Renal Vascular Beds Research Articles

Is GFR decline induced by SGLT2 inhibitor of clinical importance?

BackgroundUse of sodium-glucose-cotransporter-2 (SGLT2) inhibitors often causes an initial decline in glomerular filtration rate (GFR). This study addresses the question whether the initial decline of renal function with SGLT2 inhibitor treatment is related to vascular changes in the systemic circulation.MethodsWe measured GFR (mGFR) and estimated GFR (eGFR) in 65 patients with type 2 diabetes (T2D) at baseline and after 12 weeks of treatment randomized either to a combination of empagliflozin and linagliptin (SGLT2 inhibitor based treatment group) (n = 34) or metformin and insulin (non-SGLT2 inhibitor based treatment group) (n = 31). mGFR was measured using the gold standard clearance technique by constant infusion of inulin. In addition to blood pressure (BP), we measured pulse wave velocity (PWV) under standardized conditions reflecting vascular compliance of large arteries, as PWV is considered to be one of the most reliable vascular parameter of cardiovascular (CV) prognosis.ResultsBoth mGFR and eGFR decreased significantly after initiating treatment, but no correlation was found between change in mGFR and change in eGFR in either treatment group (SGLT2 inhibitor based treatment group: r=-0.148, p = 0.404; non-SGLT2 inhibitor based treatment group: r = 0.138, p = 0.460). Noticeably, change in mGFR correlated with change in PWV (r = 0.476, p = 0.005) in the SGLT2 inhibitor based treatment group only and remained significant after adjustment for the change in systolic BP and the change in heart rate (r = 0.422, p = 0.018). No such correlation was observed between the change in eGFR and the change in PWV in either treatment group.ConclusionsOur main finding is that after initiating a SGLT2 inhibitor based therapy an exaggerated decline in mGFR was related with improved vascular compliance of large arteries reflecting the pharmacologic effects of SGLT2 inhibitor in the renal and systemic vascular bed. Second, in a single patient with T2D, eGFR may not be an appropriate parameter to assess the true change of renal function after receiving SGLT2 inhibitor based therapy.Trial registrationclinicaltrials.gov (NCT02752113).

The vasoconstrictor activities of prostaglandin D2 via the thromboxane prostanoid receptor and E prostanoid receptor-3 outweigh its concurrent vasodepressor effect mainly through D prostanoid receptor-1 ex vivo and in vivo

Prostaglandin (PG) D2, a commonly considered vasodilator through D prostanoid receptor-1 (DP1), might also evoke vasoconstriction via acting on the thromboxane (Tx)-prostanoid receptor (the original receptor of TxA2; TP) and/or E prostanoid receptor-3 (one of the vasoconstrictor receptors of PGE2; EP3). This study aimed to test the above hypothesis in the mouse renal vascular bed (main renal arteries and perfused kidneys) and/or mesenteric resistance arteries and determine how the vasoconstrictor mechanism influences the overall PGD2 effect on systemic blood pressure under in vivo conditions. Experiments were performed on control wild-type (WT) mice and mice with deficiencies in TP (TP−/−) and/or EP3 (EP3−/−). Here we show that PGD2 indeed evoked vasoconstrictor responses in the above-mentioned tissues of WT mice, which were however not only reduced by TP−/− or EP3−/−, but also reversed by TP−/−/EP3−/− in some of the above tissues (mesenteric resistance arteries or perfused kidneys) to dilator reactions that were reduced by non-selective DP antagonism. A slight or mild pressor response was also observed with PGD2 under in vivo conditions, and this was again reversed to a depressor response in TP−/− or TP−/−/EP3−/− mice. Non-selective DP antagonism reduced the PGD2-evoked depressor response in TP−/−/EP3−/− mice as well. These results thus demonstrate that like other PGs, PGD2 activates TP and/or EP3 to evoke vasoconstrictor activities, which can outweigh its concurrent vasodepressor activity mediated mainly through DP1, and hence result in a pressor response, although the response might only be of a slight or mild extent.

Kawasaki disease or polyarteritis nodosa: coronary involvement, a diagnostic conundrum.

Polyarteritis nodosa (PAN) is a medium-vessel vasculitis presenting with cutaneous and multisystem involvement with considerable morbidity. The necrotizing vasculitis in PAN typically involves renal, celiac, and mesenteric vascular beds. Coronary artery involvement is a characteristic feature of Kawasaki disease, another medium-vessel vasculitis; however, it has been rarely reported with PAN. Here, we present 2 cases with PAN involving coronaries mimicking Kawasaki disease. A 3.5-year-old boy with classical features of Kawasaki disease with giant coronary aneurysm refractory to IVIg, methylprednisolone, infliximab presented with persistent rise in inflammatory markers and gastrointestinal bleeding. Digital subtraction angiography (DSA) revealed celiac artery branches stenosis and beading suggestive of PAN. Another 2-year-old girl presented with persistent fever, abdominal pain, and distension. She had hypertension, hepatomegaly, and splenomegaly on examination. Echocardiography revealed multiple coronary aneurysms and DSA revealed numerous renal artery aneurysms. Coronary aneurysm although is a rare presentation of childhood PAN, and can mimic Kawasaki disease. Although both are medium-vessel vasculitis differentiation between these two entities is pivotal, as there are differences in treatment modalities, duration of immunomodulatory therapy, and the outcome. This manuscript describes the salient differences which can help differentiate PAN masquerading as Kawasaki disease at initial presentation.

APOL1 promotes endothelial cell activation beyond the glomerulus

Apolipoprotein L1 (APOL1) high-risk genotypes are associated with increased risk of chronic kidney disease (CKD) in people of West African ancestry. Given the importance of endothelial cells (ECs) in CKD, we hypothesized that APOL1 high-risk genotypes may contribute to disease via EC-intrinsic activation and dysfunction. Single cell RNA sequencing (scRNA-seq) analysis of the Kidney Precision Medicine Project dataset revealed APOL1 expression in ECs from various renal vascular compartments. Utilizing two public transcriptomic datasets of kidney tissue from African Americans with CKD and a dataset of APOL1-expressing transgenic mice, we identified an EC activation signature; specifically, increased intercellular adhesion molecule 1 (ICAM-1) expression and enrichment in leukocyte migration pathways. Invitro, APOL1 expression in ECs derived from genetically modified human induced pluripotent stem cells and glomerular ECs triggered changes in ICAM-1 and platelet endothelial cell adhesion molecule 1 (PECAM-1) leading to an increase in monocyte attachment. Overall, our data suggest the involvement of APOL1 as an inducer of EC activation in multiple renal vascular beds with potential effects beyond the glomerular vasculature.

Elastin haploinsufficiency accelerates age-related structural and functional changes in the renal microvasculature and impairment of renal hemodynamics in female mice.

Age-related decline in functional elastin is associated with increased arterial stiffness, a known risk factor for developing cardiovascular disease. While the contribution of elastin insufficiency to the stiffening of conduit arteries is well described, little is known about the impact on the structure and function of the resistance vasculature, which contributes to total peripheral resistance and the regulation of organ perfusion. In this study, we determined how elastin insufficiency impinges on age-related changes in the structure and biomechanical properties of the renal microvasculature, altering renal hemodynamics and the response of the renal vascular bed to changes in renal perfusion pressure (RPP) in female mice. Using Doppler ultrasonography, we found that resistive index and pulsatility index were elevated in young Eln +/- and aged mice. Histological examination showed thinner internal and external elastic laminae, accompanied by increased elastin fragmentation in the medial layer without any calcium deposits in the small intrarenal arteries of kidneys from young Eln +/- and aged mice. Pressure myography of interlobar arteries showed that vessels from young Eln +/- and aged mice had a slight decrease in distensibility during pressure loading but a substantial decline in vascular recoil efficiency upon pressure unloading. To examine whether structural changes in the renal microvasculature influenced renal hemodynamics, we clamped neurohumoral input and increased renal perfusion pressure by simultaneously occluding the superior mesenteric and celiac arteries. Increased renal perfusion pressure caused robust changes in blood pressure in all groups; however, changes in renal vascular resistance and renal blood flow (RBF) were blunted in young Eln +/- and aged mice, accompanied by decreased autoregulatory index, indicating greater impairment of renal autoregulation. Finally, increased pulse pressure in aged Eln +/- mice positively correlated with high renal blood flow. Together, our data show that the loss of elastin negatively affects the structural and functional integrity of the renal microvasculature, ultimately worsening age-related decline in kidney function.

Reactivity of renal and mesenteric resistance vessels to angiotensin II is mediated by NOXA1/NOX1 and superoxide signaling.

Activation of NADPH oxidase (NOX) enzymes and the generation of reactive oxygen species and oxidative stress regulate vascular and renal function and contribute to the pathogenesis of hypertension. The present study examined the role of NOXA1/NOX1 function in vascular reactivity of renal and mesenteric resistance arteries/arterioles of wild-type and Noxa1-/- mice. A major finding was that renal blood flow is less sensitive to acute stimulation by angiotensin II (ANG II) in Noxa1-/- mice compared with wild-type mice, with a direct action on resistance arterioles independent of nitric oxide (NO) bioavailability. These functional results were reinforced by immunofluorescence evidence of NOXA1/NOX1 protein presence in renal arteries, afferent arterioles, and glomeruli as well as their upregulation by ANG II. In contrast, the renal vascular response to the thromboxane mimetic U46619 was effectively blunted by NO and was similar in both mouse genotypes and thus independent of NOXA1/NOX1 signaling. However, phenylephrine- and ANG II-induced contraction of isolated mesenteric arteries was less pronounced and buffering of vasoconstriction after acetylcholine and nitroprusside stimulation was reduced in Noxa1-/- mice, suggesting endothelial NO-dependent mechanisms. An involvement of NOXA1/NOX1/O2•- signaling in response to ANG II was demonstrated with the specific NOXA1/NOX1 assembly inhibitor C25 and the nonspecific NOX inhibitor diphenyleneiodonium chloride in cultured vascular smooth muscle cells and isolated mesenteric resistance arteries. Collectively, our data indicate that the NOX1/NOXA1/O2•- pathway contributes to acute vasoconstriction induced by ANG II in renal and mesenteric vascular beds and may contribute to ANG II-induced hypertension.NEW & NOTEWORTHY Renal reactivity to angiotensin II (ANG II) is mediated by superoxide signaling produced by NADPH oxidase (NOX)A1/NOX1. Acute vasoconstriction of renal arteries by ANG was blunted in Noxa1-/- compared with wild-type mice. NOXA1/NOX1/O2•- signaling was also observed in ANG II stimulation of vascular smooth muscle cells and isolated mesenteric resistance arteries, indicating that it contributes to ANG II-induced hypertension. A NOXA1/NOX1 assembly inhibitor (C25) has been characterized that inhibits superoxide production and ameliorates the effects of ANG II.

Absolute Versus Relative Near-Infrared Spectroscopy in Pediatric Cardiac Patients.

Near-infrared spectroscopy (NIRS) has been increasingly accepted as a noninvasive marker of regional tissue oxygenation despite concerns of imprecision and wide limits of agreement (LOA) with invasive oximetry. New generation absolute monitors may have improved accuracy compared with trend monitors. We sought to compare the concordance with invasive venous oximetry of a new generation absolute NIRS-oximeter (FORESIGHT ELITE; CASMED, Branford, CT) with a modern widely used trend monitor (INVOS 5100C; Medtronic, Minneapolis, MN). Prospective single-center study. Tertiary pediatric heart center. Children undergoing elective cardiac catheterization under general anesthesia. Time-paired venous oximetry samples (jugular and renal) were compared with NIRS-derived oximetry by two monitors using regression and Bland-Altman analysis. None. We enrolled 36 children (19 female, 10 cyanotic) with median age 4.1 years (25-75%, 2.5-7.8 yr) and weight 16.7 kg (12.3-29.1 kg). The absolute difference between NIRS-derived and invasive jugular oximetry was less than 10% in 67% of occasions for both monitors. Correlation was fair (Spearman rs = 0.40; p = 0.001) for the FORESIGHT ELITE and poor ( rs = 0.06; p = 0.71) for the INVOS 5100C. Bias and LOA were +6.7% (+22%, -9%) versus +1.3% (LOA = +24%, -21%), respectively. The absolute difference between NIRS-derived and invasive renal oximetry was less than 10% in 80% of occasions with moderate correlation ( rs = 0.57; p < 0.001) for the FORESIGHT ELITE and in 61% of occasions with moderate correlation ( rs = 0.58; p < 0.001) for the INVOS 5100C; bias and LOA were +3.6% (+19%, -12%) and -1.4 % (+27%, -30%), respectively. NIRS correlation with renal venous oximetry was worse for cyanotic versus noncyanotic patients ( p = 0.02). Concordance and LOA of NIRS-derived oximetry with invasive venous oximetry in the cerebral and renal vascular beds was suboptimal for clinical decision-making. Cyanosis adversely affected NIRS performance in the renal site.

A peptide fraction from hardened common beans (Phaseolus vulgaris) induces endothelium-dependent antihypertensive and renal effects in rats

Beans reached the research spotlight as a source of bioactive compounds capable of modulating different functions. Recently, we reported antioxidant and oxidonitrergic effect of a low molecular weight peptide fraction (<3 kDa) from hardened bean (Phaseolus vulgaris) in vitro and ex vivo, which necessitate further in vivo assessments. This work aimed to evaluate the hypotensive effect and the involved physiological mechanisms of the hardened common bean peptide (Phaseolus vulgaris) in normotensive (Wistar) and hypertensive (SHR) animals. Bean flour was combined with a solution containing acetonitrile, water and formic acid (25: 24: 1). Protein extract (PV3) was fractioned (3 kDa membrane). We assessed PV3 effects on renal function and hemodynamics of wistar (WT–normotensive) and spontaneously hypertensive rats (SHR) and measured systemic arterial pressure and flow in aortic and renal beds. The potential endothelial and oxidonitrergic involvements were tested in isolated renal artery rings. As results, we found that PV3: I) decreased food consumption in SHR, increased water intake and urinary volume in WT, increased glomerular filtration rate in WT and SHR, caused natriuresis in SHR; II) caused NO- and endothelium-dependent vasorelaxation in renal artery rings; III) reduced arterial pressure and resistance in aortic and renal vascular beds; IV) caused antihypertensive effects in a dose-dependent manner. Current findings support PV3 as a source of bioactive peptides and raise the potential of composing nutraceutical formulations to treat renal and cardiovascular diseases.

154 Ultrasound Visualizes Peripheral Vascular Dysfunction in Finger Pulp Blood Flow in Patients with Systemic Sclerosis

There are no reliable biomarkers of vascular severity or extension, so identification of patients with disabling or life-threatening vascular involvement is often difficult and too late. Best therapeutic effects include healing of ulcers and improvement of blood flow in pulmonary, renal and peripheral vascular beds in systemic sclerosis (SSc). Recent advance of medical devices enables precise recognition of small architectures, so that peripheral blood flow is used for one of individual identifications.

Renal artery Doppler findings in fetuses of mothers with preeclampsia

Objectives: Preeclampsia (PE), which affecting multi-organ systems, is one of the most common causes of feto-maternal morbidity and mortality. The fetal kidney is one of the vulnerable organs in PE caused by sustained vasospasm of the renal arteries. In this study, it was aimed to reveal the changes in the renal vascular bed with renal artery Doppler examinations in fetuses of pregnant women with PE. Methods: Fifty-five pregnant women with PE and 60 healthy pregnant women were included in this prospective study. Multiple pregnancies, those who did not want to participate in the study, and those with other co-morbidities were excluded from the study. Fetal renal artery Doppler studies included renal artery systolic/diastolic (S/D) ratio, pulsatility index (PI) and resistance index (RI) of the control and PE groups, and findings such as week of birth and birth weight were recorded and analyzed statistically. Results: Fetal renal artery PI values were found to be higher in pregnant women with PE compared to the control group (2.93 in the patient group, 2.28 in the control group, p &amp;lt; 0.001). There was no significant difference between RI values and S/D ratios between the two groups. In the preeclampsia group, gestational week and baby weight at birth were significantly lower. Conclusions: Due to preeclampsia, hypoxia occurs in peripheral tissues and organs at the maternal level. Fetal organs are also affected by these hypoxic conditions. Doppler is an extremely useful examination tool in the evaluation of the status of peripheral organs such as the kidney. This study suggests that PE increases the resistance of renal arteries in fetuses of mothers with PE compared to fetuses of mothers without PE, which may contribute critically to kidney disease later in life.

Elastin Insufficiency Accelerates Age‐Related Impairment of Renal Hemodynamics

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

Super-Resolution Ultrasound Imaging Can Quantify Alterations in Microbubble Velocities in the Renal Vasculature of Rats.

Super-resolution ultrasound imaging, based on the localization and tracking of single intravascular microbubbles, makes it possible to map vessels below 100 µm. Microbubble velocities can be estimated as a surrogate for blood velocity, but their clinical potential is unclear. We investigated if a decrease in microbubble velocity in the arterial and venous beds of the renal cortex, outer medulla, and inner medulla was detectable after intravenous administration of the α1-adrenoceptor antagonist prazosin. The left kidneys of seven rats were scanned with super-resolution ultrasound for 10 min before, during, and after prazosin administration using a bk5000 ultrasound scanner and hockey-stick probe. The super-resolution images were manually segmented, separating cortex, outer medulla, and inner medulla. Microbubble tracks from arteries/arterioles were separated from vein/venule tracks using the arterial blood flow direction. The mean microbubble velocities from each scan were compared. This showed a significant prazosin-induced velocity decrease only in the cortical arteries/arterioles (from 1.59 ± 0.38 to 1.14 ± 0.31 to 1.18 ± 0.33 mm/s, p = 0.013) and outer medulla descending vasa recta (from 0.70 ± 0.05 to 0.66 ± 0.04 to 0.69 ± 0.06 mm/s, p = 0.026). Conclusively, super-resolution ultrasound imaging makes it possible to detect and differentiate microbubble velocity responses to prazosin simultaneously in the renal cortical and medullary vascular beds.

Physiological roles of hydrogen sulfide in mammalian cells, tissues, and organs.

Over the last two decades, hydrogen sulfide (H2S) has emerged as an endogenous regulator of a broad range of physiological functions. H2S belongs to the class of molecules known as gasotransmitters, which typically include nitric oxide (NO) and carbon monoxide (CO). Three enzymes are recognized as endogenous sources of H2S in various cells and tissues: cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS), and 3-mercaptopyruvate sulfurtransferase (3-MST). The present article reviews the regulation of these enzymes as well as the pathways of their enzymatic and nonenzymatic degradation and elimination. The multiple interactions of H2S with other labile endogenous molecules (e.g., NO) and reactive oxygen species are also outlined. Next, the various biological targets and signaling pathways are outlined, with special reference to H2S or oxidative posttranscriptional modification (persulfidation or sulfhydration) of proteins and the effect of H2S on various channels and intracellular second messenger pathways, the regulation of gene transcription and translation, and the regulation of cellular bioenergetics and metabolism. The pharmacological and molecular tools currently available to study H2S physiology are also reviewed, including their utility and limitations. In subsequent sections, the role of H2S in the regulation of various physiological and cellular functions is reviewed, including the regulation of membrane potential, endo- and exocytosis, regulation of various cell organelles (endoplasmic reticulum, Golgi, mitochondria), regulation of cell movement, cell cycle, cell differentiation, and physiological aspects of regulated cell death. Next, the physiological roles of H2S in various cell types and organ systems are overviewed, including the role of H2S in red blood cells, immune cells, the central and peripheral nervous systems (with focus on neuronal transmission, learning, and memory formation), and regulation of vascular function (including angiogenesis as well as its specialized roles in the cerebrovascular, renal, and pulmonary vascular beds) and the role of H2S in the regulation of special senses, vision, hearing, taste and smell, and pain-sensing. Finally, the roles of H2S in the regulation of various organ functions (lung, heart, liver, kidney, urogenital organs, reproductive system, bone and cartilage, skeletal muscle, and endocrine organs) are presented, with a focus on physiology (including physiological aging) but also extending to some common pathophysiological conditions. From these data, a wide array of significant roles of H2S in the physiological regulation of all organ functions emerges and the characteristic bell-shaped biphasic effects of H2S are highlighted. In addition, key pathophysiological aspects, debated areas, and future research and translational areas are identified.

Regionally selective cardiovascular responses to adenosine A2A and A2B receptor activation.

Adenosine is a local mediator that regulates changes in the cardiovascular system via activation of four G protein‐coupled receptors (A1, A2A, A2B, A3). Here, we have investigated the effect of A2A and A2B‐selective agonists on vasodilatation in three distinct vascular beds of the rat cardiovascular system. NanoBRET ligand binding studies were used to confirm receptor selectivity. The regional hemodynamic effects of adenosine A2A and A2B selective agonists were investigated in conscious rats. Male Sprague‐Dawley rats (350–450 g) were chronically implanted with pulsed Doppler flow probes on the renal artery, mesenteric artery, and the descending abdominal aorta. Cardiovascular responses were measured following intravenous infusion (3 min for each dose) of the A2A‐selective agonist CGS 21680 (0.1, 0.3, 1 µg kg−1 min−1) or the A2B‐selective agonist BAY 60‐6583 (4,13.3, 40 µg kg−1 min−1) following predosing with the A2A‐selective antagonist SCH 58261 (0.1 or 1 mg kg−1 min−1), the A2B/A2A antagonist PSB 1115 (10 mg kg−1 min−1) or vehicle. The A2A‐selective agonist CGS 21680 produced a striking increase in heart rate (HR) and hindquarters vascular conductance (VC) that was accompanied by a significant decrease in mean arterial pressure (MAP) in conscious rats. In marked contrast, the A2B‐selective agonist BAY 60‐6583 significantly increased HR and VC in the renal and mesenteric vascular beds, but not in the hindquarters. Taken together, these data indicate that A2A and A2B receptors are regionally selective in their regulation of vascular tone. These results suggest that the development of A2B receptor agonists to induce vasodilatation in the kidney may provide a good therapeutic approach for the treatment of acute kidney injury.

Boldine, an Alkaloid from Peumus boldus Molina, Induces Endothelium-Dependent Vasodilation in the Perfused Rat Kidney: Involvement of Nitric Oxide and Small-Conductance Ca2+-Activated K+ Channel

Boldine, 2,9-dihydroxy-1,10-dimethoxyaporphine, is the main alkaloid found in the leaves and bark of Peumus boldus Molina. In recent years, boldine has demonstrated several pharmacological properties that benefit endothelial function, blood pressure control, and reduce damage in kidney diseases. However, the renal vasodilator effects and mechanisms remain unknown. Herein, perfused rat kidneys were used to study the ability of boldine to induce vasodilation of renal arteries. For that, left kidney preparations with and without functional endothelium were contracted with phenylephrine and received 10–300 nmol boldine injections. The preparations were then perfused for 15 min with phenylephrine plus L-NAME, indomethacin, KCl, tetraethylammonium, glibenclamide, apamin, charybdotoxin, or iberiotoxin. In 30, 100, and 300 nmol doses, boldine induced a dose-and endothelium-dependent relaxing effect on the renal vascular bed. No vasodilator effects were observed in preparations lacking functional endothelium. While the inhibition of the cyclooxygenase enzyme through the addition of indomethacin did not cause any change in the vasodilating action of boldine, the nonselective nitric oxide synthase inhibitor L-NAME fully precluded the vasodilatory action of boldine at all doses tested. The perfusion with KCl or tetraethylammonium (nonselective K+ channels blocker) also abolished the vasodilatory effect of boldine, indicating the participation of K+ channels in the renal action of boldine. The perfusion with glibenclamide (selective ATP-sensitive K+ channels blocker), iberiotoxin (selective high-conductance Ca2+-activated K+ channel blocker), and charybdotoxin (selective high- and intermediate-conductance Ca2+-activated K+ channel blocker) did not modify the vasodilatory action of boldine. On the other hand, the perfusion with apamin (selective small-conductance Ca2+-activated K+ channel blocker) completely prevented the vasodilatory action of boldine at all doses tested. Together, the present study showed the renal vasodilatory properties of boldine, an effect dependent on the generation of nitric oxide and the opening of a small-conductance Ca2+-activated K+ channel.

Differential Role of Renal Alpha 1 Adreno Receptors Subtypes in Renal Vasculature in Normotensive and Hypertensive Conditions Subjected to High Dietary Salt Load

Chronic high salt intake is well known to be linked to cause an increase in the blood pressure and one of the pathogenic effects of high salt on blood pressure is vascular functional impairment. The effect of sodium on vasculature involves an increase in the vascular resistance that could triggers a rise in the blood pressure. Sodium-induced increase in vascular resistance is primarily independent of any change in blood pressure; however, it could be an initiating factor for increase in the blood pressure. Salt induced increase in the vascular resistance involves alterations in several vasoregulatory mechanisms as evidenced in various vascular beds. A mechanism exhibiting a substantial effect on vascular function is the alpha (α1)-adrenergic system that significantly influences vascular resistance, thereby affecting peripheral vascular resistance and blood pressure. This review focused on the effects of increase dietary sodium intake on the α1-adrenergic system in renal vascular beds under normotensive and hypertensive conditions. Because the α1-adrenergic regulations of renal vascular function and renal hemodynamics affect blood pressure to a great extent, renal vascular assessment was performed. Study reports enhanced renal vascular sensitivity to α1-adrenergic agonist in high sodium normotensive and hypertensive condition, this could be due to functional alterations in the renal α1-adrenoreceptor density. This provide additional evidence on the underlying vascular pathology in salt-induced hypertension.

Changes in the renal function after acute mercuric chloride exposure in the rat are associated with renal vascular endothelial dysfunction and proximal tubule NHE3 inhibition

Mercury is an environmental pollutant and a threat to human health. Mercuric chloride (HgCl2)-induced acute renal failure has been described by several reports, but the mechanisms of renal dysfunction remain elusive. This study tested the hypothesis that HgCl2 directly impairs renal vascular reactivity. Additionally, due to the mercury toxicity on the proximal tubule, we investigated whether the HgCl2-induced natriuresis is accompanied by inhibition of Na+/H+ exchanger isoform-3 (NHE3). We found that 90-min HgCl2 infusion (6.5 μg/kg i.v.) remarkably increased urinary output, reduced GFR and renal blood flow, and increased vascular resistance in rats. “In vitro” experiments of HgCl2 infusion in isolated renal vascular bed demonstrated an elevation of perfusion pressure in a concentration- and time-dependent manner, associated with changes on the endothelium-dependent vasodilatation and the flow-pressure relationship. Moreover, by employing “in vivo” stationary microperfusion of the proximal tubule, we found that HgCl2 inhibits NHE3 activity and increases the phosphorylation of NHE3 at serine 552 in the renal cortex, in line with the HgCl2-induced diuresis. Changes in renal proximal tubular function induced by HgCl2 were parallel to increased urinary markers of proximal tubular injury. Besides, atomic spectrometry showed that mercury accumulated in the renal cortex. We conclude that acute HgCl2 exposure causes renal vasoconstriction that is associated with reduced endothelial vasodilator agonist- and flow-mediated responses and inhibition of NHE3-mediated sodium reabsorption. Thus, our data suggest that HgCl2-induced acute renal failure may be attributable at least in part by its direct effects on renal hemodynamics and NHE3 activity.

Physiological Function of Blood Vessels from Uncontrolled Donation after Circulatory Death in Pigs

Donation after circulatory death (DCD) has become increasingly important in kidney transplantation. Challenges, including early graft loss and delayed graft function, remain. Little is known regarding vascular properties. The aim was to examine effects of DCD on renal artery function in a novel pig extended DCD model, extending the time from circulatory arrest to retrieval of the organ to more than 4 hours, making it more feasible to recruit more organs from DCD. Renal and iliac arteries were obtained from animals immediately after euthanasia (fresh) and 4.5hr after DCD. Vessels were also analyzed after 10hr at 4°C in physiological salt solution (stored). Preparations were mounted for isometric force recording in vitro and examined at optimal stretch for active tension. Iliac arteries were more sensitive to noradrenaline compared to renal artery, possibly reflecting differences in sympathetic control of perfusion in renal and hind limb vascular beds. Active tension (depolarization, noradrenaline activation) was significantly lower in DCD renal arteries compared to fresh vessels. Stored renal arteries were also weaker, but to a lower extent, whereas iliac artery was only marginally weakened in uDCD and unaffected by storage. For both vessel types, DCD caused a significant attenuation of endothelial-mediated relaxation. Kidneys from uDCD donors performed poorly after transplantation, as expected, with a somewhat better result if the donor was given the standard protocol, including cooling after two hours. In conclusion, DCD introduces changes both in contractile function and endothelium-mediated relaxation of renal arteries. Effects were more pronounced than in iliac artery, suggesting that DCD could be one factor affecting the functional circulation of the donor kidney after transplantation. Further studies of uDCD subject to reconditioning before transplantation is underway to study the reversibility of changes to the endothelial function after our uDCD protocol.

Estimation of the vascular resistance amplifier in the renal vascular bed in conscious hypertensive rabbits: comparison with the total peripheral vasculature

ObjectivesThe vascular amplifier in hypertension is a result of structural changes in resistance arteries. We estimated the vascular amplifier hypertensive:normotensive (H:N) ratio in the renal bed compared with the total peripheral bed in conscious rabbits during infusion of vasoconstrictor and vasodilator stimuli. MethodsRabbits were subjected to bilateral renal cellophane wrap or sham operation. A perivascular ultrasonic flow probe was implanted on the left renal artery to measure renal blood flow. A catheter was inserted into the thoracic aorta for agonist administration. Blood pressure, heart rate and renal blood flow were measured on three separate days in conscious rabbits with intact effectors, ganglionic block or neurohumoral block. Dose-response curves were constructed to intra-arterial infusion of noradrenaline, angiotensin II, adenosine and acetylcholine. ResultsResting renal vascular resistance in hypertensive rabbits was markedly decreased by ganglionic block and further by neurohumoral block. With effectors intact, ganglionic block or neurohumoral block, the H:N ratio for renal vascular resistance was 2.32, 1.72 or 1.72, respectively. The ratio was generally maintained during the infusion of constrictor and dilator drugs although distortions occurred at higher concentrations of constrictor or dilator drugs. ConclusionsEstimation of the renal resistance amplifier in renal wrap hypertension with neurohumoral block accords with our earlier estimates of the total peripheral resistance amplifier (1.79). This vascular resistance amplifier is consistent with a decrease in internal radius through structural remodelling in the renal vascular bed as is reflected in the total arterial circulation in hypertension.

Exploring the Haemodynamic Effects of BAY60‐6583, in Conscious, Freely‐Moving Rats

IntroductionThe adenosine A2B receptor (A2BR) is a potential novel therapeutic target for cancer treatments, however, the effects of A2BR ligands on the cardiovascular system have yet to be fully elucidated [1]. This project explored haemodynamic responses to a selective A2BR agonist, BAY60‐6583, in conscious rats. Previous, unpublished studies have shown that BAY60‐6583 causes tachycardia and vasodilatations in the renal and mesenteric vascular beds, that are attenuated by the A2BR selective antagonist, PSB1115, proving that the effects of BAY60‐6583 are caused by agonism of the A2BR. It is not known, however, if the tachycardic response is caused directly by A2BRs situated on the heart, or by indirect catecholamine mediated homeostatic reflexes to maintain mean arterial pressure (MAP) in the presence of regional arterial vasodilatations. In this study, the haemodynamic response to BAY60‐6583 in the presence or absence of the beta‐adrenergic blocking agent propranolol was investigated to test if the tachycardic response is caused by catecholamine mediated reflexes.MethodsSprague‐Dawley rats were anaesthetised, before being implanted with pulsed Doppler flow probes for the measurement of vascular conductance in the renal, mesenteric, and hindquarter vascular beds. Subsequently, intra‐arterial and intra‐venous catheters were implanted, allowing measurements of heart rate (HR) and MAP, and drug administration, respectively. 24 hours after surgery, a bolus of either the beta‐blocker, propranolol (0.1 mL, 1.0 mg/kg), or vehicle (0.1 mL) was followed by infusion with either propranolol (0.5 mg/kg/hr) or vehicle, respectively. After 90 minutes, three doses (4, 13.3, 40 μg/kg/min) of BAY60‐6583 was consecutively infused, each for 3 minutes, respectively. Recordings were made for a further 4 hours after drug administration. BAY60‐6583 was administered on two separate experimental days, in the presence or absence of propranolol, with a washout day in between, allowing each rat to act as their control. Procedures were approved by the University of Nottingham Animal Welfare Ethical Review Board, under Home Office Project and Personal License Authority, and follow the FASEB statement of principles for the use of animals in research.ResultsInfusion of BAY60‐6583 (4, 13.3, 40 μg/kg/min) caused a dose‐dependent increase in HR, no significant change in MAP and was accompanied by an increase in renal and mesenteric vascular conductance, but no significant change in hindquarter vascular conductance (Figure 1). Treatment with propranolol attenuated the tachycardic effects of BAY60‐6583. Propranolol caused no changes to the effects of BAY60‐6583 on regional vascular beds (Figure 1).ConclusionsThe tachycardia caused by BAY60‐6583 administration can be attenuated by beta‐blockade, suggesting that BAY60‐6583 may cause catecholamine mediated reflex countermeasures to maintain MAP in the presence of vasodilatations in the renal and mesenteric vascular beds, in conscious rats.Support or Funding InformationThis work was funded by The Centre of Membrane Proteins and Receptors (COMPARE).Responses to BAY60‐6583, ± propranolol, in conscious rats. A 0.1 mL bolus of propranolol (1.0 mg/kg) or vehicle was administered, before a 90‐minute infusion of either propranolol (0.5 mg/kg/hr) or vehicle, respectively. After infusion, three doses (4, 13.3, 40 μg/kg/min, each for 3 minutes) of BAY60‐6583 was administered. *Friedman’s test, P&lt;0.05 accepted for significance versus baseline. #Wilcoxon test, P&lt;0.05 accepted for significance between conditions. Data: mean ± SEM, n=8.Figure 1