Salt Sensitivity Of Blood Pressure Research Articles

Effect of high-salt diet on blood pressure and body fluid composition in patients with type 1 diabetes: randomized controlled intervention trial

IntroductionPatients with type 1 diabetes are susceptible to hypertension, possibly resulting from increased salt sensitivity and accompanied changes in body fluid composition. We examined the effect of a high-salt diet...

Impaired NCC Activity and Regulation on Dietary High Dietary Salt Intake in Aged Sprague Dawley Rats Is Associated with Increased Salt Sensitivity of Blood Pressure

BackgroundHypertension (HTN) is one of the leading causes of death worldwide and its prevalence increases with age. Studies revealed that enhanced global sympathetic tone is related to increases in blood pressure (BP) in aged human subjects. Dietary sodium intake is associated with the regulation of blood pressure, as increased sodium retention is a well‐established precursor of hypertension risk. An excessive dietary sodium intake leads to increases in BP in individuals that demonstrate the salt sensitivity of BP and evoke the development of salt sensitive HTN (SSH). Recent studies have demonstrated that excessive release of norepinephrine by increased sympathetic nerve activity upregulates renal sodium chloride cotransporter (NCC) activity to promote sodium reabsorption. However, the underlying mechanisms of the regulation of sodium homeostasis and blood pressure in response to increase in sympathetic tone with age remain unclear.HypothesisNCC‐mediated sodium retention driven by increased sympathetic tone with age contributes to age‐related HTN. Furthermore, the activity and regulation of NCC are impaired on a high salt (HS) diet and this impaired NCC activity and regulation drives the development of age‐dependent SSH.MethodsThree different age groups (3, 8, 16 month old (MO)) of male Sprague‐Dawley (SD) rats were fed a normal salt (NS; 0.6% NaCl) or HS (4% NaCl) diet for 21 days respectively. On day 21, basal MAP, NCC activity (peak natriuresis to IV hydrochlorothiazide (2mg/kg) infusion), and vascular sympathetic tone (peak MAP change in response to ganglionic blockade (IV hexamethonium; 30mg/kg)) were measured in vivo. Plasma and renal NE concentrations were also assessed via ELISA. The expression of total NCC, phosphorylated NCC, with‐no‐lysine [K] kinases (WNK) 1, WNK4, STE20/SPS1‐related proline‐alanine‐rich protein kinase (SPAK), oxidative stress responsive kinase 1 (OxSR1), and phosphorylated SPAK/OxSR1 were assessed via immunoblotting (N=6/gp).ResultsFirst, 3MO SD rats are normotensive in both diet groups and show dietary sodium‐evoked suppression of NCC activity, expression, and phosphorylation and upstream regulatory kinases including WNK1, SPAK, and OxSR1 on a HS diet relative to a NS diet. Second, SD rats show age‐dependent HTN, increases in renal sympathetic tone, NCC activity and expression, and WNK1 expression. Last, SD rats show aged‐dependent SSH, increased sympathetic tone, and impaired suppression of NCC activity, phosphorylation, and the expression of kinases SPAK and OxSR1.ConclusionSD rats show age‐dependent HTN that is coupled with increases in sympathetic tone, NCC activity and expression, which strongly suggests that the NCC contributes to the development of age‐dependent HTN. Moreover, the NCC may play a pivotal role in the development of age‐dependent SSH as aged SD rats show impaired dietary‐sodium evoked suppression of NCC activity and regulation. Collectively, these findings suggest that increased sympathetic tone may drive NCC activity that evokes age‐dependent HTN and SSH. MO, month old; NS, 0.6% NaCl; HS, 4% NaCl. Variables 3 MO 8 MO 16 MO NS HS NS HS NS HS MAP (mmHg) 124 ± 2 126 ± 3 135 ± 4 # 143 ± 5 # 149 ± 3 # † 169 ± 1 * # † ΔUNaV to HCTZ (μeq/min) 9 ± 1 7 ± 1 * 18 ± 2 # 16 ± 1 # 15 ± 5 # 16 ± 6 # Plasma NE (nmol/L) 44 ± 4 28 ± 4 * 55 ± 3 # 42 ± 4 * # 54 ± 4 # 41 ± 4 * # Renal NE (pg/mg) 612 ± 36 368 ± 32 * 835 ± 48 # 722 ± 44 * # 974 ± 13 # † 1019 ± 134 # † ΔMAP to hexamethonium (mmHg) −33 ± 4 −24 ± 3 * −64 ± 5 # −65 ± 6 # −60 ± 3 # −67 ± 7 # Total NCC expression (fold change) 1.00 ± 0.22 0.32 ± 0.09 * 1.91 ± 0.25 # 1.13 ± 0.15 * # 1.82 ± 0.23 # 0.75 ± 0.11 * Total pNCCT53 expression (fold change) 1.00 ± 0.20 0.19 ± 0.05 * 1.24 ± 0.46 0.87 ± 0.22 0.49 ± 0.18 1.73 ± 0.22 * # WNK1 expression (fold change) 1.00 ± 0.20 0.49 ± 0.06 * 1.07 ± 0.34 1.36 ± 0.15 2.15 ± 0.38 # † 1.60 ± 0.29 # WNK4 expression (fold change) 1.00 ± 0.11 0.86 ± 0.07 1.95 ± 0.14 # 1.28 ± 0.10 # 1.05 ± 0.07 † 1.17 ± 0.09 SPAK expression (fold change) 1.00 ± 0.12 0.48 ± 0.09 * 1.25 ± 0.09 1.30 ± 0.23 # 0.42 ± 0.04 # † 0.41 ± 0.13 † OxSR1 expression (fold change) 1.00 ± 0.12 0.62 ± 0.05 * 1.09 ± 0.12 1.10 ± 0.06 # 1.19 ± 0.20 1.17 ± 0.08 # pSPAK/OxSR1 expression (fold change) 1.00 ± 0.24 0.84 ± 0.30 0.55 ± 0.23 1.42 ±0.24 * 1.12 ± 0.17 2.86 ± 0.43 * # † *p<0.05 vs. respective NS group; #p<0.05 vs. respective 3 MO group; † p<0.05 vs. respective 8 MO group.

New Model of Splenocyte Transfer Exacerbates Salt‐Sensitive Renal Injury and Hypertension in Rats

Infiltration of immune cells into target organs, including the kidney, is a hallmark of hypertensive pathology, driving the use of various experimental manipulations to interrogate the influence of the immune system. Previous studies using RAG1−/− Dahl Salt‐Sensitive (SS) rats demonstrated that the adaptive immune system plays a vital role in potentiating the hypertensive phenotype. More specifically, we created a line of Dahl SS rats with a null mutation in the CD247 gene. CD3+ T cells are absent in these SSCD247−/− rats, but a B cell population is preserved. Compared to SS rats, we observe an attenuation in renal injury in SSCD247−/− rats when subjected to a high salt (HS) challenge (−109mg/day albuminuria), mirroring an attenuation in hypertension (−19mmHg). Though adoptive transfer studies are useful in mice models of hypertension, there has yet to be a study to demonstrate adoptive transfer of immune cells potentiating a genetic model of SS hypertension. Using the male T cell deficient Dahl SS rat, SSCD247−/−, we hypothesized that splenocyte transfer from SS wildtype rats into SSCD247−/− rats would populate the T cell compartment and exacerbate the SS phenotypes. Furthermore, we tested the hypothesis that splenocytes from high‐salt fed donors (HSS) would induce a more dramatic salt‐sensitive phenotype in the recipients than donors fed a low‐salt diet (LSS). The splenocyte transfer recipients (n=11/13) were compared to naïve SSCD247−/− rats (n=7). As engraftment of adoptively transferred cells is difficult to achieve reliably, we present a new approach demonstrating that transfer of splenocytes from adult rats into recipient pups at postnatal day 5 is feasible for robust population of the T cell compartment in the circulation and spleen. Using flow cytometry, greater than 80% of the constituted CD3+ T cells were CD4+ Helper T cells. In comparison to SSCD247−/− T cell deficient rats, by HS day 21, recipients receiving splenocyte transfer from both low‐salt and high‐salt fed donors showed an exacerbated rise in SS blood pressure (LSS, 150.3±19.0mHg; HSS, 155.2+/−20.8mmHg; vs SSCD24−/− 135.6±2.9mmHg; p<0.01) negating the effect originally observed in the knockout (+15–20mmHg). No difference was observed between LSS and HSS recipients. Mirroring the blood pressure, rats receiving the transfer developed greater renal damage assessed by albuminuria (+140mg/day, p<0.001) and outer medullary protein casting (p<0.05). To determine whether T cells contributed to the renal damage observed, we used flow cytometry to assess renal immune cell infiltration. Not only were the transferred cells able to infiltrate into the kidney, these T cells were more than 92% CD4+ cells. Not one phenotype showed any significant difference between those receiving splenocytes from low‐salt or high‐salt fed donors. These studies provide the first evidence that genetic salt‐sensitivity can be enhanced using adoptive immune cell transfer. Furthermore, we have documented that CD4+ cells infiltrate into the kidney which is accompanied by increased renal damage. Lastly, we note that the amount of salt in the diet of the donors does not affect the SS phenotypes of the recipients.Support or Funding InformationF31HL144084, HL116264, and HL137748

Adrenergic regulation of the NCC in the development and maintenance of Dahl Salt‐Sensitive Hypertension occurs via a WNK/SPAK/OxSR1 pathway

BackgroundDietary sodium intake significantly influences blood pressure (BP) regulation, as increased sodium reabsorption is a well‐established precursor of hypertension risk. In a subset of individuals that demonstrate the salt sensitivity of BP, increased dietary sodium intake evokes significant increases in BP and contributes to the development of salt‐sensitive hypertension (SSH). Studies suggest that excessive Sympathetic Nervous System (SNS) release of norepinephrine (NE) stimulates activity of the sodium chloride cotransporter (NCC) via synergistic α1 or β adrenergic receptor pathways to drive SSH.HypothesisExcessive SNS release of NE influences NCC activity via an α1‐adrenoceptor gated pathway that relies upon WNK/SPAK/OxSR1 signaling to drive the development of Dahl SSH.MethodsGroups of naïve Dahl Salt Sensitive (DSS) rats, Dahl Salt Resistant (DSR), DSS rats receiving a continuous subcutaneous (s.c.) terazosin (10 mg/kg/day), or s.c. propranolol (10 mg/kg/day) infusion were fed a normal salt (NS, 0.6% NaCl) or high salt (HS, 4% NaCl) diet for 21 days respectively. On day 21 basal MAP and NCC activity (peak natriuresis to iv hydrochlorothiazide (HCTZ; 2mg/kg) infusion) were assessed. NCC, phosphoNCC, WNK1, SPAK, and OxSR1 expression were assayed via immunoblotting (N=6/gp). Additional groups of DSS rats were fed a 42 day HS diet. On day 21, rats were given s.c. saline or s.c. terazosin (10 mg/kg/day). On day 42, measurements were taken as described previously (N=6/gp).ResultsDSR rats maintain normal BP when fed a 21 day HS diet and suppress NCC activity, expression, and phosphorylation compared to rats on a NS diet. DSS rats develop SSH when fed a 21 day HS diet and exhibit increases in NCC activity, expression, and phosphorylation compared to rats on a NS diet. Chronic α1‐adrenoceptor antagonism (confirmed pharmacologically) using terazosin attenuates SSH, reduces NCC activity, expression, and phosphorylation in rats on a HS diet. β‐adrenoceptor antagonism using propranolol fails to attenuate SSH or influence NCC activity. Critically, α1‐antagonism reduces BP and NCC activity and expression in DSS rats with established SSH.ConclusionSalt resistance in DSR rats is marked by dietary sodium‐evoked suppression of NCC activity and expression. Salt sensitivity in DSS rats is driven in part by a failure to suppress NCC activity or expression and contributes to the development of SSH. α1‐adreoceptor antagonism attenuates both the development and maintenance of SSH in DSS rats by evoking suppression of NCC activity and expression. Collectively our findings suggest that excessive SNS release of NE influences NCC activity via α1‐adrenoceptor pathway to drive sodium reabsorption and the development of SSH.Support or Funding InformationThis work was supported by NIH R56 AG057687, R01 HL139867, R01 HL141406, R01 HL107330 and K02 HL112718 and AHA 16MM32090001 and 17GRNT33670023 to R.D.W., NIH F31 DK116501 to A.A.F., ASN Foundation for Kidney Research Pre‐Doctoral Fellowship award and APS William Townsend Porter Physiology Development Fellowship award to F.P. Dietary Salt Intake MAP (mmHg) Peak ΔUNaV to HCTZ (μeq/min) NCC Expression (Fold Change) Total pNCCT53 (Fold Change) WNK1 Expression (Fold Change) SPAK Expression (Fold Change) OxSR1 Expression (Fold Change) Naïve DSR rat 21‐day NS 129 ± 3 10.5 ± 1.2 1 ± 0.06 1 ± 0.14 1 ± 0.05 1 ± 0.11 1 ± 0.08 HS 131 ± 2 8.5 ± 1.0 * 0.34 ± 0.04 * 0.23 ± 0.03 * 0.76 ± 0.08 0.83 ± 0.15 0.49 ± 0.05 * Naïve DSS rat 21‐day NS 127 ± 3 9.4 ± 0.6 1 ± 0.14 1 ± 0.17 1 ± 0.08 1 ± 0.11 1 ± 0.05 HS 162 ± 4 * 11.4 ± 0.4 * 1.09 ± 0.14 1.05 ± 0.17 1.04 ± 0.12 0.96 ± 0.15 0.96 ± 0.06 DSS rat 21‐day sc Terazosin HS 143 ± 3 # 5.9 ± 0.6 # 0.25 ± 0.13 # 0.42 ± 0.20 # 0.25 ± 0.08 # 0.30 ± 0.08 # 0.71 ± 0.01 # DSS rat 21‐day sc Propanolol HS 157 ± 4 10.4 ± 0.6 0.88 ± 0.04 0.95 ± 0.06 0.99 ± 0.01 0.37 ± 0.06 # 1.09 ± 0.01 DSS rat 42‐day sc Saline HS 207 ± 5 14.4 ± 0.6 1 ± 0.10 1 ± 0.20 1 ± 0.19 1 ± 0.19 1 ± 0.05 DSS rat 42‐day sc Terazosin HS 191 ± 3 Φ 9.3 ± 2.0 Φ 0.69 ± 0.08 Φ 0.42 ± 0.15 Φ 0.48 ± 0.09 Φ 0.97 ± 0.11 0.88 ± 0.09 *p<0.05 vs. respective naive Normal Salt (NS, 0.6% NaCl) group; #p<0.05 vs. naive DSS 21 Day High Salt (HS, 4% NaCl) group; Φp<0.05 vs. 42 day subcutaneous (sc) saline group.

Glucocorticoids affect metabolic but not muscle microvascular insulin sensitivity following high versus low salt intake.

BACKGROUNDSalt-sensitive hypertension is often accompanied by insulin resistance in obese individuals, but the underlying mechanisms are obscure. Microvascular function is known to affect both salt sensitivity of blood pressure and metabolic insulin sensitivity. We hypothesized that excessive salt intake increases blood pressure and decreases insulin-mediated glucose disposal, at least in part by impairing insulin-mediated muscle microvascular recruitment (IMMR).METHODSIn 20 lean and 20 abdominally obese individuals, we assessed mean arterial pressure (MAP; 24-hour ambulatory blood pressure measurements), insulin-mediated whole-body glucose disposal (M/I value; hyperinsulinemic-euglycemic clamp technique), IMMR (contrast-enhanced ultrasound), osmolyte and water balance, and excretion of mineralocorticoids, glucocorticoids, and amino and organic acids after a low- and high-salt diet during 7 days in a randomized, double-blind, crossover design.RESULTSOn a low-, as compared with a high-salt, intake, MAP was lower, M/I value was lower, and IMMR was greater in both lean and abdominally obese individuals. In addition, natural logarithm IMMR was inversely associated with MAP in lean participants on a low-salt diet only. On a high-salt diet, free water clearance decreased, and excretion of glucocorticoids and of amino acids involved in the urea cycle increased.CONCLUSIONOur findings imply that hemodynamic and metabolic changes resulting from alterations in salt intake are not necessarily associated. Moreover, they are consistent with the concept that a high-salt intake increases muscle glucose uptake as a response to high salt-induced, glucocorticoid-driven muscle catabolism to stimulate urea production and thereby renal water conservation.TRIAL REGISTRATIONClinicalTrials.gov, NCT02068781.

Lysine-Specific Demethylase-1 Deficiency Increases Agonist Signaling Via the Mineralocorticoid Receptor.

LSD1 (lysine-specific demethylase-1) is an epigenetic regulator of gene transcription. LSD1 risk allele in humans and LSD1 deficiency (LSD1+/-) in mice confer increasing salt-sensitivity of blood pressure with age, which evolves into salt-sensitive hypertension in older individuals. However, the mechanism underlying the relationship between LSD1 and salt-sensitivity of blood pressure remains elusive. Here, we show that LSD1 genotype (in humans) and LSD1 deficiency (in mice) lead to similar associations with increased blood pressure and urine potassium levels but with decreased aldosterone levels during a liberal salt diet. Thus, we hypothesized that LSD1 deficiency leads to an MR (mineralocorticoid receptor)-dependent hypertensive state. Yet, further studies in LSD1+/- mice treated with the MR antagonist eplerenone demonstrate that hypertension, kaliuria, and albuminuria are substantially improved, suggesting that the ligand-independent activation of the MR is the underlying cause of this LSD1 deficiency-mediated phenotype. Indeed, while MR and epithelial sodium channel expression levels were increased in LSD1+/- mouse kidney tissues, aldosterone secretion from LSD1+/- glomerulosa cells was significantly lower. Collectively, these data establish that LSD1 deficiency leads to an inappropriate activation and increased levels of the MR during a liberal salt regimen and suggest that inhibiting the MR pathway is a useful strategy for treatment of hypertension in human LSD1 risk allele carriers.

Hypothalamic Paraventricular Nucleus Gαi2 (Guanine Nucleotide-Binding Protein Alpha Inhibiting Activity Polypeptide 2) Protein-Mediated Neural Control of the Kidney and the Salt Sensitivity of Blood Pressure.

We have previously reported that in salt-resistant rat phenotypes brain, Gαi2 (guanine nucleotide-binding protein alpha inhibiting activity polypeptide 2) proteins are required to maintain blood pressure and sodium balance. However, the impact of hypothalamic paraventricular nucleus (PVN) Gαi2 proteins on the salt sensitivity of blood pressure is unknown. Here, by the bilateral PVN administration of a targeted Gαi2 oligodeoxynucleotide, we show that PVN-specific Gαi2 proteins are required to facilitate the full natriuretic response to an acute volume expansion (peak natriuresis [μeq/min] scrambled (SCR) oligodeoxynucleotide 41±3 versus Gαi2 oligodeoxynucleotide 18±4; P<0.05) via a renal nerve-dependent mechanism. Furthermore, in response to chronically elevated dietary sodium intake, PVN-specific Gαi2 proteins are essential to counter renal nerve-dependent salt-sensitive hypertension (mean arterial pressure [mm Hg] 8% NaCl; SCR oligodeoxynucleotide 128±2 versus Gαi2 oligodeoxynucleotide 147±3; P<0.05). This protective pathway involves activation of PVN Gαi2 signaling pathways, which mediate sympathoinhibition to the blood vessels and kidneys (renal norepinephrine [pg/mg] 8% NaCl; SCR oligodeoxynucleotide 375±39 versus Gαi2 oligodeoxynucleotide 850±27; P<0.05) and suppression of the activity of the sodium chloride cotransporter assessed as peak natriuresis to hydrochlorothiazide. Additionally, central oligodeoxynucleotide-mediated Gαi2 protein downregulation prevented PVN parvocellular neuron activation, assessed by FosB immunohistochemistry, in response to increased dietary salt intake. In our analysis of the UK BioBank data set, it was observed that 2 GNAI2 single nucleotide polymorphism (SNP) (rs2298952, P=0.041; rs4547694, P=0.017) significantly correlate with essential hypertension. Collectively, our data suggest that selective targeting and activation of PVN Gαi2 proteins is a novel therapeutic approach for the treatment of salt-sensitive hypertension.

Genetic Predisposition and Salt Sensitivity in a Chinese Han Population: The EpiSS Study.

Objectives Genome-wide association studies and candidate gene studies have found many single nucleotide polymorphisms (SNPs) that affect salt sensitivity (SS). We constructed a polygenic risk score (PRS) to estimate the joint effect of these SNPs on SS. Methods We recruited 762 Chinese participants into the study. An unweighted PRS was constructed using 42 known genetic risk variants associated with SS or salt sensitivity blood pressure. A modified Sullivan's acute oral saline load and diuresis shrinkage test was used to detect salt sensitivity. Logistic regression was used to estimate the joint effect of the SNPs on SS both overall and after stratification by hypertension. Results The mean age of the participants was 57.1 years, and most of them were female (77.4%). The prevalence of SS was 28.7%. Both the continuous PRS and PRS tertiles were significantly associated with the risk of SS and a BP increase of more than 5 mmHg during acute salt loading but were not associated with a BP decrease of more than 10 mmHg during the diuresis shrinkage process. In the normotensive group, participants with PRSs in the middle and top tertiles had a more than twofold increased risk of SS (OR = 2.18, 95% CI: 1.15–4.12, P = 0.016, and OR = 2.28, 95% CI: 1.19–4.38, P = 0.016, and OR = 2.28, 95% CI: 1.19–4.38, P = 0.016, and OR = 2.28, 95% CI: 1.19–4.38, P = 0.016, and OR = 2.28, 95% CI: 1.19–4.38, Conclusion The 42 investigated SNPs were jointly and significantly associated with SS, especially in the normotensive Chinese population. These findings may provide genetic evidence for identifying target populations that would benefit from salt restriction policies.

Effects of an SGLT2 inhibitor on the salt sensitivity of blood pressure and sympathetic nerve activity in a nondiabetic rat model of chronic kidney disease.

The glucose-lowering effect of sodium-glucose cotransporter 2 (SGLT2) inhibitors is reduced in patients with diabetes who have chronic kidney disease (CKD). In the present study, we examined the effect of an SGLT2 inhibitor on the salt sensitivity of blood pressure (BP), circadian rhythm of BP, and sympathetic nerve activity (SNA) in nondiabetic CKD rats. Uninephrectomized Wistar rats were treated with adenine (200 mg/kg/day) for 14 days. After stabilization with a normal-salt diet (NSD, 0.3% NaCl), a high-salt diet (HSD, 8% NaCl) was administered. Mean arterial pressure (MAP) was continuously monitored using a telemetry system. We also analyzed the low frequency (LF) of systolic arterial pressure (SAP), which reflects SNA. In adenine-induced CKD rats, HSD consumption for 5 days significantly increased the mean MAP from 106 ± 2 to 148 ± 3 mmHg. However, MAP was decreased to 96 ± 3 mmHg within 24 h after switching back to a NSD (n = 7). Treatment with an SGLT2 inhibitor, luseogliflozin (10 mg/kg/day, p.o., n = 7), significantly attenuated the HSD-induced elevation of MAP, which was associated with a reduction in LF of SAP. These data suggest that treatment with an SGLT2 inhibitor attenuates the salt sensitivity of BP, which is associated with SNA inhibition in nondiabetic CKD rats.

Controlled Feeding of an 8-d, High-Dairy Cheese Diet Prevents Sodium-Induced Endothelial Dysfunction in the Cutaneous Microcirculation of Healthy, Older Adults through Reductions in Superoxide

Background:While excess dietary sodium impairs vascular function by increasing oxidative stress, the dietary incorporation of dairy foods improves vascular health. We demonstrated that single-meal cheese consumption ameliorates acute, sodium-induced endothelial dysfunction. However, controlled feeding studies examining the inclusion of cheese, a dairy product that contains both bioactive constituents and sodium, are lacking. Objectives:We tested the hypothesis that microcirculatory endothelium-dependent dilation (EDD) would be impaired by a high-sodium diet, but a sodium-matched diet high in dairy cheese would preserve EDD through oxidant stress mechanisms. Methods:We gave 11 adults without salt-sensitive blood pressure (<10 mmHg Δ mean arterial pressure; 64 ± 2 y) 4 separate 8-d controlled dietary interventions in a randomized, crossover design: a low-sodium, no-dairy intervention (LNa; 1500 mg/d sodium); a low-sodium, high-cheese intervention (LNaC; 1500 mg/d sodium, 170 g/d cheese); a high-sodium, no-dairy intervention (HNa; 5500 mg/d sodium); and a high-sodium, high-cheese intervention (HNaC; 5500 mg/d sodium, 170 g/d cheese). On Day 8 of each diet, EDD was assessed through a localized infusion (intradermal microdialysis) of acetylcholine (ACh), both alone and during coinfusion of NG-nitro-L-arginine methyl ester (NO synthase inhibitor), L-ascorbate (nonspecific antioxidant), apocynin [NAD(P)H oxidase inhibitor], or tempol (superoxide scavenger). Results:Compared with LNa, microvascular responsiveness to ACh was attenuated during HNa (LNa: –4.82 ± 0.20 versus HNa: –3.21 ± 0.55 M logEC50; P = 0.03) but not LNaC (–5.44 ± 0.20 M logEC50) or HNaC (–4.46 ± 0.50 M logEC50). Further, ascorbate, apocynin, and tempol administration each increased ACh-induced vasodilation during HNa only (Ringer's: 38.9 ± 2.4; ascorbate: 48.0 ± 2.5; tempol: 45.3 ± 2.7; apocynin: 48.5 ± 2.6% maximum cutaneous vascular conductance; all Pvalues < 0.01). Conclusions:These results demonstrate that incorporating dairy cheese into a high-sodium diet preserves EDD by decreasing the concentration of superoxide radicals. Consuming sodium in cheese, rather than in nondairy sources of sodium, may be an effective strategy to reduce cardiovascular disease risk in salt-insensitive, older adults. This trial was registered at clinicaltrials.govas NCT03376555.

Microvascular function in non-dippers: Potential involvement of the salt sensitivity biomarker, marinobufagenin-The African-PREDICT study.

Suppressed nighttime blood pressure dipping is associated with salt sensitivity and may increase the hemodynamic load on the microvasculature. The mechanism remains unknown whereby salt sensitivity may increase the cardiovascular risk of non-dippers. Marinobufagenin, a novel steroidal biomarker, is associated with salt sensitivity and other cardiovascular risk factors independent of blood pressure. The authors investigated whether microvascular function in non-dippers is associated with marinobufagenin. The authors included 220 dippers and 154 non-dippers (aged 20-30years) from the African-PREDICT study, with complete 24-hour urinary marinobufagenin and sodium data. The authors determined dipping status using 24-hour blood pressure monitoring and defined nighttime non-dipping <10%. The authors measured microvascular reactivity as retinal artery dilation in response to light flicker provocation. Young healthy non-dippers and dippers presented with similar peak retinal artery dilation, urinary sodium, and MBG excretion (P>.05). However, only in non-dippers did peak retinal artery dilation relate negatively to marinobufagenin excretion after single (r=-0.20; P=.012), partial (r=-0.23; P=.004), and multivariate-adjusted regression analyses (Adj. R2 =0.34; β=-0.26; P<.001). The authors also noted a relationship between peak artery dilation and estimated salt intake (Adj. R2 =0.30; β=-0.14; P=.051), but it was lost upon inclusion of marinobufagenin (Adj. R2 =0.33; β=-0.015; P=.86). No relationship between microvascular reactivity and marinobufagenin was evident in dippers (P=.77). Marinobufagenin, representing salt sensitivity, may be involved in early microvascular functional changes in young non-dippers and thus contributes to the development of hypertension and cardiovascular disease later in life.

Salt-sensitive blood pressure rise in type 1 diabetes patients is accompanied by disturbed skin macrophage influx and lymphatic dilation—a proof-of-concept study

Type 1 diabetes patients are more prone to have hypertension than healthy individuals, possibly mediated by increased blood pressure (BP) sensitivity to high salt intake. The classical concept proposes that the kidney is central in salt-mediated BP rises, by insufficient renal sodium excretion leading to extracellular fluid volume expansion. Recent animal-derived findings, however, propose a causal role for disturbance of macrophage-mediated lymphangiogenesis. Its relevance for humans, specifically type 1 diabetes patients, is unknown. The present study aimed to assess responses of type 1 diabetes patients to a dietary salt load with regard to BP, extracellular fluid volume (using precise iohexol measurements), and CD163+ macrophage and lymphatic capillary density in skin biopsies. Also, macrophage expression of HLA-DR (a proinflammatory marker) and CD206 (an anti-inflammatory marker) was assessed. Type 1 diabetes patients (n = 8) showed a salt-sensitive BP increase without extracellular fluid volume expansion. Whereas healthy controls (n = 12), who had no BP increase, showed increased skin CD163+ and HLA-DR+ macrophages and dilation of lymphatic skin vasculature after the dietary salt load, these changes were absent (and in case of HLA-DR more heterogenic) in type 1 diabetes patients. In conclusion, we show that salt sensitivity in type 1 diabetes patients cannot be explained by the classical concept of extracellular fluid volume expansion. Rather, we open up a potential role for macrophages and the lymphatic system. Future studies on hypertension and diabetes need to scrutinize these phenomena.

Sex-specific differences in endoplasmic reticulum aminopeptidase 1 modulation influence blood pressure and renin-angiotensin system responses.

Salt sensitivity of blood pressure (SSBP) and hypertension are common, but the underlying mechanisms remain unclear. Endoplasmic reticulum aminopeptidase 1 (ERAP1) degrades angiotensin II (ANGII). We hypothesized that decreasing ERAP1 increases BP via ANGII-mediated effects on aldosterone (ALDO) production and/or renovascular function. Compared with WT littermate mice, ERAP1-deficient (ERAP1+/-) mice had increased tissue ANGII, systolic and diastolic BP, and SSBP, indicating that ERAP1 deficiency leads to volume expansion. However, the mechanisms underlying the volume expansion differed according to sex. Male ERAP1+/- mice had increased ALDO levels and normal renovascular responses to volume expansion (decreased resistive and pulsatility indices and increased glomerular volume). In contrast, female ERAP1+/- mice had normal ALDO levels but lacked normal renovascular responses. In humans, ERAP1 rs30187, a loss-of-function gene variant that reduces ANGII degradation in vitro, is associated with hypertension. In our cohort from the Hypertensive Pathotype (HyperPATH) Consortium, there was a significant dose-response association between rs30187 risk alleles and systolic and diastolic BP as well as renal plasma flow in men, but not in women. Thus, lowering ERAP1 led to volume expansion and increased BP. In males, the volume expansion was due to elevated ALDO with normal renovascular function, whereas in females the volume expansion was due to impaired renovascular function with normal ALDO levels.

Sympathetic regulation of NCC in norepinephrine-evoked salt-sensitive hypertension in Sprague-Dawley rats.

Salt sensitivity of blood pressure is characterized by inappropriate sympathoexcitation and renal Na+ reabsorption during high salt intake. In salt-resistant animal models, exogenous norepinephrine (NE) infusion promotes salt-sensitive hypertension and prevents dietary Na+-evoked suppression of the Na+-Cl- cotransporter (NCC). Studies of the adrenergic signaling pathways that modulate NCC activity during NE infusion have yielded conflicting results implicating α1- and/or β-adrenoceptors and a downstream kinase network that phosphorylates and activates NCC, including with no lysine kinases (WNKs), STE20/SPS1-related proline-alanine-rich kinase (SPAK), and oxidative stress response 1 (OxSR1). In the present study, we used selective adrenoceptor antagonism in NE-infused male Sprague-Dawley rats to investigate the differential roles of α1- and β-adrenoceptors in sympathetically mediated NCC regulation. NE infusion evoked salt-sensitive hypertension and prevented dietary Na+-evoked suppression of NCC mRNA, protein expression, phosphorylation, and in vivo activity. Impaired NCC suppression during high salt intake in NE-infused rats was paralleled by impaired suppression of WNK1 and OxSR1 expression and SPAK/OxSR1 phosphorylation and a failure to increase WNK4 expression. Antagonism of α1-adrenoceptors before high salt intake or after the establishment of salt-sensitive hypertension restored dietary Na+-evoked suppression of NCC, resulted in downregulation of WNK4, SPAK, and OxSR1, and abolished the salt-sensitive component of hypertension. In contrast, β-adrenoceptor antagonism attenuated NE-evoked hypertension independently of dietary Na+ intake and did not restore high salt-evoked suppression of NCC. These findings suggest that a selective, reversible, α1-adenoceptor-gated WNK/SPAK/OxSR1 NE-activated signaling pathway prevents dietary Na+-evoked NCC suppression, promoting the development and maintenance of salt-sensitive hypertension.

Evaluation of the pathophysiological mechanisms of salt-sensitive hypertension.

The currently available data have indicated that dietary salt is directly correlated with blood pressure (BP) and the occurrence of hypertension. However, the salt sensitivity of BP is different in each individual. Genetic factors and environmental factors influence the salt sensitivity of BP. Obesity, stress, and aging are strongly associated with increased BP salt sensitivity. Indeed, a complex and interactive genetic and environmental system can determine an individual's BP salt sensitivity. However, the genetic/epigenetic determinants leading to salt sensitivity of BP are still challenging to identify primarily because lifestyle-related diseases, including hypertension, usually become a medical problem during adulthood, although their causes may be attributed to the earlier stages of ontogeny. The association between distinct developmental periods involves changes in gene expression, which include epigenetic phenomena. The role of epigenetic modification in the development of salt-sensitive hypertension is presently under investigation. Recently, we identified aberrant DNA methylation in the context of prenatally programmed hypertension. In this review, we summarize the existing knowledge regarding the pathophysiological mechanisms of salt-sensitive hypertension. Additionally, we discuss the contribution of epigenetic mechanisms in the development of salt-sensitive hypertension.

CeRNA network analysis and functional enrichment of salt sensitivity of blood pressure by weighted-gene co-expression analysis.

BackgroundSalt sensitivity of blood pressure (SSBP) is an independent risk factor for cardiovascular disease. The pathogenic mechanisms of SSBP are still uncertain. This study aimed to construct the co-regulatory network of SSBP and data mining strategy based on the competitive endogenous RNA (ceRNA) theory.MethodsLncRNA and mRNA microarray was performed to screen for candidate RNAs. Four criteria were used to select the potential differently expressed RNAs. The weighted correlation network analysis (WGCNA) package of R software and target miRNA and mRNA prediction online databases were used to construct the ceRNA co-regulatory network and discover the pathways related to SSBP. Gene ontology enrichment, gene set enrichment analysis (GSEA) and KEGG pathway analysis were performed to explore the functions of hub genes in networks.ResultsThere were 274 lncRNAs and 36 mRNAs that differently expressed between salt-sensitive and salt-resistant groups (P < 0.05). Using WGCNA analysis, two modules were identified (blue and turquoise). The blue module had a positive relationship with salt-sensitivity (R = 0.7, P < 0.01), high-density lipoprotein (HDL) (R = 0.53, P = 0.02), and total cholesterol (TC) (R = 0.55, P = 0.01). The turquoise module was positively related with triglyceride (TG) (R = 0.8, P < 0.01) and low-density lipoprotein (LDL) (R = 0.54, P = 0.01). Furthermore, 84 ceRNA loops were identified and one loop may be of great importance for involving in pathogenesis of SSBP. KEGG analysis showed that differently expressed mRNAs were mostly enriched in the SSBP-related pathways. However, the enrichment results of GSEA were mainly focused on basic physical metabolic processes.ConclusionThe microarray data mining process based on WGCNA co-expression analysis had identified 84 ceRNA loops that closely related with known SSBP pathogenesis. The results of our study provide implications for further understanding of the pathogenesis of SSBP and facilitate the precise diagnosis and therapeutics.

Abstract P3028: Conditional Knockout of Acid Ceramidase in Collecting Ducts Exacerbates Salt Sensitivity of Blood Pressure With High Fat Diet

Ceramidase is the rate-limit step for the production of sphingosine-1-phosphate (S1P) by controlling the immediate substrate sphingosine for S1P generation. We have previously shown that S1P increases sodium excretion via S1P receptor 1, which is mainly localized in the collecting ducts. We have also shown that conditional deletion of acid ceramidase (AC), the major form of ceramidase in collecting duct, promotes sodium retention. It is well known that salt sensitivity of blood pressure is a characteristic in obesity-associated hypertension. The present study detected levels of renal medullary AC in male C57BL6J mice fed with a high fat (HF) diet (10 weeks) and/or 1% NaCl drinking water (2 weeks). Western blot analyses showed that there was no significant difference in AC levels among normal salt (NS)-, low fat (LF)- and HF-treated mice. However, the high salt (HS) intake increased the AC levels, whereas a HF diet blocked the high salt-induced increase of AC. The relative protein levels of AC were 1.0 ± 0.06, 1.4 ± 0.07, 0.99 ± 0.23, 1.1 ± 0.05, and 0.4 ± 0.06, in NS, HS, LF, HF, and HS+HF groups, respectively. Mice with collecting duct-specific AC knockout (CD-AC-KO) were generated by crossing AC floxed mice with Aquoporin 2-Cre mice. The specific knockout of AC in collecting ducts was confirmed by immunohistochemistry and western blot. The mean arterial pressure (MAP) was significantly increased in CD-AC-KO mice compared with AC floxed mice after fed with HS+HF diet. The delta MAP before and after 2 week HS intake were 3.45 ± 0.35 mmHg in control vs. 10.6 ± 1.04 mmHg in CD-AC-KO mice measured by a DSI telemetry system. These data indicate that collecting duct AC plays an important role in salt-sensitivity of blood pressure associated with a high fat diet and that modulation of AC function in the kidneys could be a therapeutic approach for salt-sensitive hypertension associated with obesity.

Abstract 055: Sex Differences in the Development of Age-Dependent Hypertension and the Salt Sensitivity of Blood Pressure

Aim: Age-dependent hypertension (HTN) develops at different rates in men versus women. These studies tested the hypothesis that in a model of normal aging, the Sprague Dawley rat, alterations in fluid and electrolyte balance contribute to age-dependent HTN in a sex-dependent manner. Methods: Three, 8 and 16-month old male and female SD rats on a normal salt (NS; 0.6% NaCl) diet underwent an acute IV volume expansion (VE; 5% body weight) and mean arterial pressure (MAP), diuresis and natriuresis were assessed. In separate groups of aged rats fed a 21-day NS or high salt (HS; 4% NaCl) diet in vivo MAP and NCC activity (ΔUNaV to IV hydrochlorothiazide, 2mg/kg) were assessed. N=4-6/gp. Results: The diuretic and natriuretic responses to an acute VE are profoundly blunted in aged male, but not female, rats. In contrast to female rats, male rats exhibit age-dependent HTN on a lifelong NS intake and develop age-dependent salt sensitivity of blood pressure. Female rats exhibit higher baseline sodium chloride cotransporter (NCC) activity and both young male and female rats exhibit dietary sodium evoked suppression of the NCC that is lost with age. Conclusion: Aging in the Sprague Dawley rat is associated with the sex specific development of age dependent HTN and the salt sensitivity of blood pressure in the male vs. female rat. We speculate that this sex specific difference is related to the impaired ability of male rats to maintain fluid and electrolyte homeostasis - potentially via a mechanism involving increased age-dependent baseline NCC-mediated sodium retention.

Abstract P199: Gene Variants in Human Renal Proximal Tubule Alpha ENaC are Associated With Inverse Salt Sensitivity of Blood Pressure

The amiloride-sensitive epithelial sodium channel (ENaC) localizes to the apical membrane of epithelial cells in distal nephron, playing an important role in regulating whole-body Na + homeostasis and blood pressure. We were the first to describe the presence of αENaC in human renal proximal tubule cells (hRPTC). Gene variants in αENaC have been shown to be associated with salt sensitivity of blood pressure (SS) . We also verified that the specific gene variant rs4764586 was significantly associated with SS (χ 2 =9.67, P=0.046). In our salt sensitivity clinical study, 11% participants (N=27/240) had a paradoxical increase in blood pressure (BP) (≥7-mm Hg) on a low NaCl diet, defined as inverse salt sensitive ( ISS ) as compared to salt resistant ( SR , 72%) and salt sensitive ( SS , 17%). The incidence of the minor allele αENaC rs4764586 in the ISS group was 2-fold of that in SR or SS ( ISS , 14.8%; SR , 7.0%; SS , 7.1%). Expression of αENaC protein in urine derived hRPTCs was significantly lower in ISS than in SR ( ISS , 0.55±0.01, n=3; SR, 0.97±0.12, n=3; SS, 0.87±0.12, n=3; one-way ANOVA, ISS vs SR p&lt;0.05), with the lowest in the homozygous variants (HV) of rs4764586 and highest in wild type. The heterozygous variant containing hRPTCs had an intermediate expression of αENaC (WT, 0.94±0.11, n=4; Heterozygous, 0.72±0.11, n=4; HV, 0.53, n=1). ENaC-like channels were demonstrated in hRPTCs using single-channel patch-clamp electrophysiology with a conductance of 10.5±0.7 pS and E rev 39.2±5.5 mV vs 10.3±0.8 pS in SR and ISS lines, respectively. However, in ISS baseline ENaC-like channel activity was too low to be recorded without trypsin in the pipette (Po = open probability), unlike SR . In contrast, ISS cells demonstrated a higher Po than SR cells in response to trypsin both immediately and after 4 minutes of activation, even though the number of channels recorded at 4 min after GigaOhm seal formation was lower in the ISS line compared to SR line (4.7±1.7 vs 1.75±0.5, p=0.042 in SR vs ISS lines). These results suggest that ISS phenotype may be related to impaired ENaC activity in the renal proximal tubule. The long-term physiologic consequences of the ISS phenotype remain to be determined

Abstract 060: Increased Urinary Potassium Excretion Does Not Associate With Reduced Systolic Blood Pressure in the Dietary Approaches to Stop Hypertension Sodium Trial

Aim: The 2019 National Academy of Science, Engineering and Medicine Dietary Reference Intakes (DRI) for Sodium (Na) and Potassium (K) Report concluded there remains insufficient evidence to establish potassium DRIs. This study investigated the association between Na and K excretion and blood pressure in salt sensitive (SS) vs. salt resistant (SR) subjects in the Dietary Approaches to Stop Hypertension Sodium (DASH-Na) Trial. Methods: Via the NHLBI BioLINCC we accessed the DASH-Na dataset containing data on systolic blood pressure (SBP), 24-h urinary Na and K excretion at screening (regular diet [no dietary intervention]; 186 SS and 222 SR adults) and post 1-month DASH diet (increased K intake; 72 SS and 123 SR adults). The relationships between SBP, urinary Na and K excretion and Na:K ratio were assessed via linear regression with SS vs. SR as a categorical factor. Results: At screening, on a regular diet, urinary Na excretion (adjusted for gender) positively correlated with increased SBP in SS but not SR individuals (SS - 1g increase in Na excretion increases SBP 1.1±0.3mmHg - up to 5g Na excretion/day). In contrast, despite urinary K excretion of &lt;1g/day correlating with increased SBP in both SS and SS subjects, increased urinary K excretion (range 1-4g/day) did not correlate with changes in SBP in either SS or SR individuals. The urinary Na to K ratio (Na:K) was not significantly associated with SBP in SS or SR subjects. At the urinary Na excretion range 3-5g/day, equivalent to US Na intake, increased urinary K excretion had no effect on SBP in either SS or SR individuals. On the DASH diet; SBP was reduced in SS (-4.5±1.3mmHg) and SR (-8.3±0.8mmHg, P&lt;0.05) subjects. However, no correlation was observed between the reduction in SBP and urinary K excretion or urinary Na:K ratio in either in SS or SR individuals on the DASH diet. Conclusion: These data show in the DASH-Na trial population increased urinary K excretion does not correlate with reductions in SBP irrespective of the salt sensitivity of blood pressure. Our data support the recent DRI recommendation not to propose K intake guidelines and suggest that further evidence is required to support the establishment of a Na:K intake ratio to reduce SBP.