Angiotensin II-Induced Hypertension Is Associated with a Selective Inhibition of Endothelium-Derived Hyperpolarizing Factor-Mediated Responses in the Rat Mesenteric Artery

Département de Pharmacologie et Physicochimie, Unité Mixte de Recherche 7175 Centre National de Recherche Scientifique/Université Louis Pasteur (Strasbourg I), Faculté de Pharmacie 74, Illkirch, France.
Journal of Pharmacology and Experimental Therapeutics (Impact Factor: 3.86). 12/2008; 328(2):478-86. DOI: 10.1124/jpet.108.145326
Source: PubMed

ABSTRACT Hypertension has been shown to be associated with impaired endothelium-derived hyperpolarizing factor (EDHF)-mediated arterial relaxation and hyperpolarization. Treatments of hypertensive rats with inhibitors of the renin-angiotensin system have been shown to restore both EDHF-mediated responses and the expression of connexins involved in the intercellular transfer of the hyperpolarization in mesenteric arteries. The present study was designed to determine whether chronic treatment of rats with angiotensin II impairs EDHF-mediated responses and the expression of connexins in the mesenteric arterial wall. Male Wistar rats were treated with angiotensin II (0.4 mg/kg/day) for 21 days using osmotic minipumps. Arterial pressure was measured by tail-cuff plethysmography. Contractile responses and membrane potential were measured in isolated mesenteric arteries. The expression of the three connexins (Cxs), Cx37, Cx40, and Cx43, was quantified in segments of mesenteric arteries by immunohistochemistry and quantitative real-time reverse transcriptase-polymerase chain reaction. Angiotensin II administration increased the mean systolic blood pressure. EDHF-mediated relaxation and hyperpolarization to acetylcholine and red wine polyphenols were significantly impaired in mesenteric arteries from angiotensin II-treated rats in comparison with control animals, whereas nitric oxide-mediated relaxation was unaltered. The expression of connexins Cx37, Cx40, and Cx43 was significantly decreased in the mesenteric artery from angiotensin II-treated rats. These findings indicate that angiotensin II-induced hypertension is associated with a selective impairment of EDHF-mediated relaxation and hyperpolarization in the rat mesenteric artery. The inhibition of EDHF-mediated responses is due, at least in part, to a decreased expression of connexins Cx37, Cx40, and Cx43 in the arterial wall.

Download full-text


Available from: Stéphanie Dal-Ros, Jul 08, 2015
  • Source
    • "We have previously shown that prenatal T exposure leads to endothelial dysfunction with specific impairments in the EDHF function [17]. An endothelial dysfunction involving a selective blunting of EDHF-mediated relaxation in the mesenteric artery has also been observed in spontaneously hypertensive rats [46] and in Ang II-treated rats [21]. In the present study, we observed that treatment with the ACE inhibitor enalapril prevented endothelial dysfunction in T rats, as indicated by normal EDHF-mediated relaxations in mesenteric arteries, suggesting that Ang II may to be a causal factor contributing to the underlying impairment of the EDHF-mediated response observed in T rats. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Prenatal exposure to elevated testosterone levels induces adult life hypertension associated with selective impairments in endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation in mesenteric arteries. We tested whether the angiotensin-converting enzyme inhibitor enalapril restores EDHF function through regulating the activities of small (Kcnn3) and intermediate (Kcnn4) conductance calcium-activated potassium channels in the mesenteric arteries. Pregnant Sprague-Dawley rats were injected with vehicle or testosterone propionate (0.5 mg/kg/day from Gestation Day 15-19, subcutaneously), and their 6-mo-old adult male offspring were examined. A subset of rats in these 2 groups was administered enalapril (40 mg/kg/day) for 2 wk through drinking water. Blood pressures were assessed through carotid arterial catheter and endothelium-dependent mesenteric arterial EDHF relaxation using wire myograph. Ace and Kcnn3 and Kcnn4 channel expressions were also examined. Renal and vascular Ace expression and plasma angiotensin II levels were increased in testosterone offspring. Blood pressures were significantly higher in testosterone offspring compared to controls, and treatment with enalapril significantly attenuated blood pressure in testosterone offspring. EDHF relaxation in testosterone offspring was reduced compared to controls, and it was significantly restored by enalapril treatment. Kcnn4 channel expression and function were similar between control and testosterone rats, but it was not affected by enalapril treatment. The relaxations mediated by the Kcnn3 were impaired in testosterone offspring, and it was normalized by enalapril treatment. Furthermore, enalapril treatment restored expression levels of Kcnn3 channels. These findings suggest that enalapril has a positive influence on endothelial function with improvement in EDHF relaxation through normalization of Kcnn3 expression and activity. Copyright 2015 by The Society for the Study of Reproduction.
    Biology of Reproduction 05/2015; DOI:10.1095/biolreprod.115.130468 · 3.45 Impact Factor
  • Source
    • "Several groups have reported that the EDHF response is impaired in various rat models of hypertension (see Fujii et al., 1992; Sunano et al., 1999; Alvarez de Sotomayor et al., 2007; Hilgers and Webb, 2007; Dal-ros et al., 2009) although the underlying cause has not been fully established. In view of our current understanding of the EDHF response, and the differential distribution of the two endothelial K + channels (Sandow et al., 2006; Absi et al., 2007; Dora et al., 2008), the aim of the present study was to elucidate further the mechanisms underlying the reduced endothelium-dependent hyperpolarization in hypertensive rats. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Previous studies have shown that endothelium-dependent hyperpolarization of myocytes is reduced in resistance arteries from spontaneously hypertensive rats (SHRs). The aim of the present study was to determine whether this reflects down-regulation of endothelial K(+) channels or their associated pathways. Changes in vascular K(+) channel responses and expression were determined by a combination of membrane potential recordings and Western blotting. Endothelium-dependent myocyte hyperpolarizations induced by acetylcholine, 6,7-dichloro-1H-indole-2,3-dione 3-oxime (NS309) (opens small- and intermediate-conductance calcium-sensitive K(+) channels, SK(Ca) and IK(Ca), respectively) or cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine (SK(Ca) opener) were reduced in mesenteric arteries from SHRs. After blocking SK(Ca) channels with apamin, hyperpolarizations to acetylcholine and NS309 in SHR arteries were similar to those of controls. Hyperpolarization to 5 mM KCl was reduced in SHR arteries due to loss of the Ba(2+)-sensitive, inward-rectifier channel (K(IR)) component; the contribution of ouabain-sensitive, Na(+)/K(+)-ATPases was unaffected. Protein expression of both SK(Ca) and K(IR) channels was reduced in SHR arteries; the caveolin-1 monomer/dimer ratio was increased. In SHRs, the distinct pathway that generates endothelium-dependent hyperpolarization in vascular myocyte by activation of IK(Ca) channels and Na(+)/K(+)-ATPases remains intact. The second pathway, initiated by endothelial SK(Ca) channel activation and amplified by K(IR) opening on both endothelial cells and myocytes is compromised in SHRs due to down-regulation of both SK(Ca) and K(IR) and to changes in caveolin-1 oligomers. These impairments in the SK(Ca)-K(IR) pathway shed new light on vascular control mechanisms and on the underlying vascular changes in hypertension.
    British Journal of Pharmacology 03/2010; 160(4):836-43. DOI:10.1111/j.1476-5381.2010.00657.x · 4.99 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Increased consumption of low-fat milk products is inversely associated with the risk of hypertension. The beneficial effect of milk on blood pressure is attributed to high calcium and potassium content but also to specific peptide sequences, which are cleaved from milk protein during gastrointestinal digestion, fermentation of milk with proteolytic starter cultures or enzymatic hydrolysis. Milk products fermented with Lactobacillus helveticus contain casein-derived tripeptides isoleucine-proline-proline (Ile-Pro-Pro) and valine-proline-proline (Val-Pro-Pro), which have been shown to possess antihypertensive effects in humans and in experimental animals. The aim of the present series of studies was to investigate the effects of tripeptides Ile-Pro-Pro and Val-Pro-Pro or fermented milk products containing them on vascular function and blood pressure and to elucidate the mechanisms behind them by using different experimental models of hypertension. Another aim was to characterize the acute effects of tripeptides on blood pressure and arterial stiffness in mildly hypertensive humans. Ile-Pro-Pro and Val-Pro-Pro or fermented milk products containing them attenuated the development of hypertension in two experimental models of hypertension, spontaneously hypertensive rat (SHR) and type 2 diabetic Goto-Kakizaki (GK) rat fed with high-salt diet. Significant differences in systolic blood pressure (SBP) were seen after 8 weeks treatment with tripeptide-containing products compared to control product. Plant sterols did not enhance this effect. Two differently produced tripeptide powders produced a similar attenuating effect on SBP in SHR. In mildly hypertensive subjects, a single administration of tripeptide- and plant sterol-containing fermented milk product decreased both SBP and diastolic blood pressure (DBP) over a period of 8 hours. Protective effect of tripeptides Ile-Pro-Pro and Val-Pro-Pro and fermented milk products containing them on vascular function was demonstrated in in vitro studies and long-term experimental studies. The effect was shown to be endothelium-dependent and possibly involving endothelium-derived hyperpolarizing factor (EDHF). In the clinical study, single administration of tripeptide-containing fermented milk product did not affect measures of arterial stiffness. Long-term treatment with fermented milk product containing Ile-Pro-Pro and Val-Pro-Pro inhibited angiotensin-converting enzyme (ACE) and decreased aldosterone levels thus showing beneficial effects on the renin-angiotensin system (RAS) in SHR and GK. No changes in the components of RAS were observed by the single administration of the same product in mildly hypertensive subjects. Increased levels of cGMP, NOx and citrulline suggest increased nitric oxide (NO) production by the tripeptides. Taken together, Ile-Pro-Pro and Val-Pro-Pro -containing products attenuate the development of hypertension after long-term treatment in experimental models of hypertension and possess an acute antihypertensive effect in mildly hypertensive subjects. In addition, these tripeptides show endothelium-mediated beneficial effects on vascular function. Attenuation of blood pressure increase by the tripeptides in experimental animals involves RAS, but its role in the antihypertensive effect in humans remains to be elucidated. Maidon kaseiinista pilkkoutuvilla tripeptideillä (Ile-Pro-Pro ja Val-Pro-Pro) suotuisa vaikutus verenpainetaudin kehittymiseen ja verisuonten toimintaan verenpainetaudin kokeellisissa tutkimusmalleissa Tripeptidien pitkäaikainen anto esti osittain verenpainetaudin kehittymisen ja paransi verisuonten toimintaa, selviää proviisori Pauliina Ehlersin väitöskirjatyöstä. Kokeellisten löydösten lisäksi tutkimus osoitti, että tripeptidejä ja kasvisteroleja sisältävä fermentoitu maitotuote laskee verenpainetta myös lyhytaikaisesti aiempien pitkäaikaiskokeista saatujen havaintojen lisäksi henkilöillä, joilla on lievästi kohonnut verenpaine. Kohonnut verenpaine on yksi tärkeimmistä sydän- ja verisuonitautien riskitekijöistä. Lääkehoidon lisäksi elintavoilla ja ruokavaliolla voidaan vaikuttaa suotuisasti verenpaineeseen. Seuranta- ja hoitotutkimusten mukaan vähärasvaisten maitotuotteiden runsas saanti on kääntäen verrannollinen verenpainetautiriskiin. Maidon hyödylliset vaikutukset on liitetty sekä maidon sisältämiin mineraaleihin (kalsium, kalium) että maidon proteiineista pilkkoutuviin aminohappoketjuihin, peptideihin. Kahdella maidon fermentaatioprosessissa maidon kaseiinista muodostuvalla tripeptidillä, isoleusiini-proliini-proliinilla (Ile-Pro-Pro) ja valiini-proliini-proliinilla (Val-Pro-Pro) on aiemmissa tutkimuksissa havaittu olevan verenpainetta alentavaa vaikutusta, mutta tieto taustalla olevista mekanismeista sekä tripeptidien verisuonivaikutuksista on vähäistä. Väitöstutkimuksessa käytettiin pääosin perinnöllisen verenpainetaudin sekä tyypin 2 diabeteksen kokeellisia tutkimusmalleja. Näitä malleja hyödyntäen osoitettiin, että tripeptidien tai niitä sisältävien fermentoitujen maitotuotteiden päivittäinen, pitkäaikainen saanti osittain esti verenpaineen kohoamista. Kolesterolia alentavat kasvisterolit eivät lisänneet tripeptidien suotuisia verenpainevaikutuksia. Tutkimuksen mukaan tripeptidien valmistusmenetelmällä ei ole merkitystä tehon kannalta. Pienellä kliinisellä aineistolla havaittiin, että jo yksi annos tripeptidejä ja kasvisteroleja sisältävää fermentoitua maitotuotetta laski verenpainetta koehenkilöillä, joilla verenpaine oli lievästi koholla. Tämä suotuisa vaikutus kesti koko kahdeksan tunnin seuranta-ajan. Verisuonten toimintakokeet osoittivat, että Ile-Pro-Pro ja Val-Pro-Pro sekä niitä sisältävät fermentoidut maitotuotteet paransivat verisuonten laajenemiskykyä sekä lyhyt- että pitkäaikaisissa kokeellisissa tutkimuksissa. Vaikutuksen osoitettiin välittyvän verisuonen sisimmän kerroksen, endoteelin kautta. Kliinisessä kokeessa ei havaittu merkitsevää vaikutusta koehenkilöiden verisuonten toimintaan pulssiaaltoanalyysiä (PWA) käyttäen. Väitöskirjatyön biokemialliset analyysit osoittivat, että tripeptidit Ile-Pro-Pro ja Val-Pro-Pro vaikuttavat verenpaineen säätelyssä keskeiseen reniini-angiotensiinijärjestelmään. Pitkäaikaiskokeissa tripeptidejä sisältävä fermentoitu maitotuote esti verisuonia voimakkaasti supistavan ja verenpainetta nostavan angiotensiinin muodostusta. Lisäksi voidaan esittää, että tripeptidit lisäävät verisuonia laajentavan typpioksidin (NO) tuotantoa. Väitöstutkimuksen löydökset maidon kaseiinista pilkkoutuvien tripeptidien suotuisista verenpaine- ja verisuonivaikutuksista tuovat lisää tukea niitä sisältävien tuotteiden hyödyllisyydestä lievästi kohonneessa verenpaineessa. Vaikutukset reniini-angiotensiinijärjestelmään ja verisuonen endoteelin selittänevät kuitenkin vain osan tehdyistä havainnoista. Proviisori Pauliina Ehlersin farmakologian alaan kuuluva väitöskirja Milk casein-derived tripeptides: A special focus on blood pressure and vascular function tarkastetaan Helsingin yliopiston Lääketieteellisessä tiedekunnassa perjantaina 24.9.2010 klo 12 (Biomedicum Helsinki, luentosali 3, Haartmaninkatu 8, Helsinki). Vastaväittäjänä toimii professori Ilkka Pörsti Tampereen yliopistosta ja kustoksena professori Esa Korpi Helsingin yliopistosta.