Afferent Arteriolar Vasoconstriction Research Articles

The Paradise Renal Denervation System: An FDA-approved catheter-based treatment option for resistant hypertension

Resistant hypertension is defined as office blood pressure >140/90 mm Hg with a mean 24-hour ambulatory blood pressure of >130/80 mm Hg in patients who are compliant with 3 or more antihypertensive medications. Those who persistently fail pharmaceutical therapy may benefit from interventional treatment, such as renal denervation. Sympathetic nervous activity in the kidney is a known contributor to increased blood pressure because it results in efferent and afferent arteriole vasoconstriction, reduced renal blood flow, increased sodium and water reabsorption, and the release of renin. The Recor Paradise Renal Denervation System is designed to target renal sympathetic nerves via ultrasound ablation. The RADIANCE trials have demonstrated that patients who underwent renal denervation had a significant decrease in systolic blood pressure as compared with those who underwent a sham procedure. Furthermore, the device was found to have a favorable safety profile, with minimal major adverse events. The Food and Drug Administration granted approval to Recor, and the Paradise system is expected to serve as an adjunctive therapy for patients with true-resistant hypertension.

Modeling the renoprotective mechanisms of SGLT2 inhibition in hypertensive chronic kidney disease.

Sodium-glucose cotransporter (SGLT)-2 inhibitors have recently been approved for chronic kidney disease (CKD) based on their ability to lower proteinuria and slow CKD progression independent of diabetes status. In diabetic renal disease, modulation of tubuloglomerular feedback (TGF) leading to lower intraglomerular pressure has been postulated as one of the mechanisms of renal protection with SGLT2 inhibition; however, this mechanism has not been sufficiently explored in non-diabetic CKD. We hypothesized that SGLT2 inhibition exerts renoprotection in CKD through increasing TGF despite normoglycemia. To test this hypothesis, we used an integrative mathematical model of human physiology, HumMod. Stage 3 CKD conditions were simulated by reducing nephron mass which was associated with hypertension, low glomerular filtration rate (GFR) (55 mL/min), hyperfiltration of remnant nephrons, elevated albuminuria (500 mg/day), and minimal levels of urinary glucose (0.02 mmol/L). SGLT2 inhibition was associated with acute reductions in GFR associated with afferent arteriolar vasoconstriction due to TGF. After 12 months, glomerular pressure, nephron damage, and chronic GFR decline were reduced with SGLT2 inhibition with additional SGLT1 inhibitory effects further enhancing these effects. This model supports the use of SGLT2 inhibitors to reduce hyperfiltration in CKD and mitigate renal disease progression, even in the absence of diabetes.

Interaction of Angiotensin II AT1 Receptors with Purinergic P2X Receptors in Regulating Renal Afferent Arterioles in Angiotensin II-Dependent Hypertension.

In angiotensin II (Ang II)-dependent hypertension, Ang II activates angiotensin II type 1 receptors (AT1R) on renal vascular smooth muscle cells, leading to renal vasoconstriction with eventual glomerular and tubular injury and interstitial inflammation. While afferent arteriolar vasoconstriction is initiated by the increased intrarenal levels of Ang II activating AT1R, the progressive increases in arterial pressure stimulate the paracrine secretion of adenosine triphosphate (ATP), leading to the purinergic P2X receptor (P2XR)-mediated constriction of afferent arterioles. Thus, the afferent arteriolar tone is maintained by two powerful systems eliciting the co-existing activation of P2XR and AT1R. This raises the conundrum of how the AT1R and P2XR can both be responsible for most of the increased renal afferent vascular resistance existing in angiotensin-dependent hypertension. Its resolution implies that AT1R and P2XR share common receptor or post receptor signaling mechanisms which converge to maintain renal vasoconstriction in Ang II-dependent hypertension. In this review, we briefly discuss (1) the regulation of renal afferent arterioles in Ang II-dependent hypertension, (2) the interaction of AT1R and P2XR activation in regulating renal afferent arterioles in a setting of hypertension, (3) mechanisms regulating ATP release and effect of angiotensin II on ATP release, and (4) the possible intracellular pathways involved in AT1R and P2XR interactions. Emerging evidence supports the hypothesis that P2X1R, P2X7R, and AT1R actions converge at receptor or post-receptor signaling pathways but that P2XR exerts a dominant influence abrogating the actions of AT1R on renal afferent arterioles in Ang II-dependent hypertension. This finding raises clinical implications for the design of therapeutic interventions that will prevent the impairment of kidney function and subsequent tissue injury.

Mitochondria and renal microvascular dysfunction following ischemia-reperfusion in rats

The pathophysiological mechanisms underlying ischemia-reperfusion (IR) induced acute kidney injury (AKI) remain poorly understood. Preglomerular microvessels (PGMV), specifically afferent arterioles, possess an intrinsic autoregulatory ability that is vital for ensuring stable renal hemodynamics. Our recent study indicates that renal autoregulation is impaired in IR rats due to reactive oxygen species (ROS) accumulation. We hypothesized that mitochondria-derived ROS (mtROS) in preglomerular microvessels contribute to renal autoregulatory impairment in IR rats. Blood-perfused juxtamedullary nephron experiments were performed on kidneys of male Sprague-Dawley rats 24 hours after IR induction (60-min, bilateral renal artery clamping). Afferent arteriolar autoregulation was assessed as perfusion pressure (PP) was increased from 65 to 170 mmHg in 15 mmHg increments. Afferent arterioles of sham-operated control rats (n=7) established pressure-mediated autoregulatory responses. Baseline diameter (100 mmHg) averaged 13.2±0.4 μm and increased to 114±4% of baseline when PP decreased from 100 to 65 mmHg. Diameter decreased to 65±3% of baseline when PP increased to 170 mmHg. In contrast, afferent arterioles from IR rats lost autoregulatory capability and remained between 90 and 100% of baseline diameter over 65-170 mmHg (n=8). Addition of Mito-Tempo (mitochondria-targeted antioxidant, 0.1 mM, n=3) to the perfusate restored autoregulation in IR rats at lower PP (65-125 mmHg, P>0.05 vs sham) and partially restored it over 140-170 mmHg. Superfusion with oligomycin (ATP synthase inhibitor, 2.5 μM) in normal kidneys evoked vasodilation to 178±13% baseline and blunting of autoregulatory reactivity. Renal autoregulation is linked to ATP-sensitive P2X1-receptor signaling. Changes in ATP-induced intracellular calcium concentration ([Ca2+]i) were assessed in isolated PGMV myocytes using Fura-2 fluorescent dye. IR markedly attenuated [Ca2+]i responses to 10 and 100 μM ATP by 46±11% and 57±15%, respectively (P<0.05, n=3-4 rats/group), and blunted ATP-induced afferent arteriolar vasoconstriction ( P<0.05 vs. sham, n=3/group). IR markedly increased the fluorescence intensity of mitoROS (MitoSOX™ kit) in PGMV compared to sham rats. Mitochondrial respiratory function was assessed using High Resolution Respirometry in freshly isolated PGMV (n=3/group). IR significantly reduced basal respiration (20±4 vs. 58±9 pmol/s·ml in sham, P<0.05) and oxidative phosphorylation capacity (51±10 vs. 219±37 pmol/s·ml in sham, P<0.05). The percentage of ATP-linked respiration was also reduced in PGMV of IR (60±2% vs. 75±2% in sham, P<0.05). In conclusion, mitochondria of PGMV are involved in regulating renal microvascular tone and autoregulation. IR leads to autoregulatory dysfunction by causing mitochondrial dysfunction in PGMV, increased mtROS production and suppression of ATP-dependent calcium signaling. This study is supported by grants R01DK106500. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Renal blood flow during exercise: understanding its measurement with Doppler ultrasound.

The sympathetic nervous system (SNS) has a critical role in continuously coordinating responses to stimuli internal and external to the human body by appropriately modulating the activity of the organs it innervates. The SNS is activated in response to various physiological stressors, including exercise, which can involve a significant increase in SNS activity. An increase in SNS activity directed toward the kidneys causes vasoconstriction of afferent arterioles within the kidneys. This sympathetically mediated renal vasoconstriction decreases renal blood flow (RBF), causing significant blood flow redistribution toward active skeletal muscles during exercise. In research studies, different modes, intensities, and durations of exercise have been used to investigate the sympathetically mediated RBF response to exercise, and several methodological approaches have been used to quantify RBF. Doppler ultrasound provides noninvasive, continuous, real-time measurements of RBF and has emerged as a valid and reliable technique to quantify RBF during exercise. This innovative methodology has been applied in studies in which the RBF response to exercise has been examined in healthy young and older adults and patient populations such as those with heart failure and peripheral arterial disease. This valuable tool has enabled researchers to produce clinically relevant findings that have furthered our understanding of the effect of SNS activation on RBF in populations of health and disease. Therefore, the focus of this narrative review is to highlight the use of Doppler ultrasound in research studies that have provided important findings furthering our knowledge of the impact of SNS activation on RBF regulation in humans.

Dual inhibition of SGLT2 and DPP-4 promotes natriuresis and improves glomerular hemodynamic abnormalities in KK/Ta-Ins2Akita mice with progressive diabetic kidney disease

Natriuresis is closely linked to glomerular hemodynamics in diabetic kidney disease (DKD), and is known to be influenced by inhibition of sodium-glucose cotransporter 2 (SGLT2) or dipeptidyl peptidase-4 (DPP-4). In the present study, we investigated whether dual inhibition of SGLT2 and DPP-4 exerts an additive effect on promoting natriuresis and how it ameliorates glomerular hemodynamic abnormalities via the natriuretic effect in DKD. Eight-week-old male KK/Ta-Ins2Akita (KK/Ta-Akita) mice which develop progressive DKD were orally once-daily given either SGLT2 inhibitor empagliflozin (30 mg/kg) alone, DPP-4 inhibitor linagliptin (5 mg/kg) alone or a combination of empagliflozin (30 mg/kg) plus linagliptin (5 mg/kg) for 6 weeks. In vehicle-treated control KK/Ta-Akita mouse group, markedly enhanced glomerular albumin filtration and glomerular filtration rate (GFR) were observed. These renal alterations were dramatically attenuated in KK/Ta-Akita mouse group treated with a combination of empagliflozin plus linagliptin. Notably, the combination therapy provided greater reduction in glomerular albumin filtration and GFR along with higher urinary excretion of sodium and a potential afferent arteriolar vasoconstrictor adenosine than the empagliflozin monotherapy. Significant reduction in urinary excretion levels of a potential afferent arteriolar vasodilator prostaglandin E2 (PGE2) relative to the baseline values was observed after the combination therapy but not the monotherapy. These results suggest that dual inhibition of SGLT2 and DPP-4 highly promotes a distal tubular sodium delivery and thereby contributes to the appropriate modulation of preglomerular arteriolar tone and intraglomerular pressure via an increase in adenosine release and a reduction in PGE2 secretion from macula densa in DKD.

Is there any robust evidence showing that SGLT2 inhibitor use predisposes to acute kidney injury?

A novel class of oral glucose lowering drugs, sodium-glucose co-transporter type 2 inhibitors (SGLT2is), has shown additional beneficial effects on body weight, serum uric acid levels, blood pressure, and cardiac and renal function. Conflicting data have been published regarding the potential risk of acute kidney injury (AKI) when using SGLT2is. Aim of this manuscript was to review the current literature on this issue. SGLT2isinduce a mild acute decline in estimated glomerular filtration rate, attributed to the effect of proximal tubular natriuresis on tubuloglomerular feedback through increased macula densa sodium delivery, leading to afferent arteriole vasoconstriction and reduced intraglomerular pressure. This functional effect with a subsequent rise in serum creatinine fulfills the creatinine-basedcriteria for AKI,as defined in clinical practice and trial settings. Other proposed potential mechanisms as tohow SGLT2islead to AKI include osmotic diuresis leading to volume depletion, increased urinary uric acid levels, intratubular oxidative stress, local inflammation and tubular injury. Despite the warning published by the US Food and Drug Administration in 2016 about a potential risk of AKI and the report of some clinical cases of AKI after treatment with SGLT2is, large observational real-life retrospective studies, randomized controlled trials and propensity-matched analyses of data from clinical practice unambiguously demonstrate that SGLT2is are safe for the kidney and do not predispose to AKI. In conclusion, while we can probably stop worrying about AKI risk when using SGLT2is, the question whether these agents should be withheld in the presence of clinical situations at high risk for AKIremains unaddressed.

Renal sarcoidosis.

Sarcoidosis is a systemic inflammatory disease of unknown etiology. The pathogenesis rests on an aberrant T cell response to unidentified antigens in individuals predisposed by genetic and environmental factors. Increased expression of polarized macrophages and disequilibrium between effector and regulator T cells contribute to the formation of noncaseating granulomas, that are frequently found in affected organs. The main kidney abnormalities in sarcoidosis are granulomatous interstitial nephritis (GIN) and hypercalcemia-related disorders. The clinical diagnosis is difficult. The outcome is variable, ranging from spontaneous remission to end-stage kidney disease (ESKD). Early diagnosis and prompt treatment with corticosteroids can improve the prognosis. Hypercalcemia may be responsible for acute kidney injury (AKI) caused by vasoconstriction of afferent arterioles. Complications of persistent hypercalcemia include nephrocalcinosis and renal stones. In patients with ESKD, dialysis and transplantation can offer results comparable to those observed in patients with other causes of kidney failure. Based on a review of the literature, we present an overview of the etiopathogenesis, the renal manifestations of sarcoidosis and their complications, management and prognosis.

MO1034: Sodium-Glucose Cotransporter 2 Inhibitors in Patients with Alport Syndrome and Fsgs: A Case Series

Abstract BACKGROUND AND AIMS Most hereditary diseases of the glomerular filtration barrier still progress to end-stage renal failure (ESRF)—raising the urgent need for add-on therapies. Recent randomized clinical trials (RCTs) demonstrated the nephroprotective effect of sodium-glucose cotransporter-2 inhibitors (SGLT2i) in chronic kidney diseases (CKD). SGLT2-mediated afferent arteriole vasoconstriction, additive to efferent arteriole vasodilatation by angiotensin-converting enzyme inhibitors (ACEis), is postulated to correct the haemodynamic overload of the glomerular filtration barrier. For that reason, we investigated the nephroprotective effect of SGLT2i in hereditary glomerular diseases. METHOD In 2020, this monocentric prospective case series was started in six patients with Alport syndrome or FSGS, who consented to off-label therapy with empagliflozin or dapagliflozin. To our knowledge, this is the first case series on the effect of SGLT2i in patients with hereditary causes of CKD. RESULTS We report data on the use of SGLT2i in a case series of patients with Alport syndrome and FSGS in respect of the early effect on the kidney function and safety of initiation of therapy. The follow-up was 3–11 months. The mean age was 40 years (standard deviation, SD ± 17), the mean duration of treatment was 4.5 months (SD ± 2.9). The mean serum creatinine before and after SGLT2i initiation was 1.46 (SD ± 0.42) and 1.58 (SD ± 0.55). The mean urinary albumin-creatinine ratio in mg/g creatinine before SGLT2i was 1827 (SD ± 1560) and decreased to 1127 (SD ± 854) after SGLT2i initiation. The estimated glomerular filtration rate (eGFR) ‘dipped’ after initiation of SGLT2i in most patients. Overall, treatment was well tolerated, however, eGFR initially decreased by more than 30% in one patient with FSGS. The initial eGFR drop raises some safety concerns, which underlines the need to collect and evaluate the course of every patient with AS in which therapy with SGLT2i is started. CONCLUSION In conclusion, therapy with SGLT2i on top of ACEi was well tolerated and effective in terms of lowering albuminuria. As a proof of concept, SGLT2-mediated correction of the haemodynamic overload of the glomerular filtration barrier looks like a very promising therapeutic approach in hereditary diseases such as AS and FSGS. Specific RCTs are needed to confirm our findings in this genetically well-defined population with a tremendous unmet medical need for more effective, early on and safe nephroprotective therapies. Proteinuria is reported as a urinary albumin-creatinine ratio in mg/g creatinine. All male patients received SGLT2i additive to renin-angiotensin-aldosterone system (RAAS)-blockade. In the female patient, ACEi was stopped prior to the start of SGLT2i because of angioedema. In addition to ACEi and SGLT2i, one patient also received tacrolimus because of irritable bowel disease. (A) eGFR (CKD-EPI formula) at baseline and at follow-up. (B) UACr at baseline and at follow up. m, male; f, female; FSGS, focal segmental glomerulosclerosis; XLAS, X-linked Alport syndrome; IBD, irritable bowel disease; aHT, arterial hypertension; sHP, secondary hyperparathyroidism; eGFR, estimated glomerular filtration rate; UACr, urine-albumin-creatinine ratio; Crea, serum-creatinine

Physiological Changes in Subjects Exposed to Accidental Hypothermia: An Update.

BackgroundAccidental hypothermia (AH) is an unintended decrease in body core temperature (BCT) to below 35°C. We present an update on physiological/pathophysiological changes associated with AH and rewarming from hypothermic cardiac arrest (HCA).Temperature Regulation and MetabolismTriggered by falling skin temperature, Thyrotropin-Releasing Hormone (TRH) from hypothalamus induces release of Thyroid-Stimulating Hormone (TSH) and Prolactin from pituitary gland anterior lobe that stimulate thyroid generation of triiodothyronine and thyroxine (T4). The latter act together with noradrenaline to induce heat production by binding to adrenergic β3-receptors in fat cells. Exposed to cold, noradrenaline prompts degradation of triglycerides from brown adipose tissue (BAT) into free fatty acids that uncouple metabolism to heat production, rather than generating adenosine triphosphate. If BAT is lacking, AH occurs more readily.Cardiac OutputAssuming a 7% drop in metabolism per °C, a BCT decrease of 10°C can reduce metabolism by 70% paralleled by a corresponding decline in CO. Consequently, it is possible to maintain adequate oxygen delivery provided correctly performed cardiopulmonary resuscitation (CPR), which might result in approximately 30% of CO generated at normal BCT.Liver and CoagulationAH promotes coagulation disturbances following trauma and acidosis by reducing coagulation and platelet functions. Mean prothrombin and partial thromboplastin times might increase by 40–60% in moderate hypothermia. Rewarming might release tissue factor from damaged tissues, that triggers disseminated intravascular coagulation. Hypothermia might inhibit platelet aggregation and coagulation.KidneysRenal blood flow decreases due to vasoconstriction of afferent arterioles, electrolyte and fluid disturbances and increasing blood viscosity. Severely deranged renal function occurs particularly in the presence of rhabdomyolysis induced by severe AH combined with trauma.ConclusionMetabolism drops 7% per °C fall in BCT, reducing CO correspondingly. Therefore, it is possible to maintain adequate oxygen delivery after 10°C drop in BCT provided correctly performed CPR. Hypothermia may facilitate rhabdomyolysis in traumatized patients. Victims suspected of HCA should be rewarmed before being pronounced dead. Rewarming avalanche victims of HCA with serum potassium > 12 mmol/L and a burial time >30 min with no air pocket, most probably be futile.

EGFR Decline after SGLT2 Inhibitor Initiation: The Tortoise and the Hare Reimagined.

Sodium-glucose cotransporter 2 inhibitors (SGLT2is) have emerged as an effective class of medications to treat CKD and heart failure. SGLT2is improve cardiovascular outcomes in patients with type 2 diabetes mellitus (1⇓–3) and in those with heart failure with reduced ejection fraction (4⇓⇓–7). Moreover, they have been shown to attenuate kidney disease progression in patients with proteinuric CKD, irrespective of diabetes status (8,9). The rapid uptake of SGLT2is into practice necessitates a careful understanding of their risks. Furthermore, clinicians need to know what to expect when prescribing these agents, including an early decline in eGFR after initiation. We aim to put this observation into context, while providing clinicians with a practical approach to managing this scenario. The suggested mechanism of action of the SGLT2is has previously been described (10). These drugs inhibit sodium and glucose reabsorption in the proximal tubule, leading to increased sodium and chloride delivery to the macula densa. This results in afferent arteriolar vasoconstriction secondary to adenosine-mediated myogenic activation, leading to a reduction in the intraglomerular pressure and the GFR (10). Therefore, it is not surprising that the major SGLT2i outcome trials have reported an early decline in eGFR (around 3–6 ml/min per 1.73 m2) shortly after initiating these drugs compared with placebo controls (5,8,9,11,12). These early declines or dips were typically observed at 2–4 weeks after initiation of the SGLT2i, with subsequent partial recovery of the eGFR curve by week 12, and, ultimately, followed by an attenuation of the slope of eGFR decline compared with placebo controls after 52 weeks (Table 1). View this table: Table 1. Randomized controlled trials reporting an initial dip of eGFR How can we reconcile early dips in eGFR with long-term nephroprotection? Maladaptive glomerular hemodynamics play a central …

Lack of Connexins 40 and 45 Reduces Local and Conducted Vasoconstrictor Responses in the Murine Afferent Arterioles.

The juxtaglomerular apparatus (JGA) is an essential structure in the regulation of renal function. The JGA embodies two major functions: tubuloglomerular feedback (TGF) and renin secretion. TGF is one of the mechanisms mediating renal autoregulation. It is initiated by an increase in tubular NaCl concentration at the macula densa cells. This induces a local afferent arteriolar vasoconstriction and a conducted response that can be measured several 100 μm upstream from the juxtaglomerular segment. This spread of the vasomotor response into the surrounding vasculature likely plays a key role in renal autoregulation, and it requires the presence of gap junctions, intercellular pores based on connexin (Cx) proteins. Several Cx isoforms are expressed in the JGA and in the arteriolar wall. Disruption of this communication pathway is associated with reduced TGF, dysregulation of renin secretion, and hypertension. We examine if the absence of Cx40 or Cx45, expressed in the endothelial and vascular smooth muscle cells respectively, attenuates afferent arteriolar local and conducted vasoconstriction. Afferent arterioles from wildtype and Cx-deficient mice (Cx40 and Cx45) were studied using the isolated perfused juxtamedullary nephron preparation. Vasoconstriction was induced via electrical pulse stimulation at the glomerular entrance. Inner afferent arteriolar diameter was measured locally and upstream to evaluate conducted vasoconstriction. Electrical stimulation induced local vasoconstriction in all groups. The local vasoconstriction was significantly smaller when Cx40 was absent. The vasoconstriction decreased in magnitude with increasing distance from the stimulation site. In both Cx40 and Cx45 deficient mice, the vasoconstriction conducted a shorter distance along the vessel compared to wild-type mice. In Cx40 deficient arterioles, this may be caused by a smaller local vasoconstriction. Collectively, these findings imply that Cx40 and Cx45 are central for normal vascular reactivity and, therefore, likely play a key role in TGF-induced regulation of afferent arteriolar resistance.

Nephrotoxicity of Antimicrobials and Antibiotics.

Medication-induced nephrotoxicity remains one of the most common causes of acute kidney injury (AKI) among hospitalized patients. Within the extensive group of medications associated with AKI, antibiotics and other antimicrobials are well recognized triggers of structural and functional renal impairment. Clinical manifestations range from mild forms of tubular injury to significant deterioration of kidney function requiring acute renal replacement therapy. Several mechanisms are described, although the most frequent are acute interstitial nephritis, acute tubular necrosis, intratubular crystal deposition, and proximal/distal tubulopathy with electrolyte wasting abnormalities. General risk factors for antimicrobial-induced AKI include pre-existing chronic kidney disease, and concomitant use of medication with nephrotoxic potential. Prevention and early recognition of AKI represent the standard approach to mitigate AKI and avoid morbidity.

Do sodium-glucose cotransporter-2 inhibitors affect renal hemodynamics by different mechanisms in type 1 and type 2 diabetes?

Cardiovascular and renal outcome trials demonstrate nephroprotection with sodium-glucose cotransporter-2 inhibitors in people with type 2 diabetes. Attenuation of hyperfiltration is believed to be responsible for the nephroprotection, and studies in young adults with type 1 diabetes suggest that afferent arteriolar vasoconstriction induced by a tubuloglomerular feedback mechanism may be responsible for this effect. The study by van Bommel etal. suggests that this mechanism may not hold true in older adults with type 2 diabetes, who instead attenuate elevated glomerular filtration rate via post-glomerular vasodilation.

Rho kinase inhibitors reduce voltage-dependent Ca2+ channel signaling in aortic and renal microvascular smooth muscle cells.

Voltage-dependent L-type Ca2+ channels (L-VDCCs) and the RhoA/Rho kinase pathway are two predominant intracellular signaling pathways that regulate renal microvascular reactivity. Traditionally, these two pathways have been thought to act independently; however, recent evidence suggests that these pathways could be convergent. We hypothesized that Rho kinase inhibitors can influence L-VDCC signaling. The effects of Rho kinase inhibitors Y-27632 or RKI-1447 on KCl-induced depolarization or the L-VDCC agonist Bay K8644 were assessed in afferent arterioles using an in vitro blood-perfused rat juxtamedullary nephron preparation. Superfusion of KCl (30-90 mM) led to concentration-dependent vasoconstriction of afferent arterioles. Administration of Y-27632 (1, 5, and 10 µM) or RKI-1447 (0.1, 1, and 10 µM) significantly increased the starting diameter by 16-65%. KCl-induced vasoconstriction was markedly attenuated with 5 and 10 µM Y-27632 and with 10 µM RKI-1447 (P < 0.05 vs. KCl alone). Y-27632 (5 µM) also significantly attenuated Bay K8644-induced vasoconstriction (P < 0.05). Changes in intracellular Ca2+ concentration ([Ca2+]i) were estimated by fura-2 fluorescence during KCl-induced depolarization in cultured A7r5 cells and in freshly isolated preglomerular microvascular smooth muscle cells. Administration of 90 mM KCl significantly increased fura-2 fluorescence in both cell types. KCl-mediated elevation of [Ca2+]i in A7r5 cells was suppressed by 1-10 µM Y-27632 (P < 0.05), but 10 µM Y-27632 was required to suppress Ca2+ responses in preglomerular microvascular smooth muscle cells. RKI-1447, however, significantly attenuated KCl-mediated elevation of [Ca2+]i. Y-27632 markedly inhibited Bay K8644-induced elevation of [Ca2+]i in both cell types. The results of the present study indicate that the Rho kinase inhibitors Y-27632 and RKI-1447 can partially inhibit L-VDCC function and participate in L-VDCC signaling.

Afferent arteriole responsiveness to endothelin receptor activation: does sex matter?

BackgroundThe pathogenesis of hypertension is distinct between men and women. Endothelin-1 (ET-1) is a potential contributor to sex differences in the pathophysiology of hypertension. ET-1 participates in blood pressure regulation through activation of endothelin A (ETA) and endothelin B (ETB) receptors including those in the vasculature. Previous studies demonstrated that sex and sex hormones evoke discrepancies in ET-1-mediated control of vascular tone in different vascular beds. However, little is known about sex- and sex hormone-related differences in ET-1-dependent renal microvascular reactivity. Accordingly, we hypothesized that loss of sex hormones impairs afferent arteriole reactivity to ET-1.MethodsMale and female Sprague Dawley rats were subjected to gonadectomy or sham surgery (n = 6/group). After 3 weeks, kidneys from those rats were prepared for assessment of renal microvascular responses to ET-1 (ETA and ETB agonist, 10−12 to 10−8 M) and sarafotoxin 6c (S6c, ETB agonist, 10−12 to 10−8 M) using the blood-perfused juxtamedullary nephron preparation.ResultsControl afferent arteriole diameters at 100 mmHg were similar between sham male and female rats averaging 14.6 ± 0.3 and 15.3 ± 0.3 μm, respectively. Gonadectomy had no significant effect on control arteriole diameter. In sham males, ET-1 produced significant concentration-dependent decreases in afferent arteriole diameter, with 10−8 M ET-1 decreasing diameter by 84 ± 1%. ET-1 induced similar concentration-dependent vasoconstrictor responses in sham female rats, with 10−8 M ET-1 decreasing the diameter by 82 ± 1%. The afferent arteriolar vasoconstrictor responses to ET-1 were unchanged by ovariectomy or orchiectomy. Selective ETB receptor activation by S6c induced a concentration-dependent decline in afferent arteriole diameter, with 10−8 M S6c decreasing diameter by 77 ± 3 and 76 ± 3% in sham male and female rats, respectively. Notably, ovariectomy augmented the vasoconstrictor response to S6c (10−12 to 10−9 M), whereas orchiectomy had no significant impact on the responsiveness to ETB receptor activation.ConclusionThese data demonstrate that sex does not significantly influence afferent arteriole reactivity to ET receptor activation. Gonadectomy potentiated the responsiveness of the afferent arteriole to ETB-induced vasoconstriction in females, but not males, suggesting that female sex hormones influence ETB-mediated vasoconstriction in the renal microcirculation.

Rho Kinase Inhibitors Are Involved in L‐Type Voltage‐dependent Calcium Channel Pathway in Vascular Smooth Muscle Cells

Voltage‐dependent L‐type calcium channels (L‐VDCC) and the rho/rho kinase pathway are two predominate intracellular pathways that regulate renal microvascular tone and reactivity. Traditionally, these two pathways have been thought to act independently; however, recent evidence suggests these pathways are convergent. We hypothesized that the rho kinase inhibitors influenced L‐VDCC signaling. The effects of rho kinase inhibitors Y‐27632 or RKI‐1447 on KCl‐depolarization were assessed in afferent arterioles using the in vitro blood‐perfused rat juxtamedullary nephron preparation. Superfusion of KCl (30, 60, and 90mM) led to concentration‐dependent vasoconstriction of afferent arterioles reducing the diameter to 95±6, 56±4 and 42±3% of the baseline, respectively (p&lt;0.05). Addition of Y‐27632 (1, 5 and 10 μM) or RKI‐1447 (0.1, 1 and 10 μM) significantly increased starting diameter by 16–65% (n=6/each, p&lt;0.05). The KCl‐induced vasoconstriction with 1 μM Y‐27632 or 0.1 and 1 μM RKI‐1447 was similar to control, but markedly attenuated with 5 and 10 μM Y‐27632, and 10 μM RKI‐1447 (p&lt;0.05 vs KCl alone). The afferent arteriole diameter averaged 99±2, 83±2, 71±4%, and 98±0.8, 89±5, 81±6% of the baseline for 5 and 10 μM Y‐27632, and 97±2, 89±3 and 88±4% of the baseline for 10 μM RKI‐1447, respectively (n=6/each, p&lt;0.05 vs KCl alone). Changes in intracellular calcium concentration [Ca2+]i were estimated by fura‐2‐AM fluorescence (ratio F340/380) during KCl‐depolarization in cultured A7r5 cells (n=46–118/each group) and in freshly isolated renal microvascular smooth muscle cells (RMVSMCs, n=32–118/each group). Administration of 90 mM KCl increased fura‐2 fluorescence markedly in both cell types. The KCl‐induced increase of the F340/F380 ratio was unaltered by 0.1 or 0.5 μM Y‐27632 but was significantly attenuated by Y‐27632 between 1–10 μM by 50–56% (p&lt;0.05 vs KCl alone) in A7r5 cells but only at 10 μM in RMVSMCs by 42% (p&lt;0.05 vs KCl alone). RKI‐1447 however, significantly attenuated KCl‐mediated elevation of [Ca2+]i in both cell types regardless of the concentrations applied (0.1–10 μM, p&lt;0.05), indicating that Y‐27632 and RKI‐1447 decrease L‐VDCC function. These studies indicate that the rho kinase inhibitors, Y‐27632 and RKI‐1447 partially inhibit L‐VDCC function and participate in L‐VDCC signaling.Support or Funding InformationThis study was supported by a Grant‐in‐Aid (15GRNT25240015) from the American Heart Association Great Southeast Affiliate and a grant from NIH (DK106500) to ZG, and by grants from NIH (DK044628, HL074167, HL098135 and HL095499) to EWI.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Lack of contribution of nitric oxide synthase to cholinergic vasodilation in murine renal afferent arterioles.

We have previously reported significant increases in neuronal nitric oxide synthase (NOS) immunostaining in renal arterioles of angiotensin type 1A receptor (AT1A) knockout mice, and in arterioles and macula densa cells of AT1A/AT1B knockout mice. The contribution of nitric oxide derived from endothelial and macula densa cells in the maintenance of afferent arteriolar tone and acetylcholine-induced vasodilation was functionally determined in kidneys of wild-type, AT1A, and AT1A/AT1B knockout mice. Acetylcholine-induced changes in arteriolar diameters of in vitro blood-perfused juxtamedullary nephrons were measured during control conditions, in the presence of the nonspecific NOS inhibitor, Nω-nitro-l-arginine methyl ester (NLA), or the highly selective neuronal NOS inhibitor, N5-(1-imino-3-butenyl)-l-ornithine (VNIO). Acetylcholine (0.1 mM) produced a significant vasoconstriction in afferent arterioles of AT1A/AT1B mice (-10.9 ± 5.1%) and no changes in afferent arteriolar diameters of AT1A knockout mice. NLA (0.01-1 mM) or VNIO (0.01-1 μM) induced significant dose-dependent vasoconstrictions (-19.8 ± 4.0% 1 mM NLA; -7.8 ± 3.5% 1 μM VNIO) in afferent arterioles of kidneys of wild-type mice. VNIO had no effect on afferent arteriole diameters of AT1A knockout or AT1A/AT1B knockout mice, suggesting nonfunctional neuronal nitric oxide synthase. These data indicate that acetylcholine produces a significant renal afferent arteriole vasodilation independently of nitric oxide synthases in wild-type mice. AT1A receptors are essential for the manifestation of renal afferent arteriole responses to neuronal nitric oxide synthase-mediated nitric oxide release.

The mechanism of action of sodium–glucose co‐transporter 2 inhibitors is similar to carbonic anhydrase inhibitors

Butler et al.,1 in their review about the potential role of sodium–glucose co-transporter-2 inhibitors (SGLT2i) in the treatment of heart failure (HF), do not mention the carbonic anhydrase (CA) inhibitors, whose mechanism of action has remarkable similarities with SGLT2i. Although there are no studies in humans,2 it is established that around 30% of the filtered Na+ is reabsorbed through the Na+/H+ isoform 3 (NHe3) exchanger, which is located in the proximal convoluted tubule (PCT), whereas up to 15% of tubular Na+ is reabsorbed through SGLT2 in situations of hyperglycaemia. The SGLT2i inhibit both the SGLT2 and the NHe3 exchangers that share the microdomain with SGLT2,2 and they have a natriuretic effect independent of the glycaemic level.3 On the other hand, NHe3 is activated in HF and is involved in the states of resistance to diuretics.4 Carbonic anhydrase is an enzyme located on the luminal membrane of PCT cells that accelerates the formation of H2CO3 and its subsequent conversion into H2O and CO2 using H+ and HCO3−, which favours the mobilization of NHe3 substrates and increases the tubular reabsorption of Na+. CA inhibitors, such as acetazolamide, act to inhibit the CA, slowing down the H2CO3 circuit and decreasing NHe3 activity, leading to natriuresis.5 The SGLT2i and CA inhibitors indirectly inhibit NHe3, cause mild to moderate natriuresis and bicarbonaturia, and activate the juxtaglomerular system by decreasing hyperfiltration and proteinuria, secondary to increased Na+ and Cl− reabsorption by macula densa (MD). This reabsorption would activate the juxtaglomerular system allowing the local secretion of adenosine that in turn stimulates the afferent arteriole vasoconstriction, which leads to a decrease in hyperfiltration. This haemodynamic fact does not occur with loop diuretics, thiazides, or K+-sparing diuretics. The loop diuretics block the carrier Na+/K+/2Cl− in the MD, and the others act beyond the ascending loop of Henle and MD, so these drugs would have no proteinuric or nephroprotective effect.5 There are differences in the natriuretic effect between SGLT2i and CA inhibitors. CA inhibitors lose their diuretic effect in the long term due to compensatory mechanisms of distal reabsorption.5 However, the SGLT2i maintain their long-term diuretic effect. Thus, currently, the clinical use of acetazolamide in HF is restricted to patients with diuretic resistance. In contrast, the diuretic effect of SGLT2i is maintained over time, probably due to the glucosuric effect6 that modifies renin levels.1 Despite these differences in their long-term temporal effect considering the similarities in the mechanism of action of SGLT2i and CA inhibitors, and considering the benefit demonstrated by SGLT2i, it would be interesting to develop specific clinical trials with CA inhibitors in patients with diabetes and HF (https://clinicaltrials.gov/ct2/show/NCT01973335).

The role of adenosine 1a receptor signaling on GFR early after the induction of sepsis.

Sepsis and acute kidney injury (AKI) synergistically increase morbidity and mortality in the ICU. How sepsis reduces glomerular filtration rate (GFR) and causes AKI is poorly understood; one proposed mechanism includes tubuloglomerular feedback (TGF). When sodium reabsorption by the proximal tubules is reduced in normal animals, the macula densa senses increased luminal sodium chloride, and then adenosine-1a receptor (A1aR) signaling triggers tubuloglomerular feedback, reducing GFR through afferent arteriole vasoconstriction. We measured GFR and systemic hemodynamics early during cecal ligation and puncture-induced sepsis in wild-type and A1aR-knockout mice. A miniaturized fluorometer was attached to the back of each mouse and recorded the clearance of FITC-sinistrin via transcutaneous fluorescence to monitor GFR. Clinical organ injury markers and cytokines were measured and hemodynamics monitored using implantable transducer telemetry devices. In wild-type mice, GFR was stable within 1 h after surgery, declined by 43% in the next hour, and then fell to less than 10% of baseline after 2 h and 45 min. In contrast, in A1aR-knockout mice GFR was 37% below baseline immediately after surgery and then gradually declined over 4 h. A1aR-knockout mice had similar organ injury and inflammatory responses, albeit with lower heart rate. We conclude that transcutaneous fluorescence can accurately monitor GFR and detect changes rapidly during sepsis. Tubuloglomerular feedback plays a complex role in sepsis; initially, TGF helps maintain GFR in the 1st hour, and over the subsequent 3 h, TGF causes GFR to plummet. By 18 h, TGF has no cumulative effect on renal or extrarenal organ damage.