bluuebunny/crossref_metadata_2025 huggingface dataset:
Gender Differences in ET and NOS Systems in ET
B
Receptor–Deficient Rats
Authors: Taylor Traci A. , Gariepy Cheryl E. , Pollock David M. , Pollock Jennifer S.
Published: March 2003

The purpose of this study was to determine if rats lacking the ET
B
receptor have altered renal endothelin (ET) production and NO synthase (NOS) activity in response to high salt and if female rats are better able to control blood pressure through higher NOS activity in rats heterozygous (
sl/+
) and homozygous (
sl/sl
) for ET
B
receptor deficiency. On normal salt (0.4% NaCl; NS), male
sl/sl
rats had higher systolic blood pressures compared with male
sl/+
and female
sl/+
and
sl/sl
rats. On a high salt diet (10% NaCl; HS), blood pressure in male
sl/+
rats was significantly higher than female
sl/+
rats. However, ET
B
receptor deficiency caused much larger increases in blood pressure in male and female rats. On NS, urinary ET excretion was not different between male and female of either genotype. HS significantly increased ET excretion in male and female
sl/+
rats, but the increase was significantly less in
sl/sl
compared with
sl/+
. Homogenates of inner medullary collecting duct tissue were separated into particulate and cytosolic fractions and total NOS activity measured by conversion of [
3
H]L-arginine to [
3
H]L-citrulline. Female rats had significantly greater cytosolic NOS activity compared with male rats on NS. On HS, cytosolic NOS activity was lower in all groups compared with NS rats, whereas particulate NOS activity was significantly greater in male and female
sl/+
rats compared with male and female
sl/sl
rats. These data support our hypothesis that NOS protects against rises in blood pressure in female rats and ET
B
receptors prevent further increases in blood pressure due to increases in renal ET production and NOS activity.
Hypothalamic Melanocortin Receptors and Chronic Regulation of Arterial Pressure and Renal Function
Authors: Kuo Jay J. , Silva Alexandre A. , Hall John E.
Published: March 2003

This study examined control of cardiovascular and renal function during chronic melanocortin-3/4 receptor (MC3/4-R) activation or inhibition. Arterial and venous catheters were implanted in Sprague-Dawley rats for measurements of mean arterial pressure (MAP) and heart rate (HR) 24 h/d and for intravenous infusions, and the lateral ventricle was cannulated for chronic intracerebroventricular (ICV) infusions. In experiment 1, after a 5-day control period, rats were administered the MC3/4-R agonist MTII (n=7, 10 ng/h ICV) or 0.9% saline (n=6, ICV) for 14 days, followed by a 5-day recovery period. In experiment 2, after a 5-day control period, rats were administered the MC3/4-R antagonist SHU-9119 (n=7, 1 nmol/h ICV) or 0.9% saline vehicle (n=7, ICV), or pair-fed during SHU-9119 infusion (n=5, 1 nmol/h ICV) for 12 days, followed by a 5-day recovery period. MC4-R activation transiently decreased food intake from 23±1 to 10±2 g/d. Despite the hypophagia, MC3/4-R activation increased MAP by 7±1 mm Hg. MC3/4-R inhibition for 12 days increased food intake from 21±1 to 35±4 g/d, decreased HR by 53±11 bpm, and caused no change in MAP despite the marked weight gain. In rats that were pair-fed to prevent increased food intake, MC3/4-R inhibition further decreased HR (−87±9 bpm), whereas MAP was unchanged. Thus, chronic hypothalamic MC3/4-R activation raises arterial pressure despite decreased food intake, whereas MC3/4-R inhibition causes marked weight gain without raising arterial pressure. These observations are consistent with the hypothesis that an intact hypothalamic MC3/4-R may be necessary for excess weight gain to raise arterial pressure.
Cardioprotective Role of AT2 Receptor in Postinfarction Left Ventricular Remodeling
Authors: Oishi Yoshihiko , Ozono Ryoji , Yano Yoko , Teranishi Yasuhiro , Akishita Masahiro , Horiuchi Masatsugu , Oshima Tetsuya , Kambe Masayuki
Published: March 2003

The aim of this study was to determine the role of the AT2 receptor (AT2R) in left ventricular (LV) remodeling after myocardial infarction (MI). The left anterior descending arteries were ligated in AT2R gene knockout (
Agtr2-
) and wild-type (
Agtr2+
) mice. The LV remodeling was evaluated by echocardiography and histology over a period of 2 weeks after MI. The infarct sizes in hearts excised from
Agtr2+
and
Agtr2-
mice on day 1 were similar. The mortality rate of
Agtr2-
mice (62.9%) on day 14 after MI was significantly (
P
<0.05) higher than that of
Agtr2+
mice (39.7%). Accordingly, LV/body weight ratios (3.7±0.2 versus 3.0±0.1 on day 14) and LV end-diastolic (4.8±0.3 versus 3.9±0.4 mm on day 7) and end-systolic (4.4±0.3 versus 3.2±0.6 mm on day 7) dimensions evaluated by echocardiography were significantly greater in
Agtr2-
than in
Agtr2+
mice. The rates of ventricular arrhythmia, rates of cardiac rupture, and blood pressures in the 2 strains were similar after MI. Myocyte cross-sectional areas were increased after MI, but the magnitudes were similar in
Agtr2+
and
Agtr2-
mice, indicating the greater increases in LV dimensions and weight in
Agtr2-
mice are due to elongation of myocyte length and/or an increase in the interstitial weight (including vasculatures, infiltrated cells, and interstitial fluid). Interstitial fibrosis in remote myocardium was not evident in either strain. These results indicate AT2R plays a significant role in the protection against early development of LV dilation, thereby reducing the early mortality rate after MI.
Birth Weight Impacts on Wave Reflections in Children and Adolescents
Authors: Lurbe Empar , Torro Maria Isabel , Carvajal Eva , Alvarez Vicente , Redón Josep
Published: March 2003

The objective of the present study was to assess central aortic pressure and wave reflection in children and adolescents at different birth weights. Two hundred nineteen healthy children (126 girls), from 7 to 18 years of age (mean, 11.3 years) and born at term after a normotensive pregnancy, were included. The subjects were divided according to birth weight: <2.5 kg, from 2.5 to 2.999 kg, from 3.0 to 3.5 kg, and >3.5 kg. Pressure waveforms were recorded from the radial artery of the wrist, and the waveform data were then processed by the SphygmoCor radial/aortic transform software module to produce the estimated aortic pressure waveform. Augmentation index, an estimate of the pulse wave reflection, was significantly higher in children with the lowest birth weights compared with the other birth weight groups. In a multiple regression analysis, short stature, low heart rate, female gender, and lower birth weight had independent significant inverse correlations to the augmentation index when adjusted for diastolic blood pressure (
R
2
=0.21). In summary, the results showed a relatively aged phenotype of large-vessel function in the children with the lowest birth weights. These early alterations may be amplified throughout life and may contribute to the increased cardiovascular risk associated with low birth weight.
Intracellular Mechanisms Involved in Leptin Regulation of Sympathetic Outflow
Authors: Rahmouni Kamal , Haynes William G. , Morgan Donald A. , Mark Allyn L.
Published: March 2003

Leptin acts in the hypothalamus to decrease appetite and increase sympathetic nerve activity. The leptin receptor is known to signal through the janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway to modulate transcription of target genes. Alteration of the activity of phosphoinositol-3 kinase (PI3K) by leptin has also been reported, and inhibition of PI3K is known to block the leptin-induced suppression of feeding. We tested the hypothesis that leptin-induced renal sympathetic nerve activation is mediated by PI3K. We evaluated renal sympathetic nerve activity (RSNA) and feeding responses of C57BL/6J mice to intracerebroventricular (ICV) administration of leptin in the presence or absence of selective inhibitors of PI3K (LY294002 or wortmannin). As expected, ICV administration of leptin decreased food intake at 4 hours and 24 hours and increased RSNA. Pretreatment with the PI3K inhibitor LY294002 markedly attenuated both the decrease in food intake and the increase in RSNA induced by leptin. Wortmannin also inhibited the RSNA response to leptin. In contrast, PI3K inhibitors did not affect the RSNA response to MTII (melanocortin-3/4 receptor agonist). Our data demonstrate that PI3K appears to play an important role in the transduction of leptin-induced changes in renal sympathetic outflow.
Abolition of End-Organ Damage by Antiandrogen Treatment in Female Hypertensive Transgenic Rats
Authors: Baltatu Ovidiu , Cayla Cécile , Iliescu Radu , Andreev Dmitrii , Bader Michael
Published: March 2003

We aimed at studying the role of androgens in the development of cardiovascular pathology in hypertensive female rats. Female TGR(mREN2)27 rats harboring the mouse Ren-2 renin gene were treated with Flutamide (specific antagonist of the androgen receptor, 30 mg/kg per day) starting at 4 weeks of age. Flutamide treatment significantly attenuated the development of hypertension in female rats (systolic blood pressure: treated, 134.5±5.4 versus control, 165.4±3.8 mm Hg). Heart hypertrophy was significantly reduced by the treatment (treated, 0.37±0.008 versus control, 0.45±0.01 g/100 g body wt). Urinary albumin excretion was blunted (treated, 0.4±0.1 versus control, 23.1±7.5 mg/24 hours), collagen III mRNA was significantly decreased, and no histological characteristics of end-organ damage were observed in the kidney after treatment. Flutamide treatment significantly reduced plasma renin concentrations and rat renin mRNA in kidney but not plasma angiotensinogen levels. Plasma levels of estrogens, testosterone, and luteinizing hormone were not altered. These results demonstrate that the androgen receptor antagonist Flutamide protects against hypertension and end-organ damage not only in male but also in female TGR(mREN2)27 rats.
Erythrocyte Sodium-Lithium Countertransport and Blood Pressure
Authors: Weder Alan B. , Delgado Maria Carolina , Zhu Xiaofeng , Gleiberman Lillian , Kan Donghui , Chakravarti Aravinda
Published: March 2003

Increased activity of erythrocyte sodium-lithium countertransport is associated with essential hypertension. Sodium-lithium countertransport is highly heritable, but no single gene product mediating the exchange or explaining the association of increased sodium-lithium countertransport activity and hypertension has been identified. We performed a linkage study by using erythrocyte sodium-lithium countertransport as a quantitative phenotype and genome-wide markers at an average resolution of ≈10 cM to identify quantitative trait loci explaining sodium-lithium countertransport activity. A peak LOD score of 2.83 was detected on chromosome 15q at D15S642, a marker previously shown to be linked to blood pressure. Several genes mapped to this region are possible candidates for factors affecting erythrocyte sodium-lithium countertransport and/or blood pressure. Further studies confirming the presence of a quantitative trait locus in this region and evaluating these candidate genes may help explain the association of elevated sodium-lithium countertransport and hypertension.
CYP450- and COMT-Derived Estradiol Metabolites Inhibit Activity of Human Coronary Artery SMCs
Authors: Dubey Raghvendra K. , Gillespie Delbert G. , Zacharia Lefteris C. , Barchiesi Federica , Imthurn Bruno , Jackson Edwin K.
Published: March 2003

The purpose of this study is to test the hypothesis that the inhibitory effects of estradiol in human coronary vascular smooth muscle cells are mediated via local conversion to methoxyestradiols via specific cytochrome P
450s
(CYP450s) and catechol-O-methyltransferase (COMT). The inhibitory effects of estradiol on serum-induced cell activity (DNA synthesis, cell number, collagen synthesis, and cell migration) were enhanced by 3-methylcholantherene, phenobarbital (broad-spectrum CYP450 inducers), and β-naphthoflavone (CYP1A1/1A2 inducer) and were blocked by 1-aminobenzotriazole (broad-spectrum CYP450 inhibitor). Ellipticine, α-naphthoflavone (selective CYP1A1 inhibitors), and pyrene (selective CYP1B1 inhibitor), but not ketoconazole (selective CYP3A4 inhibitor) or furafylline (selective CYP1A2 inhibitor), abrogated the inhibitor effects of estradiol on cell activity, a profile consistent with a CYP1A1/CYP1B1-mediated mechanism. The inhibitory effects of estradiol were blocked by the COMT inhibitors OR486 and quercetin. The estrogen receptor antagonist ICI 182,780 blocked the inhibitory effects of estradiol, but only at concentrations that also blocked the metabolism of estradiol to hydroxyestradiols (precursors of methoxyestradiols). Western blot analysis revealed that coronary smooth muscle cells expressed CYP1A1 and CYP1B1. Moreover, these cells metabolized estradiol to hydroxyestradiols and methoxyestradiols, and the conversion of 2-hydroxyestradiol to 2-methoxyestradiol was blocked by OR486 and quercetin. These findings provide evidence that the inhibitory effects of estradiol on coronary smooth muscle cells are largely mediated via CYP1A1- and CYP1B1-derived hydroxyestradiols that are converted to methoxyestradiols by COMT.
Inhibition of Apical Na
+
/H
+
Exchangers on the Macula Densa Cells Augments Tubuloglomerular Feedback
Authors: Wang Hong , Carretero Oscar A. , Garvin Jeffrey L.
Published: March 2003

NO produced by neuronal NO synthase (nNOS) in the macula densa blunts tubuloglomerular feedback (TGF). nNOS activity is strongly pH-dependent. Increasing luminal NaCl concentration increases nNOS activity, NO production, and apical Na
+
/H
+
exchange. Na
+
/H
+
exchange alkalinizes the macula densa. We hypothesized that inhibiting apical Na
+
/H
+
exchange in macula densa cells would augment TGF by blunting nNOS activation caused by increasing luminal NaCl concentration. Rabbit afferent arterioles and attached macula densas were microperfused in vitro. TGF response was defined as the change in afferent arteriole diameter caused by increasing the NaCl concentration in the macula densa perfusate. 7-Nitroindazole (7-NI; 10 μmol/L) alone in the macula densa lumen increased the TGF response from 2.4±0.1 to 3.8±0.2 μm (
P
<0.01). When dimethyl amiloride (100 μmol/L), a Na
+
/H
+
exchange inhibitor, was added to the macula densa lumen, it increased the TGF response from 2.5±0.3 to 3.7±0.5 μm (
P
<0.01). In the presence of dimethyl amiloride, 7-NI had no effect on the TGF response (from 2.6±0.2 to 2.7±0.2 μm). Our data indicate that inhibiting apical Na
+
/H
+
exchange in the macula densa mimics the effect of inhibiting NO production by nNOS in the macula densa on TGF. Thus, it is possible that increased apical Na
+
/H
+
exchange caused by increasing the sodium concentration in the lumen of the macula densa activates macula densa nNOS. The link between nNOS and Na
+
/H
+
exchange may be intracellular pH.
Heme Oxygenase Attenuates Angiotensin II-Mediated Increase in Cyclooxygenase-2 Activity in Human Femoral Endothelial Cells
Authors: Li Volti Giovanni , Seta Francesca , Schwartzman Michal L. , Nasjletti Alberto , Abraham Nader G.
Published: March 2003

Heme oxygenase (HO) regulates cellular heme levels and catalyzes the formation of bilirubin and carbon monoxide. We hypothesize that the status of the endothelial HO system influences the angiotensin (Ang) II-induced increase in the endothelial production of prostaglandin I
2
(PGI
2
) (measured as 6-keto-PGF
1α
) and prostaglandin E
2
(PGE
2
), eicosanoids that modulate the vascular actions of Ang II. In the present study, we determined the effect of interventions that suppress HO activity or induce HO-1 gene expression on Ang II-mediated increase in 6-keto-PGF
1α
and PGE
2
in cultures of human femoral artery endothelial cells. Incubation of endothelial cells with Ang II (100 ng/mL) for 24 hours increased the levels of both 6-keto-PGF
1α
and PGE
2
in the culture media. This effect of Ang II on prostaglandin production by endothelial cells was attenuated in cells treated with SnCl
2
(10 μmol/L), an inducer of HO-1, but was magnified in cells treated with the HO inhibitor ZnDPP or heme. Upregulation of HO-1 gene expression by retrovirus-mediated delivery of the human HO-1 gene also attenuated heme and Ang II-induced prostaglandin synthesis. Of note, prostaglandin synthesis by lysates of endothelial cells stimulated with heme or Ang II appear to involve COX-2, because it was blunted by NS-398, which is presumed to inhibit COX-2 specifically. These results indicate that overexpression of the HO system exerts an inhibitory influence on Ang II-induced synthesis of prostaglandins by endothelial cells.
Role of EGFR Transactivation in Angiotensin II Signaling to Extracellular Regulated Kinase in Preglomerular Smooth Muscle Cells
Authors: Andresen Bradley T. , Linnoila Jenny J. , Jackson Edwin K. , Romero Guillermo G.
Published: March 2003

Angiotensin (Ang) II promotes the phosphorylation of extracellular regulated kinase (ERK); however, the mechanisms leading to Ang II-induced ERK phosphorylation are debated. The currently accepted theory involves transactivation of epidermal growth factor receptor (EGFR). We have shown that generation of phosphatidic acid (PA) is required for the recruitment of Raf to membranes and the activation of ERK by multiple agonists, including Ang II. In the present report, we confirm that phospholipase D-dependent generation of PA is required for Ang II-mediated phosphorylation of ERK in Wistar-Kyoto and spontaneously hypertensive rat preglomerular smooth muscle cells (PGSMCs). However, EGF stimulation does not activate phospholipase D or generate PA. These observations indicate that EGF recruits Raf to membranes via a mechanism that does not involve PA, and thus, Ang II-mediated phosphorylation of ERK is partially independent of EGFR-mediated signaling cascades. We hypothesized that phosphoinositide-3-kinase (PI3K) can also act to recruit Raf to membranes; therefore, inhibition of PI3K should inhibit EGF signaling to ERK. Wortmannin, a PI3K inhibitor, inhibited EGF-mediated phosphorylation of ERK (IC
50
, ≈14 nmol/L). To examine the role of the EGFR in Ang II-mediated phosphorylation of ERK we utilized 100 nmol/L wortmannin to inhibit EGFR signaling to ERK and T19N RhoA to block Ang II-mediated ERK phosphorylation. Wortmannin treatment inhibited EGF-mediated but not Ang II-mediated phosphorylation of ERK. Furthermore, T19N RhoA inhibited Ang II-mediated ERK phosphorylation, whereas T19N RhoA had significantly less effect on EGF-mediated ERK phosphorylation. We conclude that transactivation of the EGFR is not primarily responsible for Ang II-mediated activation of ERK in PGSMCs.
Anandamide-Induced Depressor Effect in Spontaneously Hypertensive Rats
Authors: Li Jianping , Kaminski Norbert E. , Wang Donna H.
Published: March 2003

To test the hypothesis that activation of the vanilloid receptor (VR1) contributes to the anandamide-induced depressor effect in spontaneously hypertensive rats (SHR), we used a selective VR1 antagonist capsazepine (CAPZ) and a selective cannabinoid type 1 receptor antagonist SR141716A in conjunction with a VR1 agonist capsaicin in both SHR and Wistar-Kyoto rats (WKY). Mean arterial pressure was increased in SHR compared with WKY (
P
<0.05). Intravenous administration of capsaicin caused a greater depressor response in SHR compared with WKY (
P
<0.05), which was blocked by ≈60% by CAPZ (
P
<0.05) in SHR only. Methanandamide caused a similar greater depressor response (
P
<0.05), which was blocked by ≈50% and 60% by CAPZ and SR141716A, respectively, in SHR (
P
<0.05) but not in WKY. Radioimmunoassay showed that methanandamide increased plasma calcitonin gene-related peptide (CGRP) levels from baseline in both SHR and WKY (
P
<0.05), with no difference between 2 strains. Western blot showed that protein expression for the calcitonin receptor–like receptor—but not receptor activity modifying protein 1, VR1, and cannabinoid type 1 receptors—was increased in mesenteric resistance arteries in SHR compared with WKY (
P
<0.05). These data indicate that in addition to activation of cannabinoid type 1, anandamide may serve as an endogenous compound to stimulate VR1, leading to a decrease in blood pressure via CGRP release from sensory nerve terminals. Increased mesenteric CGRP receptor expression in SHR may account for increased sensitivity of blood pressure to anandamide and may serve as a compensatory response to buffer the increase in blood pressure in SHR.
Molecular Mechanisms Mediating Inflammation in Vascular Disease
Authors: Egashira Kensuke
Published: March 2003

There are several clinical challenges for the treatment of intractable cardiovascular diseases, including restenosis, atherosclerotic complications resulting from plaque rupture, severe tissue ischemia, and heart failure. Emerging evidence suggests that an inflammatory process is involved in the pathogenesis of such intractable diseases. In particular, inflammatory responses to arterial injury, which cause continuous recruitment and activation of monocytes mainly through activation of the monocyte chemoattractant protein-1 (MCP-1) pathway, have a central role in restenosis and atherogenesis. We recently devised a new strategy for anti–MCP-1 therapy by transfecting an N-terminal deletion mutant of the MCP-1 gene into skeletal muscles. This mutant MCP-1 lacks the N-terminal amino acids 2 to 8, called 7ND, and works as a dominant-negative inhibitor of MCP-1. We demonstrated that 7ND gene transfer suppresses monocyte infiltration/activation after arterial injury and markedly inhibits experimental restenosis in animals after balloon injury or stent placement. Furthermore, 7ND gene transfer not only attenuated the development of early atherosclerotic lesions but also limited progression of preexisting atherosclerotic lesions and changed the lesion composition into a more stable phenotype in hypercholesterolemic mice. Vascular inflammation mediated by MCP-1 might create a positive feedback loop to enhance restenotic and atherosclerotic changes through activating lesional monocytes. Therefore, vascular inflammation mediated by MCP-1 has a central role in the development of experimental restenosis, atherosclerosis, and plaque destabilization, leading to acute coronary syndrome. This strategy for gene therapy might be useful against human restenosis, thereby opening a new therapeutic window for antirestenosis and antiatherosclerosis paradigms.
Endothelin-Induced Increases in Ca
2+
Entry Mechanisms of Vascular Contraction Are Enhanced During High-Salt Diet
Authors: Smith Leah , Payne Jason A. , Sedeek Mona H. , Granger Joey P. , Khalil Raouf A.
Published: March 2003

High-salt diet is often associated with increases in arterial pressure, and a role for endothelin (ET)-1 in salt-sensitive hypertension has been suggested; however, the vascular mechanisms involved are unclear. We investigated whether ET increases the sensitivity of the mechanisms of vascular contraction to changes in dietary salt intake. Active stress and
45
Ca
2+
influx were measured in endothelium-denuded aortic strips of male Sprague-Dawley rats not treated or chronically infused intravenously with ET (5 pmol/kg per minute) and fed either normal-sodium diet (NS, 1%) or high-sodium diet (HS, 8%) for 9 days. Phenylephrine (Phe) caused increases in active stress that were similar in NS and HS, but were greater in NS/ET (maximum, 10.5±0.7) than in NS (maximum, 7.4±0.9) rats, and further enhanced in HS/ET (maximum, 14.4±1.1) compared with HS rats (maximum, 8.0±0.8×10
4
N/m
2
). Phe was more potent in causing contraction in NS/ET than in NS rats and in HS/ET than in HS rats. In Ca
2+
-free (2 mmol/L EGTA) Krebs, stimulation of intracellular Ca
2+
release by Phe (10
−5
mol/L) or caffeine (25 mmol/L) caused a transient contraction that was not significantly different in all groups of rats. In contrast, membrane depolarization by high-KCl solution, which stimulates Ca
2+
entry from the extracellular space, caused greater contraction in ET-infused rats, particularly those on HS diet. Phe (10
−5
mol/L) caused an increase in
45
Ca
2+
influx that was greater in NS/ET (27.9±1.7) than in NS (20.1±1.8) rats and further enhanced in HS/ET (35.2±1.8) compared with HS rats (21.8±1.9 μmol/kg/min). The Phe-induced
45
Ca
2+
influx-stress relation was not different between NS and HS rats, but was enhanced in ET-infused rats particularly those on HS. The enhancement of the
45
Ca
2+
influx–active stress relation in ET-infused rats was not observed in vascular strips treated with the protein kinase C inhibitor GF109203X or calphostin C (10
−6
mol/L). Thus, low-dose infusion of ET, particularly during HS, is associated with increased vascular reactivity that involves Ca
2+
entry from the extracellular space, but not Ca
2+
release from the intracellular stores. The ET-induced enhancement of the Ca
2+
influx-stress relation particularly during HS suggests activation of other mechanisms in addition to Ca
2+
entry, possibly involving protein kinase C. The results suggest that ET increases the sensitivity of the mechanisms of vascular smooth muscle contraction to high dietary salt intake and may, in part, explain the possible role of ET in salt-sensitive hypertension.
20-HETE and Furosemide-Induced Natriuresis in Salt-Sensitive Essential Hypertension
Authors: Laffer Cheryl L. , Laniado-Schwartzman Michal , Wang Mong-Heng , Nasjletti Alberto , Elijovich Fernando
Published: March 2003

Cyclooxygenase metabolites of arachidonic acid modulate the natriuretic effect of furosemide. It is not known whether 20-HETE, a monooxygenase metabolite of arachidonic acid that also inhibits sodium transport, participates in the action of furosemide. We measured urine sodium (UNaV) and 20-HETE during furosemide diuresis (40 mg three times over 12 hours) in 12 salt-sensitive (SS) and 11 salt-resistant (SR), salt-replete hypertensive subjects (126±24 mmol/24 hours positive sodium balance produced by 160-mmol-sodium diet and 2 L saline infusion). Individual systolic blood pressure decreases from the salt-replete to the salt-depleted state were the index of salt-sensitivity. SS had low plasma renin with blunted responses to changes in salt balance, inappropriate plasma aldosterone, and an increased aldosterone/renin ratio. UNaV by furosemide was less in SS (263±25 mmol/12 hours) than in SR (351±25 mmol/12 hours,
P
<0.02) patients. 20-HETE was not different between SS and SR patients before (1.92±0.38 versus 1.37±0.34 μg/h) or after furosemide (1.52±0.27 versus 2.01±0.40 μg/h), but furosemide changed 20-HETE excretion in opposite direction in SR (0.63±0.26) versus SS (−0.40±0.17,
P
<0.005) patients. In all patients together, %Δ20-HETE by furosemide correlated with %ΔUNaV (
r
=0.56,
P
<0.01) and negatively with salt-sensitivity of blood pressure (
r
=−0.55,
P
<0.01). In SS, Δ20-HETE by furosemide correlated with Δaldosterone/renin ratio (
r
=0.60,
P
<0.05), whereas 20-HETE during furosemide had a negative correlation with body mass index (
r
=−0.73,
P
<0.01). Our data suggest that 20-HETE modulates the natriuretic response to furosemide, and impaired natriuresis of SS involves a mechanism that alters the 20-HETE response to furosemide and is linked to salt-sensitivity of blood pressure.
GTP Cyclohydrolase 1 Downregulation Contributes to Glucocorticoid Hypertension in Rats
Authors: Mitchell Brett M. , Dorrance Anne M. , Webb R. Clinton
Published: March 2003

NO, a potent vasodilator, has been implicated in the pathogenesis of glucocorticoid hypertension. NO synthase requires the cofactor tetrahydrobiopterin for the production of NO. Guanosine-triphosphate (GTP) cyclohydrolase 1 is the rate-limiting enzyme for the production of tetrahydrobiopterin, and in the presence of low levels of tetrahydrobiopterin, NO production is decreased. We have previously shown that tetrahydrobiopterin-dependent vasodilation is impaired in rats with glucocorticoid hypertension. However, the role GTP cyclohydrolase 1 plays in the pathogenesis of glucocorticoid hypertension has not been investigated. Therefore, we tested the hypothesis that downregulation of GTP cyclohydrolase 1 contributes to the development and maintenance of glucocorticoid hypertension in rats. Rats were implanted with dexamethasone (0.79 mg · kg
−1
· d
−1
) or sham-operated, and systolic blood pressures were measured at baseline and after 12 hours, 4 days, or 15 days. Blood pressure increased significantly after dexamethasone treatment. Isometric force generation was measured in endothelium-intact aortic ring segments. Aortas from dexamethasone-treated rats exhibited a significant time-dependent decrease in maximal relaxation to acetylcholine compared with control rats. Incubation with sepiapterin (10
−4
mol/L, 1 hour), which produces tetrahydrobiopterin via a salvage pathway, restored vasodilation to acetylcholine in aortas from 4- and 15-day dexamethasone-treated rats. GTP cyclohydrolase 1 mRNA expression levels also significantly decreased in a time-dependent manner. These results support the hypothesis that downregulation of GTP cyclohydrolase 1 contributes to increased blood pressure in glucocorticoid hypertensive rats.
Angiotensin II–Mediated Negative Regulation of Npr1 Promoter Activity and Gene Transcription
Authors: Garg Renu , Pandey Kailash N.
Published: March 2003

Atrial natriuretic peptide receptor A (NPRA) plays important role(s) in the control of extracellular fluid volume and blood pressure homeostasis. We have determined and analyzed the functional promoter region of Npr1 gene (coding for NPRA) and studied the effect of angiotensin (Ang) II on its promoter activity and expression in cultured mouse mesangial cells. The promoter analysis of Npr1 gene revealed the presence of positive regulatory
cis
-elements in the regions −1982 to −1841 bp and −916 to −496 bp and of the repressor elements in the regions −1841 to −916 bp and 56 to 382 bp relative to transcription start site. The Ang II pretreatment of cultured mouse mesangial cells transiently transfected with the promoter construct pNPRA-luc1 significantly inhibited the promoter activity in a time- and dose-dependent manner, with a maximum inhibition at 24 hours. The Ang II–dependent repression of Npr1 promoter activity was partially blocked by both angiotensin type 1 and type 2 antagonists candesartan and PD 123,319, respectively. The mRNA level of NPRA was also downregulated by Ang II treatment as determined by semiquantitative reverse transcriptase–polymerase chain reaction assay. The deletion analysis showed that the promoter region ≈916 bp upstream of transcription start site contains the
cis
-elements involved in Ang II–mediated repression of transcription of Npr1 gene. The present study thus reveals the presence of functional
cis
-regulatory elements in the promoter region of the murine Npr1 gene and its transcriptional downregulation by vasoactive peptide Ang II.
Insulin-Induced Akt Activation Is Inhibited by Angiotensin II in the Vasculature Through Protein Kinase C-α
Authors: Motley Evangeline D. , Eguchi Kunie , Gardner Carla , Hicks Adrienne L. , Reynolds Cherilynn M. , Frank Gerald D. , Mifune Mizuo , Ohba Motoi , Eguchi Satoru
Published: March 2003

Insulin resistance is an important risk factor in the development of cardiovascular diseases such as hypertension and atherosclerosis. However, the specific role of insulin resistance in the etiology of these diseases is poorly understood. Angiotensin (Ang) II is a potent vasculotrophic and vasoconstricting factor. We hypothesize that in vascular smooth muscle cells (VSMCs), Ang II interferes with insulin action by inhibiting Akt, a major signaling molecule implicated in the biological actions of insulin. By immunoblotting with a phospho-specific antibody for Akt, we found that Ang II inhibits insulin-induced Akt phosphorylation in a time- and concentration-dependent manner. The inhibitory effect of Ang II was blocked by a Ang II type 1 receptor antagonist, RNH6270. A protein kinase C (PKC) activator, phorbol 12-myristate 13-acetate, also inhibited insulin-induced Akt phosphorylation. PKC inhibitors, including Go6976 (specific for α- and β-isoforms), blocked the Ang II– and PMA-induced inhibition of Akt phosphorylation by insulin. Moreover, overexpression of PKC-α but not PKC-β isoform by adenovirus inhibited insulin-induced Akt phosphorylation. By contrast, an epidermal growth factor receptor inhibitor (AG1478), a p42/44 mitogen-activated protein kinase (MAPK) kinase inhibitor (PD 598,059), and a p38 MAPK inhibitor (SB 203,580) did not block the Ang II–induced inhibition of Akt phosphorylation. From these data, we conclude that Ang II negatively regulates the insulin signal, Akt, in the vasculature specifically through PKC-α activation, providing an alternative molecular mechanism that may explain the association of hyperinsulinemia with cardiovascular diseases.
The Kidney, Hypertension, and Obesity
Authors: Hall John E.
Published: March 2003

This paper provides a personal perspective of the role of abnormal renal-pressure natriuresis in the pathogenesis of hypertension. Direct support for a major role of renal-pressure natriuresis in long-term control of arterial pressure and sodium balance comes from studies demonstrating that (1) pressure natriuresis is impaired in all forms of chronic hypertension and (2) prevention of pressure natriuresis from operating, by servo-control of renal perfusion pressure, also prevents the maintenance of sodium balance hypertension. Although the precise mechanisms of impaired pressure natriuresis in essential hypertension have remained elusive, recent evidence suggests that obesity and overweight may play a major role. Obesity increases renal sodium reabsorption and impairs pressure natriuresis by activation of the renin-angiotensin and sympathetic nervous systems and by altered intrarenal physical forces. Chronic obesity also causes marked structural changes in the kidneys that eventually lead to a loss of nephron function, further increases in arterial pressure, and severe renal injury in some cases. Although there are many unanswered questions about the mechanisms of obesity hypertension and renal disease, this is one of the most promising areas for future research, especially in view of the growing, worldwide “epidemic” of obesity.
Ventrolateral Medulla AT
1
Receptors Support Arterial Pressure in Dahl Salt-Sensitive Rats
Authors: Ito Satoru , Hiratsuka Makoto , Komatsu Kazutoshi , Tsukamoto Kazuyoshi , Kanmatsuse Katsuo , Sved Alan F.
Published: March 2003

The present study addresses the hypothesis that angiotensin type 1 receptors (AT
1
Rs) in the rostral ventrolateral medulla (RVLM) contribute to the elevation of mean arterial pressure (MAP) in Dahl salt-sensitive (DS) rats fed a diet with a high NaCl content. Groups of DS or Dahl salt-resistant (DR) rats were fed diets containing either 0.3% NaCl (LNa) or 8% NaCl (HNa) for 3 weeks. Rats were anesthetized with α-chloralose, and the effects of microinjecting the AT
1
R antagonist valsartan (Val) or angiotensin II (Ang II) into the RVLM on MAP were measured. Bilateral injection of 100 pmol Val into the RVLM reduced the elevated MAP in the DS-HNa rats by ≈35 mm Hg. In contrast, Val had no effect on MAP in DS-LNa rats. DR rats were normotensive on either diet; Val injection into the RVLM had no significant effect on MAP in DR-HNa rats but did evoke a small decrease in MAP in DR-LNa rats. Injection of Ang II into the RVLM increased arterial pressure in all groups, but the response was substantially larger in DS-HNa rats. Inhibition of neuronal function in the vicinity of the hypothalamic paraventricular nucleus, a possible source of innervation of the RVLM AT
1
R, by local injection with muscimol also produced a substantial decrease in MAP in DS-HNa rats but not in DS-LNa rats or DR rats. Thus, RVLM AT
1
Rs appear to contribute to salt-dependent hypertension in DS rats, and the paraventricular nucleus may be a source of this tonic activation.
Roles of Oxidative Stress and AT
1
Receptors in Renal Hemodynamics and Oxygenation in the Postclipped 2K,1C Kidney
Authors: Welch William J. , Mendonca Margarida , Aslam Shakil , Wilcox Christopher S.
Published: March 2003

The spontaneously hypertensive rat (SHR) exhibits angiotensin II (Ang II)–dependent oxidative stress and reduced efficiency of renal oxygen usage (Q
O2
) for tubular sodium transport (T
Na
). We tested the hypothesis that oxidative stress determines the reduced T
Na
:Q
O2
ratio in the clipped kidney of the early 2-kidney, 1-clip (2K,1C) Ang II–dependent model. One week after sham operation (Sham) or clip placement, 2K,1C rats received for 2 weeks either a vehicle, the superoxide dismutase mimetic tempol (Temp), or candesartan (Cand). Oxidative stress was assessed from excretion of 8-isoprostaglandin F
2α
(PGF
2α
) and malondialdehyde (MDA) and renal oxygenation from pO
2
in the renal cortex and from the ratio of calculated T
Na
and Q
O2
values. The mean arterial pressure (MAP) of Sham (113±6 mm Hg) was increased in 2K,1C vehicle-treated rats (148±4 mm Hg), but both Temp and Cand restored MAP to Sham levels. The excretions of 8-iso-PGF
2α
and MDA were higher in 2K,1C vehicle-treated rats compared with Sham and were normalized by Temp. The pO
2
of Sham (42±2 mm Hg) was lower in 2K,1C vehicle-treated animals (28±2 mm Hg). This was restored to Sham values by Temp (36±3 mm Hg) but not by Cand (28±2 mm Hg). The T
Na
:Q
O2
of Sham (12.9±1.6) was reduced in 2K,1C vehicle-treated rats (9.7±2.8) and was restored to Sham values by Temp (13.7±2.5) but not by Cand (7.5±1.6). We conclude that the correction of oxidative stress in the 2K,1C model partially corrects renal cortical hypoxia and inefficient utilization of O
2
for Na
+
transport, independent of the fall in blood pressure.
Characterization of a New Selective Antagonist for Angiotensin-(1–7),
d
-Pro
7
-Angiotensin-(1–7)
Authors: Santos Robson A.S. , Haibara Andréa S. , Campagnole-Santos Maria José , Simões e Silva Ana C. , Paula Renata D. , Pinheiro Sérgio V.B. , de Fátima Leite Maria , Lemos Virginia S. , Silva Denise M.R. , Guerra Mateus T. , Khosla Mahesh C.
Published: March 2003

Angiotensin-(1–7) [Ang-(1–7)] has biological actions that can often be distinguished from those of angiotensin II (Ang II). Recent studies indicate that the effects of Ang-(1–7) are mediated by specific receptor(s). We now report the partial characterization of a new antagonist selective for Ang-(1–7),
d
-Pro
7
-Ang-(1–7).
d
-Pro
7
-Ang-(1–7) (50 pmol) inhibited the hypertensive effect induced by microinjection of Ang-(1–7) [4±1 vs 21±2 mm Hg, 25 pmol Ang-(1–7) alone] into the rostral ventrolateral medulla without changing the effect of Ang II (16±2.5 vs 19±2.5 mm Hg after 25 pmol Ang II alone). At 10
−7
mol/L concentration, it completely blocked the endothelium-dependent vasorelaxation produced by Ang-(1–7) (10
−10
to 10
−6
mol/L) in the mouse aorta. The antidiuresis produced by Ang-(1–7) (40 pmol/100 g body weight) in water-loaded rats was also blocked by its analog [1 μg/100 g body weight; 3.08±0.8 vs 1.27±0.33 mL in Ang-(1–7)–treated rats].
d
-Pro
7
-Ang-(1–7) at a molar ratio of 40:1 did not change the hypotensive effect of bradykinin. Moreover,
d
-Pro
7
-Ang-(1–7) did not affect the dipsogenic effect produced by intracerebroventricular administration of Ang II (11.4±1.15 vs 8.8±1.2 mL/h after Ang II) and did not show any demonstrable angiotensin-converting enzyme inhibitory activity in assays with the synthetic substrate Hip-His-Leu and rat plasma as a source of enzyme. Autoradiography studies with
125
I–Ang-(1–7) in mouse kidney slices showed that
d
-Pro
7
-Ang-(1–7) competed for the binding of Ang-(1–7) to the cortical supramedullary region. In Chinese hamster ovary cells stably transfected with the AT
1
receptor subtype,
d
-Pro
7
-Ang-(1–7) did not compete for the specific binding of
125
I–Ang-II in concentrations up to 10
−6
mol/L. There was also no significant displacement of Ang II binding to angiotensin type 2 receptors in membrane preparations of adrenal medulla. These data indicate that
d
-Pro
7
-Ang-(1–7) is a selective antagonist for Ang-(1–7), which can be useful to clarify the functional role of this heptapeptide.
Circulating Endothelial Cells Are a Novel Marker of Cyclosporine-Induced Endothelial Damage
Authors: Woywodt Alexander , Schroeder Maik , Mengel Michael , Schwarz Anke , Gwinner Wilfried , Haller Hermann , Haubitz Marion
Published: March 2003

Microvascular endothelial cells play a key role in transplant immunology. They are also important targets for calcineurin inhibitors. We recently demonstrated elevated numbers of circulating endothelial cells in renal transplant recipients with and without rejection in comparison with healthy controls. Because these patients received either cyclosporine or tacrolimus, we speculated that endothelial damage from calcineurin inhibitors might be responsible for these findings. In the present study, we tested the hypothesis that treatment with calcineurin inhibitors leads to an increase in circulating endothelial cells. We studied 57 renal transplant recipients: 19 on a calcineurin inhibitor–free immunosuppressive regimen and 38 patients on a standard immunosuppressive regimen, including cyclosporine, and matched them for age and serum creatinine. Endothelial cells were isolated from peripheral blood with anti-CD-146–coated immunomagnetic Dynabeads™ and were counted by fluorescence microscopy. Patients with cyclosporine therapy had elevated numbers of circulating endothelial cells (median 26, range 12 to 82 cells/mL) compared with healthy controls (median 6, range 0 to 82 cells/mL;
P
<0.001). Patients without calcineurin inhibitor treatment had significantly lower cell numbers (median 12, range 0 to 32 cells/mL;
P
<0.003) and were not significantly different from normal, untreated controls. In conclusion, renal transplant recipients who do not receive calcineurin inhibitors have significantly lower numbers of circulating endothelial cells than their age- and creatinine-matched counterparts who receive these drugs. We suggest that elevated numbers of circulating endothelial cells indicate damage from calcineurin inhibitors in renal transplant recipients and that circulating endothelial cells are a novel marker of endothelial damage.
Adult Rabbit Offspring of Mothers With Secondary Hypertension Have Increased Blood Pressure
Authors: Denton Kate M. , Flower Rebecca L. , Stevenson Kathleen M. , Anderson Warwick P.
Published: March 2003

Preexisting chronic hypertension complicates up to 5% of pregnancies and is associated with an increased risk of low-birth-weight babies. Studies suggest that an adverse intrauterine environment leading to low birth weight is linked to an increased risk of cardiovascular disease, including hypertension, in the adult. In this study, the blood pressure of offspring from mothers with hypertension were followed up into adulthood. Two-kidney, 1-wrapped hypertension was induced in 7 female rabbits; 5 other rabbits underwent sham surgery. Four weeks later, rabbits were mated, at which time mean arterial pressure was 118±3 and 87±5 mm Hg in the hypertensive and sham groups, respectively (
P
<0.001). The blood pressure of 30-week-old females was 89±2 mm Hg in the offspring of hypertensive (n=14) and 79±1 mm Hg in the offspring of normotensive (n=13) mothers (
P
<0.005). Also, plasma renin activity was significantly lower in the female offspring of hypertensive mothers at 10 weeks of age (
P
<0.05), suggesting that development of the renin-angiotensin system was altered. In contrast, male offspring from hypertensive and normotensive mothers had similar mean arterial pressure and plasma renin activity. In conclusion, maternal secondary hypertension can “program” hypertension in female adult offspring. The results also suggest that there are gender-specific differences in sensitivity to altered in utero environmental influences.
Myocardial PKC β2 and the Sensitivity of Na/K-ATPase to Marinobufagenin Are Reduced by Cicletanine in Dahl Hypertension
Authors: Fedorova Olga V. , Talan Mark I. , Agalakova Natalia I. , Droy-Lefaix Marie-Therese , Lakatta Edward G. , Bagrov Alexei Y.
Published: March 2003

Marinobufagenin (MBG), an endogenous ligand of α-1 Na/K-ATPase, becomes elevated and contributes to hypertension in NaCl-loaded Dahl-S rats (DS). Protein kinase C (PKC) phosphorylates α-1 Na/K-ATPase and increases its MBG sensitivity. Cicletanine, an antihypertensive compound with PKC-inhibitory activity, reverses MBG-induced Na/K-ATPase inhibition and vasoconstriction. We hypothesized that increased PKC levels in sodium-loaded hypertensive DS would sensitize α-1 Na/K-ATPase to MBG and that PKC inhibition by cicletanine would produce an opposite effect. We studied the effects of cicletanine on systolic blood pressure, left ventricular PKC isoforms, cardiac α-1 Na/K-ATPase levels, and sensitivity to MBG in hypertensive DS. Seven DS received 50 mg · kg
−1
· d
−1
cicletanine, and 7 DS received vehicle during 4 weeks of an 8% NaCl diet. Vehicle-treated rats exhibited an increase in blood pressure, left ventricular mass, MBG excretion (74±11 vs 9±1 pmol/24 h,
P
<0.01), myocardial α-1 Na/K-ATPase protein, and PKC β2 and δ. The sensitivity of Na/K-ATPase to MBG was enhanced at the level of high-affinity binding sites (IC
50
, 0.8 vs 4.4 nmol/L,
P
<0.01). Cicletanine-treated rats exhibited a 56-mm Hg reduction in blood pressure (
P
<0.01) and a 30% reduction in left ventricular weight, whereas cardiac α-1 Na/K-ATPase protein and MBG levels were unchanged. In cicletanine-treated rats, PKC β2 was not increased, the sensitivity of Na/K-ATPase to MBG was decreased (IC
50
=20 μmol/L), and phorbol diacetate–induced α-1 Na/K-ATPase phosphorylation was reduced versus vehicle-treated rats. In vitro cicletanine treatment of sarcolemma from vehicle-treated rats also desensitized Na/K-ATPase to MBG, indicating that this effect was not solely attributable to a reduction in blood pressure. Thus, PKC-induced phosphorylation of cardiac α-1 Na/K-ATPase is a likely target for cicletanine treatment.
Ventricular Adrenomedullin System in the Transition From LVH to Heart Failure in Rats
Authors: Nishikimi Toshio , Tadokoro Kazuyoshi , Mori Yosuke , Wang Xin , Akimoto Kazumi , Yoshihara Fumiki , Minamino Naoto , Kangawa Kenji , Matsuoka Hiroaki
Published: March 2003

We investigated whether adrenomedullin (AM) participates in the pathophysiology during the transition from left ventricular hypertrophy (LVH) to heart failure (HF). We used the Dahl salt-sensitive (DS) rat model, in which systemic hypertension causes LVH at the age of 11 weeks, followed by HF at the age of 18 weeks. Two molecular forms of AM levels in the plasma and myocardium at the LVH stage were significantly elevated compared with those in controls, and they were further increased at the HF stage. Interestingly, the LV tissue AM-mature/AM-total ratio was higher only in the HF group than in controls and LVH. The LV tissue AM-mature/AM-total ratio, AM-mature, and AM-total concentrations had close relations with the LV weight/body weight (
r
=0.72,
r
=0.79, and
r
=0.70, respectively; all
P
<0.001).
AM
gene expression was significantly increased at the LVH stage and was further increased at the HF stage. Furthermore, gene expression of AM receptor system components such as calcitonin receptor–like receptor (CRLR), receptor activity–modified protein 2 (RAMP2), and RAMP3 were significantly increased at the stage of LVH and HF. Regarding other neurohumoral factors, plasma renin and aldosterone levels were not increased at the LVH stage but were increased at the HF stage, whereas atrial natriuretic peptide was increased in both the plasma and myocardium at the LVH stage and was further increased at the HF stage. These results suggest that induction of the cardiac AM system, including the ligand, receptor, and amidating activity, may modulate pathophysiology during the transition from LVH to HF in this model.