Renin Cell Baroreceptor, a Nuclear Mechanotransducer Central for Homeostasis

[Figure: see text].

[An experimental study of expression of angiotension converting enzyme 2 in myocardium and effect of telmisartan treatment in pressure-overloaded rats]

OBJECTIVE

To study the effect of hypertension and telmisartan treatment on the protein and gene expression of cardiac angiotensin-converting enzyme 2 (ACE2) in pressure-overloaded rats.

METHODS

Coarctation of suprarenal abdominal aorta was reproduced in 8 week-old male Sprague-Dawley (SD) rats and then randomized into 4 groups, including a sham group (n=15), a suprarenal aortic coarctation group (model group, n=12), a suprarenal aortic coarctation with low-dose Telmisartan treatment group (low-dose group, 2 mgxkg(-1)xd(-1), n=11) and a suprarenal aortic coarctation with high-dose Telmisartan treatment group(high-dose group, 10 mgxkg(-1)xd(-1), n=13). Telmisartan or equivalent amount of normal saline was gavaged 24 hours before the operation and once every day afterwards for 3 weeks. At the end of 3 weeks, the concentrations of angiotensin (AngII) in plasma and myocardium were measured by radioimmunoassay. Changes in both protein quantity and gene expressions of both ACE2 and ACE were determined by Western blotting analysis and reverse transcription-polymerase chain reaction (RT-PCR) technique, respectively.

RESULTS

Suprarenal abdominal aortic coarctation induced a significant increase in the plasma and myocardium AngII concentration [plasma: (495.1+/-55.6) ng/L vs. (269.2+/-39.5)ng/L, myocardium: (103.6+/-23.7) ng/g vs. (49.5+/-13.5) ng/g, both P<0.01] and expressions of gene and protein of ACE (P<0.01) and ACE2 (P<0.05). Telmisartan further increased the concentration of AngII in plasma and myocardium in a dose-dependent manner [plasma: (702.2+/-40.6) ng/L vs. (612.6+/-35.5) ng/L, myocardium (211.5+/-21.5) ng/g vs. (189.6+/-43.6) ng/g, both P<0.05], and induced a dose-dependent increase in both protein and gene expression of ACE2 (protein 1.16+/-0.06 vs. 0.79+/-0.04, gene 0.54+/-0.08 vs. 0.41+/-0.04, both P<0.05). Expression of ACE2 protein in low-dose and high-dose groups was increased by 1.0 and 1.58 folds respectively, and gene was increased by 1.3 and 1.6 folds (all P<0.05). The expression of ACE protein and gene in model group increased significantly (protein: 2.10+/-1.07 vs. 1.02+/-0.05, gene: 1.93+/-0.09 vs. 0.26+/-0.09, both P<0.01). Telmisartan had no significant effect on ACE gene and protein expressions (both P>0.05).

CONCLUSION

Suprarenal abdominal aortic coarctation induced a significant increases of ACE and ACE2 gene and protein expressions. Telmisartan induces a dose-dependent increases of cardiac ACE2 gene and protein expression,which may be the mechanism of its therapeutic effects.

Increased hypothalamic angiotensin-(1-7) levels in rats with aortic coarctation-induced hypertension

Since angiotensin (Ang) (1-7) injected into the brain blocked Ang II pressor actions in rats made hypertensive by aortic coarctation (CH), we examined systemic and tissue angiotensin peptide levels, specifically concentrating on the hypothalamic Ang-(1-7) levels. Plasma, heart and kidney isolated from CH rats showed increased levels of Ang I, Ang II and Ang-(1-7) compared with the normotensive group, with Ang II being the predominant peptide in heart and kidney. In the hypothalamus, equimolar amounts of Ang II and Ang-(1-7) were found in the sham group, whereas only Ang-(1-7) levels increased in CH rats. We conclude that aortic coarctation activates systemic and tissue renin-angiotensin system. The increased central levels of Ang-(1-7) in the CH rats suggest a potential mitigating role of this peptide in central control of the hypertensive process.

Bisoprolol inhibits sodium current in ventricular myocytes of rats with diastolic heart failure

1. Changes in sodium currents (I(Na)) in heart failure contribute to cardiac electrophysiological alterations and, thereby, to ventricular arrhythmias. Bisoprolol has anti-arrhythmic effects, but its direct effect on I(Na) in cardiac cells remains unclear. Accordingly, in the present study we investigated the effects of bisoprolol on ventricular I(Na) in diastolic heart failure (DHF) and normal rats. 2. The DHF model was produced by abdominal aortic coarctation for 4 weeks and single ventricular myocytes were isolated by enzymatic dissociation. The electrophysiological actions of bisoprolol on I(Na) currents were investigated using a whole-cell patch-clamp technique. 3. The membrane capacitance of rats in the DHF group was significantly greater than that of the control group and the current-voltage curve was simultaneously shifted downward. Bisoprolol concentration-dependently decreased I(Na) in ventricular myocytes of both groups (at -45 mV), with IC(50) values of 19.53 +/- 0.06 and 40.78 +/- 0.03 micromol/L in the control and DHF groups, respectively. 4. In both groups, the current-voltage curves were shifted upwards, whereas activation potentials, peak currents and reversal potentials showed no significant changes. At -45 mV, the descent ratio of current densities in the DHF group was lower than that of the control group. In both groups, inactivation curves were shifted to more negative potentials, but activation curves and recovery curves were not altered. Changes in the half-inactivation voltage, V(0.5), and the slope of the inactivation curve, S, were similar for both groups. 5. In conclusion, bisoprolol concentration-dependently decreases I(Na) in ventricular myocytes of DHF and normal rats, which could be responsible, at least in part, for its anti-arrhythmic effects.

No evidence for angiotensin type 2 receptor gene polymorphism in intron 1 in patients with coarctation of the aorta and Ullrich-Turner syndrome

In male patients with congenital anomalies of the kidney and urinary tract, an increased incidence of a polymorphism in the angiotensin type 2 receptor gene (AT2R) has been identified. The AT2R has been shown to be involved in apoptosis, particularly during embryogenesis. The aim of this study was to examine the A-->1675G transition polymorphism in intron 1 of the AT2R gene that is located on the X chromosome in patients with coarctation of the aorta (CoA) with and without Ullrich-Turner syndrome (UTS). Screening of DNA samples was performed with restriction fragment length polymorphism analysis. Ninety-seven patients with CoA, 28 girls with UTS, 10 girls with UTS and CoA, and 96 control individuals were studied. There was no significant difference in the distribution of A and G-genotypes in any of the patient groups compared to controls. An A-->1675G transition in the AT2R gene seems not to be involved in the pathogenesis of aortic coarctation.

Aortic coarctation induces oxidative stress in rat tissues

The purpose of this study was to evaluate the induction of oxidative stress in heart and erythrocytes from rats with abdominal aorta coarctation (Coa) compared with sham-operated normotensive controls (Sham). The group of Coa animals developed myocardial hypertrophy, showing heart homogenates markedly increased levels of reduced glutathione (48%), lipid peroxidation (148%) and activation of superoxide dismutase and glutathione peroxidase (189% and 37%, respectively), compared with controls. Other oxidative stress indicators were also altered in erythrocytes from Coa rats: increased protein carbonyl content (141%) and total glutathione level (349%) were determined. Inactivation of the antioxidant enzymes catalase (27%), superoxide dismutase (58%) and glutathione peroxidase (25%) was observed in erythrocytes from the Coa group. Taken jointly our results provide strong evidence for the production of oxidative stress in heart and erythrocytes from aortic coarcted rats.

[Cytohistological and immunohistochemical characteristics of vascular remodelling in diseases of the blood vessels]

INTRODUCTION

Vascular remodelling is an adaptive process involving the adjustment of the structure and function of blood vessels to long-term changes in haemodynamic conditions. This process leads to structural alterations within vessel walls in different cardiovascular diseases, such as hypertension, atherosclerosis, and coarctation of the aorta.

OBJECTIVE

We investigated the histochemical and immunocytochemical characteristics of morphological lesions in coronary atherosclerosis and coarctation of the aorta.

METHOD

Twenty-one samples of atherosclerotically modified right coronary arteries, divided into 6 segments, were analysed. We also examined 10 samples of coarctation segments, excised during surgery. The segments were stained histochemically (using orcein and alcian blue-PAS), immunocytochemically (using alpha-smooth muscle actin-alpha-SMA, vimentin, desmin, myosin heavy chains-MHC, CD3, CD45, S-100, and Proliferating Cell Nuclear Antigen-PCNA), and for electron microscopy.

RESULTS

The results of our study of morphological lesions in coronary atherosclerosis demonstrated initial functional and then, in the later stages of atherosclerosis, morphological, damage to the endothelium. The preatheroma stage revealed the presence of intimal dedifferentiation of smooth muscle cells, with the expression of vimentin and alpha-SMA, and the lack of expression of desmin. Along with these changes, a huge number of foam cells of variant origin were noticed. Some of them were CD68-immunoreactive while others were both vimentin- and S-100-immunoreactive. All examined samples of the coarctation of the aorta demonstrated the presence of dedifferentiated smooth muscle cells as well as a diminution in cell numbers, followed by apoptotic smooth muscle cells, and the absence of inflammatory cells.

CONCLUSION

Some foam cells develop from monocyte-macrophage lineage (CD68-immunoreactive), while others originate from smooth muscle cells (vimentin and S-100-immunoreactive). Coarctation of the aorta is characterised by a diminution in cell numbers (apoptosis) as well as their dedifferentiation from contractile to synthetic phenotype.

Hypothalamic Antihypertensive Effect of Irbesartan in Chronic Aortic Coarctated Rats

The aim of the present work was to study the central and plasma pharmacokinetics of irbesartan (IRB) and its possible hypothalamic antihypertensive effect in sham-operated (SO) and aortic-coarctated (ACo) rats at a chronic hypertensive stage using the microdialysis technique. Anesthetized Wistar rats were used 42 days after ACo or SO. For the study of plasma pharmacokinetics, a vascular shunt probe was inserted into the carotid artery. In a separated experiment, a concentric probe was placed into the anterior hypothalamus for the study of IRB distribution in the central nervous system. Based on the hypothalamic concentrations of IRB reached in ACo rats, the anterior hypothalamus of SO and ACo animals was perfused with a Ringer solution containing approximately 6 microg x ml(-1) of the drug. IRB (10 mg x kg(-1) i.v.) induced a late decrease of heart rate (HR) in ACo animals (DeltaHR: -42 +/- 10 bpm, n = 5, p < 0.05 vs. SO rats) but not in SO rats (DeltaHR: 11 +/- 13 bpm, n = 5). Systemic administration of the drug reduced the mean arterial pressure (MAP) of both experimental groups, but the hypotensive effect was greater in ACo (DeltaMAP: -39.9 +/- 5.0 mm Hg, n = 5, p < 0.05 vs. SO rats) than in SO rats (DeltaMAP: -25.4 +/- 2.1 mm Hg, n = 5). A similar pharmacokinetic profile was observed in both experimental groups. Hypothalamic distribution of IRB was greater in ACo (AUC: 730 +/- 130 ng x ml(-1) h(-1), n = 5, p < 0.05 vs. SO rats) than in SO animals (AUC: 283 +/- 87 ng x ml(-1) h(-1), n = 5). The IRB hypothalamic perfusion induced an antihypertensive effect in ACo (DeltaMAP: -15.1 +/- 1.0 mm Hg, n = 5, p < 0.05 vs. Ringer perfusion) but not in SO rats. In conclusion, the chronic aortic coarctation did not modify the plasma pharmacokinetics of IRB, but it increased the distribution of the drug in the central nervous system. The greater hypotensive effect of IRB observed in ACo animals suggests the involvement of AT1 receptors in the maintenance of the hypertensive stage in chronic ACo rats. The hypotensive effect of IRB in ACo animals could be explained, at least in part, due an action on the anterior hypothalamic angiotensin system.

Altered expression of dystrophin within the thoracic aorta in coarctation

Although persisting endothelial dysfunction has been established in the vasculature of patients following surgical repair of coarctation, it is unknown whether there are alterations in the cytoskeleton of the aorta in such patients. We compared staining of N-terminus dystrophin in the smooth muscle of the aortic wall of a patient with coarctation to that in a patient without coarctation, the latter undergoing surgical treatment of a double aortic arch. There was a marked difference in the pattern of expression of dystrophin between the two, with the coarcted specimen demonstrating marked fragmentation but normal intensity of staining. As far as we are aware, ours is the first report to demonstrate the presence of dystrophin in the smooth muscle of the aorta. Alterations in the cytoskeletal structure may account for underlying aberrations in endothelial function in such patients, and is a topic that warrants further investigation.

Anterior hypothalamic beta-adrenoceptors in chronic aortic-coarctated hypertensive rats: An interaction with central angiotensin II receptors

1. The aim of the present study was to investigate the activity of anterior hypothalamic beta-adrenoceptors and angiotensin (Ang) II receptors on blood pressure in normotensive rats and aortic-coarctated (ACo) animals at a chronic stage of hypertension. A possible interaction between beta-adrenoceptors and AngII pressor activity was also investigated. 2. Injection of isoproterenol (0.1-10 nmol) in the anterior hypothalamic area induced a dose-dependent decrease in mean arterial pressure (MAP) in sham-operated (SO), but not in ACo, animals. Isoproterenol (1 nmol) reduced blood pressure in SO rats (DeltaMAP -10.1+/-1.4 mmHg; n=10) but not in ACo animals (DeltaMAP -0.9+/-1.6 mmHg; n=10; P<0.05 vs SO rats). Whereas previous administration of atenolol (40 nmol) enhanced the cardiovascular effect of isoproterenol (1 nmol) in ACo rats but not in SO animals, propranolol (40 nmol) prevented the hypotensive action of isoproterenol in both experimental groups. Intrahypothalamic administration of clenbuterol decreased MAP in a dose-dependent manner; however, the depressor response to clenbuterol (10 nmol) was greater in ACo rats than in SO rats (DeltaMAP -26.8+/-3.2 vs -14.4+/-2.4 mmHg, respectively; n=5 for both; P<0.05). When AngII (50 ng) was injected into the anterior hypothalamic area, a greater pressor response was observed in ACo rats than in SO rats (DeltaMAP 19.6+/-1.1 vs 11.3+/-0.6 mmHg, respectively; n=5 for both; P<0.05). Atenolol (40 nmol) pretreatment partially and significantly prevented the pressor response to AngII in ACo rats, but not in SO rats. 3. In conclusion, these results provide pharmacological evidence for the existence of a beta1-adrenoceptor-mediated pressor mechanism in the anterior hypothalamic area of ACo rats that is absent in SO rats. The enhanced depressor beta2-adrenoceptor activity observed in chronic ACo rats could be a compensatory adjustment to pressor beta1-adrenoceptor activity. Conversely, pressor overactivity of AngII was observed in the anterior hypothalamic area of ACo rats at a chronic hypertensive stage; this enhancement could be explained, at least in part, by the pressor beta1-adrenoceptor activity.

[Cytohistologic and immunohistochemical characteristics of the aortic intima and media in coarctation of the aorta of the adult type]

INTRODUCTION

Classically, coarctation of the aorta has been divided into infantile and adult forms. The vascular malformation responsible for coarctation is a defect of the vessel intima and media giving rise to a prominent posterior infolding ("the posterior shelf") which, in some cases, may extend around the entire circumference of the aorta. Histological examination of the coarcted aortic segment discloses intimal and medial lesion consisting of thickened ridges that protrude posteriorly into the aortic lumen. Intimal proliferation and disruption of elastic tissue may occur in adult type.

OBJECTIVE

The smooth muscle cells phenotype in the aortic intimal thickening, presence of inflammatory cells and contents of the intimal and medial pseudocysts were investigated.

MATERIAL AND METHODS

The samples of coarctation segments excised at surgery from 10 patients aged from 2 to 13 years were examined. For light microscopy, the specimens were dehydrated in graded ethanol (70-100%), cleared in xylol and embedded in paraffin. Sections of 5 microm thick were cut on Leica SM 2000R and Leica Reinhart Austria microtome and stained with orcein and Alcian blue-PAS at pH 1.0 and pH 2.5. Immunocytochemical staining was performed on 5 microm sections from formaldehyde-fixed paraffin-embedded blocks, using a labeled streptavidin-biotin method with an LSAB kit (Dako). Sections were deparaffinized and rehydrated. After microwave treatment of 21 minutes in citrate buffer pH 6.0, endogenous peroxidase activity was blocked with 3% H2O2 for 15 minutes. The sections were first incubated with the primary antibody for 60 minutes (alpha-smooth muscle actin-alpha-SMA, vimentin, desmin, myosin haevy chains-MHC, CD3, CD45, S-100 and Proliferating Cell Nuclear Antigen-PCNA), then with biotinylated link antibody and finally with peroxidase-labeled streptavidin. Slides were counter-stained with hematoxylin, washed in water and mounted. For electron microscopy, the primary fixative consisted of 2.5% glutaraldehyde in 0.1 M sodium cacodylate-HCl buffer (pH 7.4) for 24 h at 4 degrees C. The specimens were postfixed for 1 h at 4 degrees C in 1% osmium tetroxide in 0.1 M cacodylate buffer and 4.8% uranyl acetate for 24 h at 4 degrees C. The samples were dehydrated in graded ethanol (70-100%) and embedded in Epon 812. The samples were cut with a diamond knife on an LKB Ultratome. Ultra-thin sections were stained with 2% uranyl acetate and alkaline lead citrate.

RESULTS

All samples had focal intimal thickening on the posterior aortic wall, with accumulation of mucins which were stained with Alcian blue-PAS on pH 1.0, followed by prominent hypocellularity. Rare smooth muscle cells (SMC) showed immunoreactivity on alpha-SMA and vimentin, but not on desmin, MHC or CD3 and CD45. A large number of cells in apoptosis was noticed in the inner media on the posterior wall. On the anteromedial wall, a large number of PCNA- and S-100- positive cells was noted in the inner media while one layer of MHC- and desmin-positive cells was noted in the outer media. The elastic lamellae were focally disrupted by pools which were stained with Alcian blue-PAS at pH 1.0.

DISCUSSION

In all examined samples, the immunocytochemical and TEM results revealed the presence of dedifferentiated smooth muscle cells which express alpha-SMA and vimentin, with a lack of expression of desmin and MHC. Results of this study also showed the reduction of cell number in the intima and media, followed by apoptotic smooth muscle cells in the inner media of the posterior wall and the absence of inflammatory cells. Such finding suggests that apoptosis but not necrosis may be the mechanism of reduction of cell number. The presence of smooth muscle cell proliferation in the inner media of the anteromedial wall and one layer of differentiated SMC in the outer part may lead us to suppose that changes of media (including dedifferentiation of the cells and disruption of elastic tissue) appear from inner to outer part and from posterior to anteromedial wall. The presence of pseudocysts which are stained with Alcian blue-PAS at pH 1.0 show large amount of mucins in elastic fibers.

CONCLUSION

The intimal thickening on the posterior aortic wall is composed of small number of dedifferentiated smooth muscle cells (SMC). Some of these cells are in apoptosis. On the anteromedial wall, the intima and media are composed of proliferated SMC and small number of SMC which exhibit contractile phenotype. In all parts of the aortic wall, there is a large number of pseudocysts with large amount of mucins, without presence of inflammatory cells.

Effects of transforming growth factor-beta1 and signal protein Smad3 on rat cardiomyocyte hypertrophy

BACKGROUND

SMAD proteins have recently been identified as the first family of putative transforming growth factor-beta1 (TGF-beta1) signal transducers. This study was to investigate the effects of TGF-beta1 and signal protein Smad3 on rat cardiac hypertrophy.

METHODS

The incorporation of [(3)H]-leucine was measured to determine the hypertrophy of cardiomyocyte incubated with different doses of TGF-beta1 in cultured neonatal cardiomyocytes. The model of rat cardiac hypertrophy was produced with constriction of the abdominal aorta. At different times after the operation, rats were killed, and their left ventricular mass index (LVMI) determined. The mRNA expression of TGF-beta1 and Smad3 of cultured cells and hypertrophic left ventricles were assessed by RT-PCR. The protein expression of Smad3 was assessed by Western blot.

RESULTS

In cultured neonatal cardiomyocytes, TGF-beta1 significantly promoted incorporation of [(3)H]-leucine. With the concentration of 3 pg/L, it increased the expression of Smad3 in mRNA and protein levels after 15 minutes, and continued for up to 8 hours of cultured cardiomyocytes. The LVMI and the expression of TGF-beta1 (mRNA) and Smad3 (mRNA and protein) of hypertrophic left ventricle were increased by day 3 after the operation and continued to the 4th week. The peak expression of these was in the second week after operation.

CONCLUSION

TGF-beta1 has positive effects on rat cardiomyocyte hypertrophy. Signal protein Smad3 could be related to the pathologic progression of rat cardiac hypertrophy.

Gene expression of tropoelastin is enhanced in the aorta proximal to the coarctation in rabbits

To assess elastin biosynthesis in the aortic wall in response to acute elevation of blood pressure, we studied the aortic gene expression of tropoelastin in a rabbit midthoracic aortic coarctation model. The time points of the study were 1, 3, and 7 days and 2, 4, and 8 weeks after coarctation. Additional animals were subjected to hypercholesterolemia for analysis of tropoelastin expression in the intimal lesion. mRNA for tropoelastin was quantitated by Northern blot analysis and its distribution was revealed by in situ hybridization. The 65-kDa tropoelastin was analyzed by Western blotting and immunohistochemistry. Tropoelastin mRNA proximal to the coarctation was increased at 2 weeks and returned to baseline by 8 weeks (P < 0.05 versus control). Changes in 65-kDa tropoelastin corresponded to those of mRNA. Tropoelastin gene was expressed mainly in the intima and in the outer media at the proximal region to the stenoses, which was particularly remarkable in the intimal lesion. The results indicate that tropoelastin gene expression was enhanced in the early remodeling response to elevated blood pressure. The distribution of newly synthesized tropoelastin in the outer media suggests a reenforcement role of tropoelastin, which preserves mechanical resiliency in response to changes in tensile stress.

Hypertrophy and functional alterations in hyperdynamic phospholamban-knockout mouse hearts under chronic aortic stenosis

OBJECTIVE

To determine whether the hyperdynamic phospholamban-knockout hearts are capable of withstanding a chronic aortic stenosis.

METHODS

The transverse section of the aorta was banded in phospholamban-knockout and their isogenic wild-type mice, which were followed with echocardiography in parallel, along with sham-operated mice, before and at 2.5, 5 and 10 weeks after surgery.

RESULTS

Cardiac decompensation was evidenced by the presence of lung congestion in some banded knockouts and wild-types, giving rise to a subset of non-failing and failing hearts within each group. The incidence of heart failure was not genotype-dependent but rather associated with higher heart rates before surgery. The development of left ventricular hypertrophy was similar between knockouts and wild-types and longitudinal assessment of end-diastolic dimension indicated progressive increases after banding, with a greater dilation in failing mice. Fractional shortening was reduced in failing knockouts and wild-types to a similar degree, with an earlier onset in the knockouts. In addition, fractional shortening was decreased in non-failing knockouts but not wild-types. Ejection times shortened after aortic banding particularly for failing hearts. Assessment of the SR Ca(2+)-ATPase protein levels indicated similar downregulation for failing knockouts and wild-types, while the phospholamban levels were not significantly altered in wild-types.

CONCLUSION

The hyperdynamic phospholamban-knockout hearts are able to compensate against a sustained aortic stenosis similar to wild-types.

Pharmacokinetic and pharmacodynamic alterations of methyldopa in rats with aortic coarctation. A study using microdialysis

A pharmacokinetic-pharmacodynamic study of methyldopa (MD) was made in anesthetized sham operated (SO) and aortic coarctated (ACo) rats by using a vascular shunt probe for arterial microdialysis and simultaneous blood pressure recording. Anesthetized Wistar rats were used 7 days after aortic coarctation or sham operation. A vascular shunt probe was inserted into the carotid artery and a concentric probe was placed into the striatum or posterior hypothalamus. MD and 3,4-dihydroxyphenylacetic acid (DOPAC) were determined in the dialysates by HPLC-EC. MD (50 mg kg(-1)i.p.) induced an increase of heart rate in SO (Delta HR: 108 +/- 22 bpm, n= 6) and in ACo rats (Delta HR: 55 +/- 10 bpm, n= 6, P< 0.05, one way ANOVA). Moreover, MD also reduced the mean arterial pressure (MAP) of SO rats (Delta MAP: -10 +/- 4 mmHg, n= 6) and ACo animals (Delta MAP: -51 +/- 9 mmHg, n= 6, P< 0.05, one way ANOVA). Analysis of the arterial blood dialysates showed a lower half-life of MD in ACo rats (t(1/2): 1.5 +/- 0.3 h, n= 6, P< 0.05, 't' test) than in SO rats (t(1/2): 3.7 +/- 1.0 h, n= 6). A low accumulation and a fast decay of striatal MD levels were seen in ACo rats. However, peak levels of drug were greater in the hypothalamic dialysates of ACo rats than in SO animals samples. On the other hand, MD also induced an increase of DOPAC levels in the hypothalamic dialysates of ACo rats. In conclusion, the aortic coarctation modifies the pharmacokinetic and cardiovascular effect of MD in the rat. The action of this drug on dopaminergic neurotransmission is also altered in the ACo animals.

Rat renal prorenin concentration in experimental hypertension

The amount of renal prorenin in models of hypertension in rats was studied by using a novel enzyme (PreR-Co). Ten microgrames of PreR-Co promoted a complete conversion of inactive renin, and during the first 15-min incubation the reaction was under initial velocity conditions. The enzyme-substrate reaction obeyed Michaelis-Menten kinetics, with a Vmax of 0.97 x 10(-5) pmol Ang I/min and a Km of 5.03 x 10(-5) pmol prorenin. The difference between the total renin concentration (TRC) and active renin concentration (ARC) in the normal rat kidney (356.4 +/- 20.6 and 105.3 +/- 7.6 ng Ang I/mg tissue/h respectively), indicated that inactive renin comprised 70% of TRC. In the aortic coarctation model, inactive renin comprised 68 % of TRC in the right kidney and no or very little prorenin was found in the left kidney. In the Goldblatt 2-kidney, 1-clip rats, the right kidney prorenin comprised 61% of the TRC and 54% in the clamped left kidney. After DOCA-Salt treatment prorenin was almost absent in the rat kidneys. In conclusion, we have developed an easy and sensitive method to measure inactive renin in the kidney that may be useful to study the biochemical events of renin maturation in physiological and pathological states.

Differential transmural distribution of gene expression for collagen types I and III proximal to aortic coarctation in the rabbit

To assess the effects on the biosynthesis of collagen types I and III associated with an acute increase in blood pressure, we established a mid-thoracic aortic coarctation in the rabbit and studied gene expression and protein accumulation of these collagen types proximal to the stenosis 1, 3 and 7 days and 2, 4 and 8 weeks after coarctation. The mRNA level of type I collagen pro-alpha2(I) was maximal at 3 days and returned to normal at 4 weeks. mRNA of pro-alpha2(I) was localized mainly in the outer media, adventitia and intima. Accumulation of type I collagen and its precursors was increased by 3 days, peaked at 4 weeks, and decreased toward normal by 8 weeks, corresponding to the distribution of pro-alpha2(I) mRNA. Gene expression for pro-alpha1(III) was similar to that of pro-alpha2(I) but was distributed throughout the media. We conclude that the mechanical stresses associated with an acutely induced alteration in pressure initiate rapid gene expression for collagen types I and III in the aortic wall. The response for collagen type I, predominantly in the outer media and adventitia, suggests that these regions play an immediate role in the resistance to excessive dilatation of the aorta. The diffuse response for collagen type III in the media suggests participation in a more extensive remodeling response associated with the reinforcement and reorganization of the musculo-elastic fascicles.

Na,K-ATPase and Ca-ATPase activities of the myocardial sarcolemma in aging rats after aorta coarctation: role of invertors

In this work we used aorta coarctation as a model of myocardial hypertrophy. We studied the role of intracellular regulators of plasma membrane status-invertors-in the mechanisms of changes of membrane enzyme activities in the emergency stage of myocardial hypertrophy. We used Wistar rats of various ages: adult (6-8 months) and old (26-28 months) rats. It was shown that 4-6 days after aorta coarctation, in adult rats the activities of both Na,K-ATPase and Ca-ATPase of the sarcolemma of cardiomyocytes increased, but in old rats only the Ca-ATPase activity. Experiments with cell hybrids (cytosol of experimental rats and isolated sarcolemma of cardiomyocytes of intact rats) revealed that cytosol of cardiomyocytes of adult animals after aorta coarctation activated Na, K-ATPase and Ca-ATPase. Cytosol of old intact animals after aorta coarctation did not activate Na,K-ATPase, but activated Ca-ATPase. It was supposed that 4-6 days after aorta coarctation, intracellular regulators (invertors) activating Na,K-ATPase and Ca-ATPase of rat sarcolemma were synthesized in cytosol of adult animals. Invertors activating Na,K-ATPase did not appear after the aorta coarctation in old animals, but factors activating Ca2+-ATPase appeared. Cytosol of adult experimental rats activated Na,K-ATPase of sarcolemmas of cardiomyocytes of intact old animals. The data proved the ability of Na,K-ATPase of sarcolemma of old animals to respond to regulating factors. Based on the divergence between the results of experiments with the Na,K-ATPase and Ca-ATPase activities in old rats, it can be supposed that we were dealing with two different invertors.

Cyclooxygenase-2 inhibition decreases renin content and lowers blood pressure in a model of renovascular hypertension

It has been proposed that the macula densa participates in the regulation of increased renin expression in renovascular hypertension (RVH) and that prostaglandins may be among the mediators of macula densa function. We have previously shown that in renal cortex, cyclooxygenase-2 (COX-2) expression is localized to the macula densa and surrounding cortical thick ascending limb and increases in high-renin states, such as salt restriction and angiotensin-converting enzyme inhibition. In the present studies, we examined the effect of the selective COX-2 inhibitor SC58236 on plasma renin activity (PRA) and renal renin expression in RVH in rats. The aorta was coarcted between right and left renal arteries, and animals received either SC58236 or vehicle for 1 week. At day 8, vehicle-treated coarcted rats were hypertensive (mean carotid arterial blood pressure: 138+/-3 versus 87+/-2 mm Hg in sham-operated controls; n=9 to 11; P<0.001) and exhibited a disparity of kidney size (ratio left/right kidney: 0.78+/-0.04 versus 1.02+/-0.02; n=9 to 10; P<0.001). PRA increased significantly (84.6+/-6.5 versus 9.0+/-1.4 ng angiotensin I [Ang I] per milliliter per hour; n=8 to 9; P<0.01). In the coarcted rats, neither renin mRNA expression nor renin activity of the right kidney was altered (renin/GAPDH mRNA: 1.12+/-0.05-fold levels in control rats; n=6; P=NS; renin activity: 23.4+/-1.8 versus 27.1+/-3.4 ng Ang I per hour per milligram protein; n=8 to 9; P=NS). However, the renin mRNA of the left kidney increased to 3.0+/-0.6-fold of control (n=6), and the renin activity increased to 189.0+/-28.6 ng Ang I per hour per milligram protein (n=8; P<0.01). Expression of COX-2 mRNA and immunoreactive protein increased in the affected left kidney but was not different from control in the unaffected right kidney. SC58236 treatment to coarcted rats did not affect kidney size (ratio left/right kidney: 0.79+/-0.06; n=9). However, PRA was significantly decreased compared with the vehicle-treated coarcted rats (19.8+/-2. 8 ng Ang I per milliliter per hour; n=9; P<0.01). The left kidney renin mRNA and renin content were also decreased (1.7+/-0.3-fold control; n=6; P<0.05; and 45.7+/-7.6 ng Ang I per hour per milligram protein; n=9; P<0.01, respectively), while renin mRNA and renin content of the right kidney were not altered. SC58236 lowered mean arterial blood pressure (122+/-5 mm Hg; n=14; P<0.05 compared with vehicle). A significant correlation was observed between PRA and mean blood pressure (r=0.75; P<0.01). In summary, these studies indicate that the selective COX-2 inhibitor SC58236 decreases renin production and release in RVH and suggest an important role for COX-2 regulation of the renin-angiotensin system.

Effects of aminopeptidase P inhibition on kinin-mediated vasodepressor responses

We studied in anesthetized rats whether aminopeptidase P (AMP) may be involved in bradykinin (BK) metabolism and responses. For this we inhibited AMP with the specific inhibitor apstatin (Aps). Studies were done with Aps alone or together with the angiotensin-converting enzyme inhibitor lisinopril (Lis). Aps increased the vasodepressor response to an intravenous bolus of BK (400 ng/kg): vehicle, -3.0 +/- 0.7 mmHg; Aps, -7.8 +/- 0.7 mmHg (P < 0.01 vs. vehicle); Lis, -23.8 +/- 1.8 mmHg; Aps + Lis, -37.5 +/- 1.9 mmHg (P < 0.01 vs. Lis). Aps did not affect the vasodepressor response to BK given into the descending aorta. Plasma BK increased only in Aps + Lis-treated rats (in pg/ml): control, 48.0 +/- 1.4; Lis, 57.5 +/- 7.6; Aps + Lis, 121. 8 +/- 30.6 (P < 0.05 vs. control or Lis), whereas in rats infused with BK (400 ng. kg-1. min-1 for 5 min), Aps increased plasma BK (in pg/ml): control, 51.9 +/- 2.5; Aps, 83.5 +/- 20.5; Lis, 725 +/- 225; Aps + Lis, 1,668 +/- 318 (P < 0.05, Aps vs. control and Lis vs. Aps + Lis). In rats with aortic coarctation hypertension, the acute antihypertensive effects of Aps plus Lis were greater than Lis alone (P < 0.01). Hoe-140, a BK B2-receptor antagonist, abolished the difference. We concluded that in the rat AMP contributes to regulation of BK metabolism and responses.

Increased NPY activity in the PVN contributes to food-restriction induced reductions in blood pressure in aortic coarctation hypertensive rats

We hypothesized that hypothalamic NPYergic mechanisms mediate the blood pressure lowering effect of caloric restriction in hypertensive rats. Aortic coarctation-induced (AC) hypertensive rats (n=25) were assigned to either an ad libitum fed control group (AL) or food restricted group (FR; 60% of AL consumption) for 3 weeks. Rats were instrumented chronically with vascular catheters and bilateral guide cannulae directed at the paraventricular hypothalamic nuclei (PVN). Blood pressure (BP) and heart rate (HR) responses to bilateral PVN microinjection of saline (200 nl) or the putative NPY receptor antagonists [D-Trp32]NPY(1-36) (3.3 micrograms/200 nl) and [D-Tyr27,36 Thr32]NPY(27-36) (D-NPY(27-36); 3.3 micrograms/200 nl) were determined. The FR rats were then refed and cardiovascular responses to PVN injections of NPY receptor antagonists were again determined. FR rats had significantly reduced resting BP (159+/-4 vs. 129+/-4 mmHg) and HR (360+/-11 vs. 326+/-9 bpm) compared to AL controls. Refeeding restored BP and HR of FR rats to levels similar to AL (BP=153+/-4 mmHg, HR=359+/-11 bpm). PVN administration of [D-Trp32]NPY produced foraging behavior and concurrent increases in BP and HR in FR, AL and Re-fed rats. The behavioral activation suggests that [D-Trp32]NPY(1-36) produced activation of NPY receptors. In contrast, D-NPY (27-36) did not produce any behavioral response or affect BP or HR in AL or Re-fed rats. In FR rats, D-NPY (27-36) produced significant increases in BP (peak=15+/-3 mmHg) which partially reversed the effect of FR on BP. Thus, in FR rats with reduced BP, PVN administration of an NPY receptor antagonist increases BP. NPY blockade in the PVN accounted for about 50% of the BP effect of food restriction, thus other mechanisms are likely to be involved. These findings are consistent with the hypothesis that NPYergic mechanisms may contribute to the reduction of BP produced by food restriction.

Immunohistological and ultrastructural analysis of the intimal thickening in coarctation of human aorta

OBJECTIVES

The histological nature and characteristics of aortic coarctation are not clearly defined, the aim of this study is to analyse intimal thickening in aortic coarctation.

METHODS

In order to characterize the components of intimal thickening in coarctation, narrowed segments of aorta obtained after surgery from ten children were examined immunocytochemically and by electron microscopy.

RESULTS

Histological analysis of aortic coarctation demonstrated a widened subendothelial region with separation of endothelial cells from the internal elastic lamina. Masson's trichrome staining showed a marked increase in extracellular matrix and cell numbers in the intimal thickening compared with normal aorta. Cellular component analysis demonstrated invagination of the intima by smooth muscle actin-positive cells, with a fragmentation of the internal elastic lamina. No proliferating smooth muscle and inflammatory cells were identified in the intima. In order to characterize the smooth muscle cell phenotypes, various smooth muscle cell markers were sought using specific monoclonal antibodies: alpha-smooth muscle actin, smooth muscle-myosin heavy chain, heavy caldesmon, desmin. In moderate coarcted aorta, at least two distinct smooth muscle phenotypes were identified. In the juxtamedial part of the intima smooth muscle, cells were differentiated and expressed all smooth muscle markers; in the subendothelial part of the intimal thickening, the majority of smooth muscle cells expressed only alpha-smooth muscle actin and appeared dedifferentiated. In regions of marked stenosis, a strong expression of smooth muscle-myosin heavy chain, and heavy caldesmon in the intimal thickening pointed to the presence of redifferentiated smooth muscle cells, not still expressing desmin. Electron microscopic examination also revealed a variety of smooth muscle cell phenotypes in the intimal thickening. In the superficial layer, smooth muscle cells appeared to be in the synthetic state, while in the deeper part, both synthetic and contractile components were identified.

CONCLUSIONS

These observations indicated that human coarctation was characterized by intimal recruitment of non-proliferating smooth muscle cells with dedifferentiated phenotype. However, the presence of smooth muscle cells with an intermediate phenotype in the narrowest part of the coarctation suggest that the redifferentiation process could participate in the pathogenesis of aortic coarctation.

Effect of increased afterload on cardiac lipoprotein lipase and VLDL receptor expression

Fatty acids are a major source of fuel for energy production by myocytes. Lipoprotein lipase (LPL) and very low density lipoprotein (VLDL) receptor are abundantly expressed by the heart and skeletal muscles. LPL and possibly VLDL receptor represent the primary route of access to fatty acids contained in circulating triglyceride-rich lipoproteins. Physical exercise and thyroid hormone, which promote energy consumption, upregulate LPL expression in skeletal muscles. This study tested the hypothesis that increased cardiac workload might modulate myocardial LPL and/or VLDL receptor expressions. Accordingly, cardiac tissue LPL activity, LPL and VLDL receptor proteins and mRNA abundance were studied in Sprague-Dawley rats 4 weeks after induction of severe thoracic aorta constriction or sham operation. Elevation of afterload with thoracic aortic constriction led to a significant cardiomegaly and a marked upregulation of cardiac LPL activity, LPL mRNA and LPL protein abundance, but did not modify VLDL receptor mRNA or protein abundance. Thus, increased cardiac workload in this model results in upregulation of myocardial LPL expression which can enhance fatty acid availability to accommodate the heart's increased energy requirement.

Connexin43 is highly localized to sites of disturbed flow in rat aortic endothelium but connexin37 and connexin40 are more uniformly distributed

Vascular endothelial cells are linked by gap junctions, which facilitate the propagation of electrical and chemical signals along the vessel wall. The aim of this study was to determine the distribution and identity of the gap junction structural proteins (connexins) expressed by endothelial cells in situ. Connexin expression in different regions of the rat aortic endothelium was analyzed with the use of indirect immunofluorescence microscopy and Western blotting. Connexin40 and connexin37 were present in most, if not all, of the thoracic and abdominal aortic endothelia in the form of maculae at cell-cell appositions. In contrast, connexin43 was undetectable in most endothelia but extremely abundant in small numbers of cells localized at the downstream edge of the ostia of branching vessels and at flow dividers, regions that experience turbulent shear stress from disturbed blood flow. To examine the relationship of shear stress and connexin43 expression, localized stress was induced by surgical coarctation of the aorta, which was sufficient to cause striking local upregulation of connexin43 within 8 days. Thus, increases in connexin43 levels are an endothelial response to mechanical stress.

[The effect of aortic coarctation on nitric oxide production by the vascular endothelium]

Nitric oxide is an important regulator of vascular tone. Deficiencies in nitric oxide release have been implicated in hypertension. In the present study we evaluated vascular reactivity to phenylephrine and acetylcholine in isolated aorta ring preparations from sham and aortic coarctation-induced hypertensive rats and nitric oxide release under resting conditions and after stimulation with acetylcholine. Aortic vessels were divided in upper segment and lower segment in relation to the coarctation; both segments were tested for vascular reactivity and nitric oxide release. Phenylephrine produced higher vasoconstriction in upper segments from hypertensive rats compared to sham operated animals. Lower segments in both experimental groups were not significantly different. Relaxation produced by acetylcholine showed a higher EC50 in the upper segments from hypertensive rats; lower segments in both experimental groups were not significantly different. Aortic rings from hypertensive rats had a higher level of nitric oxide release compared to sham operated rats. Lower segments from hypertensive rats released significantly more nitric oxide. These results suggest that shear stress induced nitric oxide release in lower aortic segments from aortic coarctation-induced hypertensive rats.

Hypoplastic aortic arch morphology pertinent to growth after surgical correction of aortic coarctation

BACKGROUND

Whether a hypoplastic transverse arch will grow after successful coarctectomy remains controversial.

METHODS

We studied 15 coarctation specimens with hypoplastic transverse arch. Eight patients were less than 1 month old and 7 were between 1 and 3 months. The diameter and length of the various segments of the aortic arch were measured. The number of elastin lamellae was determined histologically. Collagen density was quantified with a microdensitophotometer. Using immunohistochemistry, we determined alpha-actin-positive smooth muscle cells in the media of the ascending aorta and the hypoplastic transverse arch.

RESULTS

Despite a hypoplastic transverse arch, the ascending and descending aorta grew. The absolute number of elastin lamellae in the hypoplastic transverse arch was low, but when expressed as a ratio versus its diameter, this number was high (p < 0.05). Collagen density showed high absolute values in the descending aorta. In the older group, 4 of 7 showed no staining for alpha-actin in the hypoplastic transverse arch, whereas under 1 month of age, only 2 of 8 cases were negative.

CONCLUSIONS

The hypoplastic transverse arch is characterized by a relatively high number of elastin lamellae. Fewer alpha-actin-positive cells in the hypoplastic transverse arch occur in older specimens, which could indicate a diminished potential growth.

Excessive anaerobic metabolism during exercise after repair of aortic coarctation

OBJECTIVES

To determine whether survivors of surgery for coarctation of the aorta (CoA) have an excessive reliance on anaerobic metabolism during exercise.

BACKGROUND

Patients with peripheral vascular disease cannot increase blood flow to their muscles normally during exercise. Consequently they acquire an early, excessive reliance on anaerobic metabolism and have depression of the ventilatory anaerobic threshold (VAT) and of the slope of the oxygen consumption-work rate relationship (delta VO2/delta WR). We speculated that the capacity to augment blood flow to the lower extremities during exercise may be impaired after CoA surgery and would result in similar metabolic disturbances.

STUDY DESIGN

Progressive exercise tests were performed on 15 patients (ages 19 +/- 7 years; range, 10 to 32) after successful repair of CoA (residual resting gradient, 7.7 +/- 7.1 mm Hg; range, 0 to 18), 15 age- and sex-matched healthy control subjects, and 10 patients (ages 13 +/- 3 years; range, 10 to 20) who had undergone ligation of a patent ductus arteriosus.

RESULTS

The CoA patients' VAT averaged 14.8 +/- 3.8 ml O2/kg per minute versus 19.3 +/- 3.1 ml O2/kg per minute for the control subjects (p < 0.01), and their delta VO2/delta WR averaged 8.2 +/- 1.8 ml/watt compared with 10.1 +/- 1.4 ml/watt for control subjects (p < 0.01). Furthermore, 10 of 15 CoA patients had a VAT of less than 40% of predicted maximal oxygen consumption, and 9 of 16 had a delta VO2/delta WR of less than 8.7 ml O2/watt (generally accepted abnormal values). Patients with patent ductus arteriosus resembled the healthy control subjects with regard to anaerobic metabolism during exercise.

CONCLUSIONS

Patients who have had CoA repairs commonly manifest an excessive reliance on anaerobic metabolism during exercise. This phenomenon may result from persistent blood flow abnormalities across the aortic arch during exercise, which may be present even after apparently successful surgery.

Eflornithine alters changes in vascular responsiveness associated with coarctation hypertension

This study examined the temporal effects of the polyamine synthesis inhibitor eflornithine (alpha-difluoromethylornithine) on vascular responses to KCI, norepinephrine, sodium nitroprusside and acetylcholine in aortic rings from coarctation hypertensive rats. Coarctation hypertension reduced the contractile response of aortic rings to KCI and norepinephrine, increased sensitivity (reduced the EC50 value) to norepinephrine and attenuated relaxation to acetylcholine by 14 days of hypertension. Treatment of coarctation hypertensive rats with eflornithine resulted in a normalization of the contractile intensity to KCI and norepinephrine and relaxations to acetylcholine by 14 days of hypertension. Responses to sodium nitroprusside were similar in all groups at all time points. Hyperresponsiveness to norepinephrine produced by coarctation of the aorta was not affected by eflornithine. These studies indicate that normalization of vascular function can occur in the presence of significantly elevated blood pressure upon chronic administration of eflornithine. This functional normalization correlates with eflornithine-mediated regression of structural abnormalities normally associated with pressure overload hypertension.

Multiple polyamine regulatory pathways control compensatory cardiovascular hypertrophy in coarctation hypertension

While a number of factors may initiate structural alterations within the cardiovascular system in response to hypertension, there are obligate cellular signaling mechanisms, such as the polyamines, through which they must operate. This study examined the effects of polyamine synthesis inhibition using eflornithine, a suicide inhibitor of ornithine decarboxylase on blood pressure, compensatory remodeling of the cardiovascular system, and cardiac and aortic polyamine contents using an aortic coarctation model in rats. Eflornithine treatment failed to reduce carotid arterial blood pressure and actually significantly elevated vascular pressure above and below the coarctation site by 14 days of hypertension. Eflornithine only transiently reduced aortic polyamine content of hypertensive rats while this agent reduced coarctation-induced aortic medial wall thickening and the synthesis/deposition of fibronectin and laminin in the hypertensive aorta. Increases in left ventricular mass and polyamine content were concomitantly reduced in hypertensive rats administered eflornithine. These results suggest that multiple polyamine regulatory pathways may maintain vascular polyamine content in response to aortic coarctation; however de novo polyamine synthesis is essential for select aspects of vascular remodeling, including matrix synthesis. Cardiac tissue, in contrast, may rely principally on de novo polyamine synthesis.

Hypertension increases insulin-like growth factor binding protein-4 mRNA levels in rat aorta

Insulin-like growth factor-I (IGF-I) is an endocrine and autocrine/paracrine growth factor. Recently, we have demonstrated that interrenal aortic coarctation in the rat increases IGF-I mRNA levels in the thoracic aorta, consistent with a role for this mitogen in hypertensive vascular remodeling. The effects of IGF-I are modulated by several IGF binding proteins including IGFBP-3, the main circulating carrier of IGF-I, and IGFBP-4, the main IGF binding protein produced by vascular smooth muscle cells in vitro. To obtain insights into the regulation of IGF-I and more specifically to study potential changes in IGF binding proteins in high-renin hypertension, we studied male Sprague-Dawley rats that had undergone abdominal aortic coarctation. Compared with sham-operated rats, the study rats showed a rapid increase in IGFBP-4 mRNA levels in the hypertensive (thoracic) aorta, reaching a plateau at 3 days (2.5-fold increase) and persisting for at least 14 days. In striking contrast, IGFBP-4 mRNA decreased slightly in the normotensive (abdominal) aorta at 14 days. IGFBP-3 mRNA levels did not change in either vascular bed after coarctation. Study of hepatic tissue indicated that in coarcted rats IGFBP-4 and IGFBP-3 mRNA levels decreased transiently (approximately 50% at 7 days compared with sham). Circulating IGF-I in coarcted animals decreased slightly (P = .08), and Western ligand analysis indicated that circulating levels of IGF binding proteins were not altered.(ABSTRACT TRUNCATED AT 250 WORDS)

Guanine nucleotide-binding proteins in aortic smooth muscle from hypertensive rats

To explore the hypothesis that altered vascular muscle signal transduction may underlie some of the vascular changes observed in hypertensive models, we measured expression of GTP-binding protein (G protein) alpha-subunits, Gs, G(i), and Gq, in aortic muscle of reduced renal mass and sham-operated rats and proximal and distal aortic segments from rats with interrenal aortic coarctation (IR-AC). G protein expression was measured by immunoblot analysis. When we probed aortic muscle membrane with G(i) and Gq alpha-subunit antibodies, we identified 41- and 42-kD immunoreactive proteins, respectively. Three immunoreactive bands specific to Gs alpha-subunit antibody were resolved. Immunoreactive blot densities were compared. In aortic muscle membrane of reduced renal mass rats (blood pressure, 148 +/- 7 mm Hg), we found significantly reduced Gs and G(i) blot densities compared with sham-operated controls (blood pressure, 99 +/- 12 mm Hg). There were no differences in Gq blot densities between reduced renal mass and control rats. Gs and G(i) blot densities were significantly lower in IR-AC proximal aortic segments (carotid pressure, 165 +/- 5 mm Hg) and distal aortic segments (femoral pressure, 121 +/- 4 mm Hg) than in aortas of sham-operated controls. In contrast, Gq expression was significantly increased in the high-pressure proximal aortic segments compared with low-pressure distal aortic segments from IR-AC rats. Thus, altered G protein expression occurs in aortic muscle from nongenetic rat models of hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Membrane current changes in left ventricular myocytes isolated from guinea pigs after abdominal aortic coarctation

OBJECTIVE

The aim was to look for membrane current changes as a basis for the prolongation of action potential duration in left ventricular myocytes following abdominal aortic coarctation.

METHODS

Immature female guinea pigs underwent laparotomy and an aortic coarctation was fashioned immediately distal to the renal arteries. After 20 weeks the hearts were removed and single myocytes were isolated from the left ventricles by standard enzymatic techniques. The switch-clamp technique was used.

RESULTS

Heart weight:body weight ratio was increased by 7% in the coarctation group (p < 0.01). Systolic left ventricular pressure was 59(SEM 4) mm Hg in control and 76(7) mm Hg in coarctation animals (p < 0.05). Cell capacity was increased by 21% in the coarctation group (p < 0.05), and mean resting potential was 4.6 mV more negative in this group (p < 0.001). Action potential duration at 90% repolarisation was 310(17) ms in the control group (n = 22) and 358(13) ms in the coarctation group (n = 34, p < 0.05). Peak density of L-type calcium current was -8.6(0.4) pA.pF-1 in control and -11.1(0.7) pA.pF-1 in coarctation cells (p < 0.01). The regression line for calcium current versus cell capacity was shifted to higher calcium currents in the coarctation group. The half inactivation potential for this current was shifted by 11.5 mV (p < 0.01). Calcium-activated tail currents were larger and the envelope of tail currents was prolonged in the coarctation cells. No significant differences were found in the amplitude of IK or of IKl.

CONCLUSIONS

After infrarenal aortic coarctation, action potential duration of left ventricular myocytes is prolonged. This prolongation may be attributed to an increase in calcium current density and a shift of its inactivation variable, together with an increased magnitude and prolonged time course of sodium-calcium exchange current. These current changes are potentially arrhythmogenic.

Decreased perfusion pressure modulates renin and ANG II type 1 receptor gene expression in the rat kidney

To determine whether decreased perfusion pressure affects the abundance and distribution of renin and its mRNA and the expression of the angiotensin II type 1 (AT1) receptor gene within the kidney, adult male Sprague-Dawley rats were subjected to aortic coarctation proximal to the renal arteries (Coarc, n = 8) and compared with sham-operated rats (Sham, n = 6). Renal renin distribution was determined by immunocytochemistry using a specific polyclonal antibody against rat renin. Renin mRNA was assessed by in situ hybridization to a 35S-labeled oligonucleotide complementary to rat renin mRNA. Kidney AT1 mRNA levels were determined by Northern analysis using a 1,133-base pair rat AT1 cDNA. Femoral arterial blood pressure, measured 24 h after surgery, was lower in Coarc than in Sham rats (75 +/- 5.4 vs. 122 +/- 2.3 mmHg, P < 0.05). Aortic coarctation increased the percent of juxtaglomerular apparatuses (%JGA) containing renin and its mRNA (85 +/- 2.5 and 66 +/- 2.8 vs. 49 +/- 5.3 and 36 +/- 1.7%, Coarc vs. Sham, P < 0.05) and the intensity of hybridization signals (497 +/- 89 vs. 71 +/- 12 grains/JGA, Coarc vs. Sham, P < 0.05). In addition, recruitment of renin gene expressing cells was observed along afferent arterioles in Coarc rats, whereas renin and its mRNA were limited to the JGAs in Sham rats. Renal AT1 receptor gene expression was threefold lower in Coarc than in Sham rats. We conclude that reduction of perfusion pressure after abdominal aortic coarctation acutely enhances renin gene expression and downregulates AT1 receptor gene expression.(ABSTRACT TRUNCATED AT 250 WORDS)

The vascular smooth muscle alpha-actin gene is reactivated during cardiac hypertrophy provoked by load

Cardiac hypertrophy triggered by mechanical load possesses features in common with growth factor signal transduction. A hemodynamic load provokes rapid expression of the growth factor-inducible nuclear oncogene, c-fos, and certain peptide growth factors specifically stimulate the "fetal" cardiac genes associated with hypertrophy, even in the absence of load. These include the gene encoding vascular smooth muscle alpha-actin, the earliest alpha-actin expressed during cardiac myogenesis; however, it is not known whether reactivation of the smooth muscle alpha-actin gene occurs in ventricular hypertrophy. We therefore investigated myocardial expression of the smooth muscle alpha-actin gene after hemodynamic overload. Smooth muscle alpha-actin mRNA was discernible 24 h after coarctation and was persistently expressed for up to 30 d. In hypertrophied hearts, the prevalence of smooth muscle alpha-actin gene induction was 0.909, versus 0.545 for skeletal muscle alpha-actin (P less than 0.05). Ventricular mass after 2 d or more of aortic constriction was more highly correlated with smooth muscle alpha-actin gene activation (r = 0.852; P = 0.0001) than with skeletal muscle alpha-actin (r = 0.532; P = 0.009); P less than 0.0005 for the difference in the correlation coefficients. Thus, smooth muscle alpha-actin is a molecular marker of the presence and extent of pressure-overload hypertrophy, whose correlation with cardiac growth at least equals that of skeletal alpha-actin. Induction of smooth muscle alpha-actin was delayed and sustained after aortic constriction, whereas the nuclear oncogenes c-jun and junB were expressed rapidly and transiently, providing potential dimerization partners for transcriptional control by c-fos.

Dynamics of shear-induced redistribution of F-actin in endothelial cells in vivo

The steady-state responses of endothelial cell F-actin distribution to changes in in vivo shear stress have been well documented. The purpose of the current work was to define the dynamics of redistribution of F-actin in the period immediately after experimental changes in shear. We used abdominal aortic coarctation in rabbits to experimentally increase shear stress downstream from the coarctation by approximately twofold. In situ staining was employed to track subsequent F-actin redistribution. Within 12-15 hours, the number of stress fibers in the central regions of the cells decreased, and some separation of junctional actin in adjacent cells occurred. Long, central stress fibers of variable thickness were evident at 24 hours, but the band of actin normally seen at the periphery of the cells could no longer be distinguished. The redistribution of F-actin was completed over the next 24 hours by an increase in thickness of central stress fibers. Restoration of normal F-actin distribution after coarctations were removed proceeded more slowly. The long, thick stress fibers that were induced by high shear were replaced by thinner or shorter microfilament bundles 48 hours after the coarctations were removed. At 72 hours, central stress fibers were primarily long, thin structures. Peripheral F-actin was not fully restored at this time. Peripheral F-actin was restored at 1 week after removal of the coarctation, but there were still more and longer stress fibers at this time than were observed in control aortas.(ABSTRACT TRUNCATED AT 250 WORDS)

Aortic glutathione-related antioxidant defences in rabbits subjected to suprarenal aortic coarctation hypertension

In seven rabbits subjected to suprarenal aortic coarctation hypertension, the segments above and below the coarctation were tested for the antioxidant defences (i.e. acid-soluble thiol compounds, selenium-dependent and selenium-independent glutathione peroxidase, glutathione reductase, glutathione transferase) and thiobarbituric acid-reactive substances. Seven sham-operated rabbits served as controls. Systolic blood pressure proximal to the ligature increased significantly with respect to pre-operative values after 16 days (117 +/- 8.3 vs 71.7 +/- 5.2 mmHg, P less than 0.05), while pressure distal to the ligature remained normotensive. Higher values of acid-soluble thiol compounds, thiobarbituric acid-reactive substances and increased activities of selenium-dependent glutathione peroxidase, glutathione reductase and glutathione transferase were assayed in the suprarenal with respect to the subrenal segment in both groups. However, the values of the upper segments were more elevated in the experimental group than in controls, but no differences were observed in the lower segments. Glutathione peroxidase activity assayed with cumene hydroperoxide was higher than the activity assayed with hydrogen peroxide in the hypertensive segments, but no differences were detected in the substenotic and control segments. Furthermore, an isoenzymatic form of glutathione transferase, analogous to rat 8-8 glutathione transferase isoenzyme, was detected by immunodiffusion in the hypertensive aorta. The following conclusions may be drawn: (1) a biochemical gradient in glutathione-related enzymes, acid-soluble thiol compounds and thiobarbituric acid-reactive substances between the proximal and distal aorta seems to exist in control rabbits; (2) suprarenal aortic coarctation induces a significant increase in glutathione-related antioxidant defences and thiobarbituric acid-reactive substances of the hypertensive aortic wall.

[The system of cyclic nucleotides during myocardial hyperfunction and hypertrophy in rats of various ages]

Simulation of myocardial hyperfunction and hypertrophy in rats exhibited the age- and hypertrophy step-dependent alterations in the system of cyclic nucleotides. Significant activation of the HC-cGMP system, decrease in content of cAMP and stimulation of the AC activity were detected in old animals at the emergency step. At the later steps content of cAMP and the AC stimulated activity were increased more distinctly in adult rats as compared with old animals. These alterations were responsible for age-related peculiarities of myocardial contractility at the emergency step as well as for development of hypertrophy at the later steps. The cyclase system appears to facilitate the age-related adaptation of myocardium to overloading during the old age.

Localization of cytoplasmic collagen mRNA in human aortic coarctation: mRNA enhancement in high blood pressure-induced intimal and medial thickening

Enhanced synthesis and deposition of extracellular matrix components, including collagen, contribute significantly to arteriosclerotic changes in the arterial vessel wall. We localized cells actively synthesizing collagen by hybridizing 35S-labeled RNA probes complementary to type I and III collagen mRNA with cytoplasmic mRNA in frozen sections of surgically removed aortic coarctations. These were chosen as a model for comparing mRNA levels in areas of high blood pressure-induced wall thickening and in unaffected post-stenotic areas. In situ hybridization revealed increased expression of type I and III collagen mRNA in intimal cells and in cells adjacent to the medial-adventitial border in the pre-stenotic part of the coarctation. In contrast, cells of the post-stenotic area showed only a very low signal. No immunohistologically detectable macrophages were seen in the pre-stenotic subendothelial areas where mRNA levels were enhanced. Higher collagen mRNA levels therefore occur in particular regions of high blood pressure-induced arterial wall thickening in the absence of macrophages. The results suggest that in situ hybridization is suitable for detection of locally occurring transcriptional activation of cells for collagens in the vessel wall.

[The lipid and phospholipid composition of the myocardium in hyperfunction caused by aortic coarctation]

It is shown that in the first 10-12 days of heart hyperfunction caused by subdiaphragmatic constriction of the aorta adaptational changes in lipid metabolism develop in the myocardium in addition to its hypertrophy. These changes are capable of leading to reduced viscosity of the myocardial membranes and activation of enzymatic processes providing for the intensified work of the heart.

Atrial natriuretic peptide and its messenger ribonucleic acid in overloaded and overload-released ventricles of rat

To study the occurrence of atrial natriuretic peptide (ANP) in overloaded ventricles, suprarenal aortic coarctation was performed on adult rats (n = 60) to induce overloaded left ventricle. In 36 rats, the overloads were released in 2 weeks. The hearts (6 rats in each group) were examined 2, 7, and 14 days after overload and 2, 7, 19, 47, and 77 days after overload release. Another group of 6 rats was coarctated for the second time for 1-6 days after 14 days of coarctation and 7 days of release. ANP immunoreactivity was examined by light and electron microscopic immunocytochemistry. ANP mRNA was studied by RNA-RNA tissue in situ hybridization. ANP immunoreactivity and ANP mRNA were found in the left ventricle 2 days after coarctation, and their amounts increased in proportion to the intraventricular pressure and the duration of coarctation. Two days after release, ANP and its mRNA began to decrease, but at 77 days ANP-containing granules still existed in the ventricular myocytes, whereas its mRNA became undetectable. The second coarctation triggered the release of the remaining ventricular ANP from the first overload and induced another cycle of increased ANP synthesis. Specific granules that do not contain ANP were found in overload-released ventricles, indicating the possible existence of other peptide hormones. These findings suggest that the extents of ventricular ANP gene expression and ANP synthesis and release are regulated by intraventricular pressure, and the occurrence of ANP in overloaded ventricles may not be a transient, immediately reversible phenomenon.

Aortic hypertrophy and "waterlogging" in the development of coarctation hypertension

To study the mechanisms and roles of vascular structural changes during the development of hypertension, we coarcted or sham-coarcted the abdominal aorta of rats. At intervals of 3 to 56 days later, we obtained standardized segments of thoracic and abdominal aortas for measurement of dry weight, water content, and amino acid content. Carotid arterial pressure was elevated by day 5 in coarcted rats and remained elevated. Femoral and tail arterial pressures remained normal. Cardiac ventricular weight and dry weight of the thoracic aorta, normalized for body weight, rose rapidly over 3-10 days in coarcted rats, remaining constant at 50-60% above levels in sham-coarcted rats thereafter. In contrast, water content of thoracic aorta in coarcted rats peaked at 123% of control values on day 7 (p less than 0.001), falling rapidly thereafter to levels about half of peak. Increments in dry weight and water content of the normotensive abdominal aortic segments were of far lesser magnitude and occurred 1 to 2 weeks later, probably reflecting the effects of initial hypotension of the hindquarters. Percent hydroxyproline of intima-media segments of the thoracic aorta remained normal during the 8-week period, indicating that increases in aortic dry weight did not represent disproportional fibrosis and thus are attributable to muscular hypertrophy. These results provide support for the hypothesis that arterial wall "waterlogging" is primarily an early manifestation of the hypertensive process. The greatest magnitude of waterlogging coincides with the rapid early increase in aortic dry weight, representing hypertrophy, which suggests common mechanisms, such as activation of Na+-H+ antiport.

Atrial natriuretic factor gene expression in rat ventricle during experimental hypertension

Activation of atrial natriuretic factor (ANF) gene expression has been reported in the rat ventricle in several models of hemodynamic overload, including hypertension. However, nothing is known about the potential trigger(s) and the time course of this activation during the development of hypertension. We measured aortic blood pressure, left ventricular hypertrophy (LVH), and left ventricular ANF mRNA concentration (LV ANF mRNA) in a first group of rats (study A) killed at 5 and 18 h and 2, 4, 6, 9, 15, and 30 days after suprarenal coarctation of the abdominal aorta. Coarctation induced a progressive rise in aortic blood pressure and left ventricular mass. We observed a biphasic accumulation of ANF mRNA in the left ventricle with a peak at day 4 averaging 20 times the control value long before stable hypertension and hypertrophy were achieved, followed by a decrease until day 9. This decrease was followed by a new rise, which stabilized around 10 times the control value seen during stable hypertension and hypertrophy. In a second group of rats killed at days 4 and 30 (study B), we determined, in addition to the previous parameters, left ventricular end-diastolic pressure (LVEDP), plasma renin (PRC), and plasma ANF concentrations. LVEDP and PRC were markedly increased at day 4, but at day 30, during stable hypertension and hypertrophy, these parameters returned to control values, whereas plasma ANF was increased. Using immunocytochemistry, we looked in a third group of rats (study C) for the presence of the immunoreactive peptide at days 4 and 30.(ABSTRACT TRUNCATED AT 250 WORDS)

Exaggerated renal thromboxane and prostaglandin release by angiotensin II in suprarenal aortic coarctation hypertension

The ability of angiotensin II and arachidonic acid to release immunoreactive prostaglandins into venous and ureteral effluents of rabbit isolated perfused kidneys was examined 7 days after suprarenal aortic coarctation (SRAC) or sham operation (SHAM). Renal vascular responses to angiotensin II were significantly enhanced in SRAC and accompanied by an enhanced venous efflux of bioassayable prostaglandins. Angiotension II-induced release of immunoreactive PGE2, PGF2 alpha, 6-keto PGF1 alpha and TxB2 into the venous effluent was exaggerated in SRAC. As angiotensin II did not stimulate TxB2 efflux in the SHAM group the induction of TxB2 release by SRAC is particularly noteworthy. These changes in eicosanoid release in response to angiotensin II were not mimicked by arachidonic acid administration. These results suggest that in renovascular hypertension angiotensin II-induced prostaglandin release is primarily augmented in the vascular compartment and is consistent with the sensitivity of renal function to cyclooxygenase inhibitors in renovascular hypertension.

Direct correlation between calcium content and blood pressure: a study of aortic coarctation in rats

The calcium content of aorta was measured by atomic absorption after coarctation in the rat. At 7 and 14 days, the calcium content was elevated on the proximal side of the coarctation, where pressure was increased significantly. On the distal, low pressure side of the aortic coarctation, calcium was reduced significantly. There is a direct correlation between the blood pressure and the content of calcium (r = 0.69, P less than 0.001). The width of the aortic media on the high pressure side was increased significantly at 7 and 14 days after coarctation, whereas no significant changes in width were present on the low pressure side of the constriction. We conclude that pressure regulates the aortic calcium content, likely acting through a local effect.

Aortic wall metabolism in relation to susceptibility and resistance to experimental atherosclerosis

Different segments of the aorta and its branches show differing susceptibilities to atherosclerosis. To identify metabolic features that may account for plaque formation and sparing, we studied aortic wall respiration and glycolysis proximal and distal to an aortic coarctation in 30 rabbits fed a standard or atherogenic diet. Three months after coarctation, blood pressure in the proximal aorta was elevated, and plaque occupied 98% +/- 28% of the intimal surface compared with 57% +/- 26% for control animals (p less than 0.05). Aortic pressure distal to the stenosis remained normal, but plaque formation was markedly decreased (5% +/- 4%) compared with controls (30% +/- 27%, p less than 0.05). Metabolic studies included measurement of oxygen consumption of proximal and distal aortic walls, lactic acid production, and 2-deoxyglucose uptake. Elevated pressure or hyperlipidemia increased respiration (22.6 +/- 4.0 or 16.3 +/- 6.0 pmol oxygen consumed/min/microgram deoxyribonucleic acid [DNA] vs 5.8 +/- 5.2 for controls; p values less than 0.05) without increasing glycolytic metabolism. The coexistence of hypertension and hyperlipidemia resulted in maximal plaque formation and a sevenfold increase in both oxidative metabolism (46.6 +/- 27.2 pmol oxygen consumed/min/microgram DNA vs 5.8 +/- 5.2 for controls, p less than 0.004) and glycolytic metabolism (44 +/- 10 ng lactic acid produced/90 min/microgram DNA vs 6 +/- 3 for controls, p less than 0.004). In the spared aortic segment distal to coarctation, glycolytic metabolism was increased (10 +/- 8 ng lactic acid produced/90 min/microgram DNA vs 2 +/- 1 for controls, p less than 0.05) but oxidative metabolism remained normal.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial beta-receptors in experimental renal and aortic coarctation hypertensive rabbits

We investigated the effect of inducing two-kidney, one clip (2K, 1C) and aortic coarctation (AC) hypertension in rabbits, on myocardial beta-adrenoreceptor number and affinity, using 3H-dihydroalprenolol as a beta-ligand. Six weeks after surgery, mean arterial blood pressures were: sham-operated controls C, 75.6 +/- 2.3 mmHg (n = 11); 2K-1C 96.3 +/- 2.5 mmHg (n = 6, P less than 0.005); and AC, 114.1 +/- 4.8 mmHg (n = 10, P less than 0.0005). Bmax values at six weeks for C, 2K,-1C and AC were 234.5 +/- 35.7, 139.0 +/- 10.3 (P less than 0.05) and 121.0 +/- 12.8 (P less than 0.005) fmol/mg protein respectively. There were no differences in KD. Both 2K, 1C and AC hypertension significantly decreased myocardial beta-receptor density; this may be a 'down-regulatory' response to increased circulating or myocardial catecholamine concentrations or to enhanced sympathetic activity.

Muscle substrate levels, muscle enzyme activities and muscle morphology in the vastus lateralis and deltoideus muscles in normal children and in children with coarctation of the aorta

Muscle biopsies from the deltoideus dx and vastus lat. dx muscles were taken in 17 children with coarctation of the aorta, aged 5.0 to 13.8 years, prior to surgery. Higher concentrations of glycogen, ATP and CP were found in the vastus lat. muscle compared to the deltoideus muscle. The same differences between these two muscles were also found in healthy controls. No differences were found between the patients with coarctation of the aorta and the control group. Nor were any differences found for the other variables studied; glucose, glucose-6-phosphate, lactate, muscle enzyme activities (SDH, LDH and phosphorylase), muscle fibre composition or fibre sizes. It seems reasonable to assume that the differences in muscle substrate levels found between the vasus lat. and the deltoideus muscles in the two groups were due to a higher degree of activity during daily life for the legs as compared to the arms. Patients with coarctation of the aorta do not seem to be influenced by the altered haemodynamic situation with regard to the studied variables.