Renal autoregulation in health and disease.

Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration rate (GFR) independent of renal perfusion pressure (RPP) over a defined range (80-180 mmHg). Such autoregulation is mediated largely by the myogenic and the macula densa-tubuloglomerular feedback (MD-TGF) responses that regulate preglomerular vasomotor tone primarily of the afferent arteriole. Differences in response times allow separation of these mechanisms in the time and frequency domains. Mechanotransduction initiating the myogenic response requires a sensing mechanism activated by stretch of vascular smooth muscle cells (VSMCs) and coupled to intracellular signaling pathways eliciting plasma membrane depolarization and a rise in cytosolic free calcium concentration ([Ca(2+)]i). Proposed mechanosensors include epithelial sodium channels (ENaC), integrins, and/or transient receptor potential (TRP) channels. Increased [Ca(2+)]i occurs predominantly by Ca(2+) influx through L-type voltage-operated Ca(2+) channels (VOCC). Increased [Ca(2+)]i activates inositol trisphosphate receptors (IP3R) and ryanodine receptors (RyR) to mobilize Ca(2+) from sarcoplasmic reticular stores. Myogenic vasoconstriction is sustained by increased Ca(2+) sensitivity, mediated by protein kinase C and Rho/Rho-kinase that favors a positive balance between myosin light-chain kinase and phosphatase. Increased RPP activates MD-TGF by transducing a signal of epithelial MD salt reabsorption to adjust afferent arteriolar vasoconstriction. A combination of vascular and tubular mechanisms, novel to the kidney, provides for high autoregulatory efficiency that maintains RBF and GFR, stabilizes sodium excretion, and buffers transmission of RPP to sensitive glomerular capillaries, thereby protecting against hypertensive barotrauma. A unique aspect of the myogenic response in the renal vasculature is modulation of its strength and speed by the MD-TGF and by a connecting tubule glomerular feedback (CT-GF) mechanism. Reactive oxygen species and nitric oxide are modulators of myogenic and MD-TGF mechanisms. Attenuated renal autoregulation contributes to renal damage in many, but not all, models of renal, diabetic, and hypertensive diseases. This review provides a summary of our current knowledge regarding underlying mechanisms enabling renal autoregulation in health and disease and methods used for its study.

Sex differences in rat renal arterial responses following exercise training.

During aerobic exercise, hemodynamic alterations occur. Although blood flow in skeletal muscle arteries increases, it decreases in visceral vessels because of mesenterial vasoconstriction. However, maintaining renal blood flow during intensive sport is also a priority. Our aim was to investigate the changes of vascular reactivity and histology of isolated renal artery of male and female rats in response to swim training. Wistar rats were distributed into four groups: male sedentary (MSed), male trained (MTr), female sedentary (FSed), and female trained (FTr). Trained animals underwent a 12-wk-long intensive swimming program. Vascular function of isolated renal artery segments was examined by wire myography. Phenylephrine-induced contraction was lower in FSed than in MSed animals, and it was decreased by training in male but not in female animals. Inhibition of cyclooxygenases by indomethacin reduced contraction in both sedentary groups, and in MTr but not in FTr animals. Inhibition of nitric oxide production increased contraction in both trained groups. Acetylcholine induced relaxation was similar in all experimental groups showing predominant NO-dependency. Elastin and smooth muscle cell actin density was reduced in female rats after aerobic training. This study shows that, as a result of a 12-wk-long training, there are sex differences in renal arterial responses following exercise training. Swimming moderates renal artery vasoconstriction in male animals, whereas it depresses elastic fiber and smooth muscle actin density in females.NEW & NOTEWORTHY We provided the first detailed analysis of the adaptation of the renal artery after aerobic training in male and female rats. As a result of a 12-wk-long training program, the pharmacological responses of renal arteries changed only in male animals. In phenylephrine-induced contraction, cyclooxygenase-mediated vasoconstriction mechanisms lost their significance in female rats, whereas NO-dependent relaxation became a significant contraction reducing factor in both sexes. Early structural changes, such as reduced elastin and smooth muscle cell actin evolves in females.

Development of the renal vasculature.

The kidney vasculature has a unique and complex architecture that is central for the kidney to exert its multiple and essential physiological functions with the ultimate goal of maintaining homeostasis. An appropriate development and coordinated assembly of the different vascular cell types and their association with the corresponding nephrons is crucial for the generation of a functioning kidney. In this review we provide an overview of the renal vascular anatomy, histology, and current knowledge of the embryological origin and molecular pathways involved in its development. Understanding the cellular and molecular mechanisms involved in renal vascular development is the first step to advance the field of regenerative medicine.

Highly individual- and tissue-specific expression of glycoprotein group A and B blood antigens in the human kidney and liver.

BACKGROUND: Currently, research on the quantitative distribution of ABO antigens in different organs and tissues remains limited. We aimed to examine the individual characteristics of blood group glycoprotein A and B antigen expression in human kidneys and livers. METHODS: We obtained human samples, including the renal artery, renal vein, renal tissue, hepatic artery, hepatic vein, portal vein, and hepatic tissue, from 24 deceased organ transplant donors. The expression of the blood group antigens glycoprotein A and B was analysed and compared by Western blotting. RESULTS: There was no significant difference in the expression between blood group glycoprotein A and B antigens at any of the seven sites (p > 0.05). The expression of both A and B antigens was highest in renal tissue and the portal vein and was lowest in the renal artery. A large difference in glycoprotein antigen expression was observed among various donors or different regions of the same individual. Univariate analysis revealed that glycoprotein A/B antigens were affected by the age and sex of donors and were significantly higher in males and in young people. CONCLUSIONS: Our study found that blood group glycoprotein antigen expression showed certain trends and distinct distribution in the kidney, liver, and vessels among individuals and in different regions of the same individual, which may explain the different clinical outcomes of patients who received ABO-incompatible transplantation.

Differential properties of E prostanoid receptor-3 and thromboxane prostanoid receptor in activation by prostacyclin to evoke vasoconstrictor response in the mouse renal vasculature.

Vasomotor reactions of prostacyclin (prostaglandin I2 ; PGI2 ) can be collectively modulated by thromboxane prostanoid receptor (TP), E-prostanoid receptor-3 (EP3), and the vasodilator I prostanoid receptor (IP). This study aimed to determine the direct effect of PGI2 on renal arteries and/or the whole renal vasculature and how each of these receptors is involved. Experiments were performed on vessels or perfused kidneys of wild-type mice and/or mice with deficiency in TP (TP-/- ) and/or EP3. Here we show that PGI2 did not evoke relaxation, but instead resulted in contraction of main renal arteries (from ~0.001-0.01 µM) or reduction of flow in perfused kidneys (from ~1 µM); either of them was reversed into a dilator response in TP-/- /EP3-/- counterparts. Also, we found that in renal arteries although it has a lesser effect than TP-/- on the maximal contraction to PGI2 (10 µM), EP3-/- but not TP-/- resulted in relaxation to the prostanoid at 0.01-1 µM. Meanwhile, TP-/- only significantly reduced the contractile activity evoked by PGI2 at ≥0.1 µM. These results demonstrate that PGI2 may evoke an overall vasoconstrictor response in the mouse renal vasculature, reflecting activities of TP and EP3 outweighing that of the vasodilator IP. Also, our results suggest that EP3, on which PGI2 can have a potency similar to that on IP, plays a major role in the vasoconstrictor effect of the prostanoid of low concentrations (≤1 µM), while TP, on which PGI2 has a lower potency but higher efficacy, accounts for a larger part of its maximal contractile activity.

Pre-ischemic renal lavage protects against renal ischemia-reperfusion injury by attenuation of local and systemic inflammatory responses.

Postischemic acute kidney injury (AKI) is a common clinical complication and often fatal, with no effective treatment available. Little is known about the role of leukocytes trapped in renal vessels during ischemia-reperfusion injury (IRI) in the postischemic AKI. We designed a new animal model in rats with preforming renal artery lavage prior to IRI to investigate the effect of diminishing the residual circulating leukocytes on kidney damage and inflammation. Moreover, the functional changes of macrophages in hypoxia reoxygenation condition were also analyzed. We found pre-ischemic renal lavage significantly decreased the serum creatinine and blood urea nitrogen levels, and downregulated the mRNA and protein expressions in kidneys and urinary secretion of kidney injury molecule-1 of rats after IRI. The renal pathological damage caused by IRI was also ameliorated by pre-ischemic renal lavage, as evidenced by fewer cast formation, diminished morphological signs of AKI in the tissue at 24 hours after IRI. Pre-ischemic renal lavage reduced the numbers of infiltrating CD68+ macrophages and MPO+ neutrophils. The mRNA expression of pro-inflammatory mediator in IRI kidneys and the levels of pro-inflammatory cytokines in circulatory system and urine were also reduced due to pre-ischemic lavage. Compared with nontreated rats with IRI, pre-ischemic renal lavage significantly reduced the phosphorylation levels of ERK and p65 subunit of NF-κB in the kidney after IRI. In addition, we found hypoxia/reoxygenation could promote the expression of pro-inflammatory mediators and inhibit the expression of anti-inflammatory factors by regulating ERK/NF-κB signaling pathway. Thus, pre-ischemic renal lavage could clearly reduce the renal damage after IRI by attenuating inflammation, and macrophages trapped in renal vessels during IRI could be important pathogenic factors driving tissue injury.

SMIT (Sodium-Myo-Inositol Transporter) 1 Regulates Arterial Contractility Through the Modulation of Vascular Kv7 Channels.

OBJECTIVE: The SMIT1 (sodium:myo-inositol transporter 1) regulates myo-inositol movement into cells and responses to hypertonic stimuli. Alteration of myo-inositol levels has been associated with several diseases, including hypertension, but there is no evidence of a functional role of SMIT1 in the vasculature. Recent evidence showed that in the nervous system SMIT1 interacted and modulated the function of members of the Kv7 family of voltage-gated potassium channels, which are also expressed in the vasculature where they regulate arterial contractility. Therefore, in this study, we evaluated whether SMIT1 was functionally relevant in arterial smooth muscle. Approach and Results: Immunofluorescence and polymerase chain reaction experiments revealed that SMIT1 was expressed in rat renal and mesenteric vascular smooth muscle cells. Isometric tension recordings showed that incubation of renal arteries with raffinose and myo-inositol (which increases SMIT1 expression) reduced the contractile responses to methoxamine, an effect that was abolished by preincubation with the pan-Kv7 blocker linopirdine and by molecular knockdown of Kv7.4 and Kv7.5. Knockdown of SMIT1 increased the contraction of renal arteries induced by methoxamine, impaired the response to the Kv7.2-Kv7.5 activator ML213 but did not interfere with the relaxant responses induced by openers of other potassium channels. Proximity ligation assay showed that SMIT1 interacted with heteromeric channels formed by Kv7.4 and Kv7.5 proteins in both renal and mesenteric vascular smooth muscle cells. Patch-clamp experiments showed that incubation with raffinose plus myo-inositol increased Kv7 currents in vascular smooth muscle cells. CONCLUSIONS: SMIT1 protein is expressed in vascular smooth muscle cells where it modulates arterial contractility through an association with Kv7.4/Kv7.5 heteromers.

GLP-1-induced renal vasodilation in rodents depends exclusively on the known GLP-1 receptor and is lost in prehypertensive rats.

Glucagon-like peptide-1 (GLP-1) is an incretin hormone known to stimulate postprandial insulin release. However, GLP-1 also exerts extrapancreatic effects, including renal effects. Some of these renal effects are attenuated in hypertensive rats, where renal expression of GLP-1 receptors is reduced. Here, we assessed the expression and vascular function of GLP-1 receptors in kidneys from young prehypertensive rats. We also examined GLP-1-induced vasodilation in the renal vasculature in wild-type (WT) and GLP-1 receptor knockout mice using wire and pressure myography and the isolated perfused juxtamedullary nephron preparation. We investigated whether GLP-1 and the metabolite GLP-1(9-36)amide had renal vascular effects independent of the known GLP-1 receptor. We hypothesized that hypertension decreased expression of renal GLP-1 receptors. We also hypothesized that GLP-1-induced renal vasodilatation depended on expression of the known GLP-1 receptor. In contrast to normotensive rats, no immunohistochemical staining or vasodilatory function of GLP-1 receptors was found in kidneys from prehypertensive rats. In WT mice, GLP-1 induced renal vasodilation and reduced the renal autoregulatory response. The GLP-1 receptor antagonist exendin 9-39 inhibited relaxation, and GLP-1(9-36)amide had no vasodilatory effect. In GLP-1 receptor knockout mice, no relaxation induced by GLP-1 or GLP-1(9-36)amide was found, the autoregulatory response in afferent arterioles was normal, and no GLP-1-induced reduction of autoregulation was found. We conclude that in prehypertensive kidneys, expression and function of GLP-1 receptors is lost. The renal vasodilatory effect of GLP-1 is mediated exclusively by the known GLP-1 receptor. GLP-1(9-36)amide has no renal vasodilatory effect. GLP-1 attenuates renal autoregulation by reducing the myogenic response.

Aggravated endothelial endocrine dysfunction and intimal thickening of renal artery in high-fat diet-induced obese pigs following renal denervation.

BACKGROUND: Renal denervation (RDN) targeting the sympathetic nerves in the renal arterial adventitia as a treatment of resistant hypertension can cause endothelial injury and vascular wall injury. This study aims to evaluate the risk of atherosclerosis induced by RDN in renal arteries. METHODS: A total of 15 minipigs were randomly assigned to 3 groups: (1) control group, (2) sham group, and (3) RDN group (n = 5 per group). All pigs were fed a high-fat diet (HFD) for 6 months after appropriate treatment. The degree of intimal thickening of renal artery and the conversion of endothelin 1 (ET-1) receptors were evaluated by histological staining. Western blot was used to assess the expression of nitric oxide (NO) synthesis signaling pathway, ET-1 and its receptors, NADPH oxidase 2 (NOX2) and 4-hydroxynonenal (4-HNE) proteins, and the activation of NF-kappa B (NF-κB). RESULTS: The histological staining results suggested that compared to the sham treatment, RDN led to significant intimal thickening and significantly promoted the production of endothelin B receptor (ETBR) in vascular smooth muscle cells (VSMCs). Western blotting analysis indicated that RDN significantly suppressed the expression of AMPK/Akt/eNOS signaling pathway proteins, and decreased the production of NO, and increased the expression of endothelin system proteins including endothelin-1 (ET-1), endothelin converting enzyme 1 (ECE1), endothelin A receptor (ETAR) and ETBR; and upregulated the expression of NOX2 and 4-HNE proteins and enhanced the activation of NF-kappa B (NF-κB) when compared with the sham treatment (all p < 0.05). There were no significant differences between the control and sham groups (all p > 0.05). CONCLUSIONS: RDN aggravated endothelial endocrine dysfunction and intimal thickening, and increased the risk of atherosclerosis in renal arteries of HFD-fed pigs.

Extracellular Matrix Analysis of Human Renal Arteries in Both Quiescent and Active Vascular State.

In vascular tissue engineering strategies, the addition of vascular-specific extracellular matrix (ECM) components may better mimic the in vivo microenvironment and potentially enhance cell-matrix interactions and subsequent tissue growth. For this purpose, the exact composition of the human vascular ECM first needs to be fully characterized. Most research has focused on characterizing ECM components in mature vascular tissue; however, the developing fetal ECM matches the active environment required in vascular tissue engineering more closely. Consequently, we characterized the ECM protein composition of active (fetal) and quiescent (mature) renal arteries using a proteome analysis of decellularized tissue. The obtained human fetal renal artery ECM proteome dataset contains higher levels of 15 ECM proteins versus the mature renal artery ECM proteome, whereas 16 ECM proteins showed higher levels in the mature tissue compared to fetal. Elastic ECM proteins EMILIN1 and FBN1 are significantly enriched in fetal renal arteries and are mainly produced by cells of mesenchymal origin. We functionally tested the role of EMILIN1 and FBN1 by anchoring the ECM secreted by vascular smooth muscle cells (SMCs) to glass coverslips. This ECM layer was depleted from either EMILIN1 or FBN1 by using siRNA targeting of the SMCs. Cultured endothelial cells (ECs) on this modified ECM layer showed alterations on the transcriptome level of multiple pathways, especially the Rho GTPase controlled pathways. However, no significant alterations in adhesion, migration or proliferation were observed when ECs were cultured on EMILIN1- or FNB1-deficient ECM. To conclude, the proteome analysis identified unique ECM proteins involved in the embryonic development of renal arteries. Alterations in transcriptome levels of ECs cultured on EMILIN1- or FBN1-deficient ECM showed that these candidate proteins could affect the endothelial (regenerative) response.

Hydrogen sulfide regulation of renal and mesenteric blood flow.

Hydrogen sulfide (H2S) dilates isolated arteries, and knockout of the H2S-synthesizing enzyme cystathionine γ-lyase (CSE) increases blood pressure. However, the contributions of endogenously produced H2S to blood flow regulation in specific vascular beds are unknown. Published studies in isolated arteries show that CSE production of H2S influences vascular tone more in small mesenteric arteries than in renal arteries or the aorta. Therefore, the goal of this study was to evaluate H2S regulation of blood pressure, vascular resistance, and regional blood flows using chronically instrumented rats. We hypothesized that during whole animal CSE inhibition, vascular resistance would increase more in the mesenteric than the renal circulation. Under anesthesia, CSE inhibition [ß-cyanoalanine (BCA), 30 mg/kg bolus + 5 mg·kg-1·min-1 for 20 min iv) rapidly increased mean arterial pressure (MAP) more than saline administration (%Δ: saline -1.4 ± 0.75 vs. BCA 7.1 ± 1.69, P < 0.05) but did not change resistance (MAP/flow) in either the mesenteric or renal circulation. In conscious rats, BCA infusion similarly increased MAP (%Δ: saline -0.8 ± 1.18 vs. BCA 8.2 ± 2.6, P < 0.05, n = 7) and significantly increased mesenteric resistance (saline 0.9 ± 3.1 vs. BCA 15.6 ± 6.5, P < 0.05, n = 12). The H2S donor Na2S (50 mg/kg) decreased blood pressure and mesenteric resistance ,but the fall in resistance was not significant. Inhibiting CSE for multiple days with dl-proparglycine (PAG, 50 mg·kg-1·min-1 iv bolus for 5 days) significantly increased vascular resistance in both mesenteric (ratio of day 1: saline 0.86 ± 0.033 vs. PAG 1.79 ± 0.38) and renal circulations (ratio of day 1: saline 1.26 ± 0.22 vs. 1.98 ± 0.14 PAG). These results support our hypothesis that CSE-derived H2S is an important regulator of blood pressure and vascular resistance in both mesenteric and renal circulations. Furthermore, inhalation anesthesia diminishes the effect of CSE inhibition on vascular tone.NEW & NOTEWORTHY These results suggest that CSE-derived H2S has a prominent role in regulating blood pressure and blood flow under physiological conditions, which may have been underestimated in prior studies in anesthetized subjects. Therefore, enhancing substrate availability or enzyme activity or dosing with H2S donors could be a novel therapeutic approach to treat cardiovascular diseases.

Comparison of Ca2+ Handling for the Regulation of Vasoconstriction between Rat Coronary and Renal Arteries.

BACKGROUND: Ca2+ plays an important role in the regulation of vasoconstriction. Ca2+ signaling is regulated by a number of Ca2+-handling proteins. However, whether differences in Ca2+ handling affect the regulation of vasoconstriction in different arteries remains elusive. OBJECTIVE: To determine whether differences in Ca2+ handling affect the response to vasoconstrictors in different arteries. METHODS: Arterial ring contraction was measured using a Multi Myograph System. Vascular smooth muscle cells (VSMCs) were digested with type 2 collagenase in DMEM, then intracellular calcium concentration was measured with the Ca2+ probe fluo-4/AM in the isolated cells. Calcium-related proteins were assayed by Western blotting. RESULTS: Phenylephrine did not induce -coronary arterial contraction. There were differences in -5-hydroxytryptamine, 9,11-dideoxy-11a,9a-epoxymethano-prostaglandin F2a, and endothelin 1-induced vasoconstriction in different solutions between coronary and renal arteries. Vasoconstrictions in the presence of Bay K8644 were stronger in coronary than in renal arteries. Store-operated calcium (SOC) channels could mediate Ca2+ influx in VSMCs of both groups. SOC channels did not participate in the contraction of coronary arteries. In addition, there were significant differences in the expressions of receptors and ion channels between the two groups. CONCLUSIONS: Ca2+ handling contributed to the different responses to vasoconstrictors between coronary and renal arteries.

Acute changes in morphology and renal vascular relaxation function after renal denervation using temperature-controlled radiofrequency catheter.

BACKGROUND: Resistant hypertension and renal sympathetic hyperactivity are closely linked, and catheter-based renal denervation (RDN) is regarded as a new treatment strategy. However, the acute changes in vascular morphology and relaxation function have yet to be evaluated, and these may be important for the efficacy and safety of the procedure. In this study, we explored these questions by conventional temperature-controlled cardiac radiofrequency catheter-based RDN in a pig model. METHODS: Six mini-pigs were randomly divided into the renal denervation (RDN) group (n = 3) and the Sham-RDN group (n = 3). Animals in the RDN group underwent unilateral radiofrequency ablation, and those in the Sham-RDN group underwent the same procedure except for the ablation. The pigs were examined by angiography pre- and post-RDN and were euthanized immediately thereafter. Renal arteries were processed for histological and molecular biology analyses as well as for in vitro vascular tension testing. RESULTS: Compared with the Sham-RDN group, the RDN caused vascular intima and media injury, renal nerve vacuolization, mild collagen fiber hyperplasia and elastic fiber cleavage (all p < 0.05). The RDN group also significantly exhibited nitric oxide synthase pathway inhibition and decreased endothelium-independent vascular relaxation function Compared to the Sham-RDN group (all p < 0.05). CONCLUSIONS: In this porcine model, renal artery denervation led to vascular wall injury and endothelial dysfunction in the acute phase, which negatively affected vascular relaxation function. Thus, this process may be detrimental to the prognosis and progress of hypertension patients.

Periarterial fat from two human vascular beds is not a source of aldosterone to promote vasoconstriction.

Mouse adipocytes have been reported to release aldosterone and reduce endothelium-dependent relaxation. It is unknown whether perivascular adipose tissue (PVAT) releases aldosterone in humans. The present experiments were designed to test the hypothesis that human PVAT releases aldosterone and induces endothelial dysfunction. Vascular reactivity was assessed in human internal mammary and renal segmental arteries obtained at surgery. The arteries were prepared with/without PVAT, and changes in isometric tension were measured in response to the vasoconstrictor thromboxane prostanoid receptor agonist U46619 and the endothelium-dependent vasodilator acetylcholine. The effects of exogenous aldosterone and of mineralocorticoid receptor (MR) antagonist eplerenone were determined. Aldosterone concentrations were measured by ELISA in conditioned media incubated with human adipose tissue with/without angiotensin II stimulation. Presence of aldosterone synthase and MR mRNA was examined in perirenal, abdominal, and mammary PVAT by PCR. U46619 -induced tension and acetylcholine-induced relaxation were unaffected by exogenous and endogenous aldosterone (addition of aldosterone and MR blocker) in mammary and renal segmental arteries, both in the presence and absence of PVAT. Aldosterone release from incubated perivascular fat was not detectable. Aldosterone synthase expression was not consistently observed in human adipose tissues in contrast to that of MR. Thus, exogenous aldosterone does not affect vascular reactivity and endothelial function in ex vivo human arterial segments, and the tested human adipose tissues have no capacity to synthesize/release aldosterone. In perspective, physiologically relevant effects of aldosterone on vascular function in humans are caused by systemic aldosterone originating from the adrenal gland.

TRPV4 channels contribute to renal myogenic autoregulation in neonatal pigs.

Myogenic response, a phenomenon in which resistance size arteries and arterioles swiftly constrict or dilate in response to an acute elevation or reduction, respectively, in intravascular pressure is a key component of renal autoregulation mechanisms. Although it is well established that the renal system is functionally immature in neonates, mechanisms that regulate neonatal renal blood flow (RBF) remain poorly understood. In this study, we investigated the hypothesis that members of the transient receptor potential vanilloid (TRPV) channels are molecular components of renal myogenic constriction in newborns. We show that unlike TRPV1-3, TRPV4 channels are predominantly expressed in neonatal pig preglomerular vascular smooth muscle cells (SMCs). Intracellular Ca2+ concentration ([Ca2+]i) elevation induced by osmotic cell swelling was attenuated by TRPV4, L-type Ca2+, and stretch-activated Ca2+ channel blockers but not phospholipase A2 inhibitor. Blockade of TRPV4 channels reversed steady-state myogenic tone and inhibited pressure-induced membrane depolarization, [Ca2+]i elevation, and constriction in distal interlobular arteries. A step increase in arterial pressure induced efficient autoregulation of renal cortical perfusion and total RBF in anesthetized and mechanically ventilated neonatal pigs. Moreover, intrarenal arterial infusion of the TRPV4 channel blockers HC 067047 and RN 1734 attenuated renal autoregulation in the pigs. These data suggest that renal myogenic autoregulation is functional in neonates. Our findings also indicate that TRPV4 channels are mechanosensors in neonatal pig preglomerular vascular SMCs and contribute to renal myogenic autoregulation.

Maternal separation diminishes α-adrenergic receptor density and function in renal vasculature from male Wistar-Kyoto rats.

Adult rats exposed to maternal separation (MatSep) are normotensive but display lower glomerular filtration rate and increased renal neuroadrenergic drive. The aim of this study was to determine the renal α-adrenergic receptor density and the renal vascular responsiveness to adrenergic stimulation in male rats exposed to MatSep. In addition, baroreflex sensitivity was assessed to determine a component of neural control of the vasculature. Using tissue collected from 4-mo-old MatSep and control rats, α1-adrenergic receptors (α1-ARs) were measured in renal cortex and isolated renal vasculature using receptor binding assay, and the α-AR subtype gene expression was determined by RT-PCR. Renal cortical α1-AR density was similar between MatSep and control tissues (Bmax = 44 ± 1 vs. 42 ± 2 fmol/mg protein, respectively); however, MatSep reduced α1-AR density in renal vasculature (Bmax = 47 ± 4 vs. 62 ± 4 fmol/mg protein, P < 0.05, respectively). In a separate group of rats, the pressor, bradycardic, and renal vascular constrictor responses to acute norepinephrine injection (NE, 0.03-0.25 µg/µl) were determined under anesthesia. Attenuated NE-induced renal vasoconstriction was observed in rats exposed to MatSep compared with control (P < 0.05). A third group of rats was infused at steady state with the α1 agonist phenylephrine (10 µg/min iv) and vasodilator sodium nitroprusside (5 µg/min iv). The difference between the change in heart rate/mean arterial pressure slopes was indicative of reduced baroreflex sensitivity in MatSep vs. control rats (-0.45 ± 0.04 vs. -0.95 ± 0.07 beats·min-1·mmHg-1, P < 0.05). These data support the notion that reduced α-adrenergic receptor expression and function in the renal vasculature could develop secondary to MatSep-induced overactivation of the renal neuroadrenergic tone.

Renal arteriovenous oxygen shunting.

PURPOSE OF REVIEW: Renal arteriovenous oxygen shunting has been proposed as a mechanism by which oxygen supplied to the kidney can bypass the renal parenchyma. Shunting could, therefore, play a crucial role in renal hypoxia and hyperoxia. In the absence of suitable quantitative experimental methods, computational modeling has been employed in recent years to estimate the extent and potential impact of oxygen shunting. RECENT FINDINGS: Overestimation of the separation distance between arteries and veins was suggested to be responsible for previous findings that only negligible amounts of oxygen are shunted in the preglomerular vasculature. However, models considering the correct separation distance and wrapping of artery-vein pairs still showed shunting at negligible levels of less than 1% of total renal oxygen delivery. The effect of reverse CO2 shunting on the oxygen-hemoglobin dissociation curve was found to impair, rather than promote, preglomerular oxygen shunting. SUMMARY: Oxygen is unlikely to be shunted along the preglomerular vasculature in sufficient quantities to affect renal oxygenation. There may be substantial shunting at the level of the postglomerular vasculature, but more extensive efforts in structural imaging and computational modeling are needed to quantify it reliably.

Stress-sensitive arterial hypertension, haemodynamic changes and brain metabolites in hypertensive ISIAH rats: MRI investigation.

NEW FINDINGS: What is the central question of this study? Stress-sensitive arterial hypertension is considered to be controlled by changes in central and peripheral sympathetic regulating mechanisms, which eventually result in haemodynamic alterations and blood pressure elevation. Therefore, study of the early stages of development of hypertension is of particular interest, because it helps in understanding the aetiology of the disease. What is the main finding and its importance? Non-invasive in vivo investigation in ISIAH rats demonstrated that establishment of sustainable stress-sensitive hypertension is accompanied by a decrease in prefrontal cortex activity and mobilization of hypothalamic processes, with considerable correlations between haemodynamic parameters and individual metabolite ratios. The study of early development of arterial hypertension in association with emotional stress is of great importance for better understanding of the aetiology and pathogenesis of the hypertensive disease. Magnetic resonance imaging (MRI) was applied to evaluate the changes in haemodynamics and brain metabolites in 1- and 3-month-old inherited stress-induced arterial hypertension (ISIAH) rats (10 male rats) with stress-sensitive arterial hypertension and in control normotensive Wistar Albino Glaxo (WAG) rats (eight male rats). In the 3-month-old ISIAH rats, the age-dependent increase in blood pressure was associated with increased blood flow through the renal arteries and decreased blood flow in the lower part of the abdominal aorta. The renal vascular resistance in the ISIAH rats decreased during ageing, although at both ages it remained higher than the renal vascular resistance in WAG rats. An integral metabolome portrait demonstrated that development of hypertension in the ISIAH rats was associated with an attenuation of the excitatory and energetic activity in the prefrontal cortex, whereas in the WAG rats the opposite age-dependent changes were observed. In contrast, in the hypothalamus of 3-month-old ISIAH rats, an increase in energetic activity and prevalence of excitatory over inhibitory neurotransmitters was noticed. The blood flow through the main arteries showed a positive correlation with glutamate and glutamine levels in the hypothalamus and a negative correlation with the hypothalamic GABA level. The blood pressure values were positively correlated with hypothalamic choline levels. Thus, the early development of stress-sensitive hypertension in the ISIAH rats is accompanied by considerable changes both in brain metabolite ratios and in the parameters of blood flow through the main arteries.

Kv7 Channel Activation Underpins EPAC-Dependent Relaxations of Rat Arteries.

OBJECTIVE: To establish the role of Kv7 channels in EPAC (exchange protein directly activated by cAMP)-dependent relaxations of the rat vasculature and to investigate whether this contributes to ß-adrenoceptor-mediated vasorelaxations. APPROACH AND RESULTS: Isolated rat renal and mesenteric arteries (RA and MA, respectively) were used for isometric tension recording to study the relaxant effects of a specific EPAC activator and the ß-adrenoceptor agonist isoproterenol in the presence of potassium channel inhibitors and cell signaling modulators. Isolated myocytes were used in proximity ligation assay studies to detect localization of signaling intermediaries with Kv7.4 before and after cell stimulation. Our studies showed that the EPAC activator (8-pCPT-2Me-cAMP-AM) produced relaxations and enhanced currents of MA and RA that were sensitive to linopirdine (Kv7 inhibitor). Linopirdine also inhibited isoproterenol-mediated relaxations in both RA and MA. In the MA, isoproterenol relaxations were sensitive to EPAC inhibition, but not protein kinase A inhibition. In contrast, isoproterenol relaxations in RA were attenuated by protein kinase A but not by EPAC inhibition. Proximity ligation assay showed a localization of Kv7.4 with A-kinase anchoring protein in both vessels in the basal state, which increased only in the RA with isoproterenol stimulation. In the MA, but not the RA, a localization of Kv7.4 with both Rap1a and Rap2 (downstream of EPAC) increased with isoproterenol stimulation. CONCLUSIONS: EPAC-dependent vasorelaxations occur in part via activation of Kv7 channels. This contributes to the isoproterenol-mediated relaxation in mesenteric, but not renal, arteries.

Endothelial overexpression of endothelin-1 modulates aortic, carotid, iliac and renal arterial responses in obese mice.

Endothelin-1 (ET-1) is essential for mammalian development and life, but it has also been implicated in increased cardiovascular risk under pathophysiological conditions. The aim of this study was to determine the impact of endothelial overexpression of the prepro-endothelin-1 gene on endothelium-dependent and endothelium-independent responses in the conduit and renal arteries of lean and obese mice. Obesity was induced by high-fat-diet (HFD) consumption in mice with Tie-1 promoter-driven, endothelium-specific overexpression of the prepro-endothelin-1 gene (TEThet) and in wild-type (WT) littermates on a C57BL/6N background. Isometric tension was measured in rings (with endothelium) of the aorta (A), carotid (CA) and iliac (IA) arteries as well as the main (MRA) and segmental renal (SRA) arteries; all experiments were conducted in the absence or presence of L-NAME and/or the COX inhibitor meclofenamate. The release of prostacyclin and thromboxane A2 was measured by ELISA. In the MRA, TEThet per se increased contractions to endothelin-1, but the response was decreased in SRA in response to serotonin; there were also improved relaxations to acetylcholine but not insulin in the SRA in the presence of L-NAME. HFD per se augmented the contractions to endothelin-1 (MRA) and to the thromboxane prostanoid (TP) receptor agonist U46619 (CA, MRA) as well as facilitated relaxations to isoproterenol (A). The combination of HFD and TEThet overexpression increased the contractions of MRA and SRA to vasoconstrictors but not in the presence of meclofenamate; this combination also augmented further relaxations to isoproterenol in the A. Contractions to endothelin-1 in the IA were prevented by endothelin-A receptor antagonist BQ-123 but only attenuated in obese mice by BQ-788. The COX-1 inhibitor FR122047 abolished the contractions of CA to acetylcholine. The release of prostacyclin during the latter condition was augmented in samples from obese TEThet mice and abolished by FR122047. These findings suggest that endothelial TEThet overexpression in lean animals has minimal effects on vascular responsiveness. However, if comorbid with obesity, endothelin-1-modulated, prostanoid-mediated renal arterial dysfunction becomes apparent.