bluuebunny/crossref_metadata_2025 huggingface dataset:
Association of Variants in Critical Core Promoter Element of Angiotensinogen Gene With Increased Risk of Essential Hypertension in Japanese
Authors: Sato Noriyuki , Katsuya Tomohiro , Rakugi Hiromi , Takami Seiju , Nakata Yukiko , Miki Tetsuro , Higaki Jitsuo , Ogihara Toshio
Published: June 2012

Abstract
We examined the association between variants in the core promoter element 1 (AGCE1) of the human angiotensinogen gene
(AGT)
, which acts as a critical regulator of
AGT
transcription, and the risk for hypertension. One hundred and eighty patients with documented essential hypertension and a family history of hypertension and 194 control subjects without hypertension were selected and frequency matched by age and sex. Genomic DNA from leukocytes was analyzed for genetic variants (position: −20 to −18) in AGCE1. The haplotype in AGCE1 was significantly associated with increased risk of essential hypertension (
P
<.05). The frequency of subjects with homozygous C allele at position −18
(CC/C-18T
) was significantly higher in case patients than in control subjects (
P
<.005), and the evaluated odds ratio for hypertension was 4.2 (95% confidence interval [CI]: 1.4 to 12.8,
CC/C-18T
versus
CT/C-18T
). The homozygous threonine allele at codon 235
(TT/M235T)
in exon 2 of
AGT
was also associated with hypertension (
P
<.02; odds ratio,
TT
versus other genotypes, 1.8; 95% CI, 1.1 to 2.7). According to haplotype analysis between
AGT
polymorphisms, we identified linkage disequilibrium between
M235T
and
A-20C
and between
M235T
and
C-18T
. We conclude that
C-18T
polymorphism in AGCE1 is a genetic risk factor for essential hypertension in the Japanese and is more tightly and directly associated with hypertension than
TT/M235T
.
Angiotensin II–Induced Phosphorylation of the AT
1
Receptor From Rat Brain Neurons
Authors: Yang Hong , Lu Di , Raizada Mohan K.
Published: June 2012

Abstract
The neuronal angiotensin II (Ang II) type 1 (AT
1
) receptor is coupled to the Ras-Raf-1–mitogen-activated protein (MAP) kinase signal-transduction pathway (Yang H, Lu D, Yu K, Raizada MK. Regulation of neuromodulatory actions of angiotensin II in the brain neurons by the Ras-dependent mitogen-activated protein kinase pathway.
J Neurosci.
1996;16:4047-4058). In this study we compared the effects of angiotensin II (Ang II) on AT
1
receptor phosphorylation and the ability of the phosphorylated receptor to bind Ang II in neuronal cultures of Wistar-Kyoto rat (WKY) and spontaneously hypertensive rat (SHR) brains to further our understanding of the Ang II signaling mechanism. Ang II caused a time-dependent phosphorylation of AT
1
receptors in both WKY and SHR brain neurons. The level of phosphorylation was higher in the SHR brain neurons; this finding was consistent with increased AT
1
receptors in these cells. MAP kinase was involved in this phosphorylation, a conclusion supported by the following evidence: (1) exogenous MAP kinase phosphorylated the AT
1
receptor; (2) PD98059, a MAP kinase kinase inhibitor, attenuated Ang II–stimulated AT
1
receptor phosphorylation; and (3) MAP kinase and AT
1
receptors were coimmunoprecipitated in Ang II–stimulated neurons. Finally, MAP kinase phosphorylation was associated with the loss of
125
I-[Sar
1
-Ile
8
]-Ang II binding ability of the AT
1
receptor in both strains of neurons. These observations show that Ang II stimulates phosphorylation of the neuronal AT
1
receptor by a mechanism involving MAP kinase and that the phosphorylated neuronal AT
1
receptor does not exhibit Ang II binding activity in the brains of either WKY or SHR.
Ramipril Prevents Endothelial Dysfunction Induced by Oxidized Low-Density Lipoproteins
Authors: Berkenboom Guy , Langer Ingrid , Carpentier Yvon , Grosfils Katrina , Fontaine Jeanine
Published: June 2012

Abstract
We wished to determine whether the acute toxic effects of oxidized LDL are attenuated in aortas isolated from rats chronically treated with an angiotensin-converting enzyme (ACE) inhibitor. In aortic rings incubated with human oxidized LDL (300 μg/mL), the endothelium-dependent relaxations to acetylcholine were attenuated, but not those to A23187 and to nitroprusside. This toxic effect of oxidized LDL was completely prevented in preparations coincubated with oxidized LDL and the nitric oxide (NO) precursor
l
-arginine (0.3 mmol/L). In aortas isolated from rats orally treated for 6 weeks with 10 mg/kg ramipril (group 1) or 1 mg/kg ramipril (group 2), this toxic effect of oxidized LDL was also markedly attenuated. In contrast, in aortas isolated from rats cotreated with ramipril (10 mg/kg) for 6 weeks and subcutaneous injections of Hoe 140 (a B
2
kinin antagonist), 500 μg/kg per day for the last 2 weeks (group 3) or from rats orally treated for 6 weeks with losartan (an AT
1
-type angiotensin II receptor antagonist), 20 mg/kg (group 4), the inhibitory effect of oxidized LDL on acetylcholine-induced relaxations was similar to that observed in the control group (group 5). Moreover, long-term treatment with ramipril increased relaxations to acetylcholine in groups 1 and 2 and also relaxations to A23187 and aortic cGMP content in group 1, suggesting an enhanced NO availability. Thus, the protective effect of long-term ACE inhibition against the acute vascular toxicity of oxidized LDL is bradykinin dependent and seems to involve a facilitation of NO release via endothelial B
2
kinin receptors.
Contractile Systolic and Diastolic Dysfunction in Renin-Induced Hypertensive Cardiomyopathy
Authors: Flesch Markus , Schiffer Frank , Zolk Oliver , Pinto Yigal , Rosenkranz Stephan , Hirth-Dietrich Claudia , Arnold Georg , Paul Martin , Böhm Michael
Published: June 2012

Abstract
The present study investigated whether functional, molecular, and biochemical alterations occurring in chronic heart failure can already be detected in compensated hypertensive cardiac hypertrophy. Force of contraction (isolated papillary muscle strip preparations), sarcoplasmic reticulum (SR) protein and myosin heavy chain isoform expression (Northern and Western blot analysis), myocardial fibrosis (collagen stains, hydroxyproline quantification), myocardial renin mRNA (RT-PCR), and angiotensin II levels and plasma aldosterone concentrations (radioimmunoassay) were studied in hypertrophied myocardium from transgenic rats harboring the mouse
Ren
-2d gene. Contraction and relaxation velocities of isolated papillary muscle strips were significantly reduced in cardiac hypertrophy. The β-/α-myosin heavy chain ratio was significantly increased in the hypertrophied left ventricles, whereas SR Ca
2+
-ATPase (SERCA 2a) and phospholamban mRNA and protein levels were significantly decreased. The decrease in SERCA 2a was more pronounced than the decrease in phospholamban levels. There was no increased myocardial fibrosis. Left ventricular myocardial renin mRNA and angiotensin II concentrations, as well as plasma aldosterone levels, were higher in transgenic than in control rats. In hypertensive cardiac hypertrophy, myosin heavy chain isoform shift and reduction of SR protein levels are related to systolic and diastolic dysfunction, respectively. These alterations precede the development of myocardial fibrosis. Increased myocardial renin mRNA and angiotensin II concentrations suggest that an activated tissue renin-angiotensin system might contribute to these alterations. Since the alterations in compensated cardiac hypertrophy apparently precede those in chronic heart failure, they might accelerate the transition from hypertrophy to failure and could therefore be targets for pharmacological interventions.
Nitric Oxide Synthase and Renin-Angiotensin System Gene Expression in Salt-Sensitive and Salt-Resistant Sabra Rats
Authors: Lippoldt Andrea , Gross Volkmar , Schneider Kerstin , Hansson Anita , Nadaud Sophie , Schneider Wolfgang , Bader Michael , Yagil Chana , Yagil Yoram , Luft Friedrich C.
Published: June 2012

Abstract
The molecular mechanisms of salt sensitivity and the contribution of the kidney to salt-induced hypertension in Sabra rats are imperfectly defined. We investigated the expression of the nitric oxide (NO) system (endothelial, inducible, and neural NO synthases) and renin-angiotensin system (renin, angiotensinogen, and angiotensin II type 1A receptor) gene components in the kidneys of SBN/y (salt-resistant) and SBH/y (salt-sensitive) Sabra rat substrains, with and without deoxycorticosterone acetate (DOCA)–salt treatment. We also looked for immunocytochemical evidence of angiotensin II, the effector peptide of the renin-angiotensin system. Inducible and neural NO synthase gene expression values were lower in SBH/y than in SBN/y before and after DOCA-salt treatment. The gene expression level of endothelial NO synthase was not different in SBH/y and SBN/y, either with or without DOCA salt. Renin gene expression was significantly higher in kidneys of SBN/y than in kidneys of SBH/y rats, whereas angiotensinogen gene expression was significantly lower in SBN/y. After DOCA-salt treatment, renin gene expression was strongly suppressed in both strains but more so in SBH/y. Angiotensinogen gene expression, on the other hand, was increased by DOCA salt in SBN/y rats so that the two strains were no longer different. Angiotensin II immunoreactivity was significantly higher in SBN/y than in SBH/y; however, after DOCA salt, immunoreactivity in both strains was no longer detectable. Angiotensin II type 1A receptor gene expression was not different between the two strains, either before or after DOCA-salt administration. We conclude that DOCA salt induced a decrease in the activity of the renin-angiotensin system but did not change NO synthase gene expression in SBH/y and SBN/y. Inducible and neural NO synthase gene expression values were less in SBH/y than in SBN/y, independent of DOCA-salt administration. Thus, the NO system could explain, at least in part, the salt resistance of SBN/y.
Reduced Sensitivity of the Renal Circulation to Angiotensin II in Pregnant Rats
Authors: Novak Jacqueline , Reckelhoff Jane , Bumgarner Leslie , Cockrell Kathy , Kassab Salah , Granger Joey P.
Published: June 2012

Abstract
The renal circulation undergoes significant changes during pregnancy and pregnancy-induced hypertension. Although numerous studies indicate that the pressor response to angiotensin II (Ang II) is reduced during pregnancy, it is unclear as to whether this altered sensitivity to Ang II occurs in the renal circulation. The first aim of this study was to determine whether the renal vascular responsiveness to exogenous Ang II is altered in the midterm pregnant rat. All rats were pretreated with an intravenous infusion of the converting-enzyme inhibitor captopril (20 μg · kg
−1
· min
−1
) to block endogenous Ang II formation. Following a control period, Ang II was infused at a dose of 10 ng · kg
−1
· min
−1
for 50 minutes into the renal arteries via a suprarenal aortic catheter. In anesthetized virgin rats, Ang II markedly decreased renal plasma flow (RPF) by 39% (5.0±0.4 to 3.1±0.4 mL/min), glomerular filtration rate (GFR) by 39% (1.9±0.1 to 1.16±0.2 mL/min), and urine flow by 47% (22.1±5.6 to 12.3±4.8 μL/min). In contrast, Ang II had no significant effect on RPF, GFR, and urine flow in the anesthetized pregnant rats. Since nitric oxide (NO) has been previously reported to modulate the renal vascular actions of Ang II in normal animals and NO synthesis is thought to be elevated in pregnancy, this study examined the role of NO in the attenuated renal response to Ang II. In pregnant rats pretreated with L-NAME, the arterial pressure was higher and RPF was lower than in the control pregnant rats. However, the renal response to Ang II in the L-NAME–pretreated pregnant rats was similar to control pregnant rats. These data indicate that the renal circulation has a reduced sensitivity to Ang II during pregnancy. We also found that NO synthesis inhibition does not alter the attenuated renal response to Ang II in the anesthetized pregnant rats.
In Vivo Plasma Lipid Oxidation in Sugar-Induced Rat Hypertriglyceridemia and Hypertension
Authors: El Hafidi Mohammed , Baños Guadalupe
Published: June 2012

Abstract
Fe(II) and Fe(III) are required for the catalysis of lipid peroxidation through generation of reactive oxygen species that damage cell membranes. This study investigated the effect of free radicals and lipid peroxidation, induced by intraperitoneal injection of iron-dextran in vivo, in the plasma of the sugar-induced hypertriglyceridemic and hypertensive male and female rats. Lipid peroxidation was measured by the malondialdehyde (MDA) equivalent, using a fluorescence method of 2-thiobarbituric acid reactive substances (TBARS). Iron increased TBARS generation by fourfold (
P
<.0001) in male control rats and by twofold (
P
<.01) in female control rats, and the difference between TBARS concentration in female as compared with male animals was statistically significant (
P
<.05). In the case of the sugar-fed group, iron-dextran produced an increase of TBARS concentration by twofold in both male (
P
<.001) and female rats (
P
<.01), and no significant difference in TBARS concentration was observed between sugar-fed female and male rats. The analysis of fatty acid composition by gas chromatography showed a significant diminution of 50% in the proportion of arachidonic acid (C20:4n-6) in the male control group in comparison with the female group (
P
<.0001). In female control rats, a small diminution in the proportion of C20:4n-6 and in the other polyunsaturated fatty acids was observed (
P
<.05). A significant difference in the C20:4n-6 proportion was found between the male and female group of control rats. In the sugar-fed group, iron induced a significant diminution of arachidonic acid (
P
<.001) in both female and male rats in comparison with the sugar-fed group without iron.
Excitatory Effects of Nitric Oxide Within the Rostral Ventrolateral Medulla of Freely Moving Rats
Authors: Martins-Pinge Marli C. , Baraldi-Passy Izabel , Lopes Oswaldo U.
Published: June 2012

Abstract
The aim of the present study was to examine the participation of NO in the rostral ventrolateral medulla (RVLM) of freely moving rats. We utilized NO donors and
l-
arginine, which were microinjected into the RVLM. Unilateral microinjection (100 nL) of 2.5 nmol sodium nitroprusside produced a biphasic response consisting of an initial, rapid increase in arterial pressure (AP) from 125±5 to 161±8 mm Hg (
P
<.01) and a second, long-lasting response with a progressive increase in AP (maximum Δpeak, 34±9 mm Hg;
P
<.01). Another NO donor,
S
-nitroso-
N
-acetylpenicillamine (SNAP; 2.5 nmol), also produced immediate hypertension from 118±5 mm Hg to 168±7 mm Hg (
P
<.01) but without the second, long-lasting response.
l-
Arginine (5, 24, and 140 nmol) produced a gradual increase in AP.
l-
Glutamate (5 nmol) microinjected into the RVLM produced an increase in AP from 122±9 mm Hg to 171±8 mm Hg (
P
<.01) and bradycardia from 342±10 to 315±8 beats/min. This AP response was significantly attenuated, from 115±7 to 128±9 mm Hg (
P
<.05), after microinjection of methylene blue (3 nmol) without alterations in heart rate. These results indicate that NO may have an excitatory effect on the RVLM of freely moving rats, probably in association with glutamatergic synapses via cGMP mechanisms.
Role of Ouabain-like Compound in the Regulation of Transmembrane Sodium and Potassium Gradients in Rats
Authors: Goto Atsuo , Yamada Kaoru , Nagoshi Hiroshi , Dan Yoshiyuki , Omata Masao
Published: June 2012

Abstract
A major biologically active Na,K-ATPase inhibitor in the mammalian body may be ouabain-like compound. We investigated the potential roles of circulating ouabain-like compound in the regulation of Na
+
and K
+
homeostasis in terms of Na
+
and K
+
distribution between the cells and the extracellular fluid (internal balance). First, we developed a population of rats immunized against ouabain to block the action of ouabain-like compound. We measured plasma and intracellular Na
+
and K
+
concentrations in skeletal muscle and determined Na
+
(extracellular-to-intracellular concentration ratio) and K
+
(intracellular-to-extracellular concentration ratio) gradients in immune rats. We examined also the ability to respond to hypertonic NaCl load in immune rats. Consistent lower plasma K
+
levels and steeper Na
+
and K
+
gradients were observed in immune rats. K
+
handling in response to hypertonic NaCl load was altered, and lower plasma K
+
level was maintained in immune rats. Second, we used PST-2238, a newly developed anti-ouabain agent, to block the action of ouabain-like compound and examined its effect on plasma Na
+
and K
+
concentrations. Chronic administration of PST-2238 significantly lowered plasma K
+
levels in rats with subtotal nephrectomy. These findings collectively suggest that ouabain-like compound may determine at least in part the internal Na
+
and K
+
distribution and the transmembrane cation gradients in vivo in rats.
Exercise Training in Aging
Authors: De Angelis K. L. D. , Oliveira A. R. , Werner A. , Bock P. , Belló-Klein A. , Fernandes T. G. , Belló A. A. , Irigoyen M. C.
Published: June 2012

Abstract
The effects of exercise training on hemodynamic and metabolic parameters as well as on responses to oxidative stress in aged individuals are controversial. The aim of the present study was to investigate changes in heart hate, mean arterial pressure, vasoreactivity, and plasma levels of insulin and glucose in male aged Wistar rats submitted to exercise training for 11 weeks (1 h/d; 5 d/wk) in a treadmill. The isolated heart was perfused by H
2
O
2
, and oxidative stress was evaluated using thiobarbituric acid reactive substances. Cardiovascular functions were recorded with a data acquisition system (CODAS, 1 kHz). Trained aged rats were bradycardic as compared with sedentary aged rats (298±7 versus 336±16 bpm) but presented similar mean arterial pressure and vasoreactivity and plasma levels of insulin and of glucose, which were quantified by radioimmunoassay and colorimetric enzymatic test. Plasma levels of insulin and of glucose ratio were increased in trained aged rats (6.9±0.7 versus 3.5±0.4 in sedentary aged rats), and the response to oxidative stress was decreased (0.4±0.1 versus 0.7±0,1 nmol/mg protein in sedentary aged rats). These results showed that exercise training produced a lower resting heart rate as well as changes in metabolic and oxidative responses. This suggests a higher myocardium protection of trained than sedentary aged rats.
Molecular Mechanism of Angiotensin II Type I and Type II Receptors in Cardiac Hypertrophy of Spontaneously Hypertensive Rats
Authors: Makino Naoki , Sugano Masahiro , Otsuka Shoji , Hata Tomoji
Published: June 2012

Abstract
We administered angiotensin (Ang) II receptor type 1 (AT
1
) blockade (losartan; 10 or 40 mg/kg per day), type II receptor (AT
2
) blockades (PD123319; 100 mg/kg per day), or angiotensin-converting enzyme (ACE) inhibitor (enalapril; 30 mg/kg per day) to spontaneously hypertensive rats (SHR) from 10 to 20 weeks of age. At the end of the treatment, high doses of losartan and enalapril significantly reduced the arterial systolic blood pressure compared with the untreated SHR to the level of WKY rats. But low doses of losartan and PD123319 were without effect. High doses of losartan and enalapril also significantly reduced both the left ventricular (LV) weight and the ratio of LV to body weight compared with the untreated SHR, which were still larger than that of WKY rats. However, the collagen concentration of SHR treated with high doses of losartan or enalapril was completely reduced to the level of WKY rats. Using reverse transcription polymerase chain reaction, we examined the mRNA expression for ACE, AT
1
, and AT
2
in experimental animals. The enhanced AT
1
mRNA expression was significantly decreased in the SHR treated with a high dose of losartan or PD123319 compared with the untreated SHR. The level of ACE mRNA was also decreased in the SHR treated with a high dose of losartan or enalapril. The level of AT
2
mRNA was not significantly different between the Wistar-Kyoto rats and the SHR; however, this expression was decreased significantly after the treatment with a high dose of losartan or PD123319. These results indicate that AT
1
receptor and ACE, but not AT
2
receptor, play a crucial role in the remodeling of matrix tissue but a smaller role in the development of the hypertrophy of LV myocyte in SHR and that the LV/body weight changes do not fully account for the complete suppression of hypertension.
Regulation of 12-Lipoxygenase by Cytokines in Vascular Smooth Muscle Cells
Authors: Natarajan Rama , Rosdahl Jullia , Gonzales Noe , Bai Wei
Published: June 2012

Abstract
Increasing evidence suggests that cytokines such as interleukin-1β (IL-1), IL-4, and IL-8 may play an important role in the chronic inflammation and cellular growth observed in cardiovascular diseases. The lipoxygenase (LO) pathway of arachidonate metabolism has also been related to the pathology of hypertension and atherosclerosis. LO products have chemotactic, hypertrophic, and mitogenic effects in vascular cells, and the LO enzyme has been implicated in the oxidation of LDL. Furthermore, earlier studies have shown that vascular smooth muscle cell (VSMC) growth factors such as angiotensin II and platelet-derived growth factor can increase LO activity and expression in VSMCs. In the present study, we have examined whether vasoactive and inflammatory cytokines such as IL-1, IL-4, and IL-8 can modulate 12-LO activity and expression in porcine VSMCs and also whether they have growth-promoting effects in these cells. Treatment of porcine VSMCs with these cytokines led to significant increases in the levels of a cell-associated 12-LO product, 12-hydroxyeicosatetraenoic acid, as well as intracellular 12-LO enzyme activity. Furthermore, each of these cytokines led to a dose-dependent increase in 12-LO mRNA expression (333-base pair PCR product) as well as 12-LO protein expression (72 kD). In addition, all three interleukins could induce significant increases in VSMC DNA synthesis as well as proliferation. These results suggest that these cytokines have mitogenic effects in VSMCs and are also potent positive regulators of the 12-LO pathway. Thus, enhanced 12-LO activity and expression may be a key mechanism for cytokine-induced VSMC migration and proliferation.
Ouabain-like Factor Quantification in Mammalian Tissues and Plasma
Authors: Ferrandi Mara , Manunta Paolo , Balzan Silvana , Hamlyn John M. , Bianchi Giuseppe , Ferrari Patrizia
Published: June 2012

Abstract
The resolution of controversies that concern the detectability of an endogenous ouabain-like factor (OLF) in mammalian tissues and plasma was approached by the application of a standardized method for its extraction and quantification. Two independent assays were used to quantify the OLF: (1) a radioimmunoassay, which used a polyclonal antiouabain antiserum, and (2) a radioenzymatic assay based on the inhibition of dog kidney Na
+
,K
+
-ATPase. Plasma and tissues were obtained from the Milan hypertensive strain (MHS) and the Milan normotensive strain (MNS) of rats and from healthy human volunteers. Results indicate that (1) a single high-performance liquid chromatography (HPLC) fraction identical to that of ouabain was identified by both assay methods in the rat hypothalamus and hypophysis and in both rat and human plasma; (2) dilution curves of OLF and standard ouabain were parallel and with a similar
K
d
, both in radioimmunoassay (3 nmol/L) and ATPase assay (14 nmol/L); (3) after HPLC, OLF was similarly quantified by the two methods in the hypothalamus, hypophysis, adrenals, and plasma of rats and in human plasma; (4) OLF was present in larger amounts in the hypothalamus, hypophysis, and plasma of MHS rats than that of MNS rats; (5) the HPLC fraction of human plasma was quantified similarly by both assays (range, 60 to 150 pmol/L); (6) recovery of standard ouabain in pre-HPLC plasma extracts was approximately 90%; and (7) pre-HPLC OLF concentrations in human plasma ranged between 0.05 and 0.75 nmol/L. Rat cerebral tissues and both rat and human plasma contained measurable amounts of OLF, which were quantified similarly by radioimmunoassay and ATPase assay, both before and after HPLC fractionation. The increased MHS tissue and plasma levels of OLF are in keeping with the pathogenetic role of this factor in MHS hypertension.
Structure and Function of Small Arteries in Salt-Induced Hypertension
Authors: d’Uscio Livius V. , Barton Matthias , Shaw Sidney , Moreau Pierre , Lüscher Thomas F.
Published: June 2012

Abstract
The involvement of endothelin in salt-induced hypertension is unclear. In the Dahl rat model, we studied the effects of a selective endothelin-subtype A (ET
A
) receptor antagonist,
LU135252
, on blood pressure, vascular structure, and function. Dahl salt-sensitive and salt-resistant rats were treated for 8 weeks with 4% NaCl alone or in combination with
LU135252
taken orally (60 mg/kg per day). The geometry and reactivity of basilar and mesenteric arteries were studied in vitro under perfused and pressurized conditions using a video dimension analyzer. Chronic salt administration increased systolic blood pressure by 37±3 mm Hg and media-lumen ratio of the basilar and mesenteric arteries in salt-sensitive rats (
P
<.05). These structural changes were caused by eutrophic remodeling in basilar and hypertrophic remodeling in mesenteric arteries. Endothelium-dependent relaxations to acetylcholine and contractions to endothelin-1 were impaired in mesenteric arteries of salt-sensitive rats on a high NaCl diet.
LU135252
prevented part of the increase in systolic blood pressure and structural and functional alterations but increased plasma endothelin 1 levels (
P
<.05 versus salt-treated, salt-sensitive rats).
LU135252
had no effect on these parameters in salt-resistant rats. These findings suggest that the long-term pressor effect of salt administration is mediated in part by the action of endogenous endothelin acting via ET
A
receptors. Thus, chronic ET
A
receptor blockade may be useful therapeutically to lower arterial pressure and prevent endothelial dysfunction and hypertrophic remodeling of resistance arteries in salt-sensitive forms of hypertension.
Brain Nitric Oxide Synthase Messenger RNA in Central Mineralocorticoid Hypertension
Authors: Takeda Yoshiyu , Miyamori Isamu , Yoneda Takashi , Furukawa Kenji , Inaba Satoru , Takeda Ryoyu , Mabuchi Hiroshi
Published: June 2012

Abstract
The mechanism underlying the central hypertensinogenic effects of mineralocorticoids remains unclear. Given that nitric oxide (NO) is thought to act at autonomic sites in the brain to regulate arterial blood pressure, the effects of the potent mineralocorticoids aldosterone and 19-noraldosterone on the abundance of neuronal NO synthase (nNOS) mRNA in the brain were investigated. Wistar-Kyoto rats received a continuous intracerebroventricular infusion of aldosterone or 19-noraldosterone (5 ng/h) from an implanted osmotic minipump for 4 weeks. Total RNA was purified from microdissected tissue blocks containing the hypothalamus, dorsal medulla, rostral ventrolateral medulla, or caudal ventrolateral medulla, and changes in the abundance of nNOS mRNA were determined with a semiquantitative competitive polymerase chain reaction method. Blood pressure was significantly increased in rats 2, 3, and 4 weeks after the onset of intracerebroventricular aldosterone or 19-noraldosterone infusion compared with that in animals receiving vehicle. Subcutaneous infusion of either mineralocorticoid had no effect on blood pressure. Compared with controls, rats treated with aldosterone or 19-noraldosterone for 4 weeks showed significant decreases in the amount of nNOS mRNA in the hypothalamus and rostral and caudal ventrolateral medulla. These data suggest that reduced nNOS activity may contribute to the increase in blood pressure in rats with central mineralocorticoid-induced hypertension.
Role of Endogenous Carbon Monoxide in Central Regulation of Arterial Pressure
Authors: Johnson Robert A. , Colombari Eduardo , Colombari Debora S. A. , Lavesa Manuel , Talman William T. , Nasjletti Alberto
Published: June 2012

Abstract
We investigated the contribution of neural mechanisms to the arterial pressure increase produced by zinc deuteroporphyrin 2,4-bis glycol (ZnDPBG), an inhibitor of endogenous carbon monoxide synthesis. The arterial baroreceptor reflex control of heart rate was examined in rats with and without ZnDPBG pretreatment (45 μmol/kg IP) by analysis of the arterial pressure–heart rate relationship during infusions of phenylephrine or sodium nitroprusside to vary arterial pressure. ZnDPBG increased arterial pressure from 110±3 to 126±2 mm Hg without eliciting bradycardia. The maximum gain of the heart rate response to changes in arterial pressure was attenuated by ZnDPBG treatment (−1.9±0.3 versus −4.8±1.0 bpm/mm Hg). The possibility that ZnDPBG elevates arterial pressure by attenuating baroreceptor reflex function was addressed by comparing the pressor response to ZnDPBG (45 μmol/kg IP) in rats with and without sinoaortic denervation. The pressor effect of ZnDPBG was similar in rats with and without arterial baroreceptor deafferentation, implying that the increase in pressure is not simply the consequence of attenuated baroreceptor reflex function per se. The possibility that ZnDPBG increases arterial pressure via an effect on the nucleus tractus solitarii (NTS) also was investigated. ZnDPBG (1 nmol in 10 0 nL) injected into the NTS of rats increased arterial pressure from 111±4 to 126±5 mm Hg, and this effect was reversed by an ipsilateral microinjection of carbon monoxide into the NTS. Accordingly, the pressor effect of ZnDPBG may rely on inhibition of carbon monoxide production in the NTS. This implies that carbon monoxide formed by brain heme oxygenase plays a role in the central regulation of arterial pressure.
Arginine Vasopressin Increases Nitric Oxide Synthesis in Cytokine-Stimulated Rat Cardiac Myocytes
Authors: Yamamoto Keiji , Ikeda Uichi , Okada Koji , Saito Toshikazu , Kawahara Yasuhiro , Okuda Masanori , Yokoyama Mitsuhiro , Shimada Kazuyuki
Published: June 2012

Abstract
We investigated the effects of arginine vasopressin (AVP) on nitric oxide (NO) synthase activity in cardiac myocytes by measuring the production of nitrite, a stable metabolite of NO, and the expression of inducible NO synthase (iNOS) mRNA and protein. Incubation of cultured neonatal rat cardiac myocytes for 24 hours with interleukin-1β (IL-1β) caused a significant increase in NO production. Both AVP and V
1a
receptor agonist [Phe
2
,Ile
3
,Orn
8
]vasopressin augmented NO synthesis in IL-1β–stimulated, but not in unstimulated myocytes, in a dose-dependent manner. The V
1a
receptor antagonist [d(CH
2
)
5
1
,
O
-Me-Tyr
2
,Arg
8
]vasopressin completely inhibited the effect of AVP. The AVP-induced NO production by IL-1β–stimulated cells was accompanied by increased iNOS mRNA and protein accumulation. AVP caused a significant increase in cytosolic free Ca
2+
levels of cardiac myocytes, whereas it showed no effect on cytosolic cAMP levels. After protein kinase C activity was functionally depleted by treating cells with phorbol 12-myristate 13-acetate for 24 hours, AVP did not augment IL-1β–induced NO production. The effect of AVP was also inhibited in the presence of the protein kinase C inhibitor calphostin C. The addition of AVP increased protein kinase C activity in cardiac myocytes, and its effect was significantly inhibited in the presence of calphostin C. These results support the hypothesis that the heart may be a target organ for AVP and that AVP modulates IL-1β–induced iNOS expression in myocytes through the V
1a
receptor, which is mediated at least partially via activation of protein kinase C.
Angiotensin-Converting Enzyme Inhibition Alters Nitric Oxide and Superoxide Release in Normotensive and Hypertensive Rats
Authors: Wiemer Gabriele , Linz Wolfgang , Hatrik Stefan , Schölkens Bernward A. , Malinski Tadeusz
Published: June 2012

Abstract
Young (≈1 month old) male normotensive Wistar-Kyoto rats (n=26) and spontaneously hypertensive rats (n=38) were randomized into three groups treated via drinking water for ≈2 years with, respectively, placebo, low doses, or high doses of an angiotensin-converting enzyme inhibitor, ramipril (10 μg · kg
−1
· d
−1
, non–blood pressure–lowering dose, or 1 mg · kg
−1
· d
−1
, blood pressure–lowering dose). Relative to placebo treatment in each respective rat strain, both ramipril dosages increased endothelial constitutive nitric oxide synthase expression (Western blot) and resultant synthesis of nitric oxide (porphyrinic sensor) in freshly excised carotids and thoracic aortas, respectively. Paradoxically, this activity was associated with an increased/decreased superoxide accumulation (chemiluminescence) in freshly excised aortas from 24-/22-month-old normotensive/hypertensive rats. In normotensive rats, relative to placebo treatment, the threefold increase in superoxide accumulation with antihypertensive ramipril treatment is most likely from the >300% increase in endothelial constitutive nitric oxide synthase expression (some of which may be disarranged by local insufficiencies in
l
-arginine or tetrahydrobiopterin). In hypertensive rats, relative to placebo treatment, the 35% increase in nitric oxide availability by long-term antihypertensive ramipril treatment may contribute to the preservation of the endothelium and prevent its dysfunction by inhibiting superoxide production. Increased nitric oxide production with concomitant decreased superoxide accumulation (approximately one third of placebo levels) correlates positively with the previously reported +40% life span extension for rats with genetic hypertension that were treated with antihypertensive doses of ramipril.
Impaired Cortisol Binding to Glucocorticoid Receptors in Hypertensive Patients
Authors: Mulatero Paolo , Panarelli Maurizio , Schiavone Domenica , Rossi Alessandro , Mengozzi Giulio , Kenyon Christopher J. , Chiandussi Livio , Veglio Franco
Published: June 2012

Abstract
We compared glucocorticoid receptor binding characteristics and glucocorticoid responsiveness of human mononuclear leukocytes (HML) from hypertensive patients and matched normotensive volunteers. We also considered associations of these variables with plasma renin activity, aldosterone, cortisol, corticotropin, and electrolyte concentrations. We calculated binding affinity (
K
d
; nmol/L) and capacity (
B
max
; sites/cell) for dexamethasone and cortisol from homologous and heterologous competition curves for specific [
3
H]dexamethasone binding sites on HML isolated from the blood of normotensive volunteers and subjects with essential hypertension. Glucocorticoid responsiveness of HML was evaluated as IC
50
values (nmol/L) for dexamethasone and cortisol for the inhibition of lysozyme release. We measured plasma hormones by radioimmunoassay.
K
d
values (mean±SE) for cortisol in HML of hypertensive patients were higher than in control subjects (24.6±2.4 versus 17.5±1.7 nmol/L,
P
<.04). Binding capacity (4978±391 versus 4131±321 sites/cell),
K
d
values for dexamethasone (6.7±0.5 versus 5.7±0.3 nmol/L), and IC
50
values for dexamethasone (3.4±0.3 versus 3.1±0.2 nmol/L) and cortisol (12.2±1.6 versus 9.5±0.3 nmol/L) were not significantly different. Patients with renin values less than 0.13 ng angiotensin I/L per second were markedly less sensitive to cortisol than those with higher values. Both
K
d
(30.3±2.5 versus 19.2±2.4 nmol/L) and IC
50
values (15.5±1.8 versus 8.9±1.2 nmol/L) for cortisol were significantly higher in patients with lower renin values (
P
<.03). Other variables, including plasma hormone and electrolyte values and binding characteristics for dexamethasone, were not different. These data suggest that cortisol binding to glucocorticoid receptor is slightly impaired in patients with essential hypertension. In vivo, this could lead to inappropriate binding of cortisol to mineralocorticoid receptors. Hence, decreased sensitivity to cortisol is associated with renin suppression. This hypothesis is supported by evidence of hypertension and low renin activity, which others have described in patients with primary glucocorticoid resistance due to mutations of the glucocorticoid receptor.
Tissue-Specific Regulation of Renal and Cardiac Atrial Natriuretic Factor Gene Expression in Deoxycorticosterone Acetate–Salt Rats
Authors: Ogawa Tsuneo , Bruneau Benoit G. , Yokota Naoto , Kuroski de Bold Mercedes L. , de Bold Adolfo J.
Published: June 2012

Abstract
Atrial natriuretic factor (ANF) is expressed in several noncardiac tissues where it may have an autocrine or paracrine function. Such function may be expected of locally synthesized ANF in the renal parenchyma. Previous investigations of the existence of ANF mRNA in the renal parenchyma have yielded conflicting results. The investigations reported here were designed to detect and measure ANF mRNA in normal rats and in rats subjected to a deoxycorticosterone acetate (DOCA)–salt treatment schedule known to strongly activate cardiac ANF gene expression. The expression of the renal ANF gene was measured using a newly developed quantitative competitive reverse transcription–polymerase chain reaction (QC-RT-PCR). This method uses an internal competitor thatserves as an internal standard and makes the procedure independent of measurement relative to housekeeping genes. It was found that renal ANF mRNA levels were 10
7
times lower than those found in left or right atria, but immunoreactive (ir) renal ANF concentration by specific radioimmunoassay was 10
4
times lower than that of atrial irANF levels. Reverse-phase high-performance liquid chromatography analysis revealed that more than 99% of renal irANF is processed ANF
99-126
. This finding suggests that most of the irANF measured in kidney extracts likely originates from atrial sources. Left atrial ANF mRNA levels after 1 week of DOCA-salt treatment was significantly higher than that of control rats ([21.06±2.99]×10
−
15
mol/μg total RNA versus [8.59±1.26]×10
−
15
mol/μg total RNA,
P
<.05). However, renal ANF mRNA levels in DOCA-salt rats were significantly decreased compared with those of control rats ([1.64±0.34]×10
−
22
mol/μg total RNA versus [3.96±0.61]×10
−
22
mol/μg total RNA,
P
<.05). These results indicate that (1) renal ANF mRNA can be consistently and specifically demonstrated after reverse transcription and PCR amplification; (2) renal and cardiac ANF synthesis are regulated in a tissue-specific, opposite manner during DOCA-salt treatment; and (3) the finding that renal ANF mRNA is downregulated by DOCA-salt treatment together with previous findings suggest the need for further investigation into the role of renal ANF mRNA downregulation in the pathogenetic mechanism that leads to volume expansion and hypertension after chronic DOCA-salt treatment.
Regulation of the Rat Atrial Natriuretic Peptide Gene After Acute Imposition of Left Ventricular Pressure Overload
Authors: Cornelius Torsten , Holmer Stephan R. , Müller Frank U. , Riegger Günter A. J. , Schunkert Heribert
Published: June 2012

Abstract
The upregulation of left ventricular (LV) atrial natriuretic peptide (ANP) mRNA is a highly conserved marker of cardiac hypertrophy. The aim of this study was to further examine the pathway leading to ANP induction during pressure overload of the heart. Systolic wall stress was imposed acutely on isovolumetrically beating rat hearts in a Langendorff apparatus (ς=300×10
3
dyne/cm
2
). Northern and Western blots revealed that elevated wall stress induced LV c-
fos
and c-
jun
mRNAs (3.5- and 3-fold,
P
<.05 after 60 minutes), c-Fos and c-Jun proteins (3.9- and 4.3-fold,
P
<.05 after 120 minutes), as well as ANP mRNA (2.2-fold,
P
<.05 after 120 minutes). ANP upregulation was prevented by inhibition of protein synthesis (cycloheximide). Electrophoresis mobility shift assays were performed to link c-Fos and c-Jun (ie, components of the heterodimeric transcription factor AP-1) and ANP induction. A putative AP-1 binding site within the rat ANP promoter (nucleotides -512 to -473) bound specifically to nuclear proteins of wall stress–stimulated hearts. Antibodies directed against c-Fos protein resulted in a shift of this DNA/protein complex, suggesting physical interaction between AP-1 and the ANP promoter. Myocardial transfection of promoter constructs revealed that after acute imposition of wall stress, this AP-1 site enhanced a reporter gene (8- to 10-fold compared with a minimal promoter,
P
<.05). Interestingly, nuclear extracts of stimulated hearts as well as pure AP-1 protein bound to a putative CRE site (nucleotides -613 to -584) as well. Like the AP-1 site, this cAMP-responsible element (CRE) site was found to enhance the transfected ANP promoter/reporter gene significantly (17.5-fold,
P
<.05). Mutation of either AP-1 or CRE sites did not decrease reporter gene activity, whereas mutation of both resulted in loss of inducibility. These experiments suggest that LV ANP regulation after acute wall stress includes the activation of AP-1 and/or CRE
cis
acting elements. However, the transient nature of c-
fos
and c-
jun
upregulation also suggests that AP-1 is not the only mediator of ANP induction in LV hypertrophy.
Relation of Exercise-Induced Myocardial Ischemia to Cardiac and Carotid Structure
Authors: Okin Peter M. , Roman Mary J. , Schwartz Joseph E. , Pickering Thomas G. , Devereux Richard B.
Published: June 2012

Abstract
There is a strong relation of carotid atherosclerosis to coronary artery disease and left ventricular hypertrophy. In addition, abnormalities of carotid structure are strongly associated with abnormal left ventricular geometry and structure. However, little is known regarding the relation of exercise-induced ST depression to carotid atherosclerosis, carotid, or left ventricular structure in the absence of apparent coronary disease. The relationship of exercise ECG myocardial ischemia to the presence of carotid atherosclerosis and to carotid and left ventricular structure was assessed in 204 asymptomatic subjects free of clinical evidence of cardiovascular disease. Myocardial ischemia on the exercise ECG, defined by a chronotropically adjusted ST/HR slope of >3.47 μV/bpm, was associated with a nearly threefold greater likelihood of discrete carotid atherosclerosis (50% [6 of 12] versus 17% [29 of 192],
P
=.007) and with older age, male sex, higher systolic and diastolic blood pressures, greater left ventricular mass and mass index, and greater common carotid artery intimal-medial thickness and cross-sectional area index. Stepwise logistic regression analyses, including standard risk factors, revealed that only carotid artery cross-sectional area index (
P
=.0007) and systolic blood pressure (
P
=.005) independently predicted an abnormal chronotropically adjusted ST/heart rate slope. Moreover, among 132 subjects with ≥10 μV of ST-segment depression, only left ventricular mass index and carotid artery cross-sectional area index were significant predictors of the chronotropically adjusted ST/heart rate slope response. Subendocardial ischemia on the exercise ECG is strongly associated with the presence of carotid atherosclerosis and is related to systolic blood pressure, carotid artery cross-sectional area index, and left ventricular mass index, independent of age, sex, and other cardiac risk factors. These findings provide additional insights into the relation between coronary and carotid atherosclerosis and suggest that an association among ischemia and left ventricular and carotid structural abnormalities may contribute to the pathogenesis of coronary events.
Mannose 6-Phosphate Receptor–Mediated Internalization and Activation of Prorenin by Cardiac Cells
Authors: van Kesteren Catharina A. M. , Danser A. H. Jan , Derkx Frans H. M. , Dekkers Dick H. W. , Lamers Jos M. J. , Saxena Pramod R. , Schalekamp Maarten A. D. H.
Published: June 2012

Abstract
The binding and internalization of recombinant human renin and prorenin (2500 μU/mL) and the activation of prorenin were studied in neonatal rat cardiac myocytes and fibroblasts cultured in a chemically defined medium. Surface-bound and internalized enzymes were distinguished by the addition of mannose 6-phosphate to the medium, by incubating the cells both at 37°C and 4°C, and by the acid-wash method. Mannose 6-phosphate inhibited the binding of renin and prorenin to the myocyte cell surface in a dose-dependent manner. At 37°C, after incubation at 4°C for 2 hours, 60% to 70% of cell surface-bound renin or prorenin was internalized within 5 minutes. Intracellular prorenin was activated, but extracellular prorenin was not. The half-time of activation at 37°C was 25 minutes. Ammonium chloride and monensin, which interfere with the normal trafficking and recycling of internalized receptors and ligands, inhibited the activation of prorenin. Results obtained with cardiac fibroblasts were comparable to those in the myocytes. This study is the first to show experimental evidence for the internalization and activation of prorenin in extrarenal cells by a mannose 6-phosphate receptor–dependent process. Our findings may have physiological significance in light of recent experimental data indicating that angiotensin I and II are produced at cardiac and other extrarenal tissue sites by the action of renal renin and that intracellular angiotensin II can elicit important physiological responses.
Increased Stiffness of Radial Artery Wall Material in End-Stage Renal Disease
Authors: Mourad Jean-Jacques , Girerd Xavier , Boutouyrie Pierre , Laurent Stéphane , Safar Michel , London Gérard
Published: June 2012

Abstract
The incremental elastic modulus (Einc), which is the slope of the relationship between stress and strain of arteries, is a marker of vascular wall material stiffness. Isobaric Einc is reduced at the site of the radial artery in patients with essential hypertension and increased at the site of the common carotid artery in subjects with end-stage renal disease (ESRD). Whether the changes in Einc are influenced by the topography of the vessels, the composition of the arterial wall, and/or by the presence of ESRD is largely ignored. Radial artery Einc was measured in 19 patients with ESRD and compared with the Einc of 89 subjects with essential hypertension and 20 normotensive control subjects. Transcutaneous measurements of radial artery internal diameter and wall thickness (echo-tracking device) and digital pulse pressure (Finapres) were allowed to calculate Einc under operational (ie, at the mean arterial pressure of each group) and isobaric (100 mm Hg) conditions, as well as for a given wall stress. Internal diameter and pulsatile changes in diameter were identical in the three groups. Wall thickness and mean blood pressure were significantly elevated in subjects with hypertension but not in ESRD patients. Circumferential wall stress was identical in the three groups. For the same operational wall stress, and therefore at the operational mean arterial pressure of each group, Einc (kPa · 10
3
) was increased in patients with ESRD (5.53±4.0 versus 3.3±2.4 in control subjects;
P
<.05) and normal in subjects with essential hypertension (3.87±4.0). Under isobaric conditions, Einc was also significantly lower in subjects with hypertension and elevated in patients with ESRD. Thus, at the site of a medium-sized muscular artery constantly devoid of atherosclerosis, the stiffness of wall material is increased in patients with ESRD. The demonstrated alterations of the arterial wall are independent of the level of blood pressure and tensile stress and should be related to the status ESRD.