bluuebunny/crossref_metadata_2025 huggingface dataset:
Central Overexpression of the TRH Precursor Gene Induces Hypertension in Rats
Authors: García Silvia I. , Porto Patricia I. , Alvarez Azucena L. , Martinez Veronica N. , Shaurli Daniela , Finkielman Samuel , Pirola Carlos J.
Published: June 2012

Abstract
Extrahypothalamic TRH participates in cardiovascular regulation and spontaneous hypertension of the rat. To investigate whether an increase in central TRH activity produces hypertension we studied the effect of the preTRH overproduction induced by ICV transfection with a naked eukaryotic expression plasmid vector which encodes preTRH (pCMV-TRH). Northern blot analysis and RT-PCR showed that pCMV-TRH was transcribed in vitro and in vivo. At 24, 48, and 72 hours, pCMV-TRH (100 μg) in a significant and dose-dependent manner increased 37%, 84%, and 49%, respectively, the diencephalic TRH content and SABP (42±3, 50±2, and 22±2 mm Hg, respectively) with respect to the vector without the preTRH cDNA insert (V
TRH(−
)
) as measured by RIA and the plethysmographic method, respectively, in awake animals. In addition, using immunohistochemistry we found that the increase of TRH was produced in circumventricular areas where the tripeptide is normally located. To further analyze the specificity of these effects we studied the actions of 23-mer sense (S), antisense (AS), and 3’self-stabilized sense (Ss) and antisense (ASs) phosphorothioate oligonucleotides against the initiation codon region. Only ASs inhibited the increase of TRH content and SABP induced by pCMV-TRH treatment. In addition, pCMV-TRH-induced hypertension seems not to be mediated by central Ang II or serum TSH. To summarize, central TRH overproduction in periventricular areas induced by ICV transfection pro-duces hypertension in rats which is reversed by specific antisense treatment. This model may help in testing effective antisense oligodeoxynucleotides against other candidate genes.
Cardiovascular Reactivity to Stress and Left Ventricular Mass in Youth
Authors: Allen Michael T. , Matthews Karen A. , Sherman Frederick S.
Published: June 2012

Abstract
We studied the relationships of cardiovascular reactivity during mental stress with left ventricular mass index in a group of prepubertal children 8 to 10 years old and in a group of peripubertal or postpubertal adolescents 15 to 17 years old. One hundred fifteen participants, varying in age group, sex, and race (black and white), took part in a laboratory stress protocol consisting of a reaction-time task, a mirror tracing task, a cold forehead challenge, and a stress interview. Cardiovascular measures included blood pressure and heart rate, as well as cardiac output, stroke volume, total peripheral resistance, and preejection period obtained noninvasively with impedance cardiography. Measures of left ventricular mass were made by echocardiography. Results indicated that across all participants, left ventricular mass index was associated with cardiovascular responses during the mirror tracing and cold forehead tasks, especially with those responses reflecting increased vasoconstriction. Subgroup analyses showed that these associations were significant for males and sometimes adolescents but not for females and children. As mirror tracing and cold forehead tasks most consistently produce α-adrenergic activation, the results suggest a model in which vasoconstriction due to mental stress is related to increased left ventricular mass in susceptible individuals, even at a young age.
A Live-Cell Assay for Studying Extracellular and Intracellular Endothelin-Converting Enzyme Activity
Authors: Parnot Charles , Le Moullec Jean-Michel , Cousin Marie-Anne , Guédin Denis , Corvol Pierre , Pinet Florence
Published: June 2012

Abstract
Endothelin-1 (ET-1) is formed from its precursor preproET-1 via the cleavage of the intermediate bigET-1 by endothelin-converting enzyme (ECE-1). However, the subcellular site at which this step occurs is not clear: It could occur intravesicularly along the secretory pathway or bigET-1 might be released and processed extracellularly. To address this point, we have developed an integrated autocrine system that uses a recombinant Chinese hamster ovary (CHO) luciferase reporter cell line that permanently expresses the human ET
A
receptor. Into these cells we transiently transfected human ECE-1a cDNA, either together with the human preproET-1 cDNA (as an endogenous source of bigET-1), or alone (in which case exogenous bigET-1 was added). Phosphoramidon inhibited the conversion of exogenous bigET-1 (IC
50
=5 to 30 μmol/L) much better than that of endogenous bigET-1 (IC
50
>1 mmol/L). Both conversions showed similar high yields (20% to 100%) that depended on the amount of ECE-1a expressed. Thus, ECE-1a has two equally relevant activities in this recombinant system for CHO cells: (1) an intracellular, probably intravesicular activity, corresponding to the ECE-1a–mediated step of ET-1 biosynthesis and (2) an extracellular activity at the plasma membrane. If this is also the case for endothelial cells, ECE-1a inhibitors would have to cross the plasma and vesicle membranes to be effective. The present system could be useful for screening such inhibitors.
Genetic Isolation of a Chromosome 1 Region Affecting Blood Pressure in the Spontaneously Hypertensive Rat
Authors: St. Lezin Elizabeth , Liu Weizhong , Wang Jia-Ming , Wang Ning , Kren Vladimir , Krenova Drahomira , Musilova Alena , Zdobinska Miroslava , Zidek Vaclav , Lau Daniel , Pravenec Michal
Published: June 2012

Abstract
Recent linkage studies in the spontaneously hypertensive rat (SHR) suggest that a blood pressure regulatory gene or genes may be located on rat chromosome 1q. To investigate this possibility, we replaced a region of chromosome 1 in the SHR (defined by the markers
D1Mit3
and
Igf2
) with the corresponding chromosome segment from the normotensive Brown-Norway (BN) strain. In male SHR congenic rats carrying the transferred BN chromosome segment, 24-hour average systolic and diastolic blood pressures were significantly lower than in male progenitor SHR. Polymerase chain reaction genotyping using 60 polymorphic microsatellite markers dispersed throughout the genome confirmed the congenic status of the new strain designated SHR.BN-
D1Mit3/Igf2
. These findings provide direct evidence that a blood pressure regulatory gene exists on the differential segment of chromosome 1 that is sufficient to decrease blood pressure in the SHR. The SHR.BN-
D1Mit3/Igf2
congenic strain represents an important new model for fine mapping and characterization of genes on chromosome 1 involved in the pathogenesis of spontaneous hypertension.
Tissue Angiotensinogen Gene Expression Induced by Lipopolysaccharide in Hypertensive Rats
Authors: Nyui Nobuo , Tamura Kouichi , Yamaguchi Satoshi , Nakamaru Masashi , Ishigami Tomoaki , Yabana Machiko , Kihara Minoru , Ochiai Hisao , Miyazaki Naomichi , Umemura Satoshi , Ishii Masao
Published: June 2012

Abstract
There is now convincing evidence that various tissues express their own tissue renin-angiotensin system, which may be regulated independently of the systemic renin-angiotensin system. However, little information is available on the regulation of the tissue renin-angiotensin system. We investigated the regulation of tissue angiotensinogen gene expression with respect to the development of hypertension. We measured basal and lipopolysaccharide-stimulated plasma angiotensinogen concentrations by radioimmunoassay and examined the expression of tissue angiotensinogen by Northern blot analysis in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) at 4 and 13 weeks of age. Basal plasma angiotensinogen concentration in SHR was comparable to that in WKY at 4 weeks of age and was significantly higher than that in WKY at 13 weeks of age. Lipopolysaccharide induced a significant increase in plasma angiotensinogen concentration in both WKY and SHR at 4 and 13 weeks of age. At 4 weeks of age, the basal levels of angiotensinogen mRNA in the liver, fat, adrenal, and aorta were higher in WKY than in SHR. At 13 weeks of age, the basal levels of angiotensinogen mRNA in the fat, adrenal, aorta, spleen, and kidney were higher in WKY than in SHR, while that in the liver did not differ significantly between the two strains. At 4 weeks of age, pretreatment with lipopolysaccharide increased the angiotensinogen mRNA levels in the liver, fat, adrenal, and aorta in both WKY and SHR. At 13 weeks of age, pretreatment with lipopolysaccharide increased the angiotensinogen mRNA levels in the liver, aorta, and adrenal; decreased those in the spleen; and had no effect in the kidney in both WKY and SHR. Interestingly, lipopolysaccharide increased the angiotensinogen mRNA level in fat only in SHR, with no effect in WKY, at 13 weeks of age. Lipopolysaccharide stimulated tumor necrosis factor-α mRNA expression in fat of WKY and SHR, and the increase in tumor necrosis factor-α mRNA level in SHR was significantly greater than that in WKY. Therefore, the increased tumor necrosis factor-α mRNA expression may be involved in the increased lipopolysaccharide-induced expression of angiotensinogen gene in fat of SHR at 13 weeks of age. These data suggest that the transcriptional and probably posttranscriptional regulation of angiotensinogen mRNA differs between SHR and WKY, that the regulation of angiotensinogen gene expression is tissue-specific, and that the altered expression of the angiotensinogen gene may be involved in the development of hypertension.
Quinaprilat Induces Arterial Vasodilation Mediated by Nitric Oxide in Humans
Authors: Haefeli Walter E. , Linder Lilly , Lüscher Thomas F.
Published: June 2012

Abstract
The beneficial therapeutic effects of angiotensin-converting enzyme (ACE) inhibitors are the result of reduced angiotensin II formation and possibly also of an accumulation of bradykinin that is inactivated by ACE. In particular, recently developed ACE inhibitors with tissue-penetrating properties, such as quinaprilat, may exert vascular effects via the bradykinin B
2
-receptor. To test direct arterial effects of quinaprilat and enalaprilat and to study their effects on vasodilation induced by bradykinin, venous occlusion plethysmography was used during local intra-arterial drug administration into the brachial artery in healthy volunteers. The response to bradykinin was augmented by both ACE inhibitors, but the effect of quinaprilat (3.9 nmol/min) was exclusively attributable to its direct vasodilator action. Enalaprilat (13 nmol/min) did not change baseline blood flow in the human forearm circulation. In contrast, quinaprilat significantly increased arterial flow from 3.5±0.5 to 4.6±0.7 mL/100 mL tissue/min, which was inhibited by
N
G
-monomethyl
-l
-arginine (8 μmol/min IA). Moreover, the effect of sodium nitroprusside (0.023 to 22.9 nmol/min) was substantially attenuated during concomitant administration of quinaprilat. These results suggest that quinaprilat induces vascular effects beyond the inhibition of angiotensin II formation; it causes vasodilation by increasing vascular nitric oxide production and thereby attenuates the relaxing effect of the nitric oxide donor sodium nitroprusside.
Immunohistochemically Detected Protein Nitration Indicates Sites of Renal Nitric Oxide Release in Goldblatt Hypertension
Authors: Bosse Hans Martin , Bachmann Sebastian
Published: June 2012

Abstract
In the kidney, nitric oxide (NO) from the macula densa (MD) is considered an integral modulator of the tubulovascular message system, whereas endothelium-derived NO is a major vasorelaxing factor. The goal of the present study was to determine extracellular pathways of NO in rats with renovascular two-kidney, one clip Goldblatt hypertension (2K1C). To localize NO in the tissue, immunohistochemical detection of NO-dependent tyrosine nitration was performed using a monoclonal antibody against nitrotyrosine. Nitration of phenolic compounds such as tyrosine results from the reaction with peroxynitrite (ONOO
−
) formed by NO and molecular oxygen or superoxide and may therefore be used as a footprint for local release of NO. Significant nitrotyrosine immunoreactivity was detected in the extraglomerular mesangium (EGM) of the stenotic kidney in 2K1C rats, whereas in the nonclipped contralateral kidney and in control animals no signal was detected at this site. Positive staining of the EGM was paralleled by enhanced NADPH diaphorase (NADPH-d) staining of the adjacent MD, signifying increased type I nitric oxide synthase (NOS) activity in the stenotic kidney. In contrast, in the cortical vasculature selectively enhanced nitrotyrosine immunoreactivity was detected in the arteriolar wall of the nonclipped contralateral kidney, and endothelial NADPH-d signal, indicating NOS Type III activity, was enhanced in parallel. Our results suggest that in MD, stimulation of NOS in the stenotic Goldblatt kidney induces the release of NO into the EGM. From there an NO-dependent intermediate stimulus may reach the glomerular vasculature. Footprints of NO-dependent effects in the vascular smooth muscle layer of the non-clipped contralateral kidney indicate a marked vasodilatory response that may have been caused by enhanced shear stress and/or angiotensin II levels.
Lovastatin Prevents Development of Hypertension in Spontaneously Hypertensive Rats
Authors: Jiang Jian , Roman Richard J.
Published: June 2012

Abstract
The present study evaluated the effects of lovastatin on renal function and the development of hypertension in spontaneously hypertensive rats (SHR). Four-week-old SHR were given lovastatin (10 mg/kg) or vehicle twice daily by gavage. After 4 weeks of treatment, mean arterial pressure was significantly lower in lovastatin-treated SHR (131±4 mm Hg, n=5) than in control animals (160±4 mm Hg, n=12) (
P
<.05). The fall in arterial pressure in lovastatin-treated rats was accompanied by changes in renal function. The slope of the relationship between arterial pressure and sodium excretion was threefold greater in lovastatin-treated SHR (n=6) than in control rats (n=6), and this was associated with significant elevations in renal medullary blood flow and renal interstitial hydrostatic pressure. Glomerular filtration rate was 17% higher in lovastatin-treated SHR (n=6) than in control rats (n=6) (0.94±0.05 versus 0.81±0.07 mL/min per g of kidney weight,
P
<.05). The wall-to-lumen area ratio of renal arterioles was significantly reduced in lovastatin-treated SHR compared with vehicle-treated rats (0.86±0.05 versus 1.08±0.04 for vessels with inner diameters <50 μm and 0.62±0.02 versus 0.75±0.04 for vessels with inner diameters of 50 to 100 μm,
P
<.05). These results indicate that chronic treatment with lovastatin shifts the relations between renal medullary blood flow, renal interstitial pressure, sodium excretion, and renal perfusion pressure to lower levels of arterial pressure and attenuates the development of hypertension and renal vascular hypertrophy in SHR.
Prostacyclin Release by Rat Cardiac Fibroblasts
Authors: Yu Hisahiro , Gallagher Ann Marie , Garfin Phillip M. , Printz Morton P.
Published: June 2012

Abstract
Cardiac fibroblasts, as the source of extracellular matrix for the left ventricle, subserve important functions to cardiac remodeling and fibrotic development following myocardial infarction or with pressure-overload cardiac hypertrophy. The fibroblast may be the target cell for angiotensin-converting enzyme inhibitors (ACEI) that are cardioprotective and reverse collagen deposition and remodeling but whose mechanisms of action remain controversial. Because we previously documented phenotypic differences between cardiac fibroblasts from the spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) left ventricle, the present study evaluated whether phenotypic differences also exist in the release of endogenous arachidonic acid metabolites or in the activation of phospholipase D, and the importance of observed differences to the formation of collagen and the mechanism of action of ACEI. The experimental design compared endogenous sources of arachidonic acid with exogenous prelabeling of cells. Angiotensin II stimulated greater arachidonic acid release than bradykinin, and WKY cells were more responsive than SHR. The major prostanoid formed by cardiac fibroblasts was prostaglandin I
2
(PGI
2
), with more prostacyclin production by WKY cells than SHR cells both under nonstimulated conditions and in response to angiotensin II or bradykinin. Beraprost, a PGI
2
analogue, was shown to decrease growth rate and DNA synthesis of fibroblasts and to inhibit mRNA expression for collagen types I and III, with SHR cells being less responsive to beraprost than WKY cells. These results potentially implicate eicosanoid metabolism, particularly PGI
2
, in collagen formation, fibrotic development, and cardiac remodeling, and they imply that the SHR genetic hypertension model may be predisposed to excess cardiac fibrosis.
Role of Endothelial Kinins in Control of Coronary Nitric Oxide Production
Authors: Zhang Xiaoping , Scicli Guillermo A. , Xu Xiaobin , Nasjletti Alberto , Hintze Thomas H.
Published: June 2012

Abstract
The purpose of the present study was to determine whether interventions that promote kinin production or decrease kinin inactivation affect nitric oxide production in isolated canine coronary microvessels. Accordingly, bradykinin (10
−8
to 10
−5
mol/L), ramiprilat (10
−10
to 10
−8
mol/L), A23187 (10
−8
to 10
−6
mol/L), kallikrein (1 to 20 U/mL), and kininogen (0.5 to 10 μg/mL) were used to stimulate endothelium-dependent nitric oxide production. Receptor antagonists, serine protease inhibitors, and a kinin antibody were used to inactivate local kallikrein-kinin activity. Nitrite, the metabolite of nitric oxide in aqueous solution, was measured using the Griess reaction. All the agonists significantly increased nitrite release. For instance, the highest dose of bradykinin, ramiprilat, A23187, kallikrein, and kininogen markedly increased nitrite production, from 60±10 to 156±12, 153±11, 161±15, 176±15, and 168±16 pmol/mg (all
P
<.05), respectively. The increased nitrite production caused by these agents was not only blocked by
N
ω
-nitro-
l
-arginine methyl ester (L-NAME) and HOE 140 (which blocks B
2
kinin receptor) but by the kinin antibody also. For instance, nitrite production elicited by bradykinin, ramiprilat, A23187, and kininogen was reduced to 95±8, 87±8, 94±11, and 85±11 pmol/mg (all
P
<.05), respectively, by the kinin antibody. Carbachol-induced nitrite production (from 66±8 to 144±13) was blocked by L-NAME but not by HOE 140 or the kinin antibody. These results suggest that either increasing kininogen to promote endogenous kinin formation or inhibiting angiotensin-converting enzyme to decrease kinin breakdown, increases nitric oxide production in isolated coronary microvessels. These data indicate that a microvessel kallikrein-kinin system has an important role in the control of nitric oxide production in coronary microvessels.
Effects of SR 49059, a New Orally Active and Specific Vasopressin V
1
Receptor Antagonist, on Vasopressin-Induced Vasoconstriction in Humans
Authors: Weber Roger , Pechère-Bertschi Antoinette , Hayoz Daniel , Gerc Vjekoslav , Brouard Rémi , Lahmy Jean-Paul , Brunner Hans R. , Burnier Michel
Published: June 2012

Abstract
We have evaluated the efficacy of SR 49059, a new orally active and specific vasopressin V
1
receptor antagonist (arginine-vasopressin [AVP]), in the blockade of the vascular effects of exogenous AVP in healthy subjects. In preliminary experiments, two procedures to measure the V
1
vascular effects of AVP were assessed. First, the AVP-induced changes in skin blood flow were investigated by the injection of increasing doses of AVP intradermally, with or without a previous local vasodilation with calcitonin gene–related peptide (CGRP). In a second protocol, AVP was infused intra-arterially, and the changes in radial artery diameter and blood flow were measured. The intradermal injection of AVP caused significant decreases in skin blood flow, and the use of CGRP increased the sensitivity of the method by a factor of 10
2
to 10
3
. AVP infused intra-arterially caused dose-dependent decreases in the radial artery diameter and blood flow. In the main study, the potency and efficacy of SR 49059 to block the AVP-induced changes in skin blood flow were assessed in 12 healthy men with a double-blind, triple crossover study design. The subjects were randomized to receive a placebo orally and 30 mg and 300 mg of the antagonist at a 1-week interval. The subjects were then further randomized to evaluate the efficacy of the same doses of the antagonist to block the vasoconstriction of the radial artery induced by an intra-arterial infusion of AVP. SR 49059 inhibits, dose-dependently and significantly, the AVP-induced changes in skin blood flow, with a peak effect occurring between 2 and 6 hours after injection. In addition, the 300-mg dose of SR 49059 completely blocked the vasoconstriction of the radial artery induced by AVP. In conclusion, skin blood-flow measurement, after intradermal injection of AVP on a skin area vasodilated with CGRP, is an effective method to investigate the V
1
vascular effect of AVP in humans. SR 49059 is a potent and specific antagonist of V
1
receptors, which blocks the AVP-induced vasoconstriction.
Endogenous Angiotensin II Produced by Endothelium Regulates Interleukin-1β–Stimulated Nitric Oxide Generation in Rat Isolated Vessels
Authors: Montón Mercedes , López-Farré Antonio , Mosquera Juan R. , Sánchez de Miguel Lourdes , García-Durán Margarita , Sierra María P. , Bellver Teresa , Rico Luis , Casado Santos
Published: June 2012

Abstract
The endothelium is a source of several factors that regulate vascular functions. Angiotensin II is one of the main active factors released by the endothelium. The aim of the present work was to analyze the role of angiotensin II released by the endothelium in the regulation of the inducible nitric oxide synthase expression in rat isolated aortic vessels. Interleukin-1β (0.03 U/L) stimulated nitrite release by the aortic vessels. The nitrite released was less in vessels with endothelium than in deendothelialized aortic segments. This effect was accompanied by a reduced expression of the inducible nitric oxide synthase in the aortic rings with endothelium. Exogenous angiotensin II inhibited IL-1β–stimulated inducible nitric oxide synthase protein expression in both deendothelialized vessels and those with endothelium, although with reduced ability on the aortic segments with endothelium by a nitric oxide–independent mechanism. In the aortic rings with endothelium, either inhibition of the AT-1 receptor with losartan or blocking of angiotensin II generation with fosinopril enhanced interleukin-1β–stimulated inducible nitric oxide synthase protein expression. In conclusion, the endothelium decreases inducible nitric oxide synthase expression in the vascular wall. Angiotensin II released from endothelial cells is a main mediator responsible for this inhibition through an AT-1–type receptor-dependent mechanism.
Endothelin and Prostaglandin H
2
Enhance Arteriolar Myogenic Tone in Hypertension
Authors: Huang An , Koller Akos
Published: June 2012

Abstract
We hypothesized that endothelin in addition to prostaglandin (PG)H
2
may also contribute to the enhanced myogenic tone of skeletal muscle arterioles of spontaneously hypertensive (SH) rats. Changes in the diameter of isolated, cannulated arterioles (≈60 μm) from cremaster muscles of 30-week-old normotensive Wistar Kyoto (WKY) and SH rats were measured as a function of perfusion pressure (20 to 140 mm Hg). Pressure-induced constrictions were significantly enhanced between 60 to 140 mm Hg in arterioles of SH rats compared with those of WKY rats; at 80 and 140 mm Hg the normalized diameter of arterioles (expressed as a percentage of corresponding passive diameter) of SH rats was 11.0% and 15.4% less (
P
<.05) than that of WKY rats. After inhibition of thromboxane A
2
–PGH
2
receptors by SQ 29,548 (10
−6
mol/L), the still enhanced myogenic response of SH arterioles was eliminated by the removal of endothelium or the administration of BQ-123 (10
−7
mol/L), an endothelin A (ET-A) receptor blocker, which also inhibited constrictions to exogenous ET-1 (10
−11
to 5×10
−10
mol/L). ET-1 elicited comparable responses in arterioles of SH and WKY rats. Thus, in SH rats the enhanced arteriolar constriction to increases in intravascular pressure seems to be due to the production of endothelium-derived constrictor factors PGH
2
and endothelin.
Calcium Signaling Mechanisms in Renal Vascular Responses to Vasopressin in Genetic Hypertension
Authors: Feng Jian J. , Arendshorst William J.
Published: June 2012

Abstract
Previous blood flow studies demonstrated that arginine vasopressin (AVP) produces exaggerated renal vasoconstriction in young spontaneously hypertensive rats (SHR) compared with Wistar-Kyoto control rats (WKY). The purpose of the present study was to determine the role of postreceptor calcium signaling pathways in AVP-induced renal vasoconstriction in vivo. Renal blood flow (RBF) was measured by electromagnetic flowmetry in anesthetized, water-loaded, 8-week-old WKY and SHR pretreated with indomethacin to avoid interactions with prostaglandins. AVP was injected into the renal artery to produce a transient 25% to 30% decrease in RBF without affecting arterial pressure. To achieve similar control levels of vasoconstriction, SHR received a lower dose (2 versus 5 ng). Coadministration of nifedipine with AVP produced dose-dependent inhibition of the AVP-induced renal vasoconstriction. Nifedipine exerted maximum inhibition by blocking 30% to 35% of the peak AVP response, indicating the involvement of dihydropyridine-sensitive voltage-dependent calcium channels. To evaluate intracellular calcium mobilization, 8-(
N,N
-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) or heparin was coadministered with AVP. Each agent produced a dose-dependent inhibition of up to 65% of the maximum blood flow change produced by AVP. The degrees of inhibition produced by maximum effective doses of nifedipine and TMB-8 were additive; the combination blocked up to 85% of the response to AVP. These observations indicate that about one third of the AVP-induced constriction of renal resistance vessels is mediated by voltage-dependent L-type calcium channels responsive to the dihydropyridine nifedipine. Approximately two thirds of the change in vascular tone is due to inositol 1,4,5-trisphosphate–mediated calcium mobilization from intracellular sources sensitive to TMB-8 and heparin. The results suggest that the exaggerated renal vascular reactivity to AVP challenge in SHR is probably not due to a strain difference in postreceptor calcium signal transduction. After AVP receptor stimulation, calcium mobilization and calcium entry signaling pathways participate to similar degrees in WKY and SHR.
Increased Expression of Ca
2+
-Sensitive K
+
Channels in Aorta of Hypertensive Rats
Authors: Liu Yanping , Pleyte Kay , Knaus Hans-Guenther , Rusch Nancy J.
Published: June 2012

Abstract
Potassium efflux through Ca
2+
-sensitive K
+
channels (K
Ca
channels) is increased in arterial smooth muscle cells from hypertensive rats, but the molecular mechanism is unknown. The goal of this study was to compare the levels of K
Ca
channel current between aortic smooth muscle cells from adult Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) and then use Western blot methods and ribonuclease protection assays to examine the expression and mRNA levels for the K
Ca
channel in these same vascular tissues. Whole-cell patch-clamp methods indicated a larger component of K
Ca
channel current, sensitive to block by iberiotoxin (100 nmol/L), in single aortic smooth muscle cells from SHR compared with WKY. Subsequent Western blot analysis using a site-specific antibody (anti–α
913–926
) directed against the S9/S10 linker of the α-subunit of the K
Ca
channel revealed a 125-kD immunoreactive band in lanes loaded with either WKY or SHR aortic muscle membranes. The immunoreactive density of this band, which corresponded to the known molecular size of the α-subunit, was 2.2-fold greater in lanes loaded with aortic smooth muscle membranes from the hypertensive animals. However, despite this evidence for an increased expression and functional enhancement of K
Ca
channels in aortic smooth muscle membranes of SHR, ribonuclease protection assays with a
32
P-labeled riboprobe targeted against the S9/S10 linker of the K
Ca
channel α-subunit revealed no difference in mRNA levels for the α-subunit between WKY and SHR aortic tissue. These findings provide initial evidence that (1) an increased expression of K
Ca
channels may be a mechanism for the enhanced K
Ca
current in aortic smooth muscle membranes of SHR, and (2) the upregulation of K
Ca
channels in arterial muscle membranes during hypertension, which is regarded as a homeostatic mechanism for buffering vascular excitability, may rely on post-transcriptional events.
Hypothalamic Hypertensive Factor
Authors: Morris Howard R. , Etienne A. Tony , Panico Maria , Tippins John R. , Alaghband-Zadeh Jamshid , Holland Sharon M. , Mehdizadeh Siroos , Jackie de Belleroche  , Das Indrajit , Khan Nusrat S. , de Wardener Hugh E.
Published: June 2012

Abstract
Human and rat plasma and rat hypothalamus contain a cytochemically detectable substance, the concentration of which rises with an increase in salt intake. The plasma concentration of this material is also raised in essential hypertension and in the spontaneously hypertensive rat (SHR), the Milan hypertensive rat, and the reduced renal mass (RRM) hypertensive rat. In the normal rat, the greatest concentration is found in the hypothalamus of the SHR and the RRM hypertensive rat. The physicochemical characteristics of this cytochemically detectable hypothalamic hypertensive factor (HHF), including chromatographic behavior and molecular weight range, suggest that it may share features common to a substituted guanidine that is present in established nitric oxide synthase (NOS) inhibitors. It was therefore decided to determine the effect on NOS activity of the HHF obtained from mature SHR. The ability of HHF to inhibit NOS activity was studied on (1) NOS extracted from bovine aorta, rat brain, and human platelets by measuring the conversion of radiolabeled
l-
arginine to
l
-citrulline and (2) rat liver NOS measured indirectly with a cytochemical technique based on the stimulation of soluble guanylate cyclase activity in hepatocytes by NO. HHF showed a biphasic inhibitory action on platelet NOS activity that was greater with HHF obtained from SHR than from Wistar-Kyoto rats. HHF also had a biphasic inhibitory effect on hepatocyte NOS activity that was more potent when obtained from SHR. It is proposed that the increase in HHF, a novel form of NOS inhibitor that is elevated in SHR, may be involved in the rise in arterial pressure.
Effect of Carbidopa on the Excretion of Sodium, Dopamine, and Ouabain-Like Substance in the Rat
Authors: Ho Chung Shun , Butt Asif , Semra Yemane K. , Swaminathan R.
Published: June 2012

Abstract
The effect of carbidopa, a competitive inhibitor of dopamine synthesis on the excretion of sodium, dopamine (DA), and endogenous sodium transport inhibitor (ESTI), was examined in rats on normal and high salt diets for 7 days. ESTI activity was measured (1) as ouabain-like substance (OLS) by radioimmunoassay using an antibody raised against ouabain, (2) by inhibition of purified Na
+
,K
+
-ATPase activity (ATPI), and (3) as digoxin-like substance (DLS) using a commercial digoxin assay. The OLS immunoassay was validated against rubidium transport studies. High salt diet caused an increase in OLS and ATPI but not DLS. Sodium excretion in rats on normal sodium intake was not affected by carbidopa treatment but was significantly lower in the high sodium diet group during the first 5 days of the study. In the low salt group, carbidopa treatment caused significant increases in OLS. We conclude that ESTI (measured as OLS) and DA are important in the natriuresis of salt loading.
Fatty Acids Augment Endothelium-Dependent Dilation in Hand Veins by a Cyclooxygenase-Dependent Mechanism
Authors: Stepniakowski Konrad T. , Lu Gang , Davda Rajesh K. , Egan Brent M.
Published: June 2012

Abstract
Evidence supports the hypothesis that elevated nonesterified fatty acids (NEFAs) in patients with insulin resistance, eg, obese hypertensive subjects, contribute to increased vascular α-adrenergic reactivity and tone by impairing endothelium-dependent vasodilation. To generate further support for this notion, we studied responses to endothelium-dependent and independent dilators under control (0.9% NaCl/heparin) conditions in one hand and with elevated NEFAs in the contralateral hand (10% intralipid/heparin). To observe venodilator responses, the dorsal hand vein diameter was first reduced by ∼60% with phenylephrine. Studies were repeated with indomethacin to block the generation of cyclooxygenase products. In contrast to previous in vitro data, elevating NEFAs locally in vivo augmented rather than suppressed venodilator responses to the two endothelium-dependent dilators acetylcholine and methacholine (
P
<.05). Responses to the endothelium-independent dilator nitroglycerin were unaffected. Indomethacin attenuated the capacity of intralipid/heparin to enhance endothelium-dependent dilator responses to acetylcholine and methacholine. Indomethacin did not affect venodilator responses to nitroglycerin. The effect of intralipid/heparin to significantly reduce the phenylephrine infusion rate required to reduce hand vein diameter by ∼60% was reversed by indomethacin. These data indicate that raising fatty acids locally augments endothelium-dependent dilation by a cyclooxygenase-dependent mechanism. The findings also suggest that NEFAs augment α
1
-adrenoceptor–mediated constriction in hand veins by a cyclooxygenase-dependent mechanism. These hand vein studies do not support the notion that the elevated NEFAs in obese hypertensive patients augment α
1
-adrenoceptor–mediated reactivity by reducing nitric oxide synthesis.
Effects of Lipid-Lowering Agents in the Dahl Salt-Sensitive Rat
Authors: Wilson Thomas W. , Alonso-Galicia Magdalena , Roman Richard J.
Published: June 2012

Inducing renal cytochrome P4504A (P4504A) activity with clofibrate prevents the development of hypertension in Dahl salt-sensitive (Dahl S) rats. To determine if this also occurs with other antilipidemic agents, we compared the effects of a related drug, fenofibrate, with those of an unrelated agent, pravastatin, on blood pressure, renal histology, and P4504A activity. Dahl S rats were pretreated with fenofibrate (95 mg/kg per day), pravastatin (70 mg/kg per day), or vehicle for 7 days before and after being switched from a low-salt (0.1% NaCl) to a high-salt (8.0% NaCl) diet. After 3 weeks on the high-salt diet, mean arterial pressures averaged 183±13 (n=9), 126±10 (n=9), and 148±11 mm Hg (n=8), respectively, in vehicle-, fenofibrate-, and pravastatin-treated animals. Both drugs reduced the degree of proteinuria and glomerular injury. P4504A protein levels and the synthesis of 20-hydroxyeicosa-5,8,11,14-tetraenoic acid (20-HETE) were increased in the liver and kidney of fenofibrate-treated, but not pravastatin-treated rats. We also administered these agents to Dahl S rats in which hypertension had previously been induced by a high-salt diet. Mean arterial pressures averaged 164±10, 113±23, and 160±15 mm Hg in rats treated with vehicle, fenofibrate, or pravastatin for 3 weeks. Fenofibrate-treated rats exhibited a natriuresis. Proteinuria and glomerular injury were reduced by pravastatin but not by fenofibrate. These results indicate that fenofibrate prevented the development of hypertension and reduced subsequent glomerular injury in Dahl S rats, probably secondary to increased renal production of 20-HETE. Although pravastatin did not induce renal P4504A activity in these animals, it reduced the severity of hypertension and renal damage through some other mechanism.
Relationship Between Endothelial Function and Fibrinolysis in Early Hypertension
Authors: Tomiyama Hirofumi , Kimura Yutaka , Mitsuhashi Hiroyuki , Kinouchi Takashi , Yoshida Hideo , Kushiro Toshio , Doba Nobutaka
Published: June 2012

Abnormalities in fibrinolysis, endothelial function, and glucose and lipid metabolism have been reported in hypertension. This study was conducted to examine the interrelationships between fibrinolytic factors, glucose and lipid metabolism, and endothelial function in hypertension. The effects of administering an angiotensin converting enzyme inhibitor, benazepril, were also examined. Blood levels of the following substances were measured in patients with borderline and mild hypertension (n=50, 51±19 years) and in age-matched controls (n=10): total cholesterol, triglycerides, tissue plasminogen activator activity and antigen, and plasminogen activator inhibitor type 1 activity and antigen. Insulin sensitivity was assessed by oral glucose tolerance test, and endothelial function was assessed by evaluating changes in diameter of the brachial artery during reactive hyperemia as observed by ultrasonography. Activities of tissue plasminogen activator and plasminogen activator inhibitor type 1 were both elevated in the hypertensive patients. Stepwise multiple regression analysis showed that plasminogen activator inhibitor type 1 antigen correlated with insulin sensitivity, total cholesterol levels, and triglycerides levels (
P
<.01). Endothelial function was negatively correlated with tissue plasminogen activator activity and antigen (
P
<.01). The chronic administration of benazepril (5–10 mg/d) for 20 weeks improved insulin sensitivity, endothelial function (6.6+3.4→9.0+2.5%,
P
<.01), and tissue plasminogen activator activity and antigen. These results indicate that abnormalities in fibrinolysis are associated with endothelial dysfunction as well as disorders of glucose and lipid metabolism in patients with borderline and mild hypertension. The treatment of such patients with benazepril appeared to improve the impairment in fibrinolysis and endothelial dysfunction.
Angiotensinases Restrict Locally Generated Angiotensin II to the Blood Vessel Wall
Authors: Hilgers Karl F. , Bingener Erik , Stumpf Christian , Müller Dominik N. , Schmieder Roland E. , Veelken Roland
Published: June 2012

We tested the hypothesis that angiotensinases limit the spillover of locally formed angiotensin II into the circulation. The release of angiotensin peptides from isolated rat hindquarters perfused with an artificial medium was measured by high-performance liquid chromatography and radioimmunoassay. The spontaneous release of angiotensins was increased by the angiotensinase inhibitors phenanthroline (850±195 versus 95±33 fmol of angiotensin I per 30 minutes in controls,
P
<.05, n=5 each) and amastatin (
P
<.05, n=5 each). Infusion of renin induced sustained local angiotensin I formation, which was also increased by phenanthroline. Stimulation of local angiotensin formation by renin infusion was compared with infusion of exogenous angiotensin II. Renin caused similar increases of perfusion pressure (11.1±2.2 versus 7.6±1.9 mm Hg after angiotensin II,
P
>.05) despite lower angiotensin II levels in the venous effluent than during infusion of exogenous angiotensin II (65±2 versus 482±33 fmol/mL,
P
<.05, n=7 each). Thus, renin must have caused higher angiotensin II tissue levels than indicated by the measurements in the venous effluent. The pressor response to renin was abolished by the type 1 angiotensin II receptor antagonist losartan. We conclude that the major part of locally generated angiotensins is not released into the circulation but degraded by angiotensinases within the tissue compartment.
Mineralocorticoid Blockade Reduces Vascular Injury in Stroke-Prone Hypertensive Rats
Authors: Rocha Ricardo , Chander Praveen N. , Khanna Kavita , Zuckerman Andrea , Stier Charles T.
Published: June 2012

Chronic treatment of saline-drinking stroke-prone spontaneously hypertensive rats (SHRSP) with agents that interfere with the formation or actions of angiotensin II (Ang II) prevents the development of stroke and renal vascular damage. Ang II, in addition to its direct vascular effects, stimulates the synthesis and release of aldosterone. To assess the role of aldosterone in the development of pathologic changes in these rats, we implanted time-release pellets containing 200 mg of the mineralocorticoid receptor antagonist, spironolactone, into 14 SHRSP at 7.5 weeks of age. Eight SHRSP littermates received placebo pellets. Over the period of study (3 to 4 weeks), systolic blood pressure (SBP) was not different between the groups. Spironolactone did not enhance water and electrolyte excretion. All placebo-treated SHRSP developed marked proteinuria (150±6 mg/d) whereas in spironolactone-treated SHRSP, urinary protein excretion (UPE) averaged 39±9 mg/d (
P
<.0001). In a second study to assess effects on survival, 6 SHRSP received spironolactone (10 mg/kg/d) and 6 received vehicle. All but one of the control rats displayed signs of stroke and died by 16 weeks of age, while the spironolactone-treated SHRSP remained asymptomatic through 19 weeks of age (
P
<.03). At 16 weeks of age, spironolactone-treated SHRSP were severely hypertensive (247±3 mm Hg), yet UPE remained at baseline levels. In contrast, preterminal UPE averaged 136±13 mg/d in control rats (
P
<.0001). In both studies, histopathologic examination revealed a marked protective effect of spironolactone against the development of malignant nephrosclerotic and cerebrovascular lesions. These observations indicate a vascular and end organ protective effect of spironolactone in the absence of lowered blood pressure in saline-drinking SHRSP and are consistent with a major role for mineralocorticoids as hormonal mediators of vascular injury.
Different Signaling Pathways Mediate Stimulated Secretions Of Endogenous Ouabain and Aldosterone From Bovine Adrenocortical Cells
Authors: Shah Jui R. , Laredo James , Hamilton Bruce P. , Hamlyn John M.
Published: June 2012

Angiotensin II stimulates secretion of corticosteroids and an ouabain-like compound from adrenocortical cells. The angiotensin AT
1
and AT
2
receptor subtypes have been linked with stimulated secretion of aldosterone and endogenous ouabain, respectively, but the second messenger mechanisms involved in the latter secretion are not known. Accordingly, we investigated the effects of several pharmacological agents that affect signaling pathways on the basal and stimulated secretions of aldosterone and endogenous ouabain from primary cell cultures of bovine adrenocortical cells. The AT
2
receptor antagonist, PD 123319, blocked the effects of angiotensin II on secretion of endogenous ouabain but not aldosterone. Treatment of the cells with either dibutyryl cAMP, a membrane permeant analog, or the phorbol ester tetradecanoyl phorbol acetate stimulated aldosterone secretion but had no effect on the secretion of endogenous ouabain. On the other hand, the membrane permeant analog, 8BcGMP, maximally activated secretion of endogenous ouabain whereas incubation of cells with sodium orthovanadate blocked angiotensin II stimulated secretion of endogenous ouabain. Neither 8BcGMP nor sodium orthovanadate affected the basal or stimulated components of aldosterone secretion. These results show that the secretions of aldosterone and endogenous ouabain from bovine adrenocortical cells are mediated by different intracellular signaling mechanisms and provide evidence that the adrenal secretions of these steroids are regulated differently.
Target-Organ Damage in Stage I Hypertensive Subjects With White Coat and Sustained Hypertension
Authors: Palatini Paolo , Mormino Paolo , Santonastaso Massimo , Mos Lucio , Dal Follo Marta , Zanata Giuseppe , Pessina Achille C.
Published: June 2012

Abstract
—Controversy remains on whether white coat hypertension is a benign clinical condition or carries an increased risk of target-organ damage. Nine hundred forty-two stage I hypertensive subjects enrolled in the HARVEST trial underwent 24-hour ambulatory blood pressure monitoring and urine collection for albumin measurement. Reliable echocardiographic data were obtained in 722 subjects. White coat hypertensive subjects were defined on the basis of three different partition values: mean daytime blood pressure <130/90 mm Hg, <135/85 mm Hg, or <140/90 mm Hg. Ninety-five normotensive subjects with similar age and sex distribution were studied as controls. With all threshold levels, left ventricular mass index and wall thicknesses were greater in the sustained hypertensive subjects than in the white coat hypertensive subjects, also when these differences were adjusted for blood pressure readings taken in the office. Relative wall thickness was similar in the two hypertensive groups. All echocardiographic dimensional data were greater in the white coat hypertensive subjects than in the normotensive subjects. Urinary albumin and the prevalence of microalbuminuria were also greater in the sustained hypertensive subjects than in the white coat hypertensive subjects. No significant differences in urinary albumin were found between the white coat hypertensive and the normotensive subjects. These results show that within a population of subjects with stage I hypertension, subjects with white coat hypertension have a smaller degree of hypertensive complications than those with sustained hypertension, irrespective of their blood pressure levels taken in the office. However, in comparison with normotensive subjects, white coat hypertensive subjects seem to be at greater risk. Cardiac involvement seems to precede glomerular damage in the early stage of hypertension.
Role of Phospholipase A
2
Isozymes in Agonist-Mediated Signaling in Proximal Tubular Epithelium
Authors: Harwalkar Subash , Chang Chung-Ho , Dulin Nickolai O. , Douglas Janice G.
Published: June 2012

Abstract
—Angiotensin II in proximal tubule epithelium is known to stimulate the release of arachidonic acid after stimulation of phospholipase A
2
(PLA
2
) independent of phospholipase C–mediated signaling. Furthermore, an angiotensin II type 2 receptor subtype has been linked to this signaling cascade. We investigated the regulation and differential stimulation of PLA
2
s by comparing the PLA
2
activities associated with the membranes and cytosol of rabbit renal proximal tubular epithelial cells after stimulation with angiotensin II, epidermal growth factor, and bradykinin. Both fractions demonstrated PLA
2
activity that was dithiothreitol insensitive, required micromolar concentrations of Ca
2+
for optimal activity, and was inhibited in a dose-dependent manner by an antiserum to a cytosolic PLA
2
with a molecular mass of 85 kD. However, membrane-associated PLA
2
did not demonstrate significant substrate specificity, whereas 1-steroyl-2-[
14
C]arachidonylphosphatidyl choline was the preferred substrate for cPLA
2
. An antiserum generated against mastoparan, a known PLA
2
activator, inhibited membrane- but not cytosol-associated PLA
2
activity. Membrane fractions showed a broad pH range (7.5 to 8.5) for optimal PLA
2
activity, whereas cytosol was maximum at pH 9.5. Angiotensin II stimulated membrane-associated PLA
2
activity by 88%, whereas bradykinin and epidermal growth factor inhibited activity by 54% and 41%, respectively. The three agonists stimulated cPLA
2
. Moreover, angiotensin II–induced activation of membrane-associated PLA
2
preceded the activation of cPLA
2
. These results demonstrate differential localization and regulation of proximal tubular epithelial PLA
2
isozymes, which may determine the pattern of subsequent arachidonic acid metabolism by the cytochrome P450 system.