Regulation Of Renal Blood Flow Research Articles

The renal vasodilation from β-adrenergic activation in vivo in rats is not driven by KV7 and BKCa channels

Aim: The underlying mechanisms behind β-adrenergic renal vasodilation is not clarified. Several classes of K+ channels are potentially activated, so we tested the hypothesis that voltage-sensitive KV7 and Ca2+-activated BKCa channels contribute to the decrease in renal vascular tone in vivo and in vitro. Methods: Changes in renal blood flow (RBF) during β-adrenergic stimulation was measured in isoflurane-anesthetized rats using an ultrasonic flow probe. The isometric tension of segmental arteries from normo- and hypertensive rats and segmental arteries from wild-type mice and mice lacking functional KV7.1 channels was examined in a wire-myograph. Results: The β-adrenergic agonist isoprenaline increased RBF significantly in vivo. Neither activation nor inhibition of KV7 or BKCa channels reduced the β-adrenergic RBF response. In segmental arteries from normo- and hypertensive rats, inhibition of KV7 channels significantly decreased the β-adrenergic vasorelaxation. However, inhibiting the BKCa channel was equally effective. The β-adrenergic vasorelaxation was not different between segmental arteries from wild-type mice and mice lacking a functional KV7.1 channel. As opposed to rats, inhibition of KV7 channels did not affect the murine β-adrenergic vasorelaxation. Conclusion: Although inhibition and activation of KV7 and BKCa channels significantly changed baseline RBF in vivo, none of the treatments affected the β-adrenergic vasodilation. In segmental arteries however, inhibition of KV7 and BKCa channels significantly reduced the β-adrenergic vasorelaxation indicating that the regulation of RBF in vivo is driven by several actors in order to maintain an adequate RBF. Our data stresses the importance of verifying data in intact animals. None. This is the full abstract presented at the American Physiology Summit 2024 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.

Non-contrast preoperative MRI for determining renal perfusion and visualizing renal arteries in potential living kidney donors at 1.5 Tesla.

The aim of this work was to create and evaluate a preoperative non-contrast-enhanced (CE) magnetic resonance imaging (MRI)/angiography (MRA) protocol to assess renal function and visualize renal arteries and any abnormalities in potential living kidney donors. In total, 28 subjects were examined using scintigraphy to determine renal function. In addition, 3D-pseudocontinuous arterial spin labeling (pCASL), a 2D-non-CE electrocardiogram-triggered radial quiescent interval slice-selective (QISS-MRA), and 4D-CE time-resolved angiography with interleaved stochastic trajectories (CE-MRA) were performed to assess renal perfusion, visualize renal arteries and detect any abnormalities. Two glomerular filtration rates [described by Gates (GFRG) and according to the Chronic Kidney Disease Epidemiology Collaboration formula (GFRCKD-EPI)]. The renal volumes were determined using both MRA techniques. The mean value of regional renal blood flow (rRBF) on the right side was significantly higher than that on the left. The agreements between QISS-MRA and CE-MRA concerning the assessment of absence or presence of an aberrant artery and renal arterial stenosis were perfect. The mean renal volumes measured in the right kidney with QISS-MRA were lower than the corresponding values of CE-MRA. In contrast, the mean renal volumes measured in the left kidney with both MRA techniques were similar. The correlation between the GFRG and rRBF was compared in the same manner as that between GFRCKD-EPI and rRBF. The combination of pCASL and QISS-MRA constitute a reliable preoperative protocol with a total measurement time of <10min without the potential side effects of gadolinium-based contrast agents or radiation exposure.

The renal vasodilatation from β-adrenergic activation in vivo in rats is not driven by KV7 and BKCa channels.

The mechanisms behind renal vasodilatation elicited by stimulation of β-adrenergic receptors are not clarified. As several classes of K channels are potentially activated, we tested the hypothesis that KV7 and BKCa channels contribute to the decreased renal vascular tone in vivo and in vitro. Changes in renal blood flow (RBF) during β-adrenergic stimulation were measured in anaesthetized rats using an ultrasonic flow probe. The isometric tension of segmental arteries from normo- and hypertensive rats and segmental arteries from wild-type mice and mice lacking functional KV7.1 channels was examined in a wire-myograph. The β-adrenergic agonist isoprenaline increased RBF significantly in vivo. Neither activation nor inhibition of KV7 and BKCa channels affected the β-adrenergic RBF response. In segmental arteries from normo- and hypertensive rats, inhibition of KV7 channels significantly decreased the β-adrenergic vasorelaxation. However, inhibiting BKCa channels was equally effective in reducing the β-adrenergic vasorelaxation. The β-adrenergic vasorelaxation was not different between segmental arteries from wild-type mice and mice lacking KV7.1 channels. As opposed to rats, inhibition of KV7 channels did not affect the murine β-adrenergic vasorelaxation. Although inhibition and activation of KV7 channels or BKCa channels significantly changed baseline RBF in vivo, none of the treatments affected β-adrenergic vasodilatation. In isolated segmental arteries, however, inhibition of KV7 and BKCa channels significantly reduced the β-adrenergic vasorelaxation, indicating that the regulation of RBF in vivo is driven by several actors in order to maintain an adequate RBF. Our data illustrates the challenge in extrapolating results from in vitro to in vivo conditions.

Chronic intermittent hypoxia promotes glomerular hyperfiltration and potentiates hypoxia-evoked decreases in renal perfusion and PO2.

Introduction: Sleep apnea (SA) is highly prevalent in patients with chronic kidney disease and may contribute to the development and/or progression of this condition. Previous studies suggest that dysregulation of renal hemodynamics and oxygen flux may play a key role in this process. The present study sought to determine how chronic intermittent hypoxia (CIH) associated with SA affects regulation of renal artery blood flow (RBF), renal microcirculatory perfusion (RP), glomerular filtration rate (GFR), and cortical and medullary tissue PO2 as well as expression of genes that could contribute to renal injury. We hypothesized that normoxic RBF and tissue PO2 would be reduced after CIH, but that GFR would be increased relative to baseline, and that RBF, RP, and tissue PO2 would be decreased to a greater extent in CIH vs. sham during exposure to intermittent asphyxia (IA, FiO2 0.10/FiCO2 0.03). Additionally, we hypothesized that gene programs promoting oxidative stress and fibrosis would be activated by CIH in renal tissue. Methods: All physiological variables were measured at baseline (FiO2 0.21) and during exposure to 10 episodes of IA (excluding GFR). Results: GFR was higher in CIH-conditioned vs. sham (p < 0.05), whereas normoxic RBF and renal tissue PO2 were significantly lower in CIH vs. sham (p < 0.05). Reductions in RBF, RP, and renal tissue PO2 during IA occurred in both groups but to a greater extent in CIH (p < 0.05). Pro-oxidative and pro-fibrotic gene programs were activated in renal tissue from CIH but not sham. Conclusion: CIH adversely affects renal hemodynamic regulation and oxygen flux during both normoxia and IA and results in changes in renal tissue gene expression.

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.

Role of coagulation in persistent renal ischemia following reperfusion in an animal model.

Ischemic acute kidney injury is common, deadly, and accelerates the progression of chronic kidney disease, yet has no specific therapy. After ischemia, reperfusion is patchy with early and persistent impairment in regional renal blood flow and cellular injury. We tested the hypothesis that intrarenal coagulation results in sustained renal ischemia following reperfusion, using a well-characterized model. Markedly decreased, but heterogeneous, microvascular plasma flow with microthrombi was found postischemia by intravital microscopy. Widespread tissue factor expression and fibrin deposition were also apparent. Clotting was accompanied by complement activation and inflammation. Treatment with exosomes derived from renal tubular cells or with the fibrinolytic urokinase, given 24 h postischemia when renal failure was established, significantly improved microvascular flow, coagulation, serum creatinine, and histological evidence of injury. These data support the hypothesis that intrarenal clotting occurs early and the resultant sustained ischemia is a critical determinant of renal failure following ischemia; they demonstrate that the coagulation abnormalities are amenable to therapy and that therapy results in improvement in both function and postischemic inflammation.NEW & NOTEWORTHY Ischemic renal injury carries very high morbidity and mortality, yet has no specific therapy. We found markedly decreased, heterogeneous microvascular plasma flow, tissue factor induction, fibrin deposition, and microthrombi after renal ischemia-reperfusion using a well-characterized model. Renal exosomes or the fibrinolytic urokinase, administered after renal failure was established, improved microvascular flow, coagulation, renal function, and histology. Data demonstrate that intrarenal clotting results in sustained ischemia amenable to therapy that improves both function and postischemic inflammation.

Divergent roles of angiotensin II upon the immediate and sustained increases of renal blood flow following unilateral nephrectomy.

Although the molecular and functional responses related to renal compensatory hypertrophy after unilateral nephrectomy (UNX) has been well described, many aspects of these events remain unclear. One question is how the remaining kidney senses the absence of the contralateral organ, and another is what the role of the renin-angiotensin system is in these responses. Both acute anesthetized and chronic unanesthetized experiments were performed using the angiotensin II type 1 receptor blocker losartan and the renin inhibitor aliskiren to determine the contribution of the renin-angiotensin system to immediate changes and losartan for chronic changes of renal blood flow (RBF) and the associated hypertrophic events in male Sprague-Dawley rats. Chronic experiments used implanted RBF probes and arterial catheters for continuous data collection, and the glomerular filtration rate was determined by noninvasive transcutaneous FITC-sinistrin measurements. The results of the acute experiments found that RBF increased nearly 25% (4.6 ± 0.5 to 5.6 ± 0.6 mL/min/g kidney wt) during the first 15 min following UNX and that this response was abolished by losartan (6.7 ± 0.7 to 7.0 ± 0.7 mL/min/g kidney wt) or aliskiren (5.8 ± 0.4 to 6.0 ± 0.4 mL/min/g kidney wt) treatment. Thereafter, RBF increased progressively over 7 days, and kidney weight increased by 19% of pre-UNX values. When normalized to kidney weight determined at day 7 after UNX, RBF was not significantly different from pre-UNX levels. Semiquantification of CD31-positive capillaries revealed increases of the glomeruli and peritubular capillaries that paralleled the kidney hypertrophy. None of these chronic changes was inhibited by losartan treatment, indicating that neither the compensatory structural nor the RBF changes were angiotensin II type 1 receptor dependent.NEW & NOTEWORTHY This study found that the immediate increases of renal blood flow (RBF) following unilateral nephrectomy (UNX) are a consequence of reduced angiotensin II type 1 (AT1) receptor stimulation. The continuous monitoring of RBF and intermittent measurement of glomerular filtration rate (GFR) in conscious rats during the 1-wk period of rapid hypertrophy following UNX provided unique insights into the regulation of RBF and GFR when faced with increased metabolic loads. It was found that neither kidney hypertrophy nor the associated increase of capillaries was an AT1-dependent phenomenon.

Long-Term Continuous Measurement of Renal Blood Flow in Conscious Rats.

The kidneys play a crucial role in maintaining the homeostasis of body fluids. The regulation of renal blood flow (RBF) is essential to the vital functions of filtration and metabolism in kidney function. Many acute studies have been carried out in anesthetized animals to measure RBF under various conditions to determine mechanisms responsible for the regulation of kidney perfusion. However, for technical reasons, it has not been possible to measure RBF continuously (24 h/day) in unrestrained unanesthetized rats over prolonged periods. These methods allow the continuous determination of RBF over many weeks while also simultaneously recording blood pressure (BP) with implanted catheters (fluid-filled or by telemetry). RBF monitoring is carried out with rats placed in a circular servo-controlled rat cage that enables the unrestrained movement of the rat throughout the study. At the same time, the tangling of cables from the flow probe and arterial catheters is prevented. Rats are first instrumented with an ultrasonic flow probe placement on the left renal artery and an arterial catheter implanted in the right femoral artery. These are routed subcutaneously to the nape of the neck, and connected to the flowmeter and pressure transducer, respectively, to measure RBF and BP. Following surgical implantation, rats are immediately placed in the cage to recover for at least one week and stabilize the ultrasonic probe recordings. Urine collection is also feasible in this system. The surgical and post-surgical procedures for continuous monitoring are demonstrated in this protocol.

Store-operated calcium entry: Pivotal roles in renal physiology and pathophysiology.

Research conducted over the last two decades has dramatically advanced the understanding of store-operated calcium channels (SOCC) and their impact on renal function. Kidneys contain many types of cells, including those specialized for glomerular filtration (fenestrated capillary endothelium, podocytes), water and solute transport (tubular epithelium), and regulation of glomerular filtration and renal blood flow (vascular smooth muscle cells, mesangial cells). The highly integrated function of these myriad cells effects renal control of blood pressure, extracellular fluid volume and osmolality, electrolyte balance, and acid-base homeostasis. Many of these cells are regulated by Ca2+ signaling. Recent evidence demonstrates that SOCCs are major Ca2+ entry portals in several renal cell types. SOCC is activated by depletion of Ca2+ stores in the sarco/endoplasmic reticulum, which communicates with plasma membrane SOCC via the Ca2+ sensor Stromal Interaction Molecule 1 (STIM1). Orai1 is recognized as the main pore-forming subunit of SOCC in the plasma membrane. Orai proteins alone can form highly Ca2+ selective SOCC channels. Also, members of the Transient Receptor Potential Canonical (TRPC) channel family are proposed to form heteromeric complexes with Orai1 subunits, forming SOCC with low Ca2+ selectivity. Recently, Ca2+ entry through SOCC, known as store-operated Ca2+ entry (SOCE), was identified in glomerular mesangial cells, tubular epithelium, and renovascular smooth muscle cells. The physiological and pathological relevance and the characterization of SOCC complexes in those cells are still unclear. In this review, we summarize the current knowledge of SOCC and their roles in renal glomerular, tubular and vascular cells, including studies from our laboratory, emphasizing SOCE regulation of fibrotic protein deposition. Understanding the diverse roles of SOCE in different renal cell types is essential, as SOCC and its signaling pathways are emerging targets for treatment of SOCE-related diseases.

Activation of the AMP-related kinase (AMPK) induces renal vasodilatation and downregulates Nox-derived reactive oxygen species (ROS) generation

AMP-activated protein kinase (AMPK) is a cellular energy sensor activated during energy stress to stimulate ATP production pathways and restore homeostasis. AMPK is widely expressed in the kidney and involved in mitochondrial protection and biogenesis upon acute renal ischemia, AMPK activity being blunted in metabolic disease-associated kidney disease. Since little is known about AMPK in the regulation of renal blood flow, the present study aimed to assess the role of AMPK in renal vascular function. Functional responses to the selective AMPK activator A769662 were assessed in intrarenal small arteries isolated from the kidney of renal tumour patients and Wistar rats and mounted in microvascular myographs to perform simultaneous measurements of intracellular calcium [Ca2+]i and tension. Superoxide (O2.-) and hydrogen peroxide (H2O2) production were measured by chemiluminescence and fluorescence and protein expression by Western blot. Activation of AMPK with A769662 increased AMPKα phosphorylation at Thr-172 and induced potent relaxations compared to AICAR in isolated human and rat intrarenal arteries, through both endothelium-dependent mechanisms involving nitric oxide (NO) and intermediate-conductance calcium-activated potassium (IKCa) channels, as well as activation of ATP-sensitive (KATP) channels and sarcoplasmic reticulum Ca2+-ATPase (SERCA) in vascular smooth muscle (VSM). Furthermore, AMPK activator reduced NADPH oxidase 4 (Nox4) and Nox2-derived reactive oxygen species (ROS) production. These results demonstrate that A769662 has potent vasodilator and antioxidant effects in intrarenal arteries. The benefits of AMPK activation in rat kidney are reproduced in human arteries and therefore vascular AMPK activation might be a therapeutic target in the treatment of metabolic disease-associated kidney injury.

DHHC21‐mediated α1 Adrenergic Receptor Palmitoylation Contributes to Renal Blood Flow Regulation During Sepsis

Palmitoylation is a reaction of 16‐carbon palmitic acid attachment to a cysteine residue of a protein via thioester linkage, catalyzed by a family of palmitoyl acyltransferases containing the DHHC motif. This post‐translational modification plays a critical role in regulating protein function, subcellular localization and interactions with other cellular molecules. A recent study shows that vascular α1 adrenergic receptor (α1AR) requires DHHC21‐mediated palmitoylation for its signaling activity to induce vasoconstriction. In the kidney, arterial vasoconstriction has been implicated in the development of renal hypoperfusion following sepsis. In this study, we sought to examine whether DHHC21 contributes to kidney dysfunction by affecting renal blood flow through α1AR palmitoylation. Cecal ligation puncture (CLP) was performed to induce polymicrobial sepsis in wild type and DHHC21 functional deficient (Zdhhc21dep/dep) mice. Their renal function was dynamically assessed based on tracer (IRdye 800CW) clearance measured by multispectral optoacoustic tomography (MSOT). The results showed that in wild‐type mice, IRdye 800CW movement from kidney cortex to the medulla/pelvis region was significantly slower after CLP, compared to sham control. The sepsis‐induced impairment in renal clearance was alleviated in Zdhhc21dep/dep mice. Consistently, histological analysis (Periodic acid‐Schiff staining) revealed that CLP caused kidney structural damages, evidenced by tubular vacuolation, brush border loss, tubular cell detachment and leukocyte infiltration; these pathologies were greatly ameliorated in DHHC21 loss‐of‐function mice. Moreover, compared with wild‐type mice, Zdhhc21dep/dep mice exhibited reduced CLP‐induced increases in circulating creatinine and urea nitrogen. Mechanistically, a decreased ratio of oxygenated to deoxygenated hemoglobin was detected in kidneys of wild‐type mice following CLP, suggesting renal tissue hypoxia in response to sepsis. We then asked whether this lack of oxygenation is associated with reduced renal blood flow due to arterial constriction and whether α1AR palmitoylation is involved in this process. Indeed, we found a significant increase in α1AR palmitoylation, along with activation of the α1AR downstream effector ERK, in renal arteries of wild‐type mice following CLP. These molecular responses occurred concomitantly with a reduced renal blood flow, measured by a transonic flowmeter. In contrast, sepsis‐induced α1AR palmitoylation/activation in renal arteries was greatly attenuated in Zdhhc21dep/dep mice, consistent with a better‐preserved renal blood flow in these mice. Taken together, our findings indicate that DHHC21‐mediated α1AR palmitoylation contributes to renal blood flow reduction and kidney injury during sepsis.Support or Funding InformationThis work was supported by the National Institutes of Health Grant HL070752 (to SYY)

Endothelin-1 Mediates the Systemic and Renal Hemodynamic Effects of GPR81 Activation.

GPR81 (G-protein-coupled receptor 81) is highly expressed in adipocytes, and activation by the endogenous ligand lactate inhibits lipolysis. GPR81 is also expressed in the heart, liver, and kidney, but roles in nonadipose tissues are poorly defined. GPR81 agonists, developed to improve blood lipid profile, might also provide insights into GPR81 physiology. Here, we assessed the blood pressure and renal hemodynamic responses to the GPR81 agonist, AZ'5538. In male wild-type mice, intravenous AZ'5538 infusion caused a rapid and sustained increase in systolic and diastolic blood pressure. Renal artery blood flow, intrarenal tissue perfusion, and glomerular filtration rate were all significantly reduced. AZ'5538 had no effect on blood pressure or renal hemodynamics in Gpr81-/- mice. Gpr81 mRNA was expressed in renal artery vascular smooth muscle, in the afferent arteriole, in glomerular and medullary perivascular cells, and in pericyte-like cells isolated from kidney. Intravenous AZ'5538 increased plasma ET-1 (endothelin 1), and pretreatment with BQ123 (endothelin-A receptor antagonist) prevented the pressor effects of GPR81 activation, whereas BQ788 (endothelin-B receptor antagonist) did not. Renal ischemia-reperfusion injury, which increases renal extracellular lactate, increased the renal expression of genes encoding ET-1, KIM-1 (Kidney Injury Molecule 1), collagen type 1-α1, TNF-α (tumor necrosis factor-α), and F4/80 in wild-type mice but not in Gpr81-/- mice. In summary, activation of GPR81 in vascular smooth muscle and perivascular cells regulates renal hemodynamics, mediated by release of the potent vasoconstrictor ET-1. This suggests that lactate may be a paracrine regulator of renal blood flow, particularly relevant when extracellular lactate is high as occurs during ischemic renal disease.

The renal molecular clock: broken by aging and restored by exercise.

The mammalian circadian clock governs physiological, endocrine, and metabolic responses coordinated in a 24-h rhythmic pattern by the suprachiasmatic nucleus (SCN) of the anterior hypothalamus. The SCN also dictates circadian rhythms in peripheral tissues like the kidney. The kidney has several important physiological functions, including removing waste and filtering the blood and regulating fluid volume, blood osmolarity, blood pressure, and Ca2+ metabolism, all of which are under tight control of the molecular/circadian clock. Normal aging has a profound influence on renal function, central and peripheral circadian rhythms, and the sleep-wake cycle. Disrupted circadian rhythms in the kidney as a result of increased age likely contribute to adverse health outcomes such as nocturia, hypertension, and increased risk for stroke, cardiovascular disease, and end organ failure. Regular physical activity improves circadian misalignment in both young and old mammals, although the precise mechanisms for this protection remain poorly described. Recent advances in the heart and skeletal muscle literature suggest that regular endurance exercise entrains peripheral clocks, and we propose that similar beneficial adaptations occur in the kidney through regulation of renal blood flow and fluid balance.

SUN-281 Electrically stimulated acupuncture improve muscle function and increases renal blood flow through exosomes-carried miR-181

our previous study found that acupuncture with low frequency electrical stimulation (Acu/LFES) can prevent muscle atrophy by increasing muscle protein anabolism in mouse models of chronic kidney disease and diabetes. Previous other studies have found that Acu/LFES decreases urinary albumin secretion and improves renal blood flow and GFR in nephropathy patients and animals. We hypothesized that Acu/LFES has benefits on both skeletal muscle and kidney. Normal C56BL6 mice were awake without any anesthesia and appeared to be comfortable throughout the Acu/LFES. Acupuncture points selected were according to the WHO Standard Acupuncture guidelines. The mice were treated with Acu/LFES (anode: Yang Ling Quan, GB34 and cathode: Zu San Li, ST36) daily for 15 days. Renal plasma flow was measured by p-Aminohippuric acid infusion (PAH Colorimetric Assay Kit, BioVision Inc.). Glomerular filtration rate was determined using inulin infusion and measured with a FIT-GFR kit (BioPhysics Assay Lab, Inc.). Muscle function was measured using a mouse grip strength meter. Exosomes were isolated by serial centrifugations. A miR deep sequencing assay and qPCR were used to identify microRNA expression in exosomes. Skeletal muscle function and protein anabolic markers were increased after Acu/LFES treatment. Interestingly, PAH clearance was increased by 45% in the mice after 15 minutes of Acu/LFES versus mice with sham Acu/LFES (sham 6.1 ± 1.3 vs. Acu/LFES 8.9 ± 2.7 ml/min/g BW, P = 0.009, n=8/group). In additional, inulin clearance was increased 39.8% (sham 65.9 ± 16.3 vs. Acu/LFES108.9 ± 19.7 ul/min/BW, P = 0.014). We found that Acu/LFES increases serum exosome abundance (Figure 1). When exosome secretion was blocked using GW4869, the Acu/LFES-induced increase in renal blood flow and GFR were limited. To identify how exosomes regulate renal blood flow, we performed microRNA deep sequencing of exosomes isolated from mouse serum and found that 34 microRNAs were altered by Acu/LFES. Notably, miR-181d-5p, a microRNA that is involved in regulating translation of renin, was significantly increased in the serum exosomes of Acu/LFES treated mice. Using a luciferase reporter assay, we demonstrated that miR-181 directly inhibits angiotensinogen, which provides potential evidence of Acu/LFES regulation of renal blood flow. Acu/LFES not only improves muscle function, but also increases miR-181 in serum exosomes and increases renal blood flow, suggesting that miR181 may regulate renal blood flow possibly by influencing the renin-angiotensin system. This study provides new insights about the mechanism(s) of muscle-organ cross talk through exosome-derived microRNA.

Electrically‐stimulated acupuncture improves muscle function and increases renal blood flow through exosomes‐carried miR‐181

Introductionour previous study found that acupuncture with low frequency electrical stimulation (Acu/LFES) can prevent muscle atrophy by increasing muscle protein anabolism in mouse models of chronic kidney disease, diabetes and denervation. Previous other studies have found that Acu/LFES improves renal blood flow and GFR in nephropathy patients and animals. We hypothesized that Acu/LFES benefits both skeletal muscle and kidney possibly through exosome carried microRNA.MethodsNormal C57BL6 mice were awake without any anesthesia and appeared to be comfortable throughout the Acu/LFES. Acupuncture points selected were according to the WHO Standard Acupuncture guidelines. The mice were treated with Acu/LFES (anode: Yang Ling Quan, GB34 and cathode: Zu San Li, ST36) daily for 15 days. Renal plasma flow was measured by p‐Aminohippuric acid infusion. Glomerular filtration rate was determined using inulin infusion and measured with a FIT‐GFR kit. Exosomes were isolated by serial centrifugations. A miR deep sequencing assay and qPCR were used to identify microRNA expression in exosomes.ResultsSkeletal muscle grip function and muscle regeneration markers were increased after Acu/LFES treatment. Acu/LFES increased muscle cross‐sectional area in normal mice vs. sham Acu‐LFES mice. The abundance of Pax7, MyoD, myogenin and embryo myosin heavy chain was significantly increased by Acu‐LFES in soleus, extensor digitorum longus (EDL) and gastrocnemius muscle. The number of central nuclei was increased in Acu‐LFES treated muscle fibers. Interestingly, PAH clearance was increased by 45% in the mice after 15 minutes of muscle Acu/LFES versus mice with sham Acu/LFES (sham 6.1 ± 1.3 vs. Acu/LFES 8.9 ± 2.7 ml/min/g BW, P = 0.009, n=8/group). Inulin clearance was increased 39.8% (sham 65.9 ± 16.3 vs. Acu/LFES108.9 ± 19.7 ul/min/BW, P = 0.014). We found that Acu/LFES increases serum exosome abundance. When exosome secretion was blocked using GW4869, the Acu/LFES‐induced increase in renal blood flow and GFR were limited. To identify how exosomes regulate renal blood flow, we performed microRNA deep sequencing of exosomes isolated from mouse serum and found that 34 microRNAs were altered by Acu/LFES. Notably, miR‐181d‐5p, a microRNA that is involved in regulating translation of renin, was significantly increased in the serum exosomes of Acu/LFES treated mice. Using a luciferase reporter assay, we demonstrated that miR‐181 directly inhibits angiotensinogen, which provides potential evidence of Acu/LFES regulation of renal blood flow.ConclusionsAcu/LFES not only improves muscle function, but also increases miR‐181 in serum exosomes and increases renal blood flow, suggesting that miR181 may regulate renal blood flow possibly by influencing the renin‐angiotensin system. This study provides new insights about the mechanism(s) of muscle‐organ cross talk through exosome‐delivered microRNA.Support or Funding InformationNIH R01 AR060268 and AHA 17IBDG33780000This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

TRPV1 protects renal ischemia-reperfusion injury in diet-induced obese mice by enhancing CGRP release and increasing renal blood flow.

BackgroundObesity is a major risk factor for end-stage renal disease. Using transient receptor potential vanilloid 1 knockout (TRPV1−/−) mice, we tested the hypothesis that TRPV1 protects against obesity-induced exacerbation of renal ischemia-reperfusion (I/R) injury.MethodsTRPV1−/− and wild-type (WT) mice were fed a chow or Western diet (WD) for 22–23 weeks. After that, mice were subjected to renal I/R injury, and renal cortical blood flow (CBF) and medullary blood flow (MBF) were measured.ResultsThe Western diet significantly increased body weight and fasting blood glucose levels in both TRPV1−/− and WT mice. WD-induced impairment of glucose tolerance was worsened in TRPV1−/− mice compared with WT mice. WD intake prolonged the time required to reach peak reperfusion in the cortex and medulla (both P < 0.05), decreased the recovery rate of CBF (P < 0.05) and MBF (P < 0.05), and increased blood urea nitrogen, plasma creatinine, and urinary 8-isoprostane levels after I/R in both mouse strains, with greater effects in TRPV1−/− mice (all P < 0.05). Renal I/R increased calcitonin gene-related peptide (CGRP) release in WT but not in TRPV1−/− mice, and WD attenuated CGRP release in WT mice. Moreover, blockade of CGRP receptors impaired renal regional blood flow and renal function in renal I/R injured WT mice.ConclusionThese results indicate that TRPV1 plays a protective role in WD-induced exacerbation of renal I/R injury probably through enhancing CGRP release and increasing renal blood flow.

The role of l-type calcium channels in the mediation of fast oscillation of arterial blood pressure and renal blood flow in rats

The investigation of dynamic characteristics of blood pressure and renal blood flow provides detailed information about the fast regulatory mechanisms involved in arterial blood pressure (ABP) and renal blood flow (RBF) autoregulation. The aim of our study was to investigate the role of L-type Ca2+ channels in the mediation of fast oscillations of arterial blood pressure and renal blood flow in rats by means of spectral analysis. The experiments were performed on anesthetized male Wistar rats (n=7) at the age of 12-14 weeks. The ABP was measured directly in femoral artery; RBF was registered by perivascular ultrasonic Doppler probe (Transonic system) in control and experimental period. The spectrograms from APB and RBF were derived in Lab View 3.11 software. In experimental period the selective L-type Ca2+ channel blocker amlodipine besylate (AML) in dose 200 mkg.kg-1 bolus followed by 50 mkg.kg-1.h infusions was applied. Our results by using a spectral method of analysis of ABP and RBF confirmed involvement of L-type Ca2+ channels in the mediation of dynamic nature of myogenic vascular response. The L-type Ca2+ channels in different specific manner participate in the regulation of renal blood flow and arterial blood pressure.

Non‐invasive Multiparametric MRI of the Kidneys

MRI can provide information of renal physiological parameters in a safe, non-invasive and relatively fast way. In this study we determined baseline values for total (tRBF) and regional (rRBF) renal blood flow, regional oxygenation level (R2*), regional true (D) and apparent (ADC) diffusion and regional T1 in healthy volunteers using the MRI techniques of Phase Contrast (PC), Arterial Spin Labeling (ASL), Blood Oxygen Level Dependent R2* (BOLD), Diffusion Weighted Imaging (DWI) and T1. Measurements of ADC and T1 are of interest since they have been shown to correlate to the degree of fibrosis. 28 healthy volunteers (15 female, 13 male) were recruited and underwent a 3T MRI scan. Since no significant differences of the investigated biomarkers were found between the corresponding regions in the left and right kidney or between the genders, only mean values are presented. Average tRBF through the kidney was 503±138 ml/min and global perfusion was 312±87 ml/min/100 g. Good correlations were found between tRBF and body surface area, BMI, and kidney volume. For cortex, outer and inner medulla, rRBF values, measured by ASL, were 290±63, 91±14 and 42±16 ml/min/100 g, resp, R2* values (BOLD) were 16.5±1.1, 26.8±1.6, and 36.8±3.8 s−1 resp, ADC values (DWI) were 2.43±0.17, 2.14±0.19 and 2.01±0.19 ×10−3 mm2/s resp, D values (DWI) were 2.11±0.23, 1.86±0.18 and 1.71±0.20 ×10−3 mm2/s resp and T1 values were 1146±76, 1403±170, and 1512±205 ms, resp. Significant interregional differences were found between cortex, outer and inner medulla in all studied parameters. In conclusion, MRI provides reliable and robust biomarkers for assessment of kidney function in an acceptable acquisition time. Knowledge of normal values of such functional biomarkers in different regions of the kidney is inevitable before their use in research or in clinical practice. Correlation between tRBF and Body Surface Area, BMI and Kidney volume ROI positions for ASL, BOLD, DWI and T1 This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Extravasal albumin concentration modulates contractile responses of renal afferent arterioles.

Afferent arterioles (AA) hold a key position in the regulation of renal blood flow and glomerular filtration rate. Being the effector site of tubuloglomerular feedback, the afferent arteriole contributes to the renal handling of sodium and fluid. Dehydration goes along with increased renal interstitial protein concentration. Here, the hypothesis was tested that extravasal protein concentration directly modulates afferent arteriolar tone, a mechanism which may contribute to body fluid volume control. The effect of increased extravasal albumin concentration on the vascular reactivity was investigated in renal AA and interlobar arteries of mice, in rat renal AA and in pancreatic islet arterioles. Albumin (2 and 4% in the bath solution) significantly potentiated the contractile response of renal afferent arterioles induced by angiotensin II and adenosine, as well as their combination, compared to the control situation (0.1% albumin). Albumin did not influence the contractility of larger renal vessels or pancreatic islet arterioles. Mimicking the increase in the osmolality induced by 4% albumin by applying mannitol to the bath solution also increased the response of renal arterioles to Ang II. However, the effect was smaller compared to that of albumin. The nitric oxide bioavailability, measured by DAF-FM fluorescence, was reduced in afferent arterioles exposed to 4% albumin. The protein-induced modulation of AA tone is mediated by the increased osmolality as well as by NO scavenging. The results suggest a possible contribution of these mechanisms to the control of extracellular fluid volume via adjustment of renal blood flow and glomerular filtration rate.

Cellular transport of l-arginine determines renal medullary blood flow in control rats, but not in diabetic rats despite enhanced cellular uptake capacity.

Diabetes mellitus is associated with decreased nitric oxide bioavailability thereby affecting renal blood flow regulation. Previous reports have demonstrated that cellular uptake of l-arginine is rate limiting for nitric oxide production and that plasma l-arginine concentration is decreased in diabetes. We therefore investigated whether regional renal blood flow regulation is affected by cellular l-arginine uptake in streptozotocin-induced diabetic rats. Rats were anesthetized with thiobutabarbital, and the left kidney was exposed. Total, cortical, and medullary renal blood flow was investigated before and after renal artery infusion of increasing doses of either l-homoarginine to inhibit cellular uptake of l-arginine or Nω-nitro- l-arginine methyl ester (l-NAME) to inhibit nitric oxide synthase. l-Homoarginine infusion did not affect total or cortical blood flow in any of the groups, but caused a dose-dependent reduction in medullary blood flow. l-NAME decreased total, cortical and medullary blood flow in both groups. However, the reductions in medullary blood flow in response to both l-homoarginine and l-NAME were more pronounced in the control groups compared with the diabetic groups. Isolated cortical tubular cells displayed similar l-arginine uptake capacity whereas medullary tubular cells isolated from diabetic rats had increased l-arginine uptake capacity. Diabetics had reduced l-arginine concentrations in plasma and medullary tissue but increased l-arginine concentration in cortical tissue. In conclusion, the reduced l-arginine availability in plasma and medullary tissue in diabetes results in reduced nitric oxide-mediated regulation of renal medullary hemodynamics. Cortical blood flow regulation displays less dependency on extracellular l-arginine and the upregulated cortical tissue l-arginine may protect cortical hemodynamics in diabetes.