Body Fluid Osmolality Research Articles

EFEKTYWNOS´ C REGULACJI HOMEOSTAZY ELEKTROLITOWEJ KRWI LISÓW POLARNYCH ´ (ALOPEX LAGOPUS, LINNAEUS, 1758)

The Arctic fox (Alopex lagopus, L. 1758) is maintained in captivity for breeding purposes due to the high quality of its winter fur. The success of breeding these animals depends primarily on their health, which determines high reproductive rates, low neonatal mortality and proper development of young animals. A prerequisite for maintaining good health is the maintenance of a constant internal environment, especially water-electrolyte and acid-base homeostasis. Sodium, potassium and chloride are the main electrolytes affecting volemia and osmolality of body fluids. In the current study, the results regarding the renal capacity of six-month-old foxes to regulate sodium, potassium, and chloride levels are presented, considering the sex of these animals. It has been shown that the concentration of sodium, potassium, and chloride in the blood serum of six-month-old polar foxes, as well as the osmotic pressure of the blood serum, were within the upper limits of physiological normal range. Higher concentrations of sodium and potassium were observed in males of these animals. Nonetheless, the results indicated efficient regulation of blood electrolyte homeostasis, both in females and males.

The Ins and Outs of Urea: Identification of Putative DUR3-like Urea Transporters in the Oligohaline Nerite Snail Theodoxus fluviatilis and Their Expression under Changing Salinities

Theodoxus fluviatilis (Linnaeus, 1758) (Gastropoda: Neritidae) is an oligohaline aquatic gastropod that inhabits most of Europe and adjacent areas of Asia. Two different ecotypes can be distinguished: One in freshwater (FW) and another along the Baltic Sea coast in brackish water habitats (BW). Individuals of either ecotype use free amino acids and urea as organic osmolytes to adjust body fluid osmolality to the external medium; however, the BW ecotype is able to accumulate them in larger quantities. The use of urea as an organic osmolyte in aquatic gastropods such as T. fluviatilis has only recently been initially described and raised the question of how urea transport between body fluids and the environment is balanced. Upon examining transcriptome and preliminary genome sequence data of T. fluviatilis, we identified putative homologues of DUR3 genes, which code for urea transporters (UTs) in other organisms. In this study, we provide evidence for the presence of four different subtypes of DUR3-like UTs that belong to two distinct families. Two of the UT subtypes were subject to qRT-PCR analyses to investigate differences in mRNA expression during the acclimation of individuals of both ecotypes to different salinities. Our results indicate that only BW animals regulate DUR3 gene expression in the context of osmoregulation.

Acclimation of marine invertebrate osmolyte systems to low salinity: A systematic review & meta-analysis

Salinity is a major environmental factor shaping the distribution and abundance of marine organisms. Climate change is predicted to alter salinity in many coastal regions due to sea level rise, evaporation, and changes in freshwater input. This exerts significant physiological stress on coastal invertebrates whose body fluid osmolality follows that of seawater (‘osmoconformers’). In this study, we conducted a systematic review and meta-analysis of osmolytes (both organic and inorganic) utilized by osmoconforming marine invertebrates during a >14-day acclimation to reduced salinity. Of the 2,389 studies screened, a total of 56 fulfilled the search criteria. Thirty-eight studies reported tissue osmolyte. Following acclimation to reduced salinity, tissue concentrations of six organic compounds and sodium were consistently reduced across phyla. This suggests that intracellular inorganic ions are not only utilized as a rapid response system during acute exposure to low salinity stress but also, in concert with reductions in organic osmolyte concentrations, during longer-term acclimation. Our systematic review demonstrates that only a few studies (n = 13) have quantified salinity-induced long-term changes in intracellular ion concentrations. In addition, no study has compiled a complete intracellular osmolyte budget. Alanine, betaine, glycine, and taurine are the major organic osmolytes that are universally employed across five phyla. The characterization of organic osmolytes was heavily weighted towards free amino acids (FAAs) and derivatives—neglecting methylamines and methylsulfonium compounds, which can be as important as FAAs in modulating intracellular osmolality. As a consequence, we suggest best-practice guidelines to streamline experimental designs and protocols in osmoregulation research in order to better understand the conserved mechanisms that define the limits of salinity acclimation in marine invertebrates. To our best knowledge, this is the first systematic review and meta-analysis on osmolyte concentrations in osmoconformers acclimated to low salinity. It creates a valuable baseline for future research and reveals large research gaps. Our meta-analysis suggests that there are common osmolyte actors employed across phyla but no uniform concept since osmolyte pool composition and proportions were taxon-specific. In light of future salinity changes and their potential consequences, it becomes more important to understand salinity tolerance capacities and limits.

Vasopressin regulation of maternal body fluid balance in pregnancy and lactation: A role for TRPV channels?

Renal water reabsorption increases in pregnancy and lactation to expand maternal blood volume to cope with the cardiovascular demands of the developing fetus and new-born baby. Vasopressin (antidiuretic hormone) promotes renal water reabsorption and its secretion is principally stimulated by body fluid osmolality. Hence, lowered osmolality normally decreases vasopressin secretion. However, despite water retention profoundly reducing osmolality in pregnancy and lactation, vasopressin levels are maintained to drive blood volume expansion. Despite its importance for successful reproduction, the cellular mechanisms that maintain vasopressin secretion in the face of decreased osmolality during pregnancy and lactation are unknown. Vasopressin is secreted by neurons that are intrinsically osmosensitive through expression of N-terminal truncated-transient receptor potential vanilloid-1 channel, ΔN-TRPV1, which is mechanically activated by osmotically-induced cell shrinkage to increase vasopressin neuron activity. Vasopressin neurons also express TRPV4 but the role of TRPV4 in vasopressin neuron function is not well characterised. Here, we summarise our novel evidence showing that TRPV4 forms functional channels with ΔN-TRPV1 that have a greater single-channel conductance compared to channels with ΔN-TRPV1 alone. We propose that upregulation of TRPV4 heteromerisation with ΔN-TRPV1 might maintain vasopressin secretion in pregnancy and lactation to expand blood volume for successful reproduction.

Complementary Role of Oxytocin and Vasopressin in Cardiovascular Regulation.

The neurons secreting oxytocin (OXY) and vasopressin (AVP) are located mainly in the supraoptic, paraventricular, and suprachiasmatic nucleus of the brain. Oxytocinergic and vasopressinergic projections reach several regions of the brain and the spinal cord. Both peptides are released from axons, soma, and dendrites and modulate the excitability of other neuroregulatory pathways. The synthesis and action of OXY and AVP in the peripheral organs (eye, heart, gastrointestinal system) is being investigated. The secretion of OXY and AVP is influenced by changes in body fluid osmolality, blood volume, blood pressure, hypoxia, and stress. Vasopressin interacts with three subtypes of receptors: V1aR, V1bR, and V2R whereas oxytocin activates its own OXTR and V1aR receptors. AVP and OXY receptors are present in several regions of the brain (cortex, hypothalamus, pons, medulla, and cerebellum) and in the peripheral organs (heart, lungs, carotid bodies, kidneys, adrenal glands, pancreas, gastrointestinal tract, ovaries, uterus, thymus). Hypertension, myocardial infarction, and coexisting factors, such as pain and stress, have a significant impact on the secretion of oxytocin and vasopressin and on the expression of their receptors. The inappropriate regulation of oxytocin and vasopressin secretion during ischemia, hypoxia/hypercapnia, inflammation, pain, and stress may play a significant role in the pathogenesis of cardiovascular diseases.

Hypertension and Fear‐Related Neuropsychiatric Disorder Co‐Morbidity: Is Body Fluid Hyperosmolality a Required Link?

High salt (NaCl) intake (HSI) is a physiological stressor that can increase the prevalence and severity of arterial hypertension (HTN), which is often comorbid with fear-related psychiatric disorders. Here, we sought to determine the contribution of HSI in HTN and fear disorder co-morbidity. Preliminary studies in male C57Bl6 mice established that salt loading (SL) introduced by replacing drinking water with a 4% NaCl solution induced significant HTN (+ 21 ± 5 mmHg, n=3) (P=0.0437) while consumption of high salt diet (HSD) by provision of chow containing 4% NaCl did not (+2 ± 5 mmHg, n=3) (P=0.06042). We formulated the hypothesis that HSI will enhance fear memory retrieval when accompanied by HTN but will not do so when HSI fails to raise mean arterial pressure (MAP). To test this, we subjected male C57Bl6 mice to 5 weeks of HSD or a normal salt diet (NSD, 0.4% NaCl). Treated mice then underwent contextual fear conditioning and retrieval testing 24 h later. Fear behavior was quantified as the percentage of time spent freezing (i.e., posturally immobile). A third cohort of HSD mice underwent surgical implantation of an osmotic mini-pump to deliver the pro-hypertensive hormone angiotensin II (Ang II, 600 ng/kg/min) or vehicle (Veh) for 14 d prior to fear conditioning. A subset of mice were instrumented with a radio telemetry transmitter to monitor MAP during AngII/Veh treatment. Blood was collected upon completion of experiments to measure serum osmolality. Analysis by unpaired t-test reveal that MAP was significantly increased by treatment with AngII (+28 ± 3 mmHg, n=5) compared to Veh (-1 ± 1 mmHg, n=2) (P=0.0014). During contextual fear memory retrieval, freezing behavior was not different between normotensive HSD mice and normotensive NSD mice (HSD: 45± 6%, n=10, NSD: 44± 7%. n=9) (P=0.9194). Furthermore, treatment of HSD mice with AngII did not significantly increase freezing behavior compared to Veh (AngII: 58 ± 3%, n=9, Veh: 62 ± 16%, n=3) (P=0.7273). These results suggest that unlike SL, which induces HTN and promotes contextual fear memory, HSD does not, even when HTN is induced by co-treatment with AngII. Overall, findings suggest that SL promotes HTN and fear memory through parallel, independent mechanisms, and that consumption of high salt-containing food does not increase fear memory regardless of whether accompanied by HTN or not. Published evidence indicates that unlike HSD alone, or in combination with AngII, SL significantly increases body fluid osmolality. This suggests that body fluid hyperosmolality, rather than salt intake per se, contributes to HTN and fear-related disorder co-morbidity. Consistent with this possibility, serum osmolality in the present study was unaltered relative to NSD (316 ± 1 mOsm, n=27) both by HSD alone (313 ± 2 mOsm, n=19) (P=0.1401) and by HSD with AngII (320 ± 2 mOsm, n=10) (P=0.0801).

Hypertension due to loss of water

In the current issue of Acta Physiologica, two papers are published investigating the development of arterial hypertension under conditions of pathological loss of free water in two disease models. Kovaric et al 1 studied rats with chronic renal failure, shedding excessive free water via their remnant kidney due to a hypostenuric concentrating defect. Wild et al. 2 investigated a transgenic mouse model for psoriasis, losing free water via the psoriatic skin lesions. In both cases the animals displayed hypertension, cutaneous vasoconstriction, and metabolic adaptations towards enhanced production of urea and organic osmolytes typical for a phylogenetically ancient water conservation response termed aestivation 3 . The international consortia of investigators spearheaded by Titze, Karbach, and Kitada therefore conclude that in both cases the hypertension was due to cutaneous vasoconstriction in an attempt to limit epidermal water loss. Because in either case the hypertension was associated with loss of water, and thus with hypo- rather than hypervolemia, the authors argue, that this concept of pathogenesis of hypertension is antipodal to the classic view that relies on hypervolemia due to sodium retention.

Hemolymph composition, gene expressions in the gills, and thus the survival of euryhaline crabs are controlled by ambient minor cations according to osmotic condition-dependent manner.

Na+ and Cl− are the most abundant dissolved ions in seawater, constituting ~ 85% of total ions. They significantly affect the osmolality of body fluids of marine invertebrates. Seawater also contains minor ions such as Mg2+, Ca2+, K+, and SO4 2‐ , but their effects on marine organisms are unclear. This study analyzed the effects of Mg2+, Ca2+, and K+ (ambient minor cations) on survival, hemolymph ionic composition, and gene expression in the gills of three euryhaline crabs: Helice tridens, Macrophthalmus japonicus, and Chiromantes dehaani. Ambient minor cations were required for survival of H. tridens and M. japonicus under isosmotic conditions with seawater. The ambient minor cations also affected the osmolality and ionic composition of hemolymph by regulating expressions of specific genes in the gills required for Na+ uptake, such as Na+/K+ ATPase, cytoplasmic carbonic anhydrase, and Na+/H+ exchanger. Administration of carbonic anhydrase and Na+/H+ exchanger inhibitors increased the survival rate even if ambient minor cations did not exist. In contrast, under hypo‐osmotic conditions, ambient minor cations had different effects on crabs, a lethal effect on M. japonicus, and an increase of the hemolymph K+ concentration in H. tridens and M. japonicus. It is thus concluded that the effects of ambient minor cations are osmolality‐dependent. In contrast, in C. dehaani, the hemolymph ionic composition and survival rate were hardly affected by ambient minor cations, probably reflecting the habitat of this species. These results strongly indicated that C. dehaani is less susceptive to ambient minor cations compared to H. tridens and M. japonicus.

Sex- and age-dependent differences in the hormone and drinking responses to water deprivation.

Maintenance of the volume and osmolality of body fluids is important, and the adaptive responses recruited to protect against osmotic stress are crucial for survival. The objective of this work was to compare the responses that occur in aging male and female rats during water deprivation. For this purpose, groups of male and female Wistar rats aged 3 mo (adults) or 18 mo (old) were submitted to water deprivation (WD) for 48 h. The water and sodium (0.15 M NaCl) intake, plasma concentrations of oxytocin (OT), arginine vasopressin (AVP), corticosterone (CORT), atrial natriuretic peptide (ANP), and angiotensin II (ANG II) were determined in hydrated and water-deprived animals. In response to WD, old male and female rats drank less water and saline than adults, and both adult and old females drank more water and saline than respective males. Dehydrated old animals displayed lower ANG II plasma concentration and CORT response compared with the respective normohydrated rats. Dehydrated adult males had higher plasma ANP and AVP as well as lower CORT concentrations than dehydrated adult females. Moreover, plasma OT and CORT levels of old female rats were higher than those in the dehydrated old male rats. Relative expression of ANG II type 1 receptor mRNA was decreased in the subfornical organ of adult and old male rats as well as adult female rats in response to WD. In conclusion, the study elucidated the effect of sex and age on responses induced by WD, altering the degree of dehydration induced by 48 h of WD.

Characterization of drought-induced rapid cold-hardening in the Antarctic midge, Belgica antarctica

Survival of the terrestrial midge, Belgica antarctica, on the Antarctic Peninsula is promoted, not only by their adaptations to prolonged exposures to seasonal stresses, but also by their ability to respond to unpredictable changes in their environments. Rapid cold-hardening (RCH) is an extremely swift acclimatory response of insects that occurs within minutes to hours. While the RCH response is most commonly induced by a brief exposure to mildly low temperatures, a similar rapid acclimatory response can also be elicited by exposure to drought. In this study, we characterized this drought-induced RCH in larvae of B. antarctica. Compared to fully hydrated larvae, those desiccated at various relative humidity (R.H.) conditions between 0 and 99% R.H. for 2 h had a significantly greater survival ( ~ 50%) to freezing at − 14 °C. The amount of water loss varied between 4 and 16% depending on R.H. conditions; however, all treatments were equally effective in eliciting the protective response against freezing stress, and its induction was evident within 30 min of desiccation. Lack of substantial changes in body-fluid osmolality or levels of major cryoprotectants suggest that accumulation of these protective solutes is not a primary mechanism of this response. Interestingly, the RCH protection induced by desiccation persisted after larvae were allowed to recover a significant portion of the lost water. Our results indicate that larval midges are highly sensitive to desiccation, capable of swiftly initiating physiological changes in response to a small reduction in their body water content.

Vasopressin receptors in islets enhance glucose tolerance, pancreatic beta-cell secretory function, proliferation and survival

Arginine vasopressin (AVP), a peptide secreted from the posterior pituitary, is chiefly regarded as a hormone involved in the regulation of body fluid balance and osmolality. However, recent evidence has revealed that posterior pituitary hormones can exert important actions on endocrine pancreatic function. In the present study, the presence of AVP receptors, namely Avpr1a (V1a), Avpr1b (V1b) and Avpr2 (V2) was demonstrated in murine islets as well as rodent BRIN BD11 and human 1.1B4 beta-cells. Further to this, AVP was shown to induce significant concentration-dependent (10−12 – 10−6 M) increases of insulin release from both rodent and human beta-cells, as well as mouse islets. Insulinotropic actions of AVP were completely annulled by specific V1a or V1b receptor antagonists, and partially abolished by an oxytocin receptor antagonist. In addition, beta-cell insulin secretory actions of AVP were augmented by both IBMX (200 μM) and KCl (30 mM) and linked to significantly increased cAMP production and [Ca2+]i. AVP substantially increased proliferation of rodent and human beta-cells. Moreover, AVP fully protected against cytokine-induced beta-cell apoptosis. AVP had no effect on glucagon secretion. Immunohistochemical examination of beta- and alpha-cells revealed co-expression of AVP with glucagon, and particularly insulin. Finally, administration of AVP in combination with glucose to mice significantly reduced blood glucose, which was associated with increased plasma insulin. These data indicate that AVP possesses novel and potentially important effects on pancreatic endocrine function. Understanding disturbances in islet AVP receptor signalling could reveal insight into the beta-cell defects associated with diabetes.

The springtail Megaphorura arctica survives extremely high osmolality of body fluids during drought.

The springtail Megaphorura arctica Tullberg 1876 is widespread in the arctic and subarctic regions where it can be abundant along beaches. This species survives winters using cryoprotective dehydration as a cold tolerance strategy during which it becomes drastically dehydrated. Several studies have investigated the physiological responses associated with water loss of M. arctica under exposure to freezing temperatures, but little is known of the dynamics of body water and hemolymph osmolality when subjected to gradually increasing drought stress at temperatures above the freezing point. Therefore, an experiment was conducted in which M. arctica was subjected to relative humidities (RH) decreasing from fully saturated conditions to ca. 89%RH over a period of 30 days. During the experiment water content of springtails decreased from about 3 to ca. 0.5mgmg-1 dry weight. Alongside with water loss, trehalose concentrations increased from nearly nothing to 0.12mg mg-1 dry weight, which contributed to an increase in hemolymph osmolality from ca. 250mOsm to at least 7Osm. All springtails survived water loss down to 0.7mgmg-1 dry weight and hemolymph osmolality of ca. 4Osm, and about 60% of the springtails survived with only 0.5mg watermg-1 dry weight and osmolality of ca. 7Osm.At this level of dehydration, Differential Scanning Calorimetry analysis showed that most, but not all, osmotically active water was lost. It is discussed that the extensive dehydration must be associated with high concentrations of salts potentially causing denaturation and precipitation of cellular proteins. M. arctica is remarkably tolerant of dehydration, but because it does not endure loss of the osmotically inactive water it cannot be categorized as a truly anhydrobiotic species.

Adaptively differential expression analysis in gill of Chinese mitten crabs (Eriocheir japonica sinensis) associated with salinity changes

Desalination of marine species has become an important development direction for aquaculture in China and other countries. However, that how to regulate the salt balance to adapt to new freshwater habitats is a serious challenge for marine species in desalination of aquaculture. In the study, Chinese mitten crabs (Eriocheir japonica sinensis) was selected to analyse the adaptively differential expression in salinity changes for their novel characteristics of life history. The results showed that gill was the most relevant tissue in osmoregulation that was validated by biomarkers (Na+/K+-ATP, V-type H+-ATPase) with qPCR. Na+/K+-ATPase is a primary transporter and maintains the body fluid osmolality by actively pumping Na+ to the hemolymph, and V-type H+-ATPase is responsible for acid-base balance and nitrogen excretion. So both transcriptome data and qPCR results showed the significantly differential expression of Na+/K+-ATPase and V-type H+-ATPase in gills. Moreover, NAK-α had the most significantly differential expression level in salinity change, and other genes such as GST, HSP90, S27, UBE, VATB also revealed significantly up-regulation. They are considered the key enzymes during the transition from a marine environment to land. Present results have provided a foundation to further understand the molecular adaptive mechanism in desalination of marine species.

Paralarvae of Octopus vulgaris Type II are stenohaline conformers: relationship to field distribution and dispersal

The degree of euryhalinity of cephalopod planktonic paralarvae potentially affects the dispersal capacity and distributional range of species. Herein, we tested the hypothesis that O. vulgaris Type II paralarvae would show some tolerance to seawater dilution, evaluated from integrated field and laboratory experiments. Paralarvae were collected from zooplankton samples (salinities of 30.3–32.6), in the Parana Bay Estuarine Complex (PBEC), Southern Brazil. In the laboratory, they were exposed to salinities of 28, 30, 33, 35 (control), and 37, from 15 min to 24 h. Survival ranged from 60 to 83%, 73–100%, and 100% at salinity of 28, 30, and 33–37, respectively. Body fluid osmolality (BFO), body water content (BWC), and ninhydrin-positive substances (NPS, amino acids) were quantified at salinities of 33, 35, and 37 (with 100% survival). BFO was always isosmotic to the external medium. BWC and the high NPS concentration remained unchanged in all salinities. Thus, these paralarvae tolerate some deviation from seawater salinity, displaying osmoconforming behavior, maintain body hydration, and show high ability of tissue volume/water regulation in short periods of time. Presumably, this physiological capacity of paralarvae might be one factor allowing their dispersal and survival along environments with moderate deviations from seawater salinity.

A field and laboratory study of the responses of cytoprotection and osmoregulation to salinity stress in mosquitofish (Gambusia affinis).

The mosquitofish (Gambusia affinis) naturally inhabits freshwater (FW; 1-3‰) and seawater (SW; 28-33‰) ponds in constructed wetland. To explore the physiological status and molecular mechanisms for salinity adaptation of the mosquitofish, cytoprotective responses and osmoregulation were examined. In the field study, activation of protein quality control (PQC) mechanism through upregulation of the abundance of heat shock protein (HSP) 90 and 70 and ubiquitin-conjugated proteins was found in the mosquitofish gills from SW pond compared to the individuals of FW pond. The levels of aggregated proteins in mosquitofish gills had no significant difference between FW and SW ponds. Furthermore, the osmoregulatory responses revealed that the body fluid osmolality and muscle water contents of the mosquitofish from two ponds were maintained within a physiological range while branchial Na+/K+-ATPase (NKA) expression was higher in the individuals from SW than FW ponds. Subsequently, to further clarify whether the cellular stress responses and osmoregulation were mainly induced by hypertonicity, a laboratory salinity acclimation experiment was conducted. The results from the laboratory experiment were similar to the field study. Branchial PQC as well as NKA responses were induced by SW acclimation compared to FW-acclimated individuals. Taken together, induction of gill PQC and NKA responses implied that SW represents an osmotic stress for mosquitofish. Activation of PQC was suggested to provide an osmoprotection to prevent the accumulation of aggregated proteins. Moreover, an increase in branchial NKA responses for osmoregulatory adjustment was required for the physiological homeostasis of body fluid osmolality and muscle water content.

Osmotic Concentration of Zebrafish (Danio rerio) Body Fluids Is Lower in Larvae than in Adults.

We intended to perform optical and structural measurements on larval zebrafish eyes at 5 days post fertilization, that is, the earliest age at which zebrafish show visually guided behavior. However, excised larval crystalline lenses deteriorated quickly if immersed in a medium that gives good results with adult lenses from a variety of fish species. We suspected that the larvae have body fluids of lower osmolality and tested a medium with 240 mOsm, which is 75% of the established adult value of 320 mOsm. The optical quality of freshly excised and immersed lenses was used to judge the osmotic matches. In addition, we tested how well the shape of the eye is preserved in fixatives of different osmolalities. In both cases, 240 mOsm produced the best results. Immersed lenses performed better and the fixed eyes had a more natural shape. Our findings indicate that zebrafish body fluids have lower osmolality in larvae than in adults. This is probably due to an unfavorable body surface-to-volume ratio and incompletely developed regulatory mechanisms. Body fluid osmolality deviating from the adult value has to be taken into account in optical and histological work.

Combined effects of drought and cold acclimation on phospholipid fatty acid composition and cold-shock tolerance in the springtail Protaphorura fimata

Terrestrial arthropods' ability to survive sub-zero winter temperatures is an important factor influencing their abundance and geographic distribution. It is, therefore, important to understand their physiological mechanisms of low-temperature survival. Acclimation to moderate-low temperature can improve cold tolerance, and pre-acclimation to mild desiccation can also improve survival of a subsequent cold exposure. However, very few studies have assessed the combined actions of cold and drought acclimations. In the present study, we combined cold acclimation with drought acclimation making it possible to assess the interactions between effects of these two stressors using the springtail Protaphorura fimata as a model organism. We investigated the interacting effects of drought and cold acclimation on body fluid osmolality, membrane phospholipid fatty acid (PLFA) composition, and cold-shock tolerance. Acclimation to mild drought (- 2.46MPa) increased body fluid osmolality from 0.33 to 1.25Osm at all acclimation temperatures (5, 10, 15, or 20°C) likely due to accumulation of the compatible osmolytes, trehalose, and alanine. Interestingly, the expected positive effect of drought acclimation on cold-shock tolerance was only evident at high acclimation temperature (20°C), whereas at intermediate temperatures (10 and 15°C), there was an interaction between acclimation temperature and drought. At 5°C, no effect of drought acclimation on cold-shock tolerance was observed despite high osmolality. The positive effect of drought acclimation at 20°C on subsequent cold-shock survival coincided with a drought-induced effect on PLFA composition only detectable at high temperature. We discuss the possible roles of drought-induced compatible osmolytes and an altered PLFA composition in the cold-shock tolerance of arthropods.

Vasopressin and Related Peptides; Potential Value in Diagnosis, Prognosis and Treatment of Clinical Disorders

Vasopressin (AVP) and its receptors play a pivotal role in maintaining body homeostasis under physiological and pathophysiological conditions. As a consequence, the vasopressin system has emerged as an important target for both diagnostic and therapeutic applications in a number of medical conditions. Stoichiometric generation of AVP with copeptin, which is relatively accessible in the blood for measurements, makes copeptin a valuable surrogate of AVP. In this review, we present the regulation of release of AVP and activation of V1a, V1b, and V2 vasopressin receptors under physiological and pathological conditions. We make a survey of the role of AVP in: the regulation of the cardiovascular system; body fluid osmolality; natraemia; endocrine regulation; food intake; metabolism; circadian rhythmicity, immunological processes; and in the formation of learning, memory, cognition, and emotional and social behaviours. We also discuss the significance of the inappropriate functioning of the vasopressin system for: the development of cardiovascular diseases; disturbances of the water-electrolyte balance; energy metabolism; inflammatory processes; pain; neurogenic stress; memory disorders; depression; anxiety; autism; and schizophrenia. The structure and biological properties of peptide and non-peptide agonists and antagonists of V1a, V1b and V2 vasopressin receptors are presented and the potential use of copeptin and the current and likely indications for AVP agonists and antagonists in the diagnosis and therapeutics of multiple pathological conditions is discussed.

Field and laboratory studies on drought tolerance and water balance in adult Pergalumna nervosa (Acari: Oribatida: Galumnidae)

We studied the water balance, body fluid osmolality and survival of the oribatid mite, Pergalumna nervosa, when exposed to drought in field and laboratory experiments. In a replicated field experiment we artificially lowered the soil water content by putting roofs over selected plots, which reduced soil water potential to levels well below the permanent wilting percentage for plants (i.e. below -1.5 MPa). Even though a slight decrease in the abundance of P. nervosa (only found in the 0-5 cm soil layer) was recorded during the most severe drought stress (ca. -3.5 MPa), the majority of adult mites clearly survived these conditions for 3 weeks in the field without migrating to deeper soil layers. Exposing field collected adults in laboratory experiments simulating even more severe drought conditions revealed that P. nervosa can survive several weeks of gradually increasing drought stress (down to -7 MPa) with moderate water loss. The osmolality of body fluids increased as dehydration progressed, but apparently as a result of simple up-concentration of solutes and not the de novo synthesis of protective osmolytes. We compare and discuss these results in the light of what is known about other arthropods.

Salinity increases total body prolactin and gill and skin prolactin receptor expression in the Chinese edible frog,Hoplobatrachus rugulosus, tadpole

Water salinity has effects on growth and metamorphosis of anuran species, including Hoplobatrachus rugulosus. Previously, we reported that cultured H. rugulosus tadpoles at low salinities (2–4‰) were of bigger size and grew faster than those in fresh water (FW). However, at a higher salinity level of 6‰, their sizes were reduced and the metamorphosis was delayed. It was therefore hypothesized that high salinity-induced osmotic stress affected secretion of prolactin (PRL), which acts as osmoregulatory hormone and a regulator of metamorphosis in amphibians. In this study, transferring tadpoles into 4‰ and 6‰ brackish water increased the PRL levels by ~1.2- and ~twofold, respectively, as compared to FW group. These osmotic challenges also increased the total body fluid osmolality and levels of Na+, Cl− and Ca2+. The contents of triiodothyronine (T3) were significantly reduced in 4‰ and 6‰ groups, but not 2‰ group. Three sizes (49, 29 and 23 kDa) of H. rugulosus PRL receptors (PRLRs) were detected, and their protein expression was found in the skin, gill, tail fin, brain, intestine, heart, liver and kidney. The expression of PRLR-49k protein was significantly higher in both skin and gills in 2–4‰ groups, whereas that of PRLR-29k and PRLR-23k were higher in gills and lower in skin of the 6‰ group than FW group. In conclusion, salinity challenge, particularly 4‰ and 6‰, increased the levels of PRL, while decreasing the T3 levels, which could explain why salinity markedly modulated growth, metamorphosis and survival of tadpoles.