Conditional knockout of collecting duct bradykinin B2 receptors exacerbates angiotensin II-induced hypertension during high salt intake

Cyp epoxygenase is responsible for metabolizing arachidonic acid to epoxyeicosatrienoic acid (EET) in the kidney and vascular tissues. EET has been shown to cause vasodilation by stimulating Ca 2+ -activated K channels in vascular smooth muscles and to have natriuretic effect by inhibiting the epithelial Na channel (ENaC) in the kidney. In the present study we used real time PCR technique to examine the effect of high salt intake or high K intake on Cyp2c44 (a major type of Cyp epoxygenase in the mouse kidney) in the proximal tubule (PxT), thick ascending limb (TAL), distal convoluted tubule (DCT) and the CNT/CCD. An increase in dietary Na content stimulates the expression of Cyp2c4 in TAL, DCT and CNT/CCD but not in PxT while an increase in dietary K intake augments the expression of Cyp2c44 only in DCT and CNT/CCD. Neither high salt intake nor high K intake has a significant effect on the blood pressure (BP) in wt mice. However, high K intake increased BP in CNT/CCD specific conditional knockout (KO) mice. In contrast, the high Na intake did not significantly increase the BP in those KO mice. This suggests that Cyp2c44 in the CNT/CCD plays a key role in preventing hypertension induced by increasing dietary K intake. Administration of amiloride (a ENaC inhibitor) restored the normal BP in KO mice fed high K diet, suggesting that down-regulation of Cyp2c44 may enhance the Na absorption in the CNT/CCD. This notion was also supported by metabolic cage study demonstrating that renal Na excretion was compromised in KO mice. We conclude that Cyp2c44 plays a key role in stimulating renal Na excretion during increasing dietary K intake and that Cyp-epoxygenase is required for antihypertensive effect induced by high K intake.

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Cyp2c44 epoxygenase in the collecting duct is essential for the high K+ intake-induced antihypertensive effect

AJP Renal Physiology ◽

10.1152/ajprenal.00123.2014 ◽

2014 ◽

Vol 307 (4) ◽

pp. F453-F460 ◽

Cited By ~ 13

Author(s):

Wen-Hui Wang ◽

Chengbiao Zhang ◽

Dao-Hong Lin ◽

Lijun Wang ◽

Joan P. Graves ◽

...

Keyword(s):

Salt Intake ◽

Collecting Duct ◽

Proximal Convoluted Tubule ◽

High Salt ◽

Conditional Knockout ◽

Thick Ascending Limb ◽

Real Time Quantitative Pcr ◽

High K ◽

High Salt Intake ◽

Cytochrome P 450

Cytochrome P-450, family 2, subfamily c, polypeptide 44 (Cyp2c44) epoxygenase metabolizes arachidonic acid (AA) to epoxyeicosatrienoic acids (EETs) in kidney and vascular tissues. In the present study, we used real-time quantitative PCR techniques to examine the effect of high salt or high K+ (HK) intake on the expression of Cyp2c44, a major Cyp2c epoxygenase in the mouse kidney. We detected Cyp2c44 in the proximal convoluted tubule, thick ascending limb, distal convoluted tubule (DCT)/connecting tubule (CNT), and collecting duct (CD). A high-salt diet increased the expression of Cyp2c44 in the thick ascending limb and DCT/CNT but not in the proximal convoluted tubule and CD. In contrast, an increase in dietary K+ intake augmented Cyp2c44 expression only in the DCT/CNT and CD. Neither high salt nor HK intake had a significant effect on the blood pressure (BP) of wild-type mice. However, HK but not high salt intake increased BP in CD-specific, Cyp2c44 conditional knockout (KO) mice. Amiloride, an epithelial Na+ channel (ENaC) inhibitor, normalized the BP of KO mice fed HK diets, suggesting that lack of Cyp2c44 in the CD enhances ENaC activity and increases Na+ absorption in KO mice fed HK diets. This notion was supported by metabolic cage experiments demonstrating that renal Na+ excretion was compromised in KO mice fed HK diets. Also, patch-clamp experiments demonstrated that 11,12-EET, a major Cyp2c44 product, but not AA inhibited ENaC activity in the cortical CD of KO mice. We conclude that Cyp2c44 in the CD is required for preventing the excessive Na+ absorption induced by HK intake by inhibition of ENaC and facilitating renal Na+ excretion.

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Hemodynamics, fluid volume, and hormonal responses to chronic high-salt intake in dogs

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1990.259.6.h1629 ◽

1990 ◽

Vol 259 (6) ◽

pp. H1629-H1636 ◽

Cited By ~ 18

Author(s):

J. E. Krieger ◽

J. F. Liard ◽

A. W. Cowley

Keyword(s):

Angiotensin Ii ◽

Salt Intake ◽

Peripheral Resistance ◽

Plasma Renin ◽

Total Body Weight ◽

High Salt ◽

Plasma Sodium ◽

Plasma Protein Concentration ◽

Hormonal Responses ◽

High Salt Intake

The sequential hemodynamics, fluid and electrolyte balances, and the hormonal responses to a 7-day high-salt (NaCl) intake were investigated in sodium-depleted conscious dogs (n = 6). Studies were carried out in metabolic cages mounted on sensitive load cells, which enabled continuous 24 h/day monitoring of total body weight (TBW) as an index of changes in body water. Beat-by-beat hemodynamics were determined 24 h/day. Water (700 ml/day iv) intake was maintained constant. Daily fluid and electrolyte balances and hormonal analyses were performed. An increase of daily salt intake from 8 to 120 meq increased TBW 251 +/- 44 g (P less than 0.05), which was sustained thereafter. Average 24-h mean arterial pressure (MAP) and heart rate (HR) remained unchanged. Average cardiac output (CO) increased 11% (P less than 0.05) above control values by day 2, while total peripheral resistance (TPR) decreased proportionally. CO and TPR returned to control values only when low salt was resumed. Blood volume (BV) was unchanged on day 2 as indicated by direct measurement of BV (51Cr-labeled red blood cells) or by analysis of plasma protein concentration. A 92-meq (P less than 0.05) sodium retention was observed initially, and plasma sodium concentration increased slightly. Plasma renin activity, angiotensin II, and aldosterone levels decreased significantly, whereas vasopressin and atrial natriuretic peptide levels remained unchanged. In summary, chronic high-salt intake resulted in a net retention of water and sodium with no changes in MAP, HR, or BV. The rise in CO was offset by a reduction in TPR, which appeared at least in part related to angiotensin II suppression.

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Central and peripheral slow-pressor mechanisms contributing to Angiotensin II-salt hypertension in rats

Cardiovascular Research ◽

10.1093/cvr/cvx214 ◽

2017 ◽

Vol 114 (2) ◽

pp. 233-246 ◽

Cited By ~ 11

Author(s):

Jiao Lu ◽

Hong-Wei Wang ◽

Monir Ahmad ◽

Marzieh Keshtkar-Jahromi ◽

Mordecai P Blaustein ◽

...

Keyword(s):

Angiotensin Ii ◽

Adrenal Cortex ◽

Salt Intake ◽

Plasma Corticosterone ◽

High Salt ◽

Ang Ii ◽

Intracerebroventricular Infusion ◽

High Salt Intake ◽

Endogenous Ouabain ◽

Salt Hypertension

AbstractAimsHigh salt intake markedly enhances hypertension induced by angiotensin II (Ang II). We explored central and peripheral slow-pressor mechanisms which may be activated by Ang II and salt.Methods and resultsIn protocol I, Wistar rats were infused subcutaneously with low-dose Ang II (150 ng/kg/min) and fed regular (0.4%) or high salt (2%) diet for 14 days. In protocol II, Ang II-high salt was combined with intracerebroventricular infusion of mineralocorticoid receptor (MR) blockers (eplerenone, spironolactone), epithelial sodium channel (ENaC) blocker (benzamil), angiotensin II type 1 receptor (AT1R) blocker (losartan) or vehicles. Ang II alone raised mean arterial pressure (MAP) ∼10 mmHg, but Ang II-high salt increased MAP ∼50 mmHg. Ang II-high salt elevated plasma corticosterone, aldosterone and endogenous ouabain but not Ang II alone. Both Ang II alone and Ang II-high salt increased mRNA and protein expression of CYP11B2 (aldosterone synthase gene) in the adrenal cortex but not of CYP11B1 (11-β-hydroxylase gene). In the aorta, Ang II-high salt increased sodium-calcium exchanger-1 (NCX1) protein. The Ang II-high salt induced increase in MAP was largely prevented by central infusion of MR blockers, benzamil or losartan. Central blockades significantly lowered plasma aldosterone and endogenous ouabain and markedly decreased Ang II-high salt induced CYP11B2 mRNA expression in the adrenal cortex and NCX1 protein in the aorta.ConclusionThese results suggest that in Ang II-high salt hypertension, MR-ENaC-AT1R signalling in the brain increases circulating aldosterone and endogenous ouabain, and arterial NCX1. These factors can amplify blood pressure responses to centrally-induced sympatho-excitation and thereby contribute to severe hypertension.

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Role of central nervous system aldosterone synthase and mineralocorticoid receptors in salt-induced hypertension in Dahl salt-sensitive rats

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.90903.2008 ◽

2009 ◽

Vol 296 (4) ◽

pp. R994-R1000 ◽

Cited By ~ 66

Author(s):

Bing S. Huang ◽

Roselyn A. White ◽

Arco Y. Jeng ◽

Frans H. H. Leenen

Keyword(s):

Salt Intake ◽

High Salt ◽

High Salt Diet ◽

Salt Diet ◽

Aldosterone Synthase ◽

High Salt Intake ◽

Induced Hypertension ◽

Synthase Inhibitor ◽

The Brain

In Dahl salt-sensitive (S) rats, high salt intake increases cerebrospinal fluid (CSF) Na+ concentration ([Na+]) and blood pressure (BP). Intracerebroventricular (ICV) infusion of a mineralocorticoid receptor (MR) blocker prevents the hypertension. To assess the role of aldosterone locally produced in the brain, we evaluated the effects of chronic central blockade with the aldosterone synthase inhibitor FAD286 and the MR blocker spironolactone on changes in aldosterone and corticosterone content in the hypothalamus and the increase in CSF [Na+] and hypertension induced by high salt intake in Dahl S rats. After 4 wk of high salt intake, plasma aldosterone and corticosterone were not changed, but hypothalamic aldosterone increased by ∼35% and corticosterone tended to increase in Dahl S rats, whereas both steroids decreased by ∼65% in Dahl salt-resistant rats. In Dahl S rats fed the high-salt diet, ICV infusion of FAD286 or spironolactone did not affect the increase in CSF [Na+]. ICV infusion of FAD286 prevented the increase in hypothalamic aldosterone and 30 mmHg of the 50-mmHg BP increase induced by high salt intake. ICV infusion of spironolactone fully prevented the salt-induced hypertension. These results suggest that, in Dahl S rats, high salt intake increases aldosterone synthesis in the hypothalamus and aldosterone acts as the main MR agonist activating central pathways contributing to salt-induced hypertension.

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High-Salt Intake Induces Cardiomyocyte Hypertrophy in Rats in Response to Local Angiotensin II Type 1 Receptor Activation

Journal of Nutrition ◽

10.3945/jn.114.192054 ◽

2014 ◽

Vol 144 (10) ◽

pp. 1571-1578 ◽

Cited By ~ 17

Author(s):

Isis A. Katayama ◽

Rafael C. Pereira ◽

Ellen P. B. Dopona ◽

Maria H. M. Shimizu ◽

Luzia N. S. Furukawa ◽

...

Keyword(s):

Angiotensin Ii ◽

Salt Intake ◽

Receptor Activation ◽

High Salt ◽

Cardiomyocyte Hypertrophy ◽

High Salt Intake

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Chronic clofibrate administration prevents salineinduced endothelial dysfunction and oxidative stress in young Sprague-Dawley rats

Clinical & Investigative Medicine ◽

10.25011/cim.v31i2.3365 ◽

2008 ◽

Vol 31 (2) ◽

pp. 62 ◽

Cited By ~ 3

Author(s):

Sowndramalingam Sankaralingam ◽

Kaushik M Desai ◽

Thomas W Wilson

Keyword(s):

Oxidative Stress ◽

Endothelial Dysfunction ◽

Salt Intake ◽

High Salt ◽

Sprague Dawley ◽

Sprague Dawley Rats ◽

High Salt Intake ◽

Induced Hypertension ◽

And Oxidative Stress ◽

Hypotensive Response

Purpose: High salt intake causes hypertension and endothelial dysfunction in young Sprague-Dawley rats. Clofibrate (clof) prevents this salt induced hypertension. We asked whether clof can prevent salt-induced endothelial dysfunction, and if so, its mechanism. We also questioned whether high salt intake can induce endothelial dysfunction without hypertension in older animals. Methods: Young (Y, 5 weeks) and old (O, 53 weeks) male Sprague-Dawley rats were given either vehicle (Con, 20 mM Na2CO3) or 0.9% NaCl (Sal) to drink for three weeks. Some young rats received clof (80 mg/d) in their drinking fluid. After three weeks, we measured mean arterial pressure (MAP), endothelial function, by comparing hypotensive responses to acetylcholine (ACh, endothelium dependent) and sodium nitroprusside (SNP, endothelium independent), plasma total nitrite+nitrate levels (PNOx), by the Griess reaction, and aortic superoxide production by lucigenin chemiluminescence. Results: Carotid artery MAP did not change in O. Sal-Y developed hypertension: 133±3 vs. 114±2 mmHg, P < 0.001, which was prevented by clof: 105±2 mmHg. ACh induced a similar dose dependent hypotensive response in Con-O and Sal-O that was inhibited by L-NAME (100mg/kg i.v.). Responses to ACh were blunted in Sal-Y but not in Con-Y. Further, L-NAME inhibited ACh responses only in Con-Y. The response to SNP was similar in all animals. Importantly, the ACh-induced hypotensive response was potentiated in clof+Sal-Y, an effect which was attenuated by blocking calcium-activated potassium channels (KCa) with a combination of apamin (50 ug/kg i.v.) + charybdotoxin (50 ug/kg i.v.), but not by L-NAME. PNOx was reduced in Sal-Y compared to Con-Y (2.09±0.26 vs. 4.8±0.35 µM, P < 0.001), but not in Sal-O. Aortic superoxide production was higher (P < 0.001) in Sal-Y (2388±40 milliunits/mg/min) than Sal-O (1107±159 milliunits/mg/min), but was reduced by clof (1378±64 milliunits/mg/min; P < 0.001). Conclusions: High salt intake increases oxidative stress in young animals, leading to impaired nitric oxide activity and endothelial dysfunction. Clofibrate prevents endothelial dysfunction partly through reduced O2?- formation but mainly via selective activation of KCa channels. Older animals are resistant to both salt induced hypertension and oxidative stress.

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