Hypertension causes various health problems, including cardiovascular and renal diseases. Although hypertension is attributed to numerous predisposing factors, such as obesity and diabetes, sodium intake predominantly impacts blood pressure (BP) regulation . Hence, dietary salt restriction and the use of diuretics remain the cornerstones of antihypertensive therapy in several guidelines [2,3]. However, current guidelines may not be very effective as the number of individuals with hypertension (caused by excessive salt intake) is still rising [4,5]. Therefore, targeting the regulation of sodium handling can be a novel therapeutic approach for hypertension.
The renal regulation of urinary sodium excretion and its relevance to hypertension have been extensively studied [6,7]. However, very few studies have focused on whether intestinal sodium absorption contributes to the pathogenesis of hypertension. The sodium/hydrogen exchanger isoform 3 (NHE3) is a major absorptive sodium transporter in the intestine [8,9]. In fact, NHE3 inhibitors reduce BP in rat models of hypertension and chronic kidney disease (CKD), and one of these NHE3 inhibitors has become clinically available for patients with CKD . Interestingly, hormonal control of electrolyte transporters in the intestinal epithelial cells is implicated in extracellular volume regulation . Among those hormones, the renin-angiotensin system (RAS) appears to impact intestinal sodium absorption [12,13]. The components of RAS are expressed in the gut [13,14]; therefore, it is conceivable that the alteration of intestinal local RAS is linked to the pathophysiology of hypertension through regulation of sodium absorption in the gut.
We previously reported the ‘salt memory’ effect, in which persistent hypertension is induced by transient salt loading in rat models of salt-sensitive hypertension, such as spontaneously hypertensive rats (SHRs) and Dahl salt-sensitive rats [6,15]. The medial hypertrophy of renal arterioles, impaired glomerular perfusion, and increased synthesis of renin are driven by transient salt administration and could be responsible for the underlying mechanisms of persistent hypertension [6,16]. Moreover, transient treatment with high-dose angiotensin II (Ang II) type 1 receptor (AT1R) blocker (ARB) is able to provide beneficial effects, including prolonged reduction of BP and regression of renal arteriolar hypertrophy in SHRs and Dahl salt-sensitive rats [17–20]. These findings suggest that the activation of the RAS because of impaired glomerular perfusion may partly mediate sustained BP elevation after transient salt loading. However, little is known about the sodium balance, including the changes of sodium excretion in the urine or dietary sodium absorption from the gut, in the ‘salt memory’ state.
Here, we demonstrate that a prolonged increase in intestinal sodium absorption and sustained excess of circulating volume seems to contribute to persistent BP elevation after transient salt loading. Intestinal local RAS appeared to be continuously activated during and after salt loading, likely leading to increased sodium absorption through the overexpression of NHE3 in the small intestine. Supporting this notion, the pharmacological reduction of the intestinal local RAS activity by short-term, high-dose administration of a RAS inhibitor attenuated salt memory effects in SHRs. Importantly, intestinal local RAS was also activated in Dahl salt-sensitive rats by salt loading, albeit limited in salt-resistant Wistar Kyoto (WKY) rats as compared with that in salt-sensitive SHRs or Dahl salt-sensitive rats. These observations reveal previously unappreciated functions of intestinal local RAS on sodium homeostasis and provide new insights into the pathophysiology of salt-sensitive hypertension.
MATERIALS AND METHODS
To investigate how sodium levels and fluid volume are altered in response to salt intake and to seek the impacts of sodium handling in the gut and the kidney, 6-week-old male SHRs (body weight approximately 130 g) were randomly divided into the following three groups (n = 16 per group): normal tap water (NT); high salt-concentration water (HS) [1% (wt/vol) NaCl]; and valsartan (ARB) administration in HS rats. HS rats were treated with high salt-concentration (1% NaCl) drinking water from 6 to 14 weeks of age, followed by normal tap water until the end of the experiment. From 18 to 20 weeks of age, HS rats were fed a normal-salt diet containing ARB.
SBP and body weight were recorded every 2 weeks, while food and water consumption, volume and sodium excretion of urine and stools, and total body water amount were examined every 4 weeks in each group of rats. At the end of the experiment (when rats reached 28 weeks of age), and additionally at 14, 15, and 21 weeks of age (n = 16 per group, per age) to investigate the changes immediately after the HS or ARB treatment, the rats were euthanized by rapid decapitation to collect their blood and tissue samples, including the kidney, jejunum, ileum, proximal colon, and distal colon. Each organ was flash frozen in liquid nitrogen apart from tissues for immunohistochemistry that were immersed and fixed in 4% paraformaldehyde before being embedded in paraffin.
To investigate the response to salt loading in different rat models, 6-week-old male WKY or DS rats were randomly divided into the following two groups (n = 8 per group): NT and HS. HS rats were treated with high salt-concentration (1% NaCl) drinking water from 6 to 14 weeks of age. Biological parameters were measured according to the method in experiment 1, and (at 14 weeks of age) the rats were euthanized to collect their blood and tissue samples.
Further details of the experiments (including animal selection, assays, RNA extraction, real-time quantitative PCR analysis, analysis of intestinal and renal histological features, and cell culture) are provided in the online-only Data Supplement, https://links.lww.com/HJH/B738.
All the data are presented as mean ± standard error of mean values. The mean value of two groups were compared using Student's t test. Results obtained over time were analyzed using two-way ANOVA with Bonferroni post hoc test, and differences in the mean values of more than three groups were statistically analyzed using one-way ANOVA and Tukey's post hoc test. (GraphPad Prism 8: GraphPad Software, San Diego, California, USA). P less than 0.05 was considered statistically significant.
Sustained elevation of blood pressure and reduction of fecal sodium content after transient salt loading, which was regressed by short-term blockade of renin-angiotensin system, in spontaneously hypertensive rats
SHRs were given either NT or HS for 8 weeks, followed by NT for 14 weeks (Fig. 1a). HS rats were treated with an ARB for 2 weeks (Fig. 1a). SBP was elevated after salt loading and sustained over the resumption of NT (Fig. 1b). ARB administration dramatically lowered BP even after the end of the treatment (Fig. 1b). The amount and proportion of total body water remained higher over the return to NT treatment in HS rats, despite the similar body weight, food intake, and stool quantity between HS and NT rats (Fig. 1c–f). In parallel, the increase in water consumption and urinary volume induced by HS were sustained after the end of HS treatment (Fig. 1e and f). Intriguingly, urinary sodium excretion from HS rats remained high, while fecal sodium content was suppressed as compared with that in NT rats after the transient salt loading (Fig. 1g, Fig. S1, https://links.lww.com/HJH/B738, and Table 1). ARB treatment persistently reduced the total body water amount, water consumption, and urinary volume, despite comparable body weight, food consumption, and stool weight except over the period of ARB administration (Fig. 1c–f). Importantly, ARB treatment increased fecal sodium content and decreased the urinary sodium excretion as compared with the HS rats without RAS inhibition (Fig. 1g, Fig. S1, https://links.lww.com/HJH/B738, and Table 1).
TABLE 1 -
Transient salt loading for 8 weeks causes a sustained increase in the sodium absorption
|Sodium balance (/mouse)
|Total intake (mEq/day)
||2.97 ± 0.04
||23.39 ± 0.19∗∗
||23.01 ± 0.39∗∗
||2.94 ± 0.22
||3.57 ± 0.08
||2.90 ± 0.07††
||3.09 ± 0.07
||3.03 ± 0.11
||2.88 ± 0.11
|Fecal excretion (mEq/day)
||0.44 ± 0.07
||1.00 ± 0.13∗∗
||1.06 ± 0.12∗∗
||0.70 ± 0.10
||0.36 ± 0.02∗∗
||0.64 ± 0.05†
||0.54 ± 0.03
||0.32 ± 0.02∗∗
||0.46 ± 0.02†
|Urinary excretion (mEq/day)
||1.85 ± 0.05
||20.86 ± 1.51∗∗
||20.56 ± 1.81∗∗
||1.64 ± 0.13
||2.24 ± 0.11∗∗
||1.76 ± 0.05††
||2.11 ± 0.06
||1.83 ± 0.13
||1.84 ± 0.08
|Estimated absorption [mEq/day (%intake)]
Time-dependent shift of sodium balance in spontaneously hypertensive rats at 14, 21, and 28 weeks of age. Estimated absorption was calculated by subtracting the total amount of sodium output (in urine and feces) from the mean of total sodium intake. Data were taken from the experiments summarized in Fig. 1
. For each of the rat groups (tap, salt, ARB) at each age (14, 21, and 28 weeks of age), the total intake, fecal excretion, and urinary excretion of sodium were compared with other rat groups. ∗∗P
less than 0.05; ∗P
less than 0.01 vs. tap; ††P
less than 0.05; †P
less than 0.01 ARB vs. salt; n
= 16 per group. ARB, angiotensin II type 1 receptor blocker.
Activation of systemic renin-angiotensin system by transient salt loading in rats with salt-induced hypertension
Levels of RAS components, such as plasma renin activity (PRA), plasma aldosterone concentration (PAC), and plasma Ang II, were markedly suppressed at the end of the salt-loading period (at 14 weeks of age), suggesting the predictable inhibition of systemic RAS by sodium overload (Fig. 2a). Plasma levels of atrial natriuretic peptide (ANP) as well as serum levels of urea nitrogen and creatinine (Cre) from HS rats were comparable with those from NT rats (Fig. 2a). At 15 weeks of age, 1 week after the end of the salt-loading period, plasma levels of RAS components were normalized, whereas the serum UN and Cre levels were elevated in HS rats (Fig. 2b). At 28 weeks of age, plasma levels of RAS components and ANP, along with serum levels of UN and Cre, were increased in HS rats as compared with that in NT rats (Fig. 2c). In contrast, such changes were reversed with ARB treatment (Fig. 2c).
Intestinal and renal genomic response of sodium transporters to salt loading relies on renin-angiotensin system
Expression of gene encoding for NHE3 was induced in both, the small intestine and the colon, from HS rats at the end of the salt-loading period (14 weeks of age; Fig. 3a and b). NHE3 gene expression was consistently upregulated in the small intestine during the return to NT, while being temporarily repressed in the colon 1 week after the end of HS treatment (15 and 28 weeks of age; Fig. 3a and b). Salt loading also caused sustained upregulation of gene encoding for sodium glucose cotransporter 1 (SGLT1) in the small intestine (Fig. 3a). In contrast, colonic expression of genes encoding for SGLT1 and the β subunit of the epithelial sodium channel ENaC (ENaCb) were both repressed by temporary sodium administration over the experimental period (Fig. 3b). In contrast, the expression of renal NHE3 was similar between the HS and NT rats at the end of the salt-loading period; however, the expression was induced in HS rats 14 weeks after the end of the salt-loading period (Fig. 3c). Renal renin gene expression was repressed by salt loading, and it was markedly induced after the resumption of tap water treatment (Fig. 3c).
Conversely, NHE3 gene expression was repressed by ARB treatment in the small intestine, colon, and kidney of HS rats (Fig. 4a–c). The SGLT1 expression was also reduced by ARB treatment in the small intestine (Fig. 4a), whereas being induced in the colon (Fig. 4b). Additionally, ENaCb expression was increased by ARB treatment in the colon (Fig. 4b). Renal renin expression was significantly inhibited by ARB treatment in HS rats (Fig. 4c).
In line with gene expression, both NHE3 and SGLT1 protein staining intensity was consistently induced in both, the jejunum and ileum after the end of salt loading, and such induction was abrogated by RAS inhibition (Fig. 5a and b). Vascular wall medial thickening was noted in the renal arterioles taken from HS rats 14 weeks after the end of salt administration (Fig. 5c). ARB attenuated medial thickening of the renal arterioles, consistent with the suppression of PRA by ARB treatment (Figs. 2c and 5c).
Intestinal local renin-angiotensin system is activated in spontaneously hypertensive rats by transient salt loading
Local RAS components in the gut were explored in SHRs (Fig. 6a–d). Transient administration of sodium significantly elevated the Ang II levels in both, the jejunum and ileum (14 weeks of age; Fig. 6a and c), and the increase in Ang II was further pronounced 14 weeks after the end of salt administration (28 weeks of age; Fig. 6a and c). Expression of genes encoding for angiotensinogen (AGT), angiotensin-converting enzyme (ACE), AT1R, and Ang II type 2 receptor (AT2R) in both, the jejunum and ileum was induced by salt loading (14 weeks of age; Fig. 6b and d), and the gene induction was partially maintained over 14 weeks after the end of salt administration (28 weeks of age; Fig. 6b and d). ARB treatment repressed intestinal Ang II levels as well as expression of genes encoding for AGT, ACE, AT1R, and AT2R (28 weeks of age; Fig. 6a–d). Expression of genes encoding for angiotensin-converting enzyme 2 (ACE2) and Mas receptor (MasR) showed mostly an opposite response to other RAS components against salt loading and RAS inhibition (Fig. 6b and d).
Potential connection of intestinal local renin-angiotensin system to salt-sensitivity
WKY and DS rats were subjected to 8 weeks of salt loading (14 weeks of age; Fig. 7a–f, Figs. S2a–h, https://links.lww.com/HJH/B738, and S3a–h, https://links.lww.com/HJH/B738). SBP and the proportion of total body water were unchanged upon HS administration in WKY rats, while a significant rise was noted in DS rats (Figs. S2a, https://links.lww.com/HJH/B738 and S3a, https://links.lww.com/HJH/B738). In line with SHRs, HS treatment in WKY and DS rats induced elevation of the water consumption, urinary volume, and urinary and fecal sodium excretion, despite almost similar body weight, food intake, and stool quantity between HS and NT rats (Figures S2b–f, https://links.lww.com/HJH/B738 and S3b–f, https://links.lww.com/HJH/B738). Plasma levels of RAS components (PRA, PAC, and Ang II) were suppressed by HS administration in both, WKY and DS rats (Figs. S2g, https://links.lww.com/HJH/B738 and S3g, https://links.lww.com/HJH/B738). Interestingly, the serum levels of UN were only increased in DS rats with HS administration (Fig. 2a, Figs. S2g, https://links.lww.com/HJH/B738, and S3g, https://links.lww.com/HJH/B738).
Contrary to SHRs, NHE3 and SGLT1 gene expressions were unchanged in both, the small intestine and colon by salt loading in WKY rats, while being induced in DS rats (Fig. 3a and b and Fig. 7a and d). Genomic response of other sodium transporters to salt loading displayed a similar tendency in WKY and DS rats as compared with that in SHRs (Fig. 3a--c and Fig. 7a and d). In line with the gene expression, intestinal NHE3 and SGLT1 protein staining intensity was increased only in DS rats at the end of salt loading (Figs. S2h, https://links.lww.com/HJH/B738 and S3h, https://links.lww.com/HJH/B738). Likewise, significant elevation of intestinal Ang II by salt loading in SHRs was recapitulated only in DS rats, but not in WKY (Fig. 6a and c and Fig. 7b, c, e, and f). Meanwhile, intestinal expression of genes encoding for AGT, ACE, AT1R, and AT2R was induced, whereas the expression of genes encoding for ACE2 and MasR was repressed with salt loading in both, WKY and DS rats (Fig. 7b, c, e, and f).
Intestinal renin-angiotensin system induces the gene expression of sodium transporters via the angiotensin II-- Ang II type 1 receptor axis
Caco-2 human intestinal epithelial cells were treated with Ang II, sodium chloride (NaCl), or aldosterone (Fig. 8a–c and Fig. S4a, https://links.lww.com/HJH/B738). Expression of genes encoding for NHE3, SGLT1, and AGT was increased with Ang II treatment (Fig. 8a). The increased expression of NHE3, SGLT1, and AGT genes was significantly repressed by an AT1R inhibitor, valsartan, but not by an AT2R inhibitor, PD123319 (Fig. 8b). It is noteworthy that the expression of genes encoding for RAS components (apart from ACE2 and MasR) as well as Ang II concentration in the cultured media, were increased with NaCl treatment (Fig. 8c). Aldosterone failed to induce the gene expression of sodium transporters (Figure S4a, https://links.lww.com/HJH/B738).
The present study identified how sustained BP elevation with transient salt loading coincided with a persistent decrease in the fecal sodium content and sustained excess of circulating volume in SHRs. Salt-induced hypertension and the acceleration of intestinal sodium absorption appeared to be reversed with RAS inhibition. Transient salt loading and treatment with ARB seemed to continuously impact renal excretion and intestinal absorption of sodium, indicating the involvement of RAS in ‘salt memory’ effects. Systemic RAS was suppressed during salt loading but was eventually activated by impaired glomerular perfusion, based on renal arteriolar hypertrophy and the prominent induction of renal renin gene expression. Intriguingly, intestinal tissue RAS was induced even from the period of salt loading, independent of systemic RAS. Intestinal sodium transporter expression was increased by salt loading, likely driven by RAS activation, suggesting a relationship to augmented intestinal sodium absorption. Salt-induced intestinal RAS activation was also observed in DS rats but only partially in WKY rats, indicating the potential connection of intestinal RAS to salt sensitivity.
The intestine engages in the digestion and absorption of dietary nutrients. Importantly, almost all sodium and fluids are absorbed through the small intestine (∼95%), and the remainder is absorbed via the colon (∼4%) . With regard to the molecular regulation of intestinal NaCl absorption, NHE3 is a major sodium transporter and is predominantly expressed in the apical brush border membrane of the intestinal epithelium in addition to the renal proximal tubule . In the renal proximal tubules, NHE3 reabsorbs up to 75% of the sodium . In the human intestine, NHE3 is expressed at a higher level in the ileum and jejunum than in the colon . NHE3-deficient mice (NHE3−/−) display moderate salt wasting from the digestive system with diarrhea and reduced BP [23,24]. Conversely, unlike nontransgenic mice, NHE3−/− mice with transgenic expression of NHE3 in the small intestine (tgNHE3−/−) are resistant to chronic volume depletion, low BP, and dietary salt deficiency [25,26]. Furthermore, an NHE3 inhibitor (which possesses low oral bioavailability and acts exclusively on the gut) increases the fecal sodium content, decreases the urinary sodium excretion, and lowers BP in SHRs .
On the basis of these observations, NHE3 in the gut is presumably a key regulator for the homeostasis of sodium balance and BP. In addition to NHE3, SGLT1 in the small intestine and the colon as well as ENaCb in the colon are known to impinge on intestinal sodium absorption. Consistent with our observations, a high-salt diet increases the expression of intestinal SGLT1 . However, the pharmacological inhibition of SGLT1 does not induce severe diarrhea . Furthermore, SGLT1−/− mice have near-normal BP . Thus, SGLT1 is likely to have a marginal impact on intestinal sodium absorption. Meanwhile, colon-specific ENaC-deficient mice exhibit increased fecal sodium excretion . Our studies indicated that the genomic response to salt loading in the small intestine and colon exhibits a distinct signature. More precisely, the intestinal expression of NHE3 and SGLT1 was persistently upregulated after transient salt loading, while ENaCb was downregulated as a reflection. Accordingly, it is conceivable that augmented sodium absorption because of increased expression of sodium transporters (especially in the small intestine) is involved in the mechanism of ‘salt memory’.
Intestinal sodium and water absorption are stimulated by Ang II . Although multiple mechanisms control the NHE3 expression , Ang II activates NHE3 through AT1R-dependent mechanisms in the kidney and cultured intestinal epithelial cells . Supporting these previous studies, our in-vitro experiments demonstrated that the expression of intestinal NHE3 was augmented by the Ang II--AT1R pathway. Thus, the intestinal Ang II--AT1R pathway likely contributes to the establishment of ‘salt memory’, whereas the Ang II--AT1R blockade may contribute to the regression of ‘salt memory’, through regulation of the expression of sodium transporters in the gut.
Local RAS is found in many tissues and is known to be regulated differently from systemic RAS. As for the reaction against salt loading, a high-salt diet causes upregulation of the tissue RAS components in the heart and kidney of DS rats [35,36]. In specific subsets of salt-sensitive rats, the regulation of intrarenal RAS seems to be independent of circulating RAS; renin dictates the Ang II levels in the plasma, whereas AGT is likely to be a critical regulator of Ang II production in the kidney . A high-salt diet induces intrarenal AGT, promoting the generation of renal Ang II, which, in turn, may further stimulate the local production of AGT, thereby creating a vicious cycle of intrarenal local RAS activation [37–39]. RAS components have been detected in the intestine, and, strikingly, the concentration of Ang II in the small intestine may be higher than that in the kidney . However, the pathophysiological roles of intestinal local RAS on BP regulation remain unclear . AT1R agonism may increase colonic sodium absorption in rats with CKD . On the contrary, intestinal tissue RAS can be repressed by the administration of ARB . In the present study, RAS components in the small intestine were upregulated with salt loading (especially in salt-sensitive rats), while circulating RAS was suppressed. More precisely, ACE--Ang II--AT1R axis was induced, whereas ACE2--MasR axis, which acts in an opposite manner than the ACE--Ang II--AT1R axis, was suppressed in the small intestine with salt loading. Given that intestinal Ang II was not augmented with salt loading in WKY rats as in SHRs or DS rats, intestinal RAS may be linked to salt sensitivity. Furthermore, in-vitro experiments have demonstrated that AGT gene expression was upregulated after both, Ang II and NaCl treatment in human intestinal epithelial cells. Hence, we propose that NaCl may directly or indirectly activate local RAS in the intestine, thereby contributing to initial or even sustained BP elevation upon salt loading. Other molecules, such as reactive oxygen species (ROS), which activate AGT expression in rat kidney during a high-salt diet [37,38], might also be involved in the intestinal RAS activation. Future studies are warranted to address this question.
Other than the AGT--Ang II vicious cycle in situ, sustained elevation of intestinal Ang II after transient salt loading in SHRs may also be explained by continuously high levels of circulating renin owing to medial thickening of the renal arterioles. In general, increased sodium intake leads to RAS suppression. In fact, our results showed reduction in the renal renin gene expression consistent with suppressed plasma renin activity during salt loading. However, in specific subsets of salt-sensitive rats, including SHRs and DS rats, intrarenal RAS gets induced by salt loading [35,36]; we believe that this leads to renal arteriolar hypertrophy and eventual acceleration of systemic RAS. From the point of view of sodium retention, although ARB reduced urinary sodium excretion, total body water was significantly reduced in the ARB group than in the HS group. Accordingly, the reduction of urinary sodium excretion would be a reflective of the decrease in the absorption of sodium from the intestine. Collectively, owing to RAS attenuation with ARB treatment, BP, circulating volume, and intestinal sodium absorption were significantly reduced, associated with similar regression of renal arteriolar hypertrophy and reduction in the plasma renin activity.
From a clinical perspective, a direct association between intestinal local RAS and hypertension has not been established to date; however, some hypotheses can be proposed based on our results. In some subsets of hypertensive patients, for example, obese hypertensive patients, systemic RAS is reported to be inappropriately normal, or even accelerated despite higher sodium intake [43,44]. Importantly, obesity-related hypertension is known to exhibit the pattern of salt-sensitive hypertension  and be modulated by the gastrointestinal tract; obesity-related hypertension can be effectively managed with metabolic surgery . Especially, elderly subjects, African Americans, Asians, and obese patients are thought to be salt-sensitive [47,48]. One hallmark of salt sensitivity is the inability to appropriately suppress renal local RAS in response to salt loading , and an ARB was shown to improve the salt sensitivity presumably through the inhibition of local RAS . Moreover, the ‘memory’ effect of antihypertensive treatment with an ARB but not with a calcium channel blocker, was observed in humans , maybe through the modification of tissue RAS. Although the precise regulation remains unclear as most previous studies on salt-sensitive hypertension were mainly focused on renal regulation, our results suggest the relation of salt-sensitive hypertension to intestinal local RAS.
In conclusion, we demonstrated that the activation of intestinal local RAS by transient salt loading was sustained in salt-sensitive rats, likely contributing to enhanced sodium transporter expression in the small intestine. Possible augmentation of intestinal sodium absorption caused the increased circulating volume and persistent BP elevation. Notably, transient salt loading induced intestinal local RAS in the gut of salt-sensitive rats, SHRs and DS rats; but incompletely in salt-resistant WKY rats. Given that the effects of diuretics in humans are influenced by renal function and that the adherence to a low-sodium diet is generally not accomplished easily, the concept of limiting intestinal sodium absorption could be a promising strategy in the development of a new type of antihypertensive therapy. In fact, our findings provide important insights into the understanding of the intestinal mechanism of ‘salt memory’ and salt-sensitive hypertension.
We thank members of the Miyashita laboratory as well as Akira Nishiyama (Kagawa University) and Sayaka Nagata (Miyazaki University) for their kind assistance in measuring intestinal Ang II levels. This work was supported by the Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research with grant numbers JP26460920 to K.M. and JP16K15471 to H.I.
Conflicts of interest
There are no conflicts of interest.
1. Guyton AC. Blood pressure control–special role of the kidneys and body fluids. Science
2. Umemura S, Arima H, Arima S, Asayama K, Dohi Y, Hirooka Y, et al. The Japanese Society of Hypertension Guidelines for the Management of Hypertension (JSH 2019). Hypertens Res
3. Whelton PK, Carey RM, Aronow WS, Casey DE Jr, Collins KJ, Dennison Himmelfarb C, et al. 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA Guideline for the Prevention, Detection, Evaluation, and Management of High Blood Pressure in Adults: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. Hypertension
4. Powles J, Fahimi S, Micha R, Khatibzadeh S, Shi P, Ezzati M, et al. Global, regional and national sodium intakes in 1990 and 2010: a systematic analysis of 24 h urinary sodium excretion and dietary surveys worldwide. BMJ Open
5. (NCD-RisC) NRFC. Worldwide trends in blood pressure from 1975 to 2015: a pooled analysis of 1479 population-based measurement studies with 19.1 million participants. Lancet
6. Oguchi H, Sasamura H, Shinoda K, Morita S, Kono H, Nakagawa K, et al. Renal arteriolar injury by salt intake contributes to salt memory for the development of hypertension. Hypertension
7. Wang X, Armando I, Upadhyay K, Pascua A, Jose PA. The regulation of proximal tubular salt transport in hypertension: an update. Curr Opin Nephrol Hypertens
8. Li XC, Zheng X, Chen X, Zhao C, Zhu D, Zhang J, et al. Genetic and genomic evidence for an important role of the Na(+)/H(+) exchanger 3 in blood pressure regulation and angiotensin II-induced hypertension. Physiol Genomics
9. Visconti L, Cernaro V, Calimeri S, Lacquaniti A, De Gregorio F, Ricciardi CA, et al. The Myth of water and salt: from aquaretics to tenapanor. J Ren Nutr
10. Spencer AG, Greasley PJ. Pharmacologic inhibition of intestinal sodium uptake: a gut centric approach to sodium management. Curr Opin Nephrol Hypertens
11. Kato A, Romero MF. Regulation of electroneutral NaCl absorption by the small intestine. Annu Rev Physiol
12. Matsushita KNY, Hosomi H, Tanaka S. Effects of atrial natriuretic peptide on water and NaCl absorption across the intestine. Am J Physiol
13. Garg M, Angus PW, Burrell LM, Herath C, Gibson PR, Lubel JS. Review article: the pathophysiological roles of the renin-angiotensin system in the gastrointestinal tract. Aliment Pharmacol Ther
14. Paul M, Poyan Mehr A, Kreutz R. Physiology of local renin-angiotensin systems. Physiol Rev
15. Itoh H, Kurihara I, Miyashita K. Organ memory: a key principle for understanding the pathophysiology of hypertension and other noncommunicable diseases. Hypertens Res
16. Sasamura H, Hayashi K, Ishiguro K, Nakaya H, Saruta T, Itoh H. Prevention and regression of hypertension: role of renal microvascular protection. Hypertens Res
17. Ishiguro K, Hayashi K, Sasamura H, Sakamaki Y, Itoh H. Pulse’ treatment with high-dose angiotensin blocker reverses renal arteriolar hypertrophy and regresses hypertension. Hypertension
18. Nakaya H. Temporary Treatment of Prepubescent Rats with Angiotensin Inhibitors Suppresses the Development of Hypertensive Nephrosclerosis. J Am Soc Nephrol
19. Nakaya H, Sasamura H, Mifune M, Shimizu-Hirota R, Kuroda M, Hayashi M, Saruta T. Prepubertal treatment with angiotensin receptor blocker causes partial attenuation of hypertension and renal damage in adult dahl salt-sensitive rats. Nephron
20. Smallegange C, Hale TM, Bushfield TL, Adams MA. Persistent lowering of pressure by transplanting kidneys from adult spontaneously hypertensive rats treated with brief antihypertensive therapy. Hypertension
21. Li XC, Shull GE, Miguel-Qin E, Zhuo JL. Role of the Na+/H+ exchanger 3 in angiotensin II-induced hypertension. Physiol Genomics
22. Dudeja PK, Rao DD, Syed I, Joshi V, Dahdal RY, Gardner C, et al. Intestinal distribution of human Na+/H+ exchanger isoforms NHE-1, NHE-2, and NHE-3 mRNA. Am J Physiol
23. Schultheis PJ, Clarke LL, Meneton P, Miller ML, Soleimani M, Gawenis LR, et al. Renal and intestinal absorptive defects in mice lacking the NHE3 Na+/H+ exchanger. Nat Gent
24. Wang T, Yang CL, Abbiati T, Schultheis PJ, Shull GE, Giebisch G, Aronson PS. Mechanism of proximal tubule bicarbonate absorption in NHE3 null mice. Am J Physiol
25. Woo AL, Noonan WT, Schultheis PJ, Neumann JC, Manning PA, Lorenz JN, Shull GE. Renal function in NHE3-deficient mice with transgenic rescue of small intestinal absorptive defect. Am J Physiol Renal Physiol
26. Noonan WT, Woo AL, Nieman ML, Prasad V, Schultheis PJ, Shull GE, Lorenz JN. Blood pressure maintenance in NHE3-deficient mice with transgenic expression of NHE3 in small intestine. Am J Physiol Regul Integr Comp Physiol
27. Linz D, Wirth K, Linz W, Heuer HO, Frick W, Hofmeister A, et al. Antihypertensive and laxative effects by pharmacological inhibition of sodium-proton-exchanger subtype 3-mediated sodium absorption in the gut. Hypertension
28. Barfull A, Garriga C, Tauler A, Planas JM. Regulation of SGLT1 expression in response to Na+ intake. Am J Physiol Regul Integr Comp Physiol
29. Song P, Onishi A, Koepsell H, Vallon V. Sodium glucose cotransporter SGLT1 as a therapeutic target in diabetes mellitus. Expert Opin Ther Targets
30. Gorboulev V, Vallon SA, Kipp V, Jaschke H, Klessen A, Friedrich D, et al. Na(+)-D-glucose cotransporter SGLT1 is pivotal for intestinal glucose absorption and glucose-dependent incretin secretion. Diabetes
31. Malsure S, Wang Q, Charles RP, Sergi C, Perrier R, Christensen BM, et al. Colon-specific deletion of epithelial sodium channel causes sodium loss and aldosterone resistance. J Am Soc Nephrol
32. Jin XH, Wang ZQ, Siragy WZ, Guerrant HM, Carey RM. Regulation of jejunal sodium and water absorption by angiotensin subtype receptors. Am J Physiol
33. Girardi AC, Di Sole F. Deciphering the mechanisms of the Na+/H+ exchanger-3 regulation in organ dysfunction. Am J Physiol Cell Physiol
34. Musch MW, Li YC, Chang EB. Angiotensin II directly regulates intestinal epithelial NHE3 in Caco2BBE cells. BMC Physiol
35. Nishiyama A, Yoshizumi M, Rahman M, Kobori H, Seth DM, Miyatake A, et al. Effects of AT1 receptor blockade on renal injury and mitogen-activated protein activity in Dahl salt-sensitive rats. Kidney Int
36. Bayorh M, Ganafa AA, Emmett N, Socci RR, Eatman D, Fridie IL. Alterations in aldosterone and angiotensin II levels in salt-induced hypertension. Clin Exp Hypertens
37. Nishiyama A, Kobori H. Independent regulation of renin-angiotensin-aldosterone system in the kidney. Clin Exp Nephrol
38. Kobori H, Nishiyama A. Effects of tempol on renal angiotensinogen production in Dahl salt-sensitive rats. Biochem Biophys Res Commun
39. Gonzalez AA, Prieto MC. Renin and the (pro)renin receptor in the renal collecting duct: role in the pathogenesis of hypertension. Clin Exp Pharmacol Physiol
40. Nagata S, Kato J, Sasaki K, Minamino N, Eto T, Kitamura K. Isolation and identification of proangiotensin-12, a possible component of the renin-angiotensin system. Biochem Biophys Res Commun
41. Hatch M, Freel RW. Increased colonic sodium absorption in rats with chronic renal failure is partially mediated by AT1 receptor agonism. Am J Physiol Gastrointest Liver Physiol
42. Patten GS, Abeywardena MY. Effects of antihypertensive agents on intestinal contractility in the spontaneously hypertensive rat: angiotensin receptor system downregulation by losartan. J Pharmacol Exp Ther
43. Galletti F, Agabiti-Rosei E, Bernini G, Boero R, Desideri G, Fallo F, et al. MINISAL-GIRCSI Program Study Group. Excess dietary sodium and inadequate potassium intake by hypertensive patients in Italy: results of the MINISAL-SIIA study program. J Hypertens
44. Sarzani R, Guerra F, Mancinelli L, Buglioni A, Franchi E, Dessi-Fulgheri P. Plasma aldosterone is increased in class 2 and 3 obese essential hypertensive patients despite drug treatment. Am J Hypertens
45. Fujita T. Aldosterone in salt-sensitive hypertension and metabolic syndrome. J Mol Med
46. Zhu Z, Xiong S, Liu D. The Gastrointestinal Tract: an Initial Organ of Metabolic Hypertension? Cell Physiol Biochem
47. Frisoli TM, Schmieder RE, Grodzicki T, Messerli FH. Salt and hypertension: is salt dietary reduction worth the effort? Am J Med
48. Kario K. The sacubitril/valsartan, a first-in-class, angiotensin receptor neprilysin inhibitor (ARNI): potential uses in hypertension, heart failure, and beyond. Curr Cardiol Rep
49. Price DA, Fisher ND, Lansang MC, Stevanovic R, Williams GH, Hollenberg NK. Renal perfusion in blacks: alterations caused by insuppressibility of intrarenal renin with salt. Hypertension
50. Imanishi M, Okada N, Konishi Y, Morikawa T, Maeda I, Kitabayashi C, et al. Angiotensin II receptor blockade reduces salt sensitivity of blood pressure through restoration of renal nitric oxide synthesis in patients with diabetic nephropathy. J Renin Angiotensin Aldosterone Syst
51. Sasamura H, Nakaya H, Julius S, Tomotsugu N, Sato Y, Takahashi F, et al. STAR CAST investigators. Feasibility of regression of hypertension using contemporary antihypertensive agents. Am J Hypertens