 8-bromo cyclic AMP, forskolin and cholera toxin individually had considerably smaller effects on surface pH, although combining forskolin or cholera toxin with theophylline resulted in alkalinization of the jejunal mucosa to a pH of 6.92 +/- 0.03 (5) and 6.76 +/- 0.04 (4). These results indicate that cyclic-GMP-dependent secretory processes are more capable of inducing surface pH changes than those dependent on cyclic AMP. The ability of STa to alter mucosal surface pH makes it a useful tool to investigate the microclimate hypothesis for weak electrolyte absorption.

Animals↗
PubMed2001

Local adaptation across a climatic gradient despite small effective population size in the rare sapphire rockcress.

When assigning conservation priorities in endangered species, two common management strategies seek to protect remnant populations that (i) are the most genetically divergent or (ii) possess the highest diversity at neutral genetic markers. These two approaches assume that variation in molecular markers reflects variation in ecologically important traits and ignore the possibility of local adaptation among populations that show little divergence or variation at marker loci. Using common garden experiments, we demonstrate that populations of the rare endemic plant Arabis fecunda are physiologically adapted to the local microclimate. Local adaptation occurs despite (i) the absence of divergence at almost all marker loci and (ii) very small effective population sizes, as evidenced by extremely low levels of allozyme and DNA sequence polymorphism. Our results provide empirical evidence that setting conservation priorities based exclusively on molecular marker diversity may lead to the loss of locally adapted populations.

Adaptation, Physiological↗
PubMed2006

Decreases in stomatal conductance of soybean under open-air elevation of [CO2] are closely coupled with decreases in ecosystem evapotranspiration.

Stomatal responses to atmospheric change have been well documented through a range of laboratory- and field-based experiments. Increases in atmospheric concentration of CO(2) ([CO(2)]) have been shown to decrease stomatal conductance (g(s)) for a wide range of species under numerous conditions. Less well understood, however, is the extent to which leaf-level responses translate to changes in ecosystem evapotranspiration (ET). Since many changes at the soil, plant, and canopy microclimate levels may feed back on ET, it is not certain that a decrease in g(s) will decrease ET in rain-fed crops. To examine the scaling of the effect of elevated [CO(2)] on g(s) at the leaf to ecosystem ET, soybean (Glycine max) was grown in field conditions under control (approximately 375 micromol CO(2) mol(-1) air) and elevated [CO(2)] (approximately 550 micromol mol(-1)) using free air CO(2) enrichment. ET was determined from the time of canopy closure to crop senescence using a residual energy balance approach over four growing seasons. Elevated [CO(2)] caused ET to decrease between 9% and 16% depending on year and despite large increases in photosynthesis and seed yield. Ecosystem ET was linked with g(s) of the upper canopy leaves when averaged across the growing seasons, such that a 10% decrease in g(s) results in a 8.6% decrease in ET; this relationship was not altered by growth at elevated [CO(2)]. The findings are consistent with model and historical analyses that suggest that, despite system feedbacks, decreased g(s) of upper canopy leaves at elevated [CO(2)] results in decreased transfer of water vapor to the atmosphere.

Carbon Dioxide↗
PubMed2004

Phenology of the tick, Ixodes ricinus, in its southern distribution range (central Spain).

The abundance, seasonal activity patterns and development rates of the tick Ixodes ricinus (L.) (Acari: Ixodidae), as well as microclimate features of the site of study, are described for a 9-year-long study (1994-2002) in north-central Spain. According to drag captures, larvae had a unimodal activity pattern, with a maximum observed around July-August, whereas nymphs displayed a bimodal pattern (May-June and August-September) with strong dominance of spring activity. An inversion of this pattern, with larger autumn peak, was observed in years with humid summers. Adults showed a small spring peak and a large autumn one. In the later years of the study, a small increase in the adult spring peak of activity was noticed, correlated with mild winters. Over the entire period of study, a clear increase in the total tick abundance was detected. Statistically significant differences between years were observed for some climate variables (saturation deficit, winter temperatures and number of days with temperatures above 6 degrees C), but a consistent and constant pattern of change was not observed in any climate variable. Temperature requirements for developing stages showed a sharp decrease in weeks 35-51 (eggs) and 38-50 (larvae and nymphs), a feature attributed to the presence of the morphogenetic diapause, beginning around September. Development rates obtained under quasi-natural conditions were almost twice those reported for other sites, suggesting an adaptation of this local, largely isolated I. ricinus population. According to drag captures and field-obtained development rates, interchange of nymphs between the two cohorts is common in this site, and seems to be influenced by the winter temperature and the date of larval engorgement.

Animals↗
PubMed1991

House dust mite allergens on different types of mattresses.

Beds and especially mattresses are important breeding grounds for house dust mites. We investigated whether supposed differences in the microclimate on water, spring and foam mattresses were reflected in the occurrence of house dust mite major allergens (Der fI, Der mI, and Der pI) in mattress dust. Fifty-one mattresses that had been in use for 8-25 months were sampled. Median concentration of total major allergens was 0.5 microgram/g dust (range 0-45) with little difference between the three major allergens and between the three types of mattresses. Occurrence of mattresses with concentrations above and below the proposed risk level (2 micrograms/g) was similar in the mattress groups. However, the allergen concentration was above risk level in 56%, if washable underblankets were not applied, compared with only 21% in the group with such underblankets. In conclusion, mattresses tend to accumulate allergen rather rapidly. Neither heated water mattresses, spring nor foam mattresses seem to be of any advantage for mite allergics, whereas underblankets made of synthetic fibres in a cotton or synthetic cover, commonly used in Denmark, might play a beneficial role in reducing allergen exposure.

Allergens↗
PubMed1979

Tarsonemid mites in Danish house dust.

From a study of 98 typical Danish city apartments it was found that pyroglyphid and tarsonemid mites dominated the housedust acarofauna. Both groups of mites show a remarkable similarity in their occurrence and dependence on the microclimate. Room air humidities above 7 g water/kg dry air involved the highest densities. Below this limit only background contamination appeared. At least 14 distinct forms of tarsonemid mites were found, with Tarsonemus floricolus Can. & Fanz., 1876 as the dominating species. As tarsonemid mites were found regularly rather than occasionally, it is suggested that these mites may be responsible for at least a part of the cases of housedust allergy that cannot be ascribed to the content of Dermatophagoides mites in the housedust.

Allergens↗
PubMed1990

Direct measurement of mucosal surface pH of pig jejunum in vivo.

The mucosal surface pH of pig jejunum was measured in vivo. When the pH in the bulk phase of the perfusing buffer solution was 7.10, the pH at the mucosa (as measured by a miniaturised glass pH electrode) was 6.19 +/- 0.04 (n = 19). This relatively acidic mucosal surface pH is not an anoxic artefact since anoxia resulted in a significant alkalinisation of the mucosa. This finding, that the pig, like man and the rat, has a jejunal "acid microclimate" has important implications for weak electrolyte absorption from the upper small intestine of this species as well as for any other pH dependent brush border process.

Animals↗
PubMed2005

Variability of Cenococcum colonization and its ecophysiological significance for young conifers at alpine-treeline.

* Plants establishing in environments that are marginal for growth could be particularly sensitive to mycorrhizal associations. We investigated ectomycorrhizal colonization and its significance for young conifers growing at, or above, their normal limits for growth, in the alpine-treeline ecotone. * Colonization of seedlings (<1 yr old) and juveniles (2- to 10-yr-old) of Picea engelmannii and Abies lasiocarpa by Cenococcum geophilum was determined in a field study, and effects of Cenococcum on Picea seedling ecophysiology were investigated in a glasshouse. * Colonization by Cenococcum was c. 20-fold greater for juveniles than seedlings, and approximately 4-fold greater adjacent compared with approximately 7 m away from trees. Juveniles of Picea were more colonized at timberline than Abies, and the opposite relationship was observed in forest. Colonization enhanced seedling water potential, but not phosphorus concentrations or photosynthesis. * These landscape and age-dependent variations in colonization correspond well with known variations in conifer physiology and establishment near timberline. Facilitation of seedling establishment by older trees at alpine-treeline may include a below-ground, mycorrhizal component that complements previously reported effects of trees on the microclimate and ecophysiology of seedlings.

Abies↗
PubMed2006

Seed fitness of hermaphrodites in areas with females and anther smut disease: Silene acaulis and Microbotryum violaceum.

Sex-dependent infection rates could change the effective sex ratio of a population. Here, I tested whether females and hermaphrodites of Silene acaulis were equally likely to be infected by Microbotryum violaceum, a fungus that sterilizes the host, and whether sex allocation in hermaphrodites differed between low and high disease plots. Sex ratios of healthy and diseased plants were estimated in five natural plots. Fitness gained through seed production was estimated by measuring seed quantity and quality for each sex morph in eight plots for 2 yr; four plots had 1-5% disease frequency and four plots had 18-25% disease frequency. Sex ratios of healthy and diseased plants did not differ in five plots. The proportion of fitness hermaphrodites gained through ovules varied from 25 to 48%, indicating that this population is near the cosexual end of gynodioecy. Variation in functional gender of hermaphrodites was not explained by sex-dependent infection rates. Spatial heterogeneity in resources and microclimate seems to be important in explaining both disease frequency and variation in seed production by females and hermaphrodites.

Basidiomycota↗
PubMed2006

Organizational silence and hidden threats to patient safety.

Organizational silence refers to a collective-level phenomenon of saying or doing very little in response to significant problems that face an organization. The paper focuses on some of the less obvious factors contributing to organizational silence that can serve as threats to patient safety. Converging areas of research from the cognitive, social, and organizational sciences and the study of sociotechnical systems help to identify some of the underlying factors that serve to shape and sustain organizational silence. These factors have been organized under three levels of analysis: (1) individual factors, including the availability heuristic, self-serving bias, and the status quo trap; (2) social factors, including conformity, diffusion of responsibility, and microclimates of distrust; and (3) organizational factors, including unchallenged beliefs, the good provider fallacy, and neglect of the interdependencies. Finally, a new role for health care leaders and managers is envisioned. It is one that places high value on understanding system complexity and does not take comfort in organizational silence.

Group Processes↗
PubMed2006

Impacts of alternative timber harvest practices on leaf-chewing herbivores of oak.

Studies of the effects of logging on Lepidoptera rarely address landscape-level effects or effects on larval, leaf-feeding stages. We examined the impacts of uneven-aged and even-aged logging on the abundance, richness, and community structure of leaf-chewing insects of white (Quercus alba L.) and black (Q. velutina L.) oak trees remaining in unharvested areas by sampling 3 years before and 7 years after harvest. After harvest, white oaks in uneven-aged sites had 32% fewer species of leaf-chewing insects than control sites. This reduction in species richness may have resulted from changes in microclimate (reducing plant quality and/or changing leaf phenology) that affected a much larger total area of each site than did even-aged cuts. For black oak after harvest, species richness in uneven- and even-aged sites increased relative to levels before harvest. Harvesting did not alter total insect density or community structure in the unlogged habitat for either oak species with one exception: insect density on black oak increased in the oldest forest block. Community structure of herbivores of black and white oaks in clearcut gaps differed from that of oaks in intact areas of even-aged sites. Furthermore, both richness and total insect density of black oaks were reduced in clearcut gaps. We suggest that low-level harvests alter herbivore species richness at the landscape level. Treatment effects were subtle because we sampled untreated areas of logged landscapes, only one harvest had occurred, and large temporal and spatial variation in abundance and richness existed. Although the effects of logging were greater in uneven-aged sites, the effects of even-aged management are likely to increase as harvesting continues.

Animals↗
PubMed1992

Epidemiological, clinical and allergological observations on pompholyx.

We have studied a group of 104 patients with pompholyx, to investigate the relationship between allergological factors and its etiopathogenesis. The following examinations were performed: blood sampling (routine tests and IgE levels), allergological tests (patch, prick, intradermal, and oral provovation tests with nickel sulphate), skin biopsy to exclude pemphigus vulgaris or bullous pemphigoid. An accurate history of familial and personal allergic diathesis was enquired for and various possible aggravating factors (season, microclimate, perspiration and emotional stress) were considered. The results were age and sex-matched with a healthy control group (208 subjects). We found familial and personal atopic diathesis in 50% of patients versus 11.5% of controls (p less than 0.001); 39 patients (37.49%) also had high levels of IgE. Nickel sulphate was the allergen with the highest positivity on patch testing: 20.19% versus 6.25% of the control group (p less than 0.001). The % of patients allergic to nickel reached 26%, including those (6 patients) reacting to the oral provocation test. Season (43 patients) and hyperhidrosis (38) were the aggravating factors most commonly claimed. We detected no correlation between age, sex, grading of pompholyx and the allergological parameters investigated. Though several different allergological findings have previously been reported in dyshidrosis, their role in its pathogenesis has not yet been fully explained. We think that different haptens or antigens can produce the same clinical and histological picture of pompholyx in predisposed subjects.

Adolescent↗
PubMed2006

Approaches for optimizing the calibration standard of Tewameter TM 300.

Calibration of devices measuring transepidermal water loss (TEWL) is in intensive discussion. Comparative studies revealed that comparable measuring systems, e.g. open and closed chamber systems, do not always deliver the same results, even when expressing the measured values in SI units, namely in g/m(2)/h. Therefore, adequate and reliable calibration procedures need to be established. We were able to test the reliability of a multi-step calibration algorithm for an open chamber system such as Tewameter TM 300. In order to achieve reliable measurements, the maintenance of stable microclimate conditions without air turbulences is mandatory. The TEWL values should be compared with those determined gravimetrically on heated skin simulators. The reproducibility of the results is warranted by consecutive measurements on different adjacent spots of a defined area. Preheating of the probe sensors is an effective approach for shortening the measuring time and gaining a rapid steady-state. The accurate calibration of the probe can be checked under laboratory conditions any time. The critical point of the calibration and ultimately the accuracy of in vivo measurements maintain the steady functional capacity of the probes during the entire duration of continuous studies. The studied calibration procedure ensures these requirements.

Air↗
PubMed1988

Carbonic anhydrase isoenzymes in the caecum and colon of normal and germ-free rats.

Histochemical and immunocytochemical methods were used to study the presence of carbonic anhydrase (CA) isoenzymes in the caecum and colon of normal and germ-free rats. Very high enzyme activity was demonstrated by histochemistry in the caecum and proximal colon of normal rats, while the activity decreased in the distal colon. Very strong immunostaining for the isoenzyme CA I was found in the cytoplasm of surface cells and upper gland cells in the caecum and colon of normal rats. In the distal colon the staining was less intense with a marked cell-to-cell variation. Ca II was found in the apical (luminal) cell region of the surface epithelium in all regions. Ca III was possibly present in small amounts, but this could not be judged with certainty. There was no difference in carbonic anhydrase between normal and germ-free rats (except for less staining of the mucosal capillaries in germ-free animals). Therefore, our data give no support to the hypothesis that CA I participates in the absorption of microbial fermentation products. The location of CA II in the apical cell region suggests a role for this isoenzyme in regulation of the microclimate close to the epithelial cells.

Animals↗
PubMed1995

Measurement of skin hydration in normal dogs and in dogs with atopy or a scaling dermatosis.

The role of the stratum corneum both as a barrier to water loss from the body and as a biological microenvironment is well recognised, although most discussion of these topics is expressed in qualitative terms. This paper describes the use of techniques for the measurement of some aspects of the skin microclimate, and their application to canine skin. The techniques used were the assessment of skin moisture, hygroscopicity and water-holding capacity by measurement of skin electrical capacitance. Meaningful deductions regarding the water dynamics of certain skin sites can be drawn, and it was shown that significant differences in hydration exist between different skin sites. The techniques were also used to show that scaly skin is 'drier' than normal skin, and that the water dynamics of the non-lesional skin of atopic dogs does not differ from that of normal dogs.

Analysis of Variance↗
PubMed1990

Role of unstirred water layer in the exsorption of quinidine.

Intestinal ++exsorption of salicylic acid, thiopentone, theophylline, and quinidine was measured during perfusion of the intestinal lumen with Tyrode solution. The effect of pectin or bovine serum albumin added to the perfusate on intestinal clearance (CLi) was investigated. Increasing pectin concentration from 0.0 to 0.5, 1.0 and 1.5% gave CLi values for quinidine of 499 +/- 18, 363 +/- 35, 237 +/- 56, and 300 +/- 28 mL h-1 kg-1, respectively. One per cent of pectin in the perfusate also decreased the CLi of thiopentone, but had no effect on the CLi of salicylic acid or theophylline. Pectin may have increased the thickness of the unstirred water layer on the mucous membrane and the resistance of drug exsorption for some drugs. When bovine serum albumin was added, drug binding in the perfusate increased, and the CLi of salicylic acid, thiopentone, and theophylline increased; the CLi of quinidine was unaltered. Co-administration of theophylline with quinidine decreased the CLi of quinidine without affecting quinidine binding in serum or in the perfusate. The CLi theophylline was not affected by quinidine. These observations are consistent with the hypothesis that the exsorption of quinidine is rate-limited by diffusion through the unstirred water layer on the mucous membrane. The CLi of quinidine is affected by the microclimate-pH in the unstirred water layer. An alternative possibility is that quinidine exsorption is mediated by a carrier-transport pathway.

Animals↗
PubMed1966

Transfer of propionate by rat small intestine in vitro.

1. The transfer of propionate by sacs of rat everted intestine has been investigated in relation to a number of physico-chemical factors which affect movement of weak electrolytes.2. Neither the observed movement nor the distribution of propionate can be accounted for by the theory of non-ionic diffusion or by modifications of it, such as the microclimate hypothesis or partial permeability to ions.3. It is not possible to account for the observed propionate movement by the electrical potential across the gut or by solvent drag.4. The most satisfactory explanation for the observations is a transfer process in the gut for volatile fatty acids, and some features of this are discussed.

Animals↗
PubMed1974

Absorption of folic acid by everted segments of rat jejunum.

1. Everted rings of rat intestine were used to study the initial uptake rate of folic acid at various concentrations and incubation temperatures in vitro.2. Folic acid was accumulated linearly for periods of at least 30 min.3. The initial uptake rate was found to reach a constant value as the concentration of folic acid in the incubation medium was increased above 5 x 10(-6)M.4. Reducing the temperature of incubation from 37 to 27 degrees C gave small Q(10) values at either end of the concentration range.5. Transfer of folic acid into the serosal compartment of everted sacs was shown to undergo a rate reduction in the same concentration range.6. A mechanism for folic acid transport is suggested in which folic acid is converted to the neutral species at the mucosal surface in an acid microclimate.

Animals↗