bluuebunny/crossref_metadata_2025 huggingface dataset:
Expression of Aminopeptidase A, an Angiotensinase, in Glomerular Mesangial Cells
Authors: Troyanovskaya Marta , Song Lijun , Jayaraman Gomathi , Healy Dennis P.
Published: June 2012

Abstract
Glomerular mesangial cells are known to express angiotensin II type 1 receptors and contract in response to circulating and/or locally produced angiotensin II. In addition, stimulation of mesangial cell matrix protein synthesis by elevated levels of angiotensin II is known to contribute to the development of glomerulosclerosis. Previously, we reported that mesangial cells were positively immunostained with antiserum directed against aminopeptidase A, the principal angiotensinase in the metabolism of angiotensin II. Here we demonstrate directly that aminopeptidase A is expressed in mesangial cells cultured from rat kidney. First, cultured mesangial cells had measurable aminopeptidase A enzymatic activity. Second, immunoblots for aminopeptidase A were positive for isolated glomeruli and mesangial cells, although two bands were seen for mesangial cells (≈138 and 144 kD), and only the larger band was seen for isolated glomeruli and kidney. Third, Northern blot hybridizations of total RNA from mesangial cells or kidney were positive and labeled similarly sized bands. Fourth, reverse transcription–polymerase chain reaction amplification of mesangial cell total RNA yielded a partial cDNA of the expected size that was confirmed by sequencing to be identical to rat kidney aminopeptidase A. These results indicate that aminopeptidase A is expressed within mesangial cells. These results further suggest that metabolism of angiotensin II by aminopeptidase A could play a protective role in minimizing the adverse effects of angiotensin II stimulation of mesangial cells.
Cardiac Insulin-like Growth Factor I and Growth Hormone Receptor Expression in Renal Hypertension
Authors: Guron Gregor , Friberg Peter , Wickman Anna , Brantsing Camilla , Gabrielsson Britt , Isgaard Jörgen
Published: June 2012

Abstract
The aim of the present study was to investigate the role of insulin-like growth factor I in the development of cardiac hypertrophy in two-kidney, one clip hypertension by relating growth hormone receptor and insulin-like growth factor I receptor mRNA levels to insulin-like growth factor I gene transcription using a solution hybridization/RNase protection assay. Two-kidney, one clip hypertension was induced in male Wistar rats, and experiments were performed 2, 4, 7, and 12 days after surgery. Systolic blood pressure was elevated 2, 7, and 12 days after clipping (
P
<.001). Left ventricular weights were increased 2, 4, 7, and 12 days after surgery (
P
<.01). Associated with the rise in blood pressure, left ventricular insulin-like growth factor I mRNA was increased 2, 7, and 12 days after surgery (
P
<.01). Furthermore, growth hormone receptor and insulin-like growth factor I receptor gene expression increased specifically in the left ventricle of renal hypertensive rats (
P
<.05 and
P
<.001, respectively). Left ventricular growth hormone receptor mRNA peaked 7 days after induction of renal artery stenosis. These results show that insulin-like growth factor I, growth hormone receptor, and insulin-like growth factor I receptor mRNA increase in the pressure-overloaded left ventricle of two-kidney, one clip rats, suggesting a role for insulin-like growth factor I and the growth hormone/insulin-like growth factor I axis in the development of cardiac hypertrophy.
Impaired Renal Vasodilation and Urinary cGMP Excretion in Dahl Salt-Sensitive Rats
Authors: Simchon Shlomoh , Manger William , Blumberg Gabriele , Brensilver Jeffrey , Cortell Stanley
Published: June 2012

Abstract
We previously have shown that Dahl salt-sensitive rats increase renal vascular resistance in response to excessive salt feeding before total peripheral resistance increases and hypertension occurs. Failure of renal vasculature to dilate, as normally occurs in Dahl salt-resistant rats fed a high salt diet, may play a role in the development of hypertension in Dahl salt-sensitive rats. We also showed that renal vasculature in salt-sensitive rats is hyperreactive to vasoconstrictors and hyporeactive to vasodilators. Atrial natriuretic peptide, by stimulating cell-bound receptors, and nitroprusside, by generating nitric oxide, cause renal vasodilation by generating cGMP. Studies were undertaken to determine whether defective renal vasodilation in Dahl salt-sensitive rats is due to impaired production of cGMP. We examined the influence of nitroprusside infusion and salt intake on renal vascular resistance and cGMP excretion in salt-sensitive and salt-resistant rats. Results demonstrate that salt feeding and nitroprusside infusion increase cGMP excretion and decrease renal vascular resistance in salt-resistant rats (
P
<.01), and, although this relationship was less clear in salt-sensitive rats, there was a reciprocal relationship between renal vascular resistance and cGMP excretion in all animals studied. Salt feeding and nitroprusside infusion caused less of an increase in cGMP excretion in salt-sensitive than in salt-resistant rats (
P
<.01). In conclusion, these studies support the concept that impairment in cGMP generation may play a primary role in the inability of the kidneys of Dahl salt-sensitive rats to vasodilate in response to increased salt intake. Such an impairment could contribute to salt retention and the development of hypertension.
Phorbol Ester Activation of the Rat Vascular Myocyte Na
+
-H
+
Exchanger Isoform 1
Authors: Siczkowski Martin , Ng Leong L.
Published: June 2012

Abstract
Vascular myocytes from the spontaneously hypertensive rat (SHR) demonstrate elevated Na
+
-H
+
exchanger activity associated with increased cell proliferation and hyperresponsiveness to agonists such as phorbol esters. Since the Na
+
-H
+
exchanger isoform 1 (NHE-1) is stimulated by protein kinase C, we have investigated the effects of phorbol esters on NHE-1 activity and its phosphorylation in vascular myocytes of these rats. SHR cells demonstrated a larger alkalinization response to 12-
O
-tetradecanoylphorbol 13-acetate than Wistar-Kyoto rat (WKY) cells. Kinetic analyses indicated that whereas 12-
O
-tetradecanoylphorbol 13-acetate increased the maximal transport capacity of NHE-1 in both cell types, affinity for H
+
was increased in WKY cells and cooperativity for H
+
at the internal modifier site was reduced in SHR cells. In neither cell type was the subcellular distribution of NHE-1 altered by phorbol ester stimulation. NHE-1 phosphorylation was markedly reduced in WKY cells stimulated by the phorbol ester, an effect abolished by inhibition of protein kinase C. In contrast, NHE-1 phosphorylation in quiescent SHR cells was approximately double that of WKY cells and was reduced after phorbol ester treatment. Inhibition of protein kinase C in SHR cells led to a marked elevation of NHE-1 phosphorylation that was not associated with a change in exchanger activity, but WKY cells exhibited a small, insignificant rise in NHE-1 phosphorylation. Thus, the kinetic responses of NHE-1 to phorbol esters in vascular myocytes of these rat strains are different, the changes in exchanger kinetics of SHR resembling those described in human hypertension. NHE-1 phosphorylation has an inverse relationship with protein kinase C activity. However, modulation of NHE-1 phosphorylation may not be associated with concurrent alterations in activity, indicating a role for non–phosphorylation-dependent mechanisms.
Differential Alteration of Neuronal and Cardiovascular Responses to Adenosine Microinjected Into the Nucleus Tractus Solitarius of Spontaneously Hypertensive Rats
Authors: Abdel-Rahman Abdel A. , Tao Shiying
Published: June 2012

Abstract
We previously reported that adenosine elicited site-dependent neuronal and cardiovascular responses in two subareas of the nucleus tractus solitarius (NTS) of normotensive rats. Pressor and tachycardic responses were obtained from the rostral NTS (adenosine pressor system), and depressor and bradycardic responses were obtained from the caudal NTS (adenosine depressor system). In both areas, adenosine inhibited the firing rate of barosensitive neurons. The present study investigated whether spontaneously hypertensive rats (SHR) exhibit abnormal neuronal and cardiovascular responses mediated by the adenosine pressor and depressor systems within the NTS. Male SHR and Wistar-Kyoto rats (WKY) were anesthetized with urethane and prepared for blood pressure and heart rate recording, stereotaxic microinjection of adenosine into the NTS, and extracellular recording of single-unit neuronal activity of NTS neurons. Chemical identification of the targeted neuronal pool was made by
l
-glutamate (5 nmol) and confirmed by histology. SHR exhibited significantly higher mean arterial pressure and firing rate of caudal NTS neurons (45.0±4.5 versus 27.3±4.7 spikes per 2.5 seconds,
P
<.05) but similar heart rate and neuronal firing rate of rostral NTS neurons compared with WKY. Adenosine (0.1, 1, and 10 nmol) elicited dose-related neuronal and cardiovascular responses in both strains. However, SHR exhibited differential alterations in both adenosine systems. Compared with WKY, SHR exhibited attenuated pressor, tachycardic, and neuronal responses mediated by the adenosine pressor system and exaggerated depressor, bradycardic, and neuronal responses mediated by the adenosine depressor system. In both strains, the responses elicited by adenosine were virtually abolished by theophylline (10 mg/kg IV), suggesting that these responses were mediated by adenosine receptors in the NTS. Furthermore, the theophylline-evoked increase in blood pressure was twofold higher in SHR (15.0±1.7 versus 6.9±1.5 mm Hg,
P
<.05); larger but nonsignificant increases in heart rate and neuronal firing rate also were evident in SHR compared with WKY. These findings suggest differential alterations in adenosine pressor and depressor systems in the NTS of SHR, which may be implicated in the pathophysiology of this model of hypertension.
Cytosolic Calcium Changes Induced by Angiotensin II in Neonatal Rat Atrial and Ventricular Cardiomyocytes Are Mediated via Angiotensin II Subtype 1 Receptors
Authors: Touyz Rhian M. , Sventek Pavol , Larivière Richard , Thibault Gaétan , Fareh Jeannette , Reudelhuber Timothy , Schiffrin Ernesto L.
Published: June 2012

Abstract
We determined the effects of angiotensin II (Ang II) on cytosolic free calcium concentrations ([Ca
2+
]
i
) in the absence and presence of the selective angiotensin subtype 1 (AT
1
) receptor antagonist losartan or the selective AT
2
antagonist PD 123319 in cultured neonatal rat atrial and ventricular cardiomyocytes. We also assessed Ang II receptor density, affinity, and mRNA expression. [Ca
2+
]
i
was measured in single cells microphotometrically and by fluorescent digital imaging with fura 2 methodology. Receptor parameters were assessed by competitive binding studies with
125
I-[Sar
1
,Ile
8
]Ang II in the presence of increasing concentrations of [Sar
1
,Ile
8
]Ang II, losartan, and PD 123319. AT
1
receptor (types AT
1A
and AT
1B
) mRNA abundance was measured by reverse transcription–polymerase chain reaction. Ang II produced concentration-dependent increases in [Ca
2+
]
i
. Basal [Ca
2+
]
i
values in atrial and ventricular cells were similar but Ang II (10
−9
mol/L)–induced [Ca
2+
]
i
changes were significantly greater in atrial compared with ventricular cells. Ang II responses were blocked by losartan (10
−7
mol/L) but not PD 123319 (10
−7
mol/L). Binding studies demonstrated a single class of high-affinity Ang II binding sites on cardiomyocyte membranes (
K
d
=0.71±0.11 μmol/L).
125
I-[Sar
1
,Ile
8
]Ang II was displaced by losartan but not by PD 123319. AT
1
receptor mRNA was detected by reverse transcription–polymerase chain reaction in cells from atria and ventricles. In atrial cardiomyocytes, both AT
1A
and AT
1B
receptor genes were expressed, whereas in ventricular cardiomyocytes, only the AT
1A
receptor gene was expressed. These data demonstrate that neonatal cardiomyocytes possess Ang II receptors of the AT
1
receptor subtype that are linked to [Ca
2+
]
i
signaling pathways. The different Ang II–induced [Ca
2+
]
i
responses between atrial and ventricular cells may be related to differences in the distribution of AT
1
receptor subtype subvariants.
Doxazosin Prevents Proteinuria and Glomerular Loss of Heparan Sulfate in Diabetic Rats
Authors: Jyothirmayi Garikiparthy N. , Alluru Indira , Reddi Alluru S.
Published: June 2012

Abstract
We examined whether blood pressure reduction or good glycemic control equally lower albuminuria by preventing glomerular loss of heparan sulfate and progression of glomerulosclerosis in streptozotocin-induced diabetic rats. We used doxazosin, an α
1
-adrenergic blocker, to lower systemic blood pressure, and good glycemic control was achieved by insulin treatment. Rats were killed after 20 weeks of treatment. Doxazosin significantly lowered systolic pressure in diabetic rats; however, it had no effect in normal rats. Good glycemic control also lowered systolic pressure. In diabetic rats with good glycemic control, doxazosin had an additive effect on blood pressure. Glomerular heparan sulfate synthesis was significantly lower and urinary albumin excretion higher in diabetic than in normal rats. Both doxazosin treatment and good glycemic control normalized these abnormalities in diabetic rats. Insulin normalized plasma glucose and glycosylated HbA
1
concentrations in diabetic rats, as did doxazosin. Significant increases in mesangial area and glomerulosclerosis were observed in diabetic rats. Only good glycemic control normalized these pathological changes in all diabetic rats. Two-way factorial ANOVA showed an interaction between the effects of doxazosin and insulin on systolic pressure and plasma glucose. The data show that after 20 weeks of doxazosin treatment, albuminuria was reduced by 80%; however, this treatment had no significant effect on mesangial expansion or progression to glomerulosclerosis. Conversely, good glycemic control prevented all three of the preceding sequelae.
Angiotensinogen Polymorphism M235T, Hypertension, and Nephropathy in Insulin-Dependent Diabetes
Authors: Doria Alessandro , Onuma Tomio , Gearin Gary , Freire M. Beatriz S. , Warram James H. , Krolewski Andrzej S.
Published: June 2012

Abstract
The allele 235T (a threonine in place of a methionine at position 235) of angiotensinogen has been found to be associated with a predisposition to essential hypertension. We investigated whether this allele also confers increased susceptibility to nephropathy in patients with insulin-dependent diabetes mellitus (IDDM). A group of 380 patients who had had IDDM for 15 to 20 years were genotyped at the angiotensinogen 235 locus. Included were 75 patients with normoalbuminuria (albumin excretion rate <30 μg/min), two series of patients with microalbuminuria (n=30 and n=136), and two series with overt proteinuria (n=41 and n=98). Allele 235T frequency was higher among cases with microalbuminuria (0.41 in the two series combined) or overt proteinuria (0.40) than in the normoalbuminuria group (0.36). However, this difference was not statistically significant with this sample size (χ
2
=1.2,
P
=NS with 2
df
). Under a recessive model, allele 235T homozygotes had a 1.6-fold risk of developing nephropathy relative to carriers of other genotypes, but this value was not significantly different from 1 (95% CI=0.8 to 3.5). The strength of the association did not improve after stratification by degree of glycemic control. With respect to the hypertension in these IDDM patients, no association with allele 235T was found. Allele 235T frequencies in normotensive and hypertensive individuals were 0.363 and 0.353, respectively, among normoalbuminuric IDDM individuals (χ
2
=0.01,
P
=NS) and 0.411 and 0.414 among microalbuminuric IDDM subjects (χ
2
=0.0,
P
=NS). We conclude that the angiotensinogen polymorphism M235T might influence susceptibility to nephropathy in insulin-dependent diabetes, but its effect, if any, is rather small and independent of hypertension.
Endothelin Adrenocortical Secretagogue Effect Is Mediated by the B Receptor in Rats
Authors: Belloni Anna S. , Rossi Gian Paolo , Andreis Paola G. , Neri Giuliano , Albertin Giovanna , Pessina Achille C. , Nussdorfer Gastone G.
Published: June 2012

Abstract
We investigated the gene expression and localization of endothelin-1 (ET-1) receptor subtypes ET
A
and ET
B
in the rat adrenal cortex as well as their involvement in the corticosteroid secretagogue effect of ET-1 in vitro. Reverse transcription–polymerase chain reaction with primers specific for ET
A
and ET
B
cDNAs demonstrated the expression of both receptor genes in homogenates of adrenocortical tissue. However, in isolated zona glomerulosa and zona fasciculata cells, only ET
B
mRNA was detected. Autoradiographic examination of the selective displacement of
125
I–ET-1 binding by BQ-123 and BQ-788 (specific ligands for ET
A
and ET
B
, respectively) indicated that zona glomerulosa possesses both ET
A
and ET
B
, whereas zona fasciculata is exclusively provided with ET
B
. ET-1 enhanced in a concentration-dependent manner aldosterone and corticosterone secretions of dispersed zona glomerulosa and zona fasciculata cells, respectively. The ET
B
antagonist BQ-788 markedly reduced the secretory response of zona glomerulosa cells and completely suppressed that of zona fasciculata cells, whereas the ET
A
antagonist BQ-123 was ineffective. These findings indicate that in the rat, the adrenocortical secretagogue action of ET-1 is mediated by the ET
B
receptor subtype and that the ET
A
receptor is not directly involved in such an effect.
Apparent Mineralocorticoid Excess
Authors: Mune Tomoatsu , White Perrin C.
Published: June 2012

Abstract
The syndrome of apparent mineralocorticoid excess is a form of hypertension inherited in an autosomal recessive manner. This disorder results from mutations in the
HSD11K
(
HSD11B2
) gene, which encodes the kidney isozyme of 11β-hydroxysteroid dehydrogenase. This enzyme converts active glucocorticoids such as cortisol and corticosterone to their inactive metabolites cortisone and 11-dehydrocorticosterone. An elevated ratio of cortisol to cortisone metabolites in the urine (tetrahydrocortisol plus allotetrahydrocortisol to tetrahydrocortisone [(THF+aTHF)/THE]) is considered pathognomic for this disorder. To determine whether the biochemical phenotype of this disorder is correlated with genotype, we expressed enzymes carrying each of the six known missense mutations in cultured cells. Only one mutant, R337C, had detectable activity in cell lysates, but five of six mutants were partially active in whole cells. Apparent kinetic constants for cortisol and corticosterone were determined in whole cells, and the apparent first-order rate constant,
V
max
/
K
m
, was used as a measure of enzymatic activity. The urinary (THF+aTHF)/THE ratio in patients carrying each mutation was strongly correlated with in vitro enzymatic activity of the corresponding mutant (
r
=.839,
P
=.001 with cortisol as the substrate). We conclude that the biochemical phenotype of the syndrome of apparent mineralocorticoid excess is largely determined by genotype.
Renal Extraction of Atrial Natriuretic Peptide in Hypertensive Patients With or Without Renal Artery Stenosis
Authors: Schreij Gerrit , van Es Paul N. , Schiffers Paul M.H. , de Leeuw Peter W.
Published: June 2012

Abstract
The renin-angiotensin-aldosterone system plays a major role in renovascular hypertension, but the relationship between renin release and the renal fractional extraction of atrial natriuretic peptide (ANP) in this condition is not well defined. We measured ANP levels in the renal veins and aortas of 49 untreated hypertensive patients studied under standardized conditions immediately before renal angiography. Twenty-one patients had renal artery stenosis, 13 of which were unilateral and 8 bilateral. Five of the 13 patients with unilateral renal artery stenosis had an elevated renin ratio (≥1.5). Patients with renal artery stenosis were older (
P
<.01) and had higher systolic pressures (
P
<.05) than patients with essential hypertension. Arterial levels of ANP were significantly higher in patients with unilateral or bilateral renal artery stenosis than in patients with essential hypertension (
P
<.05). Patients with hypertension and left ventricular hypertrophy had significantly higher arterial ANP levels than those with no hypertrophy (40 versus 26 pmol/L,
P
<.05), but in patients with renal artery stenosis, arterial ANP levels were similar in those with or without hypertrophy. Renal venous ANP levels were significantly higher in stenotic than in normal kidneys. Moreover, in unilateral renal artery stenosis, stenotic kidneys of patients with an elevated renin ratio (stenotic kidney/contralateral kidney ≥1.5) had a significantly higher renal venous ANP level than stenotic kidneys of patients with a normal renin ratio (30 versus 17 pmol/L,
P
<.05). However, the median fractional extraction of ANP was similar, around 0.50 (range, 0 to 0.83), in normal kidneys of hypertensive patients and in stenotic and contralateral kidneys of patients with renal artery stenosis. A significant inverse correlation between arterial ANP and renal venous active plasma renin concentration was found for normal kidneys (
r
=−.62,
P
<.01) of hypertensive patients without hypertrophy. However, for stenotic kidneys, no such relationship was apparent. A significant correlation between arterial ANP and the arteriovenous difference of ANP (
r
=+.92,
P
<.001) was found. This relationship was similar for normal and stenotic kidneys. In conclusion, an inverse relationship between arterial ANP and renal venous active plasma renin concentration exists in normal kidneys of essential hypertensive patients without left ventricular hypertrophy. Furthermore, data of ANP extraction through normal and stenotic kidneys suggest that saturation of ANP extraction does not occur. Increased levels of ANP in renal artery stenosis are likely caused by enhanced cardiac secretion of this peptide.
Acute and Chronic Neutral Endopeptidase Inhibition in Rats With Aortocaval Shunt
Authors: Willenbrock Roland , Scheuermann Michaela , Höhnel Klaus , Luft Friedrich C. , Dietz Rainer
Published: June 2012

Abstract
In heart failure, sodium and water retention develop despite elevated plasma levels of atrial natriuretic peptide. Atrial natriuretic peptide is degraded in part by a neutral endopeptidase. Whether neutral endopeptidase inhibition improves sodium and water excretion in heart failure is unknown. We determined the effect of neutral endopeptidase inhibition on plasma levels of atrial natriuretic peptide and the renal response to acute volume expansion in rats with aortocaval shunts and in sham-operated controls. Acute endopeptidase inhibition with SQ 28,603 (30 mg/kg) elevated atrial natriuretic peptide plasma levels in both shunted rats (523±54 to 1258±330 pmol/L,
P
<.05) and controls (184±28 to 514±107 pmol/L,
P
<.05). Urinary cGMP excretion, which reflects renal action, increased in parallel. However, the diuretic and natriuretic responses to acute volume expansion were enhanced only in control rats and not in shunted rats. In contrast to the acute effects, chronic neutral endopeptidase inhibition with SCH 34826 (30 mg/kg twice daily) in shunted rats did not change atrial natriuretic peptide plasma levels or cGMP excretion. Nevertheless, the diuretic and natriuretic responses to acute volume load were increased by chronic endopeptidase inhibition in shunted rats (1789±154 to 2674±577 μL/80 min and 99±31 to 352±96 μmol/80 min, respectively;
P
<.05). Chronic endopeptidase inhibition attenuated the cardiac hypertrophic response to aortocaval shunt without changing arterial blood pressure. Our data show that the renal effects of neutral endopeptidase inhibition are not necessarily dependent on changes in atrial natriuretic peptide plasma levels but instead may be mediated by local inhibition of the neutral endopeptidase in the kidney. In addition, chronic endopeptidase inhibition may attenuate heart failure–induced cardiac hypertrophy independent of hemodynamic effects.
Carbenoxolone Damages Endothelium and Enhances Vasoconstrictor Action in Aortic Rings
Authors: Ullian Michael E. , Hazen-Martin Debra J. , Walsh Lyle G. , Davda Rajesh K. , Egan Brent M.
Published: June 2012

Abstract
Carbenoxolone causes hypertension indirectly by inhibition of 11β-hydroxysteroid dehydrogenase and consequent elevation of intracellular glucocorticoid levels and enhancement of vasoconstrictor action. We performed the present study to determine whether carbenoxolone also enhances vascular tone directly by mechanisms independent of glucocorticoids and other systemic influences. Exposure of rat aortic rings to 10 to 100 μmol/L carbenoxolone in aerated Krebs-Henseleit buffer for 24 hours resulted in concentration-dependent increases in angiotensin II (Ang II) (100 nmol/L)–stimulated contractions and significant shifting of the phenylephrine cumulative contraction curve to the left but not increases in KCl (120 mmol/L)–stimulated contractions. Maximal enhancement of Ang II contraction was 39%. In contrast, brief (15-minute) exposure to 100 μmol/L carbenoxolone did not alter Ang II contractions. Mechanical denudation of the endothelium obviated enhancement of Ang II contractions by carbenoxolone, suggesting interaction of carbenoxolone with the endothelium. Endothelium-dependent relaxation of precontracted rings to acetylcholine or ATP was reduced by more than 90% by 24-hour pretreatment with 100 μmol/L carbenoxolone but not with 100 μmol/L deoxycorticosterone acetate (a mineralocorticoid) or 100 μmol/L glycyrrhizic acid (a natural 11β-hydroxysteroid dehydrogenase inhibitor). Vascular smooth muscle relaxation with sodium nitroprusside was not inhibited by carbenoxolone. Incubation of cultured endothelial cells with 100 μmol/L carbenoxolone for 24 hours did not inhibit nitric oxide synthase activity, as measured by conversion of [
3
H]
l
-arginine to [
3
H]
l
-citrulline. Electron micrography demonstrated that endothelial cell ultrastructure but not vascular smooth muscle cell ultrastructure was abnormal after incubation of rings for 24 hours with 100 μmol/L carbenoxolone. These studies suggest that carbenoxolone concentrations higher than 10 μmol/L enhance vasoconstrictor action via selective toxicity to the endothelium and elimination of endothelium-dependent relaxation.
Angiotensin-(1-7) Inhibits Vascular Smooth Muscle Cell Growth
Authors: Freeman Ernest J. , Chisolm Guy M. , Ferrario Carlos M. , Tallant E. Ann
Published: June 2012

Although angiotensin II (Ang II) and the heptapeptide Ang-(1-7) differ by only one amino acid, the two peptides produce different responses in vascular smooth muscle cells. We previously showed that Ang II stimulated phosphoinositide hydrolysis, whereas Ang II and Ang-(1-7) released prostaglandins. We now report that Ang II and Ang-(1-7) differentially modulate rat aortic vascular smooth muscle cell growth. Ang-(1-7) inhibited [
3
H]thymidine incorporation in response to stimulation by fetal bovine serum, platelet-derived growth factor, or Ang II. The reduction in serum-stimulated thymidine incorporation by Ang-(1-7) depended on the concentration of the heptapeptide over the range of 1 nmol/L to 1 μmol/L, with a maximal inhibition of 60% by 1 μmol/L Ang-(1-7). Ang-(1-7) also inhibited the serum-stimulated increase in cell number to a maximum of 77% by 1 μmol/L Ang-(1-7). The attenuation of serum-stimulated thymidine incorporation by Ang-(1-7) was unaffected by antagonists selective for angiotensin type 1 (AT
1
) or type 2 (AT
2
) receptors; however, [Sar
1
,Ile
8
]Ang II and [Sar
1
,Thr
8
]Ang II were effective antagonists, indicating that growth inhibition by Ang-(1-7) was a result of angiotensin receptor activation. In contrast, Ang II stimulated [
3
H]thymidine incorporation in cultured vascular smooth muscle cells over the same concentration range, with a maximal stimulation of 314% at 1 μmol/L Ang II. Ang II also increased the total number of cells (to 145% of control), suggesting that enhanced thymidine incorporation was associated with vascular smooth muscle cell proliferation. The AT
1
antagonist losartan or L-158,809 but not AT
2
antagonists blocked [
3
H]thymidine incorporation by Ang II. These results suggest that Ang-(1-7) and Ang II exhibit opposite effects on the regulation of vascular smooth muscle cell growth. The inhibition of proliferation by Ang-(1-7) appears to be mediated by a novel angiotensin receptor that is not inhibited by AT
1
or AT
2
receptor antagonists.
Association of Carotid Atherosclerosis With Electrocardiographic Myocardial Ischemia and Left Ventricular Hypertrophy
Authors: Okin Peter M. , Roman Mary J. , Devereux Richard B. , Kligfield Paul
Published: June 2012

Patients with carotid atherosclerosis have an increased risk of coronary events and an increased prevalence of echocardiographic left ventricular hypertrophy. However, little is known regarding the association between electrocardiographic abnormalities and carotid atherosclerosis. The relationship of electrocardiographic evidence of myocardial ischemia and left ventricular hypertrophy to the presence of carotid atherosclerosis was prospectively studied in 349 asymptomatic subjects who underwent echocardiography and carotid ultrasonography. Myocardial ischemia on the electrocardiogram was defined by the presence of localized T-wave inversions, and electrocardiographic hypertrophy was defined by the product of Cornell voltage and QRS duration. Carotid atherosclerosis was present in 21% (72/349) of subjects and was associated with older age, higher systolic and pulse pressures, and greater left ventricular mass. Both ischemia and hypertrophy on the electrocardiogram were strongly associated with carotid plaque. Carotid atherosclerosis was more than three times more prevalent in subjects with electrocardiographic ischemia (69% [11/16] versus 18% [61/333],
P
<.0001) or electrocardiographic left ventricular hypertrophy (78% [7/9] versus 19% [65/340],
P
=.0003) than in subjects without these findings. Logistic regression analysis, including standard risk factors, revealed that both ischemia and hypertrophy on the electrocardiogram remained significant independent predictors of the presence of carotid atherosclerosis, along with age and echocardiographic left ventricular mass. These findings suggest that the associations of ischemia and left ventricular hypertrophy with carotid atherosclerosis may contribute to the increased incidence of coronary events in patients with carotid atherosclerosis.
Effects of Angiotensin II Infusion and Inhibition of Nitric Oxide Synthase on the Rat Aorta
Authors: Kato Hiroshi , Hou Jian , Chobanian Aram V. , Brecher Peter
Published: June 2012

In previous studies, we showed that in vivo infusion of angiotensin II (Ang II) to adult rats induced vascular changes in gene expression, and this effect did not depend solely on blood pressure elevation. To determine whether nitric oxide can influence the effects of Ang II on the vessel wall, we administered to rats Ang II separately or in combination with the arginine analogue
N
ω
-nitro-
l
-arginine methyl ester, which inhibits nitric oxide synthase chronically when given in vivo. We measured changes in aortic medial thickness, the association of macrophages with the endothelial surface of the aorta, the presence of proliferating cell nuclear antigen in the intima and adventitia as an index of aortic cell cycle changes, and the expression of immunodetectable fibronectin as an index of changes in the extracellular matrix. After 18 days of nitric oxide inhibition, the major changes were increased medial thickness and a 3.5-fold increase in the number of adherent macrophages. Rats treated with two different doses of Ang II for 3 days had a fivefold and threefold increase in the number of proliferating cells from the intimal and adventitial regions, respectively. Combined treatment resulted in increased medial thickness, intimal and adventitial cell proliferation, and macrophage adherence. An increased and altered pattern of fibronectin distribution was found in all treatment groups. Losartan administration prevented the effects of Ang II but not of nitric oxide inhibition, whereas administration of
l
-arginine prevented both intimal macrophage adherence and increased adventitial proliferation in rats given combined treatment. The data suggest that nitric oxide selectively influences macrophage association with the arterial wall, whereas Ang II and nitric oxide may have opposing effects on arterial cell proliferation.
Elevated Lymphocyte Cytosolic Calcium in a Subgroup of Essential Hypertensive Subjects
Authors: Rivera Alicia , Conlin Paul R. , Williams Gordon H. , Canessa Mitzy L.
Published: June 2012

Abnormalities of intracellular calcium homeostasis and sodium-proton exchange have been implicated in the pathophysiology of essential hypertension. To further define the nature of cytosolic calcium abnormalities and whether they relate to increased sodium-proton exchange in hypertension, we have studied peripheral lymphocytes from normotensive and hypertensive subjects. Lymphocyte cytosolic calcium was significantly increased (
P
<.01) in hypertensive compared with normotensive subjects while consuming a high salt diet. Using maximum likelihood analysis, we found that cytosolic calcium levels in our study population were not normally distributed and observed three modes (
P
<.02). The means of the first mode and the two upper modes were separated (±2 SD) at a cytosolic calcium level of 120 nmol/L. We conducted further analysis in the subgroups with cytosolic calcium levels >120 nmol/L or <120 nmol/L. The majority of the normotensive subjects (86%) and half of the hypertensive subjects (52%) had levels <120 nmol/L. Clinical characteristics of the two subgroups did not differ. Subjects with levels <120 nmol/L had a rise in cytosolic calcium when changed to a low salt diet; those with levels >120 nmol/L did not show a change in cytosolic calcium but their blood pressure fell significantly with salt restriction. Hypertensive subjects also had increased sodium-proton exchange activity compared with normotensive subjects when both groups were studied in a high salt balance. A positive correlation between sodium-proton exchange and cytosolic calcium was observed in subjects with levels <120 nmol/L. There was insufficient power to draw conclusions on this relationship in subjects with levels >120 nmol/L. Thus, many hypertensive subjects have increased cytosolic calcium, but this abnormality is not associated with sodium-proton exchange activity in all individuals. The salt-induced change in cytosolic calcium in subjects with levels <120 nmol/L and its link to sodium-proton exchange suggest regulation by factors involved in salt-volume homeostasis. Individuals with cytosolic calcium >120 nmol/L, most of whom were hypertensive, may have abnormalities in this regulation, contributing to hypertension.
Association Between Persistent Pressure Overload and Ventricular Arrhythmias in Essential Hypertension
Authors: Schillaci Giuseppe , Verdecchia Paolo , Borgioni Claudia , Ciucci Antonella , Zampi Ivano , Battistelli Massimo , Gattobigio Roberto , Sacchi Nicola , Porcellati Carlo
Published: June 2012

Hypertension is a risk factor for sudden cardiac death, and some data indicate that frequent and complex ventricular arrhythmias may be additional risk markers in hypertensive individuals. We investigated the relation between ventricular arrhythmias and the persistence of increased blood pressure levels over 24 hours in subjects with essential hypertension. We studied 126 never-treated subjects with essential hypertension (83 men) who underwent 24-hour electrocardiographic monitoring, 24-hour ambulatory blood pressure monitoring, and echocardiography. Premature ventricular beats were detected in 71% of the subjects. Compared with subjects in Lown class 0-1, subjects with frequent or complex ventricular arrhythmias (Lown class ≥2) were older (54 versus 45 years) and had a longer duration of hypertension (5.4 versus 2.8 years), a greater left ventricular mass (147 versus 127 g·m
−2
), and a blunted nocturnal reduction in ambulatory blood pressure (7%/12% versus 12%/16%). The number of premature ventricular beats over 24 hours was associated with age (
r
=.25), left ventricular mass (
r
=.24), and pulse pressure (
r
=.18) and inversely associated with the percent reduction in blood pressure from day to night (
r
=−.29 for systolic and −.25 for diastolic pressures). In a multiple logistic regression analysis, frequent or complex ventricular arrhythmias (Lown class ≥2) were predicted by an age ≥60 years (odds ratio, 10.4; 95% confidence interval, 2.4-44.8), left ventricular hypertrophy at echocardiography (odds ratio, 4.2; 95% confidence interval, 1.5-11.6), and a <10% reduction in blood pressure from day to night (“nondipping” pattern: odds ratio, 2.9; 95% confidence interval, 1.2-7.0). We conclude that in addition to the strong effect of age and left ventricular hypertrophy at echocardiography, the persistence of high blood pressure levels over the 24 hours (“nondipping” pattern) is an independent predictor of the frequency and complexity of ventricular arrhythmias in never-treated subjects with essential hypertension.
Nitric Oxide and the Regulation of Blood Pressure in the Hypertension-Prone and Hypertension-Resistant Sabra Rat
Authors: Rees Daryl , Ben-Ishay Drori , Moncada Salvador
Published: June 2012

We examined the role of nitric oxide (NO) in the inherited resistance or susceptibility to hypertension in the Sabra hypertension-prone (SBH) and hypertension-resistant (SBN) rat. Basal mean arterial blood pressure was significantly greater in SBH than in SBN rats. Phenylephrine elevated blood pressure to a similar extent in both substrains, whereas the NO synthase inhibitor
N
G
-monomethyl-
l
-arginine (L-NMMA) had a greater pressor effect in SBN rats. The vasoconstrictor potency of phenylephrine was significantly higher in endothelium-intact aortic rings from the SBH rat, whereas the vasoconstrictor potency of L-NMMA was higher in those from the SBN substrain. Acetylcholine-induced endothelium-dependent relaxation was greater in aortic rings from SBN rats. The vasodilator potency of glyceryl trinitrate was significantly higher in aortic rings from SBH rats and was enhanced after endothelium removal. Both the activity of calcium-dependent NO synthase from aortic endothelial cells and the basal concentration of nitrite/nitrate in plasma were significantly greater in SBN than in SBH rats. In normotensive Wistar rats, basal mean arterial blood pressure, the pressor effect of L-NMMA, endothelial NO synthase activity, and plasma nitrite/nitrate concentrations were all between the values in SBH and SBN rats. These results indicate that a decrease in NO generation plays a role in the susceptibility of SBH rats to hypertension. Furthermore, the resistance to hypertension in the SBN strain may be related to increased NO generation.
Roles of Prostaglandins and Nitric Oxide in the Effect of Endothelin-1 on Renal Hemodynamics
Authors: Lin Huabao , Smith Manis J. , Young David B.
Published: June 2012

It is known that endothelin-1 stimulates the release of nitric oxide and prostaglandins in various vascular beds. We designed the present study to analyze the roles of prostaglandins and nitric oxide in the effect of endothelin-1 on the regulation of renal hemodynamics and renin release. We used
N
ω
-nitro-
l
-arginine methyl ester (L-NAME) and meclofenamic acid to inhibit the production of nitric oxide and prostaglandins, respectively. With a nonfiltering kidney model, renal blood flow was reduced 21% in dogs treated with L-NAME and 18% in dogs treated with meclofenamic acid. Inhibition of nitric oxide and prostaglandins, however, produced opposite effects on estimated glomerular hydraulic pressure: L-NAME increased glomerular hydraulic pressure from 63.1±0.9 to 64.6±1.3 mm Hg (
P
<.01), and meclofenamic acid reduced glomerular hydraulic pressure from 63.3±1.4 to 59.8±1.6 mm Hg (
P
<.01). Endothelin-1 infusion produced a dose-dependent reduction in renal blood flow after blockade of nitric oxide and prostaglandins. The responses of glomerular hydraulic pressure were different in the two groups during endothelin-1 infusion. Endothelin-1 progressively reduced glomerular hydraulic pressure in a dose-dependent fashion in the meclofenamic acid group. However, endothelin-1 slightly increased glomerular hydraulic pressure until the infusion rate reached 5.0 ng/kg per minute. At that rate, endothelin-1 reduced glomerular hydraulic pressure from 63.3±1.4 to 47.0±1.4 mm Hg in the meclofenamic acid group (
P
<.01), a more than 25% reduction, whereas at the same dose, endothelin-1 reduced glomerular hydraulic pressure only less than 2% in the L-NAME group. In addition, blockade of nitric oxide and prostaglandins did not alter the inhibitory effect of endothelin-1 on renin release in the nonfiltering kidney. Therefore, the present study demonstrates that the release of nitric oxide and prostaglandins might modulate the effects of endothelin-1 on the renal circulation. The present findings suggest that the differential vasoconstrictive effects of endothelin-1 on preglomerular and postglomerular vessels are associated with its stimulation of nitric oxide and prostaglandin production.
Endothelin Antagonism in End-Organ Damage of Spontaneously Hypertensive Rats
Authors: Karam Habib , Heudes Didier , Bruneval Patrick , Gonzales Marie-Françoise , Löffler Bernd-Michael , Clozel Martine , Clozel Jean-Paul
Published: June 2012

High blood pressure results in cardiac hypertrophy and fibrosis, increased thickness and stiffness of large artery walls, and decreased renal function. The objective of our study was to assess the role of endothelin, angiotensin II, and high blood pressure in the end-organ damage observed in spontaneously hypertensive rats (SHR). For this purpose, SHR were treated for 10 weeks with either a mixed endothelin-A and endothelin-B receptor antagonist, bosentan (100 mg/kg per day), an angiotensin-converting enzyme inhibitor, enalapril (10 mg/kg per day), or a long-acting calcium antagonist, mibefradil (20 mg/kg per day). A group of SHR was left untreated, and a group of normotensive Wistar rats was used as control. At the end of treatment, maximal coronary blood flow was measured in isolated perfused hearts. Cardiac hypertrophy and fibrosis, aortic medial thickness, and extracellular matrix content were evaluated by quantitative morphometry. Proteinuria and urea and creatinine clearances were measured, and renal histopathology was assessed. SHR exhibited cardiac hypertrophy, perivascular fibrosis, and decreased maximal coronary blood flow. Aortic medial thickness was increased, whereas elastin density was decreased. Finally, SHR showed decreased urinary excretion and decreased urea and creatinine clearances. No renal histological lesions were observed. Although bosentan did not affect blood pressure, it normalized renal function and slightly decreased left ventricular hypertrophy and fibrosis. Enalapril and mibefradil were both effective in significantly decreasing blood pressure, left ventricular hypertrophy, and aortic medial thickness and improving coronary blood flow, but in contrast to bosentan, they did not improve creatinine clearance. We conclude that in SHR, high blood pressure plays a major role in end-organ damage and that endothelin may partly mediate renal dysfunction and cardiac remodeling independently of a direct hemodynamic effect.
Intralymphocyte Free Magnesium in a Group of Subjects With Essential Hypertension
Authors: Delva Pietro T. , Pastori Caterina , Degan Maurizio , Montesi Germana D. , Lechi Alessandro
Published: June 2012

Despite the importance of magnesium in essential hypertension, few data are available on the ionized intracellular concentration of this ion. We therefore studied intralymphocyte free intracellular magnesium (Mg
i
) in 32 untreated essential hypertensive subjects and 27 normotensive control subjects by means of a fluorimetric technique based on the use of the new magnesium-sensitive dye furaptra. We also measured intralymphocyte ionized calcium (Ca
i
) with fura 2. No statistically significant differences were found in Mg
i
in hypertensive compared with normotensive subjects (essential hypertensive, 0.291±0.053 mmol/L; normotensive, 0.293±0.043 [mean±SD]). A statistically significant inverse correlation was established between Mg
i
and plasma triglycerides in essential hypertensive subjects (
r
=−.521,
P
=.002). The hypertensive group was arbitrarily divided into two subgroups according to plasma triglyceride levels (>2 [n=10] or <2 mmol/L [n=22]), and Mg
i
proved to be significantly lower in the subgroup with high plasma triglyceride levels compared with either the subgroup with normal triglycerides (
P
=.009; 95% confidence interval, 0.013-0.088) or the normotensive control group as a whole (
P
=.03; 95% confidence interval, 0.003-0.069) (high-triglyceride hypertensive subgroup, Mg
i
=0.256±0.045 mmol/L; normal-triglyceride hypertensive subgroup, Mg
i
=0.307±0.049). No statistically significant differences were found in Ca
i
in hypertensive compared with normotensive subjects (hypertensive, 53±12 nmol/L; normotensive, 54±14). We did not find statistically significant correlations between Ca
i
and plasma triglycerides, nor did we find any differences in Ca
i
between the subgroup of hypertensive subjects with high plasma triglyceride levels and either the subgroup of hypertensive subjects with normal triglycerides or the normotensive control group as a whole. The discrepancies between our results in lymphocytes and data relating to either erythrocytes or platelets emphasize the need for caution before the results are extrapolated from one tissue to the other. The decreased Mg
i
levels in the subgroup of high-triglyceride hypertensive subjects may suggest a role for magnesium in plurimetabolic syndrome.
Influence of Isradipine and Spirapril on Left Ventricular Hypertrophy and Resistance Arteries
Authors: Thürmann Petra A. , Stephens Nicola , Heagerty Anthony M. , Kenedi Peter , Weidinger Gottfried , Rietbrock Norbert
Published: June 2012

Left ventricular hypertrophy is a common clinical feature in hypertensive patients and may be associated with structural changes in vessel morphology. In an open prospective trial, we evaluated 14 patients with previously untreated hypertension (163±2/104±2 mm Hg) and an echocardiographically determined left ventricular mass index of 141.6±5.2 g/m
2
, indicating left ventricular hypertrophy. We obtained a gluteal skin biopsy sample before starting treatment to investigate subcutaneous small-artery (approximately 200 to 400 μm diameter) morphology and function. Patients then received antihypertensive treatment with a combination of spirapril (3 or 6 mg) and isradipine (2.5 or 5 mg). Echocardiographic recordings were made after 6 months and 1 year, and a final biopsy was taken after 1 year. After 1 year, blood pressure was significantly reduced to 142±3/90±1 mm Hg (
P
<.001), and left ventricular mass index decreased significantly to 105.3±5.8 g/m
2
(
P
<.001). Baseline media-lumen ratio (7.64±0.48%) was not markedly reduced (7.21±0.55%), although a decrease occurred in 7 of 12 evaluable patients. Norepinephrine-induced vasoconstriction was markedly reduced after 1 year. In conclusion, a significant regression of left ventricular hypertrophy was obtained after 1 year of treatment with spirapril and isradipine, whereas a similar reduction in medial thickness relative to lumen diameter of subcutaneous small arteries could not be observed in all patients. Reversal of structural changes in resistance vessels may require a longer treatment period in patients with proven left ventricular hypertrophy.