Biomedical subjects

H Sonnenberg

Publications and source records attributed to H Sonnenberg.

At least 19 recordsLinked to original sources

PubMed2000

Renal vascular morphology and haemodynamics in Dahl salt-sensitive rats on high salt-low potassium diet: neural and genetic influences.

OBJECTIVE: A dietary combination of high salt and low potassium (HS-LK) exacerbates hypertension in Dahl salt-sensitive (DS) rats and renders Dahl salt-resistant (DR) rats hypertensive. In both strains, the hypertension is accompanied by remodelling of the renal resistance vasculature, and is attenuated by peripheral chemical sympathectomy. In the current study, we sought to determine whether the sympathetic nervous system is causally involved in mediating the renal vascular and haemodynamic alterations associated with HS-LK feeding in Dahl rats. DESIGN: Two groups each of DS and DR rats were maintained on HS-LK diet (8% NaCl, 0.2% KCl) for 8 weeks. One group of DS (n = 9) and DR (n = 8) were treated with 6-hydroxydopamine (6-OHDA) in 0.001 N HCl vehicle to chemically ablate peripheral sympathetic nerve terminals. The two remaining groups (n = 8 each) received equivalent injections of vehicle. METHODS: At the end of the dietary regimen, arterial blood pressure (ABP), glomerular filtration rate (GFR) and renal blood flow (RBF) were measured, and the structure of intra-renal resistance vessels was examined by planar morphometric analysis of coronal sections prepared from perfusion-fixed kidneys. RESULTS: Both 6-OHDA-treated and untreated DS rats presented a greater degree of intra-renal vessel remodelling characterized by reduced lumen diameter in the absence (eutrophic) or presence (hypertrophic) of cross-sectional area expansion, higher renal vascular resistance (RVR) and lower GFR and RBF than DR rats. Chemical sympathectomy increased lumen diameters and reduced vascular wall expansion, resulting in a decrease in RVR and a concomitant increase in RBF and GFR in both strains; however, the effect was more prominent in the DS rats. CONCLUSIONS: We conclude that HS-LK-induced changes in intra-renal vessel structure and renal haemodynamic function in Dahl rats are, at least in part, dependent on the activity of the sympathetic nervous system.

Animals↗

PubMed1999

Chronic regulation of arterial blood pressure in ANP transgenic and knockout mice: role of cardiovascular sympathetic tone.

OBJECTIVE: Atrial natriuretic peptide (ANP) lowers arterial blood pressure (ABP) chronically, in association with vasodilation of the resistance vasculature. The mechanism mediating the chronic relaxant effect of ANP is likely indirectly mediated by interactions with tonic vasoeffector mechanisms, inasmuch as the resistance vasculature is relatively insensitive to direct cGMP-mediated relaxation by ANP. On the basis of evidence that ANP has widespread sympatholytic activity, the current study investigated whether the chronic hypotensive effect of ANP is mediated by attenuation of tonic cardiovascular sympathetic tone. METHODS: Total plasma catecholamine concentration and changes in basal ABP and heart rate (HR) following autonomic ganglionic blockade were measured as indices of underlying sympathetic nerve activity in hypotensive ANP-overexpressing transgenic mice (TTR-ANP), hypertensive ANP knockout mice (-/-) and the genetically-matched wild type (NT and +/+, respectively) control mice. Pressor and chronotropic responses to norepinephrine infusion were measured in ganglion-blocked mice of all genotypes, and norepinephrine receptor binding was assessed in representative tissues of -/- and +/+ mice, in order to determine whether peripheral adrenergic receptor responsiveness is altered by ANP-genotype. RESULTS: Basal ABP was significantly lower in TTR-ANP and higher in -/- compared to their wild-type controls. Basal HR did not differ significantly between mutant and control mice. Autonomic ganglionic blockade reduced ABP and HR in all genotypes, however, the relative decrease in ABP was significantly smaller in TTR-ANP and greater in -/- mice than in their respective controls. Total plasma catecholamine was significantly higher in -/- than in +/+ mice but did not differ significantly between TTR-ANP and NT mice. Norepinephrine infusion during ganglionic blockade elicited quantitatively similar pressor and chronotropic responses in mutant and control mice. Tissue norepinephrine binding did not differ significantly between -/- and +/+ mice. CONCLUSIONS: The present study shows that differences in endogenous ANP activity in mice, resulting in chronic alterations in ABP are accompanied by directional changes in underlying cardiovascular sympathetic tone, and suggests that the chronic vasodilator effect of ANP is, at least partially, dependent on attenuation of vascular sympathetic tone, possibly at a prejunctional site(s).

Analysis of Variance↗

PubMed1999

Chronic hypertension in ANP knockout mice: contribution of peripheral resistance.

Atrial Natriuretic Peptide (ANP) exerts a chronic hypotensive effect which is mediated by a reduction in total peripheral resistance (TPR). Mice with a homozygous disruption of the pro-ANP gene (-/-) fail to synthesize ANP and develop chronic hypertension in comparison to their normotensive wild-type (+/+) siblings. In order to determine whether alterations in basal hemodynamics underlie the hypertension associated with lack of endogenous ANP activity, we used anesthetized mice to measure arterial blood pressure (ABP) and heart rate (HR), as well as cardiac output (CO) by thermodilution technique. -/- (n = 7) and +/+ (n = 10) mice of comparable weight and age were used. Stroke volume (SV) and TPR were derived from CO, HR, and ABP by a standard formula. ABP (mm Hg) was significantly higher in -/- (132+/-4) (P < 0.0001) than in +/+ mice (95+/-2). CO (ml min(-1)), HR(beats min(-1))and SV (microl beat(-1)) did not differ significantly between -/- and +/+ mice (CO -/- = 7.3+/-0.5, +/+ = 8.3+/-0.6; HR -/- = 407+/-22, +/+ = 462+/-21; SV -/- = 17.6+/-1.1, +/+ = 17.6+/-1.7). However, TPR (mm Hg ml(-1) min(-1)) was significantly elevated in -/- mice (18.4+/-0.7) compared to +/+ mice (12.3+/-1) (P = 0.0003). Autonomic ganglion blockade with a mixture of hexamethonium and pentolinium was followed by comparable percent reductions in CO (-/- = 28+/-4, +/+ = 29+/-3), HR (-/- = 9+/-4, +/+ = 16+/-4) and SV(-/- = 21+/-4, +/+ = 15+/-6) in both genotypes. However, the concomitant decrease in ABP (%) in -/- (41+/-2) was significantly greater than in +/+ (23+/-4) mice (P = 0.0009) and was accompanied by a significant reduction in TPR. We conclude that the hypertension associated with lack of endogenous ANP is due to elevated TPR, which is determined by an increase in cardiovascular autonomic tone.

Animals↗

PubMed1999

Salt-sensitive hypertension in ANP knockout mice is prevented by AT1 receptor antagonist losartan.

Mice harboring a functional deletion of the pro-atrial natriuretic peptide (ANP) gene (-/-) develop salt-sensitive hypertension relative to their wild-type (+/+) counterparts after prolonged (>1 wk) maintenance on high-salt (HS, 8% NaCl) diet. We reported recently that the sensitization of arterial blood pressure (ABP) to dietary salt in the -/- mice is associated with failure to downregulate plasma renin activity. To further characterize the role and mechanism of ANG II in the sensitization of ABP to salt in the ANP "knockout" mice, we measured ABP, heart rate (HR), and plasma catecholamine and aldosterone concentrations in -/- and +/+ mice maintained on HS for 4 wk and treated with daily injections of AT1 receptor antagonist DuP-753 (losartan) or distilled water (control). Daily food and water intake and fluid and electrolyte excretion were also measured during the first and last weeks of the dietary regimen. Cumulative urinary excretion of fluid and electrolytes did not differ significantly between genotypes and was not altered by chronic treatment with losartan. Basal ABP and HR were significantly elevated in control -/- mice compared with control +/+ mice. Losartan did not affect ABP or HR in +/+ mice, but reduced ABP and HR in the -/- mice to the levels in the +/+ mice. Total plasma catecholamine was elevated by approximately ten-fold in control -/- mice compared with control +/+ mice. Losartan reduced plasma catecholamine concentration significantly in -/- mice and abrogated the difference in plasma catecholamine between -/- and +/+ mice on HS diet. Plasma aldosterone did not differ significantly between genotypes and was not altered by losartan. We conclude that salt sensitivity of ABP in ANP knockout mice is mediated, at least in part, by a synergistic interaction between ANG II and sympathetic nerve activity.

Angiotensin II↗

PubMed1999

Effect of saline infusion on kidney and collecting duct function in atrial natriuretic peptide (ANP) gene "knockout" mice.

Atrial natriuretic peptide (ANP) is thought to play a role in renal regulation of salt balance by reducing tubular reabsorption of sodium and chloride. Therefore, in the chronic absence of this hormone, a defect of salt excretion should be evident. We used an ANP gene deletion model to test this premise. F2 homozygous mutant mice (-/-) and their wild-type littermates (+/+) were fed an 8% NaCl diet prior to an acute infusion of isotonic saline. Arterial blood pressures, renal excretions of salt and water, as well as collecting duct transport of fluid and electrolytes were measured. Pressures were significantly higher in -/- compared with +/+ mice (139 +/- 4 vs. 101 +/- 2 mmHg; 1 mmHg = 133.3 Pa). There was no difference in glomerular filtration rate (-/- = 0.84 +/- 0.06; +/+ = 0.81 +/- 0.04 mL x min(-1) x g(-1) kidney weight). In the collecting duct, sodium and chloride reabsorptions were significantly higher in the -/- group than in the +/+ group. As a result, natriuresis and chloruresis were relatively reduced (U(Na)V: -/- = 8.6 +/- 1.1; +/+ = 14.0 +/- 1.1; U(Cl)V: -/- = 10.1 +/- 1.4; +/+ = 16.0 +/- 1.1 micromol x min(-1) x g(-1) kidney weight). We conclude that the absence of endogenous ANP activity in mice on a high-salt diet subjected to acute saline infusion causes inappropriately high reabsorption of sodium and chloride in the medullary collecting duct, resulting in a relative defect in renal excretory capacity for salt.

Absorption↗

PubMed1998

Body fluid volume status and the renal response to atrial natriuretic peptide in rats.

The effect of altering the volumes of different body fluid compartments on the renal response to atrial natriuretic peptide (ANP) was studied in anesthetized rats before and during administration of the peptide at 170 ng/min. Four different groups were used. In the first (De), reduction of total body water content was induced by 48 h water deprivation. In the second (De+NaCl), an acute intravenous infusion after the same 48 h dehydration was used to restore the extracellular, but not the intracellular, fluid compartment. In the third (Eu+NaCl), euvolemic rats were infused with isotonic saline at the same rate as in group De+NaCl to expand both intravascular and interstitial components of extracellular fluid. In the fourth group (Eu+BSA) an infusion of hyperoncotic (6%) bovine serum albumin in isotonic saline was used to expand the intravascular volume while contracting the interstitial volume. Excretion of water and salt was predictably reduced in the De group compared with the others. This reduction was associated with increased tubular reabsorption, both upstream from the medullary collecting duct and in the duct itself. Administration of ANP did not significantly affect diuresis and saluresis, or tubular transport. By contrast, there were marked and similar diuretic and natriuretic responses to ANP in groups De+NaCl and Eu+NaCl, associated with transport inhibition primarily in the medullary collecting duct. Surprisingly, the rats infused with hyperoncotic solution (Eu+NaCl) also failed to show marked excretory or duct transport responses to ANP. According to the study design, the two nonresponding groups had, respectively, a decreased or a normal intracellular compartment, and a decreased or increased plasma volume. The common feature of both nonresponding groups was a decreased interstitial fluid compartment, whereas the two responding groups had normal or increased interstitial volume. We suggest, therefore, that a replete interstitial fluid compartment is essential for the renal response to ANP.

Animals↗

PubMed1998

Chronic regulation of arterial blood pressure by ANP: role of endogenous vasoactive endothelial factors.

Atrial natriuretic peptide (ANP) exerts a chronic hypotensive effect due to a decrease in total peripheral resistance (TPR). This study examines if chronic ANP-dependent vasodilation is attributable to differences in the cardiovascular regulatory activity of vascular endothelium (VE), based on evidence that ANP affects synthesis/release and target cardiovascular effects of endothelin-1 (ET-1), C-type natriuretic peptide (CNP), and nitric oxide (NO). To determine if the synthetic activity of resistance vasculature VE is chronically altered by plasma ANP activity, we measured ET-1, CNP, and endothelial constitutive NO synthase (ecNOS) concentration and total NOS enzyme activity in homogenates of kidney, heart, lung, hindquarter skeletal muscle, and brain from hypotensive transgenic mice with elevated plasma ANP, hypertensive knockout mice (-/-) characterized by the absence of ANP, and the corresponding normotensive wild-type (NT, +/+) mice. Tissue distribution and abundance patterns of ET-1, CNP, ecNOS, and NOS enzyme activity were comparable between the different genotypes and did not differ significantly between mutant and control mice. Antagonism of ETA/B receptors in -/- and +/+ mice in vivo with SB-209670 reduced arterial blood pressure (ABP) significantly and comparably in both genotypes (-27 +/- 4 and -25 +/- 2% change for -/- and +/+ mice, respectively) independent of any significant changes in heart rate (HR) (-6 +/- 8 and -4 +/- 4% change for -/- and +/+ mice, respectively). Immunoneutralization of CNP-specific guanylate cyclase-linked receptors (GC-B) with monoclonal antibodies (3G12) increased ABP slightly, but not significantly, by similar relative amounts in both -/- (10 +/- 6% change) and +/+ mice (8 +/- 3% change), without changing HR significantly (4 +/- 1% change for both +/+ and -/- mice). Inhibition of NOS activity (by NG-nitro-L-arginine methyl ester) significantly increased ABP, but the changes were comparable between -/- (53 +/- 5% change) and +/+ mice (50 +/- 6% change) and occurred in the absence of significant changes in HR (-1 +/- 5 and 7 +/- 5% change for -/- and +/+ mice, respectively). We conclude that the differences in ABP associated with chronic variations in endogenous ANP activity are not due to alterations in synthesis or responsiveness of the cardiovascular system to the effects of ET-1, CNP, or NO.

Animals↗

PubMed1998

Salt-sensitive hypertension in ANP knockout mice: potential role of abnormal plasma renin activity.

Atrial natriuretic peptide (ANP), a peptide hormone produced by the heart, exerts a chronic hypotensive effect. Knockout mice with a homozygous disruption of the pro-ANP gene (-/-) are incapable of producing ANP and are hypertensive relative to their wild-type (+/+) siblings. Previous studies showed that arterial blood pressure (ABP) was further increased in conscious -/- mice kept for 2 wk on 2% salt, but not in anesthetized -/- mice after 1 wk on 8% salt. To determine whether inconsistencies in observed effects of salt on ABP of -/- mice are due to duration of increased salt intake and/or the state of consciousness of the animals, we measured ABP from an exteriorized carotid catheter during and after recovery from anesthesia with ketamine-xylazine in adult +/+ and -/- mice kept on low (LS; 0.008% NaCl)- or high (HS; 8% NaCl)-salt diets for 3-4 wk. Conscious ABP +/- SE (mmHg) of +/+ mice did not differ significantly on either diet (HS, 113 +/- 3; LS, 110 +/- 5). However, on HS diet -/- mice had significantly higher ABP (135 +/- 3; P < 0.001) than both -/- (115 +/- 2) and +/+ (110 +/- 5) mice on LS diet. Anesthesia decreased ABP in all groups, but the the genotype- and diet-related differences were preserved. Plasma renin activity (PRA, ng ANG I.ml-1.h-1) in blood collected at termination of experiment was appropriately different on the 2 diets in +/+ mice (HS, 4.9 +/- 1.9; LS, 21 +/- 2.8). However, PRA failed to decrease in -/- mice on HS diet (HS, 18 +/- 2.9; LS, 19 +/- 3.7). Independent of genotype, concentration of endothelin-1 (ET-1, pg/mg protein) and endothelial constitutive NOS (ecNOS, density/100 micrograms protein) was significantly elevated in kidneys of mice fed on HS diet (ET-1 -/-, 31 +/- 4.7 and +/+, 32 +/- 4.1; ecNOS -/-, 160 +/- 19 and +/+, 156 +/- 19) compared with mice fed on LS diet (ET-1 -/-, 19 +/- 1.9 and +/+, 21 +/- 1.8; ecNOS -/-, 109 +/- 13 and +/+, 112 +/- 18). We conclude that, regardless of the state of alertness, -/- mice develop salt-sensitive hypertension after prolonged feeding on HS, in part due to their inability to reduce PRA, whereas the specific renal upregulation of ecNOS and ET-1 in response to HS intake may be an ANP-independent adaptive adjustment aimed at improving kidney function and counteracting the pressor effect of salt.

Analysis of Variance↗

PubMed1998

Hypertension development in Dahl S and R rats on high salt-low potassium diet: calcium, magnesium and sympathetic nervous system.

Dietary combination of high salt with low potassium (HSLK) exacerbates hypertension development in Dahl salt-sensitive (S) rats, and produces a mild degree of hypertension in otherwise salt-resistant (R) rats. Increased blood pressure in both strains is associated with increased urinary excretion of calcium and magnesium. The objective of this study was to determine the effect of blood pressure on body balance of these ions in Dahl rats on HSLK diet. Two groups of S and two groups of R weanlings were all placed on HSLK diet (NaCl=8%, K=0.2%) for eight weeks. One group of each strain was subjected to chemical sympathectomy with 6-hydroxydopamine (6-OHDA) to counteract hypertension development. Urinary norepinephrine was used to determine efficacy of 6-OHDA treatment. Systolic blood pressures of conscious animals were measured daily throughout the study. The last three days on the diet were used to determine total dietary intake and urinary as well as fecal excretion of sodium, calcium and magnesium. At the end of the study, extracellular fluid volume, serum aldosterone and parathyroid hormone were analyzed. Final systolic blood pressures in the 4 groups were as follows: S=235+/-9 mmHg (n=9); R=155+/-3 mmHg (n=8); 6-OHDA S=151+/-6 mm Hg (n=8); 6-OHDA R=117+/-6 mm Hg. Chemical sympathectomy decreased blood pressure in both S and R rats. There was no indication of sodium accumulation in S rats. Associated with reduced parathyroid hormone levels the S strain had significantly less positive balance for calcium than the R strain, primarily due to increased urinary excretion. A less positive balance for magnesium was also observed, due mainly to relatively reduced intestinal absorption of the ion. We conclude that the HSLK diet is associated with inappropriate activation of the sympathetic nervous system and increased arterial pressure in both strains. In addition, since divalent cations may influence blood pressure, we suggest that the observed abnormalities in calcium and magnesium metabolism might independently promote hypertension development in the S strain.

Animals↗

PubMed1997

Effect of sympathetic and angiotensin-aldosterone systems on renal salt conservation in the rat.

During dietary salt deprivation, the sympathetic nervous system and the angiotensin-aldosterone system are stimulated. Both systems are thought to be essential for maximal salt conservation by the kidney. To study their relative contributions, we produced negative salt balance in rats by intraperitoneal injection of furosemide, followed by a low-salt diet (<0.008% NaCl). In a 1-wk metabolic study, the animals were unable to replace the drug-induced salt deficit. Six groups of rats were studied. A control group established baseline function, a second group of 6-hydroxydopamine (OHDA) rats were treated with OHDA to destroy sympathetic efferent nerve terminals, and a third group (losartan) were treated with the angiotensin-receptor antagonist losartan. The influence of catecholamines and aldosterone released from the adrenal gland was studied in a further three groups. Rats were sham-adrenalectomized (sham), subjected to bilateral adrenal enucleation (Enuc) to eliminate catecholamine secretion, or were bilaterally adrenalectomized (Adx), eliminating both catecholamine and corticosteroid release. Dexamethasone was used as glucocorticoid replacement in this group. Steady-state urinary salt excretion was not different between control and OHDA rats. The losartan group showed significantly increased sodium but not chloride excretion. Surprisingly, there were no differences in salt excretion among sham, Enuc, and Adx groups. We conclude that, during a state of chronic salt depletion, renal mechanism(s) independent of neuronally released or systemically circulating catecholamines or of adrenally released aldosterone can ensure maximal salt conservation by the kidney. Although our data show that losartan increased sodium excretion under these conditions, we suggest that the losartan effect can be explained by a reduction of bicarbonate reabsorption, obligating simultaneous excretion of the cation.

Adrenalectomy↗

PubMed1997

Renal resistance to ANF in salt-depleted rats is independent of sympathetic or ANG-aldosterone systems.

Chronic salt depletion was used as a model to study the mechanism of renal resistance to the natriuretic effect of atrial natriuretic factor (ANF). Rats were pretreated with furosemide and placed on a low-salt diet (<0.008% NaCl) for 1 wk before a clearance experiment. Compared with animals on a normal salt diet (0.4% NaCl), the natriuretic reponse to ANF administration was reduced by one order of magnitude and was quantitatively trivial. To assess the influence of the sympathoadrenergic system, different groups of rats were either subjected to acute unilateral renal denervation, to chronic adrenal enucleation to reduce circulating catecholamines, or to pretreatment with 6-hydroxydopamine (OHDA) to destroy sympathetic postganglionic nerve endings. None of these treatments was able to fully or even partially restore ANF natriuresis. To determine whether an effect of angiotensin on the kidney prevented the response, the specific receptor antagonist losartan (DuP-753) was administered during the week prior to the experiment. This treatment also did not influence ANF resistance. Similarly, bilateral adrenalectomy 2 wk before the experiment did not affect the renal ANF resistance in salt-depleted rats. The depressed excretory response could not be explained on the basis of reduced renal perfusion pressure or glomerular filtration rate. We conclude that undetermined compensatory mechanism(s) ensures renal salt conservation in this model in the face of even supraphysiological levels of ANF.

Adrenalectomy↗

PubMed1997

Minimum urine flow rate during water deprivation: importance of the nonurea versus total osmolality in the inner medulla.

Antidiuretic hormone leads to an increase in the permeability for water and urea in the inner medullary collecting duct. Hence, urea may not be an "effective" osmole in the inner medulla during maximal renal water conservation. Accordingly, the purpose of this study was to evaluate whether differences in the rate of urea excretion would influence maximum renal water conservation in humans. In water-deprived rats, the concentration of urea and total osmolality were somewhat higher in the urine exiting the inner medullary collecting duct than in interstitial fluid obtained from the entire papillary tip. Nevertheless, the "nonurea" (total osmolality minus urea in millimolar terms) osmolality was virtually identical in both locations. Chronically fasted human subjects that were water-deprived for 16 h had a lower rate of urea excretion (71 +/- 7 versus 225 +/- 14 mumol/min) and a somewhat lower urine osmolality (745 +/- 53 versus 918 +/- 20 mosmol/kg H2O). Nevertheless, they had identical urine flow rates (0.5 +/- 0.01 and 0.5 +/- 0.02 ml/min, respectively), and their nonurea osmolality also was similar (587 +/- 25 and 475 +/- 14 mosmol/kg H2O, respectively) to the water-deprived normal subjects. The composition of their urine differed in that the principal nonurea osmoles became NH4+ and beta-hydroxybutyrate rather than Na and C1. During water deprivation in normal subjects, the ingestion of urea caused a twofold rise in urine flow rate, a fall in the nonurea osmolality, and a rise in the rate of excretion of nonurea osmoles. The nonurea osmolality of the urine, and presumably the medullary interstitial fluid as well, was inversely related to the urea excretion rate. In chronic fasting, the nature, but not the quantity, of nonurea osmoles changed. The similar minimum urine volume was predictable from an analysis based on nonurea osmole considerations.

Administration, Oral↗

PubMed1996

Effect of nitric oxide inhibition on secretion of atrial natriuretic factor in isolated rat heart.

In addition to stretch, some hormones and neurotransmitters influence atrial natriuretic factor (ANF) secretion from the mammalian heart. In the present study, we investigated the effect of specific inhibition of nitric oxide/endothelium-derived relaxing factor (NO/ EDRF) on release of ANF from the isolated spontaneously beating heart during basal conditions and in response to arginine vasopressin (AVP; 3 x 10(-8) M), acetylcholine (ACh; 10(-6) M), and angiotensin II (ANG II; 4 x 10(-7) M) to determine whether NO is involved as a mediator of basal and hormone-modulated secretion of ANF. Basal secretion from control hearts remained stable for the duration of the experiment. Intracoronary perfusion of the heart with AVP, ACh, and ANG II reduced ANF secretion significantly by 58 +/- 4, 51 +/- 6, and 26 +/- 8%, respectively, independently of concomitant changes in coronary flow and heart rate. The NO donor sodium nitroprusside (SNP, 10(-4) M) inhibited ANF secretion comparably to AVP and ACh. The effect of SNP was not affected by inhibition of NO synthase activity with NG-nitro-L-arginine methyl ester (L-NAME; 3 x 10(-5) M). Similarly, L-arginine, (3 x 10(-4) M) but not its stereoisomer D-arginine (3 x 10(-4) M), significantly reduced ANF secretion. Subsequent perfusion with AVP singly or in combination with L-arginine or D-arginine did not affect ANF secretion further. The inhibitor of NO synthase NG-monomethyl-L-arginine (L-NMMA, 3 x 10(-5) M) did not affect basal secretion, but prevented the inhibitory effect of AVP and ACh. The effect of ANG II was not changed by L-NMMA. These results indicate that AVP and ACh inhibit ANF secretion in the isolated heart indirectly by stimulating NO/EDRF and suggest a novel function of NO/EDRF as a negative modulator of ANF secretion.

Acetylcholine↗

PubMed1996

Blood pressure and fluid-electrolyte balance in mice with reduced or absent ANP.

Atrial natriuretic peptide (ANP)-gene knockout mice of three genotypes (+/+, +/-, and -/-) were maintained on a low-salt diet (0.008% NaCl). They were then fed either the same low-salt diet or a high-salt diet (8% NaCl) for 1 wk. No differences were found among genotypes in daily food and water intakes or in urinary volume and electrolyte excretions. Arterial blood pressures measured in anesthetized animals at the end of the dietary regimen were significantly and similarly increased in -/- compared with +/+ mice on each diet. Renal excretion of fluid and electrolytes was measured in anesthetized mice before and after acute blood volume expansion. No genotype differences were observed before volume expansion. After volume expansion the wild-type (+/+) mice had much greater saluretic responses than either the heterozygous (+/-) or the homozygous mutant (-/-) animals on the low-salt diet but not on the high-salt diet. We conclude that ANP lowers blood pressure in the absence of detected changes in renal function; ANP is not essential for normal salt balance, even on high-salt intake; and ANP is essential for the natriuretic response to acute blood volume expansion on a low-salt but not high-salt intake.

Animals↗

PubMed1996

Urea recycling: an aid to the excretion of potassium during antidiuresis.

Urea absorption in the inner medullary collecting duct provides a mechanism to elevate the concentration of urea in the papillary interstitial fluid and thereby permit the excretion of urea with as little water as possible. Urea reabsorption may have another important effect - to aid in the excretion of potassium (K). K excretion depends on two processes: first, factors such as aldosterone which cause the concentration of K in the luminal fluid of the cortical distal nephron to be high and, second, factors which augment the flow rate through those nephron segments. Since, the osmolality of the luminal fluid in the cortical collecting duct (CCD) and plasma are equal when antidiuretic hormone acts, the flow rate in the CCD is dependent on solute delivery. Urea is a major solute in the lumen of the CCD and thereby plays an important role in maintaining the CCD flow rate. Since urea and K are often found in the same foods, having urea help the excretion of K is potentially advantageous. If the excretion of urea was low, the flow rate in the terminal CCD would decline. In this circumstance, the luminal K concentration would have to rise in proportion to the fall in flow rate or there would be a diminished rate of excretion of K and, possibly, hyperkalemia.

Animals↗

PubMed1996

Renal vascular morphology in male Dahl rats on high-salt diet: effect of potassium.

Inbred Dahl salt-sensitive (S) and sal-resistant (R) rats were fed with either high (4% K; HK) or low (0.2% K; LK) potassium diets (both contained 8% salt, 2.5% calcium, 0.8% magnesium, and 2.0% PO4) for 4 wk. During the last week, systolic blood pressure was measured in conscious animals. External diameter of renal vessels (ED) was used to divide renal vessels into four subgroups: less than 25 microns; greater than 25 microns but less than 55 microns; greater than 55 microns but less than 150 microns; and greater than 150 microns. Luminal diameter (LD), cross-sectional wall area (WAC) and wall-tolumen ratio (W/L) were measured or calculated. Glomerular volume (VG) was measured. Data showed that blood pressures of S rats were significantly higher than those of R rats on both diets. Reduced dietary potassium was associated with increased blood pressure in both strains. Changes in renal vessels were characterized by bigger lumen and greater wall area in S rats, compared with R rats, especially in the smallest vessels. Low potassium intake was associated with reduced lumen diameter and enlarged W/L ratio with or without changing WAC in both strains. VG showed no significant differences between strains or between diets. It was concluded that in addition to the genetically determined differences in renal vascular structure between S and R rats, dietary potassium depletion may engender further renal injury, exacerbating hypertension.

Animals↗

PubMed1995

Requirement for prostaglandin synthesis in secretion of atrial natriuretic factor from isolated rat heart.

Release of atrial natriuretic factor (ANF) from the heart is primarily affected by myocyte stretch. In addition, ANF release can be modulated by a variety of hormones and neurotransmitters, but the mechanisms involved in such modulation are not completely understood. In the present study, we investigated the effect of inhibition of cyclooxygenase activity on release of ANF from the isolated, spontaneously beating rat heart: (1) during basal conditions; and (2) in response to arginine vasopressin (AVP), acetylcholine (ACh) and angiotensin II (ANG II), in order to determine if cardiac prostaglandin synthesis is involved in modulation of basal and hormone-mediated ANF secretion. Basal secretion in the time controls remained stable for the duration of the experiment. AVP, ACh and ANG II reduced basal secretion significantly by 58 +/- 4%, 51 +/- 6% and 26 +/- 8%, respectively, independently of concomitant changes in coronary flow and heart rate. Inhibition of cyclooxygenase with indomethacin (1 x 10(-5) M) decreased basal ANF release by 38 +/- 6%, indicating that basal secretion requires prostaglandin production. The effects of AVP, ACh and ANG II were maintained during perfusion with indomethacin, suggesting a common mechanism of action which operates via inhibition of cyclooxygenase. Based on our previous findings that the effects of indomethacin, AVP and ACh are overcome by inhibition of NO/EDRF synthesis, we suggest a common mechanism of action by means of which NO/EDRF mediates the effects of these agents by inhibiting cyclooxygenase activity.

Acetylcholine↗

PubMed1995

Blood pressure and fluid-electrolyte balance in ANF-transgenic mice on high- and low-salt diets.

Transgenic mice overexpressing an atrial natriuretic factor (ANF) fusion gene (TTR-ANF) and their nontransgenic siblings were placed on a high- (8%) or low (< 0.008%)-salt diet for 14 days to determine whether the lifelong elevation of ANF in the transgenic animals compromised their ability to maintain fluid-electrolyte balance. Steady-state dietary intake and urinary output of sodium and chloride were not statistically different between TTR-ANF and control groups on either diet. By contrast, water intake and urine volume were markedly elevated in the TTR-ANF group on either diet. Arterial blood pressure, measured in anesthetized mice at the end of the dietary regimen, was significantly and similarly reduced in the TTR-ANF compared with control groups on either diet, although high salt intake was associated with increased pressure in both groups. Renal excretion of fluid and electrolytes was studied in the anesthetized mice before and after acute blood volume expansion. Although the absolute increase in fluid and electrolyte excretion was much greater on the high- than on the low-salt diet in both groups, TTR-ANF mice had an exaggerated response relative to controls on either diet. On the basis of these results, we conclude the following. 1) When they are stimulated, renal salt-conserving mechanisms are sufficiently powerful to overcome the expected natriuretic effects of chronic elevation of plasma ANF; however, the natriuretic potential of ANF can be expressed in the short term when the counterregulatory mechanisms are inactivated. 2) ANF exerts a chronic hypotensive effect that is independent of changes in renal salt excretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗