Saline Loading Research Articles

The Blood Pressure-Lowering Effect of 20-HETE Blockade in Cyp4a14(-/-) Mice Is Associated with Natriuresis.

20-Hydroxy-5,8,11,14-eicosatetraenoic acid (20-HETE) has been linked to pro-hypertensive and anti-hypertensive actions through its ability to promote vasoconstriction and inhibit Na transport in the ascending limb of the loop of Henle, respectively. In this study, we assessed the effects of 20-HETE blockade on blood pressure, renal hemodynamics, and urinary sodium excretion in Cyp4a14(-/-) male mice, which display androgen-driven 20-HETE-dependent hypertension. Administration of 2,5,8,11,14,17-hexaoxanonadecan-19-yl 20-hydroxyicosa-6(Z),15(Z)-dienoate (20-SOLA), a water-soluble 20-HETE antagonist, in the drinking water normalized the blood pressure of male Cyp4a14(-/-) hypertensive mice (±124 vs. ±153 mmHg) while having no effect on age-matched normotensive wild-type (WT) male mice. Hypertension in Cyp4a14(-/-) male mice was accompanied by decreased renal perfusion and reduced glomerular filtration rates, which were corrected by treatment with 20-SOLA. Interestingly, Cyp4a14(-/-) male mice treated with 20-SOLA displayed increased urinary sodium excretion that was paralleled by the reduction of blood pressure suggestive of an antinatriuretic activity of endogenous 20-HETE in the hypertensive mice. This interpretation is in line with the observation that the natriuretic response to acute isotonic saline loading in hypertensive Cyp4a14(-/-) male mice was significantly impaired relative to that in WT mice; this impairment was corrected by 20-SOLA treatment. Hence, endogenous 20-HETE appears to promote sodium conservation in hypertensive Cyp4a14(-/-) male mice, presumably, as a result of associated changes in renal hemodynamics and/or direct stimulatory action on tubular sodium reabsorption.

Abstract P313: Age and Response of Plasma Aldosterone to Saline Infusion in Primary Hypertension

Objective: In patients with primary hypertension, plasma aldosterone levels are significantly decreased by an intravenous saline load (IVSL), but this response is variable among patients and related to the ability of salt to modulate aldosterone production. Previous studies have reported that activity of the renin-angiotensin-aldosterone system is related with age. The aim of this study was to investigate whether age might affect the aldosterone response to an IVSL. Design and Method: In 124 hypertensive patients (48±13 y, 71 males) who were washed-out of antihypertensive drugs for 2 weeks, we measured renin and PA levels before and after an IVSL (2 lt. saline in 4 h). In all patients secondary causes of hypertension were excluded. For statistical purposes patients were subdivided into two groups based on age (< or > 60 y). Results: Twenty-three of 124 patients (18%) were had 60 y of age or more (range 61-77) and the remaining were younger than 60 y (19-60 y). No differences were found between the two groups for gender, body mass index, serum potassium and creatinine clearance. Urinary sodium excretion was comparable in patients older (159±83) or younger (159±66) than 60 y. Baseline PA (76 [49-121] pg/ml) and renin (5.0 [1.9-9.8] mcIU/ml) levels were significantly lower in patients older than 60 y than in those younger than 60 y (115 [77-162] pg/ml, P=0.019; 10.7 [5.1-20.8] mcIU/ml, P=0.026). As expected IVSL decreased significantly (P<0.001) both plasma renin and aldosterone levels. Post IVSL renin was 3.0 [1.1-4.9] mcIU/ml in patients older than 60 y and 6.2 [3.0-12.5] mcIU/ml younger than 60 y. Following IVSL, PA decreased by 87% (10 [10-13] pg/ml) in patients older than 60 y and by 76% (28 [10-49] pg/ml; P=0.003) in patients younger than 60 y. The change in PA induced by IVSL was significantly and inversely related to age (r=-0.185, P=0.039). Conclusions: PA levels are lower in hypertensive patients older than 60 y. This difference becomes more relevant after IVSL suggesting greater response of the renin-angiotensin system to volume expansion. This should be taken into account in the diagnostic work-out of hypertensive patients.

PP.17.24] THE RESPONSE OF PLASMA ALDOSTERONE TO SALINE INFUSION IS UNDER THE INFLUENCE OF AGE IN PRIMARY HYPERTENSION

Objective: In patients with primary hypertension, plasma aldosterone (PA) levels are significantly decreased by an intravenous saline load (IVSL), but this response is variable among patients and related to the ability of salt to modulate aldosterone production. Previous studies have reported that the activity of the renin-angiotensin-aldosterone system is related with age. The aim of this study was to investigate whether age might affect the aldosterone response to an IVSL. Design and method: In 124 hypertensive patients (48 ± 13 y, 71 males) who were washed-out of antihypertensive drugs for 2 weeks, we measured renin and PA levels before and after an IVSL (2 lt. saline in 4 h). In all patients secondary causes of hypertension were excluded. For statistical purposes patients were subdivided into two groups based on age (< or > 60 y). Results: Twenty-three of 124 patients (18%) were had 60 y of age or more (range 61–77) and the remaining were younger than 60 y (19–60 y). No differences were found between the two groups for gender, body mass index, serum potassium and creatinine clearance. Urinary sodium excretion was comparable in patients older (159 ± 83) or younger (159 ± 66) than 60 y. Baseline PA (76 [49–121] pg/ml) and renin (5.0 [1.9–9.8] mcIU/ml) levels were significantly lower in patients older than 60 y than in those younger than 60 y (115 [77–162] pg/ml, P = 0.019; 10.7 [5.1–20.8] mcIU/ml, P = 0.026). As expected IVSL decreased significantly (P < 0.001) both plasma renin and aldosterone levels. Post IVSL renin was 3.0 [1.1–4.9] mcIU/ml in patients older than 60 y and 6.2 [3.0–12.5] mcIU/ml younger than 60 y. Following IVSL, PA decreased by 87% (10 [10–13] pg/ml) in patients older than 60 y and by 76% (28 [10–49] pg/ml; P = 0.003) in patients younger than 60 y. The change in PA induced by IVSL was significantly and inversely related to age (r = -0.185, P = 0.039). Conclusions: PA levels are lower in hypertensive patients older than 60 y. This difference becomes more relevant after IVSL suggesting greater response of the renin-angiotensin system to volume expansion. This should be taken into account in the diagnostic work-up of hypertensive patients.

Sexual Dimorphic Pattern of Renal Transporters and Electrolyte Homeostasis.

Compared with males, females have lower BP before age 60, blunted hypertensive response to angiotensin II, and a leftward shift in pressure natriuresis. This study tested the concept that this female advantage associates with a distinct sexual dimorphic pattern of transporters along the nephron. We applied quantitative immunoblotting to generate profiles of transporters, channels, claudins, and selected regulators in both sexes and assessed the physiologic consequences of the differences. In rats, females excreted a saline load more rapidly than males did. Compared with the proximal tubule of males, the proximal tubule of females had greater phosphorylation of Na+/H+ exchanger isoform 3 (NHE3), distribution of NHE3 at the base of the microvilli, and less abundant expression of Na+/Pi cotransporter 2, claudin-2, and aquaporin 1. These changes associated with less bicarbonate reabsorption and higher lithium clearance in females. The distal nephrons of females had a higher abundance of total and phosphorylated Na+/Cl- cotransporter (NCC), claudin-7, and cleaved forms of epithelial Na+ channel (ENaC) α and γ subunits, which associated with a lower baseline plasma K+ concentration. A K+-rich meal increased the urinary K+ concentration and decreased the level of renal phosphorylated NCC in females. Notably, we observed similar abundance profiles in female versus male C57BL/6 mice. These results define sexual dimorphic phenotypes along the nephron and suggest that lower proximal reabsorption in female rats expedites excretion of a saline load and enhances NCC and ENaC abundance and activation, which may facilitate K+ secretion and set plasma K+ at a lower level.

Genetic susceptibility to salt-sensitive hypertension in a Han Chinese population: a validation study of candidate genes.

Salt-sensitive hypertension is a complex disease associated with genetic factors. This study aimed to identify the association between 29 candidate single-nucleotide polymorphisms and salt-sensitive hypertension in a Han Chinese population. Sixty-three participants with salt-sensitive hypertension and 279 controls with salt-resistant hypertension were recruited. A modified Sullivan's acute oral saline load and diuresis shrinkage test was used to detect blood pressure salt sensitivity. Lifestyle risk factors were obtained via a questionnaire. We used the Sequenom Mass ARRAY Platform to genotype the 29 candidate single-nucleotide polymorphisms, and the cumulative genetic risk score was used to evaluate the joint genetic effect. The frequencies of eight genotypes and five alleles in CYP11B2, PRKG1, ADRB2, FGF5, SLC8A1 and BCAT1 genes differed significantly between the salt-sensitive and salt-resistant hypertension groups. Multiple logistic regression adjusted for age and sex showed that subjects carrying rs7897633-A (PRKG1), rs434082-A (SLC8A1) and rs1042714-G (ADRB2) risk alleles had 1.83-, 2.84- and 2.40-fold increased risk for salt-sensitive hypertension, respectively. Combined risk allele analysis using the cumulative genetic risk score showed that subjects carrying one risk had 2.30-fold increased risk, and those carrying 2-4 risks had 3.32-fold increased risk for salt-sensitive hypertension. Among 29 candidate single-nucleotide polymorphisms, rs7897633-A in PRKG1, rs434082-A in SLC8A1 and rs1042714-G in ADRB2 were significantly associated with salt-sensitive hypertension. A joint effect of single-nucleotide polymorphisms from different pathways contributed to a high risk of salt-sensitive hypertension.

Percutaneous Pericardial Resection: A Novel Potential Treatment for Heart Failure With Preserved Ejection Fraction.

People with heart failure and preserved ejection fraction develop increases in left ventricular (LV) end-diastolic pressures during exercise that contribute to dyspnea. In normal open-chest animal preparations, the pericardium restrains LV filling when central blood volume increases. We hypothesized that resection of the pericardium using a minimally invasive epicardial approach would mitigate the increase in LV end-diastolic pressure that develops during volume loading in normal and diseased hearts with the chest intact. Invasive hemodynamic assessment was performed at baseline and after saline load before and after pericardial resection in normal canines with open (n=3) and closed chest (n=5) and in a pig model with features of human heart failure and preserved ejection fraction with sternum intact (n=4). In closed-chest animals, pericardiotomy was performed using a novel subxiphoid procedure. In both experimental preparations of normal dogs, pericardiotomy blunted the increase in LV end-diastolic pressure with saline infusion, while enhancing the saline-mediated increase in LV end-diastolic volume. With chest intact in the pig model, percutaneous pericardial resection again blunted the increase in LV end-diastolic pressure secondary to volume expansion (+4±3 versus +13±5 mm Hg; P=0.014), while enhancing the saline-mediated increase in LV end-diastolic volume (+17±1 versus +10±2 mL; P=0.016). This proof of concept study demonstrates that pericardial resection through a minimally invasive percutaneous approach mitigates the elevation in LV filling pressures with volume loading in both normal animals and a pig model with diastolic dysfunction. Further study is warranted to determine whether this method is safe and produces similar acute and chronic hemodynamic benefits in people with heart failure and preserved ejection fraction.

Perinatal Taurine Imbalance Followed by High Sugar Intake Alters the Effects of Estrogen on Renal Excretory Function in Adult Female Rats.

This study tests the hypothesis that perinatal taurine imbalance impairs renal function in adult female rats via alterations in estrogen activity. Female Sprague-Dawley rats were fed normal rat chow and water containing 3% beta-alanine (TD), 3% taurine (TS) or water alone (C) from conception until weaning. Then, female offspring received normal rat chow and water with (CG, TDG, TSG) or without (CW, TDW, TSW) 5% glucose. At 7-8 weeks of age, renal function at rest and after acute saline load was tested in conscious, restrained female rats treated with non-selective estrogen receptor blocker tamoxifen for a week. Compared to control, TD or TS did not affect mean arterial pressure (MAP). Tamoxifen significantly increased resting MAP only in TDG compared to TDW groups. Although renal blood flow did not significantly differ among the groups, renal vascular resistance increased in TSG compared to CW, CG, and TSW groups. Glomerular filtration rate and water and sodium excretion were not significantly different among the groups. Compared to CW, saline load significantly depressed fractional water excretion in CG, TDW, TDG, and TSW, and fractional sodium excretion in CG, TDW, TDG, TSW, and the TSG groups. Potassium excretion was not significantly different among the corresponding groups. Fractional potassium excretion significantly increased in TDW compared to CG and in TSG compared to CG and TSW groups. These differences were abolished by tamoxifen treatment. These data indicate that in adult female rats, perinatal taurine imbalance, particularly followed by high sugar intake, alters renal function via an estrogenic mechanism.

Perinatal Taurine Supplementation Alters Renal Function via Renin-Angiotensin System Overactivity in Adult Female Rats.

This study tests the hypothesis that perinatal taurine supplementation followed by a high sugar diet since weaning impairs renal function via renin-angiotensin system (RAS) overactivity in adult female rats. Female Sprague-Dawley rats were fed normal rat chow and given water alone or water containing 3% taurine from conception until weaning. After weaning, the female rats received normal rat chow and water with (CG, TSG) or without (CW, TSW) 5% glucose throughout the experiment. At 7-8 weeks of age, renal function at rest and after an acute saline load was tested in conscious female rats after a week of captopril treatment. Body, heart, and kidney weights were not significantly different among the eight groups. Mean arterial pressures and heart rates were also not different among the groups. While effective renal blood flow did not significantly differ among the eight groups, TSG displayed higher renal vascular resistance compared to CW, CG, and TSW groups. Glomerular filtration rate, filtration fraction, and water and sodium excretion did not significantly differ among the groups. Compared to CW, the saline load significantly depressed fractional water excretion in CG and TSW and fractional sodium excretion in CG, TSW, and TSG groups. Captopril treatment abolished these differences but significantly decreased potassium excretion in CG, TSW, and TSG compared to CW and abolished the increased fractional potassium excretion in TSG compared to CG and TSW groups. These data strongly suggest that in adult female rats, perinatal taurine supplementation, particularly followed by high sugar intake, alters renal function via altered RAS activity.

Does the saline load test still have a role in the orthopaedic world? A systematic review of the literature

IntroductionThe aim of this systematic review was to assess the efficacy of Saline load tests (SLTs) to evaluate extension of periarticular wounds into capsule in emergent settings. MethodsWe systematically reviewed the literature to evaluate the accuracy of the SLT in diagnosing penetrating joint injuries in the elbow, wrist, shoulder, knee, or ankle. ResultsThe SLT values to determine knee arthrotomies vary from 73.8 mL to 194 mL with sensitivities ranging between 91% and 99% depending on the size of the laceration. A SLT of 30 mL in the ankle yields sensitivities ranging from 95% to 99% in assessing joint penetration. A SLT of 45 mL in the elbow yields a sensitivity of 95% in assessing joint penetration. The addition of methylene blue does not change the sensitivity of the SLT. ConclusionSeveral studies have demonstrated the utility of the SLT as a diagnostic modality for penetrating joint injuries. However, the literature analyzed in this study was inconclusive and more studies are required to make definitive recommendations. In addition, more studies will be needed on joints other than the knee, pediatric patients, and the use of methylene blue dye in conjunction with SLT. Level of evidenceLevel II, Diagnostic study.

Abnormal autonomic nervous system function in rural Thai men: A potential contributor to their high risk of sudden unexplained nocturnal death syndrome

BackgroundRural compared to urban Thai populations have a higher incidence of sudden unexplained nocturnal death syndrome (SUNDS). This study tests the hypothesis that compared to young urban Thai men, the young rural northeast Thai men display autonomic system dysfunction that may contribute to their relatively high risk to develop SUNDS. MethodsForty-seven healthy second and third year students from Khon Kaen University (20–22years old) were divided into central, urban northeastern, and rural northeastern groups, based on the locality in which they had grown up and in which their parents had lived prior to their birth. ResultsBody weight, body height, serum sodium, serum potassium, fasting blood sugar, glucose tolerance, resting mean arterial pressure, resting heart rate, ulnar nerve conduction velocity, and sympathetic and parasympathetic nervous system activity were not significantly different among the three groups. In contrast, compared to urban northeasterners and central Thais, rural northeasterners displayed low sympathetic and high parasympathetic responses to cold stress and oral saline load; however, baroreflex sensitivity and the autonomic nervous system responses to upright tilt were not significantly different among the three groups. In addition, respiratory rates at rest and in response to upright tilt, cold stress, and oral saline load were not significantly different among the three groups. ConclusionsThese data indicate that compared to central or urban, individuals from rural origin display decreased sympathetic and increased parasympathetic responses to stresses. These altered responses could predispose the individuals to inappropriate autonomic control during the stresses, including those resulting in SUNDS.

Abstract 101: Alms1 (Alstrom Syndrome 1), a Novel Gene Involved in Blood Pressure Regulation, Renal Na Handling and Thick Ascending Limb (TAL) Function

Single nucleotide polymorphisms in the Alstrom syndrome 1 (ALMS1) gene are associated to hypertension, renal dysfunction, and obesity in the general population. The role of ALMS1 in regulating blood pressure or renal Na handling is unknown. In a proteomics screen, we identified ALMS1 as an interacting protein with the Na/K/2Cl cotransporter NKCC2. NKCC2 mediates NaCl reabsorption by the TAL. Thus, we hypothesized that ALMS1 regulates NKCC2 endocytosis and activity as well as blood pressure. First, we confirmed the expression of ALMS1 in isolated perfused TALs. To study ALMS1 function, we generated ALMS1 knockout (KO) rats in collaboration with the rat genome editing consortium at MCW and confirmed deletion of the ALMS1 gene. We found that 3 month old ALMS1 KO rats are hypertensive compared to wild type littermates (ALMS1 MAP: 141 ± 5 mmHg vs WT: 99 ± 6 mmHg, p&lt; 0.005) fed a normal Na diet. We measured surface and intracellular NKCC2 and found a higher percentage of NKCC2 at the surface in TALs from ALMS1 KO (ALMS1: 13.8 ± 1.2% vs WT: 9.1 ± 1.0%, p&lt;0.05, n=6). The increase in surface NKCC2 is due to lower endocytosis because the rate of NKCC2 internalization was lower in TALs from ALMS1 KO (ALMS1: 13.1 ± 1.2% vs WT: 28.2 ± 2.8% over 20 min, p&lt;0.01, n=6). To study NKCC2-mediated Na transport in vivo , we measured bumetanide-induced natriuresis and diuresis. ALMS1 KO rats exhibited higher bumetanide-induced natriuresis (ALMS1: 1292 ± 65 vs WT: 564 ± 31 μmoles, p&lt;0.01, n=5) and diuresis (ALMS1: 3.1 ± 0.32 vs WT: 1.6 ± 0.13 ml, p&lt;0.05), indicative of higher TAL Na reabsorption. To study if this decreases the ability to excrete a volume and Na load in ALMS1 KO, we instrumented anesthetized rats and measured sodium excretion (U Na V) and urine volume (UV) over 150 min after an acute saline load. We found that the cumulative U Na V was lower in ALMS1 KO rats (ALMS1: 72 ± 38 vs WT: 219 ± 55 μmoles, p&lt;0.05, n=8) as was the UV (ALMS1: 0.70 ± 0.24 vs WT: 1.78 ± 0.39 ml, p&lt;0.05). We conclude that deletion of ALMS1 decreases NKCC2 endocytosis and increases TAL Na reabsorption. Thus, the hypertension observed in ALMS1 KO rats may be in part due to higher renal Na reabsorption. It is not known whether the expression of ALMS1 protein is decreased in hypertensive patients or lowered by dietary factors that increase BP in humans.

SFE/SFHTA/AFCE consensus on primary aldosteronism, part 3: Confirmatory testing

Aldosterone/renin ratio (ARR) identifies patients at high or low risk of primary aldosteronism (PA), but sensitivity and especially specificity are suboptimal and confirmatory testing may therefore be necessary, in some but not all patients. In patients with elevated ARR and plasma aldosterone concentration above 550pmol/L (20ng/dL) on two assessments, PA can be diagnosed without confirmatory testing. Conversely, PA can be ruled out without confirmatory testing in patients with normal ARR and plasma aldosterone concentration below 240pmol/L (9ng/dL) on two assessments. In patients not corresponding to either of the previous conditions, dynamic confirmatory testing is mandatory. Several tests are available, based on aldosterone suppression by saline loading, fludrocortisone administration or converting enzyme inhibition by captopril. One test is based on renin stimulation by furosemide administration. Each of these tests has its limitations, and validation is incomplete. We recommend aldosterone suppression by saline infusion test. Renin stimulation by captopril may be used if sodium loading is contraindicated by impaired cardiac function.

Dexmedetomidine during total knee arthroplasty performed under spinal anesthesia decreases opioid use: a randomized-controlled trial

It remains unclear whether the opioid-sparing effects of dexmedetomidine seen in patients undergoing general anesthesia are reproducible in patients undergoing spinal anesthesia. We hypothesized that the administration of intravenous dexmedetomidine for sedation during total knee arthroplasty under spinal anesthesia would decrease postoperative morphine consumption in the first 24 hr following surgery. We conducted this prospective double-blind randomized-controlled trial in 40 patients (American Society of Anesthesiologists physical status I-III) undergoing total knee arthroplasty with a standardized spinal anesthetic. Patients were randomized to receive either a dexmedetomidine loading dose of 0.5 µg·kg(-1) over ten minutes, followed by an infusion of 0.5 µg·kg·hr(-1) for the duration of the surgery, or a normal saline loading dose and an infusion of an equivalent volume. The primary outcome was the consumption of morphine delivered via patient-controlled analgesia in the first 24 hr following surgery. The mean (SD) cumulative morphine at 24 hr in the dexmedetomidine group was 29.2 (11.2) mg compared with 61.2 (17.2) mg in the placebo group (mean difference, 32.0 mg; 95% confidence interval, 22.7 to 41.2; P < 0.001). In the dexmedetomidine group, there was a delay in the time to first analgesic request (P = 0.003) and a reduction in the mean morphine use at six and 12 hr following surgery (both P < 0.001). Dexmedetomidine was associated with a significant decrease in morphine use in the first 24 hr following total knee arthroplasty. Our study shows that an intraoperative infusion of dexmedetomidine for sedation in patients receiving spinal anesthesia can produce postoperative analgesic effects. This offers another potential adjunct in the multimodal pain management of these patients. This trial was registered at ClinicalTrials.gov (identifier NCT02026141).

Does the Saline Load Test Still Have a Role in the Orthopaedic World? A systematic review of the literature.

Does the Saline Load Test Still Have a Role in the Orthopaedic World? A systematic review of the literature.

Abstract 16993: Sex Differences in Renal Transporter Profile Indicate Lower Proximal Reabsorption in Females

Females have lower blood pressure than males before menopause, blunted hypertensive response to AngII, and a leftward shift in pressure natriuresis. Estrogen decreases renal ACE and AT1R and increases NO and AT2R. At the renal transporter level, distal tubule Na+-Cl- cotransporter (NCC) is upregulated by estrogen and more abundant in females, while the loop of Henle (LH) Na+-K+-2Cl- cotransporter (NKCC2) is less abundant. This study aimed to compare female to male apical Na+ transporters’ abundance, distribution, phosphorylation and cleavage and to determine the functional consequences of the differences. Sprague Dawley rats were fasted overnight then fed a 0%KCl meal before termination. The figure displays relative abundance of total and modified (P -phosphorylated, CL-cleaved, FL-full length) transporters expressed along the nephron in females versus males (defined as 1.0), determined by quantitative immunoblotting. Lower abundance of NaPi2, villin, myosin VI, together with higher NHE3-P (inactivation marker) suggest less proximal tubule (PT) reabsorption in females. Confocal immunohistochemistry confirmed that NHE3 localized to the base of the PT microvilli in females (not males) and endogenous CLi+, a marker of volume leaving the PT, was twice as high in females than males. While LH NKCC2 and its regulatory kinase SPAK were not significantly different, distal NCC, and activated NCC-P were more abundant in females, although thiazide sensitive natriuresis was not greater. ENaC α and γ subunits were more activated (-CL) in females. A saline challenge (7% of b.w. saline, i.p.) demonstrated that females excreted a saline load more rapidly than males. Taken together, these results suggest that lower proximal transporters and reabsorption provoke a volume load dependent elevation in NCC and ENaC. This profile in females likely facilitates pressure natriuresis and maintains lower blood pressures.

Redistribution of Proximal and Distal Reabsorption of Water and Ions in Rat Kidney After Treatment with Glucagon-Like Peptide-1 Mimetic.

Injection of a glucagon-like peptide-1 mimetic accelerated recovery of the initial status of water-salt balance in rats after water or saline load (2.5% NaCl). This effect is mediated by a decrease in proximal fluid reabsorption and change in ion and water transport in the distal part of renal tubules. We developed a new approach to calculation of additional fluid inflow from the proximal tubule to the distal tubule and distal sodium reabsorption under the influence of this mimetic in rats. The expected values corresponded to experimental results, which confirmed our hypothesis on the physiological mechanism for the involvement of the kidneys in the homeostatic effect of glucagon-like peptide-1 under variations in water-salt balance.

The type-1 cannabinoid receptor modulates the hydroelectrolytic balance independently of the energy homeostasis during salt load

Hydroelectrolytic imbalances, such as saline load (SL), trigger behavioral and neuroendocrine responses, such as thirst, hypophagia, vasopressin (AVP) and oxytocin (OT) release and hypothalamus–pituitary–adrenal (HPA) axis activation. To investigate the participation of the type-1 cannabinoid receptor (CB1R) in these homeostatic mechanisms, male adult Wistar rats were subjected to SL (0.3M NaCl) for four days. SL induced not only increases in the water intake and plasma levels of AVP, OT and corticosterone, as previously described, but also increases in CB1R expression in the lamina terminalis, which integrates sensory afferents, as well as in the hypothalamus, the main integrative and effector area controlling hydroelectrolytic homeostasis. A more detailed analysis revealed that CB1R-positive terminals are in close apposition with not only axons but also dendrites and secretory granules of magnocellular neurons, particularly vasopressinergic cells. In satiated and euhydrated animals, the intracerebroventricular administration of the CB1R selective agonist ACEA (0.1μg/5μL) promoted hyperphagia, but this treatment did not reverse the hyperosmolality-induced hypophagia in the SL group. Furthermore, ACEA pretreatment potentiated water intake in the SL animals during rehydration as well as enhanced the corticosterone release and prevented the increase in AVP and OT secretion induced by SL. The same parameters were not changed by ACEA in the animals whose daily food intake was matched to that of the SL group (Pair-Fed). These data indicate that CB1Rs modulate the hydroelectrolytic balance independently of the food intake during sustained hyperosmolality and hypovolemia.

Abstract 064: 20-HETE Contributes to Vasoconstriction of Renal Microvessels and Sodium Retention in Cyp4a14-/- Mice, a Model of 20-HETE Dependent Hypertension

20-HETE (20-Hydroxyeicosatetraenoic acid), is a cytochrome P450 (CYP) 4A-derived arachidonic acid metabolite. 20-HETE has been linked to both pro-hypertensive (via increased vasoconstriction, vascular remodeling and vascular injury of renal microvessels) and anti-hypertensive (inhibiting ion transport in the distal nephron) functions. In this study we examined the effect of 20-SOLA (2,5,8,11,14,17-hexaoxanonadecan-19-yl-20-hydroxyeicosa-6(Z),15(Z)-dienoate), a water soluble antagonist of the actions of 20-HETE on renal hemodynamics and sodium (Na) excretion in Cyp4a14 knockout (CYP4a14-/-) male mice. The CYP4a14-/- male mice display hypertension accompanied by increased vascular 20-HETE levels. Administration of 20-SOLA (10mg/kg/day in drinking water) normalized blood pressure (BP) in male Cyp4a14-/- mice at day 10 of treatment (124±1 vs. 153±2 mmHg in untreated male Cyp4a14-/- mice; p&lt;0.05). The normalization of blood pressure was accompanied by transient increase in the urinary sodium excretion in the Cyp4a14-/- male mice (8.3±0.7 vs. 5.8±0.5 μmol/g body weight/day; p&lt;0.05). Importantly, 20-SOLA increased glomerular filtration rate (GFR) of Cyp4a14-/- mice (2.38±0.05 vs. 1.88±0.18 μL/min/mg kidney weight, p&lt;0.05) as opposed to no changes observed in the wild type (WT: (2.26±0.18 vs. 2.33±0.20μL/min/mg kidney weight). Evaluation of the renal blood flow (RBF) by laser Doppler flowmetry showed that treatment with 20-SOLA increased the RBF in Cyp4a14-/- mice by 12.3±4%, which remained unaltered in the WT. Additionally, the pressure-induced myogenic tone of isolated preglomerular microvessels was significantly elevated in Cyp4a14-/- mice; 20-SOLA treatment prevented the increase in myogenic responses. The natriuretic response to an isotonic saline loading challenge (10% of body weight, IP) was significantly attenuated in the Cyp4a14-/- mice as compared to the WT (35.5±2.8 vs. 57.4±8.3 percentage of Na load, p&lt;0.05); this was corrected by 20-SOLA (61.7±5.7 percentage of Na load, p&lt;0.05). These results confirm that 20-SOLA normalizes blood pressure of Cyp4a14-/- male mice and demonstrates that this is associated with increases in GFR, RBF and natriuresis.

Association of Post-Saline Load Plasma Aldosterone Levels With Left Ventricular Hypertrophy in Primary Hypertension.

Left ventricular hypertrophy (LVH) is an independent risk factor for cardiovascular morbidity in hypertension. Current evidence suggests a contribution to LVH of plasma aldosterone levels that are inappropriately elevated for the salt status. The aim of this study was to investigate whether inappropriate modulation of aldosterone production by a saline load is associated with left ventricular (LV) mass in hypertensive patients. In 90 hypertensive patients free of clinically relevant cardiovascular complications in whom secondary forms of hypertension were ruled out, we performed a standard intravenous saline load (0.9% NaCl, 2 l in 4 hours) with measurement of plasma aldosterone and active renin at baseline and end of infusion. Bi-dimensional echocardiography was performed for the assessment of cardiac morphology and function. LVH was present in 19% of patients who had significantly worse renal function and higher body mass, blood pressure, and plasma aldosterone levels measured both at baseline and after the saline load than patients without LVH. LV mass was directly related to age, body mass, systolic blood pressure, duration of hypertension, baseline, and post-saline load plasma aldosterone levels and inversely to glomerular filtration. Multivariate regression analysis showed independent correlation of LV mass with body mass, systolic blood pressure, and plasma aldosterone levels measured after intravenous saline load, but not at baseline. In patients with hypertension, aldosterone levels measured after intravenous saline load are related to LV mass independent of age, body mass, and blood pressure, suggesting that limited ability of salt to modulate aldosterone production could contribute to LVH.

H2O2 generated by NADPH oxidase 4 contributes to transient receptor potential vanilloid 1 channel-mediated mechanosensation in the rat kidney.

The presence of NADPH oxidase (Nox) in the kidney, especially Nox4, results in H2O2 production, which regulates Na(+) excretion and urine formation. Redox-sensitive transient receptor potential vanilloid 1 channels (TRPV1s) are distributed in mechanosensory fibers of the renal pelvis and monitor changes in intrapelvic pressure (IPP) during urine formation. The present study tested whether H2O2 derived from Nox4 affects TRPV1 function in renal sensory responses. Perfusion of H2O2 into the renal pelvis dose dependently increased afferent renal nerve activity and substance P (SP) release. These responses were attenuated by cotreatment with catalase or TRPV1 blockers. In single unit recordings, H2O2 activated afferent renal nerve activity in response to rising IPP but not high salt. Western blots revealed that Nox2 (gp91(phox)) and Nox4 are both present in the rat kidney, but Nox4 is abundant in the renal pelvis and originates from dorsal root ganglia. This distribution was associated with expression of the Nox4 regulators p22(phox) and polymerase δ-interacting protein 2. Coimmunoprecipitation experiments showed that IPP increases polymerase δ-interacting protein 2 association with Nox4 or p22(phox) in the renal pelvis. Interestingly, immunofluorescence labeling demonstrated that Nox4 colocalizes with TRPV1 in sensory fibers of the renal pelvis, indicating that H2O2 generated from Nox4 may affect TRPV1 activity. Stepwise increases in IPP and saline loading resulted in H2O2 and SP release, sensory activation, diuresis, and natriuresis. These effects, however, were remarkably attenuated by Nox inhibition. Overall, these results suggest that Nox4-positive fibers liberate H2O2 after mechanostimulation, thereby contributing to a renal sensory nerve-mediated diuretic/natriuretic response.