bluuebunny/crossref_metadata_2025 huggingface dataset:
Salt-Sensitive Hypertension After Exposure to Angiotensin Is Associated With Inability to Upregulate Renal Epoxygenases
Authors: Zhao Xueying , Pollock David M. , Zeldin Darryl C. , Imig John D.
Published: August 2003

The current study was designed to determine whether angiotensin II infusion could lead to persistent salt-sensitive hypertension and to examine involvement of renal microvascular epoxygenases in this process. Six groups were studied: rats maintained on a normal salt diet for 4 weeks (NS); rats maintained on a high salt diet for 4 weeks (HS); and all other animals receiving angiotensin II (ANG) infusion and being fed a normal or high salt diet for 2 weeks; then the angiotensin II infusion was stopped and diets were either maintained or switched (ANG/NS-NS, ANG/NS-HS, ANG/HS-HS, ANG/HS-NS). Angiotensin II infusion resulted in a rise in blood pressure and an increase in urinary albumin excretion over the 2-week period. After angiotensin II withdrawal, blood pressure returned to normal in animals receiving a normal salt diet from weeks 2 to 4 (ANG/NS-NS and ANG/HS-NS groups). In contrast, blood pressure remained elevated in the group maintained on a high salt diet throughout the entire 4-week period (ANG/HS-HS group). Renal microvascular CYP2C11 and CYP2C23 protein levels were decreased by 50% to 60% in the ANG/HS-HS group compared with the NS group. Likewise, renal microvascular CYP2J protein was significantly decreased in the ANG/HS-HS group versus the NS group. Renal microvascular CYP2C11 and CYP2C23 mRNA levels were reduced in the ANG/HS-HS group compared with both the NS and HS groups. These results support the hypothesis that angiotensin II infusion induces persistent salt-sensitive hypertension after withdrawal of angiotensin II that may be due to downregulation of CYP2C and CYP2J epoxygenases in renal microvessels.
Role of COX-2 in the Enhanced Vasoconstrictor Effect of Arachidonic Acid in the Diabetic Rat Kidney
Authors: Quilley John , Chen Yu-Jung
Published: August 2003

In the rat isolated perfused kidney, arachidonic acid elicits cyclooxygenase-dependent vasoconstriction through activation of PGH
2
/TxA
2
receptors; responses are enhanced in kidneys from diabetic rats. This study examined the roles of cyclooxygenase-1/cyclooxygenase-2 in the enhanced renal vasoconstrictor effect of arachidonic acid in streptozotocin-diabetic rats. Release of 20-HETE was also determined, as this eicosanoid has been reported to elicit cyclooxygenase-dependent vasoconstriction. We confirmed that vasoconstrictor responses to arachidonic acid were enhanced in the diabetic rat kidney associated with a 2-fold–greater increase in the release of 6-ketoPGF
1α
, which was used as an index of cyclooxygenase activity. One and three micrograms of arachidonic acid increased perfusion pressure by 85±37 and 186±6 mm Hg, respectively, in diabetic rat kidneys compared with 3±1 and 17±8 mm Hg, respectively, in control rat kidneys. Inhibition of both cyclooxygenase isoforms with indomethacin (10 μmol/L) abolished the vasoconstrictor response to arachidonic acid in both diabetic and control rat kidneys, whereas inhibition of cyclooxygenase-2 with nimesulide (5μmol/L) reduced perfusion pressure responses to 1 and 3 μg arachidonic acid only in the diabetic rat kidney to 15±8 and 108±26 mm Hg, respectively, consistent with a 3-fold increase in the renal cortical expression of cyclooxygenase-2. 20-HETE release from the diabetic rat kidney was reduced almost 6-fold and was not increased in response to arachidonic acid. These results demonstrate that the renal vasoconstrictor effect of arachidonic acid is solely dependent on cyclooxygenase activity, with no evidence for a contribution from 20-HETE; in the diabetic rat, cyclooxygenase-2 activity contributes to the renal vasoconstrictor effect of arachidonic acid.
Pregnant Rats With 5/6 Nephrectomy Have Normal Volume Expansion Despite Lower Renin and Kallikrein
Authors: Salas Sofía P. , Giacaman Andrea , Vío Carlos P.
Published: August 2003

To test the hypothesis that normal volume expansion during pregnancy is impaired during chronic renal failure, we evaluated the effects of 5/6 nephrectomy (Nx) in Sprague-Dawley rats. Partial Nx was produced by ligation of 2/3 renal arteries and contralateral Nx. Control rats had a sham operation. Four weeks later, rats were assigned to nonpregnant (n=6/each) or pregnant groups (n=11 to 12/each). At day 21, blood pressure, plasma volume, renal function, hormonal levels, and reproductive outcome were determined. Statistical analysis was performed by ANOVA, and values were expressed as mean±SEM. Rats with 5/6 Nx had proteinuria and lower creatinine clearance; pregnancy did not affect these parameters. Blood pressure increased in 5/6 Nx rats and was reduced by pregnancy. Both pregnant groups had lower hematocrit and higher plasma volume values (nonpregnant control, 13.4±0.2; nonpregnant 5/6 Nx, 14.4±0.2; pregnant control, 19.1±0.7, pregnant 5/6 Nx, 19±0.9 mL,
P
<0.001). Pregnancy increased plasma renin activity only in control rats (nonpregnant control, 2.0±0.7; nonpregnant 5/6 Nx, 1.6±1.1; pregnant control, 36.1±7.9, pregnant 5/6 Nx, 6.1±1.8 ng AI/mL per hour,
P
<0.001). Serum aldosterone levels were unaffected by 5/6 Nx and were higher in pregnant than in nonpregnant rats. Urinary kallikrein activity was reduced by 5/6 Nx and not changed by pregnancy (nonpregnant control, 1499±237; nonpregnant 5/6 Nx, 346±90; pregnant control, 1595±180, pregnant 5/6 Nx, 374±95 nmol/16 hours,
P
<0.001). No significant differences in fetal and placental weights were observed between control and 5/6 Nx rats. Present data indicate that 5/6 Nx pregnant rats were able to normally expand plasma volume despite lower renin and kallikrein levels.
N-Domain Angiotensin I-Converting Enzyme With 80 kDa as a Possible Genetic Marker of Hypertension
Authors: Marques Georgia D.M. , Quinto Beata M.R. , Plavinik Frida L. , Krieger José E. , Marson Odair , Casarini Dulce E.
Published: August 2003

We have previously described angiotensin I-converting enzyme (ACE) forms in urine of normotensive (190 and 65 kDa) and hypertensive patients (90 and 65 kDa, N-domain ACEs). Based on the results described above, experimental and genetic models of hypertension were investigated to distinguish hemodynamic and genetic influence on the generation of ACE profile in urine: Wistar-Kyoto and Brown Norway rats (WKY and BN), spontaneously and stroke-prone spontaneously hypertensive rats (SHR and SHR-SP), one kidney/one clip rats (1K1C), deoxycorticosterone acetate (DOCA) salt-treated and untreated rats, and enalapril-treated SHR (SHRen). Two peaks with ACE activity were separated from the urine of WKY and BN rats submitted to an AcA-44 column, WK-1/BN-1 (190 kDa), and WK-2/BN-2 (65 kDa), as described for urine of normotensive subjects. The same results were obtained for urine of 1K1C and DOCA salt-treated and untreated rats, analyzed to evaluate the influence of hemodynamic factors in the ACE profile in urine. The urine from SHR, SHR-SP, and SHRen presented 80 (S-1, SP-1, Sen-1) and 65 (S-2, SP-2, Sen-2) kDa ACE forms, differing from the urine profile of normotensive rats, but similar to that described for hypertensive patients. The presence of 80 kDa ACE in urine of SHR, SHR-SP, and SHRen and its absence in urine of experimental hypertensive rats (1K1C and DOCA salt) support the hypothesis that this enzyme could be a possible genetic marker of hypertension. Taken together, our results provide evidence that ACE forms with 90/80 kDa isolated from the urine of hypertensive subjects and genetic hypertensive animals behaves as a possible genetic marker of hypertension and not as a marker of high blood pressure.
Effects of Exogenous Heme on Renal Function
Authors: Rodriguez Francisca , Kemp Rowena , Balazy Michael , Nasjletti Alberto
Published: August 2003

We examined the effects of heme administration (15 mg/kg IV) on indexes of renal carbon monoxide production and contrasted the renal functional response to heme in anesthetized rats pretreated and not pretreated with stannous mesoporphyrin (40 μmol/kg IV) to inhibit heme oxygenase or sodium meclofenamate (5 mg/kg IV plus infusion at 10 μg/kg per minute) to inhibit cyclooxygenase. In rats without drug pretreatment, heme administration decreased renal vascular resistance and increased renal blood flow, urine volume, and sodium excretion associated with augmented urinary excretion of 6-keto-PGF
1α
and enhanced concentration of carbon monoxide in the renal cortical microdialysate. Pretreatment with stannous mesoporphyrin did not prevent heme from producing renal vasodilation and increasing renal blood flow but abolished the diuretic and natriuretic responses. Conversely, pretreatment with sodium meclofenamate blunted the renal vasodilatory effect of heme but affected neither the diuretic nor the natriuretic effect. We conclude that heme-induced renal vasodilation is a cyclooxygenase-dependent response involving increased synthesis of PGI
2
, whereas heme-induced diuresis and natriuresis are heme oxygenase-dependent responses involving inhibition of tubular reabsorption of sodium and water through undefined mechanisms.
Hyperuricemia in Childhood Primary Hypertension
Authors: Feig Daniel I. , Johnson Richard J.
Published: August 2003

Experimental animal models suggest that uric acid might have a pathogenic role in the early development of primary hypertension. We hypothesized that serum uric acid is correlated with blood pressure in children with new-onset, untreated, primary hypertension. We evaluated 125 consecutive children referred to the Baylor Pediatric Renal Program for evaluation of hypertension. None of the subjects had previously been evaluated or treated for hypertension. The children ranged in age from 6 to 18 years (mean, 13.4±3.3) and had normal renal function (creatinine clearance >80 mL · min
−1
· 1.73 m
−2
). Sixty-three children had primary hypertension, 40 had secondary hypertension, and 22 had white-coat hypertension. Forty controls with normal blood pressure were recruited from the renal clinic. Uric acid levels were directly correlated with systolic (
r
=0.80,
P
=0.0002) and diastolic (
r
=0.66,
P
=0.0006) blood pressure in controls and in subjects with primary hypertension and were independent of renal function. Serum uric acid concentrations >5.5 mg/dL were found in 89% of subjects with primary hypertension, in 30% with secondary hypertension, in 0% with white-coat hypertension, and in 0% of controls. We conclude that serum uric acid is directly correlated with blood pressure in untreated children and that a serum uric acid value >5.5 mg/dL in an adolescent being evaluated for hypertension strongly suggests primary hypertension as opposed to white-coat or secondary hypertension. These results are consistent with the hypothesis that uric acid might have a role in the early pathogenesis of primary hypertension.
Elastase-Induced Suppression of Endothelin-Mediated Ca
2+
Entry Mechanisms of Vascular Contraction
Authors: Chew David K.W. , Orshal Julia M. , Khalil Raouf A.
Published: August 2003

Abdominal aortic aneurysm (AAA) is associated with increased endothelin (ET-1), both systemically and locally in the aorta. Also, elastase activity is increased in human AAA, and elastase perfusion of the aorta induces aneurysm formation in animal models of AAA. However, whether elastase directly affects the ET-1-induced mechanisms of aortic smooth muscle contraction is unclear. Isometric contraction and
45
Ca
2+
influx were measured in aortic strips isolated from male Sprague-Dawley rats and treated with elastase (5 U/mL). To avoid degradation of the extracellular matrix proteins by elastase, experiments were performed in the presence of elastin (10 mg/mL). In normal Krebs solution (2.5 mmol/L Ca
2+
), ET-1 (10
−7
mol/L) caused contraction of aortic strips that was inhibited by elastase (5 U/mL). The elastase-induced inhibition of ET-1 contraction was slow in onset (4.6±0.4 minutes), time-dependent, complete in 34±3 minutes, and reversible. In Ca
2+
-free Krebs solution, caffeine (25 mmol/L) caused a small contraction that was not inhibited by elastase, suggesting that elastase does not inhibit Ca
2+
release from the intracellular stores. Membrane depolarization by 96 mmol/L KCl, which stimulates Ca
2+
entry from the extracellular space, caused a contraction that was inhibited by elastase in a concentration-dependent, time-dependent, and reversible fashion. The reversible inhibitory effects of elastase, particularly in the presence of elastin, suggest that they are not due to dissolution of the extracellular matrix or smooth muscle contractile proteins. Elastase also inhibited ET-1 and KCl-induced
45
Ca
2+
influx. Thus, elastase directly inhibits ET-1-induced Ca
2+
entry mechanisms of vascular smooth muscle contraction, which may explain the role of elastase and ET-1 during the development of AAA.
Serum Heat Shock Protein 70 Levels Predict the Development of Atherosclerosis in Subjects With Established Hypertension
Authors: Pockley Alan G. , Georgiades Anastasia , Thulin Thomas , de Faire Ulf , Frostegård Johan
Published: August 2003

Although heat shock proteins (Hsp’s) are present in the sera of healthy individuals and at elevated levels in subjects with early cardiovascular disease, their physiologic role in and value for predicting the development and/or progression of atherosclerosis have not been evaluated. Serum was obtained from 218 subjects with established hypertension (diastolic pressure >95 mm Hg) before their enrollment in the European Lacidipine Study on Atherosclerosis. Hsp60 and Hsp70, and anti-human Hsp60, anti-human Hsp70, and anti-mycobacterial Hsp65 antibody levels were measured by enzyme immunoassay. As an indicator of the presence/progression of atherosclerosis, the means of the maximum intima-media (I-M) thicknesses in the far walls of common carotid arteries and bifurcations (CBM
max
) were determined by ultrasonography at the time of enrollment and 4 years afterward. Increases in I-M thicknesses at follow-up were less prevalent in subjects having high serum Hsp70 levels (75th percentile) at the time of enrollment (odds ratio, 0.42; 95% confidence interval [CI], 0.22 to 0.8,
P
=0.008). Although a similar trend was observed for serum Hsp60 levels, this was not statistically significant (odds ratio, 0.6; 95% CI, 0.32 to 1.11,
P
=0.10). There was no relation between anti-Hsp antibody levels and changes in I-M thicknesses. The relation between Hsp70 levels and changes in I-M thickness was independent of age, atenolol or lacidipine treatment, smoking habits, and blood lipid levels. These findings indicate that circulating Hsp70 levels predict the development of atherosclerosis in subjects with established hypertension, and an intriguing possibility is that Hsp70 protects against or modifies the progression of atherosclerosis in this subject group.
Recovery of High Blood Pressure After Chronic Lesions of the Commissural NTS in SHR
Authors: Sato Monica Akemi , Schoorlemmer Gerhardus Hermanus Maria , Menani José Vanderlei , Lopes Oswaldo Ubríaco , Colombari Eduardo
Published: August 2003

Acute electrolytic lesions of the commissural nucleus of the solitary tract (commNTS) reduce blood pressure (BP) in SHR but not in normotensive Wistar-Kyoto and Wistar rats and abolish the pressor response to intravenous injection of potassium cyanide. We investigated the chronic effect of commNTS lesions on mean arterial pressure (MAP), and on baroreceptor and chemoreceptor reflex responses in SHR. The contribution of the sympathetic nervous system and the hormones vasopressin and angiotensin II to maintenance of BP in lesioned SHR was also investigated. MAP fell to normotensive levels the day after lesioning the commNTS but returned to the hypertensive level 9 days later. The reflex tachycardia evoked by sodium nitroprusside remained attenuated for 10 days after commNTS lesions but became enhanced 30 days after commNTS lesions. The pressor component of the chemoreflex elicited by potassium cyanide remained blocked for 30 days after lesions. Vasopressin antagonist or ACE blocker did not change MAP in sham or commNTS-lesioned SHR. Ganglionic blockade with hexamethonium elicited similar reductions in MAP in sham and commNTS-lesioned SHR. Results demonstrated that commNTS lesions in SHR produce a transient fall in BP and a long-lasting inhibition of the pressor response of the chemoreflex. Therefore, the blockade of the pressor response to peripheral chemoreflex activation is not sufficient to chronically reduce MAP in SHR. In the chronic absence of the commNTS, other subnuclei of the NTS or other brain stem nuclei may reorganize to replace the function of commNTS neurons, restoring sympathetic activity and high BP in SHR.
Amlodipine Modulates THP-1 Cell Adhesion to Vascular Endothelium via Inhibition of Protein Kinase C Signal Transduction
Authors: Yu Tao , Morita Ikuo , Shimokado Kentaro , Iwai Takehisa , Yoshida Masayuki
Published: August 2003

Inflammatory responses play an important role in atherosclerosis. To critically assess the effect of dihydropyridines in inflammatory reactions, we conducted a monocyte-endothelial adhesion assay with monocytic THP-1 cells treated with amlodipine under flow conditions in vitro. THP-1 cells were incubated in the presence of amlodipine (10 μmol/L) for 48 hours and then perfused over activated (interleukin-1β, 10 U/mL, 4 hours) human umbilical vein endothelial cells. The adhesion of THP-1 cells was significantly reduced after amlodipine treatment (
P
<0.001); however, flow cytometric analysis reveled that the expression levels of integrins in THP-1 cells were not significantly altered. Furthermore, Western blotting analysis of THP-1 cell lysates revealed that translocation of RhoA from the cytosol to the membrane was significantly diminished after amlodipine treatment. In addition, activation of protein kinase C-α and -β, as well as intracellular calcium influx, induced by phorbol 12-myristate 13-acetate, was diminished after amlodipine treatment. Pretreatment of THP-1 cells with calphostin C, a potent inhibitor of protein kinase C, significantly reduced THP-1 adhesion to vascular endothelium, whereas activation of β
1
-integrin was reduced after amlodipine treatment in THP-1 cells, based on the immunoreactivity of an activation-specific antibody for β
1
-integrin. Similar inhibitory effects were observed when we used freshly isolated peripheral blood mononuclear cells. These findings suggest a potential role for amlodipine in monocyte-endothelial interactions by modulation of protein kinase C- and RhoA-dependent mechanisms, which might account for its vascular protective effects.
Specific Contribution of Estrogen Receptors on Mitogen-Activated Protein Kinase Pathways and Vascular Cell Activation
Authors: Geraldes Pedro , Sirois Martin G. , Tanguay Jean-François
Published: August 2003

Randomized clinical trials have not provided conclusive data that hormone replacement therapy confers cardioprotection against coronary artery disease in postmenopausal women. However, other studies have shown that estrogens can induce beneficial effects on the vasculature. Nevertheless, the specific contribution of estrogen receptors (ERs) α and β on vascular cells is not well characterized. Therefore, we used an antisense gene therapy approach to investigate the contribution of ERα and ERβ on p38 and p42/44 mitogen-activated protein kinase (MAPK) activation and on vascular cell responsiveness. Treatment of porcine smooth muscle cells (PSMCs) with platelet-derived growth factor-BB induced p38 and p42/44 MAPK activation and their migration and proliferation. These effects were prevented by pretreatment with 17β-estradiol (17βE). The inhibitory effects of 17βE on PSMCs were abrogated by the downregulation of ERβ protein expression with selective ERβ mRNA antisense oligomers, whereas the downregulation of ERα had no effect. However, treatment of porcine aortic endothelial cells with 17βE promoted p38 and p42/44 MAPK phosphorylation and their migration and proliferation. These effects were ERα dependent, as defined by antisense gene therapy. These results suggest that in PSMCs, 17βE reduces p42/44 and p38 MAPK activity through ERβ stimulation, whereas in contrast, in porcine aortic endothelial cells, 17βE induces p42/44 and p38 MAPK through ERα activation. 17βE may contribute to the vascular healing process and to the prevention of restenosis by improving reendothelialization through ERα activation and by decreasing smooth muscle cell migration and proliferation through ERβ stimulation.
Very-Long-Chain Acyl-Coenzyme A Dehydrogenase Deficiency in Mice
Authors: Exil Vernat J. , Roberts Richard L. , Sims Harold , McLaughlin Jacquelin E. , Malkin Robert A. , Gardner Carla D. , Ni Gemin , Rottman Jeffrey N. , Strauss Arnold W.
Published: August 2003

Fatty acid oxidation (FAO) defects are inborn errors of metabolism clinically associated with cardiomyopathy and sudden infant death syndrome (SIDS). FAO disorders often present in infancy with myocardial dysfunction and arrhythmias after exposure to stresses such as fasting, exercise, or intercurrent viral illness. It is uncertain whether the heart, in the absence of stress, is normal. We generated very-long-chain acyl-coenzyme A dehydrogenase (VLCAD)-deficient mice by homologous recombination to define the onset and molecular mechanism of myocardial disease. We found that VLCAD-deficient hearts have microvesicular lipid accumulation, marked mitochondrial proliferation, and demonstrated facilitated induction of polymorphic ventricular tachycardia, without antecedent stress. The expression of acyl-CoA synthase (ACS1), adipophilin, activator protein 2, cytochrome
c
, and the peroxisome proliferator activated receptor γ coactivator-1 were increased immediately after birth, preceding overt histological lipidosis, whereas ACS1 expression was markedly downregulated in the adult heart. We conclude that mice with VLCAD deficiency have altered expression of a variety of genes in the fatty acid metabolic pathway from birth, reflecting metabolic feedback circuits, with progression to ultrastructural and physiological correlates of the associated human disease in the absence of stress.
The Obesity-Associated Peptide Leptin Induces Hypertrophy in Neonatal Rat Ventricular Myocytes
Authors: Rajapurohitam Venkatesh , Gan Xiaohong Tracey , Kirshenbaum Lorrie A. , Karmazyn Morris
Published: August 2003

One of the major manifestations of obesity is increased production of the adipocyte-derived 16-kDa peptide leptin, which is also elevated in heart disease, including congestive heart failure. However, whether leptin can directly alter the cardiac phenotype is not known. We therefore studied the effect of leptin as a potential hypertrophic factor in cultured myocytes from 1- to 4-day-old neonatal rat heart ventricles. Using RT-PCR, we demonstrate that these cells express the short-form (OB-Ra) leptin receptor. Twenty-four hours of exposure to leptin (0.31 to 31.3 nmol/L) produces a significantly increased cell surface area that peaked at 0.63 nmol/L. Subsequent experiments were done with 3.1 nmol/L leptin, which significantly increased cell area by 42%, protein synthesis by 32%, and α-skeletal actin and myosin light chain-2 expression by 250% and 300%, respectively. These events occurred in the absence of any increased cell death. Hypertrophy was preceded by rapid activation of the mitogen-activated protein kinase system including p38 and p44/42 as early as 5 minutes after leptin addition, whereas hypertrophy was inhibited by the p38 inhibitor SB203580 but not by the p44/42 inhibitor PD98059. Our results demonstrate a direct hypertrophic effect of leptin and may offer a biological link between hypertrophy and hyperleptinemic conditions such as obesity.
Ablation and Mutation of Nonmuscle Myosin Heavy Chain II-B Results in a Defect in Cardiac Myocyte Cytokinesis
Authors: Takeda Kazuyo , Kishi Hiroko , Ma Xuefei , Yu Zu-Xi , Adelstein Robert S.
Published: August 2003

We have identified a novel form of cardiac myocyte enlargement in nonmuscle myosin heavy chain II-B (NMHC II-B) ablated mice, based on a partial failure in cytokinesis. In contrast to most cells, cardiac myocytes lack NMHC II-A, and ablation of NMHC II-B results in a heart with 70% fewer myocytes at embryonic day 14.5 (E14.5) than control mice (B
+
/B
−
and B
+
/B
+
). In addition, B
−
/B
−
cardiac myocytes show a marked increase in binucleation at E12.5, reflecting the occurrence of karyokinesis in the absence of cytokinesis. An increase in binucleation and cell size is also found in hypomorphic, homozygous mice harboring a single amino acid mutation (R709C) in the gene encoding NMHC II-B. The nonmyocytes in B
−
/B
−
hearts and homozygous mutant hearts, all of which contain NMHC II-A, do not show either of these abnormalities. B
−
/B
−
cardiac myocytes at E14.5 show a decreased bromodeoxyuridine (BrdU) labeling index compared with controls, consistent with the decrease in myocyte proliferation. This decreased BrdU labeling is not seen in nonmyocyte cells in the heart. In addition to these changes, both B
−
/B
−
mice as well as homozygous mutated mice show an increase in cyclin D2 and D3 reflecting an abnormality in earlier steps in the cell cycle. Whereas cardiac myocytes completely ablated for NMHC II-B show enlargement and binucleation, mice expressing as little as 6% of the normal amount of wild-type NMHC II-B in the heart do not show these abnormalities.
Ligand-Independent Activation of Vascular Endothelial Growth Factor Receptor 2 by Fluid Shear Stress Regulates Activation of Endothelial Nitric Oxide Synthase
Authors: Jin Zheng-Gen , Ueba Hiroto , Tanimoto Tatsuo , Lungu Andreea O. , Frame Mary D. , Berk Bradford C.
Published: August 2003

Fluid shear stress generated by blood flowing over the endothelium is a major determinant of arterial tone, vascular remodeling, and atherogenesis. Nitric oxide (NO) produced by endothelial NO synthase (eNOS) plays an essential role in regulation of vascular function and structure by blood flow, but the molecular mechanisms that transduce mechanical force to eNOS activation are not well understood. In this study, we found that laminar flow (shear stress=12 dyne/cm
2
) rapidly activates vascular endothelial growth factor receptor 2 (VEGFR2) in a ligand-independent manner and leads to eNOS activation in cultured endothelial cells. Flow-stimulated VEGFR2 recruits phosphoinositide 3-kinase and mediates activation of Akt and eNOS. Inhibiting VEGFR2 kinase with selective inhibitors blocks flow-induced activation of Akt and eNOS and production of NO. Decreasing VEGFR2 expression with antisense VEGFR2 oligonucleotides significantly attenuates activation of Akt and eNOS. Furthermore, Src kinases are involved in flow-stimulated VEGFR2 because inhibiting Src kinases by PP2, a selective inhibitor for Src kinases, abolishes flow-induced VEGFR2 tyrosine phosphorylation and downstream signaling. Finally, we show that inhibiting VEGFR2 kinase significantly reduces flow-mediated NO-dependent arteriolar dilation in vivo. These data identify VEGFR2 as a key mechanotransducer that activates eNOS in response to blood flow.
Coupling of Cardiac Electrical Activity Over Extended Distances by Fibroblasts of Cardiac Origin
Authors: Gaudesius Giedrius , Miragoli Michele , Thomas Stuart P. , Rohr Stephan
Published: August 2003

Roughly half of the cells of the heart consist of nonmyocardial cells, with fibroblasts representing the predominant cell type. It is well established that individual cardiomyocytes and fibroblasts in culture establish gap junctional communication at the single cell level (short-range interaction). However, it is not known whether such coupling permits activation of cardiac tissue over extended distances (long-range interaction). Long-range interactions may be responsible for electrical synchronization of donor and recipient tissue after heart transplantation and may play a role in arrhythmogenesis. This question was investigated using a novel heterocellular culture model with strands of cardiomyocytes interrupted by cardiac fibroblasts over defined distances. With use of optical recording techniques, it could be shown that impulse propagation along fibroblast inserts was successful over distances up to 300 μm and was characterized by length-dependent local propagation delays ranging from 11 to 68 ms (apparent local “conduction velocities” 4.6±1.8 mm/s, n=23). Involvement of mechanical stretch in this phenomenon was excluded by showing that inserts consisting of communication-deficient HeLa cells were incapable of supporting propagation. In contrast, HeLa cells expressing connexin43 permitted impulse conduction over distances as long as 600 μm. Immunocytochemistry showed that fibroblasts and cardiomyocytes expressed connexin43 and connexin45, whereas connexin40 was absent. These results illustrate that fibroblasts of cardiac origin are capable of synchronizing electrical activity of multicellular cardiac tissue over extended distances through electrotonic interactions. This synchronization is accompanied by extremely large local conduction delays, which might contribute to the generation of arrhythmias in fibrotic hearts.
Fibroblast Growth Factor Receptor-1 Is Essential for In Vitro Cardiomyocyte Development
Authors: Dell’Era Patrizia , Ronca Roberto , Coco Laura , Nicoli Stefania , Metra Marco , Presta Marco
Published: August 2003

Fibroblast growth factor (FGF)/FGF receptor (FGFR) signaling plays a crucial role in mesoderm formation and patterning.
Heartless
mutant studies in
Drosophila
suggest that FGFR1, among the different FGFRs, may play a role in cardiogenesis. However,
fgfr1
−/−
mice die during gastrulation before heart formation. To establish the contribution of FGFR1 in cardiac development, we investigated the capacity of murine
fgfr1
+/−
and
fgfr1
−/−
embryonic stem (ES) cells to differentiate to cardiomyocytes in vitro. Clusters of pulsating cardiomyocytes were observed in >90% of 3-dimensional embryoid bodies (EBs) originated from
fgfr1
+/−
ES cells at day 9 to 10 of differentiation. In contrast, 10% or less of
fgfr1
−/−
EBs showed beating foci at day 16. Accordingly,
fgfr1
−/−
EBs were characterized by impaired expression of early cardiac transcription factors
Nkx2.5
and
d-Hand
and of late structural cardiac genes
myosin heavy chain
(
MHC
)-α,
MHC
-β, and
ventricular myosin light chain
. Homozygous
fgfr1
mutation resulted also in alterations of the expression of mesoderm-related early genes, including
nodal
,
BMP2, BMP4
,
T
(
bra
), and
sonic hedgehog
. Nevertheless,
fgfr1
+/−
and
fgfr1
−/−
EBs similarly express cardiogenic precursor, endothelial, hematopoietic, and skeletal muscle markers, indicating that
fgfr1
-null mutation exerts a selective effect on cardiomyocyte development in differentiating ES cells. Accordingly, inhibitors of FGFR signaling, including the FGFR1 tyrosine kinase inhibitor SU 5402, the MEK1/2 inhibitor U0126, and the protein kinase C inhibitor GF109 all prevented cardiomyocyte differentiation in
fgfr1
+/−
EBs without affecting the expression of the hematopoietic/endothelial marker
flk-1
. In conclusion, the data point to a nonredundant role for FGFR1-mediated signaling in cardiomyocyte development.
Combination Drug Therapy and Mild Hypothermia After Transient Focal Cerebral Ischemia in Rats
Authors: Zausinger Stefan , Schöller Karsten , Plesnila Nikolaus , Schmid-Elsaesser Robert
Published: August 2003

Background and Purpose—

We have recently demonstrated that pretreatment with magnesium (calcium and glutamate antagonist) and tirilazad (antioxidant) in combination with intraischemic mild hypothermia (33°C) (MTH) offers superior neuroprotective efficacy in a rat model of focal transient cerebral ischemia. In the present study, we investigated the time window of this treatment strategy with a posttreatment regimen to define its role for stroke patients.

Methods—

We subjected 48 Sprague-Dawley rats to 90 minutes of middle cerebral artery occlusion by an intraluminal filament. Bilateral regional cerebral blood flow was continuously recorded by laser Doppler flowmetry. Combination therapy with MTH was started at 0, 1, 3, and 5 hours after induction of ischemia. Drugs were given in 1-hour intervals, and hypothermia was maintained for 2 hours. Neurological deficits were assessed daily. Infarct size was planimetrically determined on postoperative day 7.

Results—

Combination therapy with MTH significantly reduced infarct volume compared with normothermic controls by −74%, −49%, and −45% when applied at 0, 1, and 3 hours after induction of ischemia. Furthermore, these treatment groups showed less neurological deficits on postischemic days 1 and 2 (
P
<0.05). Onset of treatment 5 hours after middle cerebral artery occlusion failed to significantly reduce infarct formation and neurological deficits.

Conclusions—

The therapeutic window of the new combination therapy is at least 3 hours after onset of ischemia, comparable to that of moderate hypothermia (30°C), a grade of hypothermia associated with higher risks of severe side effects.
External Carotid Artery Territory Ischemia Impairs Outcome in the Endovascular Filament Model of Middle Cerebral Artery Occlusion in Rats
Authors: Dittmar Michael , Spruss Thilo , Schuierer Gerhard , Horn Markus
Published: August 2003

Background and Purpose—

Middle cerebral artery occlusion (MCAO) by an intraluminal filament is a widely accepted animal model of focal cerebral ischemia. In this procedure, cutting of the external carotid artery (ECA) is a prerequisite for thread insertion. However, the implications of ECA transsection have not yet been described.

Methods—

After 90 minutes of filament MCAO or sham surgery, rats were evaluated for up to 14 days in terms of body weight development, core temperature, and motor performance. Repeated in vivo MRI of the head and neck was performed for quantification of brain edema and infarct volume. The temporal muscles were histologically analyzed postmortem.

Results—

In 47% of all rats, ischemic tissue damage to the ipsilateral ECA area, including temporal, lingual, and pharyngeal musculature, was detectable by MRI. Histology of temporal muscles confirmed acute ischemic myopathy. Animals with ECA territory ischemia (ECA-I) showed delayed body weight development and poorer recovery of motor function. There was no difference in the extent of brain edema or final cerebral lesion size between ECA-I–affected and unaffected rats.

Conclusions—

Filament MCAO was complicated by the consequences of ECA ischemia in approximately half of all rats. Impaired mastication and swallowing functions restricted ingestion and resulted in postsurgical body weight loss and worse motor performance. Impaired cerebral microperfusion resulting from dehydration and reduced spontaneous motor activity resulting from reduced food and water uptake might have contributed to poorer neurological recovery in ECA ischemic rats. Thus, adverse effects caused by extracerebral ischemia with potential impact on outcome have to be considered in this stroke model.
QTc Interval Prolongation Is a Predictor of Future Strokes in Patients With Type 2 Diabetes Mellitus
Authors: Cardoso Claudia R.L. , Salles Gil F. , Deccache Waldemar
Published: August 2003

Background and Purpose—

QTc interval prolongation is a predictor of cardiovascular morbidity and mortality in general populations and in patients with diabetes. The aim of this study was to investigate the predictors of stroke in patients with type 2 diabetes, with particular emphasis on the independent role of QT interval parameters.

Methods—

We carried out a long-term follow-up study with 471 type 2 diabetics. Several clinical, laboratory, ECG, and echocardiographic variables were recorded at baseline. Predictive factors for stroke were evaluated by Kaplan-Meier estimation of survival curves and by univariate and multivariate Cox survival analyses.

Results—

After a median follow-up of 57 months (range, 2 to 84 months), 40 incident strokes were observed. QTc interval prolongation (≥470 ms
1/2
) was an independent predictor of stroke, with adjusted hazard ratios ranging from 2.2 to 2.9 (95% confidence intervals, 1.1 to 6.0). Other independent factors associated with stroke were older age; the presence of cerebrovascular disease at baseline; increased 24-hour proteinuria, serum triglycerides, and left ventricular mass; and decreased high-density lipoprotein cholesterol. Excluding patients with previous cerebrovascular disease from the analysis did not change the results significantly.

Conclusions—

QTc interval prolongation is a predictor of future stroke in patients with type 2 diabetes. Intervention studies are needed to assess whether this factor could be modified.
Levels of α
1
-Antitrypsin in Plasma and Risk of Spontaneous Cervical Artery Dissections
Authors: Vila Nicolás , Millán Mónica , Ferrer Xavier , Riutort Nadal , Escudero Domingo
Published: August 2003

Background and Purpose—

Abnormalities of dermal connective tissue have been detected in patients with spontaneous cervical artery dissections (sCAD), suggesting an underlying structural defect of the arterial wall. α
1
-Antitrypsin (A1-AT) is a circulating serine proteinase inhibitor of proteolytic enzymes that helps to maintain the integrity of elastic and collagen fibers.

Methods—

To test the hypothesis that moderate deficiency of A1-AT may be a risk factor for sCAD, 22 cases with sCAD and 113 controls were included in the study.

Results—

Patients with sCAD had significantly mean lower levels of A1-AT compared with controls (116.0±24.9 versus 141.1±31.7 mg/dL;
P
<0.01). Low levels of A1-AT (<90 mg/dL) were more frequently observed in patients with sCAD compared with controls (27.3% versus 2.7%;
P
<0.001). A positive correlation between age and plasma levels of A1-AT was found (
r
=0.22;
P
<0.01). A1-AT levels were not affected by sex or vascular risk factors, including smoking habit. On multivariate analysis, A1-AT <90 mg/dL was associated with sCAD independently of age, sex, or vascular risk factors (odds ratio, 17.7; 95% confidence interval, 2.9 to 105.6).

Conclusions—

Low plasma levels of A1-AT may be a risk factor for sCAD.
Relationship Between Periodontal Disease, Tooth Loss, and Carotid Artery Plaque
Authors: Desvarieux Moïse , Demmer Ryan T. , Rundek Tatjana , Boden-Albala Bernadette , Jacobs David R. , Papapanou Panos N. , Sacco Ralph L.
Published: August 2003

Background and Purpose—

Chronic infections, including periodontal infections, may predispose to cardiovascular disease. The present study investigates the relationship of periodontal disease and tooth loss with subclinical atherosclerosis.

Methods—

We enrolled 711 subjects with a mean age of 66±9 years and no history of stroke or myocardial infarction in the Oral Infections and Vascular Disease Epidemiology Study. Subjects received a comprehensive periodontal examination, extensive in-person cardiovascular disease risk factor measurements, and a carotid scan using high-resolution B-mode ultrasound. Regression models were adjusted for conventional risk factors (age, sex, smoking, diabetes, systolic blood pressure, low- and high-density lipoprotein cholesterol, race-ethnicity, education, physical activity) and markers of cultural background, healthy lifestyle, and psychosocial health.

Results—

Measures of both current and cumulative periodontitis became more severe as tooth loss increased. A significant association was observed between tooth loss levels and carotid artery plaque prevalence. Among those with 0 to 9 missing teeth, 46% had carotid artery plaque, whereas among those with ≥10 missing teeth, carotid artery plaque prevalence was ≈60% (
P
<0.05).

Conclusions—

Our data suggest that tooth loss is a marker of past periodontal disease in this population and is related to subclinical atherosclerosis, thereby providing a potential pathway for a relationship with clinical events.
Persistent Poststroke Hyperglycemia Is Independently Associated With Infarct Expansion and Worse Clinical Outcome
Authors: Baird Tracey A. , Parsons Mark W. , Phan Thanh , Butcher Ken S. , Desmond Patricia M. , Tress Brian M. , Colman Peter G. , Chambers Brian R. , Davis Stephen M.
Published: August 2003

Background and Purpose—

Hyperglycemia at the time of ischemic stroke is associated with increased mortality and morbidity. Animal studies suggest that infarct expansion may be responsible. The influence of persisting hyperglycemia after stroke has not previously been examined. We measured the blood glucose profile after acute ischemic stroke and correlated it with infarct volume changes using T2- and diffusion-weighted MRI.

Methods—

We recruited 25 subjects within 24 hours of ischemic stroke symptoms. Continuous glucose monitoring was performed with a glucose monitoring device (CGMS), and 4-hour capillary glucose levels (BGL) were measured for 72 hours after admission. MRI and clinical assessments were performed at acute (median, 15 hours), subacute (median, 5 days), and outcome (median, 85 days) time points.

Results—

Mean CGMS glucose and mean BGL glucose correlated with infarct volume change between acute and subacute diffusion-weighted MRI (
r
≥0.60,
P
<0.01), acute and outcome MRI (
r
=0.56,
P
=0.01), outcome National Institutes of Health Stroke Scale (NIHSS;
r
≥0.53,
P
<0.02), and outcome modified Rankin Scale (mRS;
r
≥0.53,
P
=0.02). Acute and final infarct volume change and outcome NIHSS and mRS were significantly higher in patients with mean CGMS or mean BGL glucose ≥7 mmol/L. Multiple regression analysis indicated that both mean CGMS and BGL glucose levels ≥7 mmol/L were independently associated with increased final infarct volume change.

Conclusions—

Persistent hyperglycemia on serial glucose monitoring is an independent determinant of infarct expansion and is associated with worse functional outcome. There is an urgent need to study normalization of blood glucose after stroke.
Perfusion Thresholds in Acute Stroke Thrombolysis
Authors: Butcher K. , Parsons M. , Baird T. , Barber A. , Donnan G. , Desmond P. , Tress B. , Davis S.
Published: August 2003

Background and Purpose—

Perfusion-weighted MRI has been shown to be useful in the early identification of cerebral tissue at risk of infarction during acute ischemia. Identification of threshold perfusion measures that predict infarction may assist in the selection of patients for thrombolysis.

Methods—

Mean transit time (MTT), regional cerebral blood flow (rCBF), and regional cerebral blood volume (rCBV) maps were generated in 35 acute stroke patients (17 treated with tissue plasminogen activator and 18 control patients) imaged within 6 hours from symptom onset. Day 90 outcome infarcts (T2-weighted MRI) were superimposed on acute MTT, rCBF, and rCBV maps. Perfusion-weighted MRI measures were then calculated for 2 regions: infarcted and salvaged tissue.

Results—

MTT was prolonged by 22% in infarcted regions relative to salvaged tissue (
P
<0.001). rCBF was 10% lower in infarcted tissue than in salvaged regions (
P
<0.01). rCBV did not differ significantly between infarcted and salvaged regions. When reperfusion occurred, tissue with more severely prolonged MTT was salvaged from infarction relative to patients with persistent hypoperfusion (
P
<0.05). In contrast, rCBF in salvaged regions did not differ between patients with and without reperfusion. In reperfused patients, an inverse correlation (
R
=0.93,
P
<0.001) was found between time of initial MRI scan and MTT delay in salvaged tissue.

Conclusions—

Both increases in MTT and decreases in rCBF predict infarction. Differences in MTT also predict salvage in more severely hypoperfused tissue after reperfusion, suggesting that it is the most clinically useful quantitative perfusion measure. Perfusion thresholds for infarction need to be assessed in the context of symptom duration.
Democratic Dominoes Revisited
Authors: Starr Harvey , Lindborg Christina
Published: August 2003

The impact of diffusion effects on the growth and spread of democracy in the global system is investigated. Using hazard analyses as well as previously employed transition matrices for the analysis of diffusion, a modified Freedom House data set is analyzed to delineate systemic, regional, and neighbor effects from 1974 to 1996. The dynamics of democratization are broken down by contrasting the differences and similarities of governmental transitions between the countries that were free (and moved to partially free and nonfree), the countries that were nonfree (and moved to partially free and free), and those countries that were partially free (and moved away from that status).
Peace through Insecurity
Authors: Chiozza Giacomo , Goemans H. E.
Published: August 2003

The literature on diversionary war has long argued that a leader's tenure considerations play an important role in international conflict behavior. However, for the diversionary use of force to be rational, international conflict must in turn affect the leader's tenure. A two-stage probit model on a new data set of all leaders between 1919 and 1992 is used to examine this reciprocal relationship between the probability of losing office and the probability of crisis initiation. Contrary to theories of the diversionary use of force, results show that an increase in the risk of losing office makes leaders less likely to initiate a crisis, and an increase in the risk of an international crisis makes leaders more likely to lose office. Results also suggest that democracies are overall less likely to initiate a crisis because of the domestic political insecurity of democratic leaders.
The Fruits of Good Work: Early Work Experiences and Adolescent Deviance
Authors: Staff Jeremy , Uggen Christopher
Published: August 2003

Some theories of crime suggest that “adultlike” work conditions diminish adolescent delinquency, whereas others suggest that precocious entry into adult work roles increases youth problem behaviors. The authors consider the relationship between delinquency and several dimensions of adolescent employment, including learning opportunities, freedom and autonomy, social status, demands and stress, wages, and compatibility between work and school. They find the lowest rates of 12th-grade school deviance, alcohol use, and arrest among adolescents whose jobs supported rather than displaced academic roles and provided opportunities for them to learn new things. In contrast, many qualities of work considered desirable for adults (autonomy, social status, and wages) appear to increase delinquency in adolescence. The authors conclude that work conditions have age-graded effects on delinquency that are contingent on the life course stage of the worker.
Relations of Childhood and Adolescent Factors to Offending Trajectories of Young Men
Authors: Wiesner Margit , Capaldi Deborah M.
Published: August 2003

Previous research has emphasized the importance of heterogeneity in offense trajectories. Using data from the Oregon Youth Study, a longitudinal study of at-risk boys interviewed annually from ages 9 to 10 years to ages 23 to 24 years, this study examined childhood and adolescent covariates of observed offending trajectory classes. Six trajectory classes were identified using the latent growth mixture modeling approach: chronic high-level, chronic low-level, decreasing high-level, decreasing low-level, rare, and nonoffenders. Multinomial logistic regressions revealed that nonoffenders, rare offenders, and chronic high-level offenders were distinguished by individual, family, and peer factors measured in childhood and adolescence. Only adolescent covariates (deviant peers, various problem behaviors) distinguished among trajectories of adolescents who engaged in substantive amounts of offending behavior. Overall, there was more specificity than commonality in correlates of distinctive offending trajectories.
The Threat of Terrorism as an Intervention on International Travel Flows
Authors: Coshall John T.
Published: August 2003

This article applies the method of intervention analysis to the study of flows of U.K. air passengers to a variety of destinations. The significance and form of interventions on U.K. air travel are examined for the U.S. bombing of Libya in 1986 for which implicit assistance was given by the United Kingdom, the Lockerbie air disaster (1988), and the Persian Gulf crisis (1990-1991). The effects of these interventions on U.K. air travel vary in onset, magnitude, and duration according to the destination involved and the state that a crisis has reached.