bluuebunny/crossref_metadata_2025 huggingface dataset:
Expression of Guanylyl Cyclase-A/Atrial Natriuretic Peptide Receptor Blocks the Activation of Protein Kinase C in Vascular Smooth Muscle Cells
Authors: Kumar Ravindra , Cartledge Willie A. , Lincoln Thomas M. , Pandey Kailash N.
Published: June 2012

To understand the molecular mechanisms of cellular signaling of atrial natriuretic peptide (ANP), we have studied its effect on the enzymatic activity of endogenous and overexpressed protein kinase C (PKC) in rat thoracic aortic vascular smooth muscle (RTASM) cells. Angiotensin II (ANG II), endothelin-1 (ET-1), and 12-
O
-tetradecanoylphorbol 13-acetate (TPA) stimulated fourfold to fivefold PKC activity in PKC-αcDNA-transfected RTASM cells. However, pretreatment of these cells with ANP significantly inhibited the agonist-stimulated PKC activity in a dose-dependent manner. The inhibitory effect of ANP was more effective if cells were transfected with both PKC-α and guanylyl cyclase-A/atrial natriuretic peptide receptor (Npra) cDNAs. The agonist-stimulated PKC activity was also inhibited if RTASM cells were pretreated with cGMP analog 8-bromo-cGMP; however, the treatment of cells with a cAMP analog, dibutyryl-cAMP, did not show any discernible effect. The pretreatment of cells with Npra antagonist A-71915, significantly blocked the production of cGMP as well as the inhibitory effect of ANP on PKC activity. To further examine whether the antagonistic action of ANP and 8-bromo-cGMP on agonist-stimulated PKC activity were mediated through cGMP-dependent protein kinase (PKG), cells were treated with ANP or 8-bromo-cGMP and activators of PKC in the presence of KT-5823, a specific inhibitor of PKG. The treatment of cells with KT-5823 significantly attenuated the inhibitory effects of both ANP and 8-bromo-cGMP on agonist-stimulated PKC activity. The results from these studies provide strong evidence that ANP antagonizes the activation of PKC in RTASM cells, involving guanylyl cyclase-A receptor Npra and second messenger cGMP. Our data further support the notion that ANP acts as a negative mediator of signaling cross-talks between Npra and PKC in a cGMP-dependent manner, probably involving cGMP-dependent protein kinase in this process.
Effects of Chronic ET
A
-Receptor Blockade in Angiotensin II-Induced Hypertension
Authors: d’Uscio Livius V. , Moreau Pierre , Shaw Sidney , Takase Hiroyuki , Barton Matthias , Lüscher Thomas F.
Published: June 2012

Angiotensin II, a constrictor and mitogen of vascular smooth muscle cells, affects the release of endothelium-derived factors such as nitric oxide or endothelin-1. This study investigated the influence of endothelin-1, using the selective endothelin A receptor antagonist
LU135252
, on blood pressure and endothelial function in angiotensin II-induced hypertension in the rat. Two weeks of angiotensin II administration (200 ng/kg per minute) increased systolic blood pressure (+35±5 mm Hg; tail-cuff method) compared with placebo (
P
<.05).
LU135252
alone did not affect systolic pressure but lowered the angiotensin II-induced pressure increase (
P
<.05). In isolated aortic rings, endothelium-dependent relaxations to acetylcholine were reduced in the angiotensin II group (
P
<.05 versus placebo) and improved by concomitant chronic
LU135252
treatment (
P
<.05 versus angiotensin II). Blood pressure elevation strongly correlated with impaired endothelium-dependent relaxations to acetylcholine (
r
=−.967).
LU135252
did not affect endothelium-independent relaxations to sodium nitroprusside, which were diminished after angiotensin II treatment (
P
<.05). In quiescent rings, chronic angiotensin II administration enhanced endothelium-dependent contractions to acetylcholine, which were reduced by
LU135252
(
P
<.05). Impaired contractions to endothelin-1 and norepinephrine in the angiotensin II group were normalized after treatment with
LU135252
(
P
<.05). Thus, chronic therapy with
LU135252
partially prevents angiotensin II-induced hypertension and the alternations of the endothelial function observed in this experimental model.
Kallikrein-Kinin System and Blood Pressure Sensitivity to Salt
Authors: Madeddu Paolo , Varoni Maria Vittoria , Demontis Maria Piera , Chao Julie , Simson Jo Anne , Glorioso Nicola , Anania Vittorio
Published: June 2012

We evaluated the blood pressure response to chronic salt loading in a rat strain inbred for low urinary kallikrein excretion. Low-kallikrein rats showed greater systolic blood pressure values (130±1 versus 114±2 mm Hg in controls;
P
<.05) at 9 weeks of age. Systolic blood pressure was increased after 10 days of dietary sodium loading in the low-kallikrein group and remained unchanged in controls (153±1 versus 112±2 mm Hg,
P
<.01). In additional experiments, blood pressure sensitivity to salt was tested in low-kallikrein rats receiving a chronic infusion of rat glandular kallikrein (1.7 μg/day per 100 g body weight, IV) or vehicle. Systolic blood pressure of vehicle-treated rats was increased by salt loading (from 138±1 to 158±2, 153±1, and 145±2 mm Hg at 5, 10, and 15 days, respectively;
P
<.01), while it remained unchanged in the kallikrein-treated group (from 136±2 to 146±5, 140±2, and 134±4 mm Hg at 5, 10, and 15 days, respectively;
P
=NS). Urinary kallikrein excretion was increased by kallikrein infusion (from 13.6±1.4 to 17.8±2.1 nanokatals per 24 hours;
P
<.01). Plasma immunoreactive kallikrein levels were higher in the kallikrein-treated group (66.4±4.4 versus 57.7±1.4 ng/mL in vehicle-treated rats;
P
<.05). On normal sodium diet, the ratio of kidney weight to body weight was lower in low-kallikrein rats (329±5 versus 370±8 mg/100 g body weight in controls;
P
<.01). This difference was associated with a decreased number of glomeruli per unit square area and increased width of Bowman’s space. These results indicate that kallikrein replacement prevents the exaggerated blood pressure increase observed in rats with a genetically determined defect in urinary kallikrein excretion. Histological abnormalities are present at different levels in the nephron, and they may be functionally related to the altered cardiovascular and renal phenotype of this strain.
Thrombin Inhibits Atrial Natriuretic Peptide Receptor Activity in Cultured Bovine Endothelial Cells
Authors: Zlock Douglas W. , Cao Li , Wu Jianming , Gardner David G.
Published: June 2012

Thrombin and the atrial natriuretic peptide (ANP) possess a number of functionally antagonistic properties in vascular endothelial cells. Thus, regulatory interactions that modulate the activity of one or the other could have important sequelae with regard to cardiovascular homeostasis. Thrombin treatment effected a dose- and time-dependent reduction in ANP receptor activity (maximal 70% to 80% inhibition) in cultured bovine aortic endothelial cells. This resulted from a decrease in total receptor number as well as a modest reduction in the affinity of the receptor for its ligand. The inhibition was largely confined to the type C receptor population, in that thrombin had no effect on maximal type A receptor–linked cGMP accumulation. The protein kinase C–activating phorbol ester 12-
O
-tetradecanoylphorbol 13-acetate effected a similar reduction in binding activity; however, suppression of protein kinase C activity did not reverse the thrombin effect. Pretreatment of endothelial cells with cycloheximide did not completely prevent the thrombin-dependent inhibition, and thrombin did not effect a reduction in type C receptor mRNA levels, findings that argue for a postsynthetic inhibitory locus. The inhibition of receptor activity was effectively irreversible in that suspension of protein synthesis blocked the recovery of receptor density on the cell surface. Reduction in type C receptor density was accompanied by modest increases in the stability of ANP in the culture medium and enhancement of the cellular cGMP response to the peptide, particularly at low ligand concentrations. These findings demonstrate a potentially important interaction between these two agonist systems in regulating endothelial cell function within the vascular wall.
Vascular Angiotensin-Converting Enzyme Expression Regulates Local Angiotensin II
Authors: Müller Dominik N. , Bohlender Jürgen , Hilgers Karl F. , Dragun Duska , Costerousse Olivier , Ménard Joël , Luft Friedrich C.
Published: June 2012

We tested the hypothesis that changes in angiotensin-converting enzyme (ACE) gene expression can regulate the rate of local vascular angiotensin II (Ang II) production. We perfused isolated rat hindlimbs with an artificial medium and infused renin and Ang I via the perfusate. Ang I and II were measured by radioimmunoassay. We then increased ACE gene expression and ACE levels in the rat aorta by producing two-kidney, one clip (2K1C) hypertension for 4 weeks. Gene expression was measured by RNAse protection assay, and ACE activity in the vessel wall was measured by the Cushman-Cheung assay. Angiotensin I infusion at 1, 10, 100, and 1000 pmol/mL led to 371±14 (±SEM), 3611±202, 44 828±1425, and 431 503±16 439 fmol/mL Ang II released, respectively, from the hindlimbs (
r
=.98,
P
<.001). Thus, the conversion rate did not change across four orders of magnitude, and the system was not saturable under these conditions. In 2K1C hindlimbs, Ang I infusion (0.5 pmol/mL) resulted in increased Ang II generation (157±16 versus 123±23 fmol/mL,
P
=.014 at minute 10) compared with controls. ACE gene expression and ACE activity were increased in 2K1C hindlimbs compared with controls (36±4 versus 17±1 mU/mg protein,
P
<.001). Ang II degradation in the two groups did not differ. To investigate the conversion of locally generated Ang I, we infused porcine renin (0.5 milliunits per mL) into 2K1C and control hindlimbs. Despite markedly higher Ang I release in sham-operated than in 2K1C rats (71±8 versus 37±6 pmol/mL,
P
=.008 at minute 12), Ang II was only moderately increased (36±3 versus 25±6 pmol/mL,
P
=.12 at minute 12). This difference between 2K1C rats and controls reflected a higher rate of conversion in 2K1C rats. Thus, Ang I conversion in the rat hindlimb is linear over a wide range of substrate concentrations and occurs at a fixed relationship. Nevertheless, increased ACE gene expression and ACE activity in the vessel wall lead to an increase in the conversion of Ang I to Ang II. We conclude that local ACE gene expression and ACE activity can influence the local rate of Ang II production.
Cyclosporin A Increases Nitric Oxide Activity In Vivo
Authors: Stroes Erik S.G. , Lüscher Thomas F. , de Groot Flip G. , Koomans Hein A. , Rabelink Ton J.
Published: June 2012

The use of cyclosporine is complicated by its vasoconstrictive actions. In vitro cyclosporine has been associated with both decreased endothelium-dependent vasodilatation and increased nitric oxide activity. We studied the interaction between cyclosporine and endothelium-derived nitric oxide in seven healthy volunteers. Using venous-occlusion plethysmography, we measured forearm blood flow during intra-arterial infusion of serotonin, which in the concentrations used is a selective agonist of endothelial nitric oxide release, or
N
G
-monomethyl-
l
-arginine, a specific inhibitor of nitric oxide synthase, during coinfusion of saline or cyclosporine (75 μg/min), respectively. During coinfusion of cyclosporine, forearm blood flow increased on maximal serotonin infusion from 2.9 (SE, 0.2) to 8.1 (0.9) mL/100 mL per minute in forearm tissue, which was significantly higher than the increase during saline coinfusion (3.0 [0.3] to 6.0 [0.5];
P
<.05). Cyclosporine infusion during a “free” nitric oxide system had no effect on basal forearm blood flow, but it significantly decreased forearm blood flow (21.7 [2.8]%;
P
<.05) during fixed nitric oxide activity. These data suggest that acute administration of cyclosporine enhances both basal and receptor-stimulated nitric oxide activity. The mechanism is not clear but may include cyclosporine-induced shear stress as well as direct effects of cyclosporine. The latter was supported by our observation that gene expression of the enzyme nitric oxide synthase III was enhanced by approximately 50% after coincubation with cyclosporine. In conclusion, the present observation demonstrates that nitric oxide constitutes an important regulating mechanism that protects against cyclosporine-associated vasoconstriction in vivo.
N
-Acetylcysteine Does Not Influence the Activity of Endothelium-Derived Relaxing Factor In Vivo
Authors: Creager Mark A. , Roddy Mary-Anne , Boles Kimberly , Stamler Jonathan S.
Published: June 2012

Nitric oxide forms complexes with an array of biomolecular carriers that retain biological activity. This reactivity of nitric oxide in physiological systems has led to some dispute as to whether endothelium-derived relaxing factor is nitric oxide or a closely related adduct thereof, such as a nitrosothiol. In vitro bioassays used to address this question are limited by the exclusion of biological thiols that are requisite for nitrosothiol formation. Thus, the purpose of this study was to obtain insight into the identity of endothelium-derived relaxing factor in vivo. We reasoned that if endothelium-derived relaxing factor is nitric oxide, infusion of physiological concentrations of thiol would potentiate its bioactivity by analogy with effects seen in vitro, whereas nitrosothiol would be resistant to such modulation. We used venous-occlusion plethysmography to study forearm blood flow in normal subjects. Methacholine (0.3 to 10 μg/min) and nitroglycerin (1 to 30 μg/min) were infused via the brachial artery to elicit endothelium-dependent and endothelium-independent vasodilation, respectively. Dose-response determinations were made for each drug before and after an intra-arterial infusion of the reduced thiol,
N
-acetylcysteine, at rates estimated to achieve a physiological concentration of 1 mmol/L. Methacholine increased forearm blood flow in a dose-dependent manner. Infusion of
N
-acetylcysteine did not change the sensitivity (ED
50
, 1.7 versus 1.7 μg/min,
P
=NS) or maximal response to methacholine. In contrast, thiol increased the sensitivity to nitroglycerin (ED
50
, 4.7 versus 2.8 μg/min,
P
<.01). Thus, conflicting with reports in vitro, thiol does not modulate endothelium-derived relaxing factor responses in vivo. These data indicate that sulfhydryl groups are not a limiting factor for endothelium-derived relaxing factor responses in forearm resistance vessels in normal humans and are in keeping with reports that nitrosothiol contributes to endothelium-derived relaxing factor bioactivity in plasma and vascular smooth muscle. Potentiation of the effects of nitroglycerin by
N
-acetylcysteine can be attributed to its enhanced biotransformation to an endothelium-derived relaxing factor equivalent, such as nitrosothiol. These observations support the notion of an equilibrium between nitric oxide and nitrosothiol in biological systems that may be influenced by redox state.
Role of the Lipoxygenase Pathway in Angiotensin II–Induced Vasoconstriction in the Human Placenta
Authors: Kisch Eldad S. , Jaffe Anat , Knoll Esther , Stern Naftali
Published: June 2012

We have previously shown that the vasopressor effect of angiotensin II (Ang II) is inhibited by lipoxygenase (LO) blockers. To elucidate the specific mechanism involved, we studied the relationship between the contractile effect of Ang II and LO products in a human placental preparation. In perfused placental cotyledons, Ang II (boluses of 1 to 10 μg) increased perfusion pressure and 12-hydroxyeicosatetraenoic acid (12-HETE) release. The LO blockers phenidone and
n
-propyl gallate reduced the maximal Ang II–induced increment in pressure from 26±3 to 16±3 and 18±4 mm Hg, respectively (
P
<.05 for both). Ang II alone (10 μg) increased 12-HETE release from 8.9±3.6 to 37.6±0.4 ng/min, and this rise was entirely blocked by both phenidone and
n
-propyl gallate. Pressure increase generated by an increase in flow rate had no effect on 12-HETE formation. In deendothelialized umbilical artery segments, Ang II (10
–7
mol/L) increased 12-HETE formation by 47±5% (n=20). In cultured umbilical artery smooth muscle cells, Ang II increased 12-HETE formation from 48.1±7.2 to 75.1+15.3 ng/mg protein, and this effect was also blocked by the specific LO inhibitor baicalein (10
−6
mol/L). These results provide evidence that the vasopressor effect of Ang II is functionally coupled to 12-LO activation, which apparently takes place in arterial smooth muscle cells.
Differential Central Modulation of the Baroreflex by Salt Loading in Normotensive and Spontaneously Hypertensive Rats
Authors: Ono Ayumu , Kuwaki Tomoyuki , Kumada Mamoru , Fujita Toshiro
Published: June 2012

In salt-sensitive hypertensive animal models and human subjects compared with their salt-resistant counterparts, sympathetic activity is abnormally enhanced during a high salt diet. We examined whether salt loading differentially modulates the arterial baroreceptor reflex (ABR), a major control mechanism of arterial pressure and sympathetic vasomotor activity, in young normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). Six-week-old WKY and SHR were fed a normal (0.66%) or high (8.00%) salt diet for 4 weeks. After the diet regimen, baseline levels of mean arterial pressure (MAP), renal sympathetic nerve activity (RSNA), and the overall and central properties of the ABR were compared among the four groups of rats under halothane anesthesia. In WKY, a high salt diet did not affect baseline arterial pressure and RSNA but potentiated the ABR, as evidenced by an increase in the maximal slope of MAP-RSNA and MAP–heart rate relationships. In SHR, by contrast, salt loading accelerated hypertension and sympathetic overactivity and impaired the ABR. Salt-induced modulation of the ABR was associated with that of the central property, since reflex inhibition of RSNA by stimulation of the aortic depressor nerve was augmented in WKY and attenuated in SHR. These results suggest that differential modulation of the central mechanism subserving the baroreflex control of sympathetic activity at least partly accounts for the difference in salt sensitivity between WKY and SHR.
4Intracellular Free Calcium Abnormalities in Fibroblasts From Non–Insulin-Dependent Diabetic Patients With and Without Arterial Hypertension
Authors: Duner Elena , Di Virgilio Francesco , Trevisan Roberto , Cipollina Maria Rita , Crepaldi Gaetano , Nosadini Romano
Published: June 2012

Abstract
As arterial hypertension is frequently associated with diabetes, it is possible that altered intracellular free calcium ([Ca
2+
]
i
) handling, as reported in non–insulin-dependent diabetic patients, is accounted for by abnormalities caused by hypertension rather than diabetes. Our aim was to investigate [Ca
2+
]
i
transients triggered by two extracellular agonists, bradykinin and angiotensin II, with or without chronic insulin exposure, in cultured skin fibroblasts from 10 normotensive and 10 hypertensive non–insulin-dependent patients, matched for age, body mass index, and metabolic control, with fibroblasts from 10 healthy control subjects. Long-term cultured fibroblasts were loaded with fura 2-AM for measurement of [Ca
2+
]
i
. Resting [Ca
2+
]
i
levels were similar in the three groups of subjects. [Ca
2+
]
i
spikes stimulated by angiotensin II (0.1 μmol/L) and bradykinin (1 μmol/L) were significantly greater in hypertensive non–insulin-dependent diabetic patients (216±43 and 374±39 nmol/L, respectively) than in normotensive patients (174±16 and 267±55 nmol/L) and control subjects (188±29 and 320±78 nmol/L). Also, ionomycin evoked a greater [Ca
2+
]
i
response in hypertensive than normotensive non–insulin-dependent diabetic patients and in control subjects. Chronic insulin exposure increased by 70% to 90% the [Ca
2+
]
i
response to both angiotensin II and bradykinin in control subjects and normotensive non–insulin-dependent diabetic patients but not in hypertensive patients. The presence of abnormalities in [Ca
2+
]
i
transients in fibroblasts from only hypertensive non–insulin-dependent diabetic patients supports the possibility that these defects are a feature of concomitant arterial hypertension rather than of diabetes or its disturbed metabolic milieu.
Age, Gender, and Non-modulation
Authors: Fisher Naomi D. L. , Ferri Claudio , Bellini Cesare , Santucci Anna , Gleason Ray , Williams Gordon H. , Hollenberg Norman K. , Seely Ellen W.
Published: June 2012

Abstract
The angiotensinogen gene is one of the very few related by linkage analysis to human hypertension, but the linkage has been consistently shown only among males. Moreover, polymorphisms in this gene predict an abnormal renal responsiveness to angiotensin II, a feature of non-modulation, but again, only among males. To pursue these related bridges between genetics and physiology, we evaluated the effects of sex on a second feature of non-modulation, the aldosterone response to infused angiotensin II during low sodium balance. We tested the resultant hypothesis—that non-modulation would be less frequent in women—by conducting identical protocols on 225 hypertensive inpatients (70 women, 155 men). Non-modulation was strikingly less frequent among women (26%; 95% confidence interval, 16% to 37%) than men (49%; 95% confidence interval, 40% to 57%) (
P
=.001). We tested the hypothesis that sex steroids play a role by comparing young, premenopausal women (<35 years) with women who were perimenopausal (45 to 55 years) and postmenopausal (>55 years). Among the youngest women, the frequency of non-modulation was only 7%, significantly less than in young men (41%,
P
=.02). A steady increase in non-modulation frequency accompanied advancing age in women, reaching 47% in those older than 55 years, equal to the fraction of men affected. Age influenced non-modulation frequency in men far less. We conclude that a striking sex difference underlies the non-modulation phenotype and that female sex hormones may confer protection against a genotypic predisposition in women. This “override” of genotype, manifest by a very low frequency of non-modulation in young women, may participate in their known protection against cardiovascular disease.
Tumor Recurrence and Hypertension Persistence After Successful Pheochromocytoma Operation
Authors: Plouin Pierre-François , Chatellier Gilles , Fofol Isabelle , Corvol Pierre
Published: June 2012

Abstract
Pheochromocytoma is a catecholamine-secreting tumor and a rare cause of hypertension that is usually curable. However, pheochromocytoma may recur as a benign or malignant tumor, and hypertension may persist after successful surgical intervention. The frequency of and risk indicators for tumor recurrence and hypertension persistence after successful surgical intervention have not been adequately studied. We determined tumoral and blood pressure outcome in 129 patients followed-up from initial pheochromocytoma resection to death or to 1994 (796 patient-years). We assessed several candidate indicators for their predictive value for the risk of tumor recurrence or hypertension persistence. Recurrence was defined as the reappearance of disease after normalization of biochemical tests. Pheochromocytoma caused death or persistent or recurrent disease in 28 patients. Of the 114 with benign tumors at initial operation, pheochromocytoma recurred as a benign or malignant tumor 17 to 194 months after initial operation in 16 cases. Kaplan-Meier estimates of pheochromocytoma-free survival were 92% and 80% at 5 and 10 years, respectively. In the 98 living patients without recurrence, Kaplan-Meier estimates of hypertension-free survival were 74% and 45% at 5 and 10 years. In the Cox model, familial pheochromocytoma and a low ratio of plasma epinephrine to total catecholamines were independently associated with recurrence. Familial hypertension and age were similarly associated with hypertension persistence. After surgery for pheochromocytoma, patients should be followed-up indefinitely, especially those with familial tumors or a low epinephrine secretion. Pheochromocytoma should not unreservedly be considered a surgically remediable cause of hypertension.
Differential Alteration in Vascular Structure of Resistance Arteries Isolated From the Cerebral and Mesenteric Vascular Beds of Transgenic [(m
Ren-2
)27], Hypertensive Rats
Authors: Dunn William R. , Gardiner Sheila M.
Published: June 2012

Abstract
In this study we examined the structural properties of cerebral and mesenteric resistance arteries isolated from normotensive, Sprague-Dawley (SD) rats (mean arterial pressure [MAP], 110±3 mm Hg) and hypertensive, transgenic (TG) rats (MAP, 167±4 mm Hg), which express the mouse
Ren-2
renin gene. Vessels were set up in a pressure myograph, and ID and vascular wall thickness were determined at increasing intraluminal pressures. Arteries were subsequently pressurized to the MAP of the animal from which they were isolated and were fixed with glutaraldehyde before being embedded in araldite, sectioned, and examined histologically. The middle cerebral artery (MCA) isolated from SD rats and TG rats had similar media cross-sectional areas. There was no difference in MCA diameter at 10 mm Hg in vessels from TG rats compared with SD rats. However, at higher distending pressures, the diameter of the MCA from TG rats was significantly smaller than that of vessels from SD rats. This reduced ID at the higher pressures was a consequence of a decreased distensibility of the MCA from TG rats (as shown by a leftward shift of the stress-strain relationship in arteries from TG rats) and was not caused by an increase in wall thickness. First- and second-order mesenteric resistance arteries isolated from TG rats displayed an increased wall thickness and media content compared with vessels from SD rats. However, this alteration in mesenteric artery structure did not impinge on the ID of arteries from TG rats; there was no difference in the IDs of mesenteric resistance arteries between the two strains at any distending pressure. These observations show that there are distinct regional alterations in vascular structure in hypertensive TG rats expressing the mouse
Ren-2
renin gene. Mesenteric resistance arteries isolated from TG rats display signs of vascular growth, although this structural alteration does not produce a reduction in the ID of these arteries per se. In contrast, cerebral arteries from TG rats do not show increased growth but have a reduced vascular distensibility, which results in a smaller ID compared with vessels from SD rats.
Metformin Inhibits Ganglionic Neurotransmission in Renal Nerves
Authors: Petersen Jørgen S. , Liu Wen , Kapusta Daniel R. , Varner Kurt J.
Published: June 2012

Abstract
Intravenous administration of the antihyperglycemic agent metformin decreases arterial pressure and sympathetic nerve activity (SNA). To test the hypothesis that metformin inhibits SNA by interrupting ganglionic neurotransmission, we compared the actions of intravenous administration of metformin and the ganglionic blocker trimethaphan on postganglionic renal and preganglionic adrenal sympathetic nerves in pentobarbital-anesthetized male Sprague-Dawley rats. Intravenous metformin elicited dose-dependent decreases in postganglionic renal SNA (1 mg/kg: 0±0%; 10 mg/kg: −20±4%; 100 mg/kg: −92±3%; n=7). Conversely, only the maximal dose of metformin affected preganglionic adrenal SNA (100 mg/kg: Δadrenal SNA=−14±6%; n=8). Ganglionic blockade with intravenous trimethaphan (5 mg/kg) produced a differential sympathoinhibitory response similar to the response observed after high-dose metformin (Δrenal SNA=−100±3%; Δadrenal SNA=−17±7%;
P
<.001). Preganglionic renal neurons were electrically stimulated in the spinal cord, before and during the peak of the sympathoinhibitory response to intravenous metformin, and the magnitude of the stimulus-evoked increases in postganglionic renal SNA were compared. Metformin dose-dependently attenuated the magnitude of the increase in postganglionic renal SNA elicited by stimulation of the spinal cord (30 mg/kg: −23±8%; 90 mg/kg: −65±11%; 270 mg/kg: −91±8%; n=6 per dose). We conclude that high-dose intravenous metformin interrupts ganglionic neurotransmission in renal nerves.
Nifedipine Attenuates Systemic and Renal Vasoconstriction During Nitric Oxide Inhibition in Humans
Authors: Dijkhorst-Oei Lioe-Ting , Rabelink Ton J. , Boer Peter , Koomans Hein A.
Published: June 2012

Abstract
Clinical states associated with nitric oxide deficiency are often accompanied by vasoconstriction. We studied the effects of prolonged infusion of the nitric oxide synthase inhibitor
N
G
-monomethyl-
l
-arginine (L-NMMA) on systemic and renal hemodynamics in humans and the reversibility of the established vasoconstriction by calcium channel blockade with nifedipine. Seven healthy men underwent three 7-hour clearance studies. During one study, L-NMMA (3 mg/kg priming dose plus 3 mg·kg
−1
·h
−1
) was infused during hours 2 through 5, and during another study, nifedipine (0.015 mg/kg priming dose plus 0.015 mg·kg
−1
·h
−1
) was coinfused during hours 4 and 5. A third study served as time control. L-NMMA elicited reproducible systemic and renal vasoconstriction that was stable during the 4 hours of infusion. Systemic vascular resistance index, calculated from bioimpedance-derived cardiac index, increased from 22±1 to 29±2 mm Hg·min·m
2
·L
−1
(
P
<.05). Mean arterial pressure rose by 4±1 mm Hg (
P
<.05), and heart rate, stroke index, and cardiac index decreased. Renal blood flow, calculated from renal plasma flow, decreased from 1182±101 to 785±53 mL/min, and renal vascular resistance increased from 73±5 to 115±6 mm Hg·min·L
−1
(
P
<.05). Glomerular filtration rate decreased from 114±6 to 104±6 mL/min (
P
<.05), and filtration fraction increased. Sodium excretion fell from 89±9 to 32±7 μmol/min (
P
<.05). Nifedipine completely reversed systemic vasoconstriction. Nifedipine caused partial restoration of renal vascular resistance and complete normalization of glomerular filtration rate and sodium excretion but left the elevated filtration fraction unaltered. We conclude that sustained nitric oxide deficiency in humans is accompanied by strong systemic and renal vasoconstriction, decreased glomerular filtration rate, and sodium retention. Nifedipine can reverse most of these effects, suggesting a role for calcium channel blockade in pathological states of impaired nitric oxide activity.
Safety and Feasibility of Dobutamine-Atropine Stress Testing in Hypertensive Patients
Authors: Elhendy Abdou , van Domburg Ron T. , Roelandt Jos R. T. C. , Geleijnse Marcel L. , Ibrahim M. Mohsen , Fioretti Paolo M.
Published: June 2012

Abstract
Dobutamine stress testing is increasingly used for the diagnosis and functional evaluation of coronary artery disease. The aim of this study was to assess the hemodynamic profile, safety, and feasibility of dobutamine stress testing in hypertensive patients. Dobutamine (up to 40 μg/kg per min-ute)–atropine (up to 1 mg) stress echocardiography was performed for the detection of myocardial ischemia in 1164 patients with limited exercise capacity (age, 60±12 years; 761 men); 446 patients were known to have hypertension. The test was considered feasible when 85% of the maximal heart rate and/or an ischemic end point (new or worsened wall motion abnormalities, ST segment depression, or angina) was achieved. No myocardial infarction or death occurred during the test. Dobutamine induced a significant increase of heart rate in patients with and without hypertension (59±25 and 63±23 beats per minute, respectively). Peak rate pressure product was similar in patients with and without hypertension (18 566±4584 and 18 230±4508). Hypotension (systolic pressure drop >40 mm Hg) during the test was more frequent in hypertensive patients (7% versus 4% in normotensive,
P
<.05). Independent predictors of hypotension were baseline systolic pressure greater than 140 mm Hg (odds ratio, 6.9; 95% confidence interval, 3.4 to 14), older age (odds ratio, 1.04; 95% confidence interval, 1.01 to 1.07), and medication with calcium channel blockers (odds ratio, 1.8; 95% confidence interval, 1.1 to 3.5). The prevalence of ventricular tachycardia was similar (4.1%) in both groups. Episodes of 10 beats or more (0.06% of patients) were terminated promptly by intravenous metoprolol administration. Dobutamine stress testing was considered feasible in 91% of patients with and 92% of patients without hypertension. Dobutamine-atropine stress echocardiography is a safe and feasible method for the assessment of hypertensive patients referred for evaluation of myocardial ischemia. Despite the higher prevalence of dobutamine-induced hypotension in these patients, the feasibility of the test is comparable to that in individuals without hypertension.
Adrenomedullary Secretion of Epinephrine Is Increased in Mild Essential Hypertension
Authors: Jacobs Marie-Cécile , Lenders Jacques W. M. , Willemsen Jacques J. , Thien Theo
Published: June 2012

Abstract
To assess whether patients with mild essential hypertension have excessive activities of the sympathoneuronal and adrenomedullary systems, we examined total body and forearm spillovers and norepinephrine and epinephrine clearances in 47 subjects with mild essential hypertension (25 men, 22 women, aged 38.1±6.7 years) and 43 normotensive subjects (19 men, 24 women, aged 36.5±5.9 years). The isotope dilution method with infusions of tritiated norepinephrine and epinephrine was used at rest and during sympathetic stimulation by lower body negative pressure at −15 and −40 mm Hg. Hypertensive subjects had a higher arterial plasma epinephrine concentration (0.20±0.01 nmol • L
−1
; mean±SE) than normotensive subjects (0.15±0.01) (
P
<.01). The increased arterial plasma epinephrine levels appeared to be due to a higher total body epinephrine spillover rate in the hypertensive subjects (0.23±0.02 nmol • min
−1
• m
−2
) than the normotensive subjects (0.18±0.01) (
P
<.05) and not to a decreased plasma clearance of epinephrine. The arterial plasma norepinephrine level, total body and forearm norepinephrine spillover rates, and plasma norepinephrine clearance were not altered in the hypertensive subjects. The responses of the catecholamine kinetic variables to lower body negative pressure were not consistently different between normotensive and hypertensive individuals. These data indicate that individuals with mild essential hypertension (1) have elevated arterial plasma epinephrine concentrations that are due to an increased total body epinephrine spillover rate, indicating an increased adrenomedullary secretion of epinephrine; (2) have no increased generalized sympathoneuronal activity and no increased forearm norepinephrine spillover; and (3) have similar responses of both the sympathoneuronal and adrenomedullary systems to sympathetic stimulation by lower body negative pressure.
Adrenomedullin Is a Potent Inhibitor of Angiotensin II–Induced Migration of Human Coronary Artery Smooth Muscle Cells
Authors: Kohno Masakazu , Yokokawa Koji , Kano Hiroaki , Yasunari Kenichi , Minami Mieko , Hanehira Takao , Yoshikawa Junichi
Published: June 2012

Abstract
The migration of coronary artery medial smooth muscle cells (SMCs) into the intima is proposed to be an important process of intimal thickening in coronary atherosclerotic lesions. In the current study, we examined the possible interaction of adrenomedullin, a novel vasorelaxant peptide, and angiotensin II (Ang II) on human coronary artery SMC migration using Boyden’s chamber method. Ang II stimulated SMC migration in a concentration-dependent manner between 10
−6
and 10
−8
mol/L. This stimulation was clearly blocked by the Ang II type 1 receptor antagonist losartan but not by the type 2 receptor antagonist PD 123319. The migration stimulatory effect of Ang II was chemotactic in nature for cultured human coronary artery SMCs but was not chemokinetic. Human adrenomedullin clearly inhibited Ang II–induced migration in a concentration-dependent manner. Human adrenomedullin stimulated cAMP formation in these cells. Inhibition by adrenomedullin of Ang II–induced SMC migration was paralleled by an increase in the cellular level of cAMP. 8-Bromo-cAMP, a cAMP analogue, and forskolin, an activator of adenylate cyclase, inhibited the Ang II–induced SMC migration. These results suggest that Ang II stimulates SMC migration via type 1 receptors in human coronary artery and adrenomedullin inhibits Ang II–induced migration at least partly through a cAMP-dependent mechanism. Taken together with the finding that adrenomedullin is synthesized in and secreted from vascular endothelial cells, this peptide may play a role as a local antimigration factor in certain pathological conditions.
Alterations in Calcium Stores in Aortic Myocytes From Spontaneously Hypertensive Rats
Authors: Côrtes Steyner de F. , Lemos Virgínia Soares , Stoclet Jean-Claude
Published: June 2012

Abstract
The aim of the present work was to further characterize intracellular calcium stores released by angiotensin II (Ang II) in spontaneously hypertensive rat (SHR) and Wistar-Kyoto rat (WKY) vascular smooth muscle cells (VSMCs) and to study their alterations associated with proliferation. Intracellular Ca
2+
concentration was monitored by image analysis in aortic myocytes loaded with fura 2. In the presence of extracellular Ca
2+
, sensitivity to Ang II in proliferating VSMCs was not different in the two strains, but it increased 10-fold in confluent VSMCs from SHR compared with those from WKY. In Ca
2+
-free medium, Ca
2+
release induced by thapsigargin (10 μmol/L) was significantly greater (about twofold) in SHR than WKY, in both proliferating and confluent cultures, with responses during proliferation being 0.7-fold smaller. Responses to Ang II were abolished after exposure of the cells to thapsigargin. In proliferating cultures, ryanodine (10 μmol/L) did not modify the rises in intracellular Ca
2+
concentration induced by Ang II in VSMCs from both strains. Conversely, in confluent cultures, ryanodine reduced Ang II (100 nmol/L)–induced Ca
2+
release to the same level as in proliferating cultures, and it suppressed the difference between SHR and WKY. These results show that the ryanodine-sensitive Ca
2+
release induced by Ang II is enhanced in VSMCs from SHR at confluence and is impaired dur-ing proliferation. Thus, they suggest that differences in Ca
2+
-induced Ca
2+
release from the sarcoplasmic reticulum may participate in increased responsiveness of VSMCs to Ang II in SHR and in phenotypic modulation of vascular myocytes during proliferation.
Influence of hospitalization and placebo therapy on blood pressure and sympathetic function in essential hypertension.
Authors: Hossmann V , FitzGerald G A , Dollery C T
Published: June 2012

The decline in blood pressure (BP) in essential hypertensives following hospitalization may result from: 1) regression toward the mean; 2) reduction of anxiety as patients habituate to a new environment; 3) the placebo effect of medication; and 4) an independent effect of hospitalization itself. A randomized crossover study of 12 essential hypertensives demonstrated a fall in supine blood pressure from 165.0/97.9 +/- 2.3/1.1 mm Hg to 154.3/89.6 +/- 2.7/1.1 mm Hg (p less than 0.005) due to hospitalization. A similar reduction in BP from 164.9/99.5 +/- 8.4/4.1 mm Hg to 151.9/93.4 +/- 4.5/1.9 mm Hg (p less than 0.005) resulted from regression toward the mean and habituation during the study period. Urinary catecholamines fell from 68.7 +/- 5.0 to 55.1 +/- 4.3 micrograms/g creatinine/24 hours (p less than 0.05) due to hospitalization and from 56.1 +/- 5.4 to 49.7 +/- 4.3 micrograms/g creatinine/24 hours (p less than 0.05) with time. Although placebo therapy tended to reduce BP, it failed to do so significantly. When expressed as a percentage of the individual's overall mean, urinary catecholamine excretion fell from 110.5% +/- 3.7% to 89.5% +/- 3.7% (p less than 0.001) during hospitalization and from 105.8% +/- 3.9% to 94.2% +/- 3.9% (p less than 0.05) during the outpatient period. Blood pressure and sympathetic activity rapidly returned to prehospitalization values on discharge. These factors may confound the analysis of drug effects on BP and sympathetic activity in essential hypertensives following admission to hospital.
Dynamic responses of active and inactive renin in patients with essential and renovascular hypertension.
Authors: Aoi W , Doi Y , Seto S , Suzuki S , Hashiba K
Published: June 2012

We studied the dynamic responses of inactive renin and the form of renin released by the kidney in the hypertensive patients. Significant increase of active renin concentration (p less than 0.01) and decrease of the percentage of inactive renin concentration (p less than 0.01) after sodium depletion was observed in 15 essential hypertensive subjects with normal plasma renin activity. In eight of 15 patients, significant increase of inactive renin concentration (p less than 0.01) was observed after sodium depletion. In the remaining seven patients, no significant change of inactive renin concentration was demonstrated. A small increase of active and inactive renin concentration was observed following sodium depletion in six essential hypertensive subjects with low plasma renin activity (PRA). In the unilateral renal hypertension after upright tilting, active renin concentration in the renal vein of the affected kidney was significantly (p less than 0.02) higher than that in the renal vein of the non-affected kidney and the inferior vena cava. Inactive renin concentration in the renal vein of the affected kidney was significantly (p less than 0.02) lower than that in the renal vein of the nonaffected kidney and the inferior vena cava. In four of five cases, the inactive renin concentration in the femoral artery was less than that in the inferior vena cava. Therefore, we might conclude that only active renin was released from the affected kidney, and active renin became inactive by unknown mechanisms; the ischemic kidney might also activate inactive renin.
A possible antihypertensive mechanism of propranolol: antagonism of angiotensin II enhancement of sympathetic nerve transmission through prostaglandins.
Authors: Jackson E K , Campbell W B
Published: June 2012

The effects of propranolol on angiotensin II (AII) enhancement of sympathetic nerve transmission were investigated in the in situ blood-perfused mesenteric vascular bed of the rat. Angiotensin II in subpressor concentrations (3 ng/ml) potentiated the vasoconstrictor responses to both sympathetic nerve stimulation (NS) and exogenous norepinephrine (NE). The dl-propranolol had no effect on the basal vasoconstrictor responses to NS and NE, yet inhibited the AII-enhanced vasoconstrictor responses to NS by 47% (p less than 0.05) and 81% (p less than 0.001) at 100 and 300 ng/ml respectively. In contrast, the potentiation of NE responses by AII was unaffected by propranolol. A similar blockade of AII enhancement of NS was observed with the d-isomer of propranolol. Dibucaine (300 ng/ml), a local anesthetic, failed to alter the basal or AII-enhanced responses to either NS or NE. Indomethacin, a prostaglandin synthetase inhibitor (5 mg/kg, s.c.), abolished the inhibitory effect of dl-propranolol on AII enhancement of NS. Prostaglandin E2 (PGE2), but not prostaglandin I2, (3 ng/ml) inhibited AII enhancement of NS without altering the basal response to NS or NE in indomethacin-pretreated animals. Intraarterial infusions of dl-propranolol, d-propranolol, AII, and dl-propranolol-plus-AII into the superior mesenteric artery increased mesenteric venous PGE2 concentrations from 216 +/- 33 to 355 +/- 33 (p less than 0.01), 328 +/- 44 (p less than 0.05), 325 +/- 27 (p less than 0.02), and 407 +/- 44 pg/ml (p less than 0.01) respectively. We conclude that propranolol antagonizes AII enhancement of NS by increasing prostaglandin levels in vascular tissue. Furthermore, these findings suggest that propranolol may exert its antihypertensive effect through the release of prostaglandins when used in therapeutic doses in excess of those required for beta-adrenergic blockade.
Antihypertensive effect of riboflavin analogs in rats with mineralocorticoid-induced hypertension.
Authors: Trachewsky D
Published: June 2012

This study investigated whether the riboflavin analogs, 7,8-dimethyl-10-formylmethyl isoalloxazine (FMI) and 7,8-dimethyl-10-(2'-hydroxyethyl) isoalloxazine (HEI), are effective antihypertensive agents in mineralocorticoid-induced or deoxycorticosterone acetate (DOCA)-salt hypertension. These studies are based on our previous observation tht aldosterone enhances the biosynthesis of renal flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) from riboflavin, and that FMI and HEI competitively inhibit conversion of riboflavin to FMN and reabsorption of Na+ in the kidney of adrenalectomized rats. When 1.6 mg of FMI or HEI were administered simultaneously with 3.0 mg of DOCA, the tail systolic blood pressure (SBP) of unanesthetized rats rose only to 136 +/- 5 mm Hg (standard error of the mean, SEM) compared to 163 +/- 5 mm Hg during DOCA therapy alone (p less than 0.0005). This hypotensive effect of FMI or HEI was noted after the fourth week of treatment and persisted through the ninth week. The rats tolerated the medication well and had no signs of riboflavin deficiency. DOCA administration alone resulted in a 24% increase in iliopsoas muscle Na+ concentration (p less than 0.0005), and a 0.8% increase in the water content of the muscle (p less than 0.025), suggesting a positive Na+ balance. Administration of FMI or HEI blunted the ability of DOCA to increase muscle Na+ concentration (p less than 0.025), water content (p less than 0.01). HEI treatment of the Kyoto strain of spontaneously hypertensive rats (SHR) did not lower their mean SBP. Thus it appears that the hypotensive actions of FMI or HEI are closely associated with their ability to modify the effects of mineralocorticoids on NA+ balance.
Role of mineralocorticoid in the chronic antihypertensive effect of converting enzyme inhibitor.
Authors: Maitra S R , Scicli A G , Miyazaki S , Carretero O A
Published: June 2012

The chronic antihypertensive effect of converting enzyme inhibtor (CEI) may be due to a decrease in aldosterone secretion secondary to blockade of angiotensin II formation. To study this hypothesis, changes in blood pressure (BP), in response to chronic administration of the CEI, captopril, were measured in spontaneously hypertensive (SHR) and in chronic two-kidney, one clip hypertensive (2K-1C) rats. To avoid a decrease in mineralocorticoid activity, half of the rats in these two models of hypertension were adrenalectomized and maintained with daily administrations of deoxycorticosterone acetate and hydrocortisone (steroid replacement) while the other half had the adrenal gland left in situ and no exogenous steroids administered. The doses of steroids used were devoid of hypertensive effect in Wistar Kyoto (WKY), SHR, 2K-1C, and sham-clipped rats. Chronic administration of the CEI decreased the BP to normotensive levels in the SHR with intact adrenals and no steroid replacement. However, the antihypertensive effect of the CEI was almost completely blocked in those SHR with steroid replacement. In contrast, the antihypertensive effect of the CEI in 2K-1C was similar in the rats with steroid replacement and in the rats with intact adrenals (no steroid replacement). These results suggest that the chronic antihypertensive effect of CEI in SHR is due partially to a decrease in aldosterone activity secondary to the blockade of angiotensin II formation, whereas in 2K-1C it is due to mechanisms other than lower mineralocorticoid activity.