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At least 19 recordsLinked to original sources
PubMed2004

Volume natriuresis vs. pressure natriuresis.

Body fluid regulation depends on regulation of renal excretion. This includes a fast vasopressin-mediated water-retaining mechanism, and slower, complex sodium-retaining systems dominated by the renin-angiotensin aldosterone cascade. The sensory mechanisms of sodium control are not identified; effectors may include renal arterial pressure, renal reflexes, extrarenal hormones and other regulatory factors. Since the pioneering work of Guyton more than three decades ago, pressure natriuresis has been in focus. Dissociations between sodium excretion and blood pressure are explained as conditions where regulatory performance exceeds the precision of the measurements. It is inherent to the concept, however, that sudden transition from low to high sodium intake elicits an arterial pressure increase, which is reversed by the pressure natriuresis mechanism. However, such transitions elicit parallel changes in extracellular fluid volume thereby activating volume receptors. Recently we studied the orchestration of sodium homeostasis by chronic and acute sodium loading in normal humans and trained dogs. Small increases in arterial blood pressure are easily generated by acute sodium loading, and dogs appear more sensitive than humans. However, with suitable loading procedures it is possible - also acutely - to augment renal sodium excretion by at least one order of magnitude without any change in arterial pressure whatsoever. Although pressure natriuresis is a powerful mechanism capable of overriding any other controller, it seems possible that it is not operative under normal conditions. Consequently, it is suggested that physiological control of sodium excretion is neurohumoral based on extracellular volume with neural control of renin system activity as an essential component.

Animals↗
PubMed1984

Angiotensin II natriuresis and anti-natriuresis: role of renal artery pressure in anaesthetized dogs.

The aim of this study was to determine the role of changes in renal artery pressure (RAP), renal haemodynamics, and tubular reabsorption in mediating the natriuretic and anti-natriuretic actions of angiotensin II (ANG II). In anaesthetized dogs, endogenous ANG II formation was blocked with SQ-14225 and ANG II was infused intravenously at rates of 5-1215 ng/kg/min while RAP was either servo-controlled at the normal level or permitted to increase. When RAP was servo-controlled to prevent a rise in RAP, ANG II infusion at all rates from 5-1215 ng/kg/min decreased urinary sodium excretion (INaV) and fractional sodium excretion (FENa), while increasing fractional reabsorption of lithium (FRLi), an index of proximal tubule fractional sodium reabsorption (FRDNa). When RAP was permitted to increase, ANG II infusion rates up to 45 ng/kg/min decreased UNaV, and FENam while increasing FRLi and FRDNa greater than However, at 135 ng/kg/min and above UNaV and FENE increased while FRLi and FRDNa decreased when RAP was allowed to rise, even though renal blood flow and filtration fraction were not substantially different from the values observed when RAP was servo-controlled. Filtered sodium load was slightly higher when RAP was permitted to increase during ANG II infusion, compared to the dogs in which RAP was servo-controlled, although the differences were not statistically significant. Thus, even very large doses of ANG II cause anti-natriuresis when RAP is prevented from increasing. The natriuretic effect of high doses of ANG II is caused by increased RAP which decreases fractional sodium reabsorption in proximal and distal tubules and causes slight increase in sodium delivery to the tubules.

Absorption↗
PubMed1992

Dopaminergic modulation of the pressure-natriuresis response in rats.

OBJECTIVE: The present study was carried out to examine the involvement of dopamine in the pressure-natriuresis phenomenon which has been postulated as a major regulator of extracellular fluid volume and thereby arterial pressure. DESIGN: Dopaminergic modulation of the pressure-natriuresis response was studied in the innervated and denervated rat kidney, to allow a distinction between the effects of neural and extraneural dopamine. METHODS: The pressure-natriuresis response was studied in anesthetized Sprague-Dawley rats, in which neural and hormonal influences on the kidney were fixed by denervating the kidney and by intravenous infusion of aldosterone, hydrocortisone, vasopressin and norepinephrine. The innervation to the kidney remained intact in some experiments with the selective dopamine-1 antagonist SCH 23390. Urinary excretion of dopamine during the pressure-natriuresis response was also examined in the innervated and denervated rat kidney. RESULTS: Although infusion of dopamine at a dose of 2 micrograms/kg per min had no effect on the pressure-natriuresis response in rats in which neural and hormonal influences on the kidney were fixed, the slopes of the relations between urine flow, sodium excretion and mean arterial pressure in rats given 10 micrograms/kg per min dopamine were significantly greater than those found in the control rats. Renal plasma flow increased significantly in the dopamine-treated rats whilst glomerular filtration rate did not differ between the control and dopamine-treated rats. The dopamine-induced increase in the slope of pressure-natriuresis relationship and renal plasma flow were completely blocked by 0.5 micrograms/kg per min SCH 23390. However, infusion of SCH 23390 alone at 0.5 micrograms/kg per min did not significantly alter the pressure-natriuresis response in rats with either denervated or innervated kidney. In addition, urinary excretion of dopamine derived from neither neural nor extraneural origins was altered in parallel with variations in mean arterial pressure. CONCLUSION: These results suggest that exogenous administration of dopamine may affect the pressure-natriuresis response by altering the magnitude of arterial pressure-induced changes in tubular sodium reabsorption, via an action of dopamine-1 receptors. However, endogenous dopamine does not appear to be capable of modulating the pressure-natriuresis response.

Animals↗
PubMed1999

Atrial natriuretic peptide and oxytocin induce natriuresis by release of cGMP.

Our hypothesis is that oxytocin (OT) causes natriuresis by activation of renal NO synthase that releases NO followed by cGMP that mediates the natriuresis. To test this hypothesis, an inhibitor of NO synthase, L-nitroarginine methyl ester (NAME), was injected into male rats. Blockade of NO release by NAME had no effect on natriuresis induced by atrial natriuretic peptide (ANP). This natriuresis presumably is caused by cGMP because ANP also activates guanylyl cyclase, which synthesizes cGMP from GTP. The 18-fold increase in sodium (Na+) excretion induced by OT (1 microgram) was accompanied by an increase in urinary cGMP and preceded by 20 min a 20-fold increase in NO3- excretion. NAME almost completely inhibited OT-induced natriuresis and increased NO3- excretion; however, when the dose of OT was increased 10-fold, a dose that markedly increases plasma ANP concentrations, NAME only partly inhibited the natriuresis. We conclude that the natriuretic action of OT is caused by a dual action: generation of NO leading to increased cGMP and at higher doses release of ANP that also releases cGMP. OT-induced natriuresis is caused mainly by decreased tubular Na+ reabsorption mediated by cGMP. In contrast to ANP that releases cGMP in the renal vessels and the tubules, OT acts on its receptors on NOergic cells demonstrated in the macula densa and proximal tubules to release cGMP that closes Na+ channels. Both ANP- and OT-induced kaliuresis also appear to be mediated by cGMP. We conclude that cGMP mediates natriuresis and kaliuresis induced by both ANP and OT.

Animals↗
PubMed1990

Abnormal pressure natriuresis. A cause or a consequence of hypertension?

In all forms of chronic hypertension, the renal-pressure natriuresis mechanism is abnormal because sodium excretion is the same as in normotension despite the increased blood pressure. However, the importance of this resetting of pressure natriuresis as a cause of hypertension is controversial. Theoretically, a resetting of pressure natriuresis could necessitate increased blood pressure to maintain sodium balance or it could occur secondarily to hypertension. Recent studies indicate that, in several models of experimental hypertension (including angiotensin II, aldosterone, adrenocorticotrophic hormone, and norepinephrine hypertension), a primary shift of renal-pressure natriuresis necessitates increased arterial pressure to maintain sodium and water balance. In genetic animal models of hypertension, there also appears to be a resetting of pressure natriuresis before the development of hypertension. Likewise, essential hypertensive patients exhibit abnormal pressure natriuresis, although the precise cause of this defect is not clear. It is likely that multiple renal defects contribute to resetting of pressure natriuresis in essential hypertensive patients. With long-standing hypertension, pathological changes that occur secondary to hypertension must also be considered. By analyzing the characteristics of pressure natriuresis in hypertensive patients and by comparing these curves to those observed in various forms of experimental hypertension of known origin, it is possible to gain insight into the etiology of this disease.

Animals↗
PubMed1995

Dopamine tonically modulates natriuresis in the saline-expanded dogs.

Dopamine (DA) has been shown to be an endogenous catecholamine that promotes natriuresis by activating tubular DA receptors, but its role on natriuresis appears to be equivocal, and the precise mechanisms and signaling pathway of multiple DA's receptor subtypes are not yet clarified. We used low dose of DA intravenously in saline (S) volume-expanded dogs to see the alterations in natriuresis. The results showed that there is a critical dose that induces no enhancement of natriuresis of volume expansion, and that the lower and higher doses of DA produced relatively larger natriuresis. Pretreatment of metoclopramide (MCP) in this settings caused even higher and significant increases of natriuresis. In conclusion, DA seems to determine tonically the level of natriuresis in saline-expanded dogs. DA may exert a dual effect on signal transduction pathways such that one leading to antinatriuresis with high affinity and the other to natriuresis with low affinity signaling cascades for DA. MCP may block the antinatriuretic limb of the signaling pathway.

Animals↗
PubMed2003

Digoxin antibody decreases natriuresis and diuresis in cerebral hemorrhage.

OBJECTIVE: Brain-damaged patients may develop hyponatremia and natriuresis. Clinical evidence of digoxin antibody effect on natriuresis we found in an 11-year-old boy who developed excessive natriuresis and hyponatremia after brain tumor excision. To better understand the mechanisms involved in these clinical disturbances we used an experimental model of rats subjected to intracerebroventricular (ICV) hemorrhage. The participation of serum ouabainlike activity, possibly a natriuretic compound, and the effects of a specific blocker, digoxin antibody, were studied. METHODS: The experimental study was performed in four groups of ICV infused Wistar rats: venous autologous blood infused, blood preceded by digoxin antibody, CSF-like solution, and a control group with no cannulation and no infusions. The following parameters were analyzed before and after ICV infusions: weight, urinary volume, and natriuresis. Ouabainlike activity was measured by proportional serum inhibitory activity on normal rat renal medullary Na-K-ATPase activity. RESULTS: ICV blood but not CSF-like infusion increased urinary volume, natriuresis, and serum ouabainlike activity without weight gain. Natriuresis was positively correlated with serum ouabain activity in ICV blood and blood plus antibody rats. Digoxin antibody restored urinary volume, natriuresis, and ouabainlike activity. CONCLUSIONS: These data provide evidence of ouabainlike activity involvement in natriuresis and urinary volume changes that occur in cerebral hemorrhage. A possible therapeutic action of digoxin antibody is proposed.

Animals↗
PubMed1988

Interleukin-1 induces natriuresis in conscious rats: role of renal prostaglandins.

The onset of infection is associated with increases in renal blood flow and sodium excretion. Our studies provide evidence that the natriuresis is mediated by stimulation of renal prostaglandin production by the cytokine, interleukin-1. A dose-dependent natriuresis and diuresis was elicited in conscious rats with bolus intravenous injections of human recombinant interleukin-1-beta (hrIL-1). Injection of 1.5, 3 and 24 micrograms hrIL-1 increased sodium excretion by 2.4 +/- 0.9 microEq/min, 4.0 +/- 0.8 microEq/min and 5.4 +/- 0.3 microEq/min, respectively. The natriuresis was preceded by a corresponding increase in urinary PGE excretion (80%, 110% and 296%, respectively). The natriuresis elicited by 3 micrograms hrIL-1 was independent of changes in glomerular filtration rate or effective renal plasma flow. IL-1 induced an increase in rectal temperature, (0.6 +/- 0.2 degrees C) and a modest increase in mean arterial pressure (12 +/- 3 mm Hg) within 10 minutes of injection. However, during the period of maximal natriuresis (40 to 100 min), blood pressure and rectal temperature were not significantly different from control. Pretreatment with the cyclooxygenase inhibitor, ibuprofen, significantly attenuated the natriuretic response and indomethacin completely abolished the natriuresis. These results identify IL-1 as a factor which stimulates renal PGE synthesis, and increases sodium excretion, independent of changes in glomerular filtration rate. We propose that IL-1-induced natriuresis may be a component of the overall acute phase response which is actively mounted by the host during infection.

Animals↗
PubMed1996

Dehydration natriuresis in male rats is mediated by oxytocin.

In a previous study in rats we demonstrated the existence of osmoregulatory natriuretic mechanisms distinct from the natriuretic mechanisms that are dependent on volume stimulation. At the same time, we found that oxytocin (OT) receptors were important mediators of natriuresis induced by hypernatremia but not of that induced by isotonic volume expansion. In the present study, the role of OT in dehydration natriuresis was examined in conscious rats. Dehydration for 24 h caused hypernatremia (from 142.1 +/- 0.4 to 147.7 +/- 0.7 mmol/l) and natriuresis accompanied by an approximately 30% spontaneous reduction of food intake. In conjunction with renal retention of water caused by an increase in circulating vasopressin, the natriuresis and probably the reduction of food intake can help to counteract the rise in body fluid osmolality. This natriuresis could not be fully explained by the reduction in plasma aldosterone. Plasma OT concentration had increased from 15.5 +/- 1.2 to 23.8 +/- 2.0 pg/ml at the end of 24 h of dehydration. Intravenous infusion of a selective OT-receptor antagonist [Mpa1,D-Tyr(Et)2, Thr4, Orn8]-OT using osmotic minipumps prevented dehydration natriuresis. It is concluded that in a dehydration-induced hypernatremic state OT is released, inducing natriuresis and facilitating sodium homeostasis. This mechanism is activated by Na osmoreceptors, but is not primarily dependent on the volume status.

Aldosterone↗
PubMed1999

Altered pressure-natriuresis in obese Zucker rats.

It has not been examined whether the pressure-natriuresis response is altered in the insulin-resistant condition. Furthermore, despite an important role of nitric oxide (NO) in modulating pressure-natriuresis, no investigations have been conducted assessing the renal interstitial NO production in insulin resistance. The present study examined whether pressure-natriuresis was altered in insulin-resistant obese Zucker rats (OZ) and assessed the cortical and medullary nitrate/nitrite (NOx) levels with the use of the renal microdialysis technique. In OZ, serum insulin/glucose ratio (23.0+/-4.0x10(-8), n=9) and blood pressure (119+/-3 mm Hg) were greater than those in lean Zucker rats (LZ; 7.0+/-1.9x10(-8) and 103+/-4 mm Hg, n=9). The pressure-natriuresis curve in OZ was shifted to higher renal perfusion pressure (RPP), and the slope was blunted compared with that in LZ (0.073+/-0.015 vs 0.217+/-0.047 microEq/min kidney weight/mm Hg, P<0.05). The basal renal NOx level was reduced in OZ (cortex, 4.032+/-0.331 micromol/L; medulla, 4. 329+/-0.515 micromol/L) compared with that in LZ (cortex, 7.315+/-1. 102 micromol/L; medulla: 7.698+/-0.964 micromol/L). Furthermore, elevating RPP increased the medullary NOx in LZ, but this pressure-induced response was lost in OZ. Four-week treatment with troglitazone, an insulin-sensitizing agent, improved hyperinsulinemia, systemic hypertension, and basal renal NOx levels (cortex, 5.639+/-0.286 micromol/L; medulla, 5.978+/-0.284 micromol/L), and partially ameliorated the pressure-natriuresis curves; the slope of pressure-natriuresis curves and elevated RPP-induced NOx, however, were not corrected. In conclusion, our study suggests that insulin resistance is closely associated with abnormal pressure-natriuresis and hypertension. These deranged renal responses to insulin resistance are most likely attributed to impaired medullary NO production within the medulla.

Animals↗
PubMed1993

Arginine vasopressin-induced natriuresis in the anaesthetized rat: involvement of V1 and V2 receptors.

The present study was undertaken to determine the involvement of the two established vasopressin receptor subtypes (V1 and V2) in arginine vasopressin (AVP)-induced natriuresis and also to determine whether changes in mean arterial pressure (MAP) and/or the renally active hormones atrial natriuretic peptide (ANP), angiotensin II (AII) and aldosterone are a prerequisite for the expression of AVP-induced natriuresis. In Sprague-Dawley rats which were anaesthetized with Inactin (5-ethyl-5-(1'-methylpropyl)-2-thiobarbiturate) and infused with 0.077 mol NaCl/l, infusion of 63 fmol AVP/min was found to be natriuretic whereas an approximately equipotent dose of the specific V2 agonist [deamino-cis1,D-Arg8]-vasopressin (dDAVP) did not induce natriuresis. The specific V1 antagonist [beta-mercapto-beta,beta-cyclopenta-methylene-propionyl1,O-Me- Tyr2,Arg8]-vasopressin when administered prior to infusion of 63 fmol AVP/min did not inhibit AVP-induced natriuresis. AVP-induced natriuresis was not accompanied by changes in MAP or in the plasma concentrations of the renally active hormones ANP, AII or aldosterone. These results suggest that neither the V1 nor the V2 receptors subtypes are involved in AVP-induced natriuresis. In addition, it was found that changes in MAP, plasma ANP, AII or aldosterone concentrations were not a prerequisite for AVP-induced natriuresis.

Aldosterone↗
PubMed1990

[Angiotensin and prostaglandins in the pressure-natriuresis response in rats].

The possible roles of angiotensin and prostaglandins as humoral mediators of the pressure-natriuresis response were studied in anesthetized Sprague-Dawley rats. Neural and other hormonal influences on the kidney were held constant by denervating the kidney and by maintaining fixed high plasma levels of aldosterone, corticosterone, vasopressin and norepinephrine by continuous intravenous infusion. Acute elevation of arterial pressure by tightening the ligature placed around the abdominal aorta below the renal artery produced marked increases in urine flow and sodium excretion with no detectable changes in renal blood flow or glomerular filtration rate. In rats undergoing a saline diuresis, the pressure-natriuresis response was markedly inhibited by intravenous infusion of angiotensin II at a rate of 10 ng/kg/min. Blockade of prostaglandin synthesis with indomethacin also reduced the pressure-natriuresis response in the presence of low-dose (2 ng/kg/min) of angiotensin II, but indomethacin alone did not affect significantly. On the other hand, in rats with hydropenia indomethacin alone significantly inhibited the sodium excretory response to changes in arterial pressure. This indomethacin-induced inhibitory effect on the pressure-natriuresis response was completely attenuated in rats treated with captopril. These results indicate that angiotensin II is a powerful modulator of the pressure-natriuresis response. In addition, it has been suggested that prostaglandins are also capable of modulating the response only in the presence of the renin-angiotensin system. However, neither angiotensin nor prostaglandins appears to be essential for the basic pressure-natriuresis phenomenon since the pressure-natriuresis response can occur during blockade of both the renin-angiotensin and prostaglandin systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗
PubMed1993

Pressure natriuresis following therapy for "one-clip one-kidney" hypertension in man.

Decreased renal tubular reabsorption of sodium in response to increased renal artery perfusion pressure, or "pressure natriuresis", has been demonstrated directly in animal experiments but not in man. In bilateral or single-kidney renovascular hypertension, hypertension has been attributed to reduced pressure natriuresis, and a similar mechanism may operate in chronic renal failure. We report a patient who presented with bilateral renovascular disease and was treated initially by unilateral nephrectomy. At a second operation the remaining ischemic kidney was revascularised. There followed a dramatic natriuresis, sufficient to cause clinical and biochemical features of hypovolemia. However, despite the natriuresis, systemic blood pressure remained elevated in the few weeks following surgery. We attribute the natriuresis to increased renal artery perfusion pressure, and conclude that acute pressure natriuresis sufficient to over-ride neurohormonal antinatriuretic mechanisms does occur in man. However, the failure to normalize blood pressure acutely following the natriuresis suggests that decreased sodium excretion is not the only mechanism which maintains hypertension in this unusual syndrome.

Adult↗
PubMed1998

[Renal urodilatin secretion is associated with diuresis and natriuresis after spontaneous, supraventricular tachycardia].

Patients with paroxysmal supraventricular tachycardia (SVT) may have a polyuria after termination of tachycardia. There is increasing evidence that the renal peptide urodilatin (ANP (95-126))--and not plasma ANP (ANP (99-126))--is the member of the natriuretic peptide family mediating natriuresis and diuresis in man. In patients with SVT we, therefore, analyzed the relationship between diuresis, natriuresis, plasma ANP, urinary urodilatin excretion and renal excretion of cyclic GMP, the second messenger in the ANP system. During and after clinical presentation with spontaneously occurring SVT, two patients with AV-nodal and one patient with atrioventricular reentry tachycardia (heart rate 160 to 200 bpm) were studied. Urinary urodilatin excretion was correlated to diuresis (r = 0.73) and natriuresis (r = 0.93); similarly urinary cyclic GMP excretion was related to diuresis (r = 0.80) and natriuresis (r = 0.87; p < 0.001, respectively). In contrast, there was no significant correlation between plasma ANP concentrations and diuresis (r = 0.28, n.s.) or natriuresis (r = 0.11, n.s.). As an explorative analysis, stepwise multiple linear regression identified urinary urodilatin as the most important contributor to diuresis and natriuresis after SVT. These data on polyuria after spontaneous SVT further support the view that in man urodilatin is the member of the natriuretic peptide family participating in kidney physiology.

Adult↗