Rehydration Periods Research Articles

In-vivo evaluation of the effects of short-term dehydration and rehydration on the color differences of immature permanent incisor teeth.

It is aimed to evaluate the color changes of upper central incisor teeth with different root maturation levels after 15 min of dehydration and rehydration. Using the Cvek classification, 60 participants were divided into five groups. A spectrophotometer, equipped with a specially designed jig, was utilized for color measurements. Following isolation, color measurements were conducted at the dehydration process intervals of baseline, 1st, 2nd, 3rd, 5th, 7th, 10th, and 15th minutes. After mouth rinsing, measurements were repeated at the same time intervals during the rehydration process. CIEDE2000 (ΔE00) values and the Whiteness Index (WID) were obtained to compare the color changes between the initial readings and each interval. Friedman and Repeated Measures ANOVA were applied to compare classes by time during the dehydration and rehydration periods, as well as ANOVA and Kruskal-Wallis tests to compare by classes for each time (p < 0.05). Significant differences emerged in the mean ΔE00 values during dehydration and rehydration periods across all Cvek Classes (p < 0.05). While no statistically significant differences were observed among Classes at different minutes during the rehydration period (p > 0.05), it was particularly noted that the mean ΔE00 values of Classes 2, 3, and 5 at the 2nd minute of dehydration were statistically significantly higher than the mean of Class 1 (p < 0.05). However, when evaluating the starting and ending measurements of both dehydration and rehydration processes, and the overall change in ΔE00 and ΔWID, no significant variations were detected across the Classes (p > 0.05). In teeth that have just erupted and are still undergoing root development, dehydration in the initial minutes results in noticeable color changes. However, the change in ΔE00 and ΔWID of the teeth was found to be similar after the dehydration and rehydration processes. According to the Cvek classification, the lower color change in Class 1 teeth within the first 2 min of dehydration and the need for more than 15 min of rehydration for immature teeth with an open apex to return to their initial state after a 15-min dehydration are crucial for clinicians in terms of color assessment timing.

Germination of palm seeds under periods of rehydration

Abstract Palm seeds are indicative of being recalcitrant species. Seeds germination for many species, is slow and uneven, even in favorable conditions, often due to the resistance of the woody endocarp that makes them impermeable to water. Most species also have the characteristic of not tolerating the drying process at low moisture levels, thus losing their viability. In view of these considerations, the objective was to evaluate the effect of different periods of rehydration on the germinative process of seeds of royal palm, dwarf palm and jeriva. Seeds were homogenized and immersed in water containing 3 times their volume, with daily replacement. The experimental design used was completely randomized, with 5 treatments (0, 3, 6, 9, and 12 days of rehydration), with 4 replications of 25 seeds. The seeds were placed in transparent “gerbox” plastic boxes containing medium vermiculite as substrate and placed in BOD with a photoperiod of 16-hour of light and their respective optimum temperatures for each species. The number of germinated seeds was counted every 2 days until germination stabilized. The variables analyzed were germination percentage, germination speed index (GSI), average germination time (AGT) and distribution of germination over the days. Rehydration for 3 days increased the germination rate of royal palm seeds. For dwarf and jeriva species, rehydration did not influence the analyzed variables. The GSI and AGT were negatively influenced by the rehydration periods for royal palm. Rehydration prolonged the peak of germination of the studied species.

Fluid and electrolyte balance considerations for female athletes

ABSTRACT This review explores the effects of oestrogen and progesterone fluctuations across the menstrual cycle on fluid and electrolyte balance. The review aims to provide information on this topic for the exercising female but also for researchers working in this field. Beginning with a basic introduction to fluid and electrolyte balance, the review goes on to describe how oestrogen and progesterone have independent and integrated roles to play in the regulation of fluid and electrolyte balance. Despite evidence that oestrogen can influence the osmotic threshold for arginine vasopressin release, and that progesterone can influence aldosterone production, these actions do not appear to influence fluid retention, plasma volume changes at rest and during exercise, or electrolyte losses. However, the large inter-individual variations in hormonal fluctuations throughout the menstrual cycle may mean that specific individuals with high fluctuations could experience disturbances in their fluid and electrolyte balance. During phases of oestrogen dominance (e.g. late-follicular phase) heat dissipation is promoted, while progesterone dominance (e.g. mid-luteal phase) promotes heat conservation with overall higher basal body temperature. However, these responses do not consistently lead to any change in observed sweat rates, heat-stress, or dehydration during exercise. Finally, the literature does not support any difference in fluid retention during post-exercise rehydration periods conducted at different menstrual cycle phases. Although these mean responses largely reveal no effects on fluid and electrolyte balance, further research is required particularly in those individuals who experience high hormonal fluctuations, and greater exploration of oestrogen to progesterone interactions is warranted.

Preservation of allograft bone using a glycerol solution: a compilation of original preclinical research

BackgroundBone allografts are used in many orthopedic procedures to provide structural stability as well as an osteoconductive matrix for bone ingrowth and fusion. Traditionally, bone allografts have been preserved by either freezing or freeze-drying. Each of these preservation methods has some disadvantages: Frozen grafts require special shipping and storage conditions, and freeze-drying requires special lyophilization equipment and procedures that may impact biomechanical integrity. This report describes an alternate type of preservation using glycerol, which allows storage of fully-hydrated tissues at ambient temperature avoiding the potential complications from freeze-drying.MethodsIn the in vitro three-point bend test, cortical bone was processed and frozen, freeze-dried, or treated with glycerol-based preservation (GBP). Load was applied to each graft at a rate of 2.71 mm/min. The flexural strain, flexural strength, and flexural modulus were then calculated. In the in vitro axial compression test, iliac crest wedges, fibular segments, and Cloward dowels were processed and either freeze-dried or GBP treated. The compressive strength of the grafts were tested at time zero and after real time aging of 1, 4, and 5 years. In the in vivo rat calvarial defect assessment, freeze-dried, frozen, and GBP bone implants were compared after being implanted into a critical sized defect. Samples underwent histological and biomechanical evaluation.ResultsBone grafts subjected to GBP were found to be at least biomechanically equivalent to frozen bone while also being significantly less brittle than freeze-dried bone. GBP-preserved bone demonstrated significantly greater compressive strength than freeze-dried at multiple time points. Preclinical research performed in calvaric defect models found that GBP-preserved bone had similar osteoconductivity and biocompatibility to frozen and freeze-dried samples.ConclusionPreclinical research demonstrated that glycerol–preservation of bone yields a material that maintains biomechanical strength while eliminating the need for extensive rehydration or thaw periods if used clinically. Additionally, in vivo evidence suggests no negative impact of glycerol-preservation on the ability of bone grafts to successfully participate in new bone formation and fusion.

The influence of various rehydration protocols on biomechanical properties of different acellular tissue matrices.

This study evaluated the influence of different rehydration media and time periods on biomechanical and structural properties of different acellular collagen matrices (ACMs). Specimens of three ACMs (mucoderm®, Mucograft®, Dynamatrix®) were rehydrated in saline solution (SS) or human blood for different time periods (5-60min). ACMs under dry condition served as controls. Biomechanical properties of the ACMs after different rehydration periods were determined by means of tensile testing. ACMs' properties were further characterized using Fourier-transform-infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). At dry conditions, mucoderm® presented the highest tensile strength (TS) and Dynamatrix® showed the maximum elastic modulus (EM; p each ≤0.036). Rehydration in SS and blood resulted in significant TS changes of mucoderm® (p each ≤0.05). Concering EM, mucograft® showed significantly decreased values after rehydration in SS compared to Dynamatrix® and mucoderm® after 10min (p each ≤0.024). mucoderm® hydrated for 5min in blood displayed nearly double TS and a significantly increased EM after 60min (p = 0.043) compared to rehydration in SS. TS and EM values of Dynamatrix® and Mucograft® were not altered following rehydration in blood versus SS (p each ≥0.053). FTIR analysis confirmed the recovery of the graft protein backbone with increased rehydration in all samples. DSC measurements revealed that tissue hydration decreased thermal stability of the investigated ACMs. Our findings demonstrated that the rehydration protocol affects the biomechanical properties of ACMs. Clinicians should be aware of altered handling and mechanical properties of ACMs following different rehydration protocols.

Hydration and Dehydration Periods of Crown Fragments Prior to Reattachment

Tooth fragment bonding is an excellent treatment option in dealing with traumatic injuries of the anterior teeth. Rewetting the tooth fragment has been shown to increase restoration durability. The present study examined the effect various dry and wet storage periods had on the reattached fragment's bond to the tooth. One hundred and eight human mandibular incisors were fractured and assigned to undergo a dehydration period of 30 minutes, six hours, 24 hours, or three days before the rewetting procedure. After fracturing the teeth and drying the fragments, each of the specimens was assigned to one of the three main groups (A, B, or C) intended to evaluate the effect of different rehydration periods. Groups A and B underwent a 30-minute and a 24-hour rewetting period, respectively. Group C served as a control (without a rewetting stage). Tooth fragments were then reattached and prepared for the strength test. Force was applied on the lingual side of the tooth at a 1 mm/min rate until failure. The mean loads (N) required to fracture the restored teeth were as follows: 204.43 ± 33.48 N, 322.59 ± 34.62 N, and 253.25 ± 29.05 N for groups A, B, and C, respectively. Two-way analysis of variance (p<0.05) showed that rehydration and dehydration periods as well as their interaction caused significant differences in the strength of the final restoration. Multiple comparison tests showed that, in general, significant differences were not seen among different dehydration times prior to the rewetting stage (p>0.05), except in the case of the 30-minute dehydrated specimens (p<0.05). Compared to a 30-minute period, a 24-hour rehydration of the tooth fragment before treatment seems to salvage enough moisture to result in an increase in reattachment strength.

Non-enzymatic transfer of sequence information under plausible prebiotic conditions

We simulated in our laboratory a prebiotic environment where dry and wet periods were cycled. Under anhydrous conditions, lipid molecules present in the medium could form fluid lamellar matrices and work as organizing agents for the condensation of nucleic acid monomers into polymers. We exposed a mixture of 2′-deoxyribonucleoside 5′-monophosphates and a ssDNA oligomer template to this dry environment at 90 °C under a continuous gentle stream of CO2 and we followed it with rehydration periods. After five dry/wet cycles we were able to detect the presence of a product that was complementary to the template. The reaction had a 0.5% yield with respect to the template, as measured by staining with the Pico Green® fluorescent probe. Absent initial template, the product of the reaction remained below the detection limit. In order to characterize the fidelity of replication, the synthesized strand was ligated to adapters, amplified by PCR, and sequenced. The alignment of the sequenced DNA to the expected complementary sequence revealed that the misincorporation rate was 9.9%. We present these results as a proof of concept for the possibility of having non-enzymatic transfer of sequence information in a prebiotically plausible environment.

Differential Responses of Electrolyte Leakage and Pigment Compositions in Maize and Sorghum After Exposure to and Recovery from Pre- and Post-Flowering Dehydration

Drought stress is often the most limiting factor to maize and sorghum production in the semi-arid areas. This study evaluates the response of electrolyte leakage, chlorophyll, carotenoid and anthocyanin contents in maize ( cv. Melkassa-2 and sorghum cv. Macia) after exposure to and recovery from pre- and post-flowering dehydration in plants grown in a controlled environment growth chamber under constant environmental conditions (12/12 h day/night, 28–32/17°C day/night temperature, 60–80% RH and PPFD of 1 200–1 400 μmol m −2 s −1), at the Department of Botany, University of Cape Town, South Africa. It was revealed that dehydration induced increases in electrolyte leakage was observed in both species during both pre- and post-flowering stages. Electrolyte leakage was however, higher during post- than pre-flowering dehydration in both species. Dehydration during both pre- and post-flowering stages caused a decrease in chlorophyll and carotenoid contents in both maize and sorghum. Chlorophyll and carotenoid contents of both pre- and post-flowering dehydrated sorghum was markedly higher than that of maize throughout the duration of the dehydration period. As opposed to chlorophyll and carotenoid contents, anthocyanin contents increased during pre- and post-flowering dehydration in both species. Differences were however, observed between both species in the response of anthocyanin content to pre- and post-flowering dehydration. Full recovery of chlorophyll, carotenoid and anthocyanin contents were observed in those plants rehydrated during pre-flowering stages. There was however, no recovery in both species during post-flowering rehydration. This study should help understand some adaptive mechanisms developed by maize and sorghum during the dehydration and rehydration periods and contribute to identify useful traits for breeding programs.

Freeze-dried acellular dermal matrix graft: Effects of rehydration on physical, chemical, and mechanical properties

Objectives To test the effect of rehydration time over the range prescribed in the manufacturer's protocol on (1) the biomechanical properties and on (2) the recovery and stabilization of the collagenous matrix of AlloDerm ®. Methods A sterile dish containing warm saline solution was prepared, and samples rehydrated for 5 min. Subsequently, three other dishes with the solution were prepared and samples assigned into three groups according to the total rehydration time: 10 min (G1), 20 min (G2), and 40 min (G3). Uni-axial tensile testing was used to assess the biomechanical properties of the different groups and the control (dry condition). Physico-chemical properties were examined by Fourier transform infrared spectroscopy (FT-IR), and differential scanning calorimetry (DSC) as a function of rehydration time. Results ANOVA revealed a significant change in tensile strength ( p = 0.0269) and in elastic modulus ( p = 0.0306) for AlloDerm following different rehydration times. The lowest tensile strength was in the dry condition, whereas the highest was achieved after a 40 min rehydration. The shortest rehydration periods did not result in a statistically significant ( p > 0.05) change in elastic modulus. However, after 40 min the elastic modulus increased significantly when compared to the shortest periods. FT-IR confirmed the protein backbone recovery of the graft matrix after rehydration. DSC scans of rehydrated samples showed visible shifts in the denaturation temperature to higher values compared to as-received sample (dry) suggesting stronger polymer–water bridge formation, supporting the increase in the biomechanical properties. Significance The current study suggests that there are major changes on the biomechanical properties of the collagenous graft as rehydration time increases, which were also structurally confirmed by the physico-chemical analyses. Clinicians must be aware that the rehydration times of the manufacturer's protocol result in a significant range in mechanical and physico-chemical properties. Therefore, a rehydration time of at least 20 min guarantees not only better handling and mechanical properties but, most importantly, supplies a material that closely resembles the natural tissue.

Effects of various rehydration periods on the stability and water content of bone transplants following freeze-drying, gamma sterilization and lipid extraction

Several studies demonstrated the necessity of rehydration of lyophilized bone allografts prior to implantation. The purpose of the presented study was to evaluate the influence of different rehydration periods on the stability of human cortical lyophilized and gamma-irradiated allografts, the capability of lyophilized bone for rehydration, as well as the effects of lipid extraction on rehydration. Breaking strength of lyophilized irradiated cortical bone after different rehydration periods (0.5, 1, 2, 4, 8 hours) showed no significant difference. Weight reduction after lyophilization of human femoral heads was between 7.6% and 41%. Further weight reduction occurred after lipid extraction (38.7%). Total weight loss was 56.9%. There was a significant influence of intraosseous lipid content on the rehydration capability. After lyophilization alone the rehydration weight after 8 hours was only 18.1%, whereas after lipid extraction the weight increase was 43% after 0.5 hours, 36.4% after 1 hour, 57.6% after 2 hours, 60% after 4 hours, and 92.7% after 8 hours. Based on the presented data rehydration time of 0.5 hours seems to have no disadvantage compared to longer time periods concerning breaking strength. Therefore a longer intraoperative time period seems not to be necessary. This is of advantage for a possible secondary contamination while the allograft is rehydrated. Rehydration after lipid extraction is more effective than rehydration after lyophilization alone. However, the question whether lipid extraction alter bone stability has to be proved in further studies.

Sapid solutions and food intake in repeated dehydration and rehydration periods in rats.

Experiments were performed to ascertain whether food intake in thirsty rats is influenced by palatability of solutions and whether the availability of food during tests influences taste preference, acceptance, and total fluid intake. In five groups of rats, 2-bottle preference (Experiment 1) and 1-bottle acceptance tests (Experiment 2) in either 12, 24, 36, 48 h water deprived rats were performed; food was available during tests. Results showed that food availability during tests did not affect taste preference and acceptance. In Experiment1, after 36, 48 h water deprivation, rats drinking either NaCl or sucrose, they ate less food than rats drinking either HCl, quinine, or water. In Experiment 2, rats drinking NaCl as the only source of fluid ate significantly less food than all other groups. Two different post-ingestive effects (energetic; osmotic) may explain the same behavior for intake of sucrose or NaCl solutions. Since rats drinking either sucrose or NaCl ate less food but drank more fluid, they had a fluid/food ratio significantly higher than that of rats drinking either water, quinine, or HCl; these latters ate more food but drank less fluid. Taste, together with other factors, might inhibit or enhance the amount of fluid and food intake required to restore body weight and body fluid osmolality at the end of dehydration. During recovery periods, overeating is necessary to restore body mass, Na + and electrolytes; overdrinking corrects imbalance produced by excessive eating. In conclusion, food and fluid intake appears significantly related each other, even in dehydrated rats.

Foliar phosphorus supply and CO2 assimilation in common bean (Phaseolus vulgaris L.) under water deficit

Two common bean cultivars were grown in pots under greenhouse conditions. Plants were submitted to a foliar Pi spray two days before suspending irrigation, what enhanced net CO2 assimilation rate of Ouro Negro cultivar but did not change significantly the photosynthesis of Carioca cultivar under both water deficit and rehydration periods. The results revealed that a foliar Pi spray induced an up-regulation of photosynthesis in common bean under mild water deficit, with this effect being genotype-dependent.

EFFECT OF WEATHER AND RICE MOISTURE AT HARVEST ON MILLING QUALITY OF CALIFORNIA MEDIUM-GRAIN RICE

Californias medium-grain rice industry experiences a wide range of head rice yield (HRY). Average moisture ofa representative paddy rice sample is the commercially used predictor of optimum harvest date to achieve high HRY. Atwo-year field study demonstrated that average rice moisture alone is not an adequate predictor of HRY. The history of ricemoisture caused by varying meteorological conditions was needed to predict rice quality. Under typical calm conditions inCalifornia, daytime relative humidity is low and at night humidity increases, exposing rice to dew. During this meteorologicalpattern, HRY could be predicted by assuming that all kernels that dried below 15% moisture during the day would rehydrateat night and fissure, resulting in lost HRY. Harvest weather is also characterized by occasional episodes of dry north wind,lasting several days. These periods have insufficiently long rehydration periods to completely fissure kernels that droppedbelow 15% moisture, and actual HRY was much above predicted HRY. HRY dropped significantly during periods of dry northwinds; however, rice value (government loan value minus drying costs) did not drop significantly during the windy periodbecause the lower loan value was offset by lower drying costs. After the windy period ended, rice was again subject tonighttime dew and regained moisture, resulting in a large reduction in HRY and value. A combination of the range of individualkernel moisture at harvest and history of rice moisture influenced by weather conditions explained a great deal of the totalHRY variation experienced by the California rice industry.

Basis of coffee seed sensitivity to liquid nitrogen exposure: oxidative stress or imbibitional damage?

Two hypotheses, namely the occurrence of post‐thaw oxidative stress or imbibitional damage, were tested to explain the high sensitivity of coffee seeds to liquid nitrogen (LN) exposure. Oxidative stress was studied by measuring primary and secondary products of lipid peroxidation in seeds during the desiccation and rehydration periods. The 4‐hydroxynonenal (4‐HNE) content of seeds remained constant throughout the desiccation step. No significant difference was observed between desiccated seeds and seeds desiccated and exposed to LN for the evolution of their 4‐HNE and hydroperoxide contents during rehydration. In both cases, an increase in 4‐HNE and hydroperoxide contents of seeds was observed during the first hours of culture under germination conditions, followed by a progressive decrease down to values comparable to those observed in desiccated seeds. The hydroperoxide composition of frozen seeds was not significantly different from that of control seeds. The (S)/(R) enantiomeric ratios of 9‐ and 13‐hydroxy‐octadecadienoic acid extracted from rehydrating seeds were chiral, suggesting that they originated from lipoxygenase activity. These results suggest that the high sensitivity of coffee seeds to LN exposure is not directly associated with the occurrence of an oxidative stress during post‐thaw rehydration. The effect on seed viability of different rehydration procedures previously identified to reduce membrane imbibitional injury was studied after desiccation and LN exposure. Desiccation tolerance increased with, by increasing order, seed osmoconditioning, pre‐heating and pre‐humidifying prior to their culture under germination conditions. Among the four combinations of pre‐humidification durations (24 or 48 h) and temperatures (25 or 37°C) tested, pre‐humidification for 24 h at 37°C gave the highest level of desiccation tolerance. This rehydration procedure also dramatically increased seed viability after LN exposure. Seed desiccation sensitivity modelling in combination with the calculation of the decrease in seed water activity during cooling facilitated the explanation of the beneficial effect of controlled rehydration after desiccation and LN exposure. These results support the hypothesis that imbibitional membrane damage is involved in the sensitivity of coffee seeds to LN exposure.

Sapid solutions and food intake in repeated dehydration and rehydration periods in rats.

In a previous report, it has been shown that water deprivation significantly affects the two-bottle taste preferences and one-bottle taste acceptance in rats when no food was available during tests. Since no food was available, the course of drinking was never interrupted by eating. Theoretically, if a rat faces a simultaneous choice between food and fluid, and if the course of drinking is interrupted by eating, these conditions might interfere with taste preferences, total fluid intake and eating in thirsty rats. The aims of the present experiments were: to ascertain whether food intake during both two-bottle preference and one-bottle acceptance tests in thirsty rats might be influenced by the palatability of the solutions; to verify whether the availability of food during tests influences taste preference and acceptance, and total fluid intake; to detect variations induced by dehydration on body weight and some plasma and urinary parameters that might interfere with food and fluid intake, taste preference and acceptance. Using naive rats, five groups of rats showing the same taste preferences for one of four prototypical tastes and water were selected. Then, both two-bottle preference (Expt 1) and one-bottle acceptance tests (Expt 2) were performed in rats deprived of water for either 12, 24, 36 or 48 h. The results showed that in both Expt 1 and Expt 2, inhibition of feeding and decrease of body weight during dehydration was very similar in all rats. The presence of food during the tests did not affect taste preference and acceptance. During Expt 1, after severe water deprivation (36 and 48 h), food intake was related to the palatability of the solution paired with water. When rats drank either NaCl or sucrose, they ate less food than rats drinking HCl, quinine, or water. In Expt 2, rats drinking NaCl solution as the only source of fluid ate significantly less food than all other groups. The intake of sucrose and/or NaCl solutions be may explained by two different post-ingestion effects (energetic and osmotic). Since rats drinking either sucrose or NaCl ate less food but drank more fluid, they had a significantly higher fluid/food intake ratio than that of rats who drank water, quinine, or HCl, who ate more food but drank less fluid. The increase of the fluid/food intake ratio in rats drinking sucrose or NaCl was directly correlated with the length of dehydration. Self-denial of food during dehydration may be responsible for overeating and overdrinking during the recovery period after tests. After dehydration lasting for 24 and 48 h, plasma [Na(+)], [protein], osmolality and haematocrit values increased but [K(+)] decreased. Urinary volume decreased but urinary [Na(+)] increased. These results are related to food and fluid intake, taste preference and acceptance after dehydration periods. Experimental Physiology (2001) 86.4, 489-498.

Control of pressure-chamber and rehydration-time effects on pressure–volume determination of water-relation parameters

In a study of the seasonal variation of water-relation parameters in four black spruce (Picea mariana (Mill) BSP) populations, the weekly derivation of 32 pressure–volume curves with the sap-expression method between May and October required the simultaneous use of four pressure chambers and variable sample rehydration periods. Pressure chamber had a significant effect on three of the five characteristics studied: symplastic water fraction, maximum modulus of elasticity, and osmotic potential at full turgor. These effects were constant over the growing season. On average, rehydration-time effects were significant for all water-relation parameters except osmotic potential at turgor loss point, but they were not constant over sampling dates. Variations in water-relation parameters due to chambers and rehydration times were controlled and estimated through an experimental design based on the Latin square, which allowed precise comparisons among populations despite the increase in variability due to these two factors. The efficiency of the design varied between 110 and 142% relative to a completely randomized design in which neither chambers nor rehydration times would have been controlled for. Key words: black spruce, populations, experimental design.

Chlordiazepoxide injection elevates the NaCl solution acceptance-rejection function

Injection (SC) of chlordiazepoxide (2-8 mg/kg) increased the intake of NaCl solution (0.5-3.0% NaCl) as well as water in water-deprived rats when these fluids were made available singly during daily 1-hr rehydration periods. The marked enhancement of this drug effect when NaCl solution was the available fluid does not appear to be due to the induction of a sodium appetite or the mimicking of an increase in water deprivation. The exaggeration of the drug effect when an NaCl solution is the drinking fluid, as opposed to water, may be useful as a sensitive index of action for punishment-attenuating (anxiolytic) drugs.

Renal and endocrine response to water deprivation in dog.

Plasma and urine sodium, potassium, osmolality, aldosterone, and plasma renin activity (PRA) were measured in time controls and during control dehydration and rehydration periods in conscious dogs fed a 50 mmol NaCl diet. During 4 days of water restriction, plasma sodium and osmolality and PRA were elevated, whereas plasma potassium and aldosterone were not affected. Urinary potassium excretion was elevated above intake levels during the entire dehydration period, whereas Na excretion was only elevated during the first 2 days of dehydration. Unrestricted rehydration was associated with a marked fall in plasma sodium and osmolality, a decrease in PRA, and no change in plasma potassium or aldosterone. In addition, during the 1st day of rehydration, there was marked retention of sodium and potassium. Thus, in the dog, dehydration and subsequent rehydration cause significant alterations in sodium and potassium balance and marked alterations in PRA that are not associated with changes in either plasma aldosterone concentration or urinary aldosterone excretion.