Pressure-natriuresis Response Research Articles

The role of preterm birth in stress-induced sodium excretion in young adults.

Early-life programming due to prematurity and very low birth weight (VLBW, <1500 g) is believed to contribute to development of hypertension, but the mechanisms remain unclear. Experimental data suggest that altered pressure natriuresis (increased renal perfusion pressure promoting sodium excretion) may be a contributing mechanism. We hypothesize that young adults born preterm will have a blunted pressure natriuresis response to mental stress compared with those born term. In this prospective cohort study of 190 individuals aged 18-23 years, 156 born preterm with VLBW and 34 controls born term with birth weight at least 2500 g, we measured urine sodium/creatinine before and after a mental stress test and continuous blood pressure before and during the stress test. Participants were stratified into groups by the trajectory at which mean arterial pressure (MAP) increased following the test. The group with the lowest MAP trajectory was the reference group. We used generalized linear models to assess poststress urine sodium/creatinine relative to the change in MAP trajectory and assessed the difference between groups by preterm birth status. Participants' mean age was 19.8 years and 57% were women. Change in urine sodium/creatinine per unit increase in MAP when comparing middle trajectory group against the reference group was greater in those born preterm [β 5.4%, 95% confidence interval (95% CI) -11.4 to 5.3] than those born term (β 38.5%, 95% CI -0.04 to 92.0), interaction term P = 0.002. We observed that, as blood pressure increased following mental stress, young adults born preterm exhibited decreased sodium excretion relative to term-born individuals.

Sodium-glucose cotransporter 2 inhibition does not improve the acute pressure natriuresis response in rats with type 1 diabetes.

What is the central question of this study? Sodium-glucose cotransporter 2 (SGLT2) inhibitors reduce cardiovascular risk in patients with both diabetic and non-diabetic kidney disease: can SGLT2 inhibition improve renal pressure natriuresis (PN), an important mechanism for long-term blood pressure control, which is impaired in type 1 diabetes mellitus (T1DM)? What is the main finding and its importance? The SGLT2 inhibitor dapagliflozin did not enhance the acute in vivo PN response in either healthy or T1DM Sprague-Dawley rats. The data suggest that the mechanism underpinning the clinical benefits of SGLT2 inhibitors on health is unlikely to be due to an enhanced natriuretic response to increased blood pressure. Type 1 diabetes mellitus (T1DM) leads to serious complications including premature cardiovascular and kidney disease. Hypertension contributes importantly to these adverse outcomes. The renal pressure natriuresis (PN) response, a key regulator of blood pressure (BP), is impaired in rats with T1DM as tubular sodium reabsorption fails to down-regulate with increasing BP. We hypothesised that sodium-glucose cotransporter 2 (SGLT2) inhibitors, which reduce cardiovascular risk in kidney disease, would augment the PN response in T1DM rats. Non-diabetic or T1DM (35-50mg/kg streptozotocin i.p.) adult male Sprague-Dawley rats were anaesthetised (thiopental 50mg/kg i.p.) and randomised to receive either dapagliflozin (1mg/kg i.v.) or vehicle. Baseline sodium excretion was measured and then BP was increased by sequential arterial ligations to induce the PN response. In non-diabetic animals, the natriuretic and diuretic responses to increasing BP were not augmented by dapagliflozin. Dapagliflozin induced glycosuria, but this was not influenced by BP. In T1DM rats the PN response was impaired. Dapagliflozin again increased urinary glucose excretion but did not enhance PN. Inhibition of SGLT2 does not enhance the PN response in rats, either with or without T1DM. SGLT2 makes only a minor contribution to tubular sodium reabsorption and does not contribute to the impaired PN response in T1DM.

Abstract P111: Deletion Of Na + /H + Exchanger 3 Selectively In The Proximal Tubules Doesn’T Prevent The Development Of Doca-salt Hypertension In Pt- Nhe3 -/- Mice

We have previously shown that genetic deletion of Na + /H + exchanger 3 (NHE3) selectively in the proximal tubules lowered basal blood pressure and attenuated the development of angiotensin II (Ang II)-induced hypertension by promoting the pressure-natriuresis response. However, it is not known whether deletion of the NHE3 gene selectively in the proximal tubules attenuates salt-sensitive hypertension induced by DOCA-Salt. In the present study, we tested the hypothesis that the development of DOCA-Salt hypertension is attenuated by genetic deletion of NHE3 selectively in the proximal tubules of the kidney. To test the hypothesis, mice with proximal tubule-specific deletion of NHE3, i.e., PT- Nhe3 -/- , were generated using the iL- Sglt2-Cre / Nhe3 flox approach. Adult male PT- Nhe3 -/- mice were treated with or without DOCA (10 mg/10 g body wt., subcutaneously), supplemented with 2% high salt diet, for 4 weeks. Basal and weekly systolic (SBP), diastolic (DBP), and mean arterial pressure (MAP) were determined using the indirect tail-cuff method, whereas 24 hr. urinary sodium, potassium, and chloride excretion were determined using a metabolic cage. Compared with the time-control group (n=12), treatment with DOCA-salt moderately but significantly increased systolic SBP from 96 ± 3 mmHg to 126 ± 5 mmHg in PT- Nhe3 -/- mice (n=8; P &lt;0.01). DBP and MAP increased to similar extents in response to DOCA-salt treatment ( P &lt;0.05). As expected, DOCA-salt hypertension significantly increased the pressure-natriuresis response, i.e., 24 hr. urinary sodium excretion by 55% (Control: 152 ± 19 vs. DOCA-Salt: 236 ± 2 μmol/24 hr; P &lt;0.01), potassium excretion by 52% (Control: 147 ± 16 vs. DOCA-Salt: 224 ± 18 μmol/24 hr; P &lt;0.01), and chloride excretion by 71% (Control: 181 ± 27 vs. DOCA-Salt: 310 ± 31 μmol/24 hr; P &lt;0.01), respectively. Taken together, these data do not support our hypothesis and suggest that deletion of NHE3 selectively in the proximal tubules doesn’t prevent the development of DOCA-Salt hypertension in PT- Nhe3 -/- mice.

Mice with Brain‐Specific Deletion of Hsd11b2 have an impaired renal vascular and tubular response to high salt intake

Loss‐of‐function mutations in Hsd11b2, the gene encoding the cortisol‐metabolising enzyme 11βHSD2, causes the hypertensive syndrome of Apparent Mineralocorticoid Excess. In affected individuals, overactivation of the mineralocorticoid receptor by cortisol is causative. Hypertension is salt‐sensitive, attributed to enhanced sodium reabsorption in the distal nephron and renal sodium retention. However, in the brain, 11βHSD2‐expressing neurons regulate salt appetite. We previously generated mice with conditional knockout of Hsd11b2 in the brain (Hsd11b2.BKO), which displayed enhanced salt preference and salt‐sensitive hypertension (DOI: 10.1161/CIRCULATIONAHA.115.019341). The mechanisms of salt‐sensitivity are unknown. In the current study we examined renal artery vasoreactivity and the in vivo acute pressure natriuresis response in male Hsd11b2.BKO mice and control littermates.Mice (n=10 per genotype/diet) were fed either high salt (3% Na) or 0.3% Na diet for 7 days. Animals were humanely killed, the renal arteries were isolated and mounted on a wire‐myograph to generate cumulative concentration‐response curves to phenylephrine and the nitric oxide donor, sodium nitroprusside. High salt diet significantly increased the sensitivity of the renal artery to phenylephrine‐induced vasoconstriction in Hsd11b2.BKO mice (LogEC50 0.3% diet ‐6.41±0.07 vs high salt ‐6.91±0.11; p=0.0013) but not in control mice. Sodium nitroprusside induced concentration‐dependent relaxation of renal arteries: the maximum relaxation was significantly reduced from 88±3% to 65±4% in Hsd11b2.BKO after high salt feeding (p&lt;0.01); this was not seen in control mice. In other experiments, mice (n=5‐7 per genotype/diet) were anesthetised (thiobutabarbital sodium, 120mg/kg IP) and fractional renal sodium excretion was measured at baseline and following acutely increased blood pressure, achieved by sequential arterial ligation. In all mice, sodium excretion increased with blood pressure. In the high salt group, the pressure natriuresis response was significantly attenuated in Hsd11b2.BKO mice, compared to control animals.We find that genetic amplification of mineralocorticoid signalling in the brain attenuates the normal renal vascular and tubular adaptation to high salt intake. This regulation of renal salt excretion by the central nervous system may have implications for salt‐sensitive hypertension in humans.

Angiotensin II and AT1a Receptors in the Proximal Tubules of the Kidney: New Roles in Blood Pressure Control and Hypertension.

Contrary to public perception, hypertension remains one of the most important public health problems in the United States, affecting 46% of adults with increased risk for heart attack, stroke, and kidney diseases. The mechanisms underlying poorly controlled hypertension remain incompletely understood. Recent development in the Cre/LoxP approach to study gain or loss of function of a particular gene has significantly helped advance our new insights into the role of proximal tubule angiotensin II (Ang II) and its AT1 (AT1a) receptors in basal blood pressure control and the development of Ang II-induced hypertension. This novel approach has provided us and others with an important tool to generate novel mouse models with proximal tubule-specific loss (deletion) or gain of the function (overexpression). The objective of this invited review article is to review and discuss recent findings using novel genetically modifying proximal tubule-specific mouse models. These new studies have consistently demonstrated that deletion of AT1 (AT1a) receptors or its direct downstream target Na+/H+ exchanger 3 (NHE3) selectively in the proximal tubules of the kidney lowers basal blood pressure, increases the pressure-natriuresis response, and induces natriuretic responses, whereas overexpression of an intracellular Ang II fusion protein or AT1 (AT1a) receptors selectively in the proximal tubules increases proximal tubule Na+ reabsorption, impairs the pressure-natriuresis response, and elevates blood pressure. Furthermore, the development of Ang II-induced hypertension by systemic Ang II infusion or by proximal tubule-specific overexpression of an intracellular Ang II fusion protein was attenuated in mutant mice with proximal tubule-specific deletion of AT1 (AT1a) receptors or NHE3. Thus, these recent studies provide evidence for and new insights into the important roles of intratubular Ang II via AT1 (AT1a) receptors and NHE3 in the proximal tubules in maintaining basal blood pressure homeostasis and the development of Ang II-induced hypertension.

Pressure-Natriuresis Response Is Diminished in Old Age.

BackgroundAge-related alterations in renal sodium handling affect blood pressure (BP). We aimed to clarify whether the pressure-natriuresis response changes with age, leading to BP elevation.MethodsA total of 4,859 participants with normal renal function from the Korean Genome and Epidemiology Study (KoGES) and 235 patients with non-diabetic chronic kidney disease (CKD) from the ESPECIAL trial were included and divided into the younger and older groups. In ESPECIAL, participants took olmesartan from weeks 0 to 16 and were educated about a low-salt diet (LSD) from weeks 8 to 16.ResultsIn both studies, older participants showed lower estimated glomerular filtration rate (eGFR) and urine concentration index and higher albuminuria. In KoGES, BP was higher and urine sodium was lower in older participants. In ESPECIAL, diastolic BP at 0 week was lower in older participants. Olmesartan reduced BP in both groups, whereas LSD decreased systolic BP only in older participants. Urine sodium increased in younger participants but decreased in older participants after olmesartan use. In KoGES, urine sodium was correlated with BP in both groups after adjusting for age, sex, and eGFR; however, the correlation coefficient was lower in older participants. In ESPECIAL, only younger participants showed a significant positive association between systolic BP and urine sodium in multiple regression analysis.ConclusionsThe pressure-natriuresis response was diminished in older participants with or without CKD.

The acute pressure natriuresis response is suppressed by selective ETA receptor blockade.

Hypertension is a major risk factor for cardiovascular disease. In a significant minority of people, it develops when salt intake is increased (salt-sensitivity). It is not clear whether this represents impaired vascular function or disruption to the relationship between blood pressure (BP) and renal salt-handling (pressure natriuresis, PN). Endothelin-1 (ET-1) regulates BP via ETA and ETB receptor subtypes. Blockade of ETA receptors reduces BP but promotes sodium retention by an unknown mechanism. ETB blockade increases both BP and sodium retention. We hypothesized that ETA blockade promotes sodium and water retention by suppressing PN. We also investigated whether suppression of PN might reflect off-target ETB blockade. Acute PN was induced by sequential arterial ligation in male Sprague Dawley rats. Intravenous atrasentan (ETA antagonist, 5 mg/kg) halved the normal increase in medullary perfusion and reduced sodium and water excretion by >60%. This was not due to off-target ETB blockade because intravenous A-192621 (ETB antagonist, 10 mg/kg) increased natriuresis by 50% without modifying medullary perfusion. In a separate experiment in salt-loaded rats monitored by radiotelemetry, oral atrasentan reduced systolic and diastolic BP by ∼10 mmHg, but additional oral A-192621 reversed these effects. Endogenous ETA stimulation has natriuretic effects mediated by renal vascular dilation while endogenous ETB stimulation in the kidney has antinatriuretic effects via renal tubular mechanisms. Pharmacological manipulation of vascular function with ET antagonists modifies the BP set-point, but even highly selective ETA antagonists attenuate PN, which may be associated with salt and water retention.

Genetic Deletion of AT 1a Receptors Selectively in The Proximal Tubules of The Kidney Attenuates Angiotensin II‐induced Hypertensive and Glomerular Filtration Responses in Aging PT‐ Agtr1a ‐/‐ Mice

The intratubular renin-angiotensin system (RAS) via the angiotensinogen/renin/ACE/Ang II/AT1 (AT1a) receptor signaling pathways in the proximal tubules of the kidney play a critical role in the physiological regulation of blood pressure and the development of hypertension. Whether intratubular RAS continues to exert significant impacts on blood pressure and glomerular filtration responses to Ang II remains unknown. In the present study, we tested the hypothesis that deletion of AT1a receptors selectively in the proximal tubules of the kidney attenuates Ang II-induced hypertensive and glomerular filtration responses (GFR) in aging PT-Agtr1a-/- mice. To test the hypothesis, 6 groups (n=8-12 per group) of 20- to 24-month-old male wild-type (WT) and PT-Agtr1a-/- mice were infused with or without a slow pressor dose of Ang II (~0.65 mg/kg/day, i.p.), supplemented with a 2% Na+ diet for 2 weeks. Systolic blood pressure was determined by telemetry and tail-cuff techniques, whereas GFR was measured by the transdermal GFR monitoring technique with FITC-sinistrin, and the pressure-natriuresis responses was determined before and during Ang II infusion, respectively. Basal systolic blood pressure remained significantly lower in aging PT-Agtr1a-/- (104 ± 4 mmHg) than in aging WT mice (120 ± 4 mmHg, P<0.01), whereas basal GFR was significantly higher in aging PT-Agtr1a-/- mice (196.4 ± 14.7 µl/min) than in aging WT mice (142.6 ± 11.6 µl/min, P<0.01). Furthermore, the pressure-natriuresis response was significantly augmented in aging PT-Agtr1a-/-mice (P<0.05). Ang II infusion significantly induced hypertension (152 ± 3 mmHg, P<0.01) and decreased GFR in aging WT mice (122.4 ± 3.3 µl/min, P<0.01), as expected, but the hypertensive (135 ± 3 mmHg, P<0.01) and GFR responses were significantly improved in aging PT-Agtr1a-/-mice (155.9 ± 10.1 µl/min, P<0.01), respectively. Finally, proximal tubule-specific deletion of AT1a receptors significantly augmented the pressure-natriuresis response and natriuretic responses to Ang II infusion in aging PT-Agtr1a-/-mice (P<0.01). Taken together, the results of the present study suggest that intratubular Ang II and AT1a receptors in the proximal tubules continue to play a key role in the development of Ang II-induced hypertension in aging WT mice and that deletion of AT1a receptors selectively in the proximal tubules attenuates Ang II-induced hypertension and improves glomerular filtration in aging PT-Agtr1a-/- mice.

PROXIMAL TUBULE-SPECIFIC DELETION OF AT1A RECEPTORS ATTENUATES CIRCULATING AND INTRATUBULAR ANGIOTENSIN II-INDUCED HYPERTENSION IN MICE

Objective: The present study used a novel mouse model with proximal tubule-specific knockout of AT1a receptors in the kidney, PT-Agtr1a-/-, to test the hypothesis that intratubular angiotensin II (Ang II) and AT1a receptors in the proximal tubules are required for maintaining normal blood pressure and the development of Ang II-induced hypertension. Design and method: To test our hypothesis, eight groups (n = 7–15 per group) of adult male wild-type, global Agtr1a-/-, and PT-Agtr1a-/-, and PT-Nhe3-/- mice were infused with Ang II (1.5 mg/kg/day, i.p.), or overexpressed an intracellular Ang II fusion protein (Ad-sglt2-ECFP/Ang II) in the proximal tubules of the kidney for 2 weeks. Basal blood pressure and the pressor responses, glomerular filtration rate (GFR) and 24 h urinary natriuretic response, and the pressure-natriuresis response were determined. Results: Basal telemetry blood pressure were ∼15 ± 3 mmHg lower in PT-Agtr1a-/- than wild-type mice and ∼13 ± 3 mmHg higher than Agtr1a-/- mice (P &lt; 0.01). Basal glomerular filtration was ∼23.9% higher (P &lt; 0.01), whereas fractional proximal tubule Na+ reabsorption was lower in PT-Agtr1a-/- mice (P &lt; 0.01). Deletion of AT1a receptors in the proximal tubules augmented the pressure-natriuresis response (P &lt; 0.01), and natriuretic responses to salt loading or Ang III infusion (P &lt; 0.01). Ang II induced hypertension in wild-type, PT-Agtr1a-/- and PT-Nhe3-/- mice, but the pressor response was ∼16 ± 2 mmHg lower in PT-Agtr1a-/- and PT-Nhe3-/-mice (P &lt; 0.01). Deletion of AT1a receptors or NHE3 in the proximal tubules attenuated ∼50% of Ang II-induced hypertension in wild-type mice (P &lt; 0.01), but blocked intracellular Ang II fusion protein-induced hypertension in PT-Agtr1a-/- mice (P &lt; 0.01). Conclusions: Taken together, the results of the present study provide new insights into the critical role of intratubular Ang II/AT1 (AT1a)/NHE3 pathways in the proximal tubules in normal blood pressure control and the development of Ang II-induced hypertension.

PROXIMAL TUBULE-SPECIFIC DELETION OF AT1A RECEPTORS ATTENUATES ANGIOTENSIN II-INDUCED HYPERTENSION BY INCREASING GLOMERULAR FILTRATION AND THE PRESSURE-NATRIURESIS RESPONSE

Objective: The present study tested the hypothesis that Ang II and AT1a receptors in the proximal tubules are required for normal blood pressure homeostasis and full development of Ang II-induced hypertension. Design and method: Six groups (n = 7–12 per group) of adult male wild-type (WT) and PT-Agtr1a-/- mice were infused with or without Ang II for 2 weeks (1.5 mg/kg/day, i.p.). Glomerular filtration rate (GFR) was measued using fluorescein-labeled sinistrin, and natriuretic responses were determined under basal conditions and after Ang II infusion. Results: Basal systolic blood pressure were ∼13 ± 3 mmHg lower in PT-Agtr1a-/- than WT mice (P &lt; 0.01). However, basal GFR was higher in PT-Agtr1a-/- mice (WT: 160.4 ± 7.0 μl/min vs. PT-Agtr1a-/-: 186.0 ± 10 μl/min, P &lt; 0.01). Basal 24 h urinary Na+ excretion (UNaV) was higher in PT-Agtr1a-/- than WT mice (P &lt; 0.01). In response to Ang II infusion, both WT and PT-Agtr1a-/- mice developed hypertension with similar pressor response to Ang II in WT (43 ± 3 mmHg, P &lt; 0.01) and PT-Agtr1a-/- mice (39 ± 5 mmHg, P &lt; 0.01). However, systolic blood pressure was still 16 ± 3 mmHg lower in PT-Agtr1a-/- mice (P &lt; 0.01). Ang II decreased GFR to 132.2 ± 7.0 μl/min in WT mice (P &lt; 0.01), and to 129.4 ± 18.6 μl/min in PT-Agtr1a-/- mice (P &lt; 0.01), respectively. In WT mice, UNaV increased from 139.3 ± 22.3 μmol/24 h in the control group to 196.4 ± 29.6 μmol/24 h in the Ang II-infused group (P &lt; 0.01). In PT-Agtr1a-/- mice, UNaV increased from 172.0 ± 10.2 μmol/24 h in the control group to 264.7 ± 35.4 μmol/24 h in the Ang II-infused group (P &lt; 0.01). The pressor response to Ang II was attenuated, while the natriuretic response was augmented by losartan in WT and PT-Agtr1a-/- mice (P &lt; 0.01). Finally, proximal tubule-specific deletion of AT1a receptors significantly augmented the pressure-natriuresis response and natriuretic responses to acute saline infusion (P &lt; 0.01) or a 2% high salt diet for 2 weeks (P &lt; 0.01). Conclusions: The present study supports the hypothesis that Ang II and AT1a receptors in the proximal tubules are required for normal blood pressure homeostasis and the development of Ang II-induced hypertension.

Proximal Tubule-Specific Deletion of Angiotensin II Type 1a Receptors in the Kidney Attenuates Circulating and Intratubular Angiotensin II–Induced Hypertension in PT- Agtr1a −/− Mice

[Figure: see text].

Activation of the Sympathetic Nervous System Promotes Blood Pressure Salt-Sensitivity in C57BL6/J Mice.

Global salt intake averages >8 g/person per day, over twice the limit advocated by the American Heart Association. Dietary salt excess leads to hypertension, and this partly mediates its poor health outcomes. In ≈30% of people, the hypertensive response to salt is exaggerated. This salt-sensitivity increases cardiovascular risk. Mechanistic cardiovascular research relies heavily on rodent models and the C57BL6/J mouse is the most widely used reference strain. We examined the effects of high salt intake on blood pressure, renal, and vascular function in the most commonly used and commercially available C57BL6/J mouse strain. Changing from control (0.3% Na+) to high salt (3% Na+) diet increased systolic blood pressure in male mice by ≈10 mm Hg within 4 days of dietary switch. This hypertensive response was maintained over the 3-week study period. Returning to control diet gradually reduced blood pressure back to baseline. High-salt diet caused a rapid and sustained downregulation in mRNA encoding renal NHE3 (sodium-hydrogen-exchanger 3) and EnaC (epithelial sodium channel), although we did not observe a suppression in aldosterone until ≈7 days. During the development of salt-sensitivity, the acute pressure natriuresis relationship was augmented and neutral sodium balance was maintained throughout. High-salt diet increased ex vivo sensitivity of the renal artery to phenylephrine and increased urinary excretion of adrenaline, but not noradrenaline. The acute blood pressure-depressor effect of hexamethonium, a ganglionic blocker, was enhanced by high salt. Salt-sensitivity in commercially sourced C57BL6/J mice is attributable to sympathetic overactivity, increased adrenaline, and enhanced vascular sensitivity to alpha-adrenoreceptor activation and not sodium retention or attenuation of the acute pressure natriuresis response.

Abstract P041: Proximal Tubule-specific Deletion Of Angiotensin Ii Type 1a Receptors In The Kidney Lowers Basal Blood Pressure And Attenuates Angiotensin Ii-induced Hypertension By Increasing Glomerular Filtration And The Pressure-natriuresis Response

The present study tested the hypothesis that intratubular angiotensin II (Ang II) and AT 1a receptors in the proximal tubules of the kidney plays an important role in basal blood pressure control and in the development of Ang II-induced hypertension. Mutant mice with proximal tubule-specific deletion of AT 1a receptors in the kidney, PT- Agtr1a -/- , were generated to test the hypothesis. Eight groups (n=7-12 per group) of adult male wild-type (WT) and PT- Agtr1a -/- mice were infused with or without Ang II for 2 weeks (1.5 mg/kg, i.p.). Basal systolic, diastolic, and mean arterial pressures were ~13 ± 3 mmHg lower in PT- Agtr1a -/- than WT mice ( P &lt;0.01). Basal glomerular filtration rate (GFR), as measured using transdermal FITC-sinistrin, was significantly higher in PT- Agtr1a -/- mice (WT: 160.4 ± 7.0 μl/min vs. PT- Agtr1a -/- : 186.0 ± 6.0 μl/min, P &lt;0.05). Basal 24 h urinary Na + excretion (U Na V) was significantly higher in PT- Agtr1a -/- than WT mice ( P &lt;0.01). In response to Ang II infusion, both WT and PT- Agtr1a -/- mice developed hypertension, and the magnitude of the pressor response to Ang II was similar in WT (Δ43 ± 3 mmHg, P &lt;0.01) and PT- Agtr1a -/- mice (Δ39 ± 5 mmHg, P &lt;0.01). However, the absolute blood pressure level was still 16 ± 3 mmHg lower in PT- Agtr1a -/- mice ( P &lt;0.01). Ang II significantly decreased GFR to 132.2 ± 7.0 μl/min in WT mice ( P &lt;0.01), and to 129.4 ± 18.6 μl/min in PT- Agtr1a -/- mice ( P &lt;0.01), respectively. In WT mice, U Na V increased from 139.3 ± 22.3 μmol/24 h in the control group to 196.4 ± 29.6 μmol/24 h in the Ang II-infused group ( P &lt;0.01). In PT- Agtr1a -/- mice, U Na V increased from 172.0 ± 10.2 μmol/24 h in the control group to 264.7 ± 35.4 μmol/24 h in the Ang II-infused group ( P &lt;0.01). The pressor response to Ang II was attenuated, while the natriuretic response was augmented by losartan in WT and PT- Agtr1a -/- mice ( P &lt;0.01). Finally, proximal tubule-specific deletion of AT 1a receptors significantly augmented the pressure-natriuresis response and natriuretic responses to acute saline infusion ( P &lt;0.01) or a 2% high salt diet ( P &lt;0.01). We concluded that deletion of AT 1a receptors selectively in the proximal tubules lowers basal blood pressure and attenuates Ang II-induced hypertension by increasing GFR and promoting the natriuretic response in PT- Agtr1a -/- mice.

Abstract 077: Proximal Tubule-Specific Deletion of the NHE3 (na + /h + Exchanger 3) in the Kidney Attenuates Angiotensin II-Induced Hypertension in Mice

The Na + /H + exchanger 3 (NHE3), a ~85 kDa protein encoded by the SLC9A3 gene, is the most important Na + transporter in the proximal tubules of the kidney. Angiotensin II (ANG II) is well-recognized to increase proximal tubule Na + reabsorption by stimulating NHE3 expression and activity in the proximal tubules. However, a direct cause and effect relationship between ANG II and NHE3 in the proximal tubules in ANG II-induced hypertension has not been determined previously. The present study directly tested the hypothesis that NHE3 in the proximal tubules of the kidney is required for the development of ANG II-induced hypertension using proximal tubule-specific NHE3 knockout mice (PT- Nhe3 -/- ). Specifically, PT- Nhe3 -/- mice were generated using the SGLT2-Cre / Nhe3 loxlox approach, whereas ANG II-induced hypertension was studied in 12 groups (n=5-12 per group) of adult male and female wild-type (WT) and PT- Nhe3 -/- mice. Under basal conditions, systolic (SBP), diastolic (DBP), and mean arterial blood pressure (MAP) were significantly lower in male and female PT- Nhe3 -/- than WT mice ( P &lt;0.01). A high pressor, 1.5 mg/kg/day, i.p., or a slow pressor dose of ANG II, 0.5 mg/kg/day, i.p., for 2 weeks significantly increased SBP, DBP, and MAP in male and female WT mice ( P &lt;0.01), but the hypertensive response to ANG II was markedly attenuated in male and female PT- Nhe3 -/- mice ( P &lt;0.01). ANG II impaired the pressure-natriuresis response in WT mice, whereas proximal tubule-specific deletion of NHE3 improved the pressure-natriuresis response in ANG II-infused PT- Nhe3 -/- mice ( P &lt;0.01). AT 1 receptor blocker losartan completely blocked ANG II-induced hypertension in both WT and PT- Nhe3 -/- mice ( P &lt;0.01). However, inhibition of nitric oxide synthase with L-NAME had no effect on ANG II-induced hypertension in WT or PT- Nhe3 -/- mice (n.s.). Furthermore, ANG II-induced hypertension was significantly attenuated by an orally absorbable NHE3 inhibitor AVE0657. In conclusion, NHE3 in the proximal tubules of the kidney is required for the full development of ANG II-induced hypertension. Our results suggest that NHE3 in the proximal tubules may be therapeutically targeted to treat hypertension induced by ANG II or associated with increased NHE3 expression in the proximal tubules.

Proximal Tubule-Specific Deletion of the NHE3 (Na + /H + Exchanger 3) in the Kidney Attenuates Ang II (Angiotensin II)-Induced Hypertension in Mice

The present study directly tested the hypothesis that the NHE3 (Na+/H+ exchanger 3) in the proximal tubules of the kidney is required for the development of Ang II (angiotensin II)-induced hypertension using PT-Nhe3-/- (proximal tubule-specific NHE3 knockout) mice. Specifically, PT-Nhe3-/- mice were generated using the SGLT2-Cre/Nhe3loxlox approach, whereas Ang II-induced hypertension was studied in 12 groups (n=5-12 per group) of adult male and female wild-type (WT) and PT-Nhe3-/- mice. Under basal conditions, systolic blood pressure, diastolic blood pressure, and mean arterial blood pressure were significantly lower in male and female PT-Nhe3-/- than WT mice (P<0.01). A high pressor, 1.5 mg/kg per day, intraperitoneal or a slow pressor dose of Ang II, 0.5 mg/kg per day, intraperitoneal for 2 weeks significantly increased systolic blood pressure, diastolic blood pressure, and mean arterial blood pressure in male and female WT mice (P<0.01), but the hypertensive response to Ang II was markedly attenuated in male and female PT-Nhe3-/- mice (P<0.01). Ang II impaired the pressure-natriuresis response in WT mice, whereas proximal tubule-specific deletion of NHE3 improved the pressure-natriuresis response in Ang II-infused PT-Nhe3-/- mice (P<0.01). AT1 receptor blocker losartan completely blocked Ang II-induced hypertension in both WT and PT-Nhe3-/- mice (P<0.01). However, inhibition of nitric oxide synthase with L-NG-Nitroarginine methyl ester had no effect on Ang II-induced hypertension in WT or PT-Nhe3-/- mice (not significant). Furthermore, Ang II-induced hypertension was significantly attenuated by an orally absorbable NHE3 inhibitor AVE0657. In conclusion, NHE3 in the proximal tubules of the kidney may be a therapeutical target in hypertension induced by Ang II or with increased NHE3 expression in the proximal tubules.

Acute SGLT2 Inhibition and the Pressure Natriuresis Response in Rats with Type 1 Diabetes

Increasing blood pressure (BP) induces natriuresis due to downregulation of sodium transport in the proximal tubule. This pressure natriuresis (PN) response influences long‐term BP. Type‐1 diabetic (T1DM) patients show enhanced tubular sodium reabsorption and high BP. We have found that tubular sodium reabsorption is not modulated by BP in T1DM rats. The molecular mechanism of impaired PN is unknown but the sodium‐glucose cotransporter SGLT2 is a plausible candidate and inhibitors acutely induce diuresis in T1DM rats. This study tested the hypothesis that SGLT2 inhibition with dapagliflozin would improve the acute PN response in T1DM rats.T1DM was induced in male Sprague‐Dawley rats by streptozotocin (30–45mg/kg IP; plasma glucose 13.3–&gt;35mmol). After 3 weeks rats were anaesthetised with Inactin (120mg/kg, IP). The jugular vein was cannulated and isotonic saline (containing FITC‐inulin and p‐amino hippurate for measurement of glomerular filtration rate (GFR) and renal plasma flow (RPF)) was infused. Rats were randomly allocated to receive either dapagliflozin (50mg/kg; n=7) or saline vehicle (n=7) and after an equilibration period and baseline urine collection, BP was increased by sequential arterial ligation of first the coeliac and mesenteric arteries and then the distal aorta and the natriuretic response was measured. Experiments were performed under a single blind and rats were euthanised by an overdose of anaesthetic. Data are mean +SD and comparisons were made by 2‐way ANOVA. GFR and RPF were not different between treatment groups and were unaffected by the experimentally‐induced rise in BP, consistent with autoregulation. In vehicle‐treated rats, incremental rises in BP increased urine flow rate from a baseline of 6 ± 3 to a peak of 51 ± 28μl/min/gkw (P&lt;0.01), sodium excretion from 1.7 ± 0.5 to 16.7 ± 1.4 μmol/min/gkw (P&lt;0.01) and fractional sodium excretion from 0.2 ± 7.6 to 5.4 ± 4.5% (P&lt;0.01). The dapaglifozin‐treated rats responded to increasing pressure with a diuresis and natriuresis but the peak absolute (3.8 ± 4.1μmol/min/gkw; P=0.010) and fractional (15.2 ± 8.0%; P=0.018) sodium excretion were significantly lower than in the vehicle‐ group. Dapagliflozin increased urinary glucose excretion from 0.1 ± 0.2 to 0.4 ± 0.2μmol/min/gkw: glucose excretion was not modified by increasing BP in either group. Although dapagliflozin increased urine flow and glucose excretion at steady‐state BP, it did not enhance the acute PN response in T1DM rats. Thus, impaired PN in T1DM does not reflect increased SGLT2 activity.Support or Funding InformationBritish Heart Foundation studentship FS/16/54/32730 &amp; Kidney Research UK Project Grant RP2/2014This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Mechanisms of Salt‐Sensitive Hypertension in a Mouse Model of ACTH‐Dependent Cushing Syndrome

Salt‐sensitive blood pressure (BP) reflects underlying renal and vascular (endothelial) dysfunction. People with abnormal glucocorticoid homeostasis, such as in Cushing syndrome and obesity, are often salt‐sensitive but the underlying mechanisms are not clearly defined1,2. Here, we used a mouse model to examine the effect of ACTH excess on blood pressure and salt‐sensitivity. To test this, radio telemetry was used to track BP longitudinally and measure the effect of high salt diet before and after chronic ACTH treatment in C57BL/6J mice (n=6). Data are mean ± SD. After 7 days of baseline measurements, mean BP was 105.8 ± 6.5mmHg before being placed on a high salt diet (3 % Na+ by weight) for a further 7 days. BP increased ~12 mmHg over the first 3 days before declining to 113.1 ± 7.2mmHg. BP returned to 107.7 ± 10.4mmHg, similar to baseline, after a 5‐day washout period. Mice were then treated with ACTH (2.5μg/day). ACTH increased mean BP to 115.5 ± 5.0mmHg with a flattening of the diurnal rhythm following 13 days infusion. When placing these mice on a high salt diet, mean BP increased and stabilised to 136.1 ± 13.4mmHg after 14 days. These data show that chronic ACTH excess contributes to salt‐sensitivity. To investigate potential mechanisms of salt‐sensitivity, the acute pressure natriuresis (PN) response of renal artery function were examined in separate cohorts of mice treated with either vehicle or ACTH (2.5μg/day; n=6 per group) for 14 days. PN response was induced in anaesthesised mice (120mg/kg Inactin) by sequential arterial ligation. BP increased ~40mmHg following ligations in both vehicle and ACTH groups. In vehicle‐treated mice, fractional sodium excretion increased from 0.2 ± 0.2 to 5.0 ± 4.2μmol/min. The natriuretic response was significantly blunted in ACTH‐treated mice, reaching 2.1 ± 1.1μmol/min at its peak. We next investigated vascular function in ACTH‐excess ex vivo by wire myography in isolated mesenteric and renal arteries. Vascular reactivity to phenylephrine (PHE), acetylcholine (ACh) and sodium nitroprusside (SNP) was assessed. ACTH‐excess caused vascular dysfunction in the renal artery but not in the mesenteric artery. ACTH‐excess resulted in a reduction in sensitivity to vasoconstrictor PHE (p=0.0005) and endothelium dependent (ACh) and endothelium independent (SNP) vasodilators (p=0.0128 and p=0.0002, respectively). These data show that chronic glucocorticoid excess contributes to salt‐sensitivity with potential mechanisms behind this being impairment of the acute natriuretic and diuretic response to increased BP and renal vascular dysfunction.Support or Funding InformationSupported by British Heart Foundation PhD studentships FS/16/54/32730 &amp; FS/15/63/32033.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Adaptation of C57BL/6J Mice to High Dietary Salt

Our habitually high salt intake has a detrimental relationship with blood pressure (BP); the more salt consumed per day, the higher the incidences of hypertension within the population (Meneton et al., 2005). This substantial BP effect is an important modifiable risk factor for cardiovascular and renal disease, however the underlying mechanisms responsible remain controversial. Vasodysfunction is proposed as a key event, as the normal decrease in systemic vascular resistance (SVR) is attenuated in salt‐sensitive human subjects (Morris et al., 2016), suggesting impaired vasodilation. Other main theories include a salt‐induced suppression of the acute pressure natriuresis (PN) relationship, in which renal sodium (Na) excretion does not appropriately increase to offset elevated perfusion pressure and rebalance extracellular fluid volume (Hall, 2016). Thus the current study aimed to investigate BP, vasodilatory and PN responses in adult male C57BL/6J mice fed a high salt diet. In the first experiment, mice (n=6–7) had radiotelemetry devices implanted to allow the continuous recording of BP. After 1 week of a standard (0.3% Na) salt intake, mice were fed high salt (3% Na) for a further week. Systolic BP increased significantly by 10.5mmHg during high salt feeding. Next, mice were fed either a standard or high salt diet for 1 week before culling to measure plasma aldosterone and vascular reactivity via isolating mesenteric arteries and administering vasodilatory agents acetylcholine and sodium nitroprusside by wire myography. Plasma aldosterone was substantially lower in mice on the high salt diet. No evidence of intrinsic vasodysfunction was observed: sensitivity to both acetylcholine and sodium nitroprusside did not differ between dietary groups. In the third and final experiment, mice were fed a standard (n=7) or high (n=6) salt diet for 1 week and the acute PN response was measured. This generated a curve expressing the relationship between BP and urinary Na excretion. Mice were anaesthesised with Inactin (120mg/kg) and major arteries were ligated to acutely increase BP. Urine was collected via a bladder catheter. In both groups, there was a significant increase in urinary Na excretion with increasing BP. Glomerular filtration rate (GFR) and renal blood flow also increased, with no differences between cohorts observed. The PN curve was shifted to the left, with a steeper gradient in mice fed high salt compared to those on the standard diet. To conclude, this study reports a salt‐induced increase in BP in C57BL/6J mice. There is no evidence for isolated vasodysfunction, and appropriate adaptation of the renin‐angiotensin‐aldosterone system and the acute PN response was seen to salt challenge. Since BP is a product of cardiac output and SVR, which in turn is influenced by vascular tone, current studies are investigating the contribution of these haemodynamic parameters.Support or Funding InformationThis research was funded by the University of EdinburghThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Proximal Tubule-Specific Deletion of the NHE3 (Na+/H+ Exchanger 3) Promotes the Pressure-Natriuresis Response and Lowers Blood Pressure in Mice.

The present study directly tested the hypothesis that deletion of the NHE3 (Na+/H+ exchanger 3) selectively in the proximal tubules of the kidney lowers basal blood pressure by increasing the pressure-natriuresis response in mice. Adult male and female, age-matched wild-type (WT) littermates and proximal tubule-specific NHE3 knockout mice (PT- Nhe3-/-; n=6-16 per group) were studied for (1) basal phenotypes of electrolytes and pH, blood pressure, and kidney function; (2) the pressure-natriuresis response using the mesenteric, celiac, and abdominal arterial occlusion technique; and (3) the natriuretic responses to acute saline expansion (0.9% NaCl, 10% body weight, intraperitoneal) or 2-week of 2% NaCl diet. Under basal conditions, PT- Nhe3-/- mice showed significantly lower systolic, diastolic, and mean arterial blood pressure ( P<0.01) than WT mice ( P<0.01). PT- Nhe3-/- mice also exhibited significantly greater diuretic ( P<0.01) and natriuretic responses than WT mice ( P<0.01), without altering 24-hour fecal Na+ excretion, plasma pH, Na+, and bicarbonate levels. In response to increased renal perfusion pressure by 30 mm Hg, the pressure-natriuresis response increased 5-fold in WT mice ( P<0.01), but it increased 8-fold in PT- Nhe3-/- mice ( P<0.01). In response to 10% acute saline expansion or 2-week 2% NaCl diet, more pronounced natriuretic responses were demonstrated in PT- Nhe3-/- than WT mice ( P<0.01). Our results support the scientific premise and physiological relevance that NHE3 in the proximal tubules plays an essential role in maintaining basal blood pressure homeostasis, and genetic deletion of NHE3 selectively in the proximal tubules of the kidney lowers blood pressure by increasing the pressure natriuretic response.

His and Her Computational Models of Long‐term Blood Pressure Regulation

Hypertension is a global health challenge. Hypertensive men and women are typically treated with the same approach, with less effective outcome in women. To address the critical need to better understand the mechanism of blood pressure control in both men and women, we have developed sex‐specific computational models of long‐term blood pressure control. The model represents sex differences in the kidney's pressure natriuresis response, whereby increases in renal perfusion pressure lead to increases in Na+ excretion; that in turns lowers salt and water retention and reduces effective circulating volume. Females tend to exhibit a leftward shift in the pressure‐natriuresis relation relative to males. The model also includes detailed representation of the renin‐angiotensin aldosterone system (RAAS), a non‐sex hormonal system critical for maintaining blood pressure and effective circulating volume. Major sex differences in the RAAS have been identified, including how substrate is produced and how angiotensin interacts with receptors. Those sex differences are included in the model. Using the developed model, we test the hypothesis that RAAS‐mediated anti‐natriuretic (and thus blood pressure increasing) effects are more severe in males than females, leading to more hypertension‐induced injury in males.Support or Funding InformationThis research was supported in part by the National Institutes of Health: National Institute of Diabetes and Digestive and Kidney Diseases, grant R01DK106102.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.