Excess maternal salt intake produces sex-specific hypertension in offspring: putative roles for kidney and gastrointestinal sodium handling

Hypertension is common and contributes, via cardiovascular disease, towards a large proportion of adult deaths in the Western World. High salt intake leads to high blood pressure, even when occurring prior to birth – a mechanism purported to reside in altered kidney development and later function. Using a combination of in vitro and in vivo approaches we tested whether increased maternal salt intake influences fetal kidney development to render the adult individual more susceptible to salt retention and hypertension. We found that salt-loaded pregnant rat dams were hypernatraemic at day 20 gestation (147±5 vs. 128±5 mmoles/L). Increased extracellular salt impeded murine kidney development in vitro, but had little effect in vivo. Kidneys of the adult offspring had few structural or functional abnormalities, but male and female offspring were hypernatraemic (166±4 vs. 149±2 mmoles/L), with a marked increase in plasma corticosterone (e.g. male offspring; 11.9 [9.3–14.8] vs. 2.8 [2.0–8.3] nmol/L median [IQR]). Furthermore, adult male, but not female, offspring had higher mean arterial blood pressure (effect size, +16 [9–21] mm Hg; mean [95% C.I.]. With no clear indication that the kidneys of salt-exposed offspring retained more sodium per se, we conducted a preliminary investigation of their gastrointestinal electrolyte handling and found increased expression of proximal colon solute carrier family 9 (sodium/hydrogen exchanger), member 3 (SLC9A3) together with altered faecal characteristics and electrolyte handling, relative to control offspring. On the basis of these data we suggest that excess salt exposure, via maternal diet, at a vulnerable period of brain and gut development in the rat neonate lays the foundation for sustained increases in blood pressure later in life. Hence, our evidence further supports the argument that excess dietary salt should be avoided per se, particularly in the range of foods consumed by physiologically immature young.

[Impaired gustatory sensitivity of the tongue to table salt as a risk factor of arterial hypertension]

The study included 630 patients with verified diagnosis of arterial hypertension (AH) in whom 24 hr AP monitoring was performed, threshold gustatory sensitivity of the tongue to table salt (TGS) measured, and habit to add salt to the cooked food evaluated. Measurement of Na in daily urine of 442 patients was followed by estimation of salt consumption. The results were compared with those obtained in 100 patients with newly diagnosed AH. The control group comprised 288 subjects. TGS in AH patients was significantly higher than in controls and directly related to clinical features of the disease, high AP values, age, smoking habits, hypercholesterolemia, abdominal-type obesity, and hereditary predisposition. TGS positively correlated with daily urinary excretion of NaCl (r = 0.4-0.7; p < 0.05-0.01). High TGS decreased under effect of hypotensive therapy.

Collecting duct-specific knockout of the endothelin B receptor causes hypertension and sodium retention

Collecting duct (CD)-derived endothelin-1 (ET-1) inhibits renal Na reabsorption and its deficiency increases blood pressure (BP). The role of CD endothelin B (ETB) receptors in mediating these effects is unknown. CD-specific knockout of the ETB receptor was achieved using an aquaporin-2 promoter-Cre recombinase transgene and the loxP-flanked ETB receptor gene (CD ETB KO). Systolic BP in mice with CD-specific knockout of the ETB receptor, ETA receptor (CD ETA KO) and ET-1 (CD ET-1 KO), and their respective controls were compared during normal- and high-salt diet. On a normal-sodium diet, CD ETB KO mice had elevated BP, which increased further during high salt feeding. However, the degree of hypertension in CD ETB KO mice and the further increase in BP during salt feeding were lower than that of CD ET-1 KO mice, whereas CD ETA KO mice were normotensive. CD ETB KO mice had impaired sodium excretion following acute sodium loading. Aldosterone and plasma renin activity were decreased in CD ETB KO mice on normal- and high-sodium diets, while plasma and urinary ET-1 levels did not differ from controls. In conclusion, the CD ETB receptor partially mediates the antihypertensive and natriuretic effects of ET-1. CD ETA and ETB receptors do not fully account for the antihypertensive and natriuretic effects of CD-derived ET-1, suggesting paracrine effects of this peptide.

Fluoride concentration in saliva after consumption of a dinner meal prepared with fluoridated salt

The aim was to determine the fluoride concentration in saliva after intake of a dinner meal prepared with fluoridated salt. The investigation had a randomized cross-over design, and 10 healthy adolescents with natural fluoride content (1.06 ppm) in their drinking water participated after informed consent. After a run-in week, the subjects were served a standardized dinner of spaghetti with minced meat sauce prepared with either fluoridated salt (test arm) or non-fluoridated salt (control arm). The fluoride concentration of the test salt was 250 ppm. Samples of stimulated whole saliva was collected at baseline, directly after eating (0 min) and then after 10, 30 and 180 min. After a 1-week wash-out period, the experimental procedure was repeated with the opposite salt. Fluoride concentration in saliva was measured with a fluoride-specific electrode and the post-ingestion levels were compared with baseline using repeated-measures ANOVA. The mean baseline concentrations were 10.9 and 8.0 microg/l in the test and control arms, respectively. Immediately after the intake, the mean fluoride values increased significantly to 81.6 microg/l in the test arm and to 31.5 microg/l in the control arm (p<0.05). The fluoride levels remained elevated (p<0.05) for 30 min after ingestion of the test meal but not following the control meal. In conclusion, consumption of a dinner meal prepared with fluoridated salt increased the salivary fluoride levels for about 30 min.

Patients with severe bowel malabsorption do not have changes in iodine status

OBJECTIVE

We evaluated the influence of intestinal malabsorption on iodine status in patients who had short gut syndrome and received total parenteral nutrition (group I) compared with control subjects who had eutrophia (group II) and patients who had other illnesses but normal digestive tracts (group III).

METHODS

Twenty-seven subjects were studied. Iodine intake was determined by the measurement of iodine in ingested food and in parenteral nutrition solutions. Urinary iodine excretion was measured by the Sandell-Kalthoff reaction. Urinary creatinine, anthropometric, and thyroid hormone functions were also determined.

RESULTS

Daily iodine intakes were 658 +/- 125 (mean +/- standard deviation), 573 +/- 204, and 629 +/- 208 microg for groups I, II, and III, respectively. Daily urinary iodine excretion levels were 399 +/- 308, 439 +/- 192, and 370 +/- 268 microg and ratios of urinary iodine (micrograms) to creatinine (grams) were 614 +/- 349, 354 +/- 142, and 483 +/- 292, respectively. There were no statistically significant differences across groups.

CONCLUSION

In Brazil the iodine provided by food, including iodized salt, has been sufficient to maintain iodine status in patients with short gut syndrome.

In vivo stimulation of apical P2 receptors in collecting ducts: evidence for inhibition of sodium reabsorption

In vitro evidence suggests that intraluminal nucleotides, acting on apical P2 receptors, may influence amiloride-sensitive sodium reabsorption in collecting ducts. The present study has assessed this possibility directly in anesthetized rats, by determining the urinary recovery of 22Na relative to that of [14C]inulin (Na/inulin recovery ratio) during in vivo microperfusion of late distal tubules with artificial tubular fluid containing various P2 agonists (all at 1 mM). In animals maintained on a control diet, in which amiloride-sensitive 22Na reabsorption was modest, the poorly hydrolysable, broad-spectrum P2 agonist ATPgammaS had no significant effect on the Na/inulin recovery ratio. In contrast, in rats maintained on a low-sodium diet, in which amiloride-sensitive 22Na reabsorption was considerably enhanced, ATPgammaS caused a significant increase in the Na/inulin recovery ratio (control: 14 +/- 3%; ATPgammaS: 28 +/- 4%; n = 32 pairs; P < 0.001, paired t-test). No change in the Na/inulin recovery ratio was seen in time controls (13 +/- 3 vs. 14 +/- 4%; n = 15 pairs). In subsequent experiments in rats maintained on a low-sodium diet, we used more selective agonists in an attempt to identify the receptor subtype responsible for the effect of ATPgammaS. The P2Y1 agonist 2meSADP, the P2Y2/4 agonists Ap4A and Cp4U, and the P2X agonist BzATP were all without significant effect on the Na/inulin recovery ratio. These findings constitute the first in vivo evidence for a functional role for apical P2 receptors in collecting ducts, but the identity of the receptor subtype(s) involved remains elusive.

Dual fortification of salt with iodine and micronized ferric pyrophosphate: a randomized, double-blind, controlled trial

BACKGROUND

In many developing countries, children are at high risk for both goiter and anemia. In areas of subsistence farming in rural Africa, salt is one of the few regularly purchased food items and could be a good fortification vehicle for iodine and iron, provided that a stable yet bioavailable iron fortificant is used.

OBJECTIVE

We tested the efficacy of salt dual-fortified with iodine and micronized ferric pyrophosphate for reducing the prevalence of iodine and iron deficiencies in children.

DESIGN

In rural northern Morocco, we fortified local salt with 25 microg I (as potassium iodate)/g salt and 2 mg Fe (as micronized ferric pyrophosphate; mean particle size = 2.5 microm)/g salt. After storage and acceptability trials, we compared the efficacy of the dual-fortified salt (DFS) with that of iodized salt in a 10-mo, randomized, double-blind trial in iodine-deficient 6-15-y-old children (n = 158) with a high prevalence of anemia.

RESULTS

After storage for 6 mo, there were no significant differences in iodine content or color lightness between the DFS and iodized salt. During the efficacy trial, the DFS provided approximately 18 mg Fe/d; iron absorption was estimated to be approximately 2%. After 10 mo of treatment in the DFS group, mean hemoglobin increased by 16 g/L (P < 0.01), iron status and body iron stores increased significantly (P < 0.01), and the prevalence of iron deficiency anemia decreased from 30% at baseline to 5% (P < 0.001). In both groups, urinary iodine (P < 0.001) and thyroid volume (P < 0.01) improved significantly from baseline.

CONCLUSION

A DFS containing iodine and micronized ferric pyrophosphate can be an effective fortification strategy in rural Africa.

Urinary Potassium Excretion and Sodium Sensitivity in Blacks

Based on racial differences in urinary potassium excretion and responses to diuretics, we present a model suggesting that a major cause of sodium sensitivity in blacks is an augmented activity of the Na-K-2Cl cotransport in the thick ascending limb of Henle's loop. This would result in an increased ability to conserve not only sodium but also water, and an upward and rightward shift in the operating point of tubuloglomerular feedback, which may cause an increase in the glomerular capillary hydraulic pressure and predilection to glomerular injury with and without hypertension. In this sense, the biological implication of sodium sensitivity in blacks and in humans in general has ramifications above and beyond salt-evoked increase in blood pressure.

Elevated BSC-1 and ROMK expression in Dahl salt-sensitive rat kidneys

This study compared the expression of enzymes and transport and channel proteins involved in the regulation of sodium reabsorption in the kidney of Dahl salt-sensitive (DS) and salt-resistant Brown-Norway (BN) and consomic rats (SS.BN13), in which chromosome 13 from the BN rat has been introgressed into the DS genetic background. The expression of the Na+/K+/2Cl- (BSC-1) cotransporter, Na+/H+ exchanger (NHE3), and Na+-K+-ATPase proteins were similar in the renal cortex of DS, BN, and SS.BN13 rats fed either a low-salt (0.1% NaCl) or a high-salt (8% NaCl) diet. The expression of the BSC-1 and the renal outer medullary K+ channel (ROMK) were higher, whereas the expression of the cytochrome P4504A proteins responsible for the formation of 20-hydroxyeicosatetraenoic (20-HETE) was lower in the outer medulla of the kidney of DS than in BN or SS.BN13 rats fed either a low-salt or a high-salt diet. In addition, the renal formation and excretion of 20-HETE was lower in DS than in BN and SS.BN13 rats. These results suggest that overexpression of ROMK and BSC-1 in the thick ascending limb combined with a deficiency in renal formation of 20-HETE may predispose Dahl S rats fed a high-salt diet to Na+ retention and hypertension.

GAMMA.-Tocopherol Enhances Sodium Excretion as a Natriuretic Hormone Precursor

Endogenous natriuretic factors are believed to be responsible for extracellular fluid homeostasis in mammals. A new endogenous natriuretic factor, Loma Linda University-alpha (LLU-alpha) has recently been proven to be a 2,7,8-trimethyl-2-(2'-carboxyethyl)-6-hydroxychroman (gamma-CEHC), which is a metabolite of gamma-tocopherol (gamma-Toc). The purpose of this study was to investigate whether gamma-Toc could accelerate sodium excretion into rat urine as a natriuretic hormone precursor. Male SD strain rats were divided into two groups; one was a control diet group, while the other was a high NaCl group (50 g/kg diet). Next, the two groups were each subdivided into two groups consisting of a placebo group and a gamma-Toc group. After the oral administration of one experimental dose of 20 mg gamma-Toc or placebo, rat urine was collected at 6 h intervals for 24 h, and then the urine volume, sodium and potassium and gamma-CEHC content were determined. gamma-Toc increased in the urine volume of the high-NaCl intake group. The sodium excretion in the high-NaCl group given gamma-Toc was 8.29+/-2.20 g, while in the control group given gamma-Toc it was 6.24+/-1.49 g from 12-18 h. In contrast, the potassium excretion in the rat urine did not change in any of the groups. Our findings suggested that gamma-Toc accelerates the degree of sodium excretion in rats with a high sodium intake.

Membrane ion transport in erythrocytes of salt hypertensive Dahl rats and their F2 hybrids: the importance of cholesterol

The possible association of salt hypertension and altered lipid metabolism with abnormalities of particular systems transporting sodium and potassium has been studied in erythrocytes of Dahl rats and their F2 hybrids fed a high-salt diet since weaning. Our attention was paid to the Na(+)-K+ pump, Na(+)-K+ cotransport and especially to passive membrane permeability for Na+ and Rb+ (Na+ and Rb+ leak), because the Na+ leak was found to be dependent on the genotype, age and salt intake of Dahl rats, whereas the Rb+ leak was suggested to be a potential marker of salt sensitivity in Dahl and Sabra rats. Young male Dahl salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) rats kept on a low-salt (0.3% NaCl) or high-salt diet (8% NaCl) were used for the progenitor study. The subsequent genetic study was based on 135 young male SS/Jr x SR/Jr F2 hybrids fed a high-salt diet since weaning. Ouabain (5 mmol/l) and bumetanide (10 micromol/l) were used to distinguish the contribution of the Na(+)-K+ pump, Na(+)-K+ cotransport and passive membrane permeability to measured net Na+ fluxes and unidirectional Rb+ (K+) movements. Compared to normotensive SR/Jr animals, salt-loaded SS/Jr rats had higher blood pressure (BP), elevated erythrocyte Na+ content, and increased Na+ and Rb+ leaks together with enhanced Na+ and Rb+ transport mediated by the Na(+)-K+ pump and Na(+)-K+ cotransport system. Salt hypertensive Dahl rats were also characterized by elevated plasma levels of total cholesterol and triglycerides, which were positively associated with BP of F2 hybrids (r=0.27 and 0.24, p< 0.01). In F2 hybrids, mean arterial pressure correlated significantly with erythrocyte Na+ content (r=0.24, p<0.01) and ouabain-sensitive Na+ extrusion, but not with the passive membrane permeability for Na+ or Rb+ (r=-0.02 and 0.06, not significant). Both of the above-mentioned significant associations could partially be ascribed to the dependence of erythrocyte Na+ content and ouabain-sensitive Na+ extrusion on plasma cholesterol (r=0.18 and 0.21, p<0.05). Our results support the idea that abnormal lipid metabolism and/or altered Na+,K(+)-ATPase function play an important role in the pathogenesis of salt hypertension in salt-sensitive Dahl rats.

Blood pressure relates to sodium taste sensitivity and discrimination in adolescents

To investigate salt perception and discrimination and their possible association with blood pressure (BP), 72 healthy adolescents (42 boys) aged 9-21 years (mean 16.1 years) were studied. BP was measured with a standardized technique. Anthropometric measurement and conventional renal function tests were performed. Sensitivity tests to recognize the presence of salt when given simultaneously distilled/deionized water and a low sodium concentration water solution, and discrimination tests consisting of six graded samples of different saline solutions presented in randomized order were used to assess individual gustatory sensitivity. Average systolic BP values were 113.2+/-1.6 mmHg in boys and 109.6+/-1.9 mmHg in girls. Mean threshold level for salt sensitivity was 4.55+/-0.6 mmol/l. Systolic BP and salt sensitivity showed a significant correlation ( r=-0.33, P<0.01) even when adjusting for weight. Discrimination score was correlated with salt sensitivity ( r=0.27, P<0.05). There is a significant association between gustatory perception and BP in Spain adolescents, although a real cause-effect relationship has not been established.

Influence of dietary sodium on waterborne copper toxicity in rainbow trout, Oncorhynchus mykiss

Juvenile rainbow trout were fed diets containing control (0.26 mmol/g) or elevated (1.3 mmol/g) dietary Na+ in combination with either background (19 nmol/L) or moderately elevated levels (55 or 118 nmol/L) of waterborne Cu for 21 d. Unidirectional waterborne Na+ uptake rates (measured with 22Na) were up to four orders of magnitude higher than those of Cu (measured with 64Cu). Chronic exposure to elevated dietary Na+ alone or in combination with elevated waterborne Cu decreased whole-body uptake rates of waterborne Na+ and Cu. Accumulation of new Cu and Na+ at the gills was positively and highly significantly correlated and responded to the experimental treatments in a similar fashion, suggesting that Na+ and Cu have common branchial uptake pathways and that dietary Na+ preexposure modifies these pathways. Chronic exposure to elevated waterborne Cu significantly increased Cu concentrations in the liver but caused only modest increases in total Cu concentrations in the whole body and gill. Chronic exposure to elevated dietary Na+ slightly decreased whole-body Cu concentration on day 14 and greatly reduced liver Cu concentration on days 14 and 21; new Cu accumulation in whole-body, gill, and internal organs was reduced on all days. Chronic exposure to elevated waterborne Cu or dietary Na+ alone reduced short-term gill Cu binding at low waterborne Cu concentrations. At high waterborne Cu concentrations, chronic exposure to elevated waterborne Cu had no effect, while elevated dietary Na+ increased Cu binding to the gills. Combined chronic exposure to elevated dietary Na+ and waterborne Cu decreased gill Cu binding over the entire range of Cu concentrations tested. Clearly, chronic exposure to elevated dietary Na+ and waterborne Cu appears to modify gill Cu-binding characteristics and may be important considerations in future development of a chronic biotic ligand model for Cu.

Reduced osmotically inactive Na storage capacity and hypertension in the Dahl model

Recent evidence suggested that Na can be stored in an osmotically inactive form. We investigated whether osmotically inactive Na storage is reduced in a rat model of salt-sensitive (SS) hypertension. SS and salt-resistant (SR) Dahl-Rapp rats as well as Sprague-Dawley (SD) rats were fed a high (8%)- or low (0.1%)-NaCl diet for 4 wk (n = 10/group). Mean arterial pressure (MAP) was measured at the end of the experiment. Wet and dry weights, water content, total body Na (TBS), and bone Na content were measured by dessication and dry ashing. MAP was higher in both Dahl strains than in SD rats. In SS rats, 8% NaCl led to Na accumulation, water retention, and hypertension due to impaired renal Na excretion. There was no dietary-induced Na retention in SR and SD rats. TBS was variable; nevertheless, TBS was significantly correlated with body water and MAP in all strains. However, the extent of Na-associated volume and MAP increases was strain specific. Osmotically inactive Na in SD rats was threefold higher than in SS and SR rats. Both SS and SR Dahl rat strains displayed reduced osmotically inactive Na storage capacity compared with SD controls. A predisposition to fluid accumulation and high blood pressure results from this alteration. Additional factors, including impaired renal Na excretion, probably contribute to hypertension in SS rats. Our results draw attention to the role of osmotically inactive Na storage.

Nephron specific regulation of chloride channel CLC-K2 mRNA in the rat

BACKGROUND

This study investigated the influence of salt intake on the nephron specific gene expression of the kidney chloride channel CLC-K2. To this end, male Sprague-Dawley rats were fed a low (0.02% wt/wt), normal (0.6% wt/wt), or high salt (8% wt/wt) diet for ten days, or they received the loop diuretic furosemide (12 mg/kg/day) for six days.

METHODS

Expression and regulation of messenger RNA for CLC-K2 was demonstrated by RNase protection assay and in situ hybridization in kidney cortex, outer medulla and inner medulla. Tubular localization and regulation were determined precisely by reverse transcription-polymerase chain reaction (RT-PCR) and real time PCR of microdissected nephron segments.

RESULTS

In situ hybridization analysis and RNase protection assay of the total kidney revealed a down-regulation of CLC-K2 mRNA in the high salt diet rats and an up-regulation of CLC-K2 mRNA in furosemide treated rats, which were restricted to the outer medulla. Microdissection of collagenase treated kidney revealed CLC-K2 mRNA expression in the outer medullary thick ascending limb (mTAL), cortical thick ascending limb (cTAL), distal convoluted tubule (DCT), connecting tubule and cortical collecting duct (CNT/CCD), and outer medullary collecting duct (OMCD), whereas no signals were detected in proximal convoluted and straight tubules (PCT and PST), descending thin limb from the outer medulla (dTL), descending and ascending thin limb from the inner medulla (TL), inner medullary collecting duct (IMCD) and glomeruli (glom). Using RT-PCR and real time PCR, the changing levels of CLC-K2 mRNA after furosemide treatment or high salt diet were restricted to the mTAL, whereas CLC-K2 mRNA levels in cTAL and OMCD were not changed in furosemide or high salt rats compared to time paired controls.

CONCLUSIONS

Given that CLC-K2 expressed in the thick ascending limb of Henle's loop is responsible for net chloride reabsorption in this part of the nephron, our findings suggest that in states of surplus salt and in states of severe salt deprivation, selective regulation of CLC-K2 mRNA plays a role in the adaptation of the kidney to different salt loads.

Renal segmental tubular response to salt during the normal menstrual cycle

BACKGROUND

It has been suggested that women gain weight and develop peripheral edema during the luteal phase of the menstrual cycle because they tend to retain sodium and water. However, there is actually no clear evidence for physiological, cyclic variations in renal sodium handling during the menstrual cycle. We prospectively assessed the changes in segmental renal sodium handling occurring during the menstrual cycle in response to changes in salt intake.

METHODS

Thirty-five normotensive women were enrolled. Seventeen women were randomized and studied in the follicular and 18 in the luteal phases of their menstrual cycle. All women were assigned at random to receive a low (40 mmol/day) or a high (250 mmol/day) sodium diet for seven days on two consecutive menstrual cycles. Renal sodium handling and hemodynamics were measured at the end of each diet period.

RESULTS

The changes in sodium intake induced comparable variations in sodium excretion in both phases of the menstrual cycle. In the follicular phase, the increase in salt intake was associated with no change in renal hemodynamics, an increased fractional excretion of lithium (FELi) and a decreased fractional distal reabsorption of sodium (FDRNa), suggesting that sodium reabsorption is reduced both in the proximal and the distal tubules. In contrast, in the luteal phase, the renal response to salt was characterized by a significant renal vasodilation and a marked salt escape from the distal nephron, compared to the women investigated in the follicular phase (P < 0.01). Sodium reabsorption by the proximal nephron was not reduced as indicated by the unchanged FELi.

CONCLUSIONS

These results show that the segmental renal handling of sodium differs markedly in the two phases of the menstrual cycle. They suggest that the female hormones modulate the renal handling of sodium at the proximal and distal segments of the nephron in young normotensive women.

Iron status influences the efficacy of iodine prophylaxis in goitrous children in Côte d'Ivoire

In the developing countries of Africa, many children are at high risk for both goiter and iron-deficiency anemia (IDA). Because iron (Fe) deficiency can have adverse effects on thyroid metabolism, Fe deficiency may influence response to supplemental iodine in areas of endemic goiter. Therefore, our aims were to determine: 1) if goitrous children also suffering from IDA could respond to oral iodine supplementation; and 2) if Fe supplementation in goitrous children with IDA would improve their response to oral iodized oil and iodized salt. First, we compared the efficacy of oral iodized oil in two groups of goitrous children: a nonanaemic group vs. an IDA group. The therapeutic response to iodized oil was impaired in the goitrous children with IDA. Second, an open trial of Fe treatment in goitrous children with IDA improved their response to oral iodized oil. Finally, in a randomized double-blind trial, goitrous, Fe-deficient children consuming iodized salt were given Fe supplementation or placebo. Fe supplementation improved the efficacy of the iodized salt. In these studies, both anatomic (thyroid size) and biochemical (TSH, T4) measures indicated that iodine significantly improved thyroid function in the nonanaemic children compared to the Fe deficient children. Iodine was less efficacious in children with lower Hb at baseline and in those with a poorer response to Fe. The data suggest that a high prevalence of IDA among children in areas of endemic goiter may reduce the effectiveness of iodine prophylaxis.

Interaction of NaCl and behavioral stress on endogenous sodium pump ligands in rats

Our study investigated the hypothesis that the combination of a high NaCl diet and social isolation stress would increase systolic blood pressure (SBP) and endogenous sodium pump ligands (SPL), ouabainlike compound (OLC), and marinobufagenin (MBG). Excretion of MBG and OLC, SBP, and organ weights were studied in four groups (n = 8) of male Fisher 344 x Norwegian brown rats: controls, socially isolated (Iso), 4% NaCl diet (Salt), and the combination of Salt and Iso (Iso+Salt). In Salt, MBG excretion increased by 78% (P < 0.01), whereas SBP and OLC remained unchanged. In Iso, SBP and MBG did not change, but OLC peaked on day 1. In the Iso+Salt, SBP increased by 9 mmHg, MBG excretion increased (42.0 +/- 7.6 vs. 10.0 +/- 1.5 pmol/24 h, P < 0.01), whereas OLC peaked at day 1 (25.0 +/- 2.5 vs. 10.0 +/- 2.0 pmol/24 h, P < 0.01) and remained elevated. Heart and kidney weights were increased in Salt and Iso+Salt. Aortic weights were increased in Iso and Iso+Salt. Thus a high NaCl intake stimulates MBG excretion, whereas isolation stress stimulates OLC. The combination of Salt and Iso is accompanied by marked stimulation of both SPL.

Differential gene regulation of renal salt entry pathways by salt load in the distal nephron of the rat

The aim of the present study was to determine the molecular responses of the main salt-reabsorbing systems in the distal nephron to changes of salt load of the organism. For this purpose we analysed messenger ribonucleic acid (mRNA) levels for the bumetanide-sensitive Na+K+2Cl- cotransporter (BSC1), the thiazide-sensitive Na+Cl- cotransporter (TSC), the kidney-specific inwards rectifier K+ channel (ROMK), the amiloride-sensitive epithelial Na+ channel (ENaC) and the kidney-specific Cl- channel ClC-K2, in the cortex and inner and outer medulla of kidneys from male Sprague-Dawley rats fed a high- (8% w/w), normal- (0.6%) or low-(0.02%) salt diet or treated chronically with subcutaneous infusions of furosemide (12 mg/kg per day). BSC1 and ROMK mRNA levels did not differ between the four treatment groups. TSC mRNA increased during furosemide treatment 1.75-fold versus control but was not affected by a high- or a low-salt diet. The mRNA for the alpha-subunit of ENaC increased with the low-salt diet (about 1.5-fold) and with furosemide (about 2.1-fold) in all kidney zones, but did not change with the high-salt diet. Dietary salt loading down-regulated CIC-K2 mRNA in the outer medulla 0.6-fold versus control whilst furosemide treatment, but not the low-salt diet, increased ClC-K2 mRNA in the outer (1.6-fold) and inner medulla (2.0-fold). These findings suggest that gene expression of Na+ and Cl- entry pathways in the distal nephron are at least partly regulated by the salt load of the organism, such that salt-reabsorbing systems are stimulated by salt deficiency and suppressed by salt overload.

Mechanism of sodium load-induced hypertension in non-insulin dependent diabetes mellitus model rats: defective dopaminergic system to inhibit Na-K-ATPase activity in renal epithelial cells

Obesity-related non-insulin dependent diabetes mellitus (NIDDM) is frequently accompanied by hypertension. The present study was designed to clarify this mechanism. We first determined the blood pressure in male Wistar fatty rats (WFR), one of the NIDDM model rats, and in Wistar lean rats (WLR) as the control, with a normal (0.7% NaCl) or high (7% NaCl) salt diet. We observed no difference in systolic and mean blood pressures between WFR and WLR. WFR, however, became extremely hypertensive as a result of ingesting the high salt diet. We next investigated the mechanism for sodium sensitivity in WFR. Although the urinary excretion of dopamine (DA), a potent natriuretic factor, which reflects the ability for renal DA production, was preserved in WFR, the sodium balance with the high salt diet was positive. Moreover, Na-K-ATPase activity in isolated proximal convoluted tubules (PCT) from WFR with a normal salt diet was significantly (p<0.05) higher than that from WLR. A high salt load produced a significant (p<0.05) decrease in Na-K-ATPase activity in WLR but not in WFR. Similarly, Na-K-ATPase activity in WLR with a normal salt diet was significantly (p<0.05) inhibited by DA (10(-5) M), but this was not true in WFR. Furthermore, urinary excretion of norepinephrine in WFR with a high salt diet was the highest among all the groups. These results indicate that WFR tend to develop salt-sensitive hypertension that could be caused by the excessive sodium retention occurring as the results of a defective dopaminergic system in the kidney that fails to inhibit Na-K-ATPase activity. Augmentation of the renal sympathetic nervous system may play some role in this setting.

Circadian rhythm of plasma sodium is disrupted in spontaneously hypertensive rats fed a high-NaCl diet

High-NaCl diets elevate arterial pressure in NaCl-sensitive individuals, and increases in plasma sodium may trigger this effect. The present study tests the hypotheses that 1) plasma sodium displays a circadian rhythm in rats, 2) the plasma sodium rhythm is disturbed in spontaneously hypertensive rats (SHR), and 3) excess dietary NaCl elevates plasma sodium concentration in SHR. The results demonstrate that plasma sodium has a circadian rhythm that is inversely related to the circadian rhythm of arterial pressure. Although the plasma sodium rhythms of SHR and control rats are nearly identical, the plasma sodium concentrations are significantly higher in SHR throughout the 24-h cycle. Maintenance on a high-NaCl diet increases plasma sodium concentration similarly in both SHR and control rats, but it blunts the plasma sodium rhythm only in SHR. These results demonstrate that in rats, plasma sodium has a circadian rhythm and that high-NaCl diets increase plasma sodium concentration.

Effect of salt on insulin sensitivity differs according to gender and degree of salt sensitivity

The aim of the present study was to investigate the effect of salt intake on insulin sensitivity and the relation between salt sensitivity and insulin sensitivity in genetically hypertension-prone individuals. Twenty-eight healthy subjects (13 men and 15 women) with a family history of hypertension were examined at baseline, after 1 week of salt restriction (10 mmol/d), and after 1 week of salt loading (240 mmol/d). Insulin sensitivity was measured with the hyperinsulinemic euglycemic clamp after the low- and high-salt diets. Salt sensitivity was defined as the difference in mean arterial blood pressure between the high-salt and the low-salt diets. There was no significant relationship between insulin sensitivity and salt sensitivity after either of the 2 diets. In the men, salt sensitivity was inversely related to plasma renin activity (r=-0.61, P=0.03) and plasma aldosterone (r=-0.74, P=0.004), whereas salt sensitivity in women was directly correlated with the salt-induced increase in body weight (r=0.68, P=0.005). In men, the high-salt diet induced a change in glucose disposal that was strongly correlated with the degree of salt sensitivity (r=0.83, P=0. 0004), plasma renin activity (r=-0.82, P=0.0006), and plasma aldosterone concentrations (r=-0.87, P=0.00009) (eg, the greater the salt sensitivity and the lower the activity of the renin-angiotensin-aldosterone system, the greater improvement in insulin sensitivity). No such relationships were observed in women. In conclusion, increased salt sensitivity and decreased activity of the renin-angiotensin-aldosterone system predict improved insulin sensitivity with high-salt intake compared with low-salt intake in men, suggesting an interaction among salt intake, salt sensitivity, the renin-angiotensin-aldosterone system, and insulin action.

Role of female sex hormones in the development and reversal of dahl hypertension

Female sex hormones protect against the development of Dahl hypertension mediated by increases in dietary sodium. The role of female sex hormones in the reversal of Dahl hypertension mediated by decreases in dietary sodium is unknown. The goal of this study was to identify sex differences in the reversal of Dahl hypertension and the associated changes in water and electrolyte homeostasis. Male (M, n=8), female (F, n=8), and ovariectomized female (OVX, n=9) Dahl salt-sensitive rats were instrumented with an abdominal radiotelemetry device for 24-hour monitoring of blood pressure (BP) and heart rate. Daily measurements of food intake, water intake, and urine output were recorded as diet was changed from a low-sodium diet (0.15% NaCl) to a diet containing 8% NaCl. The diet was then changed back to 0.15% NaCl. The responses to changes in the salt diet were compared with responses observed in rats (M, n=4; F, n=4; OVX, n=4) that were maintained on 0.15% NaCl during the experiment. Sex differences in BP were observed when M, F, and OVX rats were fed 8% NaCl diet for 2 weeks (152+/-4, 141+/-3, and 154+/-5 mm Hg, respectively). BP was significantly greater (P<0.05) in M and OVX rats than in F rats. Fluid balance (water intake minus urine volume) and sodium balance (sodium intake minus sodium excretion) were similar in all groups on the 8% NaCl diet. BP in time-control M, F, and OVX rats was 121+/-3, 130+/-4, and 162+/-11 mm Hg, respectively. Compared with time-control groups, differences in BP while rats were eating the 8% NaCl diet were observed in M and F rats but not OVX rats. Reinstatement of an NaCl-deficient diet reversed the hypertension in M and F but not OVX rats (124+/-4, 124+/-2, and 145+/-5 mm Hg, respectively). The changes in dietary sodium caused similar changes in renal handling of sodium and water in all groups of rats; therefore, the effect on blood pressure was independent of renal excretory function. The inability to reverse the hypertension by decreasing sodium intake in OVX rats and the development of spontaneous hypertension in OVX females maintained on a low-sodium diet indicates that removal of the female sex hormones predisposes the animal to the development of hypertension that is sodium independent. We conclude that female sex hormones protect Dahl S rats against the development of sodium-dependent and -independent hypertension.

Renin-angiotensin system genetic polymorphisms and salt sensitivity in essential hypertension

We evaluated the association between salt-sensitive hypertension and 3 different genetic polymorphisms of the renin-angiotensin system. Fifty patients with essential hypertension were classified as salt sensitive or salt resistant, depending on the presence or absence of a significant increase (P<0.05) in 24-hour ambulatory mean blood pressure (BP) after high salt intake. The insertion/deletion (I/D) angiotensin-converting enzyme (ACE) gene, the M235T angiotensinogen (AGT) gene, and the A1166C angiotensin II type 1 (AT1) receptor gene polymorphisms were determined with the use of standard polymerase chain reaction methods. Twenty-four (48%) patients with significantly increased (P<0.05) 24-hour mean BP with high salt intake (from 107.3+/-9.4 to 114.8+/-10.6 mm Hg) were classified as salt sensitive. In the remaining 26 patients (52%), high salt intake did not significantly modify 24-hour mean BP (from 107.6+/-10 to 107. 8+/-9 mm Hg), and they were classified as having salt-resistant hypertension. We did not find any significant association between either M235T AGT or A1166C AT1 receptor genotypes and the BP response to high salt intake. However, patients with essential hypertension homozygous for the insertion allele of the ACE gene (II) had a significantly higher BP increase with high salt intake (9. 8+/-8.1 mm Hg for systolic BP and 5.2+/-4.2 mm Hg for diastolic BP) than that observed in patients homozygous for the deletion allele (DD) (1.2+/-5.9 mm Hg for systolic BP; P=0.0118 and -0.2+/-4.2 mm Hg for diastolic BP; P=0.0274). Heterozygous patients (ID) exhibited an intermediate response. The prevalence of salt-sensitive hypertension also was significantly higher (P=0.012) in II (67%) and DI patients (62%) compared with DD hypertensives (19%). We conclude that a significant association exists between the I/D polymorphism of the ACE gene and salt-sensitive hypertension. Patients with II and DI genotypes have significantly higher prevalence of salt sensitivity than DD hypertensives.

[Use of iodized salt and the risk of iodine overload]

Iodine-deficiency disorders are a major problem of public health in Morocco. To mitigate this deficiency, the iodination of all the salt intended for human consumption in a proportion of 80 +/- 10 mg/kg of salt has become obligatory since a decree published in 1995. We estimated that this rate of iodized salt issued risked inducing an iodine excess in the population. To check this hypothesis, we provided 7 families made up of 28 subjects, who at the start were consuming a non-iodized salt, with the decreed, iodized salt and we followed the evolution of their urinary iodine excretion over a period of 3 weeks. The mean values of urinary iodine excretion of the 28 subjects were 12.8 micrograms/dl before use of iodized salt and 26.8, 35.5 and 63.2 micrograms/dl, respectively, after 7, 14 and 21 days from the introduction of iodized salt into their diet. After 21 days of the use of iodized salt, 84.6 per cent of the subjects had an iodine excess. We conclude that prolonged use of this iodized salt exposes the population to the risk of thyroid disorders.

Effect of sodium restriction on urinary excretion of cortisol and its metabolites in humans

The adrenal gland is involved in the control of urinary sodium excretion mainly via the secretion of the mineralocorticoid aldosterone. Although under certain conditions glucocorticoid seem to be also involved in the regulation of sodium homeostasis, there are contradictory reports on the relationship between cortisol secretion and sodium intake. Given recent findings linking regulation of physiological activity of steroids to the activity of specific enzymatic pathways, we have examined changes in urinary excretion of cortisol and its metabolites in eight healthy volunteers on a low sodium diet. Urinary steroids were measured with specific radioimmunoassays after extraction and chromatography (F and E) or after dilution (THF and THE). Excretion of cortisol (124 +/-41 nmol/day) was significantly lower on Day 2 (86 +/- 27 nmol/day, p < 0.01) and Day 7 (85 +/- 25 nmol/day, p < 0.01) of sodium restriction. On the same samples calculated ratios of THF/F (55 +/- 15; 61 +/- 22; 68 +/- 21) and E/F (2.5 +/- 0.6; 2.8 +/- 1.4; 3.0 +/- 1.3) reflecting the activity of 5 beta-reductase and 11 beta-hydroxysteroid dehydrogenase, respectively, showed significant increases in the former on both Days 2 and 7 and for the latter only on Day 7. This study supports the notion that sodium restriction decreases urinary cortisol excretion and provides evidence that increased activity of 5 beta-reductase and lowered metabolism by 11 beta-HSD are presumably the mechanisms of this decrease.