Adenosine A1-receptor deficiency diminishes afferent arteriolar and blood pressure responses during nitric oxide inhibition and angiotensin II treatment

Purinoceptor: a novel target for hypertension

Hypertension is the leading cause of morbidity and mortality globally among all cardiovascular diseases. Purinergic signalling plays a crucial role in hypertension through the sympathetic nerve system, neurons in the brain stem, carotid body, endothelium, immune system, renin-angiotensin system, sodium excretion, epithelial sodium channel activity (ENaC), and renal autoregulation. Under hypertension, adenosine triphosphate (ATP) is released as a cotransmitter from the sympathetic nerve. It mediates vascular tone mainly through P2X1R activation on smooth muscle cells and activation of P2X4R and P2YR on endothelial cells and also via interaction with other purinoceptors, showing dual effects. P2Y1R is linked to neurogenic hypertension. P2X7R and P2Y11R are potential targets for immune-related hypertension. P2X3R located on the carotid body is the most promising novel therapeutic target for hypertension. A₁R, A_2AR, A_2BR, and P2X7R are all related to renal autoregulation, which contribute to both renal damage and hypertension. The main focus is on the evidence addressing the involvement of purinoceptors in hypertension and therapeutic interventions.

The Role of Macula Densa Nitric Oxide Synthase 1 Beta Splice Variant in Modulating Tubuloglomerular Feedback

Abnormalities in renal electrolyte and water excretion may result in inappropriate salt and water retention, which facilitates the development and maintenance of hypertension, as well as acid-base and electrolyte disorders. A key mechanism by which the kidney regulates renal hemodynamics and electrolyte excretion is via tubuloglomerular feedback (TGF), an intrarenal negative feedback between tubules and arterioles. TGF is initiated by an increase of NaCl delivery at the macula densa cells. The increased NaCl activates luminal Na-K-2Cl cotransporter (NKCC2) of the macula densa cells, which leads to activation of several intracellular processes followed by the production of paracrine signals that ultimately result in a constriction of the afferent arteriole and a tonic inhibition of single nephron glomerular filtration rate. Neuronal nitric oxide (NOS1) is highly expressed in the macula densa. NOS1β is the major splice variant and accounts for most of NO generation by the macula densa, which inhibits TGF response. Macula densa NOS1β-mediated modulation of TGF responses plays an essential role in control of sodium excretion, volume and electrolyte hemostasis, and blood pressure. In this article, we describe the mechanisms that regulate macula densa-derived NO and their effect on TGF response in physiologic and pathologic conditions. © 2023 American Physiological Society. Compr Physiol 13:4215-4229, 2023.

HSPA8 Is Identified as a Novel Regulator of Hypertensive Disorders in Pregnancy by Modulating the β-Arrestin1/A1AR Axis

Heat shock protein alpha 8 (HSPA8) was found to be downregulated in the placentas of patients with hypertensive disorders in pregnancy (HDP). We aim to explore the underlying role and mechanism of HSPA8 in HDP progression. Herein, HSPA8 mRNA expression in placentas and peripheral blood of patients with HDP and normal pregnant controls was measured with RT-qPCR. We found that HSPA8 expression was downregulated in placentas and peripheral blood of patients with HDP. HTR8/SVneo human trophoblast cells were transfected with pcDNA-HSPA8 or si-HSPA8. HSPA8 overexpression promoted cell proliferation, migration, and MMP-2 and MMP-9 protein levels, and inhibited apoptosis, while HSPA8 silencing showed the opposite results. Co-immunoprecipitation assay validated the binding between HSPA8 and β-arrestin1, as well as β-arrestin1 and A1AR proteins. HSPA8 bound with β-arrestin1 protein and promoted β-arrestin1 expression. β-arrestin1 bound with A1AR protein and inhibited A1AR expression. Then, HTR8/SVneo cells were transfected with pcDNA-HSPA8 alone or together with si-β-arrestin1, as well as transfected with pcDNA-β-arrestin1 alone or together with pcDNA-A1AR. β-arrestin1 silencing reversed the effects of HSPA8 overexpression on HTR8/SVneo cell functions. β-arrestin1 overexpression promoted cell proliferation migration, and MMP-2 and MMP-9 protein levels, and inhibited apoptosis, while these effects were reversed by A1AR overexpression. Lentivirus HSPA8 overexpression vector (Lv-HSPA8) was injected into a preeclampsia (PE) rat model, which attenuated blood pressure and fetal detrimental changes in PE rats. In conclusion, HSPA8 promoted proliferation and migration and inhibited apoptosis in trophoblast cells, and attenuated the symptoms of PE rats by modulating the β-arrestin1/A1AR axis. Our study provided a novel theoretical evidence and potential strategy for HDP treatment.

Tubule-vascular feedback in renal autoregulation

Afferent arteriole (Af-Art) diameter regulates pressure and flow into the glomerulus, which are the main determinants of the glomerular filtration rate. Thus, Af-Art resistance is crucial for Na⁺ filtration. Af-Arts play a role as integrative centers, where systemic and local systems interact to determine the final degree of resistance. The tubule of a single nephron contacts an Af-Art of the same nephron at two locations: in the transition of the thick ascending limb to the distal tubule (macula densa) and again in the connecting tubule. These two sites are the anatomic basis of two intrinsic feedback mechanisms: tubule-glomerular feedback and connecting tubule-glomerular feedback. The cross communications between the tubules and Af-Arts integrate tubular Na⁺ and water processing with the hemodynamic conditions of the kidneys. Tubule-glomerular feedback provides negative feedback that tends to avoid salt loss, and connecting tubule-glomerular feedback provides positive feedback that favors salt excretion by modulating tubule-glomerular feedback (resetting it) and increasing glomerular filtration rate. These feedback mechanisms are also exposed to systemic modulators (hormones and the nervous system); however, they can work in isolated kidneys or nephrons. The exaggerated activation or absence of any of these mechanisms may lead to disequilibrium in salt and water homeostasis, especially in extreme conditions (e.g., high-salt diet/low-salt diet) and may be part of the pathogenesis of some diseases. In this review, we focus on molecular signaling, feedback interactions, and the physiological roles of these two feedback mechanisms.

Enhanced A1 adenosine receptor-induced vascular contractions in mesenteric artery and aorta of in L-NAME mouse model of hypertension

L-NAME-induced hypertension is commonly used to study endothelial dysfunction and related vascular effects. It has been reported that genetic deletion of A₁ adenosine receptor (AR) reduces blood pressure (BP) increases in mice and thus, suggesting the involvement of A₁AR. Thus, we sought to determine whether A₁AR-induced vascular responses were altered in this mouse model of hypertension. L-NAME (1 mg/ml) was given in the drinking water for 28 days to mice. The BP was monitored using non-invasive tail-cuff system. Muscle tension studies were performed using DMT for mesenteric arteries (MAs) and organ bath for aorta. Protein expression was analyzed by western blot. Significantly, higher systolic and mean arterial blood pressure was noted in L-NAME mice. In MAs, higher 2-Chloro-N⁶-cyclopentyladenosine (CCPA, selective A₁AR agonist) induced contractions in hypertensive mice were observed. This enhanced contraction was inhibited by HET0016 (Cytochrome 450 4A inhibitor, 10 µM, 15 min). Contrary, 5'-(N-Ethylcarboxamido) adenosine (NECA, non-selective AR agonist) induced vascular responses were comparable in both groups. Pinacidil (K_ATP channel opener) induced relaxation was significantly increased in hypertensive mice. In aorta, CCPA-induced contractions were enhanced and inhibited by HET0016 in hypertensive mice. Notably, NECA-induced contractions in aorta were enhanced in hypertensive mice. Higher expressions of A₁AR and Cyp4A were noted in MAs of hypertensive mice. In addition, in aorta, higher A₁AR and comparable Cyp4A levels were observed in hypertensive mice. A₁AR-induced vascular contractions were enhanced in hypertensive mice aorta and MAs. Cyp4A plays a role in altered vascular responses in MAs.

Concerted regulation of renal plasma flow and glomerular filtration rate by renal dopamine and NOS I in rats on high salt intake

Under high sodium intake renal dopamine (DA) increases while NOS I expression in macula densa cells (MD) decreases. To explore whether renal DA and NOS I, linked to natriuresis and to the stability of the tubuloglomerular feedback, respectively, act in concert to regulate renal plasma flow (RPF) and glomerular filtration rate (GFR). Male Wistar rats were studied under a normal sodium intake (NS, NaCl 0.24%) or a high sodium intake (HS, NaCl 1% in drinking water) during the 5 days of the study. For the last two days, the specific D1-like receptor antagonist SCH 23390 (1 mg kg bwt-1 day-1, sc) or a vehicle was administered. HS intake increased natriuresis, diuresis, and urinary DA while it decreased cortical NOS I expression (P < 0.05 vs. NS), Nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) activity in MD (P < 0.001 vs. NS) and cortical nitrates+nitrites (NOx) production (NS 2.04 ± 0.22 vs. HS 1.28 ± 0.10 nmol mg protein-1, P < 0.01). Treatment with SCH 23390 to rats on HS sharply decreased hydroelectrolyte excretion (P < 0.001 vs. HS) while NOS I expression, NADPH-d activity and NOx production increased (P < 0.05 vs. HS for NOS I and P < 0.001 vs. HS for NADPH-d and NOx). SCH 23390 increased RPF and GFR in HS rats (P < 0.01 HS+SCH vs. HS). It did not cause variations in NS rats. Results indicate that when NS intake is shifted to a prolonged high sodium intake, renal DA through the D1R, and NOS I in MD cells act in concert to regulate RPF and GFR to stabilize the delivery of NaCl to the distal nephron.

Adenosine contribution to normal renal physiology and chronic kidney disease

Adenosine is a nucleoside that is particularly interesting to many scientific and clinical communities as it has important physiological and pathophysiological roles in the kidney. The distribution of adenosine receptors has only recently been elucidated; therefore it is likely that more biological roles of this nucleoside will be unveiled in the near future. Since the discovery of the involvement of adenosine in renal vasoconstriction and regulation of local renin production, further evidence has shown that adenosine signaling is also involved in the tubuloglomerular feedback mechanism, sodium reabsorption and the adaptive response to acute insults, such as ischemia. However, the most interesting finding was the increased adenosine levels in chronic kidney diseases such as diabetic nephropathy and also in non-diabetic animal models of renal fibrosis. When adenosine is chronically increased its signaling via the adenosine receptors may change, switching to a state that induces renal damage and produces phenotypic changes in resident cells. This review discusses the physiological and pathophysiological roles of adenosine and pays special attention to the mechanisms associated with switching homeostatic nucleoside levels to increased adenosine production in kidneys affected by CKD.

Genetic Abrogation of Adenosine A3 Receptor Prevents Uninephrectomy and High Salt-Induced Hypertension

Background

Early‐life reduction in nephron number (uninephrectomy [UNX]) and chronic high salt (HS) intake increase the risk of hypertension and chronic kidney disease. Adenosine signaling via its different receptors has been implicated in modulating renal, cardiovascular, and metabolic functions as well as inflammatory processes; however, the specific role of the A₃ receptor in cardiovascular diseases is not clear. In this study, gene‐modified mice were used to investigate the hypothesis that lack of A₃ signaling prevents the development of hypertension and attenuates renal and cardiovascular injuries following UNX in combination with HS (UNX‐HS) in mice.

Methods and Results

Wild‐type (A₃^+/+) mice subjected to UNX‐HS developed hypertension compared with controls (mean arterial pressure 106±3 versus 82±3 mm Hg; P<0.05) and displayed an impaired metabolic phenotype (eg, increased adiposity, reduced glucose tolerance, hyperinsulinemia). These changes were associated with both cardiac hypertrophy and fibrosis together with renal injuries and proteinuria. All of these pathological hallmarks were significantly attenuated in the A₃^−/− mice. Mechanistically, absence of A₃ receptors protected from UNX‐HS–associated increase in renal NADPH oxidase activity and Nox2 expression. In addition, circulating cytokines including interleukins 1β, 6, 12, and 10 were increased in A₃^+/+ following UNX‐HS, but these cytokines were already elevated in naïve A₃^−/− mice and did not change following UNX‐HS.

Conclusions

Reduction in nephron number combined with chronic HS intake is associated with oxidative stress, chronic inflammation, and development of hypertension in mice. Absence of adenosine A₃ receptor signaling was strongly protective in this novel mouse model of renal and cardiovascular disease.

Nitric oxide generation by the organic nitrate NDBP attenuates oxidative stress and angiotensin II-mediated hypertension

BACKGROUND AND PURPOSE

NO deficiency and oxidative stress are crucially involved in the development or progression of cardiovascular disease, including hypertension and stroke. We have previously demonstrated that acute treatment with the newly discovered organic nitrate, 2-nitrate-1,3-dibuthoxypropan (NDBP), is associated with NO-like effects in the vasculature. This study aimed to further characterize the mechanism(s) and to elucidate the therapeutic potential in a model of hypertension and oxidative stress.

EXPERIMENTAL APPROACH

A combination of ex vivo, in vitro and in vivo approaches was used to assess the effects of NDBP on vascular reactivity, NO release, NADPH oxidase activity and in a model of hypertension.

KEY RESULTS

Ex vivo vascular studies demonstrated NDBP-mediated vasorelaxation in mesenteric resistance arteries, which was devoid of tolerance. In vitro studies using liver and kidney homogenates revealed dose-dependent and sustained NO generation by NDBP, which was attenuated by the xanthine oxidase inhibitor febuxostat. In addition, NDBP reduced NADPH oxidase activity in the liver and prevented angiotensin II-induced activation of NADPH oxidase in the kidney. In vivo studies showed that NDBP halted the progression of hypertension in mice with chronic angiotensin II infusion. This was associated with attenuated cardiac hypertrophy, and reduced NADPH oxidase-derived oxidative stress and fibrosis in the kidney and heart.

CONCLUSION AND IMPLICATIONS

The novel organic nitrate NDBP halts the progression of angiotensin II-mediated hypertension. Mechanistically, our findings suggest that NDBP treatment is associated with sustained NO release and attenuated activity of NADPH oxidase, which to some extent requires functional xanthine oxidase.

Angiotensin II stimulation alters vasomotor response to adenosine in mouse mesenteric artery: role for A1 and A2B adenosine receptors

BACKGROUND AND PURPOSE

Stimulation of the A1 adenosine receptor and angiotensin II receptor type-1 (AT1 receptor) causes vasoconstriction through activation of cytochrome P450 4A (CYP4A) and ERK1/2. Thus, we hypothesized that acute angiotensin II activation alters the vasomotor response induced by the non-selective adenosine receptor agonist, NECA, in mouse mesenteric arteries (MAs).

EXPERIMENTAL APPROACH

We used a Danish Myo Technology wire myograph to measure muscle tension in isolated MAs from wild type (WT), A1 receptor and A2B receptor knockout (KO) mice. Western blots were performed to determine the expression of AT1 receptors and CYP4A.

KEY RESULTS

Acute exposure (15 min) to angiotensin II attenuated the NECA-dependent vasodilatation and enhanced vasoconstriction. This vasoconstrictor effect of angiotensin II in NECA-treated MAs was abolished in A1 receptor KO mice and in WT mice treated with the A1 receptor antagonist DPCPX, CYP4A inhibitor HET0016 and ERK1/2 inhibitor PD98059. In MAs from A2B receptor KO mice, the vasoconstrictor effect of angiotensin II on the NECA-induced response was shown to be dependent on A1 receptors. Furthermore, in A2B receptor KO mice, the expression of AT1 receptors and CYP4A was increased and the angiotensin II-induced vasoconstriction enhanced. In addition, inhibition of KATP channels with glibenclamide significantly reduced NECA-induced vasodilatation in WT mice.

CONCLUSIONS AND IMPLICATIONS

Acute angiotensin II stimulation enhanced A1 receptor-dependent vasoconstriction and inhibited A2B receptor-dependent vasodilatation, leading to a net vasoconstriction and altered vasomotor response to NECA in MAs. This interaction may be important in the regulation of BP.

Abrogation of adenosine A1 receptor signalling improves metabolic regulation in mice by modulating oxidative stress and inflammatory responses

AIMS/HYPOTHESIS

Adenosine is an important regulator of metabolism; however, the role of the A1 receptor during ageing and obesity is unclear. The aim of this study was to investigate the effects of A1 signalling in modulating metabolic function during ageing.

METHODS

Age-matched young and aged A 1 (also known as Adora1)-knockout (A1(-/-)) and wild-type (A1(+/+)) mice were used. Metabolic regulation was evaluated by body composition, and glucose and insulin tolerance tests. Isolated islets and islet arterioles were used to detect islet endocrine and vascular function. Oxidative stress and inflammation status were measured in metabolic organs and systemically.

RESULTS

Advanced age was associated with both reduced glucose clearance and insulin sensitivity, as well as increased visceral adipose tissue (VAT) in A1(+/+) compared with A1(-/-) mice. Islet morphology and insulin content were similar between genotypes, but relative changes in in vitro insulin release following glucose stimulation were reduced in aged A1(+/+) compared with A1(-/-) mice. Islet arteriolar responses to angiotensin II were stronger in aged A1(+/+) mice, this being associated with increased NADPH oxidase activity. Ageing resulted in multiple changes in A1(+/+) compared with A1(-/-) mice, including enhanced NADPH oxidase-derived O2(-) formation and NADPH oxidase isoform 2 (Nox2) protein expression in pancreas and VAT; elevated levels of circulating insulin, leptin and proinflammatory cytokines (TNF-α, IL-1β, IL-6 and IL-12); and accumulation of CD4(+) T cells in VAT. This was associated with impaired insulin signalling in VAT from aged A1(+/+) mice.

CONCLUSIONS/INTERPRETATION

These studies emphasise that A1 receptors regulate metabolism and islet endocrine and vascular functions during ageing, including via the modulation of oxidative stress and inflammatory responses, among other things.

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.

Identification and function of adenosine A3 receptor in afferent arterioles

Adenosine plays an important role in regulation of renal microcirculation. All receptors of adenosine, A1, A2A, A2B, and A3, have been found in the kidney. However, little is known about the location and function of the A3 receptor in the kidney. The present study determined the expression and role of A3 receptors in mediating the afferent arteriole (Af-Art) response and studied the interaction of A3 receptors with angiotensin II (ANG II), A1 and A2 receptors on the Af-Art. We found that the A3 receptor expressed in microdissected isolated Af-Art and the mRNA levels of A3 receptor were 59% of A1. In the isolated microperfused Af-Art, A3 receptor agonist IB-MECA did not have a constrictive effect. Activation of A3 receptor dilated the preconstricted Af-Art by norepinephrine and blunted the vasoconstrictive effect of both adenosine A1 receptor activation and ANG II on the Af-Art, respectively. Selective A2 receptor antagonist (both A2A and A2B) had no effect on A3 receptor agonist-induced vasodilation, indicating that the dilatory effect of A3 receptor activation is not mediated by activation of A2 receptor. We conclude that the A3 receptor is expressed in the Af-Art, and activation of the A3 receptor dilates the Af-Art.

Adenosine A1 receptor-dependent and independent pathways in modulating renal vascular responses to angiotensin II

AIM

Renal afferent arterioles are the effector site for autoregulation of glomerular perfusion and filtration. There is synergistic interaction between angiotensin II (ANG II) and adenosine (Ado) in regulating arteriolar contraction; however, the mechanisms are not clear. In this context, this study investigated the contribution of A1 receptor-dependent and independent signalling mechanisms.

METHODS

Isolated perfused afferent arterioles from transgenic mice (A1 (+/+) and A1 (-/-) ) were used for vascular reactivity studies. Cultured vascular smooth muscle cells (VSMC) were used for phosphorylation studies of signalling proteins that induce arteriolar contraction.

RESULTS

Maximal arteriolar contraction to ANG II was attenuated in A1 (-/-) (22%) compared with A1 (+/+) (40%). Simultaneous incubation with low-dose ado (10(-8)  mol L(-1) ) enhanced ANG II-induced contraction in A1 (+/+) (58%), but also in A1 (-/-) (42%). An ado transporter inhibitor (NBTI) abolished this synergistic effect in A1 (-/-) , but not in wild-type mice. Incubation with Ado + ANG II increased p38 phosphorylation in aortic VSMC from both genotypes, but treatment with NBTI only blocked phosphorylation in A1 (-/-) . Combination of ANG II + Ado also increased MLC phosphorylation in A1 (+/+) but not significantly in A1 (-/-) , and NBTI had no effects. In agreement, Ado + ANG II-induced phosphorylation of p38 and MLC in rat pre-glomerular VSMC was not affected by NBTI. However, during pharmacological inhibition of the A1 receptor simultaneous treatment with NBTI reduced phosphorylation of both p38 and MLC to control levels.

CONCLUSION

Interaction between ANG II and Ado in VSMC normally involves A1 receptor signalling, but this can be compensated by receptor independent actions that phosphorylate p38 MAPK and MLC.

Oxidative status in the macula densa modulates tubuloglomerular feedback responsiveness in angiotensin II-induced hypertension

AIM

Tubuloglomerular feedback (TGF) is an important mechanism in control of signal nephron glomerular filtration rate. The oxidative stress in the macula densa, primarily determined by the interactions between nitric oxide (NO) and superoxide (O2-), is essential in maintaining the TGF responsiveness. However, few studies examining the interactions between and amount of NO and O2- generated by the macula densa during normal and hypertensive states.

METHODS

In this study, we used isolated perfused juxtaglomerular apparatus to directly measure the amount and also studied the interactions between NO and O2- in macula densa in both physiological and slow pressor Angiotensin II (Ang II)-induced hypertensive mice.

RESULTS

We found that slow pressor Ang II at a dose of 600 ng kg(-1) min(-1) for two weeks increased mean arterial pressure by 26.1 ± 5.7 mmHg. TGF response increased from 3.4 ± 0.2 μm in control to 5.2 ± 0.2 μm in hypertensive mice. We first measured O2- generation by the macula densa and found it was undetectable in control mice. However, O2- generation by the macula densa increased to 21.4 ± 2.5 unit min(-1) in Ang II-induced hypertensive mice. We then measured NO generation and found that NO generation by the macula densa was 138.5 ± 9.3 unit min(-1) in control mice. The NO was undetectable in the macula densa in hypertensive mice infused with Ang II.

CONCLUSIONS

Under physiological conditions, TGF response is mainly controlled by the NO generated in the macula densa; in Ang II induced hypertension, the TGF response is mainly controlled by the O2- generated by the macula densa.

Blood pressure, heart rate and tubuloglomerular feedback in A1AR-deficient mice with different genetic backgrounds

AIM

Differences in genetic background between control mice and mice with targeted gene mutations have been recognized as a potential cause for phenotypic differences. In this study, we have used A1AR-deficient mice in a C57Bl/6 and SWR/J congenic background to assess the influence of background on the effect of A1AR-deficiency on cardiovascular and renal functional parameters.

METHODS

In A1AR+/+ and A1AR-/- mice in C57Bl/6 and SWR/J congenic backgrounds, we assessed blood pressure and heart rate using radio-telemetry, plasma renin concentrations and tubuloglomerular feedback.

RESULTS

We did not detect significant differences in arterial blood pressure (MAP) and heart rates (HR) between A1AR+/+ and A1AR-/- mice in either C57Bl/6, SWR/J or mixed backgrounds. MAP and HR were significantly higher in SWR/J than in C57Bl/6 mice. A high NaCl intake increased MAP in A1AR-/- mice on C57Bl/6 background while there was less or no salt sensitivity in the SWR/J background. No significant differences in plasma renin concentration were detected between A1AR-/- and A1AR+/+ mice in any of the strains. Tubuloglomerular feedback was found to be absent in A1AR-/- mice with SWR/J genetic background.

CONCLUSIONS

While this study confirmed important differences between inbred mouse strains, we did not identify phenotypic modifications of A1AR-related effects on blood pressure, heart rate and plasma renin by differences in genetic background.

Purinergic signalling in the kidney in health and disease

The involvement of purinergic signalling in kidney physiology and pathophysiology is rapidly gaining recognition and this is a comprehensive review of early and recent publications in the field. Purinergic signalling involvement is described in several important intrarenal regulatory mechanisms, including tuboglomerular feedback, the autoregulatory response of the glomerular and extraglomerular microcirculation and the control of renin release. Furthermore, purinergic signalling influences water and electrolyte transport in all segments of the renal tubule. Reports about purine- and pyrimidine-mediated actions in diseases of the kidney, including polycystic kidney disease, nephritis, diabetes, hypertension and nephrotoxicant injury are covered and possible purinergic therapeutic strategies discussed.

Oxidative stress in hypertension: role of the kidney

SIGNIFICANCE

Renal oxidative stress can be a cause, a consequence, or more often a potentiating factor for hypertension. Increased reactive oxygen species (ROS) in the kidney have been reported in multiple models of hypertension and related to renal vasoconstriction and alterations of renal function. Nicotinamide adenine dinucleotide phosphate oxidase is the central source of ROS in the hypertensive kidney, but a defective antioxidant system also can contribute.

RECENT ADVANCES

Superoxide has been identified as the principal ROS implicated for vascular and tubular dysfunction, but hydrogen peroxide (H2O2) has been implicated in diminishing preglomerular vascular reactivity, and promoting medullary blood flow and pressure natriuresis in hypertensive animals.

CRITICAL ISSUES AND FUTURE DIRECTIONS

Increased renal ROS have been implicated in renal vasoconstriction, renin release, activation of renal afferent nerves, augmented contraction, and myogenic responses of afferent arterioles, enhanced tubuloglomerular feedback, dysfunction of glomerular cells, and proteinuria. Inhibition of ROS with antioxidants, superoxide dismutase mimetics, or blockers of the renin-angiotensin-aldosterone system or genetic deletion of one of the components of the signaling cascade often attenuates or delays the onset of hypertension and preserves the renal structure and function. Novel approaches are required to dampen the renal oxidative stress pathways to reduced O2(-•) rather than H2O2 selectivity and/or to enhance the endogenous antioxidant pathways to susceptible subjects to prevent the development and renal-damaging effects of hypertension.

L-arginine or tempol supplementation improves renal and cardiovascular function in rats with reduced renal mass and chronic high salt intake

AIM

Early life reduction in nephron number and chronic high salt intake cause development of renal and cardiovascular disease, which has been associated with oxidative stress and nitric oxide (NO) deficiency. We investigated the hypothesis that interventions stimulating NO signalling or reducing oxidative stress may restore renal autoregulation, attenuate hypertension and reduce renal and cardiovascular injuries following reduction in renal mass and chronic high salt intake.

METHODS

Male Sprague-Dawley rats were uninephrectomized (UNX) or sham-operated at 3 weeks of age and given either a normal-salt (NS) or high-salt (HS) diet. Effects on renal and cardiovascular functions were assessed in rats supplemented with substrate for NO synthase (L-Arg) or a superoxide dismutase mimetic (Tempol).

RESULTS

Rats with UNX + HS developed hypertension and displayed increased renal NADPH oxidase activity, elevated levels of oxidative stress markers in plasma and urine, and reduced cGMP in plasma. Histological analysis showed signs of cardiac and renal inflammation and fibrosis. These changes were linked with abnormal renal autoregulation, measured as a stronger tubuloglomerular feedback (TGF) response. Simultaneous treatment with L-Arg or Tempol restored cGMP levels in plasma and increased markers of NO signalling in the kidney. This was associated with normalized TGF responses, attenuated hypertension and reduced signs of histopathological changes in the kidney and in the heart.

CONCLUSION

Reduction in nephron number during early life followed by chronic HS intake is associated with oxidative stress, impaired renal autoregulation and development of hypertension. Treatment strategies that increase NO bioavailability, or reduce levels of reactive oxygen species, were proven beneficial in this model of renal and cardiovascular disease.

Regulation of atherosclerosis and associated risk factors by adenosine and adenosine receptors

Adenosine is an endogenous metabolite that has an anti-inflammatory effect across the vasculature. Extracellular adenosine activates 4 G-protein coupled receptors (A1, A3, A2A, and A2B) whose expression varies in different cells and tissues, including the vasculature and blood cells. Higher levels of adenosine are generated during stress, inflammation, and upon tissue damage. Some of the adenosine receptors (AR), such as the A2BAR, are further up-regulated following such stresses. This review discusses the role of adenosine and adenosine receptors in the development of atherosclerosis and some of the risk factors associated with this pathology. These include adenosine receptor-regulated changes in atherosclerosis, blood pressure, thrombosis, and myocardial infarction. Potential therapeutic applications are reviewed, as well as reasons for phenotypic differences occasionally observed between receptor knockout and pharmacological inhibition via drug administration.