High salt differentially regulates surface NKCC2 expression in thick ascending limbs of Dahl salt-sensitive and salt-resistant rats

NaCl reabsorption by the thick ascending limb of the loop of Henle (THAL) occurs via the apical Na-K-2Cl cotransporter, NKCC2. Overall, NKCC2 activity and NaCl reabsorption are regulated by the amount of NKCC2 at the apical surface, and also by phosphorylation. Dahl salt-sensitive rats (SS) exhibit higher NaCl reabsorption by the THAL compared with Dahl salt-resistant rats (SR), and they become hypertensive during high-salt (HS) intake. However, the effect of HS on THAL transport, surface NKCC2 expression, and NKCC2 NH(2)-terminus phosphorylation has not been studied. We hypothesized that HS enhances surface NKCC2 and its phosphorylation in THALs from Dahl SS. THAL suspensions were obtained from a group of SS and SR rats on normal-salt (NS) or HS intake. In SR rats THAL NaCl transport measured as furosemide-sensitive oxygen consumption was decreased by HS (-34%, P < 0.05). In contrast, HS did not affect THAL transport in SS rats. As expected, HS increased systolic blood pressure only in SS rats (Δ 23 ± 2 mmHg, P < 0.002) but not in SR rats (Δ 5 ± 3 mmHg). We next tested the effect of HS intake on apical surface NKCC2 and its NH(2)-terminus threonine phosphorylation (P-NKCC2) in SS and SR rats. HS intake decreased surface NKCC2 by 15 ± 2% (P < 0.03) in THALs from SR without affecting total NKCC2 or NH(2)-terminus P-NKCC2. In contrast, in SS rats HS intake increased surface NKCC2 by 54 ± 6% (P < 0.01) without affecting total NKCC2 expression or P-NKCC2. We conclude that HS intake causes different effects on surface NKCC2 in SS and SR rats. Our data suggest that enhanced surface NKCC2 in SS rats might contribute to enhanced NaCl reabsorption in SS rats during HS intake.     

High dietary cholecalciferol increases plasma 25-hydroxycholecalciferol concentration, but does not attenuate the hypertension of Dahl salt-sensitive rats fed a high salt diet

The Dahl salt-sensitive rat, a model for salt-induced hypertension, develops hypovitaminosis D during high salt intake, which is caused by loss of protein-bound vitamin D metabolites into urine. We tested the hypothesis that high dietary cholecalciferol (5- and 10-fold standard) would increase plasma 25-hydroxycholecalciferol (25-OHD(3)) concentration (indicator of vitamin D status) of salt-sensitive rats during high salt intake. Salt-sensitive rats were fed 0.3% salt (low salt, LS), 3% salt (HS), 3% salt and 7.5 microg cholecalciferol/d (HS-D5), or 3% salt and 15 microg cholecalciferol/d (HS-D10) and sacrificed at week 4. Plasma 25-OHD(3) concentrations of the two groups of HS-D rats were similar to that of LS rats and more than twice that of HS rats. Urinary cholecalciferol metabolite content of HS-D rats was more than seven times that of HS rats. Systolic blood pressures of the hypertensive HS and HS-D rats did not significantly differ, whereas LS rats were not hypertensive. We conclude that high dietary cholecalciferol increases plasma 25-OHD(3) concentration, but does not attenuate the hypertension of salt-sensitive rats during high salt intake. Low salt intake may be necessary to both maintain optimal vitamin D status and prevent hypertension in salt-sensitive individuals.     

胍丁胺对Dahl盐敏感型高血压大鼠和Dahl盐抵抗型大鼠血流动力学的影响

在麻醉Dahl盐敏感型(DS)高血压大鼠和Dahl盐抵抗型(DR)正常血压大鼠,研究了静注胍丁胺(agmatine,AGM)对血流动力学的影响.结果显示(1)静注AGM(1,10,20mg/kg)可剂量依赖性地降低DS和DR大鼠的HR,MAP,LVP,±LVdp/dtmax,CI和TPRI.在DS高血压大鼠,MAP,LVP,±LVdp/dtmax和TPRI较DR正常血压大鼠下降幅度要大;而HR和CI在两种大鼠下降幅度无差异.需特别提出的是,DS高血压大鼠在静注高剂量AGM(20mg/kg)后,各项血流动力学指标出现先降低而后升高的现象,这一结果在DR正常血压大鼠并未出现.(2)预先静注咪唑啉受体(IR)和α2-肾上腺素能受体阻断剂(α2-AR)idazoxan(2.5mg/kg)可部分阻抑AGM的血流动力学效应.(3)预先静注α2-肾上腺素能受体阻断剂yohimbine(4mg/kg)同样可部分阻抑AGM的效应.(4)预先静注咪唑啉受体(I1)和α2-肾上腺素能受体阻断剂efaroxan(2.5mg/kg)则完全阻断AGM的血流动力学效应.以上结果表明,AGM可显著降低麻醉DR和DS大鼠的HR,MAP,LVP,±LVdp/dtmax,CI和TPRI;此效应似主要由I1-IR所介导,并有I2-IR和α2-AR参与.     

Mechanisms of pressure-diuresis and pressure-natriuresis in Dahl salt-resistant and Dahl salt-sensitive rats

ABSTRACT: BACKGROUND: Data on blood flow regulation, renal filtration, and urine output in salt-sensitive Dahl S rats fed on high-salt (hypertensive) and low-salt (prehypertensive) diets and salt-resistant Dahl R rats fed on high-salt diets were analyzed using a mathematical model of renal blood flow regulation, glomerular filtration, and solute transport in a nephron. RESULTS: The mechanism of pressure-diuresis and pressure-natriuresis that emerges from simulation of the integrated systems is that relatively small increases in glomerular filtration that follow from increases in renal arterial pressure cause relatively large increases in urine and sodium output. Furthermore, analysis reveals the minimal differences between the experimental cases necessary to explain the observed data. It is determined that differences in renal afferent and efferent arterial resistance are able to explain all of the qualitative differences in observed flows, filtration rates, and glomerular pressure as well as the differences in the pressure-natriuresis and pressure-diuresis relationships in the three groups. The model is able to satisfactorily explain data from all three groups without varying parameters associated with glomerular filtration or solute transport in the nephron component of the model. CONCLUSIONS: Thus the differences between the experimental groups are explained solely in terms of difference in blood flow regulation. This finding is consistent with the hypothesis that, if a shift in the pressure-natriuresis relationship is the primary cause of elevated arterial pressure in the Dahl S rat, then alternation in how renal afferent and efferent arterial resistances are regulated represents the primary cause of chronic hypertension in the Dahl S rat.     

Plasma 24,25-dihydroxyvitamin D concentration of Dahl salt-sensitive rats decreases during high salt intake

Dahl salt-sensitive rats, but not salt-resistant rats, develop hypertension in response to high salt intake. We have previously shown an inverse relationship between plasma 25-hydroxyvitamin D (25-OHD) concentration and blood pressure of Dahl salt-sensitive rats during high salt intake. In this study, we report on the relationship between high salt intake and plasma 24,25-dihydroxyvitamin D (24,25-(OH)(2)D) concentration of Dahl salt-sensitive and salt-resistant rats. Rats were fed a high salt diet (8%) and sacrificed at day 2, 7, 14, 21, and 28. Plasma 24,25-(OH)(2)D concentrations of salt-sensitive rats were reduced to 50% of that at baseline at day 2-when blood pressure and plasma 25-OHD concentration were unchanged, but 25-OHD content in the kidney was 81% of that at baseline. Plasma 24,25-(OH)(2)D concentration was reduced further to 10% of that at baseline from day 7 to 14 of high salt intake, a reduction that was prevented in rats switched to a low salt (0.3%) diet at day 7. Exogenous 24,25-dihydroxycholecalciferol (24,25-(OH)(2)D(3)), administered at a level that increased plasma 24,25-(OH)(2)D concentration to five times normal, did not attenuate the salt-induced hypertension of salt-sensitive rats. Plasma 24,25-(OH)(2)D concentration of salt-resistant rats was gradually reduced to 50% of that at baseline at day 14 and returned to baseline value at day 28 of high salt intake. We conclude that the decrease in plasma 24,25-(OH)(2)D concentration in salt-sensitive rats during high salt intake is caused by decreased 25-OHD content in the kidney and also by another unidentified mechanism.     

Angiotensin converting enzyme inhibition in Dahl salt-sensitive rats

Angiotensin II has previously been reported to have in vivo and in vitro cardiac hypertrophic effects. We used the salt-sensitive Dahl rat genetic strain to separate mechanical (pressure overload) vs. hormonal (renin-angiotensin system) input in cardiac hypertrophy. Blood pressure was significantly increased and left ventricular hypertrophy, as indexed by LV/BW ratios, was present at 7 and 15 days in rats receiving 4% and 8% NaCl compared to the 1% controls. There was no effect of the angiotensin converting enzyme inhibitor, enalapril maleate, on lowering the blood pressure in 8% NaCl-treated animals, however, there was a significant reduction in LV/BW ratio in 8% NaCl-treated animals that received this drug. Left ventricular angiotensinogen mRNA activity was significantly reduced in rats receiving 4% and 8% NaCl. In this model of hypertension the cardiac hypertrophy which develops is largely dependent on mechanical forces though there remains a significant contribution to this process from either circulating or localized angiotensin II production. Regulation of angiotensinogen gene expression in the hypertrophied left ventricle suggests that volume and electrolyte control of angiotensinogen gene expression in the heart and/or hereditary factors are predominant in the control of regulation of this gene in the left ventricle of Dahl rats.     

Genetic and dietary salt contributors to insulin resistance in Dahl salt-sensitive (S) rats

There has in recent years been great concern about possible cardiac side effects of thiazolidinediones (TZDs). We present a case-report of a 60 year-old male who developed significant mitral regurgitation during six months treatment with pioglitazone in parallel with laboratory indications of fluid retention. Echocardiography six months after discontinuation of medication showed regression of mitral regurgitation and the laboratory parameters were also normalized. It is noteworthy that six months treatment with pioglitazone could induce significant valve dysfunction, which was reversible, and this underlines the importance of carefully monitoring patients when placing them on treatment with TZDs.     

Altered element concentrations in tissues of Dahl salt-sensitive rats

It is recognized that the development of hypertension in Dahl salt-sensitive (DS) rats as compared to Dahl salt-resistant (DR) rats is dependent on the addition of a high percentage of sodium chloride, often 8% to the diet. In this work, blood systolic pressure and the concentrations of many elements in different tissues of DS and DR rats were measured. However, to distinguish the modifications linked to the strain from the modifications owing to excess of sodium intake, no additional Na was included in the diet in all our experiments. Without any addition of sodium chloride to the diet, a statistically significant increase of the systolic blood pressure of DS rats (152±10 mmHg) in comparison to DR rats (131 +/? 3 mmHg) was observed. The analysis of the concentrations of many elements in different tissues showed no major modifications of sodium concentrations in DS rats as compared to DR rats, but a decrease of calcium in plasma (?9%), brain (?20%), and heart (?7%) and of magnesium in plasma (?13%), kidney (?11%), and bone (?7%). In conclusion, an increased intake of Na is not necessary to obtain a higher systolic blood pressure in DS rats compared to DR rats. Since we did not find noticeable modifications of Na concentration in tissues but modifications of Ca and Mg, we suggest that an alteration of the homeostasis of these two elements may be involved in the development of the hypertension in DS rats.     

Rosiglitazone reduces blood pressure in female Dahl salt-sensitive rats

Postmenopausal women (PMW) are at greater risk for salt-sensitive hypertension and insulin resistance than premenopausal women. Peroxisome-proliferator-activated receptor-gamma (PPARγ) agonists reduce blood pressure (BP) and insulin resistance in humans. As in PMW, ovariectomy (OVX) increases salt sensitivity of BP and body weight in Dahl salt-sensitive (DS) rats. This study addressed whether rosiglitazone (ROSI), a PPARγ agonist, attenuates salt-sensitive hypertension in intact (INT) and OVX DS rats, and if so, whether insulin resistance, nitric oxide (NO), oxidative stress, and/or renal inflammation were contributing mediators. Telemetric BP was similar in OVX and INT on low salt diet (0.3% NaCl), but was higher in OVX than INT on high salt (8% NaCl). ROSI reduced BP in OVX and INT on both low and high salt diet, but only attenuated salt sensitivity of BP in OVX. Nitrate/nitrite excretion (NO_x; index of NO) was similar in INT and OVX on low salt diet, and ROSI increased NO_x in both groups. High salt diet increased NO_x in all groups but ROSI only increased NO_x in OVX rats. OVX females exhibited insulin resistance, increases in body weight, plasma leptin, cholesterol, numbers of renal cortical macrophages, and renal MCP-1 and osteopontin mRNA expression compared to INT. ROSI reduced cholesterol and macrophage infiltration in OVX, but not INT. In summary, PPARγ activation reduces BP in INT and OVX females, but attenuates the salt sensitivity of BP in OVX only, likely due to increases in NO and in part to reductions in renal resident macrophages and inflammation.     

Central infusion of aliskiren prevents sympathetic hyperactivity and hypertension in Dahl salt-sensitive rats on high salt intake

Central infusion of an angiotensin type 1 (AT(1)) receptor blocker prevents sympathetic hyperactivity and hypertension in Dahl salt-sensitive (S) rats on high salt. In the present study, we examined whether central infusion of a direct renin inhibitor exerts similar effects. Intracerebroventricular infusion of aliskiren at the rate of 0.05 mg/day markedly inhibited the increase in ANG II levels in the cerebrospinal fluid and in blood pressure (BP) caused by intracerebroventricular infusion of rat renin. In Dahl S rats on high salt, intracerebroventricular infusion of aliskiren at 0.05 and 0.25 mg/day for 2 wk similarly decreased resting BP in Dahl S rats on high salt. In other groups of Dahl S rats, high salt intake for 2 wk increased resting BP by ～25 mmHg, enhanced pressor and sympathoexcitatory responses to air-stress, and desensitized arterial baroreflex function. All of these effects were largely prevented by intracerebroventricular infusion of aliskiren at 0.05 mg/day. Aliskiren had no effects in rats on regular salt. Neither high salt nor aliskiren affected hypothalamic ANG II content. These results indicate that intracerebroventricular infusions of aliskiren and an AT(1) receptor blocker are similarly effective in preventing salt-induced sympathetic hyperactivity and hypertension in Dahl S rats, suggesting that renin in the brain plays an essential role in the salt-induced hypertension. The absence of an obvious increase in hypothalamic ANG II by high salt, or decrease in ANG II by aliskiren, suggests that tissue levels do not reflect renin-dependent ANG II production in sympathoexcitatory angiotensinergic neurons.     

Renal medullary endothelin-1 is decreased in Dahl salt-sensitive rats

Although it is well established that the renal endothelin (ET-1) system plays an important role in regulating sodium excretion and blood pressure through activation of renal medullary ET(B) receptors, the role of this system in Dahl salt-sensitive (DS) hypertension is unclear. The purpose of this study was to determine whether the DS rat has abnormalities in the renal medullary endothelin system when maintained on a high sodium intake. The data indicate that Dahl salt-resistant rats (DR) on a high-salt diet had a six-fold higher urinary endothelin excretion than in the DR rats with low Na(+) intake (17.8 ± 4 pg/day vs. 112 ± 44 pg/day). In sharp contrast, urinary endothelin levels increased only twofold in DS rats in response to a high Na(+) intake (13 ± 2 pg/day vs. 29.8 ± 5.5 pg/day). Medullary endothelin concentration in DS rats on a high-Na(+) diet was also significantly lower than DR rats on a high-Na(+) diet (31 ± 2.8 pg/mg vs. 70.9 ± 5 pg/mg). Furthermore, DS rats had a significant reduction in medullary ET(B) receptor expression compared with DR rats while on a high-Na(+) diet. Finally, chronic infusion of ET-1 directly into the renal medulla blunted Dahl salt-sensitive hypertension. These data indicate that a decrease in medullary production of ET-1 in the DS rat could play an important role in the development of salt-sensitive hypertension observed in the DS rat.     

Renal NF-kappaB activation and TNF-alpha upregulation correlate with salt-sensitive hypertension in Dahl salt-sensitive rats

Molecular mechanisms of salt-sensitive (SS) hypertension related to renal inflammation have not been defined. We seek to determine whether a high-salt (HS) diet induces renal activation of NF-kappaB and upregulation of TNF-alpha related to the development of hypertension in Dahl SS rats. Six 8-wk-old male Dahl SS rats received a HS diet (4%), and six Dahl SS rats received a low-sodium diet (LS, 0.3%) for 5 wk. In the end, mean arterial pressure was determined in conscious rats by continuous monitoring through a catheter placed in the carotid artery. Mean arterial pressure was significantly higher in the HS than the LS group (177.9 +/- 3.7 vs. 109.4 +/- 2.9 mmHg, P < 0.001). There was a significant increase in urinary albumin secretion in the HS group compared with the LS group (22.3 +/- 2.6 vs. 6.1 +/- 0.7 mg/day; P < 0.001). Electrophoretic mobility shift assay demonstrated that the binding activity of NF-kappaB p65 proteins in the kidneys of Dahl SS rats was significantly increased by 53% in the HS group compared with the LS group (P = 0.007). ELISA indicated that renal protein levels of TNF-alpha, but not IL-6, interferon-gamma, and CCL28, were significantly higher in the HS than the LS group (2.3 +/- 0.8 vs. 0.7 +/- 0.2 pg/mg; P = 0.036). We demonstrated that plasma levels of TNF-alpha were significantly increased by fivefold in Dahl SS rats on a HS diet compared with a LS diet. Also, we found that increased physiologically relevant sodium concentration (10 mmol/l) directly stimulated NF-kappaB activation in cultured human renal proximal tubular epithelial cells. These findings support the hypothesis that activation of NF-kappaB and upregulation of TNF-alpha are the important renal mechanisms linking proinflammatory response to SS hypertension.     

Elevated atrial natriuretic polypeptide in plasma of hypertensive Dahl salt-sensitive rats

The relationship between circulating atrial natriuretic polypeptide (ANP) and blood pressure was studied in inbred Dahl salt-sensitive (S) and inbred Dahl salt-resistant (R) rats. Two month old S and R rats raised on normal rat chow had only small differences in blood pressure and no difference in plasma ANP levels. In contrast, when 6-month-old rats also raised on normal chow were studied, S had markedly elevated blood pressure and a 4 fold increase in plasma ANP compared to R. Similar strain differences in blood pressure and plasma ANP could be induced in young rats by feeding them diets high in salt. In six week old S and R rats which had been fed high salt diet for 3 weeks the S rats showed higher blood pressure and plasma ANP than R rats. The high plasma ANP levels seen in the hypertensive S rats were interpreted to be a response to hypertension and not a cause of hypertension. There was no qualitative strain difference in the plasma ANP molecule as assessed by reverse phase high pressure liquid chromatography.     

Maternal obesogenic diet combined with postnatal exposure to high-fat diet induces metabolic alterations in offspring

Maternal obesity has been shown to impact the offspring health during childhood and adult life. This study aimed to evaluate whether maternal obesity combined with postnatal exposure to an obesogenic diet could induce metabolic alterations in offspring. Female CD1 mice were fed a control diet (CD, 11.1% of energy from fat) or with a high-fat diet (HFD, 44.3% of energy from fat) for 3 months. After weaning, pups born from control and obese mothers were fed with CD or HFD for 3 months. Both mothers and offspring were weighted weekly and several blood metabolic parameters levels were evaluated. Here, we present evidence that the offspring from mothers exposed to a HFD showed increased acetylation levels of histone 3 on lysine 9 (H3K9) in the liver at postnatal Day 1, whereas the levels of acetylation of H4K16, dimethylation of H3K27, and trimethylation of H3K9 showed no change. We also observed a higher perinatal weight and increased blood cholesterol levels when compared to the offspring on postnatal Day 1 born from CD-fed mothers. When mice born from obese mothers were fed with HFD, we observed that they gained more weight, presented higher blood cholesterol levels, and abdominal adipose tissue than mice born to the same mothers but fed with CD. Collectively, our results point toward maternal obesity and HFD consumption as a risk factor for epigenetic changes in the liver of the offspring, higher perinatal weight, increased weight gain, and altered blood cholesterol levels.     

Superoxide dismutase and oxidative stress in Dahl salt-sensitive and -resistant rats

The roles of oxidative stress and renal superoxide dismutase (SOD) levels and their association with renal damage were studied in Dahl salt-sensitive (S) and salt-resistant (R)/Rapp strain rats during changes in Na intake. After 3 wk of a high (8%)-Na diet in S rats, renal medullary Cu/Zn SOD was 56% lower and Mn SOD was 81% lower than in R high Na-fed rats. After 1, 2, and 3 wk of high Na, urinary excretion of F(2)-isoprostanes, an index of oxidative stress, was significantly greater in S rats compared with R rats. Plasma F(2)-isoprostane concentration increased in the 2-wk S high Na-fed group. After 3 wk, renal cortical and medullary superoxide production was significantly increased in Dahl S rats on high Na intake, and urinary protein excretion, an index of renal damage, was 273 +/- 32 mg/d in S high Na-fed rats and 35 +/- 4 mg/d in R high Na-fed rats (P < 0.05). In conclusion, salt-sensitive hypertension in the S rat is accompanied by marked decreases in renal medullary SOD and greater renal oxidative stress and renal damage than in R rats.     

Effects of tempol on renal angiotensinogen production in Dahl salt-sensitive rats

We have recently reported that Dahl salt-sensitive rats (DS) on high salt diet (HS) have an inappropriate augmentation of intrarenal angiotensinogen. Recent studies also reported that the augmented superoxide anion formation plays important roles in this animal model of hypertension. This study was performed to address the hypothesis that an inappropriate augmentation of intrarenal angiotensinogen by HS is caused by the augmented reactive oxygen species. Male DS (200-220 g) were maintained on low salt diet LS (N = 7) or HS (N = 27) for 4 weeks. The HS group was subdivided into three subgroups to receive null (N = 12), superoxide dismutase mimetic, tempol (3 mmol/l, N = 8), or vasodilator, hydralazine (0.5 mmol/l, N = 7) in drinking water during the period. Systolic BP was significantly increased in the DS+HS group compared to the DS+LS group (184+/-7 mmHg vs. 107+/-5 at 4-week). Tempol or hydralazine treatment equivalently attenuated the hypertension (128+/-3 and 127+/-5 at 4-week, respectively). Urinary excretion of thiobarbituric acid reactive substances at 4-week was significantly increased in the DS+HS group compared to the DS+LS group (0.66+/-0.05 micromol/day vs. 0.14+/-0.01). Tempol treatment prevented this effect (0.24+/-0.04) but hydralazine treatment only partially prevented the effect (0.40+/-0.03). Kidney angiotensinogen levels, measured by Western blot analysis, were significantly increased in the DS+HS group compared to the DS+LS group (32+/-5 densitometric units vs. 21+/-1). Tempol (14+/-3) but not hydralazine (32+/-5) treatment prevented the intrarenal angiotensinogen augmentation. The evidence suggests that the enhanced intrarenal angiotensinogen in DS challenged with HS is associated with the augmented reactive oxygen species.     

Myocardial cross-bridge kinetics in transition to failure in Dahl salt-sensitive rats

The role of altered cross-bridge kinetics during the transition from cardiac hypertrophy to failure is poorly defined. We examined this in Dahl salt-sensitive (DS) rats, which develop hypertrophy and failure when fed a high-salt diet (HS). DS rats fed a low-salt diet were controls. Serial echocardiography disclosed compensated hypertrophy at 6 wk of HS, followed by progressive dilatation and impaired function. Mechanical properties of skinned left ventricular papillary muscle strips were analyzed at 6 wk of HS and then during failure (12 wk HS) by applying small amplitude (0.125%) length perturbations over a range of calcium concentrations. No differences in isometric tension-calcium relations or cross-bridge cycling kinetics or mechanical function were found at 6 wk. In contrast, 12 wk HS strips exhibited increased calcium sensitivity of isometric tension, decreased frequency of minimal dynamic stiffness, and a decreased range of frequencies over which cross bridges produce work and power. Thus the transition from hypertrophy to heart failure in DS rats is characterized by major changes in cross-bridge cycling kinetics and mechanical performance.     

Structural differences in the renin gene of Dahl salt-sensitive and salt-resistant rats

Genomic libraries in lambda EMBL4 phage were constructed from both inbred Dahl salt-hypertension-sensitive (S) and inbred Dahl salt-hypertension-resistant (R) rats. Overlapping clones containing the renin genes were isolated from these libraries by screening with a renin cDNA probe. Clones were characterized by a combination of restriction mapping and Southern blot analysis. The results showed that the S-rat renin gene is remarkably different from the R-rat renin gene. The major differences are 1) a 1.2-kilobase (kb) insertion in the first intron of the S-gene which accounts for most of the restriction fragment length polymorphisms found in the renin genes between S and R strains, such as those generated with Bg/II [2.7 kb (S)/1.5 kb (R)], EcoRI [6.4 kb (S)/5.2 kb (R)], and HindIII [9.6 kb (S)/8.4 kb (R)]; 2) an additional HindIII site located at the 3' end of the R-gene which accounts for another HindIII restriction fragment length polymorphisms [25 kb (S)/22 kb, 3.4 kb (R)]; 3) two SmaI sites at the 5' flanking region of the first exon of the S-gene, whereas there is only one SmaI site in the corresponding region of the R-gene; and 4) three AvaI sites in the first intron of the S-gene in contrast to two AvaI sites in the same region of the R-gene These differences in the renin genes of Dahl rats might affect renin gene expression, which could account for the known strain differences in plasma and tissue renin activities. These structural studies provide a basis for genetic investigation into the relationship of the renin gene to blood pressure in Dahl rats.