The functions of the renal nerves

Manual treatment for kidney mobility and symptoms in women with nonspecific low back pain and urinary infections

CONTEXT

Recent studies have suggested a connection between low back pain (LBP) and urinary tract infections (UTI). These disturbances could be triggered via visceral-somatic pathways, and there is evidence that kidney mobility is reduced in patients suffering from nonspecific LBP. Manual treatment of the perinephric fascia could improve both kidney mobility and LBP related symptoms.

OBJECTIVES

To assess whether manual treatment relieves UTI and reduces pain in patients with nonspecific LBP through improvement in kidney mobility.

METHODS

Records from all patients treated at a single physical therapy center in 2019 were retrospectively reviewed. Patients were included if they were 18 years of age or older, had nonspecific LBP, and experienced at least one UTI episode in the 3 months before presentation. Patients were excluded if they had undergone manipulative treatment in the 6 months before presentation, if they had one of several medical conditions, if they had a history of chronic pain medication use, and more. Patient records were divided into two groups for analysis: those who were treated with manipulative techniques of the fascia with thrust movement (Group A) vs those who were treated without thrust movement (Group B). Kidney Mobility Scores (KMS) were analyzed using high resolution ultrasound. Symptoms as reported at patients' 1 month follow up visits were also used to assess outcomes; these included UTI relapse, lumbar spine mobility assessed with a modified Schober test, and lumbar spine pain.

RESULTS

Of 126 available records, 20 patients were included in this retrospective study (10 in Group A and 10 in Group B), all of whom who completed treatment and attended their 1 month follow up visit. Treatments took place in a single session for all patients and all underwent ultrasound of the right kidney before and after treatment. The mean (± standard deviation) KMS (1.9 ± 1.1), mobility when bending (22.7 ± 1.2), and LBP scores (1.2 ± 2.6) of the patients in Group A improved significantly in comparison with the patients in Group B (mean KMS, 1.1 ± 0.8; mobility when bending, 21.9 ± 1.1; and LBP, 3.9 ± 2.7) KMS, p<0.001; mobility when bending, p=0.003; and LBP, p=0.007). At the 1 month follow up visit, no significant statistical changes were observed in UTI recurrence (secondary outcome) in Group A (-16.5 ± 4.3) compared with Group B (-20.4 ± 7) (p=0.152).

CONCLUSIONS

Manual treatments for nonspecific LBP associated with UTI resulted in improved mobility and symptoms for patients in this retrospective study, including a significant increase in kidney mobility.

Renal 123I-MIBG Uptake before and after Live-Donor Kidney Transplantation

Increased sympathetic activity is suggested to be part of the pathogenesis in several diseases. Methods to evaluate sympathetic activity and renal nervous denervation procedural success are lacking. Scintigraphy using the norepinephrine analog Iodine-123 Metaiodobenzylguanidine (123I-MIBG) might provide information on renal sympathetic nervous activity. Renal transplantation induces complete denervation of the kidney and as such represents an ideal model to evaluate the renal 123I-MIBG scintigraphy method. The aim of this study was to evaluate whether renal 123I-MIBG scintigraphy can detect changes in renal sympathetic nervous activity following renal transplantation. Renal 123I-MIBG scintigraphy was performed in eleven renal transplant recipients at 1, 3, and 6 months following transplantation and in their respective living donors prior to their kidney donation. Relative uptake as well as washout was obtained. In transplanted patients, the relative 4 h uptake of 123I-MIBG, as measured by the kidney/background ratio, was 2.7 (0.4) (mean (SD)), 2.7 (0.5), and 2.5 (0.4) at 1, 3, and 6 months post-transplantation, respectively, as compared with the 4.0 (0.4) value in the donor kidney before donor nephrectomy (p < 0.01). There was no significant change in washout-rate between pre-transplantation and any of the follow-up time points. Living donor kidney transplantation was at 6 months post transplantation, associated with an almost 40% reduction in the relative 4 h 123I-MIBG uptake of the kidney. Further studies will help to fully establish its implications as a marker of renal innervation or denervation.

Renal Nerves and Long-Term Control of Arterial Pressure

The objective of this review is to provide an in-depth evaluation of how renal nerves regulate renal and cardiovascular function with a focus on long-term control of arterial pressure. We begin by reviewing the anatomy of renal nerves and then briefly discuss how the activity of renal nerves affects renal function. Current methods for measurement and quantification of efferent renal-nerve activity (ERNA) in animals and humans are discussed. Acute regulation of ERNA by classical neural reflexes as well and hormonal inputs to the brain is reviewed. The role of renal nerves in long-term control of arterial pressure in normotensive and hypertensive animals (and humans) is then reviewed with a focus on studies utilizing continuous long-term monitoring of arterial pressure. This includes a review of the effect of renal-nerve ablation on long-term control of arterial pressure in experimental animals as well as humans with drug-resistant hypertension. The extent to which changes in arterial pressure are due to ablation of renal afferent or efferent nerves are reviewed. We conclude by discussing the importance of renal nerves, relative to sympathetic activity to other vascular beds, in long-term control of arterial pressure and hypertension and propose directions for future research in this field. © 2017 American Physiological Society. Compr Physiol 7:263-320, 2017.

The sympathetic nervous system alterations in human hypertension

Several articles have dealt with the importance and mechanisms of the sympathetic nervous system alterations in experimental animal models of hypertension. This review addresses the role of the sympathetic nervous system in the pathophysiology and therapy of human hypertension. We first discuss the strengths and limitations of various techniques for assessing the sympathetic nervous system in humans, with a focus on heart rate, plasma norepinephrine, microneurographic recording of sympathetic nerve traffic, and measurements of radiolabeled norepinephrine spillover. We then examine the evidence supporting the importance of neuroadrenergic factors as promoters and amplifiers of human hypertension. We expand on the role of the sympathetic nervous system in 2 increasingly common forms of secondary hypertension, namely hypertension associated with obesity and with renal disease. With this background, we examine interventions of sympathetic deactivation as a mode of antihypertensive treatment. Particular emphasis is given to the background and results of recent therapeutic approaches based on carotid baroreceptor stimulation and radiofrequency ablation of the renal nerves.

Is the failure of SYMPLICITY HTN-3 trial to meet its efficacy endpoint the "end of the road" for renal denervation?

Resistant hypertension is a common medical problem that is increasing with the advent of an increasingly older and heavier population. The etiology of resistant hypertension is almost always multifactorial, but the results of numerous studies indicate that renal sympathetic activation is a particularly common cause of resistance to antihypertensive treatment. Consistent with the belief in a pivotal role of renal sympathetic stimulation, there has been a growing interest in renal denervation (RDN) treatment strategies. The long-awaited results of SYMPLICITY HTN-3 study disclosed that the reduction in blood pressure by the SYMPLICITY device did not differ from that in the sham-procedure arm of the study. In the present article, we identify several factors that explain why the study failed to demonstrate any benefit from the intervention. The reasons are multifactorial and include inadequate screening at entry and frequent medication changes during the study. Additional problems include the lack of experience of many operators with the SYMPLICITY device and procedure variability, as attested to by a diminished number of ablation "quadrants." Also a factor was the inability of the first generation Medtronic device to allow four ablations to be performed simultaneously. We recommend that future RDN studies adhere to more rigorous screening procedures, and utilize newer multi-site denervation systems that facilitate four ablations simultaneously. Drug optimization should be achieved by monitoring adherence throughout the study. Nevertheless, we are optimistic about a future role of RDN. To optimize chances of success, increased efforts are necessary to identify the appropriate patients for RDN and investigators must use second and third generation denervation devices and techniques.

Olfactory stimulatory with grapefruit and lavender oils change autonomic nerve activity and physiological function

This review summarizes the effects of olfactory stimulation with grapefruit and lavender oils on autonomic nerve activity and physiological function. Olfactory stimulation with the scent of grapefruit oil (GFO) increases the activity of sympathetic nerves that innervate white and brown adipose tissues, the adrenal glands, and the kidneys, decreases the activity of the gastric vagal nerve in rats and mice. This results in an increase in lipolysis, thermogenesis, and blood pressure, and a decrease in food intake. Olfactory stimulation with the scent of lavender oil (LVO) elicits the opposite changes in nerve activity and physiological variables. Olfactory stimulation with scent of limonene, a component of GFO, and linalool, a component of LVO, has similar effects to stimulation with GFO and LVO, respectively. The histamine H1-receptor antagonist, diphenhydramine, abolishes all GFO-induced changes in nerve activity and physiological variables, and the hitstamine H3-receptor antagonist, thioperamide, eliminates all LVO-induced changes. Lesions to the hypothalamic suprachiasmatic nucleus and anosmic treatment with ZnSO4 also abolish all GFO- and LVO-induced changes. These findings indicate that limonene and linalool might be the active substances in GFO and LVO, and suggest that the suprachiasmatic nucleus and histamine are involved in mediating the GFO- and LVO-induced changes in nerve activity and physiological variables.

Sympathetic renal innervation and resistant hypertension

Hypertension in chronic renal disease and renovascular disease is often resistant to therapy. Understanding the pathogenic mechanisms responsible for hypertension in these conditions may lead to improved and more targeted therapeutic interventions. Several factors have been implicated in the pathogenesis of hypertension associated with renal disease and/or renal failure. Although the role of sodium retention, total body volume expansion, and hyperactivity of the renin-angiotensin-aldosterone system (RAAS) are well recognized, increasing evidence suggests that afferent impulses from the injured kidney may increase sympathetic nervous system activity in areas of the brain involved in noradrenergic regulation of blood pressure and contribute to the development and maintenance of hypertension associated with kidney disease. Recognition of this important pathogenic factor suggests that antiadrenergic drugs should be an essential component to the management of hypertension in patients with kidney disease, particularly those who are resistant to other modalities of therapy.

Translational medicine: the antihypertensive effect of renal denervation

Translational medicine is concerned with the translation of research discoveries into clinical applications for the prevention, diagnosis, and treatment of human diseases. Here we briefly review the research concerning the role of the renal sympathetic nerves (efferent and afferent) in the control of renal function, with particular reference to hypertension. The accumulated evidence is compelling for a primary role of the renal innervation in the pathogenesis of hypertension. These research discoveries led to the development of a catheter-based procedure for renal denervation in human subjects. A proof-of-principle study in patients with hypertension resistant to conventional therapy has demonstrated that the procedure is safe and produces renal denervation with sustained lowering of arterial pressure.

Central endogenous vasopressin induced by central salt-loading participates in body fluid homeostasis through modulatory effects on neurones of the paraventricular nucleus in conscious rats

Peripherally secreted arginine vasopressin (AVP) plays a role in controlling body fluid homeostasis, and central endogenous AVP acts as a neurotransmitter or neuromodulator. The limbic system, which appears to exert an inhibitory effect on the endocrine hypothalamus, is also innervated by fibres that contain AVP. We examined whether central endogenous AVP is also involved in the control of body fluid homeostasis. To explore this possibility, we examined neuronal activity in the paraventricular nucleus of the hypothalamus (PVN), periventricular parts of the PVN and limbic brain areas, as well as AVP mRNA expression in the PVN and the peripheral secretion of AVP after central salt-loading in rats that had been pretreated i.c.v. with the AVP V(1) receptor antagonist OPC-21268. Neuronal activity in the PVN evaluated in terms of Fos-like immunoreactivity (FLI), especially in the parvocellular subdivisions, was suppressed. On the other hand, FLI was enhanced in the lateral septum, the bed nucleus of the stria terminalis and the anterior hypothalamic area. Similarly, AVP mRNA expression was enhanced in the magnocellular subnucleus of the PVN, despite the lack of a significant difference in the peripheral AVP level between OPC-21268- and vehicle-pretreated groups. We recorded renal sympathetic nerve activity (RSNA) as sympathetic nerve outflow during central salt-loading. The suppression of RSNA was significantly attenuated by i.c.v. pretreatment with OPC-21268. These results suggest that the suppression of RSNA during central salt-loading might be the result of a decrease in neuronal activity in the parvocellular subdivisions of the PVN via the inhibitory action of central endogenous AVP. The parvocellular and magnocellular neurones in the PVN might show different responses to central salt-loading to maintain body fluid homeostasis as a result of the modulatory role of central endogenous AVP.

Significant relationship between renin suppression and atrial natriuretic peptide (alpha-hANP) during volume loading in hypertensive men

We have studied eight men with moderate hypertension to determine the atrial natriuretic peptide (alpha-hANP) response to acute volume expansion. Rapid infusion of 1,000 ml 0.9% saline (10-20 min) caused an increase in central venous pressure (4.7 +/- 1.6 cmH2O) while blood pressure and pulse pressure (arterial baroreceptor load) did not change. Stroke volume and heart rate were not affected by the volume load but plasma renin activity (PRA) was significantly suppressed (from 0.83 +/- 0.14 to 0.68 +/- 0.34 microgram AI I/ml-h; p less than 0.01). A significant hemodilution was also observed. Renal sodium excretion was significantly increased. Arterial alpha-hANP increased significantly from 21.1 +/- 6.1 to 30.5 +/- 4.0 pmol/l (p less than 0.02) during volume expansion. There was a significant correlation between corrected plasma volume increase (urine volume subtracted from the infused volume) and alpha-hANP plasma elevation (r = 0.78; p less than 0.05). There was also a significant negative correlation between changes alpha-hANP and PRA (r = -0.78, p less than 0.05). We conclude that only moderate volume loading in human hypertensives is a mechanism for increase in plasma alpha-hANP levels. The significant negative correlation between changes in alpha-hANP and PRA suggests that alpha-hANP may be the humoral factor at least partly responsible for suppression of renin in hypertensive man. Since increased fluid volume also affects sympathetic renal efferents as well as vasopressin secretion, our observed relationship between volume load and renin may well be related also to such mechanisms.

Auditory stimulation affects renal sympathetic nerve activity and blood pressure in rats

Here, we examined the effects of auditory stimulation at 50 dB with white noise (WN) or music (Traeumerei [TM] by Schumann or Etude by Chopin) on renal sympathetic nerve activity (RSNA) and BP in urethane-anesthetized rats. Auditory stimulation with TM, but not with WN or the Etude, significantly decreased RSNA and BP. Complete bilateral destruction of the cochleae and bilateral lesions of the auditory cortex (AuC) eliminated the effects of TM stimulation on RSNA and BP, but bilateral lesions of primary somatosensory cortex (S1C) had no effect. Bilateral lesions of the hypothalamic suprachiasmatic nucleus (SCN) or intracerebral administration of thioperamide, a histaminergic H3 receptor antagonist, also abolished TM-induced decreases in RSNA and BP. These findings suggest that exposure to music can decrease RSNA and BP through the auditory pathway, histaminergic neurons, and the SCN.

Oxidative stress mediates the stimulation of sympathetic nerve activity in the phenol renal injury model of hypertension

Renal injury caused by the injection of phenol in the lower pole of one kidney increases blood pressure (BP), norepinephrine secretion from the posterior hypothalamic nuclei (PH), and renal sympathetic nerve activity in the rat. Renal denervation prevents these effects of phenol. We have also demonstrated that noradrenergic traffic in the brain is modulated by NO and interleukin-1beta. In this study, we tested the hypothesis that the increase in sympathetic nervous system (SNS) activity in the phenol renal injury model is because of activation of reactive oxygen species. To this end, first we examined the abundance of several components of reduced nicotinamide-adenine dinucleotide phosphate oxidase (identified as the major source of reactive oxygen species), including gp91phox/Nox2, p22phox, p47phox, and Nox3 using real-time PCR. Second, we evaluated the effects of 2 superoxide dismutase mimetic, tempol (4-hydroxy-2,2,6,6-tetramethyl piperidinoxyl), and superoxide dismutase-polyethylene glycol on central and peripheral SNS activation caused by intrarenal phenol injection. Intrarenal injection of phenol raised BP, NE secretion from the PH, renal sympathetic nerve activity, and the abundance of reduced nicotinamide-adenine dinucleotide phosphate and reduced the abundance of interleukin-1beta and neural-NO synthase mRNA in the PH, paraventricular nuclei, and locus coeruleus compared with control rats. When tempol or superoxide dismutase-polyethylene glycol were infused in the lateral ventricle before phenol, the effects of phenol on BP and SNS activity were abolished. The studies suggest that central activation of the SNS in the phenol-renal injury model is mediated by increased reactive oxygen species in brain nuclei involved in the noradrenergic control of BP.

Olfactory stimulation with scent of essential oil of grapefruit affects autonomic neurotransmission and blood pressure

Previously, we observed that olfactory stimulation with scent of grapefruit oil (SGFO) enhances sympathetic nerve activities and suppresses gastric vagal (parasympathetic) nerve activity (GVNA), increases plasma glycerol concentration and body temperature, and decreases appetite in rats. Here, we show that olfactory stimulation with SGFO for 10 min elevates renal sympathetic nerve activity (RSNA) and blood pressure (BP) and lowers GVNA in urethane-anesthetized rats. Olfactory stimulation with limonene, a major component of grapefruit oil, also elicited increases in RSNA and BP in urethane-anesthetized rats. Anosmic treatment with ZnSO(4) eliminated both the effects of SGFO and scent of limonene on RSNA and BP. Intracerebral administration of diphenhydramine, a histaminergic H1-antagonist, abolished SGFO- or scent of limonene-mediated increases in RSNA and BP as well as the decrease in GVNA. Moreover, bilateral lesions of the hypothalamic suprachiasmatic nucleus (SCN) eliminated the SGFO- and limonene-mediated increases in RSNA and BP and decrease in GVNA, but bilateral lesions of the cerebral cortex did not have any affect on these parameters. These findings suggest that scent of grapefruit oil and its active component, limonene, affect autonomic neurotransmission and blood pressure through central histaminergic nerves and the suprachiasmatic nucleus.

A neural set point for the long-term control of arterial pressure: beyond the arterial baroreceptor reflex

Arterial baroreceptor reflex control of renal sympathetic nerve activity (RSNA) has been proposed to play a role in long-term control of arterial pressure. The hypothesis that the “set point” of the acute RSNA baroreflex curve determines the long-term level of arterial pressure is presented and challenged. Contrary to the hypothesis, studies on the long-term effects of sinoaortic denervation (SAD) on arterial pressure and RSNA, as well as more recent studies of chronic baroreceptor “unloading” on arterial pressure, suggest that the basal levels of sympathetic nerve activity and arterial pressure are regulated independent of arterial baroreceptor input to the brainstem. Studies of the effect of SAD on the long-term salt sensitivity of arterial pressure are consistent with a short-term role, rather than a long-term role for the arterial baroreceptor reflex in regulation of arterial pressure during changes in dietary salt intake. Renal denervation studies suggest that renal nerves contribute to maintenance of the basal levels of arterial pressure. However, evidence that baroreflex control of the kidney plays a role in the maintenance of arterial pressure during changes in dietary salt intake is lacking. It is proposed that a “baroreflex-independent” sympathetic control system must exist for the long-term regulation of sympathetic nerve activity and arterial pressure. The concept of a central nervous system “set point” for long-term control of mean arterial pressure (CNS-MAP set point), and its involvement in the pathogenesis of hypertension, is discussed.

Central autonomic innervation of the kidney. What can we learn from a transneuronal tracing study in an animal model?

PURPOSE

Renal sympathetic innervation is involved in the maintenance of fluid homeostasis, modulation of renal secretion from juxtaglomerular cells, sodium resorption from renal tubular cells and renal hemodynamics. The understanding of central innervation and neuronal connections is important for studying the consequences of renal disease and surgical interventions compromising renal nerves.

MATERIALS AND METHODS

A total of 38 individual adult male Sprague-Dawley rats were used for retrograde transneuronal mapping of the spinal cord and brain stem after pseudorabies virus (PRV) injection into the left kidney in 30 and control experiments in 8. After a survival time of 72, 96 or 120 hours the animals were sacrificed. Exploration of the abdominal and pelvic visceral organs was done, and the brain and spinal cord were harvested via dorsal laminectomy. After cutting on a freezing microtome the tissue was immunostained for PRV.

RESULTS

After kidney injection inspection of the abdominal and pelvic cavity revealed an enlarged bladder with hemic urine. The urine was sterile and the bladder wall showed signs of neurogenic inflammation. Other organs were not affected. PRV positive cells were primarily found within the ipsilateral nucleus intermediolateralis of thoracic spinal cord segments T6 to T13. At the supraspinal level PRV positive cells were found within certain regions, namely the nuclei raphes, rostral ventromedial and ventrolateral medulla, A5 noradrenergic cell region, locus coeruleus and nucleus paraventricularis of the hypothalamus.

CONCLUSIONS

This investigation demonstrates the anatomical basis for broad central sympathetic innervation of the kidney. The neurogenic inflammation within the spinal cord inherent to the PRV tracing method causes an inflammatory reaction within the bladder. This can be due to increased sympathetic nerve activity, followed by peripheral, neurogenically mediated inflammation.

Dose-dependent effects of l-carnosine on the renal sympathetic nerve and blood pressure in urethane-anesthetized rats

The physiological function of l-carnosine (β-alanyl-l-histidine) synthesized in mammalian muscles has been unclear. Previously, we observed that intravenous (IV) injection of l-carnosine suppressed renal sympathetic nerve activity (RSNA) in urethane-anesthetized rats, and l-carnosine administered via the diet inhibited the elevation of blood pressure (BP) in deoxycorticosterone acetate salt hypertensive rats. To identify the mechanism, we examined effects of IV or intralateral cerebral ventricular (LCV) injection of various doses of l-carnosine on RSNA and BP in urethane-anesthetized rats. Lower doses (1 μg IV; 0.01 μg LCV) of l-carnosine significantly suppressed RSNA and BP, whereas higher doses (100 μg IV; 10 μg LCV) elevated RSNA and BP. Furthermore, we examined effects of antagonists of histaminergic (H1 and H3) receptors on l-carnosine-induced effects. When peripherally and centrally given, thioperamide, an H3 receptor antagonist, blocked RSNA and BP decreases induced by the lower doses of peripheral l-carnosine, whereas diphenhydramine, an H1 receptor antagonist, inhibited increases induced by the higher doses of peripheral l-carnosine. Moreover, bilateral lesions of the hypothalamic suprachiasmatic nucleus eliminated both effects on RSNA and BP induced by the lower (1 μg) and higher (100 μg) doses of peripheral l-carnosine. These findings suggest that low-dose l-carnosine suppresses and high-dose l-carnosine stimulates RSNA and BP, that the suprachiasmatic nucleus and histaminergic nerve are involved in the activities, and that l-carnosine acts in the brain and possibly other organs.

Effect of muscimol and L-NAME in the PVN on the RSNA response to volume expansion in conscious rabbits

In the present study, we have investigated whether the hypothalamic paraventricular nucleus (PVN) contributed to the reflex reduction in renal sympathetic nerve activity (RSNA) normally elicited by volume expansion in the conscious rabbit. RSNA was monitored after volume expansion (Dextran 70, 2 ml/min for 30 min) in animals microinjected into, and outside, the PVN with muscimol (10 nmol), to acutely inhibit neuronal function. Because nitric oxide within the PVN inhibits RSNA, we also examined the effect of NG-nitro-L-arginine methyl ester (L-NAME; 20 nmol) to block nitric oxide synthase. Compared with vehicle, the reduction in RSNA elicited by volume expansion was abolished by injection of muscimol into the PVN. The effect was specific to the PVN because microinjections of muscimol outside the PVN had no effect on the response. L-NAME microinjected into or outside the PVN had no effect on the RSNA response. The findings suggest that the PVN is essential in the central pathways mediating the renal sympathetic nerve response elicited by elevations in plasma volume but that nitric oxide does not play a major role.

Neuroendocrine control of body fluid metabolism

Mammals control the volume and osmolality of their body fluids from stimuli that arise from both the intracellular and extracellular fluid compartments. These stimuli are sensed by two kinds of receptors: osmoreceptor-Na+ receptors and volume or pressure receptors. This information is conveyed to specific areas of the central nervous system responsible for an integrated response, which depends on the integrity of the anteroventral region of the third ventricle, e.g., organum vasculosum of the lamina terminalis, median preoptic nucleus, and subfornical organ. The hypothalamo-neurohypophysial system plays a fundamental role in the maintenance of body fluid homeostasis by secreting vasopressin and oxytocin in response to osmotic and nonosmotic stimuli. Since the discovery of the atrial natriuretic peptide (ANP), a large number of publications have demonstrated that this peptide provides a potent defense mechanism against volume overload in mammals, including humans. ANP is mostly localized in the heart, but ANP and its receptor are also found in hypothalamic and brain stem areas involved in body fluid volume and blood pressure regulation. Blood volume expansion acts not only directly on the heart, by stretch of atrial myocytes to increase the release of ANP, but also on the brain ANPergic neurons through afferent inputs from baroreceptors. Angiotensin II also plays an important role in the regulation of body fluids, being a potent inducer of thirst and, in general, antagonizes the actions of ANP. This review emphasizes the role played by brain ANP and its interaction with neurohypophysial hormones in the control of body fluid homeostasis.

Effects of Salt Rich Diet in the Obese Zucker Rats: Studies on Renal Function During Isotonic Volume Expansion

Obese Zucker rats (OZR) are hyperinsulenemic, hyperglycemic and dyslipidemic and develop salt dependent hypertension. Since salt sensitivity is considered to be due to impaired handling of renal sodium excretion, these studies were conducted in the obese and lean Zucker rats (LZR) anesthetized with Inactin to evaluate renal function under basal conditions and during acute isotonic fluid volume expansion (VE). Mean Arterial blood pressure (MBP), heart rate (HR), renal blood flow(RBF) and glomerular filtration rate (GFR) were not significantly different between the lean Zucker rats fed normal diet or that fed salt rich diet(8% NaCI). However, basal UV and UNaV were significantly greater in the LZR fed high salt. During VE essentially identical increases occurred in GFR, UV and UNaV in both the lean groups. In the OZR fed salt rich diet also, there were no significant changes in the heart rate, RBF and GFR. However, arterial blood pressure of the OZR fed salt rich diet was significantly greater than that of the OZR on the normal diet as well as that of both the lean groups. Also, as in the LZR, basal UV and UNaV were significantly greater in the salt fed obese rats. During volume expansion there were no impairments in the ability of the obese groups fed normal or salt rich diet to eliminate sodium and water during volume load. In fact, the net sodium and water excretions during and 60 min after VE in both the obese groups were significantly greater than that of corresponding lean groups. Furthermore, these values in the OZR fed salt rich diet were significantly greater than that of the obese rats on normal salt diet perhaps due to the contribution of pressure natriuretic mechanisms'. These data demonstrate that although OZR are salt sensitive, the renal mechanisms that would collectively respond to acute isotonic VE were fully functional. An unexpected and a novel finding in these studies is that the salt rich diet, in addition to increasing arterial blood pressure also significantly lowered plasma of insulin levels and enhanced glucose and cholesterol levels in the obese Zucker rats.

Renal denervation chronically lowers arterial pressure independent of dietary sodium intake in normal rats

The present study was designed to test the hypothesis that renal nerves chronically modulate arterial pressure (AP) under basal conditions and during changes in dietary salt intake. To test this hypothesis, continuous telemetric recording of AP in intact (sham) and renal denervated (RDNX) Sprague-Dawley rats was performed and the effect of increasing and decreasing dietary salt intake on AP was determined. In protocol 1, 24-h AP, sodium, and water balances were measured in RDNX (n = 11) and sham (n = 9) rats during 5 days of normal (0.4% NaCl) and 10 days of high (4.0% NaCl) salt intake, followed by a 3-day recovery period (0.4% NaCl). Protocol 2 was similar with the exception that salt intake was decreased to 0.04% NaCl for 10 days after the 5-day period of normal salt (0.04% NaCl) intake (RDNX; n = 6, sham; n = 5). In protocol 1, AP was lower in RDNX (91 +/- 1 mmHg) compared with sham (101 +/- 2 mmHg) rats during the 5-day 0.4% NaCl control period. During the 10 days of high salt intake, AP increased <5 mmHg in both groups so that the difference between sham and RDNX rats remained constant. In protocol 2, AP was also lower in RDNX (93 +/- 2 mmHg) compared with sham (105 +/- 4 mmHg) rats during the 5-day 0.4% NaCl control period, and AP did not change in response to 10 days of a low-salt diet in either group. Overall, there were no between-group differences in sodium or water balance in either protocol. We conclude that renal nerves support basal levels of AP, irrespective of dietary sodium intake in normal rats.

Are sodium-dependent V1 receptors and sympathetic nerve activations involved in regulation of blood pressure in borderline-hypertensive Hiroshima rats?

Sympathetic nerve activity (SNA) was estimated by the magnitude of depressor response after ganglionic blockade with hexamethonium bromide (C6; 25 mg/kg weight). The depressor effects of C6 were significantly less in borderline-hypertensive Hiroshima rats (BHR) than in deoxycorticosterone acetate (DOCA)-salt hypertensive rats (DOCA rats) or in spontaneously hypertensive rats (SHR), but they were not different in BHR and normotensive control Wistar rats (NCR). After sympatho-inhibition, the depressor effects of a selective vasopressin V1 receptor antagonist (V1A; 10 microg/kg: [d(CH2)5(1), O-Me-Tyr2, Arg8]-vasopressin) were significantly greater in BHR than in DOCA rats, SHR or NCR. In a previous study, we reported that the depressor effects of C6 were significantly less in BHR than in SHR, but after sympatho-inhibition, the depressor effects of V1A were significantly greater in BHR than in SHR (Hypertens Res 2002; 25: 241-248). After high-salt diet loading in the present study (8% salt-containing diet for 10 weeks), the magnitudes of increase in mean arterial pressure in BHR and NCR were almost the same. There was almost no difference in the depressor effects of V1A after sympatho-inhibition between BHR with high-salt intake and BHR without high-salt intake. The depressor effects of an angiotensin-converting enzyme inhibitor, captopril (1 mg/kg), were almost the same between BHR and NCR both before and after sympatho-inhibition. However, these effects were completely inhibited after the high-salt diet. The results show that SNA was within the normal range in BHR and that no further accelerated responsiveness of endogenous vasopressin was observed in BHR after high-salt intake.

Neurogenic factors in renal hypertension

Hypertension is very common in patients with chronic renal failure and contributes to cardiovascular morbidity and mortality. Several mechanisms may contribute to hypertension in these patients, but recently a large body of evidence supports the notion that activation of the sympathetic nervous system (SNS) may play a very important role. In rats with 5/6 nephrectomy, the turnover rate of norepinephrine was increased in brain nuclei involved in the noradrenergic control of blood pressure, and dorsal rhizotomy prevented hypertension. Studies in human subjects with chronic renal failure and hypertension have also shown increased peripheral SNS activity measured my microneurography in the peroneal nerve and normalization with nephrectomy. In all, these studies indicate that renal injuries may activate renal afferent pathways that connect with integrative brain structures in SNS activity and blood pressure. We have also shown that central SNS activity is modulated by local expression of nitric oxide, which, in turn, is regulated by interleukin-1b.

Phosphorylation of CREB in thoracolumbar spinal neurons and dorsal root ganglia after renal artery occlusion in rat

These studies have demonstrated that ipsilateral renal artery occlusion (RAO) in rat results in the phosphorylation of cyclic AMP (cAMP) response element binding protein (p-CREB) in the thoracolumbar (T8-L2) spinal cord and associated dorsal root ganglia (DRG). p-CREB-immunoreactivity (IR) was expressed bilaterally in the thoracolumbar spinal cord, whereas expression in the DRG was ipsilateral relative to RAO. p-CREB-IR was primarily expressed in four distinct regions of the spinal cord: medial or lateral dorsal horn (MDH or LDH), dorsal commissural nucleus (DCN) and the region of the intermediolateral cell column (IML). After RAO, p-CREB-IR was greatest in the T13-L2 spinal segments. Within the T13-L1 spinal segments, p-CREB-IR was greatest in the MDH, LDH and DCN and expression in each of these regions was comparable within a segment. Following RAO, there was a significant (p < or = 0.001) increase in the percentage (86-98%) of p-CREB-IR spinal neurons expressing choline acetyltransferase (ChAT)-IR (a marker of preganglionic neurons) in the IML of the T10, T12 and L1 spinal segments examined. After ipsilateral RAO, expression of p-CREB-IR was increased in the ipsilateral, T8-L2 DRG with the greatest number of p-CREB-IR dorsal root ganglion cells being located in the L1 dorsal root ganglion. Retrograde tracing with Fluorogold (FG) to label renal afferent cells in the DRG revealed a significant (p < or = 0.01) increase in the percentage (75-86%) of renal afferent cells expressing p-CREB-IR after ipsilateral RAO. These studies demonstrate that p-CREB-IR is a useful tool for examining the distribution of spinal neurons and DRG involved in reflexes of renal origin. In addition, expression of p-CREB-IR may be coupled to late response genes that may exert long-term changes in neuronal function after RAO.

Frontiers of hypoxia research: acute mountain sickness

Traditionally, scientists and clinicians have explored peripheral physiological responses to acute hypoxia to explain the pathophysiological processes that lead to acute mountain sickness (AMS) and high-altitude cerebral edema (HACE). After more than 100 years of investigation, little is yet known about the fundamental causes of the headache and nausea that are the main symptoms of AMS. Thus, we review the evidence supporting a change in focus to the role of the central nervous system in AMS. Our justification is (i) that the symptoms of AMS and HACE are largely neurological, (ii) that HACE is considered to be the end-stage of severe AMS and was recently identified as a vasogenic edema, opening the door for a role for blood–brain barrier permeability in AMS, (iii) that new, non-invasive techniques make measurement of brain water levels and cerebral blood volume possible and (iv) that the available experimental evidence and theoretical arguments support a significant role for brain swelling in the pathophysiology of AMS. We believe that an examination of the responses of the central nervous system to acute hypoxia will reveal important new pathophysiological processes that may help explain AMS and HACE.

Role of the alpha(1)- and alpha(2)-adrenoceptors of the paraventricular nucleus on the water and salt intake, renal excretion, and arterial pressure induced by angiotensin II injection into the medial septal area

In this study we investigated the influence of alpha-adrenergic antagonists injections into the paraventricular nucleus (PVN) of the hypothalamus on the thirst and salt appetite, diuresis, natriuresis, and pressor effects of angiotensin II (ANG II) stimulation of medial septal area (MSA). ANG II injection into the MSA induced water and sodium intake, diuresis, natriuresis, and pressor responses. The previous injection of prazosin (an alpha(1)-adrenergic antagonist) into the PVN abolished, whereas previous administration of yohimbine (an alpha(2)-adrenergic antagonist) into the PVN increased the water and sodium intake, urinary, natriuretic, and pressor responses induced by ANG II injected into the MSA. Previous injection of a nonselective alpha-adrenergic antagonist, regitin, into the PVN blocked the urinary excretion, and reduced the water and sodium intake, sodium intake, and pressor responses induced by ANG II injected into the MSA. The present results suggest that alpha-adrenergic pathways involving the PVN are important for the water and sodium excretion, urine and sodium excretion, and pressor responses, induced by angiotensinergic activation of the MSA.

High dose angiotensin-converting enzyme inhibition prevents fluid volume expansion in heart transplant recipients

OBJECTIVES

We sought to test the hypothesis that plasma volume (PV) expansion in heart transplant recipients (HTRs) is caused by failure to reflexively suppress the renin-angiotensin-aldosterone (RAA) axis.

BACKGROUND

Extracellular fluid volume expansion occurs in clinically stable HTRs who become hypertensive. We have previously demonstrated that the RAA axis is not reflexively suppressed by a hypervolemic stimulus in HTRs.

METHODS

Plasma volume and fluid regulatory hormones were measured in eight HTRs (57+/-6 years old) both before and after treatment with captopril (225 mg/day). Antihypertensive and diuretic agents were discontinued 10 days before. The HTRs were admitted to the Clinical Research Center (CRC), and, after three days of a constant diet containing 87 mEq/day of Na+, PV was measured by using the modified Evans blue dye dilution technique. After approximately four months (16+/-5 weeks), the same HTRs again discontinued all antihypertensive and diuretic agents; they were progressed to a captopril dose of 75 mg three times per day over 14 days, and the CRC protocol was repeated.

RESULTS

Captopril pharmacologically suppressed (p<0.05) supine rest levels of angiotensin II (-65%) and aldosterone (-75%). The reductions in vasopressin and atrial natriuretic peptide levels after captopril did not reach statistical significance. The PV, normalized for body weight (ml/kg), was significantly reduced by 12% when the HTRs received captopril.

CONCLUSIONS

Extracellular fluid volume is expanded (12%) in clinically stable HTRs who become hypertensive. Pharmacologic suppression of the RAA axis with high-dose captopril (225 mg/day) returned HTRs to a normovolemic state. These findings indicate that fluid retention is partly engendered by a failure to reflexively suppress the RAA axis when HTRs become hypervolemic.

Reduction in renal haemodynamics by exaggerated vesicovascular reflex in rats with acute urinary retention

1. We examined the possibility that a vesicovascular reflex is exaggerated by acute urinary retention, and that the increase in renal vascular resistance caused by this reflex may lead to renal dysfunction. We evaluated the vesicovascular responses to normal micturition (NM, transcystometric condition) and acute urinary retention (isovolumetric condition mimicking complete bladder-outlet obstruction (CBOO) and partial urethral ligation mimicking partial bladder-outlet obstruction (PBOO)) in anaesthetized female Wistar rats. 2. Acute urinary retention due to CBOO or PBOO provoked a prolonged or increased intravesical pressure, an enhancement in both bladder pelvic afferent and bladder pelvic efferent nervous activity, and an elevation in mean arterial blood pressure. 3. Single-unit analysis showed that these vesicovascular reflexes were triggered by activation of low-threshold and high-threshold bladder mechanoreceptors, but not by renal uretropelvic mechanoreceptors. 4. Bladder contraction in CBOO and PBOO conditions and graded increases in bladder volume significantly reduced renal blood flow and cortical microvascular blood flow. The acute urinary retention-induced renal vasoconstriction was mediated by the renal nerve. Renal denervation, but not bilateral ureteral resection, abolished the renal vasoconstriction associated with the vesicovascular reflexes. 5. These findings indicate that exaggerated activation of bladder afferents exerts a positive feedback effect to increase sympathetic outflow to the kidney further, thereby contributing to significant renal vasoconstriction via a renal nerve-dependent mechanism.

Neurogenic factors and hypertension in renal disease

Hypertension in chronic renal failure (CRF) is very common and contributes to morbidity and mortality and to the progression of renal disease. The pathogenesis of hypertension in CRF has been attributed mostly to sodium retention and to activation of the renin-angiotensin-aldosterone system. More recently an abundance of evidence has accumulated to support a role for increased sympathetic nervous system (SNS) activity in the genesis of hypertension associated with CRF. Evidence from our laboratory has also demonstrated that the rise in central SNS activity is mitigated by increased local expression of nitric oxide synthase (NOS)-mRNA and nitric oxide (NO) production, and that the upregulation of NO production in the brain is mediated by IL-1beta.

Diuretic and natriuretic action of adrenomedullin administered intracerebroventricularly in conscious rats

Intracerebroventricular administration of rat adrenomedullin (AM) to conscious hydrated or salt-loaded rats, resulted in a significant increase in urinary volume. The diuretic effect of adrenomedullin occurred during the 6-h period of urine collection and was most effective during the 3 and 6 h. Most remarkably, AM given IVT induced a dose-related increase in urinary sodium excretion at all periods of urine collection. In addition, AM induced significant kaliuresis. Our results strongly suggest that AM may play a significant role in the central regulation of fluid and electrolyte homeostasis, and that its diuretic and natriuretic effect may be, at least in part, centrally mediated.

Mechanisms of ascites formation

Ascites is the most common complication of cirrhosis. It is associated with profound changes in the splanchnic and systemic circulation and with renal abnormalities. The development of ascites is related to the existence of severe sinusoidal portal hypertension that causes marked splanchnic arterial vasodilation and a forward increase in the splanchnic production of lymph. Splanchnic arterial vasodilation also produces arterial vascular underfilling, arterial hypotension, compensatory activation of the RAAS, SNS, and AVP, and a continuous sodium and water retention, leading to ascites formation. Now, therefore, the splanchnic arterial circulation, rather than the venous portal system, is believed to be involved in the pathogenesis of ascites formation.

Activation of renal afferent pathways following furosemide treatment. I. Effects Of survival time and renal denervation

Three experiments were performed to determine whether renal afferent pathways were activated by the diuretic drug, furosemide. It was hypothesized that activated neurons of the renal afferent pathway would express the protein product Fos of the c-fos immediate early gene and be identified by immunocytochemical staining for Fos in the cell nucleus. In the first two experiments, rats were injected with either furosemide (5 mg) or vehicle solution (sterile isotonic saline) and sacrificed either 1.75 h (short-survival experiment) or 3.5 h (long-survival experiment) after injection. In both experiments, the furosemide-treated rats had significantly more Fos-positive cell nuclei than vehicle-treated rats in the subfornical organ (SFO), organum vasculosum lamina terminalis (OVLT), supraoptic nuclei (SON), and magnocellular region of the paraventricular nuclei (PVN) - areas previously shown to be activated by hypovolemia or peripheral angiotensin. In the short-survival experiment, the furosemide-treated rats had more Fos-positive cell nuclei in the nucleus of the solitary tract (NTS) and in the dorsal horn of the spinal cord at spinal levels T(11), T(12), and T(13). In contrast, furosemide treatment did not produce more Fos-positive cell nuclei in the NTS and dorsal horn of the spinal cord in the long-survival experiment. These results suggest that the activation of the SFO, OVLT, SON and PVN may be via a different mechanism than that of NTS or spinal cord dorsal horn. Based upon our previous work, we hypothesized that the NTS and spinal cord dorsal horn labeling was due to activation of sympathetic afferents originating in the kidney and labeling in forebrain structures was due to stimulation by angiotensin generated by renal renin release. To test this hypothesis, a third experiment was devised that was identical to the short-survival experiment, except that all rats had bilateral renal denervation surgery 1 week previously. In this experiment, furosemide administration increased the number of Fos-positive cells in the SFO, OVLT, SON and PVN, but not in the caudal thoracic spinal cord or NTS. These results together with the results of first two experiments lend support to our hypothesis that furosemide-induced neuronal activation in the thoracic spinal cord and NTS is due to activation of second- and/or third-order neurons of a renal sympathetic afferent pathway. Furosemide-induced activation in the SFO, OVLT, SON and PVN does not depend on renal innervation. It is hypothesized that activation in these forebrain regions depends on the action of angiotensin II that is generated after furosemide treatment. Our results indicate that both a hormonal pathway and a renal sympathetic afferent pathway conduct information from the kidney to the central nervous system (CNS) after furosemide treatment.

Participation of arterial baroreceptors input and peripheral vasopressin in the suppression of renal sympathetic nerve activity induced by central salt loading in conscious rats

We examined whether renal sympathetic nerve activity (RSNA) is suppressed in response to intracerebroventricular (i.c.v.) administration of hypertonic saline (HS) in conscious rats. RSNA was suppressed by i.c.v. administration of HS (0.3 M, 0.67 M, and 1.0 M, 1 microl/min for 20 min) in a concentration-dependent manner, which was attenuated under pentobarbital anesthesia. To elucidate mechanisms responsible for central HS-induced decrease in RSNA, possible involvement of arterial baroreceptors and peripheral arginine vasopressin (AVP) secreted from the posterior pituitary gland was examined using sinoaortic denervated (SAD) rats and non-peptide vasopressin receptor antagonists. The maximum suppression of RSNA (-81.5 +/- 5.5%) in control rats was significantly attenuated to -32.5 +/- 6.7% in SAD rats and to -55.8 +/- 5.7% in rats pretreated with intravenous vasopressin V1 receptor antagonist, OPC-21268 (5 mg/kg, i.v.). However, in SAD rats, pretreatment with vasopressin V1 receptor antagonist did not further affect the RSNA inhibition induced by central salt loading. The results suggest that the suppression of RSNA during central salt loading is mainly dependent on the arterial baroreceptors input and the 'additive' role of peripheral vasopressin.

Afferent renal inputs to paraventricular nucleus vasopressin and oxytocin neurosecretory neurons

Extracellular single-unit recording experiments were done in pentobarbital sodium-anesthetized rats to investigate the effects of electrical stimulation of afferent renal nerves (ARN) and renal vein (RVO) or artery (RAO) occlusion on the discharge rate of putative arginine vasopressin (AVP) and oxytocin (Oxy) neurons in the paraventricular nucleus of the hypothalamus (PVH). PVH neurons antidromically activated by electrical stimulation of the neurohypophysis were classified as either AVP or Oxy secreting on the basis of their spontaneous discharge patterns and response to activation of arterial baroreceptors. Ninety-eight putative neurosecretory neurons in the PVH were tested for their response to electrical stimulation of ARN: 44 were classified as putative AVP and 54 as putative Oxy neurons. Of the 44 AVP neurons, 52% were excited, 7% were inhibited, and 41% were nonresponsive to ARN stimulation. Of the 54 Oxy neurons, 43% were excited, 6% inhibited, and 51% were not affected by ARN. An additional 45 neurosecretory neurons (29 AVP and 16 Oxy neurons) were tested for their responses to RVO and/or RAO. RVO inhibited 42% of the putative AVP neurons and 13% of the putative Oxy neurons. On the other hand, RAO excited 33% of the AVP and 9% of the Oxy neurons. No AVP or Oxy neurons were found to be excited by RVO or inhibited by RAO. These data indicate that sensory information originating in renal receptors alters the activity of AVP and Oxy neurons in the PVH and suggest that these renal receptors contribute to the hypothalamic control of AVP and Oxy release into the circulation.

Renal nerve stimulation restores tubuloglomerular feedback after acute renal denervation

Renal nerves play an important role in the setting of the sensitivity of the tubuloglomerular feedback (TGF) mechanism. We recently reported a time-dependent resetting of TGF to a lower sensitivity 3-4 h after acute unilateral renal denervation (aDNX). This effect persisted after 1 week, but was then less pronounced. To determine whether normal TGF sensitivity could be restored in aDNX kidneys by low-frequency renal nerve stimulation (RNS), the following experiments were performed. Rats with aDNX were prepared for micropuncture. In one experimental group proximal tubular free flow (Pt) and stop flow pressures (Psf) were measured during RNS at frequencies of 2, 4 and 6 Hz. In another series of experiments the TGF sensitivity was evaluated from the Psf responses at different loop perfusion rates after 20 min of RNS at a frequency of 2 Hz. The maximal drop in Psf (delta Psf) and the tubular flow rate at which half the maximal response in delta Psf was observed (turning point, TP), were recorded. At RNS frequencies of 2, 4 and 6 Hz, Pt decreased from the control level of 14.1 +/- 0.8-13.1 +/- 1.0, 12.4 +/- 1.1 and 11.2 +/- 0.8 mmHg (decrease 21%, P < 0.05), respectively, while at zero perfusion and during RNS at 2 and 4 Hz Psf decreased from 42.5 +/- 1.6 to 38.2 +/- 1.4 and 32.8 +/- 4.3 mmHg (decrease 23%, P < 0.05), respectively. The TGF characteristics were found to be reset from the normal sensitivity with TP of 19.0 +/- 1.1 nL min-1 and delta Psf of 8.7 +/- 0.9 mmHg to TP of 28.3 +/- 2.4 nL min-1 (increase 49%, P < 0.05) and delta Psf of 5.8 +/- 1.2 mmHg (decrease 33%) after aDNX. After 20 min of RNS at 2 Hz TP was normalized and delta Psf was 33% higher. Thus the present findings indicate that the resetting of the TGF sensitivity that occurred 2-3 h after aDNX could be partially restored by 20 min of RNS at a frequency of 2 Hz. These results imply that renal nerves have an important impact on the setting of the sensitivity of the TGF mechanism.

Effect of YM435, a dopamine DA1 receptor agonist, in a canine model of ischemic acute renal failure

1. The effects of (-)-(S)-4-(3,4-dihydroxyphenyl)- 1,2,3,4-tetrahydroisoquinoline-7,8-diol monohydrochloride monohydrate (YM435), a dopamine DA1 receptor agonist, were evaluated in a canine model of ischemic acute renal failure (ARF). 2. ARF was induced by clamping the left renal artery for 1 hr and subsequent reperfusion of the left kidney in anesthetized uninephrectomized dogs. 3. After 1-hr complete renal artery occlusion, an intravenous infusion of either YM435 (0.3 microg/kg/ min) or 0.9% saline (vehicle) was begun and continued for 1 hr. 4. In the vehicle group, renal ischemia markedly decreased glomerular filtration rate, urine flow and urinary sodium excretion. The YM435 group was characterized by significant recoveries in glomerular filtration rate, urine flow, and urinary sodium excretion as compared with the vehicle group. 5. These results indicate that YM435 can facilitate recovery in glomerular filtration rate, urine flow, and urinary sodium excretion in a canine model of ARF induced by ischemia. YM435 may be useful in the preservation of renal function in ischemia-induced ARF.

Neuronal cell bodies in paraventricular nucleus affect renal hemodynamics and excretion via the renal nerves

Several lines of evidence support the existence of an oligosynaptic projection from the paraventricular nucleus of the hypothalamus (PVN) to the kidney in the rat. We sought to provide evidence that this neural pathway is capable of influencing renal function in rats. Bilateral microinjections of bicuculline (Bic; 1 nmol) into the PVN decreased glomerular filtration rate (59%), effective renal plasma flow (71%), urine flow (UV; 57%), and urinary sodium excretion (UNaV; 54%), accompanied by increased mean arterial pressure (17%) and heart rate (17%). These results were not obtained when Bic was injected outside the PVN or when vehicle (0.9% saline) was injected into the PVN. Bilateral renal denervation (5-7 days before the experiments) significantly reduced the renal vasoconstriction, attenuated the antidiuresis, and abolished the antinatriuresis evoked by PVN stimulation. On the other hand, both the antidiuresis and antinatriuresis evoked by PVN stimulation were undiminished after treatment with either of two vasopressin receptor antagonists ([beta-mercapto-beta,beta-cyclopentamethylenepropionyl1,O-Et-Tyr2, Val4,Arg8]vasopressin, a vasopressin V1 receptor antagonist, or [adamantaneacetyl1,O-Et-D-Tyr2,Val4,aminobutyryl6,Arg8, 9]-vasopressin, a V2 receptor antagonist). In renal-denervated rats treated with the same V2 receptor antagonist, PVN stimulation produced highly variable increases in both UV and UNaV, which overall were not statistically different than zero. We conclude that the activation of neurons in PVN evokes 1) renal vasoconstriction accompanied by antinatriuresis, both of which are attributable to the renal nerves, and 2) decreased water excretion, which is mediated by the renal nerves and vasopressin V2 receptors.