Renal Sympathetic Nerve Stimulation Research Articles

Impacts of Renal Sympathetic Activation on Atrial Fibrillation: The Potential Role of the Autonomic Cross Talk Between Kidney and Heart

BackgroundRecent studies have demonstrated that there is a high variability of renal sympathetic nerve density distribution from proximal to distal renal artery segments. The aim of our study was to investigate the roles of renal sympathetic nerve stimulation (RSS) on atrial fibrillation and cardiac autonomic nervous activity.Methods and ResultsTwenty‐eight dogs were randomly assigned to the proximal RSS group (P‐RSS, N=7), middle RSS group (M‐RSS, N=7), distal RSS group (D‐RSS, N=7), and the control group (sham RSS, N=7). RSS was performed using electrical stimulation on the bilateral renal arteries for 3 hours. Effective refractory period and the window of vulnerability were measured at atrial and pulmonary veins sites. Superior left ganglionated plexi (SLGP) and left stellate ganglion (LSG) function and neural activity were determined. C‐fos and nerve growth factor protein expression in the SLGP and LSG were examined. Only P‐RSS (1) caused pronounced blood pressure rises, induced a significant decrease in effective refractory period, and generated a marked increase in cumulative window of vulnerability and effective refractory period dispersion; (2) increased the frequency and amplitude of the neural activity in the SLGP and LSG; (3) increased SLGP and LSG function; and (4) upregulated the level of c‐fos and nerve growth factor expression in the SLGP and LSG.ConclusionsThis study demonstrated that renal sympathetic nerve activation induced by 3 hours of P‐RSS facilitated atrial fibrillation inducibility by upregulating cardiac autonomic nervous activity, suggesting a potential autonomic cross talk between kidney and heart.

Alkaline Phosphatase Inhibitors Attenuate Renovascular Responses to Norepinephrine.

Tissue nonspecific alkaline phosphatase (TNAP) contributes to the production of adenosine by the kidney, and A1-receptor activation enhances renovascular responses to norepinephrine. Therefore, we hypothesized that TNAP regulates renovascular responsiveness to norepinephrine. In isolated, perfused rat kidneys, the TNAP inhibitor l-p-bromotetramisole (0.1 mmol/L) decreased renal venous levels of 5'-AMP (adenosine precursor) and adenosine by 61% (P<0.0384) and 62% (P=0.0013), respectively, at 1 hour into treatment and caused a 10-fold rightward shift of the concentration-response relationship to exogenous norepinephrine (P<0.0001). Similarly, 2 other TNAP inhibitors, levamisole (1 mmol/L) and 2,5-dimethoxy-N-(quinolin-3-yl)benzenesulfonamide (0.02 mmol/L), also right shifted the concentration-response relationship to norepinephrine. The ability of TNAP inhibition to blunt renovascular responses to norepinephrine was mostly prevented or reversed by restoring A1-adenosinergic tone with the A1-receptor agonist 2-chloro-N6-cyclopentyladenosine (100 nmol/L). All 3 TNAP inhibitors also attenuated renovascular responses to renal sympathetic nerve stimulation, suggesting that TNAP inhibition attenuates renovascular responses to endogenous norepinephrine. In control propranolol-pretreated rats, acute infusions of norepinephrine (10 μg/kg/min) increased mean arterial blood pressure from 95±5 mm Hg to a peak of 169±4 mm Hg and renovascular resistance from 12±2 mm Hg/mL/min to a peak of 55±12 mm Hg/mL/min; however, in rats also treated with intravenous l-p-bromotetramisole (30 mg/kg), the pressor and renovascular effects of norepinephrine were significantly attenuated (blood pressure: basal and peak, 93±7 and 146±6 mm Hg, respectively; renovascular resistance: basal and peak, 13±2 and 29±5 mm Hg/mL/min, respectively). TNAP inhibitors attenuate renovascular and blood pressure responses to norepinephrine, suggesting that TNAP participates in the regulation of renal function and blood pressure.

OP.7D.06] RENAL HEMODYNAMIC CHANGES AFTER RENAL DENERVATION

Abstract Stimulation of renal sympathetic nerves causes reduced renal blood flow. To elucidate whether renal denervation (RDN) affects renal perfusion, we analysed renal blood flow of parenchymal areas perfused by arteries that were non-treated versus treated with RDN. In a pilot study 8 patients with treatment-resistant hypertension that had multiple renal arteries in either kidney were included. All patients underwent catheter-based RDN using the Symplicity FlexTM RDN System of the main renal arteries, but not of accessory renal arteries. Renal perfusion was measured noninvasively by magnetic resonance imaging on a 1.5-T scanner with arterial spin labelling before (day-1), after (day + 1) and again after 3 months (3 M) of RDN. Renal parenchyma was divided into areas that were perfused by renal arteries which were treated with RDN versus those areas perfused by accessory renal arteries not treated with RDN. Hence, every patient could serve at its own control with respect to changes of renal blood flow in the same kidney. In addition renal function was assessed by eGFR according CKD-Epi formula. There was an acute increase of renal perfusion in areas supplied by arteries not undergoing RDN (day-1: 242.3 [229.2-263.2] vs. day + 1: 260.0 [243.5-296.6] ml/min/100 g, p = 0.008), which returned to baseline values after 3 M (257.0 [240.5-277.8] ml/min/100 g, p = 0.260). In contrast, renal perfusion did not change in areas supplied by arteries undergoing RDN in acute (day-1: 263.5 [245.9-273.6] vs. day + 1: 256.5 [242.9-273.5] ml/min/100 g, p = 0.953) and 3 M (245.4 [235.5-269.7] ml/min/100 g, p = 0.594). Accordingly, the acute change in renal perfusion between day-1 and day + 1 was significantly greater in parenchymal areas supplied by arteries without compared to areas with RDN (p = 0.014), but not after 3 M. Renal function assessed by eGFR did not change between day-1 and day + 1 (80.3 ± 20 versus 79.8 ± 20 ml/min/1.73m, p = 0.885) as well as after 3 M of RDN (80.8 ± 18 ml/min/1.73m, p = 0.889). Despite an average of 7.0 ± 1.5 antihypertensive drugs, baseline office BP was 157/85mmHg, and was reduced by -11/-7mmHg after 3 M of RDN. Our data indicate an acute increase of renal perfusion in renal parenchymal areas perfused by arteries with intact renal nerves, whereas no change occurred in parenchymal areas perfused by arteries after RDN.

The Potential Role of Catheter-Based Renal Sympathetic Denervation in Chronic and End-Stage Kidney Disease.

Sympathetic activation is a hallmark of chronic and end-stage renal disease and adversely affects cardiovascular prognosis. Hypertension is present in the vast majority of these patients and plays a key role in the progressive deterioration of renal function and the high rate of cardiovascular events in this patient cohort. Augmentation of renin release, tubular sodium reabsorption, and renal vascular resistance are direct consequences of efferent renal sympathetic nerve stimulation and the major components of neural regulation of renal function. Renal afferent nerve activity directly influences sympathetic outflow to the kidneys and other highly innervated organs involved in blood pressure control via hypothalamic integration. Renal denervation of the kidney has been shown to reduce blood pressure in many experimental models of hypertension. Targeting the renal nerves directly may therefore be specifically useful in patients with chronic and end-stage renal disease. In this review, we will discuss the potential role of catheter-based renal denervation in patients with impaired kidney function and also reflect on the potential impact on other cardiovascular conditions commonly associated with chronic kidney disease such as heart failure and arrhythmias.

5-HT1D receptor inhibits renal sympathetic neurotransmission by nitric oxide pathway in anesthetized rats

Although serotonin has been shown to inhibit peripheral sympathetic outflow, serotonin regulation on renal sympathetic outflow has not yet been elucidated. This study investigated which 5-HT receptor subtypes are involved. Wistar rats were anesthetized (sodium pentobarbital; 60mg/kg, i.p.), and prepared for in situ autoperfused rat kidney, which allows continuous measurement of systemic blood pressure (SBP), heart rate (HR) and renal perfusion pressure (PP). Electrical stimulation of renal sympathetic nerves resulted in frequency-dependent increases in PP (18.3±1.0, 43.7±2.7 and 66.7±4.0 for 2, 4 and 6Hz, respectively), without altering SBP or HR. 5-HT, 5-carboxamidotryptamine (5-HT1/7 agonist) (0.00000125–0.1μg/kg each) or l-694,247 (5-HT1D agonist; 0.0125μg/kg) i.a. bolus inhibited vasopressor responses by renal nerve electrical stimulation, unlike i.a. bolus of agonists α-methyl-5-HT (5-HT2), 1-PBG (5-HT3), cisapride (5-HT4), AS-19 (5-HT7), CGS-12066B (5-HT1B) or 8-OH-DPAT (5-HT1A) (0.0125μg/kg each). The effect of l-694,247 did not affect the exogenous norepinephrine-induced vasoconstrictions, whereas was abolished by antagonist LY310762 (5-HT1D; 1mg/kg) or l-NAME (nitric oxide; 10mg/kg), but not by indomethacin (COX1/2; 2mg/kg) or glibenclamide (ATP-dependent K+ channel; 20mg/kg). These results suggest that 5-HT mechanism-induced inhibition of rat vasopressor renal sympathetic outflow is mainly mediated by prejunctional 5-HT1D receptors via nitric oxide release.

The Effect of Renal Sympathetic Denervation (RSD) in Atrial Fibrillation (AF) Inducibility

Objective: The purpose of this study is to investigate the effects of renal sympathetic nerve stimulation (RSN-S) and ablation (RSN-A) on atrial effective refractory period (ERP) and AF in normal canine heart. Atrial Fibrillation (AF) is a complex disease and one of the most frequent arrhythmias, especially in elderly patients. Multiple mechanisms are involved including interaction between the autonomic nervous system (ANS), electrophysiological properties of the atria, and vulnerability for AF. Cardiac overload increases the incidence of AF. In lone AF the triggers are in the pulmonary veins. AF caused by underlying disease has different mechanism. Atrial fibrillation (AF) is associated with activity of renin-angiotensin-aldosterone system (RAAS). Reduction in renal nor-adrenaline spillover could be achieved after renal sympathetic denervation (RSD). Methods: 1) Establish of atrial fibrillation model; 2) Ventricular rate analysis of AF; 3) Statistical analysis. Results: 1) The establishment of atrial fibrillation model; 2) Inducibility and duration of AF; 3) The changes of AERP dispersion. Conclusion: Left RSN-S shortened left atrial ERP, increased ERP dispersion, but did not change right atrial ERP. Bilateral RSN-A produced significant prolongation in both atrial ERP, but did not affect ERP dispersion. The on time of RD effect is at 4 hrs after RD procedure and the RD effect on AF will last for 20 hrs after RD procedure.

Role of CD73 in renal sympathetic neurotransmission in the mouse kidney

Adenosine formed during renal sympathetic nerve stimulation (RSNS) enhances, by activating A1 receptors, the postjunctional effects of released norepinephrine and participates in renal sympathetic neurotransmission. Because in many cell types CD73 (ecto-5′-nucleotidase) is important for the conversion of 5′-AMP to adenosine, we investigated whether CD73 is necessary for normal renal sympathetic neurotransmission. In isolated kidneys from CD73 wild-type mice (CD73+/+; n = 17) perfused at a constant rate with Tyrode's solution, RSNS increased perfusion pressure by 17 ± 4, 36 ± 8, and 44 ± 10 mm Hg at 3, 5, and 7 Hz, respectively. Similar responses were elicited from kidneys isolated from CD73 knockout mice (CD73−/−; n = 13; 28 ± 11, 43 ± 10, and 44 ± 10 mm Hg at 3, 5, and 7 Hz, respectively); and a high concentration (100 μmol/L) of α,β-methyleneadenosine 5′-diphosphate (CD73 inhibitor) did not alter responses to RSNS in C57BL/6 mouse kidneys (n = 5; 21 ± 5, 36 ± 8, and 43 ± 9 at 3, 5, and 7 Hz, respectively). Measurements of renal venous adenosine and inosine (adenosine metabolite) by liquid chromatography-tandem mass spectrometry demonstrated that the metabolism of exogenous 5′-AMP to adenosine and inosine was similar in CD73−/− versus CD73+/+ kidneys. A1 receptor mRNA expression was increased in CD73−/− kidneys, and 2-chloro-N6-cyclopentyladenosine (0.1 μmol/L; A1 receptor agonist) enhanced renovascular responses to norepinephrine more in CD73−/− versus CD73+/+ kidneys. We conclude that CD73 is not essential for renal sympathetic neurotransmission because in the absence of renal CD73 other enzymes metabolize 5′-AMP to adenosine and because of compensatory upregulation of postjunctional coincident signaling between norepinephrine and adenosine.

Role of A1 receptors in renal sympathetic neurotransmission in the mouse kidney

A(1) receptors may participate in renal sympathetic neurotransmission by enhancing the postjunctional effects of norepinephrine. The purpose of this study was to test this concept using A(1) receptor knockout (A(1)AR-/-) mice. In isolated kidneys from nontransgenic mice perfused with Tyrode's solution at a constant rate, renal sympathetic nerve stimulation (RSNS) increased (P < 0.0001) renal venous perfusate levels of inosine (adenosine metabolite) from 23.9 ± 3.7 to 32.7 ± 5.1, 68.2 ± 12.4, and 94.0 ± 14.3 ng/ml at 3, 5, and 7 Hz, respectively (n = 28), suggesting frequency-dependent production of adenosine. Conversely, RSNS decreased (P < 0.0001) renal venous perfusate levels of 5'-AMP (adenosine precursor) from 1.4 ± 0.3 to 1.1 ± 0.3, 0.80 ± 0.2, and 0.6 ± 0.2 ng/ml at 3, 5, and 7 Hz, respectively (n = 28), suggesting frequency-dependent increased metabolism of 5'-AMP. In kidneys from nontransgenic mice, blockade of adenosine receptors with 1,3-dipropyl-8-p-sulfophenylxanthine attenuated (P = 0.0130) vasoconstrictor responses to RSNS at 3, 5, and 7 Hz [control (n = 29): 22 ± 4, 34 ± 6, 42 ± 6 mmHg, respectively; 1,3-dipropyl-8-p-sulfophenylxanthine-treated (n = 11): 6 ± 1, 12 ± 3, 15 ± 3 mmHg, respectively]. In A(1)AR-/- kidneys (n = 10), vasoconstrictor responses to RSNS at 3, 5, and 7 Hz were 7 ± 3, 20 ± 5, and 36 ± 9 mmHg, respectively. In kidneys from wild-type littermates (n = 9), responses were 27 ± 9, 58 ± 14, and 59 ± 11 mmHg, respectively (effect of genotype: P = 0.0363). In kidneys from nontransgenic mice, 2-chloro-N(6)-cyclopentyladenosine (CCPA; highly selective A(1) receptor agonist) increased renal vasoconstriction induced by norepinephrine (P = 0.0008; n = 28). In kidneys from A(1)AR-/- the response to norepinephrine was attenuated and the ability of CCPA to enhance responses to norepinephrine was abolished. In conclusion, adenosine formed during RSNS enhances the postjunctional effects of released norepinephrine by activating A(1) receptors.

Reduction of mean arterial pressure and proteinuria by the effect of ACEIs (Lisinopril) in Kurdish hypertensive patients in Hawler City.

The angiotensin converting enzyme inhibitors (ACEIs) are a group of pharmaceuticals that are used primarily in treatment of hypertension and congestive heart failure, in some cases as the drugs of first choice. The renin-angiotensin system is activated in response to hypotension, decreased sodium concentration in the distal tubule, decreased blood volume and in renal sympathetic nerve stimulation. This study examines the effects of angiotensin converting enzyme inhibitor (Lisinopril) on blood pressure (BP) 131±2.4 and proteinuria 0.198±0.005 in Kurd hypertensive patients, mean arterial blood pressure and proteinuria excretion were measured weekly along the period of 12 weeks. Lisinopril significantly reduced mean arterial blood pressure, and attenuated proteinuria level in patients subjected to this study in lisinopril 10mg dose dependent manner (p<0.05, n=24). In conclusion, lisinopril is of beneficial of renoprotection and in lowering BP

Endogenous adenosine contributes to renal sympathetic neurotransmission via postjunctional A1receptor-mediated coincident signaling

Adenosine A(1) receptor antagonists have diuretic/natriuretic activity and may be useful for treating sodium-retaining diseases, many of which are associated with increased renal sympathetic tone. Therefore, it is important to determine whether A(1) receptor antagonists alter renal sympathetic neurotransmission. In isolated, perfused rat kidneys, renal vasoconstriction induced by renal sympathetic nerve simulation was attenuated by 1) 1,3-dipropyl-8-p-sulfophenylxanthine (xanthine analog that is a nonselective adenosine receptor antagonist, but is cell membrane impermeable and thus does not block intracellular phosphodiesterases), 2) xanthine amine congener (xanthine analog that is a selective A(1) receptor antagonist), 3) 1,3-dipropyl-8-cyclopentylxanthine (xanthine analog that is a highly selective A(1) receptor antagonist), and 4) FK453 (nonxanthine analog that is a highly selective A(1) receptor antagonist). In contrast, FR113452 (enantiomer of FK453 that does not block A(1) receptors), MRS-1754 (selective A(2B) receptor antagonist), and VUF-5574 (selective A(3) receptor antagonist) did not alter responses to renal sympathetic nerve stimulation, and ZM-241385 (selective A(2A) receptor antagonist) enhanced responses. Antagonism of A(1) receptors did not alter renal spillover of norepinephrine. 2-Chloro-N(6)-cyclopentyladenosine (highly selective A(1) receptor agonist) increased renal vasoconstriction induced by exogenous norepinephrine, an effect that was blocked by 1,3-dipropyl-8-cyclopentylxanthine, U73122 (phospholipase C inhibitor), GF109203X (protein kinase C inhibitor), PP1 (c-src inhibitor), wortmannin (phosphatidylinositol 3-kinase inhibitor), and OSU-03012 (3-phosphoinositide-dependent protein kinase-1 inhibitor). These results indicate that adenosine formed during renal sympathetic nerve stimulation enhances the postjunctional effects of released norepinephrine via coincident signaling and contributes to renal sympathetic neurotransmission. Likely, the coincident signaling pathway is: phospholipase C → protein kinase C → c-src → phosphatidylinositol 3-kinase → 3-phosphoinositide-dependent protein kinase-1.

Arterial hypertension defeated? Attacked from another angle

the cumulative sodium retention. Furthermore, this renal denervation was shown to prevent, markedly attenuate or delay the development of hypertension in a diverse number of models of elevated blood pressure. 4 These promising experimental results of renal sympathetic nerve denervation for the treatment of hypertension prompted the establishment of the first clinical trial of this approach as a proof-of-principle study. 3 In brief, in 45 patients with resistant hypertension a catheter connected to a radiofrequency generator was introduced into renal arteries via femoral access and up to six discrete radiofrequency ablations were delivered within each renal artery. The major aims of this study were to assess firstly the efficacy of blood pressure lowering and s econdly the safety of this procedure. The initial blood pressure in these patients who had been treated with four to seven anti-hypertensive medications was 177/101 mmHg. The highly significant average reduction in office measured systolic/diastolic blood pressure at 1 month after the renal sympathetic denervation procedure was 14/10 mmHg. Blood pressure was further reduced at 3 months by 22/10 mmHg, with this effect persisting on s ubsequent assessments with the reduction 12 months after the procedure being 27/17 mmHg. Only six out of 45 patients did not benefit from this treatment, defined as a s ystolic blood pressure reduction of less than 10 mmHg. In 12 patients, 24 hour ambulatory blood pressure monitoring was performed before and after the denervation procedure. The change in office systolic blood pressure correlated closely with the change in mean ambulatory blood pressure (r 2 50.62, p50.002). Furthermore, renal sympathetic denervation was associated with an increase in the number of n octurnal dippers in the group of patients that had responded to this treatment. The effectiveness of the radiofrequency method in achieving efferent renal denervation was assessed in a subgroup of patients (n 51 0) by measuring renal Arterial hypertension is a major risk factor for an array of cardiovascular diseases, particularly in the context of concomitant diabetes. Furthermore, elevated blood pressure is at least twice as prevalent in type 2 diabetes as in the g eneral population. Clinical data suggest that lower blood pressure may induce even greater cardiovascular benefits in diabetic subjects than in individuals without diabetes. With respect to renal disease, recent data from the Action in Diabetes and Vascular Disease (ADVANCE) study indicate that there is no lower threshold for blood pressure reduction when one is aiming to reduce the burden of renal disease. 1 So far, the major therapeutic strategy for arterial hypertension has focused on pharmacological treatments. Despite the abundance of available antihypertensive drugs, arterial hypertension remains undertreated, in particular in diabetes and specifically in the setting of associated chronic kidney disease. Clinical trials involving patients with diabetes or renal impairment have demonstrated that achieving lower blood pressure goals requires treatment with on average at least three different antihypertensive agents. 2 Moreover, it has been shown that with current standard antihypertensive therapies only one of out seven patients with type 2 diabetes can achieve a target blood pressure of less than 130/80 mmHg. Recently, a multi-centre prospective cohort study has demonstrated the efficacy of a non-pharmacological, minimally invasive percutaneous radiofrequency catheter-based treatment to disrupt renal sympathetic nerves in the management of patients with resistant hypertension, which included a significant subgroup with type 2 diabetes. 3 The rationale for renal sympathetic nerves denervation as a treatment strategy for systemic hypertension lies in the hypothesis that abnormal excretory function is crucial for the initiation, p rogression and maintenance of primary hypertension with sodium and water balance considered to be of central importance in the long-term control of systemic blood pressure. In addition, in animal models it has been confirmed that renal sympathetic nerve stimulation results in a substantial increase in the renin secretion rate and promotes antinatriuresis without affecting glomerular filtration rate and renal plasma flow. Moreover, in animal models renal sympathetic denervation has been used to demonstrate that renal sympathetic nerve activity is responsible for approximately 40% of

Endogenous nitric oxide minimizes vasoconstriction during low frequency renal sympathetic nerve stimulation

Low frequency renal nerve stimulation (LFRNS) decreases medullary (MBF) and cortical (CBF) blood flows. The impact of endogenous nitric oxide (NO) on LFRNS mediated changes in MBF and CBF was determined in anesthetized Sprague Dawley (SD) rats. Animals (n=13) were anesthetized and Laser Doppler flow probes were positioned on or below the kidney surface to measure CBF and MBF. After control, LFRNS was conducted at 0.5 and 1.5 Hz for 15 minutes each. LFRNS (0.5 Hz) decreased MBF by ‐1.89 ± 0.39% and CBF by ‐2.12 ± 0.77% of control. At 1.5 Hz, LFRNS decreased MBF and CBF by ‐8.70+2.31% and ‐10.84 ± 3.7% of control, respectively. Following a 30 minute recovery period from LFRNS, L‐arginine (L‐ARG; 300 ug/kg/hr, i.v.) was infused for 30 minutes and LFRNS was repeated. L‐ARG infusion did not change control MBF or CBF but abolished renal vasoconstriction elicited by 0.5 Hz LFRNS. Furthermore, 1.5 Hz LFRNS mediated vasoconstriction was attenuated in both medullary and cortical regions (‐3.75 ± 1.78% and ‐6.87 ± 2.67%, respectively; p&lt;0.05 vs. control constrictor responses). Thus, endogenous NO significantly decreases renal vascular constriction during LFRNS in renal medullary and cortical vessels. NO may provide protection against both cortical and medullary vasoconstriction during small and subtle changes in renal sympathetic outflow. (Supported by an APS Predoctoral Fellowship to J. Kretzer and UK Biology Ribble Foundation).

Sitagliptin Augments Sympathetic Enhancement of the Renovascular Effects of Angiotensin II in Genetic Hypertension

Dipeptidyl peptidase IV converts neuropeptide Y(1-36) (Y(1)-receptor agonist released from renal sympathetic nerves) to neuropeptide Y(3-36) (selective Y(2)-receptor agonist). Previous studies suggest that Y(1), but not Y(2), receptors enhance renovascular responses to angiotensin II in kidneys from genetically-susceptible animals. Therefore, we hypothesized that inhibition of dipeptidyl peptidase IV with sitagliptin (antidiabetic drug) would augment the ability of exogenous and endogenous neuropeptide Y(1-36) to enhance renal vascular responses to angiotensin II in kidneys from spontaneously hypertensive rats. This hypothesis was tested using 3 protocols in isolated perfused kidneys. Results from Protocol 1: Exogenous neuropeptide Y(1-36) enhanced renovascular responses to angiotensin II. This effect of neuropeptide Y(1-36) was blocked by BIBP3226 (selective Y(1) receptor antagonist); Exogenous neuropeptide Y(3-36) did not enhance renovascular responses to angiotensin II. Results from Protocol 2: Sitagliptin augmented the ability of exogenous neuropeptide Y(1-36) to enhance renovascular responses to angiotensin II. This effect of sitagliptin was blocked by BIBP3226. Results from Protocol 3: Renal sympathetic nerve stimulation enhanced renovascular responses to angiotensin II; this enhancement was augmented by sitagliptin and abolished by BIBP3226. Neuropeptide Y(1-36) via Y(1) receptors enhances renovascular responses to angiotensin II in kidneys from genetically hypertensive animals. Sitagliptin, by blocking dipeptidyl peptidase IV, prevents metabolism of neuropeptide Y(1-36) and thereby increases the effects of neuropeptide Y(1-36) released from renal sympathetic nerves on Y(1) receptors leading to augmentation of neuropeptide Y(1-36)-induced enhancement of the renovascular effects of angiotensin II. The renal effects of dipeptidyl peptidase IV inhibitors in hypertensive diabetic patients merit a closer examination.

Assessment of Nerve Stimulation-Induced Release of Purines from Mouse Kidneys by Tandem Mass Spectrometry

Adenosine, formed from AMP and metabolized to inosine, modulates renal sympathetic neurotransmission. The present study had two goals: 1) to develop ultrasensitive and specific mass spectrometry-based assays for cAMP, AMP, adenosine, inosine, and, for comparison, guanosine using state-of-the-art tandem liquid chromatography-mass spectrometry (LC-MS-MS); and 2) to quantify the effects of renal sympathetic nerve stimulation on the release of cAMP, AMP, adenosine, inosine, and guanosine from the isolated, perfused mouse kidney. Using LC-MS-MS, we developed highly sensitive (detection limit of 0.02-0.05 pg/microl) and accurate (r(2) > 0.99) assays for all the aforementioned compounds. In the perfused mouse kidney (n = 9), periarterial (renal sympathetic) nerve stimulation elicited a frequency-dependent (0, 3, 5, 7, and 9 Hz) and significant (p = 0.0148, repeated measures analysis of variance) increase in the concentration of inosine in the renal venous perfusate (29 +/- 8, 51 +/- 8, 54 +/- 11, 65 +/- 15, and 80 +/- 20 pg/microl, respectively), yet concomitantly decreased (p = 0.0239, repeated measures analysis of variance) the concentration of AMP in the renal venous perfusate (3.8 +/- 1.3, 3.2 +/- 1.7, 2.4 +/- 1.5, 2.0 +/- 1.1, and 1.1 +/- 0.4 pg/microl, respectively). No significant changes were observed in the levels of adenosine, cAMP, or guanosine in the renal venous perfusate. These results indicate that using state-of-the-art mass spectrometric methods, it is possible to investigate trace amounts of purines released from mouse organs in perfusion and that renal sympathetic nerve stimulation is associated with a robust increase in the main metabolite of adenosine (inosine), while concomitantly decreasing AMP. This suggests that renal sympathetic nerve stimulation influences the efficiency of AMP conversion to adenosine and hence to inosine.

$alpha;-Adrenoceptor subtypes mediating regional kidney blood flow responses to renal nerve stimulation

<h2>Abstract</h2> The mechanisms underlying the relative insensitivity of the renal medullary circulation to renal sympathetic nerve stimulation (RNS) remain unknown. Therefore, we tested the effects of systemic α₁- and α₂-adrenoceptor blockade on responses to electrical RNS in pentobarbitone anaesthetized rabbits. Renal blood flow (RBF), cortical laser Doppler flux (CLDF), and to a lesser extent medullary LDF (MLDF) were reduced by RNS in a frequency-dependent manner. Prazosin decreased responses of RBF and CLDF, but not MLDF, to RNS. For example, during the control period 4 Hz stimulation reduced RBF, CLDF and MLDF by 85±3%, 89±2%, and 20±12%, respectively, but after prazosin, corresponding responses were 39±3%, 42±5% and 28±7%, respectively. Prazosin markedly blunted pressor and renal vasoconstrictor responses to intravenous phenylephrine, without altering pressor responses to intravenous xylazine. Rauwolscine enhanced renal vasoconstrictor responses to RNS, although this was statistically significant for RBF and CLDF but not MLDF. For example, during the control period 2 Hz stimulation reduced RBF, CLDF and MLDF by 63±7%, 58±7%, and 29±17%, respectively, and after rauwolscine, corresponding responses were 83±4%, 87±1%, and 53±12%, respectively. Rauwolscine markedly blunted renal vasoconstrictor responses to renal arterial guanabenz, but not phenylephrine. These data suggest that α₁-adrenoceptors contribute to RNS-induced vasoconstriction in the renal cortex, but contribute less in vascular elements controlling medullary perfusion. Activation of α₂-adrenoceptors appears to blunt RNS-induced renal vasoconstriction, but this mechanism does not underlie the relative insensitivity of medullary perfusion to RNS.

α-Adrenoceptor subtypes mediating regional kidney blood flow responses to renal nerve stimulation

The mechanisms underlying the relative insensitivity of the renal medullary circulation to renal sympathetic nerve stimulation (RNS) remain unknown. Therefore, we tested the effects of systemic α 1- and α 2-adrenoceptor blockade on responses to electrical RNS in pentobarbitone anaesthetized rabbits. Renal blood flow (RBF), cortical laser Doppler flux (CLDF), and to a lesser extent medullary LDF (MLDF) were reduced by RNS in a frequency-dependent manner. Prazosin decreased responses of RBF and CLDF, but not MLDF, to RNS. For example, during the control period 4 Hz stimulation reduced RBF, CLDF and MLDF by 85±3%, 89±2%, and 20±12%, respectively, but after prazosin, corresponding responses were 39±3%, 42±5% and 28±7%, respectively. Prazosin markedly blunted pressor and renal vasoconstrictor responses to intravenous phenylephrine, without altering pressor responses to intravenous xylazine. Rauwolscine enhanced renal vasoconstrictor responses to RNS, although this was statistically significant for RBF and CLDF but not MLDF. For example, during the control period 2 Hz stimulation reduced RBF, CLDF and MLDF by 63±7%, 58±7%, and 29±17%, respectively, and after rauwolscine, corresponding responses were 83±4%, 87±1%, and 53±12%, respectively. Rauwolscine markedly blunted renal vasoconstrictor responses to renal arterial guanabenz, but not phenylephrine. These data suggest that α 1-adrenoceptors contribute to RNS-induced vasoconstriction in the renal cortex, but contribute less in vascular elements controlling medullary perfusion. Activation of α 2-adrenoceptors appears to blunt RNS-induced renal vasoconstriction, but this mechanism does not underlie the relative insensitivity of medullary perfusion to RNS.

Effect of renal denervation on dynamic autoregulation of renal blood flow.

Vasoconstrictor intensities of renal sympathetic nerve stimulation elevate the renal arterial pressure threshold for steady-state stepwise autoregulation of renal blood flow. This study examined the tonic effect of basal renal sympathetic nerve activity on dynamic autoregulation of renal blood flow in rats with normal (Sprague-Dawley and Wistar-Kyoto) and increased levels of renal sympathetic nerve activity (congestive heart failure and spontaneously hypertensive rats). Steady-state values of arterial pressure and renal blood flow before and after acute renal denervation were subjected to transfer function analysis. Renal denervation increased basal renal blood flow in congestive heart failure (+35 +/- 3%) and spontaneously hypertensive rats (+21 +/- 3%) but not in Sprague-Dawley and Wistar-Kyoto rats. Renal denervation significantly decreased transfer function gain (i.e., improved autoregulation of renal blood flow) and increased coherence only in spontaneously hypertensive rats. Thus vasoconstrictor intensities of renal sympathetic nerve activity impaired the dynamic autoregulatory adjustments of the renal vasculature to oscillations in arterial pressure. Renal denervation increased renal blood flow variability in spontaneously hypertensive rats and congestive heart failure rats. The contribution of vasoconstrictor intensities of basal renal sympathetic nerve activity to limiting renal blood flow variability may be important in the stabilization of glomerular filtration rate.

Nitric oxide modulation of neurally induced proximal tubular fluid reabsorption in the rat.

This study investigated the role of NO in mediating the renal sympathetic nerve-mediated increases in proximal tubular fluid reabsorption (Jva). In inactin-anesthetized Wistar rats, renal sympathetic nerve stimulation (15 V, 2 ms) at 0.75 and 1.0 Hz did not change blood pressure or glomerular filtration rate but did decrease urine flow and sodium excretion in a frequency-related fashion by 40% to 50% at 1.0 Hz (both, P<0.01). Renal nerve stimulation in control animals increased Jva by 11% at 0.75 Hz (P<0.05) and 31% at 1.0 Hz (P<0.01). Intraluminal N(omega)-nitro-L-arginine methyl ester (L-NAME) resulted in a higher basal Jva (19%, P<0.05), and renal nerve stimulation had no effect on Jva. When L-NAME plus sodium nitroprusside was present intraluminally, however, there were frequency-dependent increases in Jva that were similar in pattern and magnitude to the control rats. Introduction of the relatively selective nNOS blocker 7-nitroindazole intraluminally, at 10(-6) and 10(-4) M, raised basal Jva by 18% and 24%, respectively (P<0.01), and renal nerve stimulation did not change Jva. Intraluminal aminoguanidine (10(-4) M), a relatively selective iNOS blocker, did not affect basal Jva, which remained unchanged during renal nerve stimulation. These data are consistent with NO exerting a tonic inhibitory action on the basal levels of Jva, which, in part, is caused by NO generated by the nNOS isoform. Moreover, the findings have revealed that the presence of NO is necessary to ensure that renal nerves can stimulate fluid reabsorption by the proximal tubules, requiring NO generated from both nNOS and iNOS.

Autoinhibitory function of the sympathetic prejunctional neuropeptide Y Y 2 receptor evidenced by BIIE0246

The significance of neuropeptide Y Y 2 receptors in sympathetic nonadrenergic transmission was investigated using the novel selective antagonist BIIE0246 (( S)- N2-[[1-[2-[4-[( R, S)-5,11-dihydro-6(6 h)-oxodibenz[ b, e]azepin-11-yl]-1-piperazinyl]-2-oxoethyl]cyclopentyl]acetyl]- N-[2-[1,2-dihydro-3,5 (4 H)-dioxo-1,2-diphenyl-3 H-1,2,4-triazol-4-yl]ethyl]-argininamide). In anaesthetized pigs pretreated with reserpine, and after transection of sympathetic nerves (depleted of noradrenaline), electrical stimulation of renal and splanchnic sympathetic nerves evoked vasoconstriction in, and overflow of neuropeptide Y-like immunoreactivity from, kidney and spleen, respectively. In the presence of BIIE0246, the nerve-evoked overflows of neuropeptide Y-like immunoreactivity were markedly increased and the splenic vasoconstrictor response prolonged. In addition, BIIE0246 caused splenic vasodilatation per se in this model where basal levels of circulating neuropeptide Y exceed 40 pM. It is concluded that endogenous neurogenical neuropeptide Y regulates its own release via activation of sympathetic prejunctional inhibitory neuropeptide Y Y 2 receptors in both spleen and kidney in the reserpinized pig. Moreover, when circulating levels of neuropeptide Y are moderately increased, activation of neuropeptide Y Y 2 receptors seems to contribute to basal splenic vascular tone.

Effects of the neuropeptide Y Y2 receptor antagonist BIIE0246 on sympathetic transmitter release in the pig in vivo.

This study investigated the effects of BIIE0246, a novel neuropeptide Y (NPY) Y(2) receptor antagonist, on renal sympathetic nerve-evoked release of noradrenaline and NPY-like immunoreactivity (-LI) in the pig in vivo. Stimulation (5 Hz, 60 s) of renal sympathetic nerves evoked vasoconstriction and overflow of noradrenaline and NPY-LI. Infusion of peptide YY (PYY; 1 microg/kg per min) strongly inhibited the stimulation-evoked overflow of noradrenaline and NPY-LI. BIIE0246 (100 nmol/kg) abolished the inhibitory effect of PYY. BIIE0246 did not however affect the stimulation-evoked overflow of noradrenaline and NPY-LI, or basal cardiovascular parameters, per se. The alpha(2)-adrenoceptor antagonist yohimbine (0.2 mg/kg) significantly elevated both basal plasma levels and the nerve stimulation-evoked overflow of noradrenaline and NPY-LI. Subsequent administration of BIIE0246 did not further alter these effects. However, BIIE0246 caused splenic vasodilatation per se when given after yohimbine. It is concluded that the renal sympathetic nerves in the pig possess NPY Y(2) receptors, which upon activation inhibit transmitter (noradrenaline and NPY) release. Furthermore, when circulating levels of NPY were enhanced after blockade of alpha(2)-adrenoceptors, an involvement of endogenous NPY, acting on the NPY Y(2) receptor, in regulation of basal splenic vascular tone was unveiled.