24-h Water Deprivation Research Articles

Disinhibition augments thirst perception from two dehydrating stimuli in men

Physiological systems controlling water and energy ingestion are coordinated. Whether maladaptive eating behavior and appetite for water are linked is unknown. Thus, we sought to investigate the association between maladaptive eating and both thirst and water drinking behavior with two dehydrating conditions. Twenty-two lean men and 20 men with obesity (mean age 32.3 ± 8.4 years and 30.0 ± 11.1 years, respectively) completed the Three-Factor Eating Questionnaire (TFEQ) and Gormally Binge Eating Scale. On separate days, volunteers were dehydrated by a 2-h hypertonic saline infusion and a 24-h water deprivation, and thirst was measured on a 100-mm visual analogue scale (VAS) during each procedure. After each dehydrating condition, ad libitum water intake was measured. In the saline infusion, higher Disinhibition on the TFEQ was associated with thirst in the lean group (β = 4.2 mm VAS, p = 0.03) but not in the group with obesity (p = 0.51). In the water-deprivation condition, higher Disinhibition was also associated with thirst in the lean group (β = 5.6 mm VAS, p = 0.01) with the strength of relationship being 3.5-fold stronger than that observed in the group with obesity (β = 1.6 mm VAS, p = 0.0003). Hunger, Restraint, and binge-eating scores were not associated with thirst in either dehydrating condition (all p > 0.05). Maladaptive eating behaviors were not associated with ad libitum water intake (all p > 0.05). Disinhibition is associated with higher thirst perception in healthy weight individuals and may be attenuated in obesity. The characteristics of disinhibition which typically includes a heightened readiness to eat, may reflect a more general phenotype that also reflects a readiness to drink.

Abstract 042: A Novel (pro)renin Receptor Variant Prr24 As A Specific Renin Receptor And Key Regulator Of Nkcc2 And Urine Concentrating Capability

(Pro)renin receptor (PRR) has emerged as a key regulator of renal handling of Na + and water, and blood pressure (BP). Renal action of PRR is at least in part mediated through its ability to activate tissue prorenin and renin. In preliminary studies, investigation of a “non-specific” protein band recognized by an anti-PRR antibody against the extracellular domain led to identification of a novel 24-kDa isoform of PRR, termed as PRR24. PRR24 was encoded by a novel cDNA with part of 5’UTR arising from retention of intron 3 and an ATG in exon 5 as an alternative start codon so that this isoform overlaps completely with PRR except that N-terminal 136 amino acids are missing. PRR24 selectively bound and activated renin but not prorenin whereas PRR non-selectively interacted both prorenin and renin. PRR24 protein and mRNA expression was exclusively detected in the renal medulla but not renal cortex or extrarenal organs. Within the kidney, PRR24 mRNA was restricted to medullary thick ascending limb (mTAL) as assessed by RT-PCR on microdissected nephron segments. Using CRISP/Cas9 strategy, we generated a mouse model with mutagenesis of the start codon in exon 5 (termed PRR24 mut ) by replacing methionine with glutamine in PRR. Renal medullary protein expression of PRR24 was barely detectable contrasting unchanged PRR abundance in the null mice. PRR24 mut mice was born at Mendelian ratio and didn’t exhibit developmental abnormalities or mortality as seen in systemic PRR KO mice. PRR24 mut mice developed polyuria, hypoosmotic urine, polydipsia, hypotension (radiotelemetry MAP: WT 120 + 0.8 vs. Mutant 112 + 1.4 mmHg; p<0.05). Plasma volume assessed indirectly by hematocrit and directly assessed by using a fluorescent tracer was consistently reduced by 5-10%. Renal expression of NKCC2 was downregulated by 70% in parallel with reduced diuretic response to furosemide. Following 24-h water deprivation, the upregulation of NKCC2 expression was blunted in PRR24 mut mice associated with impaired urine concentrating capability as assessed by urine volume and osmolality. Overall, PRR24 is a novel PRR variant and serves as a specific renin receptor to regulate renal NKCC2 expression to ultimately determine urine concentrating capability.

Dose-dependent renoprotective impact of Lactoferrin against glycerol-induced rhabdomyolysis and acute kidney injury

Acute kidney injury (AKI) is a clinical disorder with a serious impact on the quality of patients' lives. Considering its increased worldwide prevalence, investigating novel therapeutic approaches for the management of AKI has been inevitable. Lactoferrin (LF), a glycoprotein belonging to the transferrin family, is known to play an important role in regulating iron homeostasis. This study aimed to evaluate the renoprotective effect of LF (30, 100, and 300 mg/kg orally) against glycerol (GLY)-induced rhabdomyolysis (RM) in rats. RM was induced by a single intramuscular injection of GLY 50% (10 mL/kg) after 24-h water deprivation in male Sprague–Dawley rats. LF administration conferred significant dose-dependent renoprotective impact against GLY-induced RM as evidenced by the decreased renal/somatic index and the significant improvement in renal functions as confirmed by the significant increase in creatinine clearance, decrease in serum creatinine and blood urea nitrogen, and improvement in albuminuria and proteinuria. Redox homeostasis was significantly restored in a dose-dependent manner as well. Moreover, serum interleukin-1β (IL-1β) was significantly decreased with a parallel significant decrease in renal NOD-like receptor family pyrin domain containing 3 (NLRP3) and thioredoxin interacting protein (TXNIP), kidney injury molecule-1 (KIM-1), caspase-3 expression, nuclear factor kappa B (NF-κB), cluster of differentiation (CD68) expression, and a significant increase in renal nuclear factor erythroid 2-related factor 2 (NRF2) expression. Ultimately, LF administration was associated with a significant amelioration of GLY-induced renal necrotic and inflammatory alterations. In conclusion, the observed dose-dependent nephroprotective effect of LF can be attributed to its modulatory impact on inflammatory/apoptotic/oxidative signaling.

PSIX-25 Feed and water deprivation at weaning and subsequent heat stress impacts serum and ileal markers of gastrointestinal integrity in nursery pigs

Abstract Social and environmental stressors impact nursery pig performance and may be linked to gastrointestinal dysfunction. The current experiment was conducted to investigate the impact of feed and water deprivation on serum stress markers and ileal mucosal gene expression in nursery pigs. Mixed-sex pigs were allotted on the basis of IBW (7.0 kg ± 0.89) in a RCBD with treatments in a split-plot arrangement and consisting of the whole-plot factor of with or without a 24-h feed and water deprivation at weaning and the sub-plot factor of with or without a cyclic 3-d heat stress starting 27 d post-weaning. On 1, 27, and 30 d post-weaning one pig from each pen was selected, blood was collected for measurement of serum cortisol, corticotrophin releasing factor (CRF), and endotoxins, and an ileal mucosal scraping was taken and gene expression of claudin 1 (CL-1), occludin (OC), and zonula occludens 1 (ZO-1) were measured by RT PCR. There was an increase (P < 0.05) in serum CRF and endotoxins and a tendency for an increase (P = 0.09) in serum cortisol due to the deprivation 1 d post-weaning. Further, there was a tendency for an increase (P < 0.10) in serum endotoxins and CRF due to the deprivation at 27 and 30 d post-weaning, respectively. Gene expression of CL-1 tended to increase (P = 0.10), and OC decreased (P = 0.05) due to the deprivation 1 d post-weaning. Expression of the OC gene decreased (P < 0.05) due to the deprivation 27 d post-weaning and OC and ZO-1 gene expression tended to decrease (P = 0.07) due to the heat stress 30 d post-weaning. These results show that post-weaning stress events alter serum stress markers and impact intestinal barrier function.

Acute stress-induced neuronal plasticity in the corticoid complex of 15-day-old chick, Gallus domesticus.

Several studies conducted on chicken have shown that a single stress exposure may impair or improve memory as well as learning processes. However, to date, stress effects on neuronal morphology are poorly investigated wherefore it was of interest to evaluate this further in chicks. Thus, the present study aims to investigate the role of single acute stress (AS) of 24h food and water deprivation in neuronal plasticity in terms of spine density of the corticoid complex (CC) in 15-day-old chick, Gallus domesticus, by using three neurohistological techniques: Cresyl Violet, Golgi Colonnier, and Golgi Cox technique. The dorsolateral surface of the cerebral hemisphere is occupied by CC which can be differentiated into two subfields: an intermediate corticoid (CI) subfield (arranged in layers) and a dorsolateral corticoid (CDL) subfield. Based on different criteria such as soma shape, dendritic branching pattern, and dendritic spine density, two main moderately spinous groups of neuronal cells were observed in the CC, namely, projection neurons (comprising of multipolar and pyramidal neurons) and stellate neurons. In the present study, the stellate neurons have shown a significant decrease as well as an increase in their spine density in both CI and CDL subfields, whereas the multipolar neurons had shown a significant increase in their spine density in the CDL region only. The present study shows that AS induces neuronal plasticity in terms of spine density in both CI and CDL neurons. The morphological changes in the form of decreased dendritic branches due to stress have been observed in the CI region in comparison to CDL region, which could be linked to more effect of stress in this region. The avian CDL corresponds to the entorhinal cortex of mammals on the basis of neuronal morphology and bidirectional connections between adjacent areas. The projection neurons increase their branches and also their spine number to cope with the stress effects, while the stellate neurons show contrasting effect in their spine density. Therefore, this study will establish that slight modifications in natural stimuli or environmental changes faced by the animal may affect their dorsolateral forebrain which shows neuronal plasticity that help in the development of an adaptive capacity of the animal to survive under changing environmental conditions.

A noninvasive method to study the evolution of extracellular fluid volume in mice using time-domain nuclear magnetic resonance.

Maintaining water homeostasis is fundamental for cellular function. Many diseases and drugs affect water balance and plasma osmolality. Water homeostasis studies in small animals require the use of invasive or terminal methods that make intracellular fluid volume and extracellular fluid volume (ECF) monitoring over time stressful and time consuming. We examined the feasibility of monitoring mouse ECF by a noninvasive method using time-domain nuclear magnetic resonance (TD-NMR). This technique allows differentiation of protons in a liquid environment (free fluid) from protons in soft tissues containing a majority of either small molecules (lean) or large molecules (fat). Moreover, this apparatus enables rapid, noninvasive, and repeated measurements on the same animal. We assessed the feasibility of coupling TD-NMR analysis to a longitudinal metabolic cage study by monitoring mice daily. We determined the effect of 24-h water deprivation on mouse body parameters and detected a sequential and overlapping decrease in free fluid and lean mass during water deprivation. Finally, we studied the effect of mineralocorticoids that are known to induce a transient increase in ECF but for which no direct measurements have been performed in mice. We showed, for the first time, that mineralocorticoids induced a transient ~15% increase in free fluid in conscious mice. TD-NMR is, therefore, the first method to allow direct measurement of discrete changes in ECF in conscious small animals. This method allows analysis of kinetic changes to stimuli before investigating with terminal methods and will allow further understanding of fluid disorders.

Primary Cilia of Supraoptic Nucleus Regulate Drinking and Blood pressure

Fluid intake is tightly related to blood pressure control through balance between electrolytes and water in the body. Virtually, every mammalian cell is equipped with a primary cilium, a cell surface protrusion that is thought to act as a sensory organelle. However, the contribution of primary neuronal cilia to cardiovascular regulation and fluid homeostasis has not been addressed. We hypothesized that primary neuronal cilia contribute to the control of fluid intake and blood pressure. For this, we first examined the length of primary neuronal cilia in the brain nuclei that contribute to osmolarity and cardiovascular regulation in 3‐week DOCA‐salt treated mice vs sham controls (n=5/group). Cilia length was examined by immunostaining a ciliary protein, adenylate cyclase 3 (AC3), followed by confocal 3D reconstruction, and quantification by IMARIS imaging analysis software. We found changes in cilia length in a number of brain nuclei of DOCA‐salt mice. The supraoptic nucleus (SON), a key brain nucleus in the regulation of osmolarity and fluid homeostasis, displayed the most significant changes in cilia length (average primary cilia: 7.46±□□□□□m in DOCA‐salt mice vs 6.76±□□□□□m in sham, p=0.0509). Moreover, the number of primary cilia that are over 10□□m was significantly increased in the SON of DOCA‐salt mice by 8% (p=0.0114). On the other hand, the number of cilia that are 4–5□□m in length was significantly decreased in the SON of DOCA‐salt mice (11.73±1.70%) compared to sham controls (18.73±2.02%, p=0.0385). Next, we assessed the relevance of SON cilia by targeting the ift88 gene which encodes a protein necessary for the formation of cilia. For this, we performed targeted stereotaxic injection of AAV‐Cre into the SON of IFT88flox/flox mice. We found that disruption of SON ift88 (AAV‐Cre group had a 38% ift88 expression level relative to AAV‐GFP control group) caused impairment in water intake in response to 24h water deprivation (30min water intake: 0.78±0.06 ml in AAV‐Cre vs 1.07±0.08 ml in AAV‐GFP, p=0.0129) without affecting total daily water and food consumption. Moreover, ift88 deletion in SON increased systolic blood pressure (133.7±1.71 mmHg vs 115.8±2.33 in AAV‐GFP, p=0.0008) without altering heart rate. Our data demonstrate the importance of primary cilia in the SON in the regulation of water intake and blood pressure. We speculate that primary neuronal cilia may function as part of environmental surveillance system in the brain that ensures cardiovascular homeostasis.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

N-(2-hydroxyphenyl)acetamide and its gold nanoparticle conjugation prevent glycerol-induced acute kidney injury by attenuating inflammation and oxidative injury in mice.

The protective activity of N-(2-hydroxyphenyl)acetamide (NA-2) and NA-2-coated gold nanoparticles (NA-2-AuNPs) in glycerol-treated model of acute kidney injury (AKI) in mice was investigated. NA-2 (50mg/kg) and NA-2-AuNPs (30mg/kg) were given to the animals for four days followed by 24-h water deprivation and injection of 50% glycerol (10ml/kg im). The animals were sacrificed on the next day. Blood and kidneys were collected for biochemical investigations (urea and creatinine), histological studies (hematoxylin and eosin; and periodic acid-Schiff staining), immunohistochemistry (actin and cyclooxygenase-2, Cox-2), and real-time RT-PCR (inducible nitric oxide synthase, iNOS; nuclear factor-κB p50, NFκB; hemeoxygenase-1, HO-1; and kidney injury molecule-1, Kim-1). NA-2 protected renal tubular necrosis and inflammation, though the result of NA-2-AuNPs was better than compound alone and it also exhibited the activity at far less dose. The test compound and its gold nano-formulation decreased the levels of serum urea and creatinine level in the treated animals. Both NA-2 and NA-2-AuNPs also conserved actin cytoskeleton, and lowered COX-2 protein expression. Moreover, the mRNA expressions of iNOS and NFkB p50 were down-regulated, and HO-1 and Kim-1 genes were up-regulated. We conclude that NA-2 and NA-2-AuNPs ameliorates kidney inflammation and injury in glycerol-induced AKI animal model via anti-oxidant and anti-inflammatory mechanisms which make it a suitable candidate for further studies. We believe that these findings will contribute in the understanding of the mechanism of action of paracetamol-like drugs and can be considered for clinical research for the prevention of AKI.

Osmotic Diuresis and Impaired Urinary Concentrating Ability in Epac Knockouts

Cyclic adenosine monophosphate (cAMP) is a universal second messenger regulating a plethora of processes in the kidney, such as water‐electrolyte transport and epithelial cell proliferation, to name a few. Downstream effectors of cAMP include protein kinase A (PKA) and exchange proteins directly activated by cAMP (Epac) – Epac1 and Epac2. The role of PKA as a classical cAMP acceptor in renal cells has been widely established. While both Epac isoforms are abundantly expressed in various segments of the nephron, their physiological relevance in the kidney remains obscure. Recent studies suggest that Epac is pivotal for arginine‐vasopressin (AVP) dependent water reabsorption in the collecting duct (CD) cells. Activation of Epac triggers intracellular Ca2+ ([Ca2+]i) mobilization in response to AVP, facilitating apical exocytosis of Aquaporin 2 water channels (AQP2) in inner medullary collecting ducts. AVPinduced stimulation of Epac activity may also contribute to long‐term regulation of AQP2 expression in CD cells.Here, we combined ratiometric calcium imaging with quantitative immunoblotting and balance studies in mice with targeted deletion of Epac1 or Epac2 to determine the role of Epac in renal water handling.Both Epac1 and Epac2 knockouts exhibit pronounced polyuria, with urine volumes 30% (Epac1‐/−) to 50% (Epac2−/−) larger than in wild‐type controls. Ablation of either Epac isoform results in moderate (10–15%, statistically significant) decrease in urine osmolality. Mice lacking Epac1 exhibit a prominent increase in total AQP2 protein expression, but largely unaltered plasma membrane resident AQP2 levels and AVP‐dependent [Ca2+]i signal in the CD principal cells. Deletion of Epac2 decreases the sustained AVP‐induced [Ca2+]i signal, markedly reduces total AQP2 abundance, but only mildly diminishes AQP2 levels on the plasma membrane of CD cells. Sodium and potassium concentration was not different in urine samples from Epac1−/−, Epac2−/− and wild‐type mice. Thus, the observed polyuria is, at large, the result of osmotic diuresis, which was attributed to the decreased abundance and activity of sodium‐hydrogen exchanger 3 (NHE3) in the proximal tubule. The ability to concentrate urine is modestly impaired in both knockouts, as evidenced by excessive production of diluted urine after 24h water deprivation. Interestingly, water deprivation markedly increased urea excretion in both Epac knockouts. In mice lacking Epac2−/− this loss of urea was attributed to decreased abundance of UT‐A2 transporter. Expression and activity of NHE3 in both knockouts remained significantly lower than in wild‐type controls, similarly pointing to a major contribution of solute diuresis into the observed increase in urine production.In summary, deletion of either Epac1 or Epac2 impairs water and electrolyte reabsorption in the proximal tubule, resulting in polyuria. The latter is exacerbated in Epac2−/− by defective urea and water handling in the distal nephron segments.Support or Funding InformationASN Ben J. Lipps Research Fellowship (to V. Tomilin), NIH‐NIAID 5R01AI111464‐04, NIH‐NIGMS 1R35GM122536‐01 (to X. Cheng), AHA‐15SDG25550150 (to M. Mamenko), NIH‐NIDDK DK095029, AHA 17GRNT33660488 (to O. Pochynyuk),This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

A low-salt diet increases the expression of renal sirtuin 1 through activation of the ghrelin receptor in rats.

Previous studies have shown that sirtuin 1 (Sirt1) is renoprotective; however, details regarding its distribution and functions in the kidney remain unknown. Here, we demonstrated that Sirt1 was mainly expressed in the tubulointerstitial cells of normal rat kidneys and was co-localized with aquaporin 2, indicating it may be involved in water/salt regulation. Renal Sirt1 expression increased in the non-glomerular cytoplasmic portion of the kidney after a 24-h fast, but no significant changes in Sirt1 expression occurred after water loading (50 mL/kg) or 24-h water deprivation. After consuming a low-salt (0.075%) or 60% calorie restriction diet for 7 days, Sirt1 expression in the rat kidney was significantly increased, whereas a high-salt (8%) diet did not change the level of Sirt1 expression. The low-salt diet also increased Sirt1 expression in the heart, muscle, brain, and fat tissues. The increased Sirt1 that was observed in rats on a low-salt diet was associated with increased ghrelin expression in the distal nephron, with both molecules exhibiting similar distribution patterns. An in vitro experiment suggested that ghrelin increases Sirt1 expression in cortical collecting duct cells by activating ghrelin receptors. Our study indicates that this ‘ghrelin-Sirt1 system’ may participate in regulating sodium reabsorption in the distal nephron.

Effects of hydrogen sulfide (H2S) on water intake and vasopressin and oxytocin secretion induced by fluid deprivation

During dehydration, responses of endocrine and autonomic control systems are triggered by central and peripheral osmoreceptors and peripheral baroreceptors to stimulate thirst and sodium appetite. Specifically, it is already clear that endocrine system acts by secreting vasopressin (AVP), oxytocin (OT) and angiotensin II (ANG II), and that gaseous molecules, such as nitric oxide (NO) and carbon monoxide (CO), play an important role in modulating the neurohypophyseal secretion as well as ANG II production and thirst. More recently, another gas—hydrogen sulfide (H2S)—has been studied as a neuronal modulator, which is involved in hypothalamic control of blood pressure, heart frequency and temperature. In this study, we aimed to investigate whether H2S and its interaction with NO system could participate in the modulatory responses of thirst and hormonal secretion induced by fluid deprivation. For this purpose, Wistar male rats were deprived of water for 12 and 24h, and the activity of sulfide-generating enzymes was measured. Surprisingly, 24-h water deprivation increased the activity of sulfide-generating enzymes in the medial basal hypothalamus (MBH). Furthermore, the icv injection of sodium sulfide (Na2S, 260nmol), a H2S donor, reduced water intake, increased AVP, OT and CORT plasma concentrations and decreased MBH nitrate/nitrite (NOX) content of 24-h water-deprived animals compared to controls. We thus suggest that H2S system has an important role in the modulation of hormonal and behavioral responses induced by 24-h fluid deprivation.

Impact of acute water and feed deprivation events on growth performance, intestinal characteristics, and serum stress markers in weaned pigs.

The impact of acute stressors (24-h feed or water deprivation) on growth performance, intestinal characteristics, and serum stress markers in weaned pigs was evaluated. Pigs (6.21 ± 0.29 kg) were allotted in a randomized complete block design to 4 treatments on the basis of BW at the time of weaning. There were 8 mixed-sex pigs in each of 12 pens per treatment. Treatments were arranged as a 2 × 2 factorial and consisted of a feed or water stressor that included a 0- or 24-h deprivation period postweaning, and pigs were subsequently allowed access to feed and water. Growth performance was measured 1, 7, 14, and 28 d postweaning. Serum and intestinal samples were taken 1 and 7 d postweaning. Serum was analyzed for cortisol and corticotrophin-releasing factor, and villus height, crypt depth, and mast cell density were measured in the jejunum and the ileum. Expression of mucin (MUC2), tumor necrosis factor α (TNF-α), interleukin 6 (IL-6), claudin 1 (CL-1), occludin (OC), and zonula occludens 1 (ZO-1) genes were measured on d 1 and 7 postweaning in the jejunum and ileum by real-time PCR. There was a decrease (P < 0.05) in ADG with the water stressor 1 d postweaning, although subsequently, there were improvements (P < 0.05) in ADG and feed efficiency. Furthermore, the water stressor reduced ADFI during the last 14 d of the trial and cumulatively (P < 0.05). Seven days postweaning there was an increase (P < 0.05) in jejunal villous height to depth ratio due to the feed stressor and a decrease (P < 0.05) in the ileal villous height to depth ratio due to the water stressor. There was an increase (P < 0.05) in serum cortisol levels due to the water stressor both 1 and 7 d postweaning. Furthermore, there was an increase in serum corticotrophin-releasing factor 1 d but not 7 d postweaning due to the water stressor (P < 0.05). The feed stressor reduced (P < 0.05) TNF-α gene expression, and the water stressor reduced (P < 0.05) OC gene expression in the jejunum 1 d postweaning. In the ileum, there was a reduction in CL-1 and ZO-1 gene expression (P < 0.05) due to the water stressor 7 d postweaning. The results from the current investigation showed that a 24-h feed or water deprivation at the time of weaning has negative impacts on growth performance, intestinal characteristics, and serum stress responses immediately following the stress event and throughout the nursery period.

Attenuated Benzodiazepine-Sensitive Tonic GABAA Currents of Supraoptic Magnocellular Neuroendocrine Cells in 24-h Water-Deprived Rats

In supraoptic nucleus (SON) magnocellular neurosecretory cells (MNCs), γ-GABA, via activation of GABAA receptors (GABAA Rs), mediates persistent tonic inhibitory currents (Itonic ), as well as conventional inhibitory postsynaptic currents (IPSCs, Iphasic ). In the present study, we examined the functional significance of Itonic in SON MNCs challenged by 24-h water deprivation (24WD). Although the main characteristics of spontaneous IPSCs were similar in 24WD compared to euhydrated (EU) rats, Itonic , measured by bicuculline (BIC)-induced Iholding shifts, was significantly smaller in 24WD compared to EU rats (P < 0.05). Propofol and diazepam prolonged IPSC decay time to a similar extent in both groups but induced less Itonic in 24WD compared to EU rats, suggesting a selective decrease in GABAA receptors mediating Itonic over Iphasic in 24WD rats. THIP (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol), a preferential δ subunit agonist, and L-655,708, a GABAA receptor α5 subunit selective imidazobenzodiazepine, caused a significantly smaller inward and outward shift in Iholding , respectively, in 24WD compared to EU rats (P < 0.05 in both cases), suggesting an overall decrease in the α5 subunit-containing GABAA Rs and the δ subunit-containing receptors mediating Itonic in 24WD animals. Consistent with a decrease in 24WD Itonic , bath application of GABA induced significantly less inhibition of the neuronal firing activity in 24WD compared to EU SON MNCs (P < 0.05). Taken together, the results of the present study indicate a selective decrease in GABAA Rs functions mediating Itonic as opposed to those mediating Iphasic in SON MNCs, demonstrating the functional significance of Itonic with respect to increasing neuronal excitability and hormone secretion in 24WD rats.

MPGES-1-derived PGE2 mediates dehydration natriuresis.

PGE(2) is a natriuretic factor whose production is elevated after water deprivation (WD) but its role in dehydration natriuresis is not well-defined. The goal of the present study was to investigate the role of microsomal prostaglandin E synthase-1 (mPGES-1) in dehydration natriuresis. After 24-h WD, wild-type (WT) mice exhibited a significant increase in 24-h urinary Na(+) excretion accompanied with normal plasma Na(+) concentration and osmolality. In contrast, WD-induced elevation of urinary Na(+) excretion was completely abolished in mPGES-1 knockout (KO) mice in parallel with increased plasma Na(+) concentration and a trend increase in plasma osmolality. WD induced a 1.8-fold increase in urinary PGE(2) output and a 1.6-fold increase in PGE(2) content in the renal medulla of WT mice, both of which were completely abolished by mPGES-1 deletion. Similar patterns of changes were observed for urinary nitrate/nitrite and cGMP. The natriuresis in dehydrated WT mice was associated with a significant downregulation of renal medullary epithelial Na channel-α mRNA and protein, contrasting to unaltered expressions in dehydrated KO mice. By quantitative RT-PCR, WD increased the endothelial nitric oxide synthase (eNOS), inducible NOS, and neuronal NOS expressions in the renal medulla of WT mice by 3.9-, 1.48-, and 2.6-fold, respectively, all of which were significantly blocked in mPGES-1 KO mice. The regulation of eNOS expression was further confirmed by immunoblotting. Taken together, our results suggest that mPGES-1-derived PGE(2) contributes to dehydration natriuresis likely via NO/cGMP.

Reductions in water and sodium intake by aged male and female rats

Aging results in reduced water and sodium intake responses in male rats. Because sex differences exist for water and sodium ingestion of young adult animals, we hypothesized that these sex differences would protect against the diminished water and sodium ingestion of aged female rats. Water and sodium intakes were examined in male and female young adult and aged Brown Norway rats in response to dipsogenic stimuli. Aged rats of both sexes consumed less water than young adult rats in response to 24-h water deprivation, thermal dehydration and hypertonic NaCl injection, but not to peripheral angiotensin II. Aged females consumed more water than males in response to hypertonic NaCl injection. Following sodium depletion, intake of 0.5 M NaCl solution over 2 h was higher in young adult rats than in aged rats. Aged animals had reduced angiotensin receptor 1A (AT1A) and atrial natriuretic peptide (ANP) mRNA expression in hypothalamic tissue with no sex differences. These data indicate that female rats are not protected from water and sodium intake deficits that occur in aging and that sex differences in sodium intake in young adult rats are eliminated with aging.

Effects of twenty-four hour transport or twenty-four hour feed and water deprivation on physiologic and performance responses of feeder cattle1

The objective of this study was to compare the effects of 24-h road transport or 24-h feed and water deprivation on acute-phase and performance responses of feeder cattle. Angus × Hereford steers (n = 30) and heifers (n = 15) were ranked by gender and BW (217 ± 3 kg initial BW; 185 ± 2 d initial age) and randomly assigned to 15 pens on d -12 of the experiment (3 animals/pen; 2 steers and 1 heifer). Cattle were fed alfalfa-grass hay ad libitum and 2.3 kg/animal daily (DM basis) of a corn-based concentrate throughout the experiment (d -12 to 28). On d 0, pens were randomly assigned to 1 of 3 treatments: 1) transport for 24 h in a livestock trailer for 1,200 km (TRANS), 2) no transport but feed and water deprivation for 24 h (REST), or 3) no transport and full access to feed and water (CON). Treatments were concurrently applied from d 0 to d 1. Total DMI was evaluated daily from d -12 to d 28. Full BW was recorded before treatment application (d -1 and 0) and at the end of experiment (d 28 and 29). Blood samples were collected on d 0, 1, 4, 7, 10, 14, 21, and 28. Mean ADG was greater (P < 0.01) in CON vs. TRANS and REST cattle but similar (P = 0.46) between TRANS and REST cattle (1.27, 0.91, and 0.97 kg/d, respectively; SEM = 0.05). No treatment effects were detected for DMI (P ≥ 0.25), but CON had greater G:F vs. TRANS (P < 0.01) and REST cattle (P = 0.08) whereas G:F was similar (P = 0.21) between TRANS and REST cattle. Plasma cortisol concentrations were greater (P ≤ 0.05) in REST vs. CON and TRANS cattle on d 1, 7, 14, and 28 and also greater (P = 0.02) in TRANS vs. CON cattle on d 1. Serum NEFA concentrations were greater (P < 0.01) in REST and TRANS vs. CON cattle on d 1 and greater (P < 0.01) in REST vs. TRANS cattle on d 1. Plasma ceruloplasmin concentrations were greater (P = 0.04) in TRANS vs. CON cattle on d 1, greater (P = 0.05) in REST vs. CON on d 4, and greater (P ≤ 0.05) in REST vs. TRANS and CON on d 14. Plasma haptoglobin concentrations were greater (P < 0.01) in TRANS vs. CON and REST cattle on d 1 and greater (P ≤ 0.05) for REST vs. TRANS and CON cattle on d 7. In conclusion, 24-h transport and 24-h nutrient deprivation elicited acute-phase protein reactions and similarly reduced feedlot receiving performance of feeder cattle. These results suggest that feed and water deprivation are major contributors to the acute-phase response and reduced feedlot receiving performance detected in feeder cattle transported for long distances.

AT1a receptor signaling is required for basal and water deprivation-induced urine concentration in AT1a receptor-deficient mice

It is well recognized that ANG II interacts with arginine vasopressin (AVP) to regulate water reabsorption and urine concentration in the kidney. The present study used ANG II type 1a (AT(1a)) receptor-deficient (Agtr1a(-/-)) mice to test the hypothesis that AT(1a) receptor signaling is required for basal and water deprivation-induced urine concentration in the renal medulla. Eight groups of wild-type (WT) and Agtr1a(-/-) mice were treated with or without 24-h water deprivation and 1-desamino-8-d-AVP (DDAVP; 100 ng/h ip) for 2 wk or with losartan (10 mg/kg ip) during water deprivation. Under basal conditions, Agtr1a(-/-) mice had lower systolic blood pressure (P < 0.01), greater than threefold higher 24-h urine excretion (WT mice: 1.3 ± 0.1 ml vs. Agtr1a(-/-) mice: 5.9 ± 0.7 ml, P < 0.01), and markedly decreased urine osmolality (WT mice: 1,834 ± 86 mosM/kg vs. Agtr1a(-/-) mice: 843 ± 170 mosM/kg, P < 0.01), without significant changes in 24-h urinary Na(+) excretion. These responses in Agtr1a(-/-) mice were associated with lower basal plasma AVP (WT mice: 105 ± 8 pg/ml vs. Agtr1a(-/-) mice: 67 ± 6 pg/ml, P < 0.01) and decreases in total lysate and membrane aquaporin-2 (AQP2; 48.6 ± 7% of WT mice, P < 0.001) and adenylyl cyclase isoform III (55.6 ± 8% of WT mice, P < 0.01) proteins. Although 24-h water deprivation increased plasma AVP to the same levels in both strains, 24-h urine excretion was still higher, whereas urine osmolality remained lower, in Agtr1a(-/-) mice (P < 0.01). Water deprivation increased total lysate AQP2 proteins in the inner medulla but had no effect on adenylyl cyclase III, phosphorylated MAPK ERK1/2, and membrane AQP2 proteins in Agtr1a(-/-) mice. Furthermore, infusion of DDAVP for 2 wk was unable to correct the urine-concentrating defects in Agtr1a(-/-) mice. These results demonstrate that AT(1a) receptor-mediated ANG II signaling is required to maintain tonic AVP release and regulate V(2) receptor-mediated responses to water deprivation in the inner medulla.

A urine-concentrating defect in 11β-hydroxysteroid dehydrogenase type 2 null mice

In aldosterone target tissues, 11β-hydroxysteroid dehydrogenase type 2 (11βHSD2) is coexpressed with mineralocorticoid receptors (MR) and protects the receptor from activation by glucocorticoids. Null mutations in the encoding gene, HSD11B2, cause apparent mineralocorticoid excess, in which hypertension is thought to reflect volume expansion secondary to sodium retention. Hsd11b2(-/-) mice are indeed hypertensive, but impaired natriuretic capacity is associated with significant volume contraction, suggestive of a urine concentrating defect. Water turnover and the urine concentrating response to a 24-h water deprivation challenge were therefore assessed in Hsd11b2(-/-) mice and controls. Hsd11b2(-/-) mice have a severe and progressive polyuric/polydipsic phenotype. In younger mice (∼2 mo of age), polyuria was associated with decreased abundance of aqp2 and aqp3 mRNA. The expression of other genes involved in water transport (aqp4, slc14a2, and slc12a2) was not changed. The kidney was structurally normal, and the concentrating response to water deprivation was intact. In older Hsd11b2(-/-) mice (>6 mo), polyuria was associated with a severe atrophy of the renal medulla and downregulation of aqp2, aqp3, aqp4, slc14a2, and slc12a2. The concentrating response to water deprivation was impaired, and the natriuretic effect of the loop diuretic bumetanide was lost. In older Hsd11b2(-/-) mice, the V2 receptor agonist desmopressin did not restore full urine concentrating capacity. We find that Hsd11b2(-/-) mice develop nephrogenic diabetes insipidus. Gross changes to renal structure are observed, but these were probably secondary to sustained polyuria, rather than of developmental origin.

MPGES-1 deletion potentiates urine concentrating capability after water deprivation

PGE(2) plays an important role in the regulation of fluid metabolism chiefly via antagonizing vasopressin-induced osmotic permeability in the distal nephron, but its enzymatic sources remain uncertain. The present study was undertaken to investigate the potential role of microsomal PGE synthase (mPGES)-1 in the regulation of urine concentrating ability after water deprivation (WD). Following 24-h WD, wild-type (WT) mice exhibited a significant reduction in urine volume, accompanied by a significant elevation in urine osmolality compared with control groups. In contrast, in response to WD, mPGES-1 knockout (KO) mice had much less urine volume and higher urine osmolality. Analysis of plasma volume by measurement of hematocrit and by using a nanoparticle-based method consistently demonstrated that dehydrated WT mice were volume depleted, which was significantly improved in the KO mice. WD induced a twofold increase in urinary PGE(2) output in WT mice, which was completely blocked by mPGES-1 deletion. At baseline, the KO mice had a 20% increase in V(2) receptor mRNA expression in the renal medulla but not the cortex compared with WT controls; the expression was unaffected by WD irrespective of the genotype. In response to WD, renal medullary aquaporin-2 (AQP2) mRNA exhibited a 60% increase in WT mice, and this increase was greater in the KO mice. Immunoblotting demonstrated increased renal medullary AQP2 protein abundance in both genotypes following WD, with a greater increase in the KO mice. Similar results were obtained by using immunohistochemistry. Paradoxically, plasma AVP response to WD seen in WT mice was absent in the KO mice. Taken together, these results suggest that mPGES-1-derived PGE(2) reduces urine concentrating ability through suppression of renal medullary expression of V(2) receptors and AQP2 but may enhance it by mediating the central AVP response.

Human CYP3A Expression under Hypertonic Stimuli In Vivo

We previously showed that human CYP3A expression in vitro is under the transcriptional control mediated by NFAT5, which is a tonicity responsive transcriptional factor. Interestingly, hypertonicity increases CYP3A expression, while hypotonicity decreases it, suggesting constitutive regulation roles of the NFAT5‐CYP3A pathway. In contrast, mouse Cyp3a was unresponsive to ambient hypertonicity in vitro. In the present study, our objective was to show if human CYP3A expression can be induced by hypertonic stimuli in vivo. The humanized CYP3A4–3A7 transgenic mice were subjected to 4 cycles of 24h water deprivation every other day, or to a 7‐day high‐salt diet (8% salt content, HSD), that mimics the dehydration and hypertonic luminal content in the intestine, respectively. In the kidney of mice undergoing the cyclic dehydration, NFAT5‐regulated BGT1 mRNA was significantly increased compared to control (5.9±1.1 fold: M±SEM; p=0.003). Fold‐changes of the CYP3A4 and 3A7 were 2.5±0.5 (p=0.02) and 0.7±0.2 (p=0.13), respectively. In mice after HSD, fold‐induction of the duodenal BGT1, CYP3A4 and 3A7 expressions were 25.2±8.2 (p=0.02), 4.7±0.9 (p=0.01) and 2.0±0.3 (p=0.08), respectively. Our findings suggest that human CYP3A transcription is under the influence of ambient tonicity. Direct involvement of NFAT5 in vivo awaits further studies.CIHR supported