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PubMed1993

Common diarrhea pathogens and the risk of dehydration in young children with acute watery diarrhea: a case-control study.

The role of common diarrheal pathogens in dehydration was examined in children with acute watery diarrhea who attended the treatment center of the International Centre for Diarrhoeal Disease Research, Bangladesh, in Dhaka. Two hundred sixty-nine children with moderate or severe dehydration were matched with 700 children with no dehydration. Vibrio cholerae O1 infections were 5.5 times more likely to be associated with dehydration than in cases without this agent. No significant association could be found between the presence of enterotoxigenic Escherichia coli. Campylobacter jejuni, or rotavirus infection and dehydration. These results were obtained after simultaneously controlling for age, lack of oral rehydration therapy (ORT) at home, protein energy malnutrition, withdrawal of breast-feeding during diarrhea at home, poor housing, longer duration of diarrhea at home, and delay in reaching the treatment center. The cholera isolation rate was only 4.5% and thus explains only a small proportion of the cases of dehydration. In cholera-endemic areas, a strategy to prevent dehydration in small children is needed to ensure correct use of ORT at home, prompt referral, and the use of a suitable antibiotic when cholera is clinically suspected.

Acute Disease↗
PubMed2000

Relationship of breast-feeding and hand-washing with dehydration in infants with diarrhoea due to Escherichia coli.

This prospective cohort study was carried out in the neonatal unit of the Yangon Children Hospital, Myanmar, to gather more information on the types of feedings and hand-washing practices of mothers as the determinant of severe dehydration in infants with acute diarrhoea due to Escherichia coli. The study subjects included 100 infants with diarrhoea, aged less than 4 months, admitted to the hospital from June 1997 to May 1998. Data on isolation of E. coli from rectal swab samples, types of feedings, hand-washing practices, and dehydration status were collected. Of the 100 cases, E. coli was isolated from rectal swab samples of 48 infants. Of these 48 cases, 28 had some dehydration and 20 had severe dehydration. Exclusive breast-feeding was observed only in the age group < 1 and > 1-2 month(s). The association of the severity of dehydration with other types of feedings compared to exclusive breast-feeding was not statistically significant. In this study, most mothers washed their hands with water only after cleansing their children's defaecation, and before and after feeding their children. The severity of dehydration was statistically significant in hand-washing practices when compared to washing with water only and washing with soap and water. This study has shown the association between types of feedings and hand-washing practices with dehydration in infants with acute diarrhoea due to E. coli. The results of the study suggest that there is a need for appropriate intervention programmes to promote exclusive breast-feeding and hand-washing practices with soap and water after cleansing children's defaecation, and before and after feeding children.

Breast Feeding↗
PubMed1992

Maternal practices and risk factors for dehydration from diarrhoea in young children: a case-control study in central Thailand slums.

To determine factors related to dehydration from diarrhoea, we conducted a hospital-based, case-control study in children aged 24 months or younger who had acute watery diarrhoea and attended Chonburi Regional Hospital in central Thailand during November 1988 through May 1989. The study compared 48 cases who had moderate or severe dehydration with 48 controls who had no dehydration. Both cases and controls belonged to low socioeconomic families and were living in urban slum areas. They had adequate health care facilities and access to ORS packets. Overall, 56% of the mothers used ORS solution at home. None of the mothers knew how to administer ORS, i.e. the fluid was not given at the onset of diarrhoea to prevent dehydration, and they gave no more than 60 ml over a 24-hour period to their dehydrated children. They also did not use home fluids. Multivariate analysis of data showed two factors significantly associated with dehydration: children's dirty fingernails that indicated inadequate maternal hygiene-related behaviour (Odds Ratio 6.4; 95% Confidence Intervals 1.5-27.6, p < 0.01), and frequency of vomiting in the 24 hours before rehydration (Odds Ratio 1.3; 95% Confidence Intervals 1.1-1.6, p < 0.001). Cases and controls had similar aetiologic agents and nutritional status. Providing proper education to mothers about oral rehydration therapy with special emphasis on the volume of ORS to be given, along with guidance to improve their personal hygiene should be considered important interventions in reducing the risk of dehydration and deaths from diarrhoea in these children.

Case-Control Studies↗
PubMed1978

The neurohypophysial vasopressin content as influenced by modified cholinergic or adrenergic transmission during long-term dehydration in the white rat.

In rats dehydrated up to 12 days the neurohypophysial vasopressin content was determined by Dekański's method. Carbamylcholine inhibited somewhat the vasopressin depletion in the neurohypophysis, but not earlier than under severe dehydration (8th and 12th day). A single dose of atropine given 24 h prior to sacrifice to not dehydrated animals resulted in a diminution of the vasopressin content in the neurohypophysis; in animals dehydrated for four days and parallely atropinized the decrease of the neurohypophyseal vasopressin content was, on the contrary, considerably inhibited. Under severe dehydration, the treatment with atropine did not change the vasopressin stores in the neural lobe. Phenoxybenzamine inhibited the vasopressin depletion in the neural lobe following four days of dehydration. Under severe dehydration, amphetamine potentiated the effect of osmoreceptor stimulation. It is supposed that impulses of osmoreceptor origin are of some importance in determining the vasopressin release following changes of cholinergic or adrenergic transmission.

Amphetamine↗
PubMed1995

[The ecological-morphological aspects of adaptation and the role of the macrophages in body dehydration].

The morphological aspects of rearrangement of macrophages in white rats' subcutaneous areolar tissue during dehydration and their impact on the recovery of osmotic homeostasis were studied. A response of macrophages to dehydration with preliminary injection of antioxidant dibunol was revealed. Macrophages respond to dehydration by a rise in number, elevated cytoplasmic activity of lipolytic enzymes (beta-oxibutyrate dehydrogenase), and a peculiar ultrastructural rearrangement, i.e. a decrease of vacuoles, their sizes, an increase of the lipid volumetric fraction. However, the higher activity of macrophages in terms of production of metabolic water is concurrent to increased malonic dialdehyde production and inhibited activity of the cell antioxidant defense (superoxide dismutase). To correct the observed changes, dehydration was performed on the background of antioxidant dibunol injection. The antioxidant and subsequent dehydration did not annul the response of macrophages to increased intrabody osmolality although slightly masked the effect of dehydration. Survivability in this group of animals was by 22% higher than in the water-deprived group. Hence, the areolar macrophages can be considered the controllers of adaptive reactions of the body during dehydration, whereas antioxidants are the correction factor for these reactions.

Adaptation, Physiological↗
PubMed1998

Hemodynamic response to vasopressin in dehydrated human subjects.

BACKGROUND: Despite the known potent vasoconstrictor effects of vasopressin, the role of this hormone in the maintenance of blood pressure is incompletely understood. In studies performed in animals with increased plasma vasopressin concentrations, several complex cardiovascular effects have been noted, including decreases in heart rate and cardiac output, which may account for a lack of effect on arterial pressure despite the vasopressin-induced increase in total peripheral resistance. Only a few studies have been done to assess the cardiovascular effects of vasopressin in human subjects, and most of these have been limited to measurement of heart rate and arterial pressure only. The present study was designed to identify more fully the cardiovascular effects of vasopressin when plasma vasopressin concentrations are increased by osmotic stimulation without the superimposition of major nonosmotic stimuli associated with severe volume depletion. METHOD: Studies were performed on 11 normal human subjects in supine and erect posture before and after 24 hours of fluid deprivation, and following administration of a selective V1 receptor antagonist, [d(CH2)5Tyr(ME)]AVP, after dehydration. Cardiovascular parameters were measured noninvasively by thoracic electrical bioimpedance cardiography and blood samples for measurements of plasma concentrations of vasopressin and other hormones affected by dehydration and differences in posture were collected for subsequent analysis. RESULTS: After 24 hours of fluid restriction, plasma osmolality was increased from 287 +/- 0.9 to 294 +/- 0.7 mosm/kg H20 and plasma vasopressin concentrations (Pavp) were increased in both supine and erect posture. Mean arterial (MAP) and systolic blood pressure (SBP) were reduced by fluid restriction but were higher in erect than in supine posture both before and after fluid restriction. Heart rate (HR), diastolic blood pressure (DBP), and systemic vascular resistance (SVRI) were also higher in erect than in supine posture, while cardiac index (CI), stroke index (SI), end-diastolic index (EDI), and an index of total thoracic fluid content (TFC) were all reduced in erect posture, both before and after dehydration. Plasma renin activity (PRA) and plasma norepinephrine concentrations (Pne) were increased in erect posture, both before and after dehydration, but there was no effect of erect posture on plasma vasopressin concentrations (Pavp), either before or after dehydration. Administration of the V1 receptor antagonist after dehydration had no effect on hemodynamic parameters other than small reductions in DBP and cardiac preload. CONCLUSION: It is concluded from these studies that small increases in Pavp associated with moderate dehydration do not play a role in the maintenance of arterial pressure in normal human subjects in either supine or erect posture.

Adult↗
PubMed2004

The effect of dehydration history on PVA/PVP hydrogels for nucleus pulposus replacement.

The feasibility of the use of a copolymer gel prepared from blends of polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) for endoscopic replacement of the nucleus pulposus of a lumbar intervertebral disc was examined in this study. Hydrogels were processed with the use of three freeze/thaw cycles to induce crystallinity. As-prepared samples were dehydrated to various levels: 70.4, 46.3, 25.1, and 10.3% of their as-prepared masses and subsequently rehydrated. The dehydration history controlled the dimensions upon swelling and caused distortion of the material, with major distortion occurring when the hydrogel reached around 25% of the initial hydrated mass. The dehydration history affected the mechanical behavior of the rehydrated gels. Increased dehydration resulted in increased compressive modulus for the reswollen gels. Experiments were performed to investigate the formation of a skin layer that was found on the hydrogels during the dehydration process. The skin was found to dehydrate quickly and form a barrier to further dehydration from the core. Rubber elasticity theory was used to describe the differences in the network characteristics between the skin and the core of a drying hydrogel. The dehydration/rehydration process used in this study and an implantation of a cadaver model demonstrate the feasibility of endoscopic nucleus replacement.

Biocompatible Materials↗
PubMed2005

Mechanism of the formation of a dehydrated ion by an unusual loss of oxygen at the 4'-carbonyl group of abscisic acid methyl ester in electron ionization mass spectrometry.

Methyl ester of abscisic acid (ABA), a plant hormone, gives a dehydrated ion at m/z 260 in electron ionization mass spectrometry (EI-MS). This dehydrated ion had been considered to be derived only from the elimination of the tertiary hydroxyl group at C-1'. We found that 34% of the dehydrated ion was formed by elimination of the oxygen atom at the 4'-carbonyl group, and the remaining 66% by elimination of the 1'-hydroxyl group. This unusual elimination of the carbonyl oxygen was shown with [4'-(18)O]ABA methyl ester. Involvement of the 4'-carbonyl oxygen in dehydration was observed in methyl ester of phaseic acid (PA), a natural metabolite of ABA, but not in 1'-deoxy-ABA methyl ester or isophorone. This suggested that the 1'-hydroxyl group was necessary for the elimination of the 4'-carbonyl oxygen. ABA methyl esters labeled with stable isotopes showed that hydrogen atoms at the 1'-hydroxyl group and at C-4 or -5 or -3' or - 5' or -7' were eliminated with the 4'-carbonyl oxygen. These results allow us to propose a formation mechanism of the dehydrated ion derived from the elimination of 4'-carbonyl oxygen and hydrogen atoms at C-4 and 1'-oxygen in ABA methyl ester as follows: first, ionization at the 1'-hydroxyl group occurs to give an ion radical, and the proton at the 1'-oxygen migrates to the 4'-carbonyl oxygen after the bond fission between C-1'-C-6'; second, migration of the proton at C-4 to the 1'-oxygen is followed by migration of the protons at C-5 and C-7' to C-4 and C-5, respectively; finally, the proton at the 1'-oxygen migrates to the 4'-hydroxyl group, and H(2)O at C-4' is eliminated to give the dehydrated ion. Our findings point out that a dehydrated ion is not always derived from the elimination of a hydroxyl group.

Abscisic Acid↗
PubMed2003

Model-free treatment of the dehydration kinetics of nedocromil sodium trihydrate.

The conventional model-fitting approach to kinetic analysis assumes a fixed mechanism throughout the reaction and therefore may be too simplistic for many solid-state reactions. Even for a reaction with a fixed mechanism, model fitting sometimes cannot identify the reaction model uniquely. The alternative model-free approach is sufficiently flexible to allow for a change of mechanism during the course of a reaction and therefore provides a more realistic treatment of solid-state reactions kinetics. The application of model-free analysis to solid-state dehydrations was investigated using the two consecutive dehydration reactions of nedocromil sodium trihydrate. The complexity of such reactions is illustrated by the variation of the activation energy as each dehydration proceeds. The 1st-step dehydration follows one-dimensional phase boundary kinetics until the fraction dehydrated reaches 0.75, and deviates from this model thereafter. The 2nd-step dehydration follows a mechanism intermediate between two- and three-dimensional diffusion that cannot be described by any of the common models. The model-free approach is clearly better than the model-fitting approach for understanding the details of these solid-state dehydration reactions.

Desiccation↗
PubMed2004

Dehydration kinetics of piroxicam monohydrate and relationship to lattice energy and structure.

The dehydration kinetics of piroxicam monohydrate (PM) is analyzed by both model-free and model-fitting approaches. The conventional model-fitting approach assuming a fixed mechanism throughout the reaction is found to be too simplistic. The model-free approach allows for a change of mechanism and activation energy, Ea, during the course of a reaction and is therefore more realistic. The complexity of the dehydration of PM is illustrated by the dependence of Ea on both the heating conditions, isothermal or nonisothermal, and on the fraction of conversion, alpha (0 < or = alpha < or = 1). Under both isothermal and nonisothermal conditions, Ea increases with alpha for 0 < or = alpha < or = 0.25, followed by an approximately constant value of Ea during further dehydration. In the constant-Ea region, isothermal dehydration follows the two-dimensional phase boundary model (R2), whereas nonisothermal dehydration follows a mechanism intermediate between two- and three-dimensional diffusion that cannot be described by any of the common models. Structural studies suggest that the complex hydrogen-bond pattern in PM is responsible for the observed dehydration behavior. Ab initio calculations provide an explanation for the changes in the molecular and crystal structures accompanying the reversible change in hydration state between anhydrous piroxicam Form I and PM. This work also demonstrates the utility of model-free analysis in describing complex dehydration kinetics.

Crystallization↗
PubMed1986

Plasma levels of arginine vasotocin, prolactin, aldosterone and corticosterone during prolonged dehydration in the domestic fowl: effect of dietary NaCl.

Three groups of White Plymouth Rock laying hens were adapted to three levels of dietary NaCl: low-NaCl food with tap water (LOW), high-NaCl food (1% NaCl w/w added) with tap water (HT), and high-NaCl food with 0.5% NaCl for drinking (HS). The birds were subjected to water deprivation (dehydration) for 18 days. Blood sampling was done at 2-4 day intervals. Plasma concentrations of arginine vasotocin (AVT), prolactin (PRL), aldosterone (ALDO) and corticosterone (CS) were determined by radioimmunoassay. Plasma osmolality, sodium, chloride, and potassium were also determined. In the normally hydrated hens fully adapted to the diets, there was a stepwise increase from LOW to HS in plasma osmolality (305, 315, 332 mOsm, for LOW, HT and HS, respectively), [Na+] (144, 153, 161 mM) and [Cl-] (109, 119, 127 mM) as well as in [AVT] (6, 14, 18 pg/ml) and [PRL] (16, 24, 34 ng/ml). Regressing [AVT] on osmolality gave a slope of 0.30 pg . ml-1/mOsm and a threshold of 273 mOsm. The slope of [PRL] on osmolality was 0.73 ng . ml-1/mOsm. The correlation coefficient of [AVT] and [PRL] was 0.67. LOW had high [ALDO] (165 pg/ml) which was suppressed to low levels in HT and HS (5-8 pg/ml), while [CS] was the same in all groups (0.9-1.1 ng/ml). Plasma [K+] was decreased in the high-NaCl groups (5.8 mM in LOW, 4.4 and 4.7 mM in HT and HS). Dehydration resulted within 2 days generally in a sharp (5-15%) increase in osmolality, [Na+] and [Cl-], which thereafter increased more slowly during the remaining 16 days in all groups, with the slowest increase in LOW. The levels of osmolality [Na+] and [Cl-] were 5% lower in LOW than in HT and HS, which showed the same levels during the dehydration period. Plasma [AVT] and [PRL] increased 2-4 fold within 2 days of dehydration; [AVT] reached a plateau at 29 pg/ml in all groups, but [PRL] continued to rise in all groups, fastest in LOW, reaching similar levels in all groups after 14-18 days of dehydration, about 85 ng/ml. The correlation coefficient of [AVT] and [PRL] was decreased by half (to 0.32) during dehydration. Plasma [ALDO] increased in all groups with dehydration, 1.7 fold in LOW and 3-6 fold in HT and HS, but the levels reached in HT and HS were only 15-30% of that seen in LOW.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenal Cortex Hormones↗
PubMed2003

Hydraulic adjustment in jack pine and black spruce seedlings under controlled cycles of dehydration and rehydration.

Drought adjustments were compared in black spruce (Picea mariana[Mill] B.S.P), and jack pine (Pinus banksiana[Lamb.]) by subjecting seedlings to five cycles of dehydration and rehydration. A computer-controlled root misting chamber system, supplied low (-1.5 MPa), moderate (-2.0 MPa), and severe (-2.5 MPa) dehydration, respectively, in cycles 1, 3 and 5. Although cell water relations failed to adjust to chronic dehydration, there was limited osmotic adjustment in black spruce (cycle 3), and water was re-allocated from the apoplast to the symplast in jack pine (cycles 1 and 3). Dehydration postponement was more important than dehydration tolerance. Jack pine was better able to postpone dehydration than black spruce. Specific conductivity, the hydraulic conductivity per unit stem cross-sectional area, was lower in jack pine and slower to decline during chronic dehydration. When specific conductivity was corrected for the greater leaf area in black spruce, the leaf-specific conductivity did not differ in the two species. There was no increase in needle leakage in jack pine and stomata in jack pine seedlings reopened fully after rehydration. Black spruce was more of a 'water spender', and less water stress (-2.0 MPa, cycle 3) was required to lower specific conductivity, compared to jack pine (-2.5 MPa, cycle 5). Leakage from needle membranes increased in black spruce, and stomata failed to reopen after rewatering (cycles 3 and 5). A greater needle area, smaller root system, and a higher specific conductivity lowered the water stress threshold for cavitation in black spruce, which is confined to moister sites in the boreal forest. Jack pine had a larger root system, smaller needle area and lower specific conductivity than black spruce. Because of these static features, jack pine is more drought tolerant and it is often found on sites that are too hot and dry for black spruce.

Journal Article↗
PubMed1994

Dehydration: a model for (low-temperature) argon laser tissue bonding.

Despite considerable investigation, the mechanism of laser assisted vascular anastomosis remains unknown. Indications suggest that bonding is the result of thermal action, particularly the thermal denaturation of tissue proteins. However, our own work has led us to conclude that dehydration is an important factor. Hence, we have proposed that laser anastomosis is the result of dehydration at the apposed tissue faces, induced by laser irradiation. This was investigated by comparing the properties of bonds created by dehydration with those created by laser. The bonds were created using parameters consistent with laser anastomoses created in vivo. Results revealed that anastomoses created by dehydration were equivalent to those created by laser, with little difference in strength, histology or response to rehydration. The only significant difference (p < 0.02) was mean bond strength created at temperatures above the denaturation temperature of the tissue (548 g cm(-2) by laser, 994 g cm(-2) by dehydration). Given the similarity of bonds created by the two methods, we conclude that the same mechanism (i.e. dehydration) is likely to be responsible for bonding in both cases and therefore that argon laser bonding is mediated by dehydration.

Anastomosis, Surgical↗
PubMed2002

Plasma membrane lipids in the resurrection plant Ramonda serbica following dehydration and rehydration.

Plants of Ramonda serbica were dehydrated to 3.6% relative water content (RWC) by withholding water for 3 weeks, afterwards the plants were rehydrated for 1 week to 93.8% RWC. Plasma membranes were isolated from leaves using a two-phase aqueous polymer partition system. Compared with well-hydrated (control) leaves, dehydrated leaves suffered a reduction of about 75% in their plasma membrane lipid content, which returned to the control level following rewatering. Also the lipid to protein ratio decreased after dehydration, almost regaining the initial value after rehydration. Lipids extracted from the plasma membrane of fully-hydrated leaves were characterized by a high level of free sterols and a much lower level of phospholipids. Smaller amounts of cerebrosides, acylated steryl glycosides and steryl glycosides were also detected. The main phospholipids of control leaves were phosphatidylcholine and phosphatidylethanolamine, whereas sitosterol was the free sterol present in the highest amount. Following dehydration, leaf plasma membrane lipids showed a constant level of free sterols and a reduction in phospholipids compared with the well-hydrated leaves. Both phosphatidylcholine and phosphatidylethanolamine decreased following dehydration, their molar ratio remaining unchanged. Among free sterols, the remarkably high cholesterol level present in the control leaves (about 14 mol%) increased 2-fold as a result of dehydration. Dehydration caused a general decrease in the unsaturation level of individual phospholipids and total lipids as well. Upon rehydration the lipid composition of leaf plasma membranes restored very quickly approaching the levels of well-hydrated leaves.

Cerebrosides↗
PubMed2000

Metabolic dysfunction and unabated respiration precede the loss of membrane integrity during dehydration of germinating radicles.

This study shows that dehydration induces imbalanced metabolism before loss of membrane integrity in desiccation-sensitive germinated radicles. Using a photoacoustic detection system, responses of CO(2) emission and fermentation to drying were analyzed non-invasively in desiccation-tolerant and -intolerant radicles of cucumber (Cucumis sativa) and pea (Pisum sativum). Survival after drying and a membrane integrity assay showed that desiccation tolerance was present during early imbibition and lost in germinated radicles. However, tolerance could be re-induced in germinated cucumber radicles by incubation in polyethylene glycol before drying. Tolerant and polyethylene glycol (PEG)-induced tolerant radicles exhibited a much-reduced CO(2) production before dehydration compared with desiccation-sensitive radicles. This difference was maintained during dehydration. In desiccation-sensitive tissues, dehydration induced an increase in the emission of acetaldehyde and ethanol that peaked well before the loss of membrane integrity. Acetaldehyde emission from sensitive radicles was significantly reduced when dehydration occurred in 50% O(2) instead of air. Acetaldehyde/ethanol were not detected in dehydrating tolerant radicles of either species or in polyethylene glycol-induced tolerant cucumber radicles. Thus, a balance between down-regulation of metabolism during drying and O(2) availability appears to be associated with desiccation tolerance. Using Fourier transform infrared spectroscopy, acetaldehyde was found to disturb the phase behavior of phospholipid vesicles, suggesting that the products resulting from imbalanced metabolism in seeds may aggravate membrane damage induced by dehydration.

Carbon Dioxide↗
PubMed1992

Expression of "Dehydrin-Like" Proteins in Embryos and Seedlings of Zizania palustris and Oryza sativa during Dehydration.

Proteins inducible by dehydration and abscisic acid (ABA), termed dehydrins or RAB (Responsive to ABA) proteins, have been identified in a number of species and have been suggested to play a role in desiccation tolerance, particularly during seed development. Seeds (caryopses) of North American wild rice (Zizania palustris var interior [Fassett] Dore) are tolerant of dehydration to <10% moisture content (fresh weight basis) only under restricted dehydration and rehydration conditions. In comparison, seeds of paddy rice (Oryza sativa L.) readily tolerate desiccation to <5% water content. Expression of "dehydrin-like" proteins in Zizania and Oryza seedlings and embryos was examined to investigate the relationship between the presence of such proteins and desiccation tolerance. [(35)S]Methionine labeling of newly synthesized proteins showed that seedlings (first leaf stage) of both Zizania and Oryza synthesized a novel "heat-stable" protein of apparent molecular weight = 20,000 when dehydrated to <75% of their initial fresh weight. ABA (100 micromolar) induced synthesis of a protein with similar electrophoretic mobility in both species. Western blots using antiserum raised against maize (Zea mays L.) dehydrin detected a protein band from dehydrated Zizania shoots and mature embryonic axes that comigrated with the labeled 20-kilodalton polypeptide. Northern blots using a cDNA for an ABA-responsive protein from Oryza (rab 16a) showed that both seedlings and excised embryonic axes of Zizania accumulated RNA similar in sequence to rab 16a in response to water loss. Zizania seedlings and embryonic axes were also capable of ABA accumulation during dehydration. The intolerance of Zizania seeds to dehydration at low temperature is apparently not due to an absence of dehydrin-like proteins or an inability to accumulate ABA.

Journal Article↗
PubMed1997

The effects of maturity and dehydration shrinkage on resin-modified glass-ionomer restorations.

The dimensional change, including hygroscopic change, of adhesive dental materials is a clinically important topic, since excessive changes could cause debonding from tooth structure. The water balance of glass-ionomer cements arises mainly from their sensitivity to the environment; depending on the surroundings, they can gain or lose water, either of which can be potentially damaging. These effects become less noticeable as the cement ages. The effects of maturity of the newer resin-modified glass-ionomer materials and their responses to changes in moisture are unknown. Using confocal microscopy, we examined the effects of dehydration stress on the glass-ionomer/tooth interface in specimens of various degrees of maturity. Wedge-shaped cervical cavities in extracted teeth were restored with one of three resin-modified glass-ionomer restorative materials. The control specimens were restored with a conventional glass ionomer. The samples were left to mature, then sectioned and examined at 1 day, 1 wk, 1 mo, 3 mos, 6 mos, and 1 yr. After being sectioned, each specimen was examined immediately with a confocal microscope with water-immersion objectives so that the subsurface interfacial characteristics could be studied. The specimen was then allowed to dehydrate under the microscope, with further examinations at 15, 30, and 60 min. Generally, gap formation at the interface occurred within 15 min of dehydration. All materials showed a different pattern of gap change with maturity, probably due to the different setting mechanisms involved. All of them were susceptible to dehydration shrinkage up to 3 mos of maturity. At 6 mos and 1 yr, Fuji II and Fuji II LC showed insensitivity to dehydration. Vitremer and Photac-Fil showed less sensitivity to dehydration at 1 yr than at 6 mos. The results of this study of the maturing polymerized resin-modified cements have potential clinical implications in the handling of these materials; the addition of resin has not significantly reduced the glass ionomer's susceptibility to dehydration problems.

Analysis of Variance↗
PubMed2000

Catalase transcript accumulation in response to dehydration and osmotic stress in leaves of maize viviparous mutants.

The effect of osmotic stress and dehydration on maize catalase transcript accumulation was examined in leaves of abscisic acid (ABA)-deficient and ABA-insensitive mutants. We have found that the response of Cat1 to osmotic stress and dehydration is not via an ABA-mediated pathway in young leaves, suggesting that there are two different mechanisms by which Cat1 responds to osmotic stress in embryos and in leaves. The Cat2 transcript increased in response to osmotic stress, but was repressed by dehydration. On the other hand, the Cat3 transcript is up-regulated by dehydration and osmotic stress only in ABA-deficient mutant leaves, implying that ABA may act as a repressor for Cat3 expression in response to dehydration and high osmoticum. We also found that the VP1 trans-acting factor is not required for the induction of Cat1 by ABA in leaves, but may play a role in stabilizing the Cat1 transcript after an initial induction. The exact nature of the signals triggering Cat responses to osmotic stress and dehydration is not clear. We speculate that oxygen free radicals may play a role in this response. Osmotic stress and dehydration may indirectly induce production of oxygen free radicals in leaves, thus triggering the antioxidant response.

Abscisic Acid↗