bluuebunny/crossref_metadata_2025 huggingface dataset:
ET
B
Receptor and Nitric Oxide Synthase Blockade Induce BQ-123–Sensitive Pressor Effects in the Rabbit
Authors: Gratton Jean-Philippe , Cournoyer Ghislain , Löffler Bernd-Michael , Sirois Pierre , D’Orléans-Juste Pedro
Published: June 2012

Abstract
Endothelin-1 (0.25 nmol/kg, injected into the left cardiac ventricle) induces a protracted increase of mean arterial pressure that is significantly reduced by the selective ET
A
receptor antagonist BQ-123 (1 and 10 mg/kg) in the anesthetized rabbit. The sole administration of the selective ET
B
antagonist BQ-788 (0.25 mg/kg) induces a pressor response abolished by BQ-123 (1 mg/kg). Concomitant to the increase in mean arterial pressure, BQ-788 induces a significant increase in plasma levels of endothelin-1 and its precursor big endothelin-1. The nitric oxide synthase inhibitor
N
ω
-nitro-
l
-arginine methyl ester (L-NAME; 10 mg/kg) also increases arterial blood pressure, and the response is reduced dose-dependently by BQ-123 (1 and 10 mg/kg). In addition, the administration of BQ-788 in the presence of L-NAME induced a further increase in arterial blood pressure. The duration of the pressor response to L-NAME is also significantly reduced by an endothelin-converting enzyme inhibitor, phosphoramidon (10 mg/kg). Finally, L-NAME induces an increase in plasma levels of big endothelin-1 but not endothelin-1. Our results illustrate that blockade of either nitric oxide synthase or ET
B
receptors triggers a raise in plasma levels of endothelin-1 or its precursor. These later moieties are suggested to be significantly involved, through the activation of ET
A
receptors, in the pressor effects of L-NAME and BQ-788 in the anesthetized rabbit.
Association of Calcitriol and Blood Pressure in Normotensive Men
Authors: Kristal-Boneh Estela , Froom Paul , Harari Gil , Ribak Joseph
Published: June 2012

Abstract
The purpose of this study was to clarify the possible associations between the serum 1,25-dihydroxyvitamin D (calcitriol) level and blood pressure. Cross-sectional analysis of data was performed. Data collected included levels of serum calcitriol, parathyroid hormone, serum calcium, and blood lead; blood pressure; dietary history; and demographic and anthropometric variables. One hundred normotensive male industrial employees made up the study population. Systolic blood pressure and diastolic blood pressure were main outcome measures. After possible confounders were controlled for, multivariate analyses yielded an inverse, independent, and statistically significant association between calcitriol level and systolic blood pressure (standardized β=−0.2704,
P
=.0051). A similar trend of borderline significance was found for the association between calcitriol and diastolic blood pressure (standardized β=−0.1814,
P
=.0611). Parathyroid hormone, serum calcium, and blood lead levels were not associated with blood pressure. When subjects were divided into four groups by calcitriol level, those in the lowest quartile showed significantly higher systolic and diastolic blood pressures than those in the upper quartile (difference=11 mm Hg,
P
=.007, and difference=4 mm Hg,
P
=.071, respectively). There is an inverse association between serum calcitriol level and blood pressure. This suggests that in addition to its role in calcium homeostasis, the active metabolite of vitamin D may play a role in determining blood pressure. The differences in both systolic and diastolic blood pressures between the upper and lower quartiles of serum calcitriol were substantial and may be of clinical significance.
Essential Hypertension and 5′ Upstream Core Promoter Region of Human Angiotensinogen Gene
Authors: Ishigami Tomoaki , Umemura Satoshi , Tamura Kouichi , Hibi Kiyoshi , Nyui Nobuo , Kihara Minoru , Yabana Machiko , Watanabe Yasujiro , Sumida Yoichi , Nagahara Toshihiro , Ochiai Hisao , Ishii Masao
Published: June 2012

Abstract
The angiotensinogen (AGT) gene M235T variant is associated with essential hypertension and elevated plasma AGT concentrations, although the underlying mechanisms are unknown. Recent studies have suggested that AGCE 1 (human
AG
T gene
c
ore promoter
e
lement 1) located in the 5′ upstream core promoter region (position −25 to −1) of the human AGT gene has an important part in the expression of AGT mRNA by binding with transcription factor AGCF 1 (human
AG
T gene
c
ore promoter element binding
f
actor 1), and a mutation at −20 from adenine to cytosine (A-20C) increases the level of expression of this transcript. We therefore examined subjects with this mutation to study the association with increased plasma AGT concentrations and with essential hypertension. One hundred eighty-eight subjects receiving no antihypertensive medication were examined with regard to the correlation between A-20C and plasma AGT concentrations, and 234 subjects were studied with respect to the association between A-20C and essential hypertension. A-20C was determined by polymerase chain reaction–restriction fragment length polymorphism analysis with
Eco
OR 109I. Multiple regression analysis showed a weak but significant correlation between A-20C and plasma AGT concentrations (
P
=.047) and essential hypertension (
P
=.049). The results suggest that A-20C may underlie the increase in plasma AGT concentrations and be involved in the development of essential hypertension.
α-Adrenergic Signal Transduction in Renin Transgenic Rats
Authors: Schnabel Petra , Nohr Theo , Nickenig Georg , Paul Martin , Böhm Michael
Published: June 2012

Abstract
The α
1
-adrenoceptor–G protein–phosphoinositide-specific phospholipase C (PLC) signal transduction pathway is assumed to play an important role in the regulation of contractile force and in the pathophysiology of myocardial hypertrophy. In the present study, the components of this pathway were investigated in left ventricles of hearts from hypertensive transgenic rats overexpressing the mouse renin gene [TG(mREN2)27] in comparison to age- and weight-matched Sprague-Dawley control rats. Contractile force was assessed in isolated electrically driven left ventricular papillary muscle strips. α
1
-adrenoceptor density was measured by radioligand binding using [
3
H]prazosin, steady state levels of αq/11, and G protein β-subunits by Western blotting. PLC activity was determined by a cell-free assay using exogenous phospholipid vesicles containing [
3
H]phosphatidylinositol (4,5)-bisphosphate as a substrate. α
1
-Adrenoceptor density was significantly increased (by 80%) in transgenic rats compared with control rats, while the positive inotropic response to the α
1
-adrenoceptor agonist phenylephrine was significantly reduced, suggesting a postreceptor defect in TG(mREN2)27. The expression of αq and α11 was verified by reverse transcription–polymerase chain reaction, and αq/11 steady state protein levels were shown to be similar in transgenic and control rats. Western blotting using a β-common antibody revealed two bands at approximately 35 and 36 kD. The quantities of both were similar in TG(mREN2)27 compared with those in control rats. In contrast, PLC activity was significantly reduced (by 32%) in transgenic rats. In conclusion, our findings are consistent with a desensitization of the α
1
-adrenergic signal transduction pathway at the level of the effector.
Cardiac Production and Secretion of Adrenomedullin Are Increased in Heart Failure
Authors: Nishikimi Toshio , Horio Takeshi , Sasaki Tatsuya , Yoshihara Fumiki , Takishita Shuichi , Miyata Atsuro , Matsuo Hisayuki , Kangawa Kenji
Published: June 2012

Abstract
Plasma adrenomedullin (AM) levels are reportedly increased in heart failure, but whether the cardiac production and secretion of AM is increased in heart failure remains unknown. To investigate the sites of production and secretion of AM in heart failure, we measured plasma AM levels and peptide and mRNA levels of AM in various tissues in rats with heart failure. We also examined whether the heart actually secretes AM into the circulation in patients with heart failure. We measured plasma and tissue AM levels by specific radioimmunoassay and AM mRNA by Northern blot analysis in rats with heart failure produced by aortocaval fistula. We also measured plasma AM levels in the coronary sinus and aorta in patients with left ventricular dysfunction before and after rapid right ventricular pacing. The increase in plasma AM levels in heart failure rats correlated with ventricular weight. Tissue AM levels were increased in the heart and lungs but not in the kidneys or adrenals of rats with heart failure. Similarly, tissue AM mRNA levels were also increased in the heart and lungs of heart failure rats. Plasma AM levels were higher in the coronary sinus than in the aorta in patients with left ventricular dysfunction. Rapid right ventricular pacing increased plasma atrial natriuretic peptide but not AM. These results suggest that plasma AM levels are increased in heart failure in proportion to the severity of heart failure and that cardiac production and secretion of AM is increased in heart failure rats. The lung may be another site for increased production of AM in heart failure rats. Human failing heart actually secretes AM into the circulation, and the regulation of AM secretion appears to differ from that of atrial natriuretic peptide.
Reduced Cardiac Contractile Responsiveness to Isoproterenol in Obese Rabbits
Authors: Carroll Joan F. , Jones Alan E. , Hester Robert L. , Reinhart Glenn A. , Cockrell Kathy , Mizelle H. Leland
Published: June 2012

Abstract
Although obesity is characterized by increased sympathetic nervous system activity, there is often a paradoxical reduction in cardiovascular end-organ response to sympathetic stimulation. Mechanisms involved in reduced sympathetic responsiveness in obesity have not been well characterized. Therefore, we determined cardiac contractile responsiveness to β-stimulation in the obese rabbit model using both isolated heart (IH) and isolated papillary muscle (IPM) preparations. Female New Zealand White rabbits were fed control (IH: n=9; IPM: n=6) or 10% fat diets (IH: n=9; IPM: n=7) for 12 weeks. Contractile responsiveness in the IH was determined using a modified Langendorff preparation to evaluate the dose-response relationship between isoproterenol and 1) peak developed pressure/g of left ventricular wet weight and 2) maximal rate of pressure development (+dP/dt/P). Contractile responsiveness in the IPM was determined using right ventricular papillary muscles to evaluate the dose-response relationship between isoproterenol and (1) peak developed tension (T)/mm
2
cross-sectional area (CSA) and (2) maximal rate of tension development (dT/dt/CSA). In the IH, baseline and maximum developed pressure/g were reduced in obese rabbits by 37% and 31%, respectively (
P
≤.05). In the IPM, baseline and maximum T/CSA responses were reduced in obese rabbits by 59% and 33%, respectively (
P
≤.05). Potency of isoproterenol as reflected by the EC
50
did not differ between lean and obese animals in either preparation. These results demonstrate that left ventricular contractility in obesity is reduced at baseline and in response to stimulation with isoproterenol and suggest that decreased responsiveness to β-stimulation may be a factor in the obesity-related systolic dysfunction.
Cardiovascular Effects of Nitric Oxide and
N
-Methyl-
d
-Aspartate Receptors in the Nucleus Tractus Solitarii of Rats
Authors: Lo Wan-Chen , Lin Hui-Ching , Ger Luo-Ping , Tung Che-Se , Tseng Ching-Jiunn
Published: June 2012

Abstract
Nitric oxide (NO) is an endogenously synthesized effector molecule that acts as a neurotransmitter with novel properties in both the central and peripheral nervous systems. We previously reported that NO was involved in central cardiovascular regulation and modulated the baroreflex in the nucleus tractus solitarii (NTS) of rats. The aim of the present study was to determine whether NO and excitatory amino acids reciprocally release each other in the NTS. In normotensive Sprague-Dawley rats, intra-NTS microinjection of
l
-arginine (1 to 100 nmol/60 nL) produced a dose-dependent decrease in blood pressure and heart rate. Microinjection of excitatory amino acids
l
-glutamate and NMDA also produced depressor and bradycardic effects. These effects of
l
-glutamate or NMDA were blocked by prior administration of NO synthase inhibitor
N
G
-methyl-
l
-arginine or
N
G
-nitro-
l
-arginine methyl ester. Similarly, prior administration of
N
-methyl-
d
-aspartate (NMDA) receptor antagonist MK-801 and non-NMDA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione significantly attenuated the depressor and bradycardic effect of
l
-arginine. These results demonstrated a reciprocal attenuation of NO synthase inhibitor and NMDA receptor antagonist on NMDA and
l
-arginine responses, respectively, in the NTS and suggest that NO and NMDA receptors may interact in central cardiovascular regulation.
Sex Differences in the Abundance of Endothelial Nitric Oxide in a Model of Genetic Hypertension
Authors: McIntyre Martin , Hamilton Carlene A. , Rees Daryl D. , Reid John L. , Dominiczak Anna F.
Published: June 2012

Abstract
A deficiency of nitric oxide may be responsible for the increased vascular resistance associated with human essential hypertension and that seen in animal models of hypertension. Premenopausal females are relatively protected from hypertension and cardiovascular complications. Levels of superoxide can influence the availability of nitric oxide. We hypothesize that there are differences in nitric oxide availability between stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto rats (WKY) and that superoxide may be responsible for at least some of these differences. We studied vascular reactivity in endothelium-intact aortic rings from WKY and SHRSP. We measured nitric oxide synthase activity in endothelial cells removed from aortas and also measured circulating nitrite/nitrate levels. We found the response to
N
G
-nitro-
l
-arginine methyl ester to be significantly greater in WKY compared with SHRSP (95% CI: 20 to 174;
P
=.015) and in females compared with males in WKY (95% CI: 143 to 333;
P
=.00004) and SHRSP (95% CI: 70 to 224;
P
=.0006). Endothelial nitric oxide synthase activity was significantly greater in SHRSP compared with WKY (95% CI: 2.3 to 17.6;
P
=.016). The EC
50
for relaxation to carbachol was significantly greater in male rats compared with female rats (95% CI: −1.1 to −0.2;
P
=.003) within the SHRSP strain. The maximum relaxation to carbachol was significantly attenuated in stroke prone spontaneously hypertensive compared with Wistar-Kyoto rats (95% CI: 1.7 to 14.4;
P
=.015). Diethyldithiocarbamate had a significantly greater effect on the stroke prone spontaneously hypertensive rats’ carbachol response than that of Wistar-Kyoto rats (95% CI: 14.3 to 47.0;
P
=.0008). We conclude that superoxide may be responsible for strain differences in vascular reactivity, whereas nitric oxide availability may be responsible for sex differences independently of endothelial nitric oxide synthase activity and superoxide.
Antihypertensive Agent Moxonidine Enhances Muscle Glucose Transport in Insulin-Resistant Rats
Authors: Henriksen Erik J. , Jacob Stephan , Fogt Donovan L. , Youngblood Erik B. , Gödicke Jochen
Published: June 2012

Abstract
The sympatholytic antihypertensive agent moxonidine, a centrally acting selective I
1
-imidazoline receptor modulator (putative agonist), may be beneficial in hypertensive patients with insulin resistance. In the present study, the effects of chronic in vivo moxonidine treatment of obese Zucker rats—a model of severe glucose intolerance, hyperinsulinemia and insulin resistance, and dyslipidemia—on whole-body glucose tolerance, plasma lipids, and insulin-stimulated skeletal muscle glucose transport activity (2-deoxyglucose uptake) were investigated. Moxonidine was administered by gavage for 21 consecutive days at 2, 6, or 10 mg/kg body weight. Body weights in control and moxonidine-treated groups were matched, except at the highest dose, at which final body weight was 17% lower in the moxonidine-treated animals compared with controls. The moxonidine-treated (6 and 10 mg/kg) obese animals had significantly lower fasting plasma levels of insulin (17% and 19%, respectively) and free fatty acids (36% and 28%, respectively), whereas plasma glucose was not altered. During an oral glucose tolerance test, the glucose response (area under the curve) was 47% and 67% lower, respectively, in the two highest moxonidine-treated obese groups. Moreover, glucose transport activity in the isolated epitrochlearis muscle stimulated by a maximally effective insulin dose (13.3 nmol/L) was 39% and 70% greater in the 6 and 10 mg/kg moxonidine-treated groups, respectively (
P
<.05 for all effects). No significant alterations in muscle glucose transport were elicited by 2 mg/kg moxonidine. These findings indicate that in the severely insulin-resistant and dyslipidemic obese Zucker rat, chronic in vivo treatment with moxonidine can significantly improve, in a dose-dependent manner, whole-body glucose tolerance, possibly as a result of enhanced insulin-stimulated skeletal muscle glucose transport activity and reduced circulating free fatty acids.
Oxidative Stress in the Dahl Hypertensive Rat
Authors: Swei Allen , Lacy Fred , DeLano Frank A. , Schmid-Schönbein Geert W.
Published: June 2012

Abstract
Enhanced production of oxygen free radicals may play a role in hypertension by affecting vascular smooth muscle contraction, resistance to blood flow, and organ damage. The aim of this study was to determine whether oxygen free radicals are involved in the development of salt-induced hypertension. Dahl salt-sensitive (Dahl-S) and salt-resistant (Dahl-R) rats were fed either a high salt (6.0% NaCl) or low salt (0.3% NaCl) diet for 4 weeks. The high salt diet caused the development of severe hypertension in Dahl-S animals and had no effect on blood pressure in Dahl-R animals. A tetranitroblue tetrazolium dye was used to detect superoxide radicals in microvessels of the mesentery. Light absorption measurements revealed enhanced staining along the endothelium of arterioles and venules in hypertensive Dahl-S animals, with significantly lower values in normotensive animals. In addition, a Clark electrochemical electrode was used to measure hydrogen peroxide levels in fresh plasma. Hypertensive Dahl-S animals had a higher plasma hydrogen peroxide concentration compared with their normotensive counterparts (2.81±0.43 versus 2.10±0.41 μmol/L), while no difference was detected between high- and low salt–treated Dahl-R animals (1.70±0.35 versus 1.56±0.51 μmol/L). The plasma hydrogen peroxide levels of all groups correlated with mean arterial pressure (
r
=.77). These findings demonstrate an enhanced production of oxygen free radicals in the microvasculature of hypertensive Dahl-S rats.
Venous Tone in the Developmental Stages of Spontaneous Hypertension
Authors: Martin Douglas S. , Rodrigo Manoj C. , Appelt Christopher W.
Published: June 2012

Abstract
—The initial stages of hypertension in the spontaneously hypertensive rat (SHR) are characterized by an increase in cardiac output. Venous capacitance plays an important role in the control of cardiac output. This study tested the hypothesis that venous tone is elevated in the developmental stages of spontaneous hypertension. Male SHR or normotensive Wistar-Kyoto (WKY) rats were instrumented for the measurement of arterial pressure (FAP) and intrathoracic vena caval pressure (FVP). A latex-tipped catheter was advanced into the right atrium via the jugular vein. Mean circulatory filling pressure (MCFP), an index of integrated venomotor tone, was calculated as MCFP=FVP+(FAP−FVP)/VAR. FAP and FVP were recorded after 5 seconds of right atrial balloon inflation. The venous to arterial compliance ratio (VAR) was estimated as 76 for WKY and 106 for SHR. Mean arterial pressure (MAP), heart rate, and MCFP were recorded in conscious rats of 4 to 6 and 8 to 10 weeks of age. In 4- to 6-week-old rats, both MAP and MCFP were significantly elevated in the SHR (MAP, 129±6 mm Hg; MCFP, 6.6±0.4 mm Hg) compared with the age-matched WKY (MAP, 91±6 mm Hg; MCFP, 5.4±0.4 mm Hg), whereas heart rate was not significantly different. The elevations in MAP (SHR, 144±4 mm Hg; WKY, 102±3 mm Hg) and MCFP (SHR, 7.7±0.3 mm Hg; WKY, 6.0±0.2 mm Hg) in SHR were exaggerated at 8 to 10 weeks of age. After ganglionic blockade (chlorisondamine; 10 mg/kg), the differences in MCFP were no longer statistically significant between SHR and WKY at both 4 to 6 weeks of age (3.9±0.2 versus 4.0±0.3 mm Hg) and 8 to 10 weeks of age (5.0±0.3 versus 4.3±0.3 mm Hg, respectively). The differences in MAP at 4 to 6 weeks of age (79±7 versus 67±5 mm Hg, respectively) also were not statistically significant after ganglionic blockade. However, a significant difference in MAP between strains remained after ganglionic blockade in 8- to 10-week-old rats (90±5 versus 63±3 mm Hg, respectively). These findings indicate that venous tone is increased via autonomic effector systems during the developmental stages of spontaneous hypertension. These data also suggest that autonomic mechanisms predominate at very early stages, whereas nonautonomic mechanisms assume more importance in maintaining the elevated MAP as hypertension progresses.
Effects of Mechanical Forces on Signal Transduction and Gene Expression in Endothelial Cells
Authors: Chien Shu , Li Song , Shyy John Y-J.
Published: June 2012

Fluid shear stress and circumferential stretch play important roles in maintaining the homeostasis of the blood vessel, and they can also be pathophysiological factors in cardiovascular diseases such as atherosclerosis and hypertension. The uses of flow channels and stretch devices as in vitro models have helped to elucidate the mechanisms of signal transduction and gene expression in cultured endothelial cells in response to shear stress, which is a function of blood flow and vascular geometry, or mechanical strain, which is a function of transmural pressure and the mechanical properties and geometry of the vessel. Shear stress has been found to increase the activities of a number of kinases to modulate the phosphorylation of many signaling proteins in endothelial cells, eg, the proteins in focal adhesion sites and the proteins in the mitogen-activated protein kinase pathways. Downstream to such signaling cascades, multiple transcription factors such as AP-1, NF-κB, Sp-1, and Egr-1 are activated. The actions of these transcription factors on the corresponding
cis
-elements result in the induction of genes encoding for vasoactivators, adhesion molecules, monocyte chemoattractants, and growth factors in endothelial cells, thus modulating vascular structure and function. Some of the effects of mechanical strain on endothelial cells are similar to those by shear stress, eg, the signaling pathways and the genes activated, but there are differences, eg, the time course of the responses. Studies on the effects of mechanical forces on signal transduction and gene expression provide insights into the molecular mechanisms by which hemodynamic factors regulate vascular physiology and pathophysiology.
Methacholine-Induced Contraction of Rabbit Pulmonary Artery: Role of Platelet-Endothelial Transcellular Thromboxane Synthesis
Authors: Pfister Sandra L. , Deinhart David D. , Campbell William B.
Published: June 2012

Arachidonic acid- and methacholine-induced contractions of rabbit pulmonary arteries are mediated by thromboxane (TX) A
2
. Although removal of the endothelium abolishes the contractions, endothelial cells isolated from pulmonary arteries do not synthesize TXA
2
. Further studies described here showed that the expression of TX synthase was evident in platelets and intact pulmonary artery but not in endothelial cells. These studies examined the role of platelet TXA
2
production in the vasoconstrictor response to methacholine. Endothelial cells were incubated with platelets in the presence or absence of methacholine. Methacholine caused an increase in TXB
2
production. Pretreatment of endothelial cells with aspirin (100 μmol/L) before the addition of platelets did not impair the ability of methacholine to increase TXB
2
synthesis. Conversely, if platelets were pretreated with aspirin, methacholine failed to stimulate TXB
2
. Using endothelial cells with their cellular lipids labeled with [
3
H]arachidonic acid, methacholine did not stimulate the production of [
3
H]TXB
2
. When the endothelial cells were incubated with methacholine and control platelets, [
3
H]TXB
2
was detected. If aspirin-treated platelets were incubated with endothelial cells, methacholine did not increase the production of [
3
H]TXB
2
. However, pretreatment of the endothelial cells with aspirin did not affect the ability of methacholine to induce [
3
H]TXB
2
release. This suggests that methacholine stimulated the endothelial cell to release arachidonic acid, which was transferred to the platelets and metabolized to TXA
2
. To test whether this cell-cell interaction is necessary for methacholine-induced contractions, rabbits were administered aspirin (20 mg/kg) for 2 days. On day 4, methacholine-induced contractions of pulmonary arteries were depressed in aspirin-treated compared with control subjects. Control arteries synthesized 6-keto-prostaglandin F
1α
and TXB
2
. Aspirin treatment inhibited both pulmonary artery and platelet TXB
2
production but had no effect on vessel 6-keto-prostaglandin F
1α
. These studies implicate platelets as a vascular source of TXA
2
and indicate that both endothelial cells and platelets may be required for methacholine-induced TXA
2
synthesis and vasoconstriction.
Cyclic AMP-Adenosine Pathway Induces Nitric Oxide Synthesis in Aortic Smooth Muscle Cells
Authors: Dubey Raghvendra K. , Gillespie Delbert G. , Jackson Edwin K.
Published: June 2012

The main purpose of this investigation was to evaluate whether the cyclic AMP-adenosine pathway, ie, the conversion of cAMP to AMP and, hence, to adenosine, is involved in the regulation of nitric oxide (NO) synthesis by vascular smooth muscle cells (SMCs). Treatment of confluent monolayers of SMCs with adenosine, 2-chloroadenosine (stable analog of adenosine), and agents that elevate endogenous (SMC-derived) adenosine (EHNA and iodotubericidin) increased nitrite/nitrate (stable metabolites of NO) levels in the medium and enhanced the conversion of
3
H-L-arginine to
3
H-L-citrulline by cytosolic extracts obtained from the pretreated SMCs. The stimulatory effects of adenosine were not mimicked by low (1 to 100 nmol/L) concentrations of
CGS21680
, an A
2A
receptor agonist, or CPA, a selective A
1
receptor agonist. The stimulatory effects of 2-chloroadenosine and EHNA plus iodotubericidin were significantly inhibited by KF17837, a selective A
2
receptor antagonist, and by DPSPX, and A
1
/A
2
receptor antagonist, but not by DPCPX, a selective A
1
receptor antagonist. DDA (adenylyl cyclase inhibitor) and Rp-cyclic AMP (protein kinase A inhibitor) did not block the effects of adenosine on NO synthesis. Incubation of SMCs with exogenous cyclic AMP, at concentrations previously shown to elevate levels of adenosine in the medium, also increased nitrite/nitrate levels and
3
H-L-citrulline formation, and the effects of cyclic AMP on NO synthesis were blocked by DPSPX and KF17837, but not by DPCPX. These findings provide evidence that exogenous and SMC-derived adenosine induce NO synthesis via A
2B
receptors linked to a pathway not involving adenylyl cyclase/protein kinase A. Moreover, extracellular cyclic AMP induces NO synthesis via conversion to adenosine and activation of A
2B
adenosine receptors. The cyclic AMP-adenosine pathway may be importantly involved in the vascular production of NO.
Endothelin-Converting Enzyme
Authors: Barnes Kay , Brown Carolyn , Turner Anthony J.
Published: June 2012

Abstract
—The potent vasoconstrictor endothelin-1 (ET-1) is secreted constitutively by endothelial cells and has been implicated in the pathophysiology of several cardiovascular diseases. It is generated from its inactive intermediate, big ET-1, through the action of endothelin-converting enzyme (ECE). Using several complementary techniques, we have demonstrated that ECE is present at the cell surface and on intracellular vesicles and that it recycles from the cell surface in endothelial cells. This is the first ultrastructural localization of ECE in lung and the first time big ET-1 and ECE have been colocalized by immunogold in a vesicular population, 50 to 100 nm in diameter. In addition, by double immunogold staining of ultrathin cryosections, we have localized ECE together with angiotensin-converting enzyme on the luminal membrane of endothelial cells. With cell surface biotinylation of a transformed rat endothelial cell line and of human umbilical vein endothelial cells, we have confirmed the presence of ECE on the plasma membrane. After treatment of endothelial cells with chloroquine, ECE and trans-Golgi network 38 protein were shown by immunofluorescence staining to localize to the same intracellular compartment.
Estrogen Preserves Regulation of Shear Stress by Nitric Oxide in Arterioles of Female Hypertensive Rats
Authors: Huang An , Sun Dong , Kaley Gabor , Koller Akos
Published: June 2012

Previously we found that flow-induced arteriolar dilation in male spontaneously hypertensive rats (SHR) is significantly impaired, due to the absence of the nitric oxide (NO)-mediated portion of the response, resulting in an elevation of maintained wall shear stress. Since estrogen has been shown to affect NO-mediated responses, we hypothesized that in female SHR (fSHR) the NO-mediated portion of flow-induced responses is preserved. Gracilis muscle arterioles (≈45 to 55 μm) from 12-week-old fSHR, ovariectomized fSHR (OV fSHR), or ovariectomized and supplemented with estrogen fSHR (OVE fSHR) were isolated, cannulated, and pressurized at 80 mm Hg of perfusion pressure. Arteriolar dilations elicited by step increases in perfusate flow from 0 to 25 μL/min were significantly less (by ≈30%) in OV fSHR compared with fSHR and OVE fSHR (Δ19.4±1.5 versus 26.0±0.9 and 26.8±2.0 μm, respectively at maximum flow rate). Inhibition of prostaglandin synthesis with indomethacin elicited a ≈50% reduction in flow-dependent dilation in all three groups of rats.
N
ο
-nitro-
l
-arginine (L-NNA) significantly inhibited flow-induced responses in arterioles of fSHR and OVE fSHR (by ≈50%) but not in those of OV fSHR. Constrictions to norepinephrine (10
−7
−3×10
−7
mol/L) were significantly greater (up to ≈40%) in arterioles of OV fSHR compared with those of fSHR and OVE fSHR; these differences, however, were abolished in the presence of L-NNA. In conclusion, estrogen seems to preserve the NO-mediated portion of flow/shear stress-induced dilation in female hypertensive rats resulting in a lower maintained wall shear stress in female than in male SHR. The lower wall shear stress may contribute to the mechanisms by which estrogen lowers systemic blood pressure and the incidence of cardiovascular diseases in women.
Systemic Hemodynamics and Regional Blood Flow During Chronic Nitric Oxide Synthesis Inhibition in Pregnant Rats
Authors: Kassab Salah , Miller M. Todd , Hester Robert , Novak Jacqueline , Granger Joey P.
Published: June 2012

Pregnancy-induced hypertension in women is associated with severe vasoconstriction and reductions in organ blood flow and cardiac output. Recent studies have indicated that nitric oxide (NO) synthesis inhibition during mid to late gestation in pregnant rats results in severe hypertension and proteinuria. The purpose of this study was to determine the systemic hemodynamic and regional blood flow alterations associated with chronic NO synthesis inhibition in the pregnant rat. The study was conducted in four groups of rats: virgin rats (n=6), pregnant rats (n=10), virgin rats treated with
l
-NAME (n=6), and pregnant rats treated with
l
-NAME (n=11). Rats were treated with
l
-NAME in drinking water at a dose of 1 mg/d for a week starting from day 13 of gestation in pregnant rats or an equivalent time for virgins. Mean arterial pressure (MAP), cardiac output, total peripheral resistance (TPR), and regional flows were measured by tracing radiolabeled microspheres in conscious rats. Pregnant rats that were given
l
-NAME showed significantly higher MAP (137±6 versus 96±2 mm Hg), higher TPR (5.08±0.58 versus 2.90±0.44 mm Hg/mL/min/100 g), and lower cardiac output (87.4±8.4 versus 113.3±11.1 mL/min) than pregnant controls. Chronic NO synthesis inhibition decreased the renal blood flow in pregnant rats at a significantly greater magnitude than in virgin rats. Significant reductions in regional blood flow to the heart, lungs, liver, diaphragm, and skeletal muscles were also observed in pregnant rats treated with
l
-NAME. The results of this study indicate that NO may play a role in mediating the alterations in systemic hemodynamics and regional blood flow in late pregnant rats.
Endothelial Dysfunction in Hypertension Is Independent From the Etiology and From Vascular Structure
Authors: Rizzoni Damiano , Porteri Enzo , Castellano Maurizio , Bettoni Giorgio , Muiesan Maria Lorenza , Tiberio Guido , Giulini Stefano M. , Rossi Gianpaolo , Bernini Gianpaolo , Agabiti-Rosei Enrico
Published: June 2012

The aim of our study was to evaluate the relationships between endothelial function, small resistance artery structure, and blood pressure in patients with primary or secondary hypertension. Sixty subjects were included in the study: 9 patients with pheochromocytoma, 10 with primary aldosteronism, 17 with renovascular hypertension, and 13 with essential hypertension with 11 normotensive subjects who served as controls. Clinic and 24-hour ambulatory blood pressure (ABPM) were evaluated. All subjects were submitted to a biopsy of subcutaneous fat. Small resistance arteries were dissected and mounted on a micromyograph and the media/lumen ratio was calculated. A dose-response curve to acetylcholine was performed at cumulative concentrations from 10
−9
to 10
−5
mol/L. The vasodilator response to acetylcholine was similarly impaired in the four groups of hypertensive patients (ANOVA
P
<.05 versus normotensive controls), without any significant difference among them. In subcutaneous small arteries of patients with either primary aldosteronism or renovascular hypertension, a marked increase in media:lumen ratio was observed, while in patients with pheochromocytoma, the extent of vascular structural alterations was similar to that observed in essential hypertension. No significant correlation between media-lumen ratio or clinic blood pressure and maximum acetylcholine-induced vasodilatation was observed. On the contrary, a significant, albeit not very close, correlation between ABPM values and maximum acetylcholine-induced vasodilatation was observed (
r
=34,
P
<.05 with 24-hour systolic blood pressure,
r
=0.36,
P
<.05 with 24-hour diastolic blood pressure). In conclusion, endothelial dysfunction seems to be independent from the degree of vascular structural alterations and from the etiology of hypertension, and it is probably more linked to the hemodynamic load.
Downregulation of Angiotensin II Type 1 Receptor Gene Transcription by Nitric Oxide
Authors: Ichiki Toshihiro , Usui Makoto , Kato Makoto , Funakoshi Yuko , Ito Kiyoko , Egashira Kensuke , Takeshita Akira
Published: June 2012

Nitric oxide (NO) plays an important role not only in the regulation of blood vessel tone, but also in the growth of vascular smooth muscle cells (VSMC). The precise mechanism involved in the inhibition of VSMC growth by NO is not known. To further explore the effect of NO on VSMC growth, we examined the effect of NO on the expression of angiotensin II type 1 receptor (AT
1
-R) that is important for hypertrophy and hyperplasia of VSMC. S-nitroso acetyl DL-penicillamine (SNAP; 200μmol/L), a potent NO donor, suppressed expression level of AT
1
-R mRNA by 90% and AT
1
-R number by 60% after 24 hours of stimulation. The suppressive effect was dose-dependent. Actinomycin D, which is an inhibitor of gene transcription, did not affect the decrease of AT
1
-R mRNA by NO. Cyclic guanosine monophosphate (cGMP) analogue, 8 bromo-cGMP, did not affect AT
1
-R mRNA level. Deletion mutants of the promoter region of rat AT
1
a-R gene were fused to luciferase reporter gene and introduced to VSMC. Transfected cells were stimulated with SNAP, and luciferase activity was measured. Inhibitory effect of NO was still observed in the shortest deletion mutant that contained 61 bp upstream from transcription start site. In this DNA segment, two DNA binding protein were observed by gel mobility shift assay, and one of these binding proteins was decreased on stimulation by NO. NO downregulates AT
1
-R gene expression independently of cGMP. A DNA binding protein that binds to the proximal promoter region of AT
1
-R gene may be responsible for this inhibitory effect. The inhibition of AT
1
-R gene expression may be implicated in the anti-atherogenic property of NO.
AT
2
Receptor Stimulation Increases Aortic Cyclic GMP in SHRSP by a Kinin-Dependent Mechanism
Authors: Gohlke Peter , Pees Christiane , Unger Thomas
Published: June 2012

In the present study we tested the hypothesis whether an angiotensin AT
2
receptor-mediated stimulation of the bradykinin (BK)/nitric oxide (NO) system can account for the effects of AT
1
receptor antagonism on aortic cGMP described previously in SHRSP. Adult SHRSP were treated for 4 hours with angiotensin II (ANG II) (30 ng/kg per min IV) or vehicle (0.9% NaCl IV). Animals were pretreated with vehicle, losartan (100 mg/kg PO), PD 123319 (30 mg/kg IV), losartan plus PD 123319, icatibant (500 μg/kg IV), N
G
-nitro-
l
-arginine methyl ester (L-NAME; 1 mg/kg IV), or minoxidil (3 mg/kg IV). Mean arterial blood pressure (MAP) was continuously monitored over the 4-hour experimental period, and plasma ANG II and aortic cGMP were measured by RIA at the end of the study. ANG II infusion over 4 hours raised MAP by about 20 mm Hg. Losartan alone or losartan plus ANG II as well as minoxidil plus ANG II markedly reduced blood pressure when compared to vehicle-treated or ANG II-treated animals, respectively. Plasma levels of ANG II were increased 2-fold by ANG II infusion alone or by ANG II in combination with icatibant, L-NAME, or minoxidil. The increase in plasma ANG II levels was even more pronounced after losartan treatment. Aortic cGMP content was significantly increased by ANG II, losartan, losartan plus ANG II, and minoxidil plus ANG II by 60%, 45%, 68%, and 52%, respectively (
P
<.05). The effects of ANG II and of losartan plus ANG II on aortic cGMP content were both blocked by cotreatment with the AT
2
receptor antagonist PD 123319. Icatibant and L-NAME abolished the effects of ANG II on aortic cGMP. Our results demonstrate the following: (1) ANG II increases aortic cGMP by an AT
2
receptor-mediated action because the effect could be prevented by an AT
2
receptor antagonist; (2) the effect of ANG II was not secondary to blood pressure increase because it remained under reduction of MAP with minoxidil; (3) losartan increased aortic cGMP most likely by increasing plasma ANG II levels with a subsequent stimulation of AT
2
receptors; and (4) the effects of AT
2
receptor stimulation are mediated by BK and, subsequently, NO because they were abolished by B
2
receptor blockade as well as by NO synthase inhibition.
Angiotensin-(1–7) Contributes to the Antihypertensive Effects of Blockade of the Renin-Angiotensin System
Authors: Iyer Shridhar N. , Ferrario Carlos M. , Chappell Mark C.
Published: June 2012

Angiotensin-converting enzyme (ACE) inhibition alone or in combination with the angiotensin type-I receptor (AT
1
) antagonist losartan augments circulating levels of the bioactive peptide angiotensin-(1–7) [Ang-(1–7)]. Hence, we determined whether Ang-(1–7) contributes to the hypotensive effects produced by the combined administration of lisinopril and losartan in spontaneously hypertensive rats by blocking the peptide’s synthesis with either of two structurally different neprilysin inhibitors. Intravenous administration of CGS 24592 (30 mg/kg) to rats in which blood pressure was normalized by 9 days of therapy with lisinopril and losartan elicited an elevation of mean arterial pressure that was sustained throughout the infusion period and for 20 minutes thereafter. The hypertensive response was associated with a 62% reduction in circulating levels of Ang-(1–7) and no change in plasma angiotensin II (Ang II). Intravenous infusion of one other neprilysin inhibitor (SCH 39370, 30 mg/kg) produced an increase in mean blood pressure of a magnitude similar to that found with CGS 24592. Pretreatment with the nonselective antagonist [Sar,
1
Thr
8
]-Ang II abolished any additional pressor effects of either neprilysin inhibitor in spontaneously hypertensive rats treated with lisinopril or losartan. However, neither the endothelin A antagonist BQ123 nor the kinin B2 antagonist HOE 140 had an effect on basal blood pressure or altered the pressor or heart rate effects of the neprilysin inhibitors. These data suggest that inhibition of Ang-(1–7) formation in rats exposed to the combined blockade of Ang II production and activity is associated with a reversal of the antihypertensive actions produced by these therapies. Thus, endogenous Ang-(1–7) functions as a vasodilator hormone in this form of genetic hypertension.
Impact of Dietary Na
+
on Glycyrrhetinic Acid-Like Factors (Kidney 11β-(HSD2)-GALFs) in Human Essential Hypertension
Authors: Morris David J. , Lo Ying H. , Lichtfield W. Reid , Williams Gordon H.
Published: June 2012

Our previous studies have shown that human urine contains glycyrrhetinic acid-like factors (GALFs) that possess inhibitory activity against kidney 11β-hydroxysteroid dehydrogenase isoform 2 (HSD2). The present studies were undertaken to determine the impact of dietary Na
+
intake on the levels of kidney 11β(HSD2)-GALFs. The excretion of kidney 11β(HSD2)-GALFs in 24-hour urine samples of 30 unmedicated subjects (10 normotensive and 10 high/normal-renin and 10 low-renin essential hypertensive subjects) on both 200- and 10-mmol Na
+
diets was studied. No differences in the urinary levels of kidney 11β(HSD2)-GALFs were observed among the three groups on the high-Na
+
diet. However, with a low-Na
+
diet, the levels of kidney 11β(HSD2)-GALFs were significantly increased in hypertensive subjects but not in normal subjects. Levels increased from 8.3±1.4 to 17.3±2.9 and 6.7±1.3 to 10.6±1.4 carbenoxolone sodium units/d in high/normal-renin (
P
=.01) and low-renin hypertensive subjects (
P
=.07), respectively; normal subjects changed from 8.0±1.9 to 10.6±2.4. The levels of kidney 11β(HSD2)-GALFs were significantly higher in the high/normal-renin hypertensive subjects than in either the control normotensive subjects or the low-renin hypertensive subjects when challenged with the low-Na
+
diet (
P
<.05 by Wilcoxon rank-sum test). The greater response of the high/normal-renin hypertensive subjects indicated that they may utilize kidney 11β(HSD2)-GALFs when challenged with a low-Na
+
diet, whereas the low-renin essential hypertensive subjects do not.
Oxytocin Pathways Mediate the Cardiovascular and Behavioral Responses to Substance P in the Rat Brain
Authors: Maier Tanja , Dai Wen-Jie , Csikós Tamás , Jirikowski Gustav F. , Unger Thomas , Culman Juraj
Published: June 2012

Stimulation of brain periventricular and hypothalamic substance P receptors induces a pressor response and tachycardia associated with mesenteric and renal vasoconstriction and hindlimb vasodilation resembling thus the classical defense reaction. This cardiovascular response is brought about by the activation of the sympathoadrenal system and is accompanied by grooming behavior. To address the role of oxytocinergic pathways in the brain in the mediation of these responses, we investigated the effects of central pretreatment of rats with oxytocin antisense, mixed base, and sense oligodeoxynucleotides on mean arterial pressure, heart rate, and grooming behavior induced by intracerebroventricular injections of substance P (50 pmol). Central pretreatment of conscious rats with the oxytocin antisense oligodeoxynucleotide (intracerebroventricular injections, 8 and 4 hours before administration of substance P) attenuated the mean arterial pressure (by 55%) and heart rate responses (by 58%) as well as grooming behavior induced by the peptide. A complete recovery of all substance P-induced responses was observed 28 hours after antisense oligodeoxynucleotide pretreatment. Intracerebroventricular pretreatment of rats with mixed base and sense oligodeoxynucleotides did not affect the cardiovascular and behavioral responses to substance P. The signal for oxytocin mRNA in the paraventricular nucleus was reduced only in rats pretreated with the antisense oligodeoxynucleotide. These results demonstrate that oxytocin neurons in the paraventricular nucleus, which innervate the cardiovascular centers in the hindbrain and the spinal cord, mediate the increases in blood pressure and heart rate induced by stimulation of substance P receptors in the forebrain. These neurons may also transmit signals, which are generated by substance P in the hypothalamus and are responsible for the sympathoadrenal activation in response to stress.
Cardiac Mitogen-Activated Protein Kinase Activities Are Chronically Increased in Stroke-Prone Hypertensive Rats
Authors: Izumi Yasukatsu , Kim Shokei , Murakami Tomohisa , Yamanaka Shinya , Iwao Hiroshi
Published: June 2012

Abstract
—To examine chronic changes in mitogen-activated protein (MAP) kinases in cardiac hypertrophy, we determined the activities of two subfamilies of MAP kinases, including extracellular signal-regulated kinases (ERKs) and c-Jun NH
2
-terminal kinases (JNKs), in the heart of stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto rats (WKY) aged 5, 8, 14, and 24 weeks. MAP kinases were determined by using in-gel kinase assay. In both the left and right ventricles of WKY, the activities of ERKs (p44ERK and p42ERK) and JNKs (p46JNK and p55JNK) decreased significantly with age, indicating that aging remarkably downregulated cardiac MAP kinase activities. In SHRSP, left ventricular ERK and JNK activities were already significantly higher at the mild hypertensive phase than they were in the same age of WKY, and they remained higher until development of left ventricular hypertrophy. On the contrary, the right ventricle of SHRSP, which did not exhibit cardiac hypertrophy, had no significant increase in ERK or JNK activities compared with WKY, except for the slight increase in p55JNK in 24-week-old SHRSP. Antihypertensive treatment of SHRSP with imidapril, an angiotensin-converting enzyme inhibitor, decreased the left ventricular JNK activities (
P
<.01) but did not affect ERK activities, suggesting the contribution of hypertension or the renin-angiotensin system to the increase in JNKs. Our observations provide the first evidence that both ERK and JNK activities are higher in the left ventricle of SHRSP than WKY. However, further study is needed to elucidate the mechanism and the significance of the increased cardiac MAP kinases in SHRSP.