scholarly journals Modulation of Plasma Sphingosine-1-Phosphate Levels via Dietary Salt Intervention in Chinese Adults:an Intervention Trial

2020 ◽  
Author(s):  
Qiong Ma ◽  
Chao Chu ◽  
Yan-bo Xue ◽  
Jia-wen Hu ◽  
Wen-ling Zheng ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Mean Arterial Pressure ◽  
Repeated Measures ◽  
Salt Intake ◽  
High Salt ◽  
Intervention Trial ◽  
Dietary Salt ◽  
Salt Diet ◽  
Low Salt ◽  
Sphingosine 1 Phosphate

Abstract Background Sphingosine-1-phosphate (S1P), a pleiotropic bioactive sphingolipid metabolite, is involved in various pathophysiological processes,including blood pressure regulation. Salt is a crucial factor for blood pressure modulation,especially in salt-sensitive individuals who may develop earlier, more severe subclinical target organ damage than salt-resistant individuals.However, the relationships among salt intake, circulating S1P levels, and blood pressure changes are unknown. Thus, we conducted this intervention trial to explore the effect of dietary salt intake on plasma S1P levels and examine the relationship between S1P and blood pressure in Chinese adults.Methods Forty-two participants (aged 18–65 years) were recruited from a rural community in Shaanxi, China. All participants first maintained their normal diet for 3 days, then sequentially ate a low-sodium diet (3.0 g/day NaCl) for 7 days, followed by a high-sodium diet (18.0 g/day NaCl) for 7 days. We assessed their plasma S1P concentrations on the last day of each intervention phase by liquid chromatography–tandem mass spectrometry. We classified the subjects who demonstrated at least a 10% increase in mean arterial pressure upon transitioning from a low-salt to a high-salt diet as salt-sensitive and the others as salt-resistant. Differences in repeated measures were analyzed by repeated-measures analysis of variance.Results Plasma S1P levels decreased significantly from the baseline to low-salt diet period and increased from the low-salt tohigh-salt diet period. We observed this response in both salt-sensitive and salt-resistant individuals. Plasma S1P levels positively correlated with 24-hour urinary sodium excretion, but not 24-hour urinary potassium excretion. In line with plasma S1P level responses to salt intervention, systolic blood pressure and mean arterial pressure decreased from the baseline to low-salt diet period and increased from the low-salt to high-salt period.Systolic blood pressure positively correlated with plasma S1P; the correlation was stronger in salt-sensitive individuals than in salt-resistant individuals.Conclusion Low-salt intervention decreased plasma S1P levels, whereas high-salt intervention reversed this changein Chinese adults. This finding provides evidence that salt moderation may be a high-efficiency, low-cost intervention for regulating circulating S1P levels, with implications for salt-induced blood pressure modulation.Trial registration:NCT02915315.Registered 27 September,2016,http://www.clinicaltrials.gov

scholarly journals Modulation of Plasma Sphingosine-1-phosphate Levels via Dietary Salt Intervention in Chinese Adults: An Intervention Trial

2020 ◽  
Author(s):  
Qiong Ma ◽  
Chao Chu ◽  
Yanbo Xue ◽  
Yu Yan ◽  
Jiawen Hu ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Repeated Measures ◽  
Salt Intake ◽  
High Salt ◽  
Dietary Salt ◽  
Chinese Adults ◽  
Salt Diet ◽  
Low Salt ◽  
Sphingosine 1 Phosphate ◽  
Pressure Modulation

Abstract Background: Salt is a crucial factor for blood pressure modulation, especially in salt-sensitive individuals. Sphingosine-1-phosphate (S1P), a pleiotropic bioactive sphingolipid metabolite participating in blood pressure regulation, has recently been identified as a novel lipid diuretic factor. However, the relationships among salt intake, circulating S1P levels, and blood pressure changes in human beings are unknown. Thus, we conducted this intervention trial to explore the effect of dietary salt intake on plasma S1P levels and to examine the relationship between S1P and blood pressure in Chinese adults.Methods: 42 participants (aged 18–65 years) were recruited from a rural community in Shaanxi, China. All participants first maintained their normal diet for 3 days, then sequentially ate a low-sodium diet (3.0 g/day NaCl) for 7 days, followed by a high-sodium diet (18.0 g/day NaCl) for 7 days. We assessed their plasma S1P concentrations on the last day of each intervention phase by liquid chromatography-tandem mass spectrometry. We classified the subjects who demonstrated at least a 10% increase in mean arterial pressure upon transitioning from a low-salt to a high-salt diet as salt-sensitive and the others as salt-resistant. Differences in repeated measures were analyzed by repeated-measures analysis of variance. Results: Plasma S1P levels decreased significantly from the baseline to low-salt diet period and increased from the low-salt to high-salt diet period. We observed this response in both salt-sensitive and salt-resistant individuals. Plasma S1P levels positively correlated with 24-hour urinary sodium excretion, but not 24-hour urinary potassium excretion. In line with plasma S1P level responses to salt intervention, systolic blood pressure (SBP) and mean arterial pressure (MAP) decreased from the baseline to low-salt diet period and increased from the low-salt to high-salt period. SBP positively correlated with plasma S1P and the correlation was stronger in salt-sensitive individuals than that in salt-resistant individuals. Conclusion: Low-salt dietary intervention decreases plasma S1P levels, whereas high-salt intervention reverses this change and S1P levels positively correlated with SBP in Chinese adults. This provides a high-efficiency and low-cost intervention for plasma S1P levels modulation, with implications for salt-induced blood pressure modulation. Trial registration: NCT02915315. Registered 27 September 2016, http://www.clinicaltrials.gov

scholarly journals Modulation of Plasma Sphingosine-1-Phosphate Levels via Dietary Salt Intervention in Chinese Adults:an Intervention Trial

2020 ◽  
Author(s):  
Qiong Ma ◽  
Chao Chu ◽  
Yan-bo Xue ◽  
Jia-wen Hu ◽  
Wen-ling Zheng ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Repeated Measures ◽  
Salt Intake ◽  
High Salt ◽  
Dietary Salt ◽  
Chinese Adults ◽  
Salt Diet ◽  
Low Salt ◽  
Sphingosine 1 Phosphate ◽  
Pressure Modulation

Abstract Background: Sphingosine-1-phosphate (S1P), a pleiotropic bioactive sphingolipid metabolite, is involved in various pathophysiological processes,including blood pressure regulation. Salt is a crucial factor for blood pressure modulation,especially in salt-sensitive individuals who may develop earlier, more severe subclinical target organ damage than salt-resistant individuals.However, the relationships among salt intake, circulating S1P levels, and blood pressure changes are unknown. Thus, we conducted this intervention trial to explore the effect of dietary salt intake on plasma S1P levels and examine the relationship between S1P and blood pressure in Chinese adults.Methods:Forty-two participants (aged 18–65 years) were recruited from a rural community in Shaanxi, China. All participants first maintained their normal diet for 3 days, then sequentially ate a low-sodium diet (3.0 g/day NaCl) for 7 days, followed by a high-sodium diet (18.0 g/day NaCl) for 7 days. We assessed their plasma S1P concentrations on the last day of each intervention phase by liquid chromatography–tandem mass spectrometry. We classified the subjects who demonstrated at least a 10% increase in mean arterial pressure upon transitioning from a low-salt to a high-salt diet as salt-sensitive and the others as salt-resistant. Differences in repeated measures were analyzed by repeated-measures analysis of variance. Results:Plasma S1P levels decreased significantly from the baseline to low-salt diet period and increased from the low-salt tohigh-salt diet period. We observed this response in both salt-sensitive and salt-resistant individuals. Plasma S1P levels positively correlated with 24-hour urinary sodium excretion, but not 24-hour urinary potassium excretion. In line with plasma S1P level responses to salt intervention, systolic blood pressure and mean arterial pressure decreased from the baseline to low-salt diet period and increased from the low-salt to high-salt period.Systolic blood pressure positively correlated with plasma S1P; the correlation was stronger in salt-sensitive individuals than in salt-resistant individuals. Conclusion:Low-salt intervention decreased plasma S1P levels, whereas high-salt intervention reversed this changein Chinese adults. This finding provides evidence that salt moderation may be a high-efficiency, low-cost intervention for regulating circulating S1P levels, with implications for salt-induced blood pressure modulation. Trial registration: NCT02915315.Registered 27 September，2016,http://www.clinicaltrials.gov

Prolonged NOS inhibition in the brain elevates blood pressure in normotensive rats

1998 ◽  
Vol 275 (2) ◽  
pp. R410-R417 ◽  
Author(s):  
Atsushi Sakima ◽  
Hiroshi Teruya ◽  
Masanobu Yamazato ◽  
Rijiko Matayoshi ◽  
Hiromi Muratani ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Salt Intake ◽  
High Salt ◽  
Salt Loading ◽  
Salt Diet ◽  
Intracerebroventricular Infusion ◽  
Air Jet ◽  
Sd Rats ◽  
Low Salt ◽  
The Brain

Systemic inhibition of nitric oxide synthase (NOS) evokes hypertension, which is enhanced by salt loading, partly via augmented sympathetic activity. We investigated whether inhibition of brain NOS elevates blood pressure (BP) in normotensive rats and, if so, whether the BP elevation is enhanced by salt loading. After a 2-wk low-salt (0.3%) diet, male Sprague-Dawley (SD) rats were divided into four groups. Groups 1 and 2 received a chronic intracerebroventricular infusion of 0.5 mg ⋅ kg−1 ⋅ day−1of N G-monomethyl-l-arginine (l-NMMA), and groups 3 and 4 were given artificial cerebrospinal fluid (aCSF). Groups 1 and 3 were placed on a high-salt (8%) diet, whereas groups 2 and 4 were on a low-salt diet. On day 9or 10, group 1 showed significantly higher mean arterial pressure (MAP) in a conscious unrestrained state (129 ± 3 mmHg vs. 114 ± 3, 113 ± 1, and 108 ± 3 mmHg in groups 2, 3, and 4, respectively, P < 0.05). On a high-salt diet, response of renal sympathetic nerve activity but not of BP to air-jet stress was significantly larger in rats givenl-NMMA than in rats given aCSF (29 ± 4% vs. 19 ± 3%, P < 0.05). When the intracerebroventricular infusions were continued for 3 wk, MAP was significantly higher in rats givenl-NMMA than in rats given aCSF irrespective of salt intake, although the difference was ∼7 mmHg. Thus chronic inhibition of NOS in the brain only slightly elevates BP in SD rats. Salt loading causes a more rapid rise in BP. The mechanisms of the BP elevation and its acceleration by salt loading remain to be elucidated.

Effect of Salt Intake and Potassium Supplementation on Urinary Renalase and Serum Dopamine Levels in Chinese Adults

Cardiology ◽  
2015 ◽  
Vol 130 (4) ◽  
pp. 242-248 ◽  
Author(s):  
Yang Wang ◽  
Dan Wang ◽  
Chao Chu ◽  
Jian-Jun Mu ◽  
Man Wang ◽  
...  
Keyword(s):  
Salt Intake ◽  
High Salt ◽  
Dietary Salt ◽  
High Potassium ◽  
High Salt Diet ◽  
Salt Diet ◽  
Dietary Salt Intake ◽  
Potassium Intake ◽  
Potassium Supplementation ◽  
Low Salt

Objective: The aim of our study was to assess the effects of altered salt and potassium intake on urinary renalase and serum dopamine levels in humans. Methods: Forty-two subjects (28-65 years of age) were selected from a rural community of northern China. All subjects were sequentially maintained on a low-salt diet for 7 days (3.0 g/day of NaCl), a high-salt diet for an additional 7 days (18.0 g/day of NaCl), and a high-salt diet with potassium supplementation for a final 7 days (18.0 g/day of NaCl + 4.5 g/day of KCl). Results: Urinary renalase excretions were significantly higher during the high-salt diet intervention than during the low-salt diet. During high-potassium intake, urinary renalase excretions were not significantly different from the high-salt diet, whereas they were significantly higher than the low-salt levels. Serum dopamine levels exhibited similar trends across the interventions. Additionally, a significant positive relationship was observed between the urine renalase and serum dopamine among the different dietary interventions. Also, 24-hour urinary sodium excretion positively correlated with urine renalase and serum dopamine in the whole population. Conclusions: The present study indicates that dietary salt intake and potassium supplementation increase urinary renalase and serum dopamine levels in Chinese subjects.

Abstract MP22: Dietary Salt Restriction And High Salt Intake Exaggerate Sympathetic Reflexes And Sensitize Central Autonomic Networks: Potential Mechanisms Of The J-shaped Curve

Hypertension ◽  
2021 ◽  
Vol 78 (Suppl_1) ◽  
Author(s):  
Sean D Stocker ◽  
Megan M Wenner ◽  
William B Farquhar
Keyword(s):  
Blood Pressure ◽  
Salt Intake ◽  
Cardiovascular Responses ◽  
Cardiovascular Morbidity ◽  
High Salt ◽  
Dietary Salt ◽  
Salt Restriction ◽  
Salt Diet ◽  
Dietary Salt Intake ◽  
Autonomic Networks

Observational cohort studies suggest that severe salt restriction increases cardiovascular morbidity/mortality, and the relationship between cardiovascular morbidity and dietary salt intake resembles a J-shaped curve. A high salt diet exaggerates sympathetic nerve activity (SNA) and arterial blood pressure (ABP) responses to several cardiovascular reflexes in salt-resistant animals. This study assessed whether salt restriction also exaggerates cardiovascular reflex responses and sensitizes central autonomic networks. To test this hypothesis, male Sprague-Dawley rats were fed low (0.01% NaCl), normal (0.1% NaCl), and high (4.0% NaCl) salt diet for 14-21 days. Baseline mean ABP was not different across groups (low: 104±4, normal: 107±4, high: 107±4mmHg). Activation of sciatic afferents (1ms pulse, 500uA, 5s duration, 2-20Hz) produced significantly greater increases in renal SNA (5Hz; low: 196±12, normal: 136±9, high: 177±8%, n=8, P<0.05) and ABP (5Hz; low: 29±3, normal: 16±1, high: 24±2 mmHg, n=8, P<0.05) of rats fed low and high versus normal NaCl diets. Activation of the aortic depressor nerve (2ms pulse, 500uA, 15s duration, 2-20Hz) produced significantly greater decreases in renal SNA (5Hz; low: -55±9, normal: -34±8, high: -63±13%, n=7-8, P<0.05) and ABP (5Hz; low: -31±3, normal: -15±5, high: -32±5 mmHg, n=7-8, P<0.05) of rats fed low and high versus normal NaCl diets. To test whether dietary salt intake sensitized central sympathetic circuits, microinjection of L-glutamate (0.1-1nmol, 30nL) in the rostral ventrolateral medulla produced significantly greater increases in renal SNA (0.1nmol; low: 212±15, normal: 149±8, high: 183±17%, n=7-8, P<0.05) and ABP (0.1Hz; low: 20±2, normal: 12±2, high: 22±2 mmHg, n=7-8, P<0.05) of rats fed low and high versus normal NaCl diets. Finally, rats fed low or high NaCl versus normal NaCl diets displayed exaggerated cardiovascular responses to cage switch or mild restraint and increased 24-h blood pressure variability. The present findings show that severe salt restriction and excess dietary salt intake exaggerate sympathetic and cardiovascular responses, and may be explained by a parallel change in the sensitivity of central autonomic networks to resemble a J-shaped curve.

Regulation ofP-450 4A activity in the glomerulus of the rat

1999 ◽  
Vol 276 (6) ◽  
pp. R1749-R1757 ◽  
Author(s):  
Osamu Ito ◽  
Richard J. Roman
Keyword(s):  
Arachidonic Acid ◽  
Salt Intake ◽  
High Salt ◽  
Dependent Manner ◽  
Hydroxyeicosatetraenoic Acid ◽  
Dietary Salt ◽  
High Salt Diet ◽  
Salt Diet ◽  
Dietary Salt Intake ◽  
Low Salt

We recently reported that an enzyme of the cytochrome P-450 4A family is expressed in the glomerulus, but there is no evidence that 20-hydroxyeicosatetraenoic acid (20-HETE) can be produced by this tissue. The purpose of present study was to determine whether glomeruli isolated from the kidney of rats can produce 20-HETE and whether the production of this metabolite is regulated by nitric oxide (NO) and dietary salt intake. Isolated glomeruli produced 20-HETE, dihydroxyeicosatrienoic acids, and 12-hydroxyeicosatetraenoic acid (4.13 ± 0.38, 4.20 ± 0.38, and 2.10 ± 0.20 pmol ⋅ min−1⋅ mg protein−1, respectively) when incubated with arachidonic acid (10 μM). The formation of 20-HETE was dependent on the availability of NADPH and the[Formula: see text] of the incubation medium. The formation of 20-HETE was inhibited by NO donors in a concentration-dependent manner. The production of 20-HETE was greater in glomeruli isolated from the kidneys of rats fed a low-salt diet than in kidneys of rats fed a high-salt diet (5.67 ± 0.32 vs. 2.83 ± 0.32 pmol ⋅ min−1⋅ mg protein−1). Immunoblot experiments indicated that the expression of P-450 4A protein in glomeruli from the kidneys of rats fed a low-salt diet was sixfold higher than in kidneys of rats fed a high-salt diet. These results indicate that arachidonic acid is primarily metabolized to 20-HETE and dihydroxyeicosatrienoic acids in glomeruli and that glomerular P-450 activity is modulated by NO and dietary salt intake.

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

1996 ◽  
Vol 271 (1) ◽  
pp. R109-R114 ◽  
Author(s):  
S. W. John ◽  
A. T. Veress ◽  
U. Honrath ◽  
C. K. Chong ◽  
L. Peng ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Blood Volume ◽  
Volume Expansion ◽  
Salt Intake ◽  
High Salt ◽  
High Salt Diet ◽  
Salt Diet ◽  
Blood Volume Expansion ◽  
High Salt Intake ◽  
Low Salt

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.

Effect of naloxone on hypertension in Dahl salt-sensitive rats

1992 ◽  
Vol 262 (1) ◽  
pp. H162-H167 ◽  
Author(s):  
M. D. Johnson ◽  
B. K. Richmond
Keyword(s):  
Blood Pressure ◽  
Salt Intake ◽  
Salt Content ◽  
Chronic Administration ◽  
High Salt ◽  
Acute Administration ◽  
Developmental Phase ◽  
Dietary Salt ◽  
Low Salt ◽  
Blood Pressures

Experiments were conducted to test the hypothesis that chronic administration of an opioid receptor antagonist, naloxone, would affect the outcome of the developmental phase of hypertension in Dahl salt-sensitive (S/JR strain) rats. Accordingly, S/JR rats were maintained on either a low-salt (0.45% NaCl) or a high-salt (7% NaCl) diet for 4 wk. Half of the animals of each dietary group were treated with naloxone (100-130 micrograms/h) by osmotic minipump. Food and water intakes of the high-salt animals were measured for the first 25 days, and blood pressure was measured at the end of the 4 wk via an indwelling femoral arterial catheter. Naloxone treatment slightly but significantly reduced the level of hypertension attained in the high-salt animals (158 +/- 2 mmHg in naloxone-treated animals vs. 168 +/- 3 mmHg in control animals; P less than 0.05) and also attenuated food (and hence salt) and water intakes. Naloxone did not affect the blood pressure of the low-salt animals. To determine whether the slight attenuation of hypertension might be secondary to a reduction of salt intake, a group of control S/JR animals were fed a moderately high-salt diet (2% NaCl), and naloxone-treated S/JR animals were salt-intake matched to this group by daily adjustment of the dietary salt content. Blood pressures after 4 wk of treatment were not different between these two groups. Finally, acute administration of 1 and 30 mg/kg of naloxone failed to lower blood pressure of animals with established hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Abstract MP70: Aldosterone And Inverse Salt Sensitivity Of Blood Pressure

Hypertension ◽  
2021 ◽  
Vol 78 (Suppl_1) ◽  
Author(s):  
Peng Xu ◽  
John J Gildea ◽  
Mahabuba Akhter ◽  
Robert M Carey ◽  
Wei Yue ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Salt Intake ◽  
Salt Sensitivity ◽  
High Salt ◽  
Sodium Reabsorption ◽  
High Salt Diet ◽  
Salt Diet ◽  
High Salt Intake ◽  
Low Salt ◽  
Harmful Effects

Salt sensitivity affects approximately 20% of adults worldwide and has similar mortality and morbidity sequalae as hypertension. Research has focused on the harmful effects of a high salt diet but have not focused on the harmful effects of a low salt diet. Inverse salt sensitive (ISS) individuals require high salt intake in order to maintain a normal blood pressure. Aldosterone increases ENaC and sodium reabsorption via the mineralocorticoid receptor (MR). We previously reported that αENaC was significantly lower in ISS renal tubule cells isolated from urine (uRTC), while these cells showed higher ENaC like activities under trypsin stimulation. We hypothesized that aldosterone may act as a stimulus and play a role in ISS high blood pressure on a low salt diet (LSD). Plasma aldosterone was significantly increased on LSD in all salt study participants, and ISS individuals showed the highest aldosterone level (ISS HS 3.8±0.38, n=26; ISS LS 35±3.38, n=22; SR HS 4.34±0.18, n=180; SR LS 32.62±1.6, n=152; SS HS 4.65±0.35, n=43; SS LS 26.08±2.18, n=38; HS Vs LS, p<0.001, two-way ANOVA). Moreover, both aldosterone and plasma renin activity (PRA) were significantly lower in salt sensitive (SS) individuals on LSD (PRA LS: ISS 6.05±0.87, n=17; SR 5.94±0.36, n=108; SS 4.43±0.57, n=34; p<0.05, one-way ANOVA), indicating LSD was protective to SS individuals. Treatment of uRTCs with 1 μM aldosterone increased MR and αENaC expression in ISS but not in SR (salt resistant) cells (MR: SR VEH 12164±213; SR Aldosterone 12327±128; ISS VEH 12128±40 vs ISS Aldosterone 13506±128, n=3, p<0.001, two-way ANOVA; αENaC: SR VEH 5023±46; SR Aldosterone 4895±55; ISS VEH 4270±21 vs ISS Aldosterone 5013±113, n=3, p<0.001, two-way ANOVA). High salt treatment further decreased MR in ISS but not in SR cells (ISS: 142mM 11066±188 vs 192mM 10425±74; p<0.05, n=3 two-way ANOVA). These results are consistent with the hypothesis that ISS individuals retain excess Na + and exhibit decreased BP when compared to SR or SS individuals under high salt diet, but reabsorb more sodium and exhibit elevated blood pressure under low salt diet. Higher circulating aldosterone and ex-vivo urine derived renal cell aldosterone sensitivity under low salt conditions may be a novel diagnostic test to identify ISS individuals.

Coordinate regulation of renal expression of nitric oxide synthase, renin, and angiotensinogen mRNA by dietary salt

1996 ◽  
Vol 270 (6) ◽  
pp. F1027-F1037 ◽  
Author(s):  
I. Singh ◽  
M. Grams ◽  
W. H. Wang ◽  
T. Yang ◽  
P. Killen ◽  
...  
Keyword(s):  
Renal Cortex ◽  
Salt Intake ◽  
High Salt ◽  
Mrna Levels ◽  
Dietary Salt ◽  
High Salt Diet ◽  
Salt Diet ◽  
Dietary Salt Intake ◽  
Low Salt ◽  
Oxide Synthase

Experiments were performed to examine the effect of changes in dietary salt intake on the neuronal form of the constitutive nitric oxide synthase (ncNOS, type I NOS), renin, and angiotensinogen mRNA expression in the kidney. Three groups of Sprague-Dawley rats were studied as follows: rats maintained on a 3% Na diet plus 0.45% NaCl in the drinking fluid for 7 days (high salt), rats given a single injection of furosemide (2 mg/kg i.p.) and a 0.03% Na diet for 7 days (low salt), and rats on a diet containing 0.2% Na (control). mRNA expression was assessed with reverse transcription-polymerase chain reaction (RT-PCR) methods using cDNA prepared from samples of renal cortex and microdissected tubular segments. ncNOS PCR products were quantified by comparison with a dilution series of a mutant deletion template. Compared with their respective control, ncNOS mRNA levels in renal cortical tissue were elevated in rats on a low-salt diet and reduced in rats on a high-salt diet. Similar changes were seen in the expression of renin and angiotensinogen mRNA. Dietary salt intake did not alter the mRNA levels for ncNOS from the inner medulla or for endothelial constitutive NOS (ecNOS, type III NOS) and inducible NOS (iNOS, type II NOS) in the renal cortex. ncNOS mRNA was found in glomeruli dissected with the macula densa-containing segment (MDCS), but only at marginal levels in glomeruli without MDCS. Furthermore, a low-salt diet stimulated ncNOS mRNA in glomeruli with MDCS by 6.2-fold compared with a high-salt diet. There was no effect of salt diet on ncNOS mRNA in glomeruli without MDCS or in inner medullary collecting ducts. These results suggest that ncNOS expression in macula densa cells is inversely regulated by salt intake, thus following the known response of the renin-angiotensin system to changes in salt balance.

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