Renal Blood Flow Rate Research Articles

Endothelial KCa 1.1 and KCa 3.1 channels mediate rat intrarenal artery endothelium-derived hyperpolarization response.

Endothelium-derived hyperpolarization (EDH)-mediated response plays an essential role in the control of kidney preglomerular circulation, but the identity of the K+ channels involved in this response is still controversial. We hypothesized that large- (KCa 1.1), intermediate- (KCa 3.1) and small (KCa 2.3) -conductance Ca2+ -activated K+ (KCa ) channels are expressed in the endothelium of the preglomerular circulation and participate in the EDH-mediated response. We study the functional expression of different K+ channels in non-cultured, freshly isolated native endothelial cells (ECs) of rat intrarenal arteries using immunofluorescence and the patch-clamp technique. We correlate this with vasorelaxant responses ex vivo using wire myography. Immunofluorescence revealed the expression of KCa 1.1, KCa 3.1 and KCa 2.3 channels in ECs. Under voltage-clamp conditions, acetylcholine induced a marked increase in the outward currents in these cells, sensitive to the blockade of KCa 1.1, KCa 3.1 and KCa 2.3 channels respectively. Isometric myography experiments, under conditions of endothelial nitric oxide synthase and cyclooxygenase inhibition, showed that blockade either of KCa 1.1 or KCa 3.1 channels was able to reduce the endothelium-derived vasorelaxation of isolated interlobar arteries, while their combined blockade completely abolished it. In contrast, blockade of KCa 2.3 channels did not reduce this vasorelaxant response, despite being functionally expressed in the endothelial cells. This study shows that KCa 1.1 and KCa 3.1 channels are functionally expressed at the renal vascular endothelium and play a central role in the EDH-mediated relaxation of kidney preglomerular arteries, which is important in the control of renal blood flow and glomerular filtration rate.

Percutaneous transluminal renal angioplasty attenuates poststenotic kidney mitochondrial damage in pigs with renal artery stenosis and metabolic syndrome.

Percutaneous transluminal renal angioplasty (PTRA) has been used to treat renovascular disease (RVD), a chronic condition characterized by renal ischemia and metabolic abnormalities. Mitochondrial injury has been implicated as a central pathogenic mechanism in RVD, but whether it can be reversed by PTRA remains uncertain. We hypothesized that PTRA attenuates mitochondrial damage, renal injury, and dysfunction in pigs with coexisting renal artery stenosis (RAS) and metabolic syndrome (MetS). Four groups of pigs (n = 6 each) were studied after 16 weeks of diet-induced MetS and RAS (MetS + RAS), MetS + RAS treated 4 weeks earlier with PTRA, and Lean and MetS Sham controls. Single-kidney renal blood flow (RBF) and glomerular filtration rate (GFR) were assessed in vivo with multidetector computed tomography, and renal tubular mitochondrial structure and function and renal injury ex vivo. PTRA successfully restored renal artery patency, but mean arterial pressure remained unchanged. Stenotic kidney RBF and GFR, which fell in MetS + RAS compared to MetS, rose after PTRA. PTRA attenuated MetS + RAS-induced mitochondrial structural abnormalities in tubular cells and peritubular capillary endothelial cells, decreased mitochondrial H2 02 production, and increased renal cytochrome-c oxidase-IV activity and ATP production. PTRA also improved cortical microvascular and peritubular capillary density and ameliorated tubular injury and tubulointerstitial fibrosis in the poststenotic kidney. Importantly, renal mitochondrial damage correlated with poststenotic injury and dysfunction. Renal revascularization attenuated mitochondrial injury and improved renal hemodynamics and function in swine poststenotic kidneys. This study suggests a novel mechanism by which PTRA might be relatively effective in ameliorating mitochondrial damage and improving renal function in coexisting MetS and RAS.

Kidney Physiology in Pregnancy.

A woman's body undergoes a myriad of changes throughout the course of a normal gestation. The kidneys play a central role in driving adjustments that guarantee maternal and fetal well-being, including a dramatic increase in glomerular filtration rate, alterations in tubular function, and changes in electrolyte and acid/base handling. Early in gestation, systemic vasodilation, driven by both a change in quantity of and response to various hormones, leads to increased renal blood flow and glomerular filtration rate. Vasodilation also results in activation of the renin-angiotensin-aldosterone axis, which combined with changing tubular handling causes alterations in total body stores of electrolytes and total body water, resulting in a lower serum sodium concentration. In addition, mild proteinuria, glucosuria, and a decrease in serum calcium and magnesium are common. The primary acid/base change seen in pregnancy is a mild respiratory alkalosis due to progesterone effects. This article provides an overview of the current understanding of the healthy response of the kidneys to pregnancy, an understanding of which is key to caring for the pregnant patient, and early identification of alterations that may indicate underlying kidney pathology in pregnancy.

Экспериментальная фармакокинетика новых нейротропных пептидных лекарственных средств

Представлены результаты исследований сравнительной экспериментальной фармакокинетики и метаболизма 3 новых нейротропных пептидных лекарственных препаратов: аналогов природных нейропептидов — ноотропного препарата ноопепт, антипсихотического средства — дилепт и селективного анксиолитика — соединения ГБ-115 у 2 видов животных (крыс и кроликов). Установлено, что эфирные производные нейропептидов ноопепт и дилепт, в отличие от анксиолитика ГБ-115, являющегося амидом, подвергаются интенсивной биотрансформации у крыс с образованием активного метаболита ноопепта — циклопролил-L-глицина (ЦПГ) и активного метаболита дилепта — капроил-L-пролил-L-тирозина (М-1). Фармакокинетические параметры, характеризующие распределение анксиолитика ГБ-115 у крыс, свидетельствуют о его возможном накоплении во внутренних органах и тканях, что следует учитывать при его повторном введении. Установлено, что изучаемые соединения в организме кроликов в меньшей степени подвергаются энзиматическому воздействию и более продолжительное время определяются в плазме крови в неизмененном виде, что связано не только со структурными особенностями изучаемых дипептидов, но и с различиями активности энзиматических систем ЖКТ, принимающих участие в их пресистемном метаболизме, а также с различиями в скорости печеночного и почечного кровотока у крыс и кроликов.

Recovery of Renal Function following Kidney-Specific VEGF Therapy in Experimental Renovascular Disease

Background: Chronic renovascular disease (RVD) can lead to a progressive loss of renal function, and current treatments are inefficient. We designed a fusion of vascular endothelial growth factor (VEGF) conjugated to an elastin-like polypeptide (ELP) carrier protein with an N-terminal kidney-targeting peptide (KTP). We tested the hypothesis that KTP-ELP-VEGF therapy will effectively recover renal function with an improved targeting profile. Further, we aimed to elucidate potential mechanisms driving renal recovery. Methods: Unilateral RVD was induced in 14 pigs. Six weeks later, renal blood flow (RBF) and glomerular filtration rate (GFR) were quantified by multidetector CT imaging. Pigs then received a single intrarenal injection of KTP-ELP-VEGF or vehicle. CT quantification of renal hemodynamics was repeated 4 weeks later, and then pigs were euthanized. Ex vivo renal microvascular (MV) density and media-to-lumen ratio, macrophage infiltration, and fibrosis were quantified. In parallel, THP-1 human monocytes were differentiated into naïve macrophages (M0) or inflammatory macrophages (M1) and incubated with VEGF, KTP-ELP, KTP-ELP-VEGF, or control media. The mRNA expression of macrophage polarization and angiogenic markers was quantified (qPCR). Results: Intrarenal KTP-ELP-VEGF improved RBF, GFR, and MV density and attenuated MV media-to-lumen ratio and renal fibrosis compared to placebo, accompanied by augmented renal M2 macrophages. In vitro, exposure to VEGF/KTP-ELP-VEGF shifted M0 macrophages to a proangiogenic M2 phenotype while M1s were nonresponsive to VEGF treatment. Conclusions: Our results support the efficacy of a new renal-specific biologic construct in recovering renal function and suggest that VEGF may directly influence macrophage phenotype as a possible mechanism to improve MV integrity and function in the stenotic kidney.

Hepatorenal syndrome: pathophysiology, diagnosis, and management

Hepatorenal syndrome (HRS), the extreme manifestation of renal impairment in patients with cirrhosis, is characterized by reduction in renal blood flow and glomerular filtration rate. Hepatorenal syndrome is diagnosed when kidney function is reduced but evidence of intrinsic kidney disease, such as hematuria, proteinuria, or abnormal kidney ultrasonography, is absent. Unlike other causes of acute kidney injury (AKI), hepatorenal syndrome results from functional changes in the renal circulation and is potentially reversible with liver transplantation or vasoconstrictor drugs. Two forms of hepatorenal syndrome are recognized depending on the acuity and progression of kidney injury. The first represents an acute impairment of kidney function, HRS-AKI, whereas the second represents a more chronic kidney dysfunction, HRS-CKD (chronic kidney disease). In this review, we provide critical insight into the definition, pathophysiology, diagnosis, and management of hepatorenal syndrome.

Abstract P004: Endothelial Function In Rat Juxtamedullary Afferent Arterioles After Renal Ischemia-reperfusion Injury

Renal ischemia-reperfusion (IR) induced kidney injury exhibits reduced renal blood flow (RBF) and glomerular filtration rate (GFR). Both RBF and GFR are regulated by renal microvascular function. Our previous study showed that IR caused impaired afferent arteriole autoregulatory capability via excess ROS accumulation and inflammation in renal microvessels. Other mechanisms contributing to renal microvascular dysfunction in IR have not been fully defined. In this study, we conducted acetylcholine (ACh) concentration-response experiments (n=5-7/each group) to assess endothelial function using the in vitro blood-perfused juxtamedullary nephron preparation. IR was induced by 60 minutes of bilateral renal artery occlusion followed by 24 hours or 7 days of reperfusion. Renal microvessels (RMV) were collected at either 24 hours or 7 days post-surgery for mRNA analysis. Systolic blood pressure was normal in IR rats vs. sham ranging from 126-136 mmHg (>0.05) over 7 days. IR markedly increased plasma creatinine concentration (Cr) to 3.9±0.2 mg/dL at 24 hours post-IR ( P <0.05 vs. 0.9±0.1 mg/dL in sham). Plasma Cr remained elevated in IR rats by day 7 of reperfusion (1.5±0.2 vs. 1.0±0.0 mg/dL in sham, P <0.05). Baseline afferent arteriole diameter was smaller in IR rats 24 hours post-IR and averaged 11.1±0.7 μm (P<0.05 vs. 14.2±0.7 μm in sham). Superfusion of ACh (10 -8 to 10 -4 M) caused concentration-dependent vasodilation in sham rats, increasing diameter to 23.5±2.6 μm (169±14% of the control, P <0.05) at 10 -4 M ACh. The ACh-induced vasodilation was not altered by IR insult and was indistinguishable from the sham responses. IR diameter reached a maximum of 19.7±0.9 μm (179±8% of the control) at 10 -5 M ACh. The ACh responses were also similar between sham and IR rats on day 7 post-IR. mRNA expression of endothelial markers, iCAM and vCAM, were not statistically different in RMV collected at 24 hours post-surgery between two groups, but was markedly elevated in IR RMV on day 7 post-IR (4-fold in iCAM and 2-fold in vCAM, P<0.05 vs. sham). In conclusion, upregulation of iCAM and vCAM mRNA expression in RMV 7 days post-IR suggests renal microvascular inflammation, but rat juxtamedullary afferent arterioles still maintain normal endothelium-dependent reactivity to ACh.

Abstract P147: Attenuation Of Diuretic And Natriuretic Responses To Acute Saline Volume Expansion In Mice Pre-treated With Tumor Necrosis Factor-alpha (TNFα) Inhibitor, Etanercept.

High salt intake induces an immune response that activates the mononuclear phagocyte system (MPS) cells to produce TNFα. We have previously demonstrated that intravenous infusion of TNFα in mice induces diuresis and natriuresis by inhibiting renal tubular sodium reabsorption. We hypothesize that the intravenous saline infusion can also induce the production of TNFα from MPS cells and such increase in TNFα influences saline induced natriuresis in the kidney. To examine this hypothesis, we measured the changes in TNFα levels in plasma and in urinary excretion rate (U TNFα V) during intravenous infusion of isotonic saline (0.9% NaCl), first at euvolemic condition (3 μL/min for 60 min; Baseline period) and then at an enhanced infusion rate (12 μL/min for 90 min; Volume expansion period) in anesthetized mice (n=5). Renal blood flow (RBF) and glomerular filtration rate (GFR) were measured by PAH and inulin clearances respectively. TNFα concentration in plasma and urine samples were determined using ELISA kit (Ebioscience, Woburn, MA). TNFα level in plasma collected during baseline period was undetectable, however, TNFα was increased to 3.7±1.3 pg/mL during volume expansion (VE) period. Baseline U TNFα V level was 0.01±0.002 pg/min/g (kidney wt), which was increased to 0.11±0.03 pg/min/g (P<0.05) during VE period. VE increased urine flow (V, 5.4±0.5 to 22.0±5.1 μL/min/g; P<0.05) and sodium excretion (U Na V; 0.54±0.19 to 4.84 ±1.16 μmol/min/g; P<0.05) without significant changes in RBF (7.1±1.0 to 6.0±1.8 mL/min/g) and GFR (1.18±0.11 to 0.94±0.28 mL/min/g). Interestingly, the diuretic and natriuretic responses to VE were markedly attenuated in mice (n=5) pretreated with a TNFα inhibitor, etanercept (ETN; 0.5 mg/kg intraperitoneally once daily for 3 days prior to the experiment day). VE induced changes in ETN treated mice are as follows: V, 5.9±0.65 to 7.9 ±1.6 μL/min/g; U Na V, 0.43±0.6 to 1.1±0.28 μmol/min/g; RBF, 5.4±0.4 to 6.6±0.9 mL/min/g and GFR, 0.87±0.09 to 0.98±0.13 mL/min/g. These findings demonstrate for the first time that an intravenous saline volume infusion resulted an increase in TNFα level in plasma and in urine. These results strongly suggest a physiological role for TNFα in regulating renal excretory function during saline volume expansion.

Purinoceptors, renal microvascular function and hypertension.

Proper renal blood flow (RBF) and glomerular filtration rate (GFR) are critical for maintaining normal blood pressure, kidney function and water and electrolyte homeostasis. The renal microvasculature expresses a multitude of receptors mediating vasodilation and vasoconstriction, which can influence glomerular blood flow and capillary pressure. Despite this, RBF and GFR remain quite stable when arterial pressure fluctuates because of the autoregulatory mechanism. ATP and adenosine participate in autoregulatory control of RBF and GFR via activation of two different purinoceptor families (P1 and P2). Purinoceptors are widely expressed in renal microvasculature and tubules. Emerging data show altered purinoceptor signaling in hypertension-associated kidney injury, diabetic nephropathy, sepsis, ischemia-reperfusion induced acute kidney injury and polycystic kidney disease. In this brief review, we highlight recent studies and new insights on purinoceptors regulating renal microvascular function and renal hemodynamics. We also address the mechanisms underlying renal microvascular injury and impaired renal autoregulation, focusing on purinoceptor signaling and hypertension-induced renal microvascular dysfunction. Interested readers are directed to several excellent and comprehensive reviews that recently covered the topics of renal autoregulation, and nucleotides in kidney function under physiological and pathophysiological conditions (Inscho 2009, Navar et al. 2008, Carlstrom et al. 2015, Vallon et al. 2020).

Extracellular vesicles released by adipose tissue-derived mesenchymal stromal/stem cells from obese pigs fail to repair the injured kidney.

Aims:Mesenchymal stromal/stem cell (MSC)-derived extracellular vesicles (EVs) shuttle select MSC contents and are endowed with an ability to repair ischemic tissues. We hypothesized that exposure to cardiovascular risk factors may alter the microRNA cargo of MSC-derived EVs, blunting their capacity to repair the post-stenotic kidney in pigs with metabolic syndrome (MetS) and renal artery stenosis (RAS).Methods:Porcine MSCs were harvested from abdominal fat after 16wks of Lean- or MetS-diet, and their EVs isolated and characterized using microRNA-sequencing. Lean- and MetS-EV protective effects were assessed in-vitro in human umbilical endothelial cells (HUVECs). To compare their in-vivo efficacy to repair ischemic tissues, allogeneic-EVs were intrarenally delivered in pigs after 6wks of MetS + RAS, and 4wks later, single-kidney renal blood flow (RBF) and glomerular filtration rate (GFR) were studied in-vivo, and microvascular architecture and injury ex-vivo. Lean-, MetS-, and MetS + RAS-sham served as controls (n = 6 each).Results:Ten microRNAs, capable of targeting several pro-angiogenic genes, were upregulated in MetS-EVs versus Lean-EVs. In vitro, MetS-EVs failed to increase tube number and length, and to boost HUVEC migration compared to Lean-EVs. Lean- and MetS-EVs were detected in the stenotic-kidney 4wks after injection in the vicinity of small vessels. RBF and GFR were lower in MetS + RAS versus MetS, and restored in MetS + RAS + Lean-EVs, but not in MetS + RAS + MetS-EVs. Furthermore, MetS-EVs failed to restore renal expression of angiogenic factors, improve microvascular density, or attenuate fibrosis.Conclusions:MetS alters the microRNA cargo of MSC-derived EVs and impairs their functional potency, limiting the therapeutic efficacy of this endogenous cellular repair system.

Renal Ischemia‐Reperfusion Impairs Whole Kidney Blood Flow Autoregulation in Male and Female Rats

Renal autoregulation is critical in maintaining a stable renal blood flow (RBF) and glomerular filtration rate over a wide range of renal perfusion pressure. Our recent in vitro work demonstrated that accumulating reactive oxygen species (ROS) contribute to loss of renal autoregulatory capability in ischemia reperfusion (IR)‐induced acute kidney injury (IR‐AKI) in male rats. Evidence shows that sex differences might contribute to differential injury in IR‐AKI. Therefore, we hypothesized that renal IR leads to impaired RBF autoregulation which may be associated with ROS accumulation and inflammation in male and female rats. IR was induced by occluding both renal arteries for 60 minutes followed by 24 hours or 1 week of reperfusion. Plasma creatinine was markedly increased in IR rats but more so in males than females at 24 hours (3.8±0.2 vs 1.9±0.4 mg/dl, P<0.05, n=7/group). Plasma creatinine was still elevated in IR males one week post‐IR (1.3±0.1 vs 1.1±0.0 mg/dl in sham, P<0.05, n=13–14/group). Whole kidney autoregulation was assessed in vivo. IR significantly lowered baseline RBF in males (5.9±0.6 vs. 9.1±0.5 ml/min/gkw in sham, P<0.05, n=6/group) but not in females (8.3±0.6 vs. 10.3±0.9 ml/min/gkw in sham, P>0.05, n=5–8/group) 24 hours post‐IR. RBF was lower in IR males compared to IR females (P<0.05). RBF decreased further in IR rats at week 1 (4.1±1.0 ml/min/gkw in males and 4.5±0.2 ml/min/gkw in females, n=2–3). RBF remained constant during stepwise reduction of renal perfusion pressure from 120 to 100 mmHg in both sham males and females at 24 hours and 1 week, indicating intact autoregulation as reflected by autoregulatory index (ARI) between 0.1±0.0 and 0.2±0.1. IR led to impaired RBF autoregulation in males at 24 hours and 1 week, and in females at 24 hours as indicated by ARI between 0.8±0.1 and 1.1±0.2. Interestingly, autoregulation partially recovered in females at week 1 as indicated by ARI of 0.5. Preglomerular microvessels (PGMV) were collected for mRNA measurement (n=4–7 rats/each group). IR increased mRNA expression of p67phox in males at 24 hours (7.3±1.5 vs. 1.1±0.2 in sham, P<0.05) and 1 week (2.2±0.3 vs. 1.0±0.1 in sham, P<0.05). In contrast, IR elevated p67phox mRNA expression in females at 24 hours only (3.9±0.4 vs. 1.5±0.2 in sham, P<0.05) but to a lesser degree compared to IR males (P<0.05). The p47phox mRNA expression was elevated in IR males at 1 week (2±0.3 vs. 1.0±0.1 in sham, P<0.05) but remained unchanged in IR females. IR also markedly increased mRNA expression of MCP‐1 in both male and female rats at 24 hours and 1 week (P<0.05 vs respective sham). TGF‐β mRNA expression tends to increase in IR males at 24 hours and reached statistical significance at week 1 (2.5±0.2 vs 1.1±0.1 in sham, P<0.05). TGF‐β was significantly elevated in IR females though still lower compared to IR males at week 1 (1.7±0.2 vs 2.5±0.2, P<0.05). In conclusion, these results suggest that IR impairs RBF autoregulation in male and female rats which might be associated with activation of NOX, MCP‐1 and TGF‐β pathways in PGMV. Female rats have less kidney injury which might be attributed to less NOX expression in PGMV.Support or Funding InformationThis study was supported by grants from NIH (DK106500) to ZG, and NIH (DK044628 and HL095499) to EWI.

Renal hyperinsulinemia causes thickening of glomerular basement membrane independent of hypertension and hyperglycemia

IntroductionGlomerular basement membrane (GBM) thickening is one of the earliest detectable pathological features of obesity‐related kidney damage. Kidney damage observed in obesity or pre‐diabetic condition is almost always preceded with hyperinsulinemia but its role in the kidney damage is largely overlooked. Our unpublished preliminary data in ex‐vivo preparation of rabbit afferent‐arteriole suggests that insulin causes afferent‐arteriole dilation that may lead to glomerular hyperfiltration. Additionally, in humans insulin increases renal blood flow and glomerular filtration rate indicating potential role of insulin in renal pathology.HypothesisChronic renal hyperinsulinemia increases GBM thickness and this detrimental effect of insulin is independent of hyperglycemia and hypertension.Materials and methodsTo test this hypothesis, we infused insulin (1.8 IU/kg.bw/day) directly to the left kidney of male sprague dawley (SD) rats by custom made subcapsular catheter attached with osmotic minipumps for 6 weeks. Contralateral right kidney was also inserted with subcapsular catheter but without insulin infusion and served as internal control. Normal SD rats without any insulin infusion in any of its kidneys were also included in this study as a separate group for the comparison of various parameters. Blood glucose level was measured every week until 6 weeks of insulin infusion. At the end of the 6 weeks study, mean arterial pressure (MAP) was measured in inactin‐anesthetized rats using femoral artery catheter. Kidneys were perfused with normal saline and fixed by gluteraldehyde for the GBM thickness measurement using electron microscope.ResultsBlood glucose levels in the left‐kidney‐insulin‐infused rats were similar throughout the study including at the end of 6 weeks study to the normal non‐insulin infused SD rats group indicating no significant leakage of insulin (Normal SD rats: 104.5 ±10.3 vs. Insulin infused SD rats: 111.9±4.3mmol/L, p>0.05). MAP was also similar in both of these groups (Normal SD rats: 104.8±6.3 vs. Insulin infused SD rats: 99.7±5.5mmHg, p>0.05). GBM thickness was significantly increased in the insulin infused left kidney compared with contralateral non‐insulin infused right kidney (Insulin‐infused‐left kidney: 199.40±17.0 vs. contralateral non‐insulin infused right kidney: 149.57±5.12 nm, n=4, p<0.05) indicating renal hyperinsulinemia causes GBM thickening. Additionally, GBM thickness of normal SD rat’s kidney was similar to non‐insulin infused right kidney (Normal SD rat’s kidney: 145.53±3.58, n=3 vs. non‐insulin‐infused‐right kidney: 149.57±5.12 nm, n=4, p>0.05) and was significantly less compared to the insulin‐infused left kidney (Normal SD rat’s kidney: 145.53±3.58, n=3 vs. insulin‐infused‐left kidney: 199.40±17.0, n=4, p<0.05).ConclusionRenal hyperinsulinemia per se increases GBM thickness that is independent of systemic factors such as hyperglycemia and hypertension. To our knowledge, this is the first study that directly establishes the role of hyperinsulinemia in the initiation of kidney damage.PerspectiveHyperinsulinemia observed in obesity or prediabetic conditions may be a significant initiating factor in the renal damage possibly via glomerular hyperfiltration.Support or Funding InformationFund for Henry Ford Hospital (Monu,S).

Influence of connexin45 on renal autoregulation.

Renal autoregulation is mediated by the myogenic response and tubuloglomerular feedback (TGF) working in concert to maintain renal blood flow and glomerular filtration rate despite fluctuations in renal perfusion pressure. Intercellular communication through gap junctions may play a role in renal autoregulation. We examine if one of the building blocks in gap junctions, connexin45 (Cx45), which is expressed in vascular smooth muscle cells, has an influence on renal autoregulatory efficiency. The isolated perfused juxtamedullary nephron preparation was used to measure afferent arteriolar diameter changes in response to acute changes in renal perfusion pressure. In segmental arteries, pressure myography was used to study diameter changes in response to pressure changes. Wire myography was used to study vasoconstrictor and vasodilator responses. A mathematical model of the vascular wall was applied to interpret experimental data. We found a significant reduction in the afferent arteriolar constriction in response to acute pressure increases in Cx45 knockout (KO) mice compared with wild-type (WT) mice. Abolition of TGF caused a parallel upward shift in the autoregulation curve of WT animals but had no effect in KO animals, which is compatible with TGF providing a basal tonic contribution in afferent arterioles whereas Cx45 KO animals were functionally papillectomized. Analysis showed a shift toward lower stress sensitivity in afferent arterioles from Cx45 KO animals, indicating that the absence of Cx45 may also affect myogenic properties. Finally, loss of Cx45 in vascular smooth muscle cells appeared to associate with a change in both structure and passive properties of the vascular wall.

Therapeutic Effects of Hydralazine on Renal Ischemia-Reperfusion Injury in Rat.

Objective: Renal ischemia-reperfusion (I-R) induces acute kidney injury (AKI). In this study, the effect of hydralazine was investigated on the renal injury induced by the I-R in rats. Methods: AKI was induced with bilateral obstruction of the renal artery and vein for 20 minutes following with 24 hours of reperfusion. Hydralazine (5mg/kg) was injected intraperitoneally as post- treatment. Results: Hydralazine significantly increased the levels of renal clearance of creatinine and renal blood flow, while was decreasing by I-R. Also, hydralazine significantly improved levels of serum electrolytes (sodium and potassium) that were impaired by I-R. The tissue MDA levels were significantly suppressed by hydralazine. Conclusion: According to the results, the post treatment of hydralazine had a therapeutic effect on renal ischemia-reperfusion because improved ion reabsorption and excretion and increased renal blood flow and glomerular filtration rate and decreased lipid peroxidation.

Coexisting renal artery stenosis and metabolic syndrome magnifies mitochondrial damage, aggravating poststenotic kidney injury in pigs.

Renovascular disease (RVD) produces chronic underperfusion of the renal parenchyma and progressive ischemic injury. Metabolic abnormalities often accompany renal ischemia, and are linked to poorer renal outcomes. However, the mechanisms of injury in kidneys exposed to the ischemic and metabolic components of RVD are incompletely understood. We hypothesized that coexisting renal artery stenosis (RAS) and metabolic syndrome (MetS) would exacerbate mitochondrial damage, aggravating poststenotic kidney injury in swine. Domestic pigs were studied after 16 weeks of either standard diet (Lean) or high-fat/high-fructose (MetS) with or without superimposed RAS (n = 6 each). Single-kidney renal blood flow (RBF) and glomerular filtration rate (GFR) were assessed in vivo with multidetector-CT, and renal tubular mitochondrial structure, homeostasis and function and renal injury ex vivo. Both RAS groups achieved significant stenosis. Single-kidney RBF and GFR were higher in MetS compared with Lean, but decreased in Lean+RAS and MetS+RAS vs. their respective controls. MetS and RAS further induced changes in mitochondrial structure, dynamics, and function, and their interaction (diet × ischemia) decreased matrix density, mitophagy, and ATP production, and lead to greater renal fibrosis. Coexisting RAS and MetS synergistically aggravate mitochondrial structural damage and dysfunction, which may contribute to structural injury and dysfunction in the poststenotic kidney. These observations suggest that mitochondrial damage precedes loss of renal function in experimental RVD, and position mitochondria as novel therapeutic targets in these patients.

Abstract P1115: Decreased Tubuloglomerular Feedback (TGF) Response in High-Fat Diet Induced Obesity

Obesity is associated with increased renal and glomerular damage and hypertension, but the mechanisms are not clear. Normally, kidneys autoregulate to keep the glomerular capillary pressure (P GC ), renal blood flow and glomerular filtration rate in a steady state. In obesity, the kidney loses its autoregulatory capacity, leading to higher P GC , renal blood flow and glomerular filtration rate. Together, these may lead to glomerular damage. P GC is controlled mainly by the afferent arteriole (Af-Art) resistance. Af-Art resistance in turn is regulated by an intrinsic renal feedback mechanism known as tubuloglomerular feedback (TGF). TGF causes Af-Art constriction in response to an increase in sodium chloride (NaCl) in the macula densa, via the Na-K-2Cl cotransporter NKCC2. We previously found that in the Zucker rat model of obesity, TGF was decreased and this was associated with higher blood pressure (BP) and proteinuria. However, it is not known whether obesity induced by a high fat diet in normal Sprague Dawley (SD) rats could also affect TGF. We hypothesized that TGF would be attenuated in obesity caused by 16 weeks of high fat fed (HFD) feeding (60% fat) in SD rats. SD rats fed normal-fat diet (12% fat, NFD) served as control. HFD fed rats exhibited higher body weight (HFD: 833.7±33.3 vs. NFD: 682.3±24.8 grams, p<0.05) and were hypertensive under Inactin anesthesia (mean BP HFD: 131.4±3.6 vs.115.8±3.8 mmHg, p<0.05). We performed in-vivo renal micropuncture of individual rat nephrons while measuring stop-flow pressure (P SF ), an index of P GC. P SF decreases with an increase in Af-Art resistance. TGF response was measured as a decrease in P SF induced by changing the rate of late proximal perfusion from 0 to 40nl/min. Maximal TGF response was significantly smaller in HFD fed rats compared to the NFD rats (HFD: 4.1±0.9 vs. NFD: 10.2±0.6 mmHg, p<0.05) indicating attenuation of TGF by HFD. Baseline P GC was higher in HFD rats compared to NFD rats (HFD: 41.6±0.8 vs. NFD: 38.7.2±0.5 mmHg, p<0.05). We conclude that TGF is attenuated in HFD fed obese SD rats and this may contribute to increased renal blood flow and GFR observed in obesity. Hypertension, combined with an attenuated TGF response and increased P GC may explain higher renal damage caused by obesity.

Effects of Nitroglycerine on Renal Ischemia-Reperfusion Injury in Adult Male Rats.

Ischemia-reperfusion (I-R) leads to acute kidney injury (AKI). The present study investigated the effects of nitroglycerine (NG) on improving renal dysfunctions caused by I-R in rats. Twenty-four rats were equally divided into four groups: (1) the control group, (2) the sham group, (3) the I-R group, and (4) NG-treated groups.NG (50 μg/kg) was injected intraperitoneally after induction of IR. I-R was induced through clamping of the bilateral renal artery and vein of both kidneys for 20 min followed by 24 h of reperfusion. NG significantly increased the creatinine clearance levels and renal blood flow rate (which was reduced by I-R). NG also significantly improved serum electrolytes (sodium and potassium) that were disordered by I-R. In addition, NG significantly offset impaired antioxidant defense mechanism and inhibited lipid peroxidation. The results show NG has a protective effect on renal tissue against AKI caused by I-R. These protective effects mediated through antioxidant activity and decrease of lipid peroxidation.

Pharmacological inhibition of TRPV4 channels protects against ischemia-reperfusion-induced renal insufficiency in neonatal pigs.

Renal vasoconstriction, an early manifestation of ischemic acute kidney injury (AKI), results in renal hypoperfusion and a rapid decline in kidney function. The pathophysiological mechanisms that underlie ischemia-reperfusion (IR)-induced renal insufficiency are poorly understood, but possibilities include alterations in ion channel-dependent renal vasoregulation. In the present study, we show that pharmacological activation of TRPV4 channels constricted preglomerular microvessels and elicited renal hypoperfusion in neonatal pigs. Bilateral renal ischemia followed by short-term reperfusion increased TRPV4 protein expression in resistance size renal vessels and TRPV4-dependent cation currents in renal vascular smooth muscle cells (SMCs). Selective TRPV4 channel blockers attenuated IR-induced reduction in total renal blood flow (RBF), cortical perfusion, and glomerular filtration rate (GFR). TRPV4 inhibition also diminished renal IR-induced increase in AKI biomarkers. Furthermore, the level of angiotensin II (Ang II) was higher in the urine of IR- compared with sham-operated neonatal pigs. IR did not alter renal vascular expression of Ang II type 1 (AT1) receptors. However, losartan, a selective AT1 receptor antagonist, ameliorated IR-induced renal insufficiency in the pigs. Blockade of TRPV4 channels attenuated Ang II-evoked receptor-operated Ca2+ entry and constriction in preglomerular microvessels. TRPV4 inhibition also blunted Ang II-induced increase in renal vascular resistance (RVR) and hypoperfusion in the pigs. Together, our data suggest that SMC TRPV4-mediated renal vasoconstriction and the ensuing increase in RVR contribute to early hypoperfusion and renal insufficiency elicited by renal IR in neonatal pigs. We propose that multimodal signaling by renal vascular SMC TRPV4 channels controls neonatal renal microcirculation in health and disease.

Ethnopharmacological approaches to Talinum paniculatum (Jacq.) Gaertn. - Exploring cardiorenal effects from the Brazilian Cerrado

Talinum paniculatum (Jacq.) Gaertn. (Talinaceae), popularly known as "major gomes" and "erva gorda", is a non-conventional food plant extensively distributed throughout the Brazilian territory. In Brazilian folk medicine, this species is used as aphrodisiac, to treat gastrointestinal problems, and as a cardioprotective agent. However, there are no reports in the literature proving its cardiovascular effects. To perform a whole-ethnopharmacological investigation of the cardiorenal properties of the ethanol soluble fraction from T. paniculatum (ESTP) in Wistar rats. First, plant samples were collected, properly identified and a morpho-anatomical characterization was carried out to provide quality control parameters. Then, ESTP was obtained and its chemical profile was determined by LC-DAD-MS. In addition, an acute toxicity assay was conducted in female Wistar rats in order to observe any toxic effects after one single administration. Finally, the diuretic and hypotensive potential of ESTP (30, 100 and 300 mg/kg) were investigated in male rats followed by the evaluation of its possible effects on peripheral vascular resistance. Chemical compounds identified from ESTP were chlorogenic acids, amino acids, nucleosides, O-glycosylated flavones and organic acids. No signs of toxicity as well as no changes in urine volume or electrolyte elimination were observed after ESTP acute treatment. On the other hand, prolonged treatment with all doses of ESTP significantly increased urine volume and electrolyte excretion (Na+, K+ and Cl-) without affecting blood pressure or heart rate. Apparently, these effects are involved with the activation of the small conductance calcium-activated potassium channels contributing to the increase of renal blood flow and glomerular filtration rate. Data presented show important information about the ethnomedicinal properties of T. paniculatum. In addition, the study presents the ESTP as a possible herbal medicine, especially when a sustained diuretic effect is required.

Inhibition of TLR4 Activation Prevents Renal Autoregulatory Impairment in Ang II Hypertensive Rats

Autoregulation by afferent arterioles regulates renal blood flow and glomerular filtration rate across widely ranging arterial pressures. Autoregulatory function is impaired in hypertension, perhaps due to release of damage associated molecular patterns that activate renal toll‐like receptor (TLR4). Autoregulatory impairment can promote hypertensive kidney injury. We hypothesize that inhibition of TLR4 activation preserves afferent arteriole autoregulatory function in Angiotensin II (AngII) hypertension.Three groups (n=4/group) of male Sprague‐Dawley rats were implanted with osmotic minipumps set to deliver: saline (0.9% NaCl) or AngII (60ng/min). Group three received AngII+anti‐TLR4 Ab (3 μg/ml/kg/day, i.p.) for 14 days. Systolic blood pressure (SBP) was assessed (days 0, 3, 7 and 13). Kidneys were harvested on day 14 for juxtamedullary nephron assessment of afferent arteriole autoregulatory function.SBP increased in the AngII and AngII+Anti‐TLR4 Ab groups compared to saline controls over the 14 days (P<0.05), averaging 198 ± 11, 200 ± 8 and 135 ± 3 mmHg, respectively. Baseline arteriole diameters (100 mmHg) averaged 14 ± 0.8, 15.6 ± 1.7, and 13 ± 0.3 microns for control, AngII and AngII+Anti‐TLR4 Ab, respectively. Perfusion pressure was decreased to 65 mmHg and increased to 170 mmHg in 15 mmHg increments. At 170 mmHg, arteriole diameters decreased by 31 ± 6% and 33 ± 8% of baseline in the control and Ang II+Anti‐TLR4 Ab groups whereas the AngII group had a decline of 11.7 ± 3.7%.These data establish that autoregulatory function is Impaired in AngII hypertensive rats while it is preserved by anti‐TLR4 Ab‐treatment. These findings implicate chronic TLR4 activation as causative in the hypertensive decline in autoregulatory capability.Support or Funding InformationFunded by NHLBI; 1R25 HL115473‐01 and DK044628‐20.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.