Splenorenal reflex modulates renal blood flow in the rat

Research status and frontiers of renal denervation for hypertension: a bibliometric analysis from 2004 to 2023

BACKGROUND

Renal Denervation (RDN) is a novel non-pharmacological technique to treat hypertension. This technique lowers blood pressure by blocking the sympathetic nerve fibers around the renal artery, then causing a decrease in system sympathetic nerve excitability. This study aimed to visualize and analyze research hotspots and development trends in the field of RDN for hypertension through bibliometric analysis.

METHODS

In total, 1479 studies were retrieved on the Web of Science Core Collection (WoSCC) database from 2004 to 2023. Using CiteSpace (6.2.R4) and VOSviewer (1.6.18), visualization maps were generated by relevant literature in the field of RDN for hypertension to demonstrate the research status and frontiers.

RESULTS

The number of publications was found to be generally increasing. Europe and the United States were the first countries to carry out research on different techniques and related RDN clinical trials. The efficacy and safety of RDN have been repeatedly verified and gained increasing attention. The study involves multiple disciplines, including the cardiovascular system, peripheral vascular disease, and physiological pathology, among others. Research hotspots focus on elucidating the mechanism of RDN in the treatment of hypertension and the advantages of RDN in appliance therapy. Additionally, the research frontiers include improvement of RDN instruments and techniques, as well as exploration of the therapeutic effects of RDN in diseases with increased sympathetic nerve activity.

CONCLUSION

The research hotspots and frontiers reflect the status and development trend of RDN in hypertension. In the future, it is necessary to strengthen international collaboration and cooperation, conduct long-term clinical studies with a large sample size, and continuously improve RDN technology and devices. These measures will provide new options for more patients with hypertension, thereby improving their quality of life.

82 Rb tissue kinetics in humans

AIM

The study aim was to compare the kinetics of the potassium analogue, ⁸² Rb, between spleen, liver and kidney.

METHODS

Patients had myocardial stress/rest perfusion imaging using adenosine (n = 45) or regadenoson (n = 33) for stressing. Hepatic arterial (HAP), splenic (SP) and renal (RP) perfusions were measured from first-pass and blood ⁸² Rb clearances (Ki) from Gjedde-Patlak-Rutland graphical analysis of data between 1 and 2 min postinjection, using regions of interest over left ventricular cavity or abdominal aorta to monitor arterial concentration. Tissue ⁸² Rb extraction efficiency (E) was calculated as [Ki/perfusion]*100. Tissue extracellular fluid volume (ECV) was derived from the GPR plot intercept.

RESULTS

SP (24%) and RP (23%) increased after regadenoson but decreased (-41% and -19%) after adenosine. HAP increased after adenosine (91%) and regadenoson (68%). Resting E was high in kidney (69%) and low in spleen (26%). After adenosine, it increased to 91% in kidney and 49% in spleen. Assuming an arterial contribution of 25% to hepatic blood flow, resting E in liver was estimated as 23%. Relationships between Ki and perfusion in spleen and kidney were consistent with the Crone-Renkin equation (Ki = [1 - A.e^-B/perfusion ]*perfusion), with respective values of A of 0.95 and 0.94 and B of 31 and 186 ml/min/100 ml. Splenic ECV decreased following adenosine from 62 to 39 ml/100 ml and showed a logarithmic correlation with SP.

CONCLUSION

Kidney, spleen and liver display contrasting tissue kinetics. E is high in kidney and low in spleen and liver. Spleen is erectile, collapsing when perfusion decreases.

Right Heart Failure and Cardiorenal Syndrome

Cardiorenal syndrome is a complex interplay of dysregulated heart and kidney interaction that leads to multiorgan system dysfunction, which is not an uncommon occurrence in the setting of right heart failure. The traditional concept of impaired perfusion and forward flow recently has been modified to include the recognition of systemic venous congestion as a contributor, with direct and indirect mechanisms, including elevated renal venous pressure, reduced renal perfusion pressure, increased renal interstitial pressure, tubular dysfunction, splanchnic congestion, and neurohormonal and inflammatory activation. Treatment options beyond diuretics and vasoactive drugs remain limited and lack supportive evidence.

Membrane rafts-redox signalling pathway contributes to renal fibrosis via modulation of the renal tubular epithelial-mesenchymal transition

KEY POINTS

Membrane rafts (MRs)-redox signalling pathway is activated in response to transforming growth factor-β1 (TGF-β1) stimulation in renal tubular cells. This pathway contributes to TGF-1β-induced epithelial-mesenchymal transition (EMT) in renal tubular cells. The the MRs-redox signalling pathway is activated in renal tubular cells isolated from angiotensin II (AngII)-induced hypertensive rats. Inhibition of this pathway attenuated renal inflammation and fibrosis in AngII-induced hypertension.

ABSTRACT

The membrane rafts (MRs)-redox pathway is characterized by NADPH oxidase subunit clustering and activation through lysosome fusion, V-type proton ATPase subunit E2 (encoded by the Atp6v1e2 gene) translocation and sphingomyelin phosphodiesterase 1 (SMPD1, encoded by the SMPD1 gene) activation. In the present study, we hypothesized that the MRs-redox-derived reactive oxygen species (ROS) are involved in renal inflammation and fibrosis by promoting renal tubular epithelial-mesenchymal transition (EMT). Results show that transforming growth factor-β1 (TGF-β1) acutely induced MR formation and ROS production in NRK-52E cells, a rat renal tubular cell line. In addition, transfection of Atp6v1e2 small hairpin RNAs (shRNA) and SMPD1 shRNA attenuated TGF-β1-induced changes in EMT markers, including E-cadherin, α-smooth muscle actin (α-SMA) and fibroblast-specific protein-1 (FSP-1) in NRK-52E cells. Moreover, Erk1/2 activation may be a downstream regulator of the MRs-redox-derived ROS, because both shRNAs significantly inhibited TGF-β1-induced Erk1/2 phosphorylation. Further in vivo study shows that the renal tubular the MRs-redox signalling pathway was activated in angiotensin II (AngII)-induced hypertension, as indicated by the increased NADPH oxidase subunit Nox4 fraction in the MR domain, SMPD1 activation and increased ROS content in isolated renal tubular cells. Finally, renal transfection of Atp6v1e2 shRNA and SMPD1 shRNA significantly prevented renal fibrosis and inflammation, as indicated by the decrease of α-SMA, fibronectin, collagen I, monocyte chemoattractant protein-1 (MCP-1), intercellular cell adhesion molecule-1 (ICAM-1) and tumour necrosis factor-α (TNF-α) in kidneys from AngII-infused rats. It was concluded that the the MRs-redox signalling pathway is involved in TGF-β1-induced renal tubular EMT and renal inflammation/fibrosis in AngII-induced hypertension.

Doppler assessment of splanchnic arterial flow in patients with liver cirrhosis: correlation with ammonia plasma levels and MELD score

PURPOSE

To assess the clinical significance of blood flow velocity and resistance index (RI) in the visceral arteries of patients with liver cirrhosis with respect to plasma ammonia (NH3) level and liver function.

METHODS

We included 80 patients with liver cirrhosis (58 men) and 20 healthy controls (11 men). Duplex Doppler ultrasonography was used to assess flow velocity and RI in the hepatic (HA), right (RRA), and left renal (LRA), and splenic (SA) (LA) artery. Plasma NH3 was measured by biochemistry. Liver function was assessed by MELD score (model of end-stage liver disease).

RESULTS

HA, LRA, and SA systolic flow velocities were greater, whereas RRA diastolic velocity was lower in patients with liver cirrhosis than in controls RI was higher in LRA, RRA, SA, and HA in patients with liver cirrhosis than in controls. NH3 levels were significantly elevated in all patients with liver cirrhosis (p < 0.05) and significantly correlated with RI of RRA, LRA, and SA.

CONCLUSION

We found greater renal, hepatic, and LA RI in patients with liver cirrhosis than in healthy controls. The correlation we found between elevated renal artery RI (≥0.70) and MELD score emphasizes the risk of renal dysfunction during progression of liver cirrhosis.

The neural regulation of the kidney in hypertension and renal failure

NEW FINDINGS

What is the topic of this review? Reports that bilateral renal denervation in resistant hypertensive patients results in a long-lasting reduction in blood pressure raise the question of the underlying mechanisms involved and how they may be deranged in pathophysiological states of hypertension and renal failure. What advances does it highlight? The renal sensory afferent nerves and efferent sympathetic nerves work together to exert an important control over extracellular fluid volume, hence the level at which blood pressure is set. This article emphasizes that both the afferent and the efferent renal innervation may contribute to the neural dysregulation of the kidney that occurs in chronic renal disease and resistant hypertension. Autonomic control is central to cardiovascular homeostasis, and this is exerted not only at the level of the heart and blood vessels but also at the kidney. At the kidney, the sympathetic neural regulation of renin release and fluid reabsorption may influence fluid balance and, in the longer term, the level at which blood pressure is set. The role of the renal innervation in the regulation of blood pressure has received renewed attention over the past few years, following the reports that bilateral renal denervation of resistant hypertensive patients resulted in a marked reduction in blood pressure, which has been maintained for several years. Such has been the interest that this approach of renal denervation is being applied in other patient groups with diabetes, obesity and renal failure, with the hope that there may be a sustained reduction in blood pressure as well as the amelioration of some aspects of the metabolic syndrome. However, the factors that come into play to cause the rise in blood pressure in these patient groups, particularly the resistant hypertensive patients, are far from clear. Moreover, the mechanisms leading to the fall in blood pressure following renal denervation of resistant hypertensive patients currently elude our understanding and is therefore an area that requires much more investigation to enhance our insight.

Abdominal contributions to cardiorenal dysfunction in congestive heart failure

Current pathophysiological models of congestive heart failure unsatisfactorily explain the detrimental link between congestion and cardiorenal function. Abdominal congestion (i.e., splanchnic venous and interstitial congestion) manifests in a substantial number of patients with advanced congestive heart failure, yet is poorly defined. Compromised capacitance function of the splanchnic vasculature and deficient abdominal lymph flow resulting in interstitial edema might both be implied in the occurrence of increased cardiac filling pressures and renal dysfunction. Indeed, increased intra-abdominal pressure, as an extreme marker of abdominal congestion, is correlated with renal dysfunction in advanced congestive heart failure. Intriguing findings provide preliminary evidence that alterations in the liver and spleen contribute to systemic congestion in heart failure. Finally, gut-derived hormones might influence sodium homeostasis, whereas entrance of bowel toxins into the circulatory system, as a result of impaired intestinal barrier function secondary to congestion, might further depress cardiac as well as renal function. Those toxins are mainly produced by micro-organisms in the gut lumen, with presumably important alterations in advanced heart failure, especially when renal function is depressed. Therefore, in this state-of-the-art review, we explore the crosstalk between the abdomen, heart, and kidneys in congestive heart failure. This might offer new diagnostic opportunities as well as treatment strategies to achieve decongestion in heart failure, especially when abdominal congestion is present. Among those currently under investigation are paracentesis, ultrafiltration, peritoneal dialysis, oral sodium binders, vasodilator therapy, renal sympathetic denervation and agents targeting the gut microbiota.

Autonomic regulation of kidney function

The kidneys play a central role in cardiovascular homeostasis by ensuring a balance between the fluid taken in and that lost and excreted during everyday activities. This ensures stability of extracellular fluid volume and maintenance of normal levels of blood pressure. Renal fluid handling is controlled via neural and humoral influences, with the former determining a rapid dynamic response to changing intake of sodium whereas the latter cause a slower longer-term modulation of sodium and water handling. Activity in the renal sympathetic nerves arises from an integration of information from the high and low pressure cardiovascular baroreceptors, the somatosensory and visceral systems as well as the higher cortical centers. Each sensory system provides varying input to the autonomic centers of the hypothalamic and medullary areas of the brain at a level appropriate to the activity being performed. In pathophysiological states, such as hypertension, heart failure and chronic renal disease, there may be an inappropriate sympathoexcitation causing sodium retention which exacerbates the disease process. The contribution of the renal sympathetic nerves to these cardiovascular diseases is beginning to be appreciated with the demonstration that renal denervation of resistant hypertensive patients results in a long-term normalization of blood pressure.

Congestive renal failure: the pathophysiology and treatment of renal venous hypertension

Longstanding experimental evidence supports the role of renal venous hypertension in causing kidney dysfunction and "congestive renal failure." A focus has been heart failure, in which the cardiorenal syndrome may partly be due to high venous pressure, rather than traditional mechanisms involving low cardiac output. Analogous diseases are intra-abdominal hypertension and renal vein thrombosis. Proposed pathophysiologic mechanisms include reduced transglomerular pressure, elevated renal interstitial pressure, myogenic and neural reflexes, baroreceptor stimulation, activation of sympathetic nervous and renin angiotensin aldosterone systems, and enhanced proinflammatory pathways. Most clinical trials have addressed the underlying condition rather than venous hypertension per se. Interpreting the effects of therapeutic interventions on renal venous congestion are therefore problematic because of such confounders as changes in left ventricular function, cardiac output, and blood pressure. Nevertheless, there is preliminary evidence from small studies of intense medical therapy or extracorporeal ultrafiltration for heart failure that there can be changes to central venous pressure that correlate inversely with renal function, independently from the cardiac index. Larger more rigorous trials are needed to definitively establish under what circumstances conventional pharmacologic or ultrafiltration goals might best be directed toward central venous pressures rather than left ventricular or cardiac output parameters.

Clinical characteristics and outcomes of patients with improvement in renal function during the treatment of decompensated heart failure

BACKGROUND

In the setting of acute decompensated heart failure, worsening renal function (WRF) and improved renal function (IRF) have been associated with similar hemodynamic derangements and poor prognosis. Our aim was to further characterize IRF and its associated mortality risk.

METHODS AND RESULTS

Consecutive patients with a discharge diagnosis of congestive heart failure at the Hospital of the University of Pennsylvania were reviewed. IRF was defined as a ≥20% improvement and WRF as a ≥20% deterioration in glomerular filtration rate. Overall, 903 patients met the eligibility criteria, with 31.4% experiencing IRF. Baseline venous congestion/right-side cardiac dysfunction was more common (P ≤ .04) and volume of diuresis (P = .003) was greater in patients with IRF. IRF was associated with a greater incidence of preadmission (odds ratio [OR] 4.2, 95% confidence interval [CI] 2.6-6.7; P < .0001) and postdischarge (OR 1.8, 95% CI 1.2-2.7; P = .006) WRF. IRF was associated with increased mortality (adjusted hazard ratio 1.3, 95% CI, 1.1-1.7; P = .011), a finding largely restricted to patients with postdischarge recurrence of renal dysfunction (P interaction = .038).

CONCLUSIONS

IRF is associated with significantly worsened survival and may represent the resolution of venous congestion-induced preadmission WRF. Unlike WRF, the renal dysfunction in IRF patients occurs independently from the confounding effects of acute decongestion and may provide incremental information for the study of cardiorenal interactions.

John Sutton MG, Keane MG, Wiegers SE, Shannon RP, Kirkpatrick JN. Effect of right ventricular function and venous congestion on cardiorenal interactions during the treatment of decompensated heart failure

Recent reports have demonstrated the adverse effects of venous congestion on renal function (RF) and challenged the assumption that worsening RF is driven by decreased cardiac output (CO). We hypothesized that diuresis in patients with right ventricular (RV) dysfunction, despite decreased CO, would lead to a decrease in venous congestion and resultant improvement in RF. We reviewed consecutive admissions with a discharge diagnosis of heart failure. RV function was assessed by multiple echocardiographic methods and those with >or=2 measurements of RV dysfunction were considered to have significant RV dysfunction. Worsening RF was defined as an increase in creatinine of >or=0.3 mg/dl and improved RF as improvement in glomerular filtration rate >or=25%. A total of 141 admissions met eligibility criteria; 34% developed worsening RF. Venous congestion was more common in those with RV dysfunction (odds ratio [OR] 3.3, p = 0.009). All measurements of RV dysfunction excluding RV dilation correlated with CO (p <0.05). Significant RV dysfunction predicted a lower incidence of worsening RF (OR 0.21, p <0.001) and a higher incidence of improved RF (OR 6.4, p <0.001). CO emerged as a significant predictor of change in glomerular filtration rate during hospitalization in those without significant RV dysfunction (r = 0.38, p <0.001). In conclusion, RV dysfunction is a strong predictor of improved renal outcomes in patients with acute decompensated heart failure, an effect likely mediated by relief of venous congestion.

Role of spleen in integrated control of splanchnic vascular tone: physiology and pathophysiology

Aside from its established immunologic and hematologic functions, the spleen also plays an important role in cardiovascular regulation. This occurs through changes in intrasplenic microvascular tone, as well as through splenic neurohormonal modulation of the renal and mesenteric vascular beds. Splenic regulation of blood volume occurs predominantly through fluid extravasation from the splenic circulation into lymphatic reservoirs; this is controlled by direct modulation of splenic pre- and postcapillary resistance by established physiologic agents such as atrial natriuretic peptide (ANP), nitric oxide (NO), and adrenomedullin (ADM). In addition to physiologic fluid regulation, splenic extravasation is a key factor in the inability to maintain adequate intravascular volume in septic shock. The spleen also controls renal microvascular tone through reflex activation of the splenic afferent and renal sympathetic nerves. This splenorenal reflex not only contributes to the physiologic regulation of blood pressure, but also contributes to the cardiovascular dysregulation associated with both septic shock and portal hypertension. In septic shock, the splenorenal reflex protectively limits splenic extravasation and potentially promotes renal sodium and water reabsorption and release of the vasoconstrictor angiotensin II; this function is eventually overwhelmed as shock progresses. In portal hypertension, on the other hand, the splenorenal reflex-mediated reduction in renal vascular conductance exacerbates sodium and water retention in the kidneys and may eventually contribute to renal dysfunction. Preliminary evidence suggests that the spleen also may play a role in the hemodynamic complications of portal hypertension via neurohormonal modulation of the mesenteric vascular bed. Lastly, the spleen itself may be a source of a vasoactive factor.

The spleen is required for 5-HT1A receptor agonist-mediated increases in mean circulatory filling pressure during hemorrhagic shock in the rat

The 5-HT(1A) receptor agonist, 8- OH-DPAT, increases whole body venous tone (mean circulatory filling pressure; MCFP), and attenuates metabolic acidosis in a rat model of unresuscitated hemorrhagic shock. To determine whether improved acid-base balance was associated with sympathetic activation and venous constriction, MCFP, sympathetic activity (SA), and blood gases were compared in hemorrhaged rats following administration of 5-HT(1A) receptor agonist 8-OH-DPAT, the arterial vasoconstrictor arginine vasopressin (AVP), or saline. To further determine whether protection of acid-base balance was dependent on splenic contraction and blood mobilization, central venous pressure (CVP), MCFP, and blood gases were determined during hemorrhage and subsequent 8-OH-DPAT-administration in rats subjected to real or sham splenectomy. Subjects were hemorrhaged to an arterial pressure of 50 mmHg for 25 min and subsequently were treated with 8-OH-DPAT (30 nmol/kg iv), AVP titrated to match the pressor effect of 8-OH-DPAT (approximately 2 ng/min iv), or infusion of normal saline. 8-OH-DPAT increased MAP, CVP, MCFP, and SA, and decreased lactate accumulation. AVP did not affect CVP or SA, but raised MCFP slightly to a level intermediate between 8-OH-DPAT- and saline-treated rats. Infusion of AVP also produced a modest protection against metabolic acidosis. Splenectomy prevented the rise in CVP, MCFP, and protection against metabolic acidosis produced by 8-OH-DPAT but had no effect on the immediate pressor response to the drug. Together, the data indicate that 8-OH-DPAT produces a pattern of cardiovascular responses consistent with a sympathetic-mediated venoconstriction that is, in part, responsible for the drug's beneficial effect on acid-base balance. Moreover, blood mobilization stimulated by the spleen is required for the beneficial effects of 8-OH-DPAT.

Effect of mesenteric vascular congestion on reflex control of renal blood flow

Portal hypertension initiates a splenorenal reflex, whereby increases in splenic afferent nerve activity and renal sympathetic nerve activity cause a decrease in renal blood flow (RBF). We postulated that mesenteric vascular congestion similarly compromises renal function through an intestinal-renal reflex. The portal vein was partially occluded in anesthetized rats, either rostral or caudal to the junction with the splenic vein. Portal venous pressure increased (6.5 +/- 0.1 to 13.2 +/- 0.1 mmHg; n = 78) and mesenteric venous outflow was equally obstructed in both cases. However, only rostral occlusion increased splenic venous pressure. Rostral occlusion caused a fall in RBF (-1.2 +/- 0.2 ml/min; n = 9) that was attenuated by renal denervation (-0.5 +/- 0.1 ml/min; n = 6), splenic denervation (-0.2 +/- 0.1 ml/min; n = 11), celiac ganglionectomy (-0.3 +/- 0.1 ml/min; n = 9), and splenectomy (-0.5 +/- 0.1 ml/min; n = 6). Caudal occlusion induced a significantly smaller fall in RBF (-0.5 +/- 0.1 ml/min; n = 9), which was not influenced by renal denervation (-0.2 +/- 0.2 ml/min; n = 6), splenic denervation (-0.1 +/- 0.1 ml/min; n = 7), celiac ganglionectomy (-0.1 +/- 0.3 ml/min; n = 8), or splenectomy (-0.3 +/- 0.1 ml/min; n = 7). Renal arterial conductance fell only in intact animals subjected to rostral occlusion (-0.007 +/- 0.002 ml.min(-1).mmHg(-1)). This was accompanied by increases in splenic afferent nerve activity (15.0 +/- 3.5 to 32.6 +/- 6.2 spikes/s; n = 7) and renal efferent nerve activity (32.7 +/- 5.2 to 39.3 +/- 6.0 spikes/s; n = 10). In animals subjected to caudal occlusion, there were no such changes in renal arterial conductance or splenic afferent/renal sympathetic nerve activity. We conclude that the portal hypertension-induced fall in RBF is initiated by increased splenic, but not mesenteric, venous pressure, i.e., we did not find evidence for intestinal-renal reflex control of the kidneys.

Splenic reflex modulation of central cardiovascular regulatory pathways

The splenorenal reflex induces changes in mean arterial pressure (MAP) and renal function. We hypothesized that, in addition to spinal pathways previously identified, these effects are also mediated through central pathways. We investigated the effect of elevated splenic venous pressure on central neural activation in intact, renal-denervated, and renal + splenic-denervated rats. Fos-labeled neurons were quantified in the nucleus of the tractus solitarius (NTS), paraventricular nucleus (PVN), supraoptic nucleus (SON), and subfornical organ (SFO) after 1-h partial splenic vein occlusion (SVO) in conscious rats bearing balloon occluders around the splenic vein, telemetric pressure transducers in the gastric vein (splenic venous pressure), and abdominal aorta catheters (MAP). SVO stimulated Fos expression in the PVN and SON, but not NTS or SFO of intact rats. Renal denervation abolished this response in the parvocellular PVN, while renal + splenic denervation abolished activation in the magnocellular PVN and the SON. In renal-denervated animals, SVO depressed Fos expression in the NTS and increased expression in the SFO, responses that were abolished by renal + splenic denervation. In intact rats, SVO also induced a fall in right atrial pressure, an increase in renal afferent nerve activity, and an increase in MAP. We conclude that elevated splenic venous pressure does induce hypothalamic activation and that this is mediated through both splenic and renal afferent nerves. However, in the absence of renal afferent input, SVO depressed NTS activation, probably as a result of the accompanying fall in cardiac preload and reduced afferent signaling from the cardiopulmonary receptors.

Splenic baroreceptors control splenic afferent nerve activity

Stenosis of either the portal or splenic vein increases splenic afferent nerve activity (SANA), which, through the splenorenal reflex, reduces renal blood flow. Because these maneuvers not only raise splenic venous pressure but also reduce splenic venous outflow, the question remained as to whether it is increased intrasplenic postcapillary pressure and/or reduced intrasplenic blood flow, which stimulates SANA. In anesthetized rats, we measured the changes in SANA in response to partial occlusion of either the splenic artery or vein. Splenic venous and arterial pressures and flows were simultaneously monitored. Splenic vein occlusion increased splenic venous pressure (9.5 +/- 0.5 to 22.9 +/- 0.8 mmHg, n = 6), reduced splenic arterial blood flow (1.7 +/- 0.1 to 0.9 +/- 0.1 ml/min, n = 6) and splenic venous blood flow (1.3 +/- 0.1 to 0.6 +/- 0.1 ml/min, n = 6), and increased SANA (1.7 +/- 0.4 to 2.2 +/- 0.5 spikes/s, n = 6). During splenic artery occlusion, we matched the reduction in either splenic arterial blood flow (1.7 +/- 0.1 to 0.7 +/- 0.05, n = 6) or splenic venous blood flow (1.2 +/- 0.1 to 0.5 +/- 0.04, n = 5) with that seen during splenic vein occlusion. In neither case was there any change in either splenic venous pressure (-0.4 +/- 0.9 mmHg, n = 6 and +0.1 +/- 0.3 mmHg, n = 5) or SANA (-0.11 +/- 0.15 spikes/s, n = 6 and -0.05 +/- 0.08 spikes/s, n = 5), respectively. Furthermore, there was a linear relationship between SANA and splenic venous pressure (r = 0.619, P = 0.008, n = 17). There was no such relationship with splenic venous (r = 0.371, P = 0.236, n = 12) or arterial (r = 0.275, P = 0.413, n = 11) blood flow. We conclude that it is splenic venous pressure, not flow, which stimulates splenic afferent nerve activity and activates the splenorenal reflex in portal and splenic venous hypertension.

Neural control of renal function

The renal nerves are the communication link between the central nervous system and the kidney. In response to multiple peripheral and central inputs, efferent renal sympathetic nerve activity is altered so as to convey information to the major structural and functional components of the kidney, the vessels, glomeruli, and tubules, each of which is innervated. At the level of each of these individual components, information transfer occurs via interaction of the neurotransmitter released at the sympathetic nerve terminal-neuroeffector junction with specific postjunctional receptors coupled to defined intracellular signaling and effector systems. In response to normal physiological stimuli, changes in efferent renal sympathetic nerve activity contribute importantly to homeostatic regulation of renal blood flow, glomerular filtration rate, renal tubular epithelial cell solute and water transport, and hormonal release. Afferent input from sensory receptors located in the kidney participates in this reflex control system via renorenal reflexes that enable total renal function to be self-regulated and balanced between the two kidneys. In pathophysiological conditions, abnormal regulation of efferent renal sympathetic nerve activity contributes significantly to the associated abnormalities of renal function which, in turn, are of importance in the pathogenesis of the disease.