Enhanced cardiac angiotensinogen gene expression and angiotensin converting enzyme activity in tachypacing-induced heart failure in rats

Animal models of arrhythmia: classic electrophysiology to genetically modified large animals

Arrhythmias are common and contribute substantially to cardiovascular morbidity and mortality. The underlying pathophysiology of arrhythmias is complex and remains incompletely understood, which explains why mostly only symptomatic therapy is available. The evaluation of the complex interplay between various cell types in the heart, including cardiomyocytes from the conduction system and the working myocardium, fibroblasts and cardiac immune cells, remains a major challenge in arrhythmia research because it can be investigated only in vivo. Various animal species have been used, and several disease models have been developed to study arrhythmias. Although every species is useful and might be ideal to study a specific hypothesis, we suggest a practical trio of animal models for future use: mice for genetic investigations, mechanistic evaluations or early studies to identify potential drug targets; rabbits for studies on ion channel function, repolarization or re-entrant arrhythmias; and pigs for preclinical translational studies to validate previous findings. In this Review, we provide a comprehensive overview of different models and currently used species for arrhythmia research, discuss their advantages and disadvantages and provide guidance for researchers who are considering performing in vivo studies.

Alteration at transcriptional level of cardiac renin-angiotensin system by letrozole treatment

INTRODUCTION

The use of aromatase inhibitors (AIs) for breast cancer led to a marked change in ventricular function. Since accumulating evidence indicates that overactivation of the cardiac renin-angiotensin system (RAS) plays an important role in the development of cardiovascular diseases such as hypertrophy and remodelling, we aimed to investigate whether letrozole alters the transcription level of RAS related genes in the cardiac tissue.

METHODS

Twenty four rats were randomly divided into four groups (n = 6 per group): two groups were letrozole treated (1 and 2 mg/kg/day orally), one group was vehicle treated (DMSO) and one group was the control group without any treatment. 12 weeks after beginning treatment with letrozole, we examined the rate of transcription of renin, angiotensinogen, AngII type 1a and 1b (AT1a and AT1b) and type 2 receptors (AT2) in the rat heart using real-time polymerase chain reaction.

RESULTS

The cardiac mRNA levels of several components of the RAS in the rats treated with letrozole were significantly increased including AT1a receptor (80%), renin (51%), and angiotensinogen (33%). Though not significant, AT2 receptor levels were observed to decrease with increasing doses of letrozole.

CONCLUSIONS

Letrozole can induce significant changes in some RAS related genes. These alterations are important to understand the pathways and consequences beyond cardiac events induced by breast cancer treatments.

Cardiac intracrine renin angiotensin system. Part of genetic reprogramming?

The hypothesis that intracrine renin-angiotensin system activated during heart failure is part of the tendency of the heart to return to embryological conditions when organogenesis is possible is presented and discussed. The hypothesis proposes that the change in genetic makeup, which is known to occur during heart failure, includes a drastic change of intercellular chemical and electrical communication such as second messengers and other signal molecules which are involved in cell proliferation and growth. The role of angiotensin II, which is a growth factor, reduces cell coupling in the failing heart through the activation of AT1 receptors and intracellular pathways, such as PKC, MAPK family and increment of intracellular calcium, might play a key role in the genetic reprogramming of the failing heart.

Angiotensinogen gene M235T polymorphism predicts left ventricular hypertrophy in endurance athletes

OBJECTIVES

We studied whether left ventricular mass in athletes associates with polymorphisms in genes encoding components of the renin-angiotensin system.

BACKGROUND

Adaptive left ventricular hypertrophy is a feature of the athlete's heart. However, similarly training athletes develop left ventricular mass to a different extent, suggesting that genetic factors may modulate heart size.

METHODS

We measured left ventricular mass by echocardiography in 50 male and 30 female elite endurance athletes aged 25 +/- 4 (mean +/- SD) years. Deoxyribonucleic acid samples were prepared for genotyping of angiotensinogen (AGT) gene M235T polymorphism, angiotensin-converting enzyme (ACE) gene insertion/deletion (I/D) polymorphism and angiotensin II type 1 receptor (AT1) gene A1166C polymorphism.

RESULTS

The AGT gene M235T genotypes were significantly associated with left ventricular mass independently of blood pressure in both genders (p = 0.0036 for pooled data). TT homozygotes had greater mass compared with MM homozygotes in both men (147 +/- 12 g/m vs. 132 +/- 15 g/m, p = 0.032) and women (121 +/- 12 g/m vs. 101 +/- 13 g/m, p = 0.019). There was a gender difference in the relation between myocardial mass and AGT genotype, MT heterozygotes resembling MM homozygotes among women and TT homozygotes among men. The other studied gene polymorphisms were not associated with left ventricular mass.

CONCLUSIONS

Angiotensinogen gene M235T polymorphism is associated with the variability in left ventricular hypertrophy induced by endurance training, with athletes homozygous for the T allele having the largest hearts. We found no association between ACE gene I/D or AT1 gene A1166C polymorphisms and left ventricular mass.

Synergistic exacerbation of diastolic stiffness from short-term tachycardia-induced cardiodepression and angiotensin II

Synergistic interaction between angiotensin II (Ang II) and evolving cardiodepression may play an important role in worsening chamber function, particularly in diastole. To test this hypothesis, Ang II was infused at 10 or 17 ng.kg(-1).min(-1) in 18 conscious dogs 4 days before and during induction of subacute cardiodepression by 48-hour tachypacing. The lower dose yielded negligible systemic pressure changes. Twelve additional animals served as paced-only controls. Pressure-dimension relations were recorded, and serial endocardial biopsies were obtained to assess histological and metalloproteinase (MMP) changes. Forty-eight-hour pacing alone depressed systolic function but had little effect on diastolic stiffness. Ang II alone only modestly raised diastolic stiffness at both doses and enhanced contractility at the higher dose. These changes recovered toward baseline after a 7-day infusion. However, Ang II (at either dose) combined with 48-hour pacing markedly increased ventricular stiffness (110+/-26% over baseline) and end-diastolic pressure (22+/-1.7 mm Hg). In contrast, pacing-induced inotropic and relaxation abnormalities were not exacerbated by Ang II. Zymography revealed MMP activation (72- and 92-kD gelatinases and 52-kDa caseinase) after a 4-day Ang II infusion (at both doses), which persisted during pacing. Tachypacing initiated 24 hours after cessation of a 7-day Ang II infusion also resulted in diastolic stiffening and corresponded with MMP reactivation. Ang II also induced myocyte necrosis, inflammation, and subsequent interstitial fibrosis, but these changes correlated less with chamber mechanics. Thus, Ang II amplifies and accelerates diastolic dysfunction when combined with evolving cardiodepression. This phenomenon may also underlie Ang II influences in late-stage cardiomyopathy, when chamber distensibility declines.

Association of angiotensin-converting enzyme gene I/D polymorphism with change in left ventricular mass in response to physical training

BACKGROUND

The absence (deletion allele [D]) of a 287-base pair marker in the ACE gene is associated with higher ACE levels than its presence (insertion allele [I]). If renin-angiotensin systems regulate left ventricular (LV) growth, then individuals of DD genotype might show a greater hypertrophic response than those of II genotype. We tested this hypothesis by studying exercise-induced LV hypertrophy.

METHODS AND RESULTS

Echocardiographically determined LV dimensions and mass (n=140), electrocardiographically determined LV mass and frequency of LV hypertrophy (LVH) (n=121), and plasma brain natriuretic peptide (BNP) levels (n=49) were compared at the start and end of a 10-week physical training period in male Caucasian military recruits. Septal and posterior wall thicknesses increased with training, and LV mass increased by 18% (all P<.0001). Response magnitude was strongly associated with ACE genotype: mean LV mass altered by +2.0, +38.5, and +42.3 g in II, ID and DD, respectively (P<.0001). The prevalence of electrocardiographically defined LVH rose significantly only among those of DD genotype (from 6 of 24 before training to 11 of 24 after training, P<.01). Plasma brain natriuretic peptide levels rose by 56.0 and 11.5 pg/mL for DD and II, respectively (P<.001).

CONCLUSIONS

Exercise-induced LV growth in young males is strongly associated with the ACE I/D polymorphism.

Increased angiotensin-converting enzyme activity in the left ventricle after infarction

An increase in angiotensin-converting enzyme (ACE) activity has been observed in the heart after myocardial infarction (MI). Since most studies have been conducted in chronically infarcted individuals exhibiting variable degrees of heart failure, the present study was designed to determine ACE activity in an earlier phase of MI, before heart failure development. MI was produced in 3-month old male Wistar rats by ligation of the anterior branches of the left coronary artery, control rats underwent sham surgery and the animals were studied 7 or 15 days later. Hemodynamic data obtained for the anesthetized animals showed normal values of arterial blood pressure and of end-diastolic pressure in the right and left ventricular cavities of MI rats. Right and left ventricular (RV, LV) muscle and scar tissue homogenates were prepared to determine ACE activity in vitro by measuring the velocity of His-Leu release from the synthetic substrate Hyp-His-Leu. ACE activity was corrected to the tissue wet weight and is reported as nmol His-Leu g-1 min-1. No significant change in ACE activity in the RV homogenates was demonstrable. A small nonsignificant increase of ACE activity (11 +/- 9%; P > 0.05) was observed 7 days after MI in the surviving left ventricular muscle. Two weeks after surgery, however, ACE activity was 46 +/- 11% (P < 0.05) higher in infarcted rats compared to sham-operated rats. The highest ACE activity was demonstrable in the scar tissue homogenate. In rats studied two weeks after surgery, ACE activity in the LV muscle increased from 105 +/- 7 nmol His-Leu g-1 min-1 in control hearts to 153 +/- 11 nmol His-Leu g-1 min-1 (P < 0.05) in the remaining LV muscle of MI rats and to 1051 +/- 208 nmol His-Leu g-1 min-1 (P < 0.001) in the fibrous scar. These data indicate that ACE activity increased in the heart after infarction before heart failure was demonstrable by hemodynamic measurements. Since the blood vessels of the scar drain to the remaining LV myocardium, the high ACE activity present in the fibrous scar may increase the angiotensin II concentration and decrease bradykinin in the cardiac tissues surrounding the infarcted area. The increased angiotensin II in the fibrous scar may contribute to the reactive fibrosis and hypertrophy in the left ventricular muscle surviving infarction.

Evidence for the existence of a functional cardiac renin-angiotensin system in humans

BACKGROUND

The presence of mRNA for the essential components of the renin-angiotensin system (RAS) has been found in animal and human hearts. The present study was designed to provide evidence for the existence of a (functional) cardiac RAS.

METHODS AND RESULTS

Twenty-four patients with atypical chest pain undergoing coronary angiography for diagnostic purposes were investigated. The cardiac production rate of angiotensins was estimated by measurement of the cardiac extraction of 125I-angiotensin I and 125I-angiotensin II associated with the determination of endogenous angiotensins in aortic and coronary sinus blood in normal, low, or high sodium diets. In a normal sodium diet, angiotensin I and II aorta-coronary sinus gradients were tendentially negative (-1.8 +/- 2.5 and -0.9 +/- 1.7 pg/mL, respectively), and the amounts of angiotensin I and II added by cardiac tissues were 6.5 +/- 3.1 and 2.7 +/- 1.3 pg/mL, respectively. The low sodium diet caused a significant increase in both plasma renin activity (PRA) and angiotensin I concentration in aortic but not in coronary sinus blood, resulting in a more negative aorta-coronary sinus gradient (-9.7 +/- 3.1 pg/mL, P < .01). Angiotensin formation by PRA in blood during transcardiac passage increased (P < .001), whereas angiotensin I formed by cardiac tissues decreased dramatically. Accordingly, in the low sodium diet, 125I-angiotensin II extraction did not change, the cardiac fractional conversion rate of 125I-angiotensin I to 125I-angiotensin II notably decreased (P < .01), and angiotensin II formation by cardiac tissues was undetectable. The high sodium diet caused a decrease in PRA and no changes in cardiac extraction of radiolabeled angiotensins; conversely, angiotensin I formed by cardiac tissues, cardiac Ang I fractional conversion rate, and angiotensin II formed during transcardiac passage significantly (P < .01 for all) increased.

CONCLUSIONS

These results provide evidence for the existence of a functional cardiac RAS independent of but related to the circulating RAS.

Local stress, not systemic factors, regulate gene expression of the cardiac renin-angiotensin system in vivo: a comprehensive study of all its components in the dog

Cardiac hypertrophy is associated with altered expression of the components of the cardiac renin-angiotensin system (RAS). While in vitro data suggest that local mechanical stimuli serve as important regulatory modulators of cardiac RAS activity, no in vivo studies have so far corroborated these observations. The aims of this study were to (i) examine the respective influence of local, mechanical versus systemic, soluble factors on the modulation of cardiac RAS gene expression in vivo; (ii) measure gene expression of all known components of the RAS simultaneously; and (iii) establish sequence information and an assay system for the RAS of the dog, one of the most important model organisms in cardiovascular research. We therefore examined a canine model of right ventricular hypertrophy and failure (RVHF) in which the right ventricle (RV) is hemodynamically loaded, the left ventricle (LV) is hemodynamically unloaded, while both are exposed to the same circulating milieu of soluble factors. Using specific competitive PCR assays, we found that RVHF was associated with significant increases in RV mRNA levels of angiotensin converting enzyme and angiotensin II type 2 receptor, and with significant decreases of RV expression of chymase and the angiotensin II type 1 receptor, while RV angiotensinogen and renin remained unchanged. All components remained unchanged in the LV. We conclude that (i) dissociated regional regulation of RAS components in RV and LV indicates modulation by local, mechanical, not soluble, systemic stimuli; (ii) components of the cardiac RAS are independently and differentially regulated; and (iii) opposite changes in the expression of angiotensin converting enzyme and chymase, and of angiotensin II type I and angiotensin II type 2 receptors, may indicate different physiological roles of these RAS components in RVHF.

Association between an angiotensinogen microsatellite marker in children and coronary events in their grandparents

BACKGROUND

Recently we found that the deletion (D) allele of the insertion/deletion (I/D) polymorphism of the ACE gene in 404 children was associated with a history of coronary artery disease (CAD) in their grandparents. This led us to explore polymorphisms in other genes of the renin-angiotensin system in this same population.

METHODS AND RESULTS

We determined the genotypes for three microsatellite markers located near or in the angiotensinogen, angiotensin II (type-1) receptor, and renin genes in the children and related the allele frequencies to grandparental CAD. We found a significant association between the angiotensinogen marker in children and grandparental CAD (chi2 = 42.2, P = .00001) with these children having an excess of the 125-bp and 129-bp alleles (odds ratio, 2.5; 95% confidence interval, 1.7 to 3.7). Greatest grandparental risk was when their grandchildren had the 125-bp/125-bp, 129-bp/129-bp, or 125-bp/129-bp genotypes (odds ratio, 7.75; 95% confidence interval, 2.2 to 27). There was no association between the microsatellites at either the angiotensin II (type-1) receptor (P = .8) or renin (P = .2) genes in children and grandparental CAD and none between the angiotensinogen and ACE polymorphisms in relation to CAD family history.

CONCLUSIONS

This study identifies a significant association between an angiotensinogen marker in children and grandparental CAD. There was no association between the microsatellites at either the angiotensin II (type-1) receptor or renin genes and CAD in this population. We conclude that the angiotensinogen polymorphism as well as the ACE polymorphism may explain a part of the risk related to a family history of CAD.

Angiotensin-converting enzyme inhibition and the progression of congestive cardiomyopathy. Effects on left ventricular and myocyte structure and function

BACKGROUND

Clinical trials have demonstrated that angiotensin-converting enzyme inhibition (ACEI) improves survival in patients with long-term left ventricular (LV) dysfunction. However, it remained unclear from these clinical reports whether the beneficial effects of ACEI were due to direct improvements in LV myocardial structure and function. Accordingly, the overall objective of the present study was to examine the direct effects of ACEI on both LV and myocyte structure and function in the setting of cardiomyopathic disease.

METHODS AND RESULTS

LV and isolated myocyte function and structure were examined in control dogs (n = 6), in dogs after the development of dilated cardiomyopathy caused by rapid ventricular pacing (RVP, 216 beats per minute, 4 weeks, n = 6), and in dogs with RVP and concomitant ACEI (RVP/ACEI, fosinopril 30 mg/kg BID, n = 6). LV ejection fraction fell with RVP compared with control values (35 +/- 3 versus 73 +/- 2%, P < .05) and was higher with RVP/ACEI compared with RVP values (41 +/- 4%, P = .048). LV end-diastolic volume increased with RVP compared with control values (78 +/- 7 versus 101 +/- 7 cm3, P < .05) and was lower with RVP/ACEI (82 +/- 3 cm3, P < .05). Isolated myocyte length increased with RVP (182 +- 1 versus 149 +/- 1 micron), and the velocity of shortening decreased (36 +/- 1 versus 57 +/- 1 micron/s) compared with control values (P < .05). With RVP/ACEI, myocyte length was reduced (169 +/- 1 micron) and velocity of shortening was increased (45 +/- 1 micron/s) compared with RVP values (P < .05). Myocyte velocity of shortening after beta-adrenergic receptor stimulation with 25 nmol/L isoproterenol was reduced with RVP compared with control values (142 +/- 5 versus 193 +/- 8 micron/s, P < .05) and significantly improved with RVP/ACEI (166 +/- 6 micron/s, P < .05). In the RVP group, beta-adrenergic receptor density fell 26%, and cAMP production with beta-adrenergic receptor stimulation was reduced 48% from control values. RVP/ACEI resulted in a normalization of beta-adrenergic receptor density and cAMP production. LV myosin heavy-chain content when normalized to dry weight of myocardium was unchanged with RVP (149 +/- 11 mg per gram dry weight of myocardium [gdwt]) and RVP/ACEI (150 +/- 4 mg/gdwt) compared with control values (165 +/- 4 mg/gdwt). LV collagen content decreased with RVP compared with control values (7.6 +/- 0.4 versus 9.6 +/- 0.8 mg per gram wet weight of myocardium [gwwt], P < .05) but was increased with RVP/ACEI (14.4 +/- 1.3 mg/gwwt, P < .05).

CONCLUSIONS

Concomitant ACEI with chronic tachycardia reduced LV chamber dilation and improved myocyte contractile function and beta-adrenergic responsiveness. Contributory cellular and extracellular mechanisms for the beneficial effects of ACEI in this model of dilated cardiomyopathy included a normalization of beta-adrenergic receptor function and enhanced myocardial collagen support. The results from this study provide evidence that ACEI during the development of cardiomyopathic disease provided beneficial effects on LV myocyte contractile processes and myocardial structure.

DD genotype of the angiotensin-converting enzyme gene is a risk factor for left ventricular hypertrophy

BACKGROUND

The cardiac renin-angiotensin system has been suggested to be involved in the development of left ventricular hypertrophy. In humans, a strong correlation has been found between plasma angiotensin I-converting enzyme (ACE) activity and the insertion/deletion (I/D) polymorphism of the ACE gene, which has been reported to be associated with myocardial infarction, ischemic and idiopathic dilated cardiomyopathy, sudden death in hypertrophic cardiomyopathy, and restenosis after percutaneous transluminal coronary angioplasty. In the present study, we examined the possibility that the genotype of the ACE gene might influence the development of left ventricular hypertrophy.

METHODS AND RESULTS

The study population consisted of 268 subjects randomly selected from our outpatient clinic. In 142 subjects, left ventricular mass (LVM) was determined by echocardiogram. The genotype of the ACE gene was determined by the polymerase chain reaction. ANCOVA revealed that the genotype of the ACE gene had no effect on blood pressure. The percentage of the explained variance of LVM with variables including diastolic blood pressure (DBP, P = .0001), body mass index (BMI, P = .0001), sex (P = .0009), and the genotype of the ACE gene (P = .0017) was 34.61%. Significant differences in the effects of the genotype of the ACE gene on LVM were observed between the II and DD (P = .0004) and between the ID and DD (P = .0077) genotypes. The percentage of the explained variance of the LVM/ht ratio with variables including sex (P = .134), age (P = .3655), the genotype of the ACE gene (P = .0014), BMI (P = .0001), and DBP (P = .0001) was 31.25%. Significant differences in the effects of the genotype of the ACE gene on LVM/ht were observed between the II and DD genotypes (P = .0003) and between the ID and DD genotypes (P = .0091).

CONCLUSIONS

In addition to BMI and DBP, the genotype of the ACE gene was a significant predictor of LVM and LVM/ht in our study population.

Diverse factors influencing angiotensin metabolism during ACE inhibition: insights from molecular biology and genetic studies

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Increased angiotensin-I converting enzyme gene expression in the failing human heart. Quantification by competitive RNA polymerase chain reaction

Local activation of the components of the renin angiotensin system in the heart is regarded as an important modulator of cardiac phenotype and function; however, little is known about their presence, regulation, and potential activation in the human heart. To investigate the gene expression of major angiotensin-II-forming enzymes in left ventricles of normal (n = 9) and failing human hearts (n = 20), we established a competitive RNA-polymerase chain reaction (PCR) for mRNA quantification of angiotensin-I converting enzyme (ACE) and human heart chymase. For each gene, competitor RNA targets with small internal deletions were used as internal standards to quantify the original number of transcripts and to control reverse transcription and PCR. In PCR, each target and the corresponding competitor were amplified by competing for the same primer oligonucleotides. The variability of ACE RNA-PCR was 11% indicating a high reproducibility of this method. In addition, ACE mRNA levels obtained by competitive RNA-PCR correlated favorably with traditional slot blot hybridization (r = 0.69, n = 10; P < 0.05). Compared with nonfailing hearts, the number of ACE transcripts referred to 100 ng of total RNA was increased threefold in patients with chronic heart failure (4.2 +/- 2.5 vs. 12.8 +/- 6 x 10(5); P < 0.0005). In contrast, no significant difference was found in chymase gene expression between normal and failing hearts. Thus, the expression of the cardiac ACE but not of human heart chymase is upregulated in failing human heart indicating an activation of the cardiac renin-angiotensin system in patients with advanced heart failure.

Levels of angiotensin and molecular biology of the tissue renin angiotensin systems

The cloning of renin, angiotensinogen and angiotensin converting enzyme genes have established a widespread presence of these components of the renin-angiotensin system in multiple tissues. New sites of gene expression and peptide products in different tissues has provided strong evidence for the production of angiotensin independently of the endocrine blood borne system. In addition, the cloning of the angiotensin receptor (AT1) gene has confirmed the widespread distribution of angiotensin and suggested new functions for the peptide. This review of various tissues shows the variation in gene expression between tissues and angiotensin levels, and the fragmentary state of our knowledge in this area. As yet we cannot state that the gene expression of the substrates, enzymes and peptide products are involved in a single cell synthesis. This is not so much evidence against a paracrine function for tissue angiotensin, as lack of detailed, accurate intracellular information. The low abundance of renin in brain, spleen, lung and thymus compared to kidney, adrenal, heart, testes, and submandibular gland may suggest that there are both tissue renin-angiotensin systems (RAS) and nonrenin-angiotensin systems (NRAS). The NRAS could function through cleavage of angiotensinogen by serine proteinases such as tonin and cathepsin G to form Ang II directly. Although much angiotensinogen is extracellular and could therefore be a site of synthesis outside of the cell, intracellular angiotensinogen in a NRAS process could produce Ang II intracellularly without requiring extracellular conversion of Ang I to Ang II by ACE. In summary, renin mRNA is found in high concentrations in kidney, adrenal and testes and decreasing lower concentrations in ovary, liver, brain, spleen, lung and thymus. Angiotensinogen mRNA is found in the following tissues in descending order of abundance: liver, fat cells, brain (glial cells), kidney, ovary, adrenal gland, heart, lung, large intestine and stomach. It is debatable whether angiotensinogen and renin mRNA are expressed in blood vessels. The evidence that is lacking for a paracrine function of angiotensin is a complete description of the intracellular molecular synthesis and release of Ang II from single cells of promising tissues. Such tissues, SMG, ovary, testes, adrenal, pituitary and brain (neurons and glia) are potent sources of RAS components for future studies. Although the evidence for a paracrine function of angiotensin II is incomplete, it is an important concept for progressing toward the understanding of tissue peptide physiology and the significance of their gene regulation.

Pathophysiology of heart failure and the renin-angiotensin-system

For more than a decade, the inhibition of the renin-angiotensin system in heart failure has been regarded as pure vasodilator therapy. Consequently, the role of the renin-angiotension system has been seen as contributing to hemodynamic overload by vasoconstriction and volume retention. Meanwhile, clinical experience was indicated that important additional aspects of ACE-inhibition in heart failure are attenuation of the enhanced neuroendocrine activity and reversal or prevention of inappropriate trophic reactions of the overloaded myocardium. In overloaded hearts there is enhanced intracardiac formation of angiotensin due to enhanced expression of angiotensinogen and ACE, and due to accumulation of circulating, nephrogenic active renin. In human hearts, a mast-cell-derived chymase, which is not blocked by ACE-inhibition, contributes to intracardiac angiotensin formation. The enhanced intracardiac angiotensin-II formation in overloaded hearts is involved in coronary constriction, impairment of diastolic relaxation, myocyte enlargement and interstitial fibrosis, which aggravate the diastolic impairment. The major problem in overloaded, hypertrophied cardiocytes is the dedifferentiation with instabilization of Ca(++)-homeostasis due to an altered program of gene expression. Dedifferentiated cardiocytes have a reduced expression of sarcoplasmic reticulum Ca(++)-ATPase and an enhanced expression of the sarcolemmal Na+/Ca(++)-exchanger, resulting in an attenuation of active diastole (Ca(++)-reaccumulation into the sarcoplasmic reticulum), a depressed force-frequency relation, and an enhanced susceptibility for fatal arrhythmias. Furthermore, an enhanced local renin-angiotensin system in distensible coronary and systemic arteries seems to contribute to a reduced releasability of endothelium-derived relaxing factor, probably by reducing bradykinin availability. This modulation of endothelial function appears to contribute to the localization and progression of atheroma development in presence of risks factors for atherosclerosis.

Capillary diffusion capacity for Cr-EDTA and cyanocobalamine in spontaneously beating rat hearts

In order to obtain a functional estimate of the diffusional capacity of the myocardial capillary bed, the permeability surface area product (PS) for Cr-EDTA (mol. wt = 341) and cyanocobalamine (vitamin B12, mol. wt = 135) was determined in spontaneously beating Langendorff-perfused rat hearts over a wide range of coronary flow rates (700-3000 ml min-1 100 g-1). PS was determined by a single injection, colorimetric indicator dilution technique, allowing multiple, rapid and accurate determinations to be made in the same heart. During maximal vasodilation with nitroprusside Na PS averaged 535 +/- 33 and 220 +/- 22 ml min-1 100 g-1 for Cr-EDTA and vitamin B12 respectively at the highest flow (2917 +/- 74 ml min-1 100 g-1). The vasculature of the heart was found to be highly heterogeneous, since PS increased with flow and there were marked variations of extraction over transit times. A functional estimate of 'equivalent pore radius' was obtained from the ratio PSCr-EDTA/PSB12, which was 2.61 +/- 0.15 demonstrating a marked restriction to diffusion corresponding to a pore radius of 51 (41-75) A. This value is similar to that from skeletal muscle determined by the same method while PS-values are 40-45 times higher in the heart (Haraldsson & Rippe 1986). Taken together with morphological estimations of capillary surface area and endothelial path depth, these data indicate a 3-fold increase in the density of pores available for diffusion in the myocardium, compared to skeletal muscle.

Neurohormonal inhibition and hemodynamic unloading during prolonged inhibition of ANF degradation in patients with severe chronic heart failure

BACKGROUND

The purpose of this study was to investigate the therapeutic potential of prolonged inhibition of atrial natriuretic factor (ANF) degradation in patients with severe chronic heart failure.

METHODS AND RESULTS

The effects of repeated doses of the endopeptidase inhibitor candoxatrilat (150 mg i.v.) were examined over a 24-hour period in patients with severe chronic heart failure (New York Heart Association class III-IV). Plasma alpha-hANF(99-126) was elevated at baseline (235 +/- 59 pg/ml), increased 2.5-fold at 2 hours after the first dose, and remained significantly elevated throughout the 24-hour protocol. In contrast, pro-hANF(31-67) decreased from 3,151 +/- 616 to 2,072 +/- 362 pg/ml (p less than 0.05). Cardiac index (CI) increased only transiently after the first dose of candoxatrilat (CI, 2.11 +/- 0.2 to 2.67 +/- 0.28 l/min/m2, p less than 0.05). Sodium excretion increased sixfold (p less than 0.05) 2 hours after the first dose of candoxatrilat and remained significantly elevated throughout the protocol. Degree of natriuresis and diuresis in response to candoxatrilat was closely related to baseline cardiac output. Glomerular filtration rate and volume excretion did not change significantly. Pulmonary capillary wedge pressure fell from 23 +/- 3 to 18 +/- 3 mm Hg (p less than 0.05) and remained below baseline throughout the 24 hours. Arterial pressure, heart rate, and total peripheral resistance did not change significantly during the 24-hour period. Urinary cGMP excretion increased fivefold (p less than 0.05), whereas urinary ANF immunoreactivity and plasma cGMP levels remained unchanged. Excretion of prostacyclin metabolite 6-keto-PGF-1 alpha increased 3.3-fold (p less than 0.05). Plasma norepinephrine and epinephrine levels decreased significantly after candoxatrilat and remained suppressed over the 24-hour period. There was also a transient reduction in plasma vasopressin, aldosterone levels, and plasma renin activity. Hematocrit, total protein content, and plasma albumin concentrations did not change, indicating that no fluid shift into the extravascular space had occurred.

CONCLUSIONS

1) The inhibition of ANF degradation causes sustained drop in left and right atrial pressures that appears to be mediated by an inhibition of neurohumoral activity; 2) concomitant inhibition of bradykinin breakdown (which in turn stimulates renal prostacyclin synthesis) contributes to natriuresis; 3) the close correlation between renal response and baseline cardiac index indicates that an inadequate renal perfusion secondary to low cardiac output diminishes the efficacy of this treatment modality. This spectrum of action would be advantageous for a first-line diuretic agent early in the course of disease rather than in patients with advanced chronic heart failure.

Modulation of myocardial sarcoplasmic reticulum Ca(++)-ATPase in cardiac hypertrophy by angiotensin converting enzyme?

Myocardial hypertrophy in response to hemodynamic overload is an established risk factor for cardiovascular morbidity and mortality. Partially, this may be due to alterations in cardiac gene expression, resulting in a more fetal-like myocyte phenotype with a fragile Ca(++)-homeostasis. Depressed expression of the sarcoplasmic reticulum Ca(++)-ATPase is the hallmark of this overload phenotype, contributing to prolonged cytosolic Ca(++)-transients, disturbed diastolic relaxation, altered force-frequency relation, and probably, electrophysiologic instability with susceptibility to malignant arrhythmias. Since angiotensin II is a growth-promoting factor in several cellular systems, the local formation of angiotensin II within the myocardium might contribute to the trophic response and the phenotype shift of overloaded myocardium. Several observations are consistent with this hypothesis: the cardiac expression of ACE and angiotensinogen is enhanced in experimental myocardial overload and in human endstage congestive heart failure; prolonged observations of experimental cardiac overload with hypertrophy-induced putative normalisation of myocardial systolic wall stress demonstrated a renormalization of ventricular tissue ACE activity and of ventricular sarcoplasmic Ca(++)-ATPase expression and activity; normalizing ventricular tissue ACE activity in experimental cardiac overload by chronic nonhypotensive ACE inhibitor therapy caused a parallel partial normalization of hypertrophy and underexpression of sarcoplasmic CA(++)-ATPase. This partial normalization of myocyte Ca(++)-homeostasis in overload hypertrophy by non-hypotensive chronic ACE-inhibition is attenuated by concomitant chronic application of bradykinin-2 receptor blockade, indicating an involvement of altered bradykinin metabolism in the phenotype modulation due to chronic ACE inhibition. While these observations are consistent with a direct influence of local ACE activity on the sarcoplasmic reticulum, the cell type contributing to the enhanced ACE expression in overload and the specific mechanism of this influence are unknown.