Increase In Renal Perfusion Pressure Research Articles

Maladaptation of renal hemodynamics contributes to kidney dysfunction resulting from thoracic spinal cord injury in mice.

Renal dysfunction is a hallmark of spinal cord injury (SCI). Several SCI sequalae are implicated; however, the exact pathogenic mechanism of renal dysfunction is unclear. Herein, we found that T3 (T3Tx) or T10 (T10Tx) complete thoracic spinal cord transection induced hypotension, bradycardia, and hypothermia immediately after injury. T3Tx-induced hypotension but not bradycardia or hypothermia slowly recovered to levels in T10Tx SCI and uninjured mice ∼16 h after injury as determined by continuous radiotelemetry monitoring. Both types of thoracic SCI led to a marked decrease in albuminuria and proteinuria in all phases of SCI, whereas the kidney injury marker neutrophil gelatinase-associated lipocalin rapidly increased in the acute phase, remaining elevated in the chronic phase of T3Tx SCI. Renal interstitial and vascular elastin fragmentation after SCI were worsened during chronic T3Tx SCI. In the chronic phase, renal vascular resistance response to a step increase in renal perfusion pressure or a bolus injection of angiotensin II or norepinephrine was almost completely abolished after T3Tx SCI. Bulk RNA-sequencing analysis showed enrichment of genes involved in extracellular matrix remodeling and chemokine signaling in the kidney from T3Tx SCI mice. The serum level of interleukin-6 was elevated in the acute but not chronic phase of T3Tx and T10Tx SCI, whereas the serum amyloid A1 level was elevated in both acute and chronic phases. We conclude that tissue fibrosis and hemodynamic impairment are involved in renal dysfunction resulting from thoracic SCI; these pathological alterations, exacerbated by high thoracic-level injury, is mediated at least partly by renal microvascular extracellular matrix remodeling.NEW & NOTEWORTHY Urinary complications resulting from thoracic spinal cord injury (SCI) greatly affects quality of life and contributes to morbidity and mortality in patients with SCI. Herein, we showed that thoracic SCI initiates changes in the structure and function of the renal microvasculature that leads to autoregulation failure in the chronic phase of high thoracic-level injury. Our study identified extracellular matrix regulators and cytokine/chemokine signaling as potential targets for developing novel therapeutics for restoring renal function following SCI.

Elastin Insufficiency Accelerates Age‐Related Impairment of Renal Hemodynamics

Gradual loss of functional elastin fibers during aging leads to increased arterial stiffening and decreased compliance. Elastin insufficiency in mice and humans has been shown to be associated with arteriopathy and the development of hypertension. However, it is unclear whether elastin insufficiency in the resistance vasculature, as occurs in the renal vascular bed, contributes to age‐related decline in renal function. We hypothesized that elastin insufficiency exacerbates age‐related impairment of renal hemodynamics by accelerating functional and structural changes of the renal microvasculature. We assessed renal hemodynamics in anesthetized young (4‐6‐month‐old) and old (14–16‐month‐old) female wild‐type (WT) and elastin heterozygous (Eln+/‐) mice. Renal autoregulation was assessed by a stepwise increase in renal perfusion pressure (RPP) by simultaneously occluding the superior mesenteric and celiac arteries. Autonomic activity was clamped by continuous infusion of a cocktail containing vasoactive hormones. Baseline systolic blood pressure (SBP; 91.1±4.2 vs 90.1±3.1mmHg) and renal vascular resistance (RVR; 13.1±2.4 vs 10.0±1.5 mmHg/μL/min/g left kidney weight) were elevated in old versus young WT mice. Renal blood flow (RBF; 7.3±1.7 vs 9.8±1.4 μL/min/g left kidney weight), renal plasma flow (RPF; 5±1.2 vs 6±1mL/min/g left kidney weight) and glomerular filtration rate (GFR), all trended lower in old WT mice compared to young WT mice. However, in Eln+/‐mice, SBP was lower in old mice (78.2±9.4 vs 104.6±4.9mmHg), while RVR (13.5± 2.6 vs 14.4±1.1), RBF (6.7±1.2 vs 7.5±0.6), RPF (4.2±0.7 vs 4.5±0.3) and GFR were all similar between young and old mice. Increasing RPP caused a robust RVR and RPF response in young vs old WT mice. In contrast, the maximal changes in RBF (5.8±0.6 vs 5.5±1 μL/min/g left kidney weight), RVR (23.8±2.5 vs 21.8±7.0 mmHg/μL/min/g left kidney weight) were less robust and similar between young and old Eln+/‐mice. Autoregulatory index average values were closer to 0 in young and old Eln+/‐and old WT miceindicating greater impairment of renal autoregulation compared to young WT mice. Correlation analysis between pulse pressure and RBF showed that a high pulse pressure was more positively correlated to high RBF in young and old Eln+/‐mice as well as old WT mice. Together, our data demonstrate that elastin insufficiency accelerates age‐related impairment of renal hemodynamics and autoregulation likely mediated by functional and structural remodeling of the renal microvasculature.

Postoperative Acute Kidney Injury in Williams Syndrome Compared With Matched Controls.

Cardiovascular manifestations occur in over 80% of Williams syndrome (WS) patients and are the leading cause of morbidity and mortality. One-third of patients require cardiovascular surgery. Renal artery stenosis (RAS) is common in WS. No studies have assessed postoperative cardiac surgery-related acute kidney injury (CS-AKI) in WS. Our objectives were to assess if WS patients have higher risk of CS-AKI postoperatively than matched controls and if RAS could contribute to CS-AKI. This was a retrospective study of all patients with WS who underwent cardiac surgery at our center from 2010 to 2020. The WS study cohort was compared with a group of controls matched for age, sex, weight, and surgical procedure. Patients underwent cardiac surgery and postoperative care at Lucile Packard Children's Hospital Stanford. There were 27 WS patients and 43 controls (31% vs 42% female; p = 0.36). Median age was 1.8 years (interquartile range [IQR], 0.7-3.8 yr) for WS and 1.7 years (IQR, 0.8-3.1 yr) for controls. None. Postoperative hemodynamics, vasopressor, total volume input, diuretic administration, and urine output were collected in the first 72 hours. Laboratory studies were collected at 8-hour intervals. Multivariable analysis identified predictors of CS-AKI.Controlled for renal perfusion pressure (RPP) and vasoactive inotrope score (VIS), compared with controls, the odds ratio (OR) of CS-AKI in WS was 4.2 (95% CI, 1.1-16; p = 0.034). Higher RPP at postoperative hours 9-16 was associated with decreased OR of CS-AKI (0.88 [0.8-0.96]; p = 0.004). Increased VIS at hour 6 was associated with an increased OR of CS-AKI (1.47 [1.14-1.9]; p = 0.003). Younger age was associated with an increased OR of CS-AKI (1.9 [1.13-3.17]; p = 0.015). The OR of CS-AKI is increased in pediatric patients with WS compared with controls. CS-AKI was associated with VIS at the sixth postoperative hour. Increases in RPP and mean arterial pressure were associated with decreased odds of CS-AKI.

Abstract P247: Elastin Insufficiency Impairs Renal Hemodynamics And Accelerates Aging-associated Structural And Functional Remodeling Of Preglomerular Arterioles

Elastin degradation and fragmentation are hallmarks of arterial stiffness and renal dysfunction associated with aging. However, it is unclear whether elastin insufficiency contributes to the changes in the structure and function of the resistance vasculature of the kidney during aging. Here we determined how increased vascular stiffness due to elastin insufficiency alters renal hemodynamics and mechanical properties of preglomerular arterioles. We assessed renal hemodynamics under anesthesia in 14-16-month-old female wild type (WT) and elastin heterozygous ( Eln +/- ) mice. Renal autoregulation was assessed by a stepwise increase in renal perfusion pressure (RPP) by simultaneously occluding the superior mesenteric and celiac arteries. Myogenic constriction and arterial stiffness were assessed by pressure myography of isolated renal interlobar arteries. Baseline renal vascular resistance (RVR) was elevated in Eln +/- mice (13.8 ± 2.9 vs 11.2 ± 1.4 mmHg/μL/min/g left kidney weight), while systolic blood pressure (SBP; 75.1 ± 7.4 vs 91 ± 4.2mmHg), renal blood flow (RBF; 6.3 ± 1.2 vs 7.4 ± 1.7 μL/min/g left kidney weight), renal plasma flow (RPF; 3.4 ± 0.8 vs 5 ± 1.2 mL/min/g/ left kidney weight) and urine flow rate, all trended lower in Eln +/- mice compared to WT mice. Glomerular filtration rate (GFR) and filtration fraction (FF) were similar between the two groups. A stepwise increase in RPP caused a slower decline and rise in RBF and RVR, respectively, in Eln +/- relative to WT mice. The maximal changes in RBF (5 ± 1.1 vs 4.7 ± 0.8 μL/min/g left kidney weight), RVR (17.6 ± 7.3 vs 22.5 ± 2.1 mmHg/μL/min/g left kidney weight), urine flow rate,GFR, and FF were less robust in Eln +/- mice. RPF decreased in WT mice in response to raising RPP, whereas it remained unchanged in Eln +/- mice. Myogenic response and increases in elastic modulus and wall tension following stepwise changes in intraluminal pressure were all augmented in interlobar arteries from Eln +/- relative to WT mice. However, there was no difference in kidney weight/tibia length ratio between the two genotypes. We conclude that elastin insufficiency impairs renal hemodynamics by exacerbating age associated increase in vascular stiffness.

Current Understanding of Pressure Natriuresis.

Pressure natriuresis refers to the concept that increased renal perfusion pressure leads to a decrease in tubular reabsorption of sodium and an increased sodium excretion. The set point of blood pressure is the point at which pressure natriuresis and extracellular fluid volume are in equilibrium. The term "abnormal pressure natriuresis" usually refers to the expected abnormal effect of a certain level of blood pressure on sodium excretion. Factors that cause abnormal pressure natriuresis are known. Sympathetic nerve system, genetic factors, and dietary factors may affect an increase in renal perfusion pressure. An increase in renal perfusion pressure increases renal interstitial hydrostatic pressure (RIHP). Increased RIHP affects tubular reabsorption through alterations in tight junctional permeability to sodium in proximal tubules, redistribution of apical sodium transporters, and/or release of renal autacoids. Renal autocoids such as nitric oxide, prostaglandin E2, kinins, and angiotensin II may also regulate pressure natriuresis by acting directly on renal tubule sodium transport. In addition, inflammation and reactive oxygen species may mediate pressure natriuresis. Recently, the use of new drugs associated with pressure natriuretic mechanisms, such as angiotensin receptor neprilysin inhibitor and sodium glucose co-transporter 2 inhibitors, has been consistently demonstrated to reduce mortality and hypertension-related complications. Therefore, the understanding of pressure natriuresis is gaining attention as an antihypertensive strategy. In this review, we provide a basic overview of pressure natriuresis to the target audience of nephrologists.

Purinergic P2X1 receptor, purinergic P2X7 receptor, and angiotensin II type 1 receptor interactions in the regulation of renal afferent arterioles in angiotensin II-dependent hypertension.

In ANG II-dependent hypertension, ANG II activates ANG II type 1 receptors (AT1Rs), elevating blood pressure and increasing renal afferent arteriolar resistance (AAR). The increased arterial pressure augments interstitial ATP concentrations activating purinergic P2X receptors (P2XRs) also increasing AAR. Interestingly, P2X1R and P2X7R inhibition reduces AAR to the normal range, raising the conundrum regarding the apparent disappearance of AT1R influence. To evaluate the interactions between P2XRs and AT1Rs in mediating the increased AAR elicited by chronic ANG II infusions, experiments using the isolated blood perfused juxtamedullary nephron preparation allowed visualization of afferent arteriolar diameters (AAD). Normotensive and ANG II-infused hypertensive rats showed AAD responses to increases in renal perfusion pressure from 100 to 140 mmHg by decreasing AAD by 26 ± 10% and 19 ± 4%. Superfusion with the inhibitor P2X1Ri (NF4490; 1 μM) increased AAD. In normotensive kidneys, superfusion with ANG II (1 nM) decreased AAD by 16 ± 4% and decreased further by 19 ± 5% with an increase in renal perfusion pressure. Treatment with P2X1Ri increased AAD by 30 ± 6% to values higher than those at 100 mmHg plus ANG II. In hypertensive kidneys, the inhibitor AT1Ri (SML1394; 1 μM) increased AAD by 10 ± 7%. In contrast, treatment with P2X1Ri increased AAD by 21 ± 14%; combination with P2X1Ri plus P2X7Ri (A438079; 1 μM) increased AAD further by 25 ± 8%. The results indicate that P2X1R, P2X7R, and AT1R actions converge at receptor or postreceptor signaling pathways, but P2XR exerts a dominant influence abrogating the actions of AT1Rs on AAR in ANG II-dependent hypertension.

Abstract 142: Purinergic P2 X Receptors and a T 1 Receptors Share Post - Receptor Signaling Pathways Regulating Renal Afferent Arterioles in Angiotensin I I ( Ang I I) Dependent Hypertension

In Ang II dependent hypertension, the increased afferent arteriolar resistance (AAR) is assumed to be primarily due to the increased intrarenal levels of Ang II activating AT1 receptors. Because the renal interstitial ATP levels increase with increased renal perfusion pressure (RPP), purinergic P2X receptors (P2XR) also influence AAR. However, the interactions between the respective receptors has not been fully established. Accordingly, experiments were performed to test the hypothesis that P2XR and AT1R share post-receptor signaling pathways which allow dominance of P2XR to control AAR. Experiments using the in vitro juxtamedullary nephron preparation allowed direct visualization of afferent arteriolar diameters (AAD). Normotensive and Ang II infused hypertensive rats showed AAD responses to increases in RPP from 100 to 140 mmHg by decreasing AAD by 26% ± 10% and 19% ± 4% demonstrating autoregulation. In kidneys from normotensive rats, superfusion at 100 mmHg RPP with 5 μM ATP induced a rapid vasoconstriction from a control of 14.5 ± 0.9 μm to 11.2 ± 0.7 μm (n=8, P < 0.05). P2X1 receptor inhibition with NF449 (1 μM) increased AAD by 28% ± 7% returning it close to control values (14.0 ± 0.8 μm). P2X7 receptor inhibition with A438079 (1 μM) did not significantly alter the AAD (12.2 ± 0.6 μm), but combined treatment with P2X1R plus P2X7R inhibitors fully returned the AAD to control values (14.8 ± 0.7 μm), reflecting a dominant role of P2X1R in mediating ATP afferent vasoconstriction in normotensive kidneys. In Ang II infused hypertensive rats, at RPP 140 mmHg, treatment with AT1R inhibitor by SML1394 (1 μM) increased AAD by 10% ± 7% (13.44 ± 0.73 μm vs. 12.21 ± 0.63 μm, n=10, P<0.05). Treatment with P2X1R inhibitor increased AAD by 21% ± 14% (14.42 ± 0.51 μm vs. 11.94 ± 1.20 μm, n=5, P<0.05), and treatment with the P2X7R inhibitor also dilated AAD by 15% ± 3% (12.98 ± 0.64 μm vs. 11.26 ± 0.61 μm, n=5, P<0.05) reflecting a greater role of P2X7R in hypertension. Importantly, treatment with P2X1R inhibitor plus P2X7R inhibitor fully restored AAD to control levels (15.00 ± 0.65 μm vs. 12.02 ± 0.70 μm, n=5, P<0.05). The results suggest that in Ang II dependent hypertension, P2X1R, P2X7R and AT1R act through post-receptor converging signaling pathways allowing dominance of P2XR to regulate AAR.

Immune mechanisms of salt-sensitive hypertension and renal end-organ damage.

Immune mechanisms have been recognized to have a role in the pathogenesis of hypertension, vascular disease and kidney damage in humans and animals for many decades. Contemporary advances in experimentation have permitted a deeper understanding of the mechanisms by which inflammation and immunity participate in cardiovascular disease, and multiple observations have demonstrated strong correlations between the discoveries made in animals and those made in patients with hypertension. Of note, striking phenotypic similarities have been observed in the infiltration of immune cells in the kidney and the development of end-organ damage in patients and animal models with sodium-sensitive hypertension. The available data suggest that an initial salt-induced increase in renal perfusion pressure, which is likely independent of immune mechanisms, induces the infiltration of immune cells into the kidney. The mechanisms mediating immune cell infiltration in the kidney are not well understood but likely involve tissue damage, the direct influence of salt to stimulate immune cell activation, sympathetic nerve stimulation or other factors. The infiltrating cells then release cytokines, free radicals and other factors that contribute to renal damage as well as increased retention of sodium and water and vascular resistance, which lead to the further development of hypertension.

Intra-Renal Angiotensin Levels Are Increased in High-Fructose Fed Rats in the Extracorporeal Renal Perfusion Model.

Overconsumption of fructose leads to metabolic syndrome as a result of hypertension, insulin resistance, and hyperlipidemia. In this study, the renal function of animals submitted to high fructose intake was analyzed from weaning to adulthood using in vivo and ex vivo methods, being compared with a normal control group. We investigated in ex vivo model of the role of the renin Angiotensin system (RAS) in the kidney. The use of perfused kidney from animals submitted to 8-week fructose treatment showed that high fructose intake caused metabolic and cardiovascular alterations that were consistent with other studies. Moreover, the isolated perfused kidneys obtained from rats under high fructose diet showed a 33% increase in renal perfusion pressure throughout the experimental period due to increased renal vascular resistance and a progressive fall in the glomerular filtration rate, which reached a maximum of 64% decrease. Analysis of RAS peptides in the high fructose group showed a threefold increase in the renal concentrations of angiotensin I (Ang I) and a twofold increase in angiotensin II (Ang II) levels, whereas no change in angiotensin 1-7 (Ang 1-7) was observed when compared with the control animals. We did not detect changes in angiotensin converting enzyme (ACE) activity in renal tissues, but there is a tendency to decrease. These observations suggest that there are alternative ways of producing Ang II in this model. Chymase the enzyme responsible for Ang II formation direct from Ang I was increased in renal tissues in the fructose group, confirming the alternative pathway for the formation of this peptide. Neprilysin (NEP) the Ang 1-7 forming showed a significant decrease in activity in the fructose vs. control group, and a tendency of reduction in ACE2 activity. Thus, these results suggest that the Ang 1-7 vasodilator peptide formation is impaired in this model contributing with the increase of blood pressure. In summary, rats fed high fructose affect renal RAS, which may contribute to several deleterious effects of fructose on the kidneys and consequently an increase in blood pressure.

Abstract 064: Purinergic P2X1 and P2X7 Receptors Activation Attenuate Angiotensin AT1 Receptors Dominance in Regulating the Preglomerular Renal Microcirculation in Angiotensin II Dependent Hypertension

Two important mechanisms regulating afferent arterioles (AA) in angiotensin II (ANG II) hypertension are the purinergic receptors (P2R) and the angiotensin AT1 receptors (AT1R); however, the nature of the interactions between the respective receptors has not been established. Accordingly, studies were performed in rats subjected to 2 weeks of ANG II infusion (80 ng/min via osmotic minipumps) which has been shown to increase interstitial ATP and ANG II concentrations. Experiments using the in vitro isolated juxtamedullary nephron preparation allowed direct visualization of the AA. To determine the interaction between P2XR and AT1R on AA at hypertensive renal perfusion pressure, afferent arteriolar inside diameters (AAD) were measured in response to increases in renal perfusion pressure (RPP) from 100 mmHg to 140 mmHg followed by superfusion with the inhibitors (i). P2X1Ri (NF-449) 1 μM, P2X7Ri (A-438079) 1 μM and P2X1Ri 1 μM plus P2X7Ri 1 μM followed by superfusion with AT1Ri (SML-1394) 1 μM. Increases in RPP to 140 mmHg decreased AAD from 14.75±0.19 μm to 11.69±0.23 μm (n=15, P<0.05) demonstrating autoregulation. Treatment with P2X1Ri significantly increased AAD from 11.94±0.54 μm to 14.33±0.15 μm (n=5, P<0.05) and increased further to 15.33±0.33 μm by treatment with the AT1Ri to values similar to those at RPP 100 mmHg (14.88±0.39 μm). Treatment with the P2X7Ri also vasodilated afferent arteriolar but to a lesser extent (13.34±0.06 μm vs. 10.94±0.21 μm, n=5, P<0.05); and further treated by AT1Ri, AAD returned to values similar to those at RPP 100 mmHg (14.05±0.20 μm vs. 14.16 ± 0.19 μm). Treatment with P2X1Ri plus P2X7Ri significantly increased AAD from 12.2±0.13 μm to 14.76±0.12 μm (n=5, P<0.05) a value not significantly different from the value at RPP 100 mmHg (15.22±0.17 μm). Further treatment with AT1Ri after treatment with the P2X1Ri plus P2X7Ri significantly increased AAD to values higher than the value observed at treatment with P2X1Ri plus P2X7Ri (15.43±0.23 μm vs. 14.76 ± 0.12 μm, P<0.05). The results indicate that renal P2X1R and P2X7R exert dominant roles in the regulation of AAD during elevation in arterial pressure and attenuate most of the AT1R influence on AAD in kidneys from ANG II hypertensive rats.

Interaction Between Angiotensin AT1 Receptors and Purinergic P2X Receptors in Regulating the Preglomerular Renal Microcirculation Under Elevated Angiotensin II and High Renal Perfusion Pressure Environments

Angiotensin II (ANG II) exerts a powerful role in the pathogenesis of hypertension and renal injury via activation of angiotensin II type 1 receptors (AT1R). However augmented ANG II levels alone are not sufficient to cause renal microvascular dysfunction in hypertension. Extracellular nucleotides increase in response to increases in arterial pressure and elicit vasoconstriction via P2 purinergic receptors (P2XR and P2YR). In ANG II hypertensive rats, treatment with P2XR antagonists restores glomerular hemodynamics to near normal values and reduces renal injury suggesting interaction between AT1R and P2XR in regulating renal vascular resistance. Accordingly, experiments were performed using the in vitro isolated juxtamedullary nephron preparation to test the hypothesis that P2XR and AT1R have substantial overlap in their actions on afferent arteriolar resistance under elevated ANG II and high renal perfusion pressure (RPP) environments. Afferent arteriolar inside diameters (AAD) were measured in response to increases in perfusion pressure from 100 mmHg to 140 mmHg and superfusion with the P2X1R inhibitor (NF‐449) 1μM, P2X7R inhibitor (A‐438079) 1μM and AT1R inhibitor (RNH‐6270) 1μM. An increase in RPP decreased AAD (12.83±0.54 μm vs. 9.11±0.48μm, n=14, P<0.05) demonstrating intact autoregulatory capability. Treatment with an AT1R inhibitor alone did not restore AAD (9.4±0.56 μm vs. 9±0.51μm, n=5). However vasodilation occurred after treatment with P2X1R inhibitor and AAD returned to values similar to those at RPP 100 mmHg (9.12±0.95 μm vs. 13.22±0.76μm, n=5, P<0.05). Treatment with the P2X7R inhibitor also vasodilated but did not fully restore the AAD to baseline value at RPP 100 mmHg (8.73±1.2 μm vs. 11.53±1.96 μm, n=4, P<0.05). These results support the roles of P2X1R and P2X7R in regulating renal microvascular function in the autoregulatory response to increases in perfusion pressure. Further studies evaluated the acute effects of P2X1R inhibition in the presence of elevated ANG II and increased RPP. The low dose of ANG II (1nM) caused slight decreases in AAD; an increase in RPP caused further decreases in AAD (12.7±0.82 μm, 10.77±0.9 μm, 9.03±0.87 μm, respectively, n=7, P<0.05). Treatment with the P2X1R inhibitor significantly increased AAD to values higher than the value observed at 100 mmHg plus ANG II (11.47±0.62 μm vs.10.77±0.9 μm, P<0.05) but did not return AAD to the baseline value at 100 mmHg (12.7±0.82 μm). The results indicate that renal P2X1 and AT1 receptors are both important in the regulation of AAD during combined elevation in arterial pressure and treatment with ANG II and suggest that P2XR and AT1R have substantial overlap in their actions on afferent arteriolar resistance in kidneys taken from normotensive rats.Support or Funding InformationFunding for this study was provided by the National Institute of General Medical Sciences (NIGMS; CoBRE P30GM103337).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

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.

The influence of connexin 45 on renal autoregulation

The kidney maintains constant renal blood flow and glomerular filtration rate despite acute changes in renal perfusion pressure (RPP) via renal autoregulation. Renal autoregulation is made up of the myogenic response and the tubuloglomerular feedback (TGF) mechanism, both acting on the afferent arteriole. Both mechanisms have a conducted component, believed to proceed via gap junctions (GJ). These fluid‐filled pores are made up of two connexons, one from each cell, with connexins (Cx) as building blocks. Several Cx isoforms are expressed in the renal vessel wall, including connexin 45 (Cx45), making it a functional syncytium. Disruption of Cx expression and function in the vasculature reduces myogenic response and causes TGF dysregulation, and is associated with hypertension development. The aim of the study was to explore the influence Cx45 has on renal autoregulation.To investigate the TGF mechanism, experiments were performed using the isolated perfused juxtamedullary nephron preparation. Kidneys were isolated from wild type (WT) and smooth muscle cell knockout (KO) Cx45 mice and perfused with a Tyrode's buffer containing BSA and amino acids mixture, at pH 7.4. Local afferent vasoconstriction was induced by electrical pulse stimulation administered via microelectrode, at the glomerular entrance. RPP was kept constant at 95 mmHg and inner afferent arteriolar diameter was measured locally and at upstream sites to evaluate vascular conduction. Responses between WT and KO were compared.To investigate the myogenic response, arteriolar diameter was measured in response to changes in RPP. Experiments were performed in the same setup as previously mentioned, using a stepwise increase in RPP. Perfusion was initiated at 95 mmHg and increased in steps of 20 mmHg until 195 mmHg is reached. Inner afferent arteriolar diameter was measured 100 μm upstream from the glomerulus, and responses between WT and KO were compared. To eliminate the TGF mechanism and isolate only the myogenic response in the kidneys, papillectomy were performed before repeating the same experimental protocol. Responses between WT and KO were compared.To further investigate the influence of Cx45 in the renal vascular function, interlobar arteries from WT and KO mice were isolated and mounted in a pressure myograph. An experimental protocol consisted of stepwise pressure increases of 25 mmHg, starting at 25 mmHg until 175 mmHg is reached. Inner diameter from both WT and KO were measured and compared. In this set‐up no TGF is present.In both WT and KO mice, electrical stimulation at the glomerular pole of the afferent arteriole reduces the diameter at the local site. The conducted vasoconstriction at upstream sites was attenuated in KO mice. The conducted response is observed at 400 μm in the WT mice and 250 μm in the KO. Preliminary myogenic data shows that pressure increases induce a greater afferent vasoconstriction in WT mice and less so in the Cx45 KO. These results suggest that Cx45 may play a role in TGF signaling and myogenic response in the preglomerular vasculature and thus renal autoregulation.Support or Funding InformationThe work is part of the Dynamical Systems Interdisciplinary Network, University of CopenhagenThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Modulation of the myogenic mechanism: concordant effects of NO synthesis inhibition and O2- dismutation on renal autoregulation in the time and frequency domains.

Renal blood flow autoregulation was investigated in anesthetized C57Bl6 mice using time- and frequency-domain analyses. Autoregulation was reestablished by 15 s in two stages after a 25-mmHg step increase in renal perfusion pressure (RPP). The renal vascular resistance (RVR) response did not include a contribution from the macula densa tubuloglomerular feedback mechanism. Inhibition of nitric oxide (NO) synthase [N(G)-nitro-l-arginine methyl ester (l-NAME)] reduced the time for complete autoregulation to 2 s and induced 0.25-Hz oscillations in RVR. Quenching of superoxide (SOD mimetic tempol) during l-NAME normalized the speed and strength of stage 1 of the RVR increase and abolished oscillations. The slope of stage 2 was unaffected by l-NAME or tempol. These effects of l-NAME and tempol were evaluated in the frequency domain during random fluctuations in RPP. NO synthase inhibition amplified the resonance peak in admittance gain at 0.25 Hz and markedly increased the gain slope at the upper myogenic frequency range (0.06-0.25 Hz, identified as stage 1), with reversal by tempol. The slope of admittance gain in the lower half of the myogenic frequency range (equated with stage 2) was not affected by l-NAME or tempol. Our data show that the myogenic mechanism alone can achieve complete renal blood flow autoregulation in the mouse kidney following a step increase in RPP. They suggest also that the principal inhibitory action of NO is quenching of superoxide, which otherwise potentiates dynamic components of the myogenic constriction in vivo. This primarily involves the first stage of a two-stage myogenic response.

No apparent role for T-type Ca²⁺ channels in renal autoregulation.

Renal autoregulation protects glomerular capillaries against increases in renal perfusion pressure (RPP). In the mesentery, both L- and T-type calcium channels are involved in autoregulation. L-type calcium channels participate in renal autoregulation, but the role of T-type channels is not fully elucidated due to lack of selective pharmacological inhibitors. The role of T- and L-type calcium channels in the response to acute increases in RPP in T-type channel knockout mice (CaV3.1) and normo- and hypertensive rats was examined. Changes in afferent arteriolar diameter in the kidneys from wild-type and CaV3.1 knockout mice were assessed. Autoregulation of renal blood flow was examined during acute increases in RPP in normo- and hypertensive rats under pharmacological blockade of T- and L-type calcium channels using mibefradil (0.1 μM) and nifedipine (1 μM). In contrast to the results from previous pharmacological studies, genetic deletion of T-type channels CaV3.1 did not affect renal autoregulation. Pharmacological blockade of T-type channels using concentrations of mibefradil which specifically blocks T-type channels also had no effect in wild-type or knockout mice. Blockade of L-type channels significantly attenuated renal autoregulation in both strains. These findings are supported by in vivo studies where blockade of T-type channels had no effect on changes in the renal vascular resistance after acute increases in RPP in normo- and hypertensive rats. These findings show that genetic deletion of T-type channels CaV3.1 or treatment with low concentrations of mibefradil does not affect renal autoregulation. Thus, T-type calcium channels are not involved in renal autoregulation in response to acute increases in RPP.

Abstract P167: Conditional Deletion of the Na+/H+ Exchanger 3 in the Proximal Tubule of the Kidney Promotes Pressure Natriuresis in Mice

The development and progression of most, if not all, forms of hypertension appear to converge on a final common pathway or mechanism, i.e., increased renal salt retention due to significantly impaired pressure natriuresis responses. Yet the factors responsible for resetting the pressure natriuresis response in hypertension remain to be determined. The present study tested the hypothesis that the upregulation of the sodium and hydrogen exchanger 3 (NHE3) impairs while selective knockout of this transporter in the proximal tubule promotes pressure natriuresis and lowers blood pressure in mice. Proximal tubule-specific NHE3 knockout mice (PT-NHE3-KO) were generated by the Cre/Lox approach, and confirmed by complementary PCR, Western blot, and immunofluorescent imaging of NHE3 expression in the proximal tubule of the kidney, respectively. No abnormal histological phenotypes were observed in small intestines and the kidney of PT-NHE3-KO mice. Compared with wild-type mice (WT, n=12), PT-NHE3-KO mice (n=10) had significantly lower basal systolic blood pressure (WT: 116 ± 3 mmHg versus PT-NHE3-KO: 103 ± 3 mmHg, p<0.01). Mean intra-arterial pressure was also significantly lower in anesthetized PT-NHE3-KO mice (WT: 91 ± 3 mmHg versus PT-NHE3-KO: 77 ± 5 mmHg, p<0.01) (n=8 each). The lower basal blood pressure in PT-NHE3-KO mice was associated with higher basal urine flow (WT: 0.81 ± 0.09 ml/day versus PT-NHE3-KO: 1.12 ± 0.06 ml/day, p<0.05), urinary sodium (WT: 120.1 ± 17.5 μmol/day versus PT-NHE3-KO: 197.1 ± 24.5 μmol/day, p<0.01), potassium (WT: 171.7 ± 26.0 μmol/day versus PT-NHE3-KO: 310.3 ± 24.3 μmol/day, p<0.01), and chloride excretion (WT: 125.7 ± 22.5 μmol/day versus PT-NHE3-KO: 222 ± 29.2 μmol/day, p<0.05) (n=8-12 for each group). In response to ~25 mmHg increase in renal perfusion pressure in both strains, urinary sodium excretion was increased by 4-fold in WT mice (n=12, p<0.01), whereas it increased by 7-fold in PT-NHE3-KO mice (n=10, p<0.01). We concluded that NHE3 in the proximal tubule of the kidney plays an important role in the regulation of proximal tubular sodium reabsorption and blood pressure homeostasis, and that selective deletion of NHE3 in the proximal tubule promotes the pressure natriurestic response and lowers blood pressure in mice.

Regulation of Renal Hemodynamics and Function by RGS2.

Regulator of G protein signaling 2 (RGS2) controls G protein coupled receptor (GPCR) signaling by acting as a GTPase-activating protein for heterotrimeric G proteins. Certain Rgs2 gene mutations have been linked to human hypertension. Renal RGS2 deficiency is sufficient to cause hypertension in mice; however, the pathological mechanisms are unknown. Here we determined how the loss of RGS2 affects renal function. We examined renal hemodynamics and tubular function by monitoring renal blood flow (RBF), glomerular filtration rate (GFR), epithelial sodium channel (ENaC) expression and localization, and pressure natriuresis in wild type (WT) and RGS2 null (RGS2-/-) mice. Pressure natriuresis was determined by stepwise increases in renal perfusion pressure (RPP) and blood flow, or by systemic blockade of nitric oxide synthase with L-NG-Nitroarginine methyl ester (L-NAME). Baseline GFR was markedly decreased in RGS2-/- mice compared to WT controls (5.0 ± 0.8 vs. 2.5 ± 0.1 μl/min/g body weight, p<0.01). RBF was reduced (35.4 ± 3.6 vs. 29.1 ± 2.1 μl/min/g body weight, p=0.08) while renal vascular resistance (RVR; 2.1 ± 0.2 vs. 3.0 ± 0.2 mmHg/μl/min/g body weight, p<0.01) was elevated in RGS2-/- compared to WT mice. RGS2 deficiency caused decreased sensitivity and magnitude of changes in RVR and RBF after a step increase in RPP. The acute pressure–natriuresis curve was shifted rightward in RGS2-/- relative to WT mice. Sodium excretion rate following increased RPP by L-NAME was markedly decreased in RGS2-/- mice and accompanied by increased translocation of ENaC to the luminal wall. We conclude that RGS2 deficiency impairs renal function and autoregulation by increasing renal vascular resistance and reducing renal blood flow. These changes impair renal sodium handling by favoring sodium retention. The findings provide a new line of evidence for renal dysfunction as a primary cause of hypertension.

Influence of Connexin40 on the renal myogenic response in murine afferent arterioles.

Renal autoregulation consists of two main mechanisms; the myogenic response and the tubuloglomerular feedback mechanism (TGF). Increases in renal perfusion pressure activate both mechanisms causing a reduction in diameter of the afferent arteriole (AA) resulting in stabilization of the glomerular pressure. It has previously been shown that connexin-40 (Cx40) is essential in the renal autoregulation and mediates the TGF mechanism. The aim of this study was to characterize the myogenic properties of the AA in wild-type and connexin-40 knockout (Cx40KO) mice using both in situ diameter measurements and modeling. We hypothesized that absence of Cx40 would not per se affect myogenic properties as Cx40 is expressed primarily in the endothelium and as the myogenic response is known to be present also in isolated, endothelium-denuded vessels. Methods used were the isolated perfused juxtamedullary nephron preparation to allow diameter measurements of the AA. A simple mathematical model of the myogenic response based on experimental parameters was implemented. Our findings show that the myogenic response is completely preserved in the AA of the Cx40KO and if anything, the stress sensitivity of the smooth muscle cell in the vascular wall is increased rather than reduced as compared to the WT. These findings are compatible with the view of the myogenic response being primarily a local response to the local transmural pressure.

Impaired myogenic responses of the Af‐Art contributes to chronic kidney disease in Milan Normotensive rats

We have recently reported that the development of glomerular injury, proteinuria and chronic kidney disease (CKD) in Dahl Salt Sensitive and Fawn Hooded Hypertensive rats are associated with an impaired myogenic response of the afferent arteriole (Af-Art) and autoregulation of renal blood flow (RBF), whereas the myogenic response is enhanced in Spontaneously Hypertensive rats that are resistant to the development of renal disease. Milan normotensive rats (MNS) are more susceptible to development of CKD than the Milan Hypertensive rat (MHS) even though blood pressure is much lower. This study compared the myogenic response in the Af-Art and autoregulation of RBF in 6-9 week old MNS and MHS rats. Autoregulation of RBF was measured following an increase in renal perfusion pressure (RPP) from 100 to 140 mmHg. The diameter of Af-Art of MNS rats increased from 14.0 ± 0.5 to 14.1 ± 0.6 µm (n=6, p>0.05) in response to an increase in perfusion pressure from 60 to 120 mmHg. In contrast, the diameter of the Af-Art decreased significantly from 14.0 ± 0.8 to 11.7 ± 1.1 µm (n=6, p<0.05) in MHS rats. In vivo, MNS rats exhibited poor autoregulation of RBF, it increased by 27% when RPP was increased from 100 to 140 mmHg. In contrast, MHS rats exhibited nearly perfect autoregulation and RBF was not significantly altered. Glomerular capillary pressure estimated from measurement of proximal tubular stop flow pressure increased by 10 mmHg in MNS following the elevation in RPP, but not in MHS rats. These data indicate that impaired myogenic response of the Af-Art contributes to the progression of proteinuria and renal injury in MNS rats. This studies were supported by NIH Grants HL36279 and DK104184-01.

Impaired Renal Autoregulation in Susceptible Models of Renal Disease

One of the major functions of the kidney is to maintain constant renal blood flow and glomerular filtration rate in response to increases in renal perfusion pressure. This phenomenon is referred to autoregulation and involves two independent mechanisms: tubular glomerular feedback and myogenic response. The latter, the renal myogenic response, involves constriction of the preglomerular vasculature to increases in transmural pressure. Over the last three decades, there has been substantial evidence that demonstrates that the myogenic response plays an important role in protecting the kidney from hypertension-induced renal injury. Furthermore, impairment of the renal myogenic response allows the transmission of systemic pressures to the glomerular capillaries leading to the development of glomerular injury and progressive proteinuria during hypertension. This review article discusses the role of the myogenic response in the pathogenesis of renal disease in various genetic and experimental rodent models that develop hypertension-induced renal injury.