Angiotensin-converting enzyme (ACE) inhibitors favorably influence cardiac remodeling (1) and improve clinical condition in patients with heart failure (2,3) and after myocardial infarction (4). Similar actions of ACE inhibitors are observed in the rat myocardial infarction model, in which hemodynamic improvement and increased survival after long-term therapy (5,6) are associated with reductions in blood pressure and total peripheral resistance, attenuation of left ventricular remodeling, restoration of minimal coronary resistance, increased capillary density, attenuation of myocardial interstitial fibrosis, and improved β-adrenergic responsiveness (6-9). In addition, ACE inhibition increases venous compliance (10), reverses arterial remodeling (11), and prevents heart failure-induced endothelial dysfunction(12).
Several mechanisms may contribute to these effects of ACE inhibition on the cardiovascular response to myocardial infarction. In addition to vasodilatation, with consequent reduction of myocardial load, and neurohumoral inhibition (13), other actions of ACE inhibitors must be considered (1). ACE catalyzes both the conversion of angiotensin I (Ang I) to angiotensin II (Ang II) and the metabolism of the nonapeptide bradykinin [BK-(1-9)] to the heptapeptide bradykinin-(1-7) [BK-(1-7)]. We previously showed that ACE inhibitors decrease Ang II levels and increase BK-(1-9) levels in blood and tissues of normal rats (14). The effects of ACE inhibitors after myocardial infarction may result in part from the reduction of Ang II-mediated myocyte hypertrophy and fibrosis (15-19). Moreover, the finding that BK-(1-9)-receptor antagonists may prevent some of the actions of ACE inhibitors suggests an involvement of BK-(1-9) in the response to ACE inhibition(20-22).
We investigated the potential role of changes in Ang II and BK-(1-9) levels in mediating the actions of ACE inhibitors on cardiac remodeling and cardiac failure by studying the effects of perindopril on circulating and tissue levels of Ang and BK peptides in rats with myocardial infarction.
Male Sprague-Dawley rats (120-130 g) were fed GR 2+ pellets (Clarke King, Gladesville, Australia) and tap water ad libitum. Perindopril, from Servier Laboratories, Courbevoie, France, was administered in drinking water. This study was performed in accordance with the guidelines of the Animal Experimentation Ethics Committee of St. Vincent's Hospital.
Left ventricular free-wall myocardial infarction was induced by ligation of the proximal anterior descending coronary artery in 174 rats, as described previously (5,23), by using enflurane anesthesia. On the second day after operation, six-lead electrocardiograms (ECGs, leads I, II, III, aVL, aVR, and aVF) were obtained by using sodium methohexitone anesthesia and compared with a preoperative ECG from each rat. Only rats with the development of Q waves, associated with the loss of R waves in at least two of leads I, II, and aVL, were considered to have transmural infarcts and were used in this study. Of operated-on rats, 74% survived to 48 h; of the surviving rats, 72% met the ECG criteria for transmural infarction.
Two groups of ≥40 rats were studied. For group 1, systolic blood pressures were measured by the tail-cuff method (model 12-38L BP system; IITC, Life Science Instrumentation, Woodland Hills, CA, U.S.A.), twice before surgery, and on days 2, 7, 14, 21, and 27 after infarction. On day 27, rats were anesthetized with sodium methohexitone, and a carotid arterial cannula was inserted and exteriorized at the back of the neck. The cannulas were filled with heparinized saline (5,000 IU/ml). On the following day, intraarterial recordings of blood pressure were made in conscious unrestrained rats. Subsequently, 2 ml blood was collected from the cannula directly into a syringe containing 10 ml of 4 M guanidine thiocyanate, 1% trifluoroacetic acid (GTC/TFA) for the measurement of bradykinin peptide levels. The rats were given an overdose of sodium pentobarbitone, and the heart was excised and fixed in 10% buffered formalin. Each heart was cut in cross-section at four levels from the base to the apex, paraffin fixed, and sections cut and stained with Masson's trichrome. A slide of each section was projected and infarct size determined as described by Pfeffer et al.(5).
Rats of group 2 were weighed before surgery, and on days 2, 7, 14, 21, and 27 after infarction. These rats were killed by decapitation without prior anesthetic on day 28, for the measurement of plasma renin, angiotensinogen, ACE, and Ang peptides, and tissue levels of Ang and BK peptides. The weights of both cardiac ventricles, total lung weight, and liver weight were also measured.
Extraction and radioimmunoassay of angiotensin peptides from plasma
Plasma levels of angiotensin-(1-7) [Ang-(1-7)], Ang II, and Ang I were measured as described previously (24). In brief, trunk blood (1-2 ml) was rapidly collected into tubes containing 0.33 ml inhibitor solution (220 mM pepstatin, 76 mM 1,10-phenanthroline, 190 mM ethylenediaminetetraacetate, 3 g/L neomycin sulfate, 3% dimethyl sulfoxide, and 3% ethanol in water) at 4°C. The renin inhibitor JF1 (0.17 ml of 3 mM) was immediately mixed with the blood (25). The blood was centrifuged and the plasma (1-2 ml) was immediately extracted with Sep-Pak C18 cartridges (Waters Chromatography Division, Milford, MA, U.S.A.). Angiotensin peptides were acetylated and piperidine treated before high-performance liquid chromatography (HPLC), and assay of HPLC fractions was performed by N-terminal directed radioimmunoassay (RIA) (24,26). Data were corrected for recovery, as reported elsewhere(24).
Extraction and radioimmunoassay of angiotensin and bradykinin peptides from blood and tissues
Heart (cardiac ventricles), lung, aorta, and kidney were rapidly removed, weighed, and immediately homogenized in GTC/TFA and then processed as described previously (27), before ether extraction, acetylation and piperidine treatment, HPLC, and measurement of Ang and BK peptides by N-terminal directed RIA (24,27). Blood collected from cannulae of group 1 rats into GTC/TFA was processed in the same manner for the measurement of bradykinin peptides. Data were corrected for recovery, as reported elsewhere (24,27). The time delay between decapitation and homogenization for heart was ≈60 s, and for lung was ≈80 s; aorta was homogenized within 100 s, and kidney was homogenized within 120 s.
Measurement of renin, angiotensinogen, and ACE in plasma
Trunk blood for measurement of renin, angiotensinogen, and ACE was collected into heparinized tubes on ice and then centrifuged, and the plasma was rapidly frozen on dry ice and stored at -30°C. The plasma concentrations of active renin, angiotensinogen, and ACE enzymatic activity were measured as described previously (28). ACE enzymatic activity was measured by using 3-(2-furylacryloyl)-L-phenylalanyl-glycyl-glycine as substrate(29).
Data are presented as means ± SEM. Tail-cuff blood pressures and body weights were analyzed by repeated measures analysis of variance (ANOVA), and other variables were analyzed by one-way ANOVA. Post hoc comparisons between control and perindopril-treated rats were performed by using Dunnett's two-tailed test; a value of p < 0.05 was considered statistically significant. When more than half of the samples comprising a mean had values below the minimum detectable, the sample mean is shown as less than the minimum detectable. Where values were below the minimum detectable, they were set at half the minimum detectable for statistical calculations. Logarithmic transformation of data was performed where appropriate to obtain similar variances among groups.
Histologic analysis of hearts from group 1 rats showed that 90% had transmural infarcts of >25% of the left ventricular wall (mean, 38%; SD, 10.4%; n = 40). Only one rat (receiving 2,000 μg/kg/day perindopril) died after day 2. In a separate study (A.- M. Duncan et al., unpublished data) we showed that, compared with sham-operated rats, infarct rats at 28 days had reduced blood pressure (sham, 160 ± 4 mm Hg; infarct, 124 ± 10; p < 0.01; n = 10-12; measured by tail cuff) and body weight (sham, 332 ± 6 g; infarct, 305 ± 7; p < 0.05), 19% increase in heart weight/body weight ratio (sham, 2.86 ± 0.05 mg/g; infarct, 3.41 ± 0.19; p < 0.01), and 54% increase in lung weight/body weight ratio (sham, 3.72 ± 0.10 mg/g; infarct, 5.73 ± 0.84; p < 0.05); plasma levels of renin, angiotensinogen, Ang II, Ang I, and Ang-(1-7) were no different from those of sham-operated rats. Moreover, at 28 days, Ang II and Ang I levels in heart, lung, and kidney, and BK-(1-7) and BK-(1-9) levels in heart, lung, aorta, and kidney of infarct rats were no different from those of sham-operated rats. However, infarct rats had increased plasma ACE levels (sham, 250 ± 20 U/L; infarct, 327 ± 20; p < 0.05) and increased Ang II levels in aorta (sham, 75 ± 13 fmol/g; infarct, 161 ± 27; p < 0.01) 28 days after infarct.
Because perindopril was commenced 2 days after infarction, no effect on infarct size was expected. However, infarct size was higher in the 20 μg/kg/day perindopril rats than in control for group 1 rats (Table 1). Rats receiving the two highest doses of perindopril showed reduced weight gain (Table 1). Only the highest dose of perindopril reduced the tail-cuff blood pressure of infarct rats below that of untreated control; this was confirmed by intraarterial blood pressure measurement on day 28 (Fig. 1). Perindopril caused a dose-related decrease in heart weight, heart weight/body weight ratio, lung weight, and lung weight/body weight ratio (Table 1, Fig. 2). Perindopril had no effect on liver weight or liver weight/body weight ratio (data not shown).
The lowest dose of perindopril (20 μg/kg/day) was without effect on plasma levels of renin and ACE, although there was a decrease in plasma angiotensinogen levels at this dose (Fig. 3). Higher doses of perindopril increased plasma renin up to 23-fold, inhibited plasma ACE to 23% of control, and decreased plasma angiotensinogen to 16% of control.
Plasma and all tissues showed dose-related decreases in Ang II/Ang I ratio in response to perindopril, consistent with inhibition of both circulating and tissue ACE (Figs. 4-8). The two higher doses of perindopril increased plasma Ang I and Ang-(1-7) levels, although plasma Ang II levels were no different from control (Fig. 4). Perindopril caused a dose-related decrease in cardiac Ang II levels and increase in cardiac Ang I levels, although these changes were statistically significant for only the highest dose (Fig. 5). The two highest doses of perindopril reduced Ang II levels and increased Ang I levels in lung (Fig. 6). Perindopril did not affect aortic levels of Ang II, although the highest dose increased Ang I levels (Fig. 7). Renal Ang II levels showed a dose-related decrease in response to perindopril, with no change in Ang I levels (Fig. 8).
Perindopril increased blood BK-(1-9) levels by 1.6-to 3.6-fold, with no change in BK-(1-7) levels and a decrease in BK-(1-7)/BK-(1-9) ratio in blood (Table 2). However, none of the tissues showed an increase in BK-(1-9) levels, and lung showed a decrease in BK-(1-9) levels, which achieved statistical significance for 200 mg/kg/day perindopril. Although cardiac levels of BK-(1-9) showed a 45% increase for the highest dose of perindopril, this did not achieve statistical significance (ANOVA: F3,38 = 2.15, p = 0.1) However, heart showed a decrease in BK-(1-7)/BK-(1-9) ratio for 20 and 2,000 μg/kg/day perindopril, consistent with inhibition of BK-(1-9) metabolism. Lung, aorta, and kidney did not show decreases in either BK-(1-7) levels or BK-(1-7)/BK-(1-9) ratio.
In this study, we applied highly sensitive and specific HPLC-based RIA to examine the effects of ACE inhibition on circulating and tissue levels of Ang and BK peptides in rats with myocardial infarction. The accurate measurement of tissue levels of Ang and BK peptides requires that the tissue be immediately homogenized in a denaturant that prevents both peptide generation and degradation. Our methods have been extensively validated for this purpose (26-28). These precautions prevented our dissection of hearts or quantification of infarct size in hearts used for peptide measurement. However, by using ECG criteria, we ensured that these rats had moderate to large infarcts of uniform size. By commencing perindopril 2 days after infarction, we avoided any influence of perindopril on infarct size, apart from the increased infarct size in group 1 rats receiving 20 μg/kg/day perindopril.
The doses of perindopril used in our study were based on our previous study of Ang and BK peptides in normal rats given perindopril doses ranging from 0.006 to 12.6 mg/kg/day (14). The effects of perindopril on the circulating renin/angiotensin system and tissue Ang peptide levels in infarct rats in this study were similar to those we observed in normal rats. The dose-related effects of perindopril demonstrate a complex interaction between the various components of the renin/angiotensin system and emphasize that the effects of ACE inhibition on plasma and tissue levels of Ang II are dependent on the concomitant changes in Ang I levels, which themselves are dependent on the associated changes in renin and angiotensinogen (14,28). We previously described the marked decreases in plasma and renal angiotensinogen levels that accompany ACE inhibition (28), and we attribute the lack of increase in renal Ang I levels to a local exhaustion of renal angiotensinogen consequent to the large increase in renin secretion by the kidney (14,28). Differences between plasma and tissues in Ang II response to perindopril were a consequence of differences in the perindopril-induced increase in Ang I levels. Thus plasma and tissues showed dose-related decreases in Ang II/Ang I ratio at perindopril doses much lower than those required to decrease Ang II levels.
As evidence of the tissue-specific effects of perindopril on circulating and tissue Ang II levels, perindopril reduced cardiac Ang II levels without change in plasma Ang II levels. In agreement with our findings, Yamagishi et al. (30) reported that delapril was without effect on plasma Ang II levels but reduced cardiac Ang II levels in rats with myocardial infarction. A large body of evidence supports a role for direct cardiac actions of Ang II in cardiac remodeling after myocardial infarction. There is an increase in ACE gene expression (31-35), angiotensinogen mRNA (36), and angiotensin-receptor number (37,38) in the noninfarcted myocardium. Cell-culture experiments demonstrated that autocrine release of Ang II may mediate stretch-induced hypertrophy of cardiac myocytes in vitro (16,18). Ang II increases protein synthesis in cultured neonatal cardiac myocytes and both protein and DNA synthesis in cultured neonatal cardiac fibroblasts (17). Consistent with these experiments, studies in intact hearts and in vivo suggest that Ang II effects on the heart may be due in part to direct cardiac effects (15,19,39). Other studies provided evidence that at least some of the effects of ACE inhibition are mediated by mechanisms other than decreased myocardial load (9,15). Together, these studies support the proposal that the effects of ACE inhibition in myocardial infarction may be the result in part of the reduction of cardiac Ang II levels.
Our study is the first to measure the effects of ACE inhibition on BK peptide levels in myocardial infarction. In our study of normal rats, we found that perindopril increased blood and tissue BK-(1-9) levels. Moreover, for blood, heart, lung, and aorta of normal rats, BK-(1-9) levels were increased by perindopril doses that were less than those required to suppress Ang II levels. One question raised by our study is why perindopril was without effect on tissue levels of BK-(1-9) in infarct rats, despite the increase in circulating BK-(1-9) levels. In assessing the effects of perindopril in rats with myocardial infarction, it is important to note the dramatic effects of ACE inhibition on the cardiac remodeling process, with associated changes in cardiovascular hemodynamics and prevention of cardiac failure, which may have reduced BK-(1-9) production, thereby masking an effect of perindopril on BK-(1-9) metabolism. Myocardial infarction is associated with increased ACE gene expression in heart (31-35). Many other enzymes also metabolize BK-(1-9), including aminopeptidase P, endopeptidase 24.11 (neutral endopeptidase), endopeptidase 24.15, carboxypeptidases M and N, and prolyl endopeptidase (27), and some of these may also be increased after myocardial infarction. Moreover, Helin et al. (40) reported that ACE inhibition induces both ACE and neutral endopeptidase in lung; however, these authors did not examine heart. Thus the failure of perindopril to increase tissue BK-(1-9) levels may have resulted from more efficient metabolism of BK-(1-9) by other enzymes, consequent to infarction or ACE inhibition or both. It is of note that heart showed evidence of decreased conversion of BK-(1-9) to BK-(1-7) by perindopril, in that the BK-(1-7)/BK-(1-9) ratio was reduced by 20 and 2,000 μg/kg/day perindopril. Lung showed a decrease in BK-(1-9) levels, associated with a marked reduction in lung weight/body weight ratio. The congested lungs of untreated infarct rats may have had both increased production and increased metabolism of BK-(1-9), and the perindopril-induced decrease in lung BK-(1-9) levels may have been caused by the reduction of pulmonary congestion by ACE inhibition, with consequent reduction of BK-(1-9) production.
Whereas there is much evidence in support of a role for BK-(1-9) in the cardioprotective effects of ACE inhibitors in ischemic myocardium and in mediating a reduction in infarct size by ACE inhibition (20,21,41,42), there is conflicting evidence regarding the role of BK-(1-9) in mediating the effects of ACE inhibition in myocardial remodeling and heart failure after myocardial infarction. In some studies, angiotensin type 1 (AT1)-receptor antagonists mimic the effects of ACE inhibitors in the established phase of myocardial infarction, with reduction of remodeling, increased venous compliance, and improvement of heart failure, thus providing evidence for a primary role for decreased Ang II levels in mediating these effects of ACE inhibitors (7,30,43-45). However, BK-(1-9) antagonism prevents the antihypertrophic effects of ACE inhibition in rats with coarctation (46) and in dogs with DC shock-induced myocardial necrosis (22), suggesting that BK-(1-9) may contribute to the antihypertrophic effects of ACE inhibition. However, the failure of perindopril to increase cardiac BK-(1-9) levels in our study suggests that BK-(1-9) does not contribute to the antihypertrophic effects of ACE inhibition in myocardial infarction.
We chose to study rats 28 days after infarct, at which time scar formation was complete, cardiac hypertrophy was well developed, and cardiac failure was present. Perindopril was administered from days 2 to 28 after infarct. Therefore it may be argued that perindopril had effects on cardiac BK-(1-9) levels earlier after infarct and that they were no longer detectable by 28 days. However, the effects of perindopril on cardiac hypertrophy and cardiac failure at 28 days after infarct were dramatic, and it seems reasonable to propose that if changes in BK-(1-9) levels mediated these effects, then these changes in BK-(1-9) levels should be evident at 28 days, as was seen for Ang II levels. This study does not exclude a role for cardiac BK-(1-9) in mediating the effects of perindopril. Perindopril may have increased cardiac BK-(1-9) levels in a small compartment, and such a localized increase may not have been detected in our study of whole ventricular tissue. Moreover, if kinin-receptor levels were increased, this would amplify the actions of kinins(47).
In conclusion, we showed that in rats with myocardial infarction, the reduction of cardiac remodeling and cardiac failure by perindopril was associated with decreases in both blood pressure and cardiac Ang II levels, but with no detectable alteration in cardiac BK-(1-9) levels. The failure of perindopril to increase tissue BK-(1-9) levels may have been the result of a reduction in BK-(1-9) production, consequent to the reduction in cardiac hypertrophy and cardiac failure by the ACE inhibitor and also may relect an increased metabolism of bradykinin by enzymes other than ACE in myocardial infarction. These data support a role for reduced blood pressure and cardiac Ang II levels in mediating the effects of ACE inhibition but do not support a role for tissue bradykinin in this process.
Acknowledgment: This study was funded by grants from the National Health and Medical Research Council of Australia and from Servier Laboratories. We are grateful to Thaddeus P. Gorski for performing the assays for plasma ACE.
1. Cohn JN. Structural basis for heart failure: ventricular remodeling and its pharmacological inhibition. Circulation
2. The CONSENSUS Trial Study Group. Effects of enalapril on mortality in severe congestive heart failure: results of the Cooperative North Scandinavian Enalapril Survival Study (CONSENSUS). N Engl J Med
3. The SOLVD Investigators. Effect of enalapril on survival in patients with reduced left ventricular ejection fractions and congestive heart failure. N Engl J Med
4. Latini R, Maggioni AP, Flather M, Sleight P, Tognoni G, for the meeting participants. ACE inhibitor use in patients with myocardial infarction: summary of evidence from clinical trials. Circulation
5. Pfeffer MA, Pfeffer JM, Steinberg C, Finn P. Survival after an experimental myocardial infarction: beneficial effects of long-term therapy with captopril. Circulation
6. Pfeffer JM, Pfeffer MA, Braunwald E. Influence of chronic captopril therapy on the infarcted left ventricle of the rat. Circ Res
7. Schieffer B, Wirger A, Meybrunn M, et al. Comparative effects of chronic angiotensin-converting enzyme inhibition and angiotensin II type 1 receptor blockade on cardiac remodeling after myocardial infarction in the rat. Circulation
8. Sanbe A, Takeo S. Long-term treatment with angiotensin I-converting enzyme inhibitors attenuates the loss of cardiac β-adrenoceptor responses in rats with chronic heart failure. Circulation
9. Van Krimpen C, Smits JFM, Cleutjens JPM, et al. DNA synthesis in the non-infarcted cardiac interstitium after left coronary artery ligation in the rat: effects of captopril. J Mol Cell Cardiol
10. Raya TE, Gay RG, Aguirre M, Goldman S. Importance of venodilatation in prevention of left ventricular dilatation after chronic large myocardial infarction in rats: a comparison of captopril and hydralazine. Circ Res
11. Gaballa MA, Raya TE, Goldman S. Large artery remodeling after myocardial infarction. Am J Physiol
12. Mulder P, Devaux B, El Fertak L, et al. Vascular and myocardial protective effects of converting enzyme inhibition in experimental heart failure. Am J Cardiol
13. Francis GS, Cohn JN, Johnson G, Rector TS, Goldman S, Simon A, for the V-HeFT VA Cooperative Studies Group. Plasma norepinephrine, plasma renin activity, and congestive heart failure: relations to survival and the effects of therapy in V-HeFT II. Circulation
14. Campbell DJ, Kladis A, Duncan A-M. Effects of converting enzyme inhibitors on angiotensin and bradykinin peptides. Hypertension
15. Crawford DC, Chobanian AV, Brecher P. Angiotensin II induces fibronectin expression associated with cardiac fibrosis in the rat. Circ Res
16. Sadoshima J, Xu Y, Slayter HS, Izumo S. Autocrine release of angiotensin II mediates stretch-induced hypertrophy of cardiac myocytes in vitro. Cell
17. Sadoshima J, Izumo S. Molecular characterization of angiotensin II-induced hypertrophy of cardiac myocytes and hyperplasia of cardiac fibroblasts: critical role of the AT1
receptor subtype. Circ Res
18. Yamazaki T, Komuro I, Kudoh S, et al. Angiotensin II partly mediates mechanical stress-induced cardiac hypertrophy. Circ Res
19. Schunkert H, Sadoshima J, Cornelius T, et al. Angiotensin II-induced growth responses in isolated adult rat hearts: evidence for load-independent induction of cardiac protein synthesis by angiotensin II. Circ Res
20. Linz W, Wiemer G, Gohlke P, Unger T, Schölkens BA. Contribution of kinins to the cardiovascular actions of angiotensin-converting enzyme inhibitors. Pharmacol Rev
21. Martorana PA, Kettenbach B, Breipohl G, Linz W, Schölkens BA. Reduction of infarct size by local angiotensin-converting enzyme inhibition is abolished by a bradykinin antagonist. Eur J Pharmacol
22. McDonald KM, Mock J, D'Aloia A, et al. Bradykinin antagonism inhibits the antigrowth effect of converting enzyme inhibition in the dog myocardium after discrete transmural myocardial necrosis. Circulation
23. Hodsman GP, Kohzuki M, Howes LG, Sumithran E, Tsunoda K, Johnston CI. Neurohumoral responses to chronic myocardial infarction in rats. Circulation
24. Campbell DJ, Kladis A, Duncan A-M. Nephrectomy, converting enzyme inhibition and angiotensin peptides. Hypertension
25. Campbell DJ, Rong P, Kladis A, Rees B, Skinner SL. Angiotensin and bradykinin peptides in the TGR(mRen-2)27 rat. Hypertension
26. Campbell DJ, Lawrence AC, Kladis A, Duncan A-M. Strategies for measurement of angiotensin and bradykinin peptides and their metabolites in central nervous system and other tissues. In: Smith AI, ed. Methods in neurosciences, vol 23: peptidases and neuropeptide processing
. Orlando: Academic Press, 1995:328-43.
27. Campbell DJ, Kladis A, Duncan A-M. Bradykinin peptides in kidney, blood, and other tissues of the rat. Hypertension
28. Campbell DJ, Lawrence AC, Towrie A, Kladis A, Valentijn AJ. Differential regulation of angiotensin peptide levels in plasma and kidney of the rat. Hypertension
29. Johansen KB, Marstein S, Aas P. Automated method for the determination of angiotensin-converting enzyme in serum. Scand J Clin Lab Invest
30. Yamagishi H, Kim S, Nishikimi T, Takeuchi K, Takeda T. Contribution of cardiac renin-angiotensin system to ventricular remodelling in myocardial-infarcted rats. J Mol Cell Cardiol
31. Fabris B, Jackson B, Kohzuki M, Perich R, Johnston CI. Increased cardiac angiotensin-converting enzyme in rats with chronic heart failure. Clin Exp Pharmacol Physiol
32. Hirsch AT, Talsness CE, Schunkert H, Paul M, Dzau VJ. Tissue-specific activation of cardiac angiotensin converting enzyme in experimental heart failure. Circ Res
33. Sun Y, Cleutjens JPM, Diaz-Arias AA, Weber KT. Cardiac angiotensin converting enzyme and myocardial fibrosis in the rat. Cardiovasc Res
34. Falkenhahn M, Franke F, Bohle RM, et al. Cellular distribution of angiotensin-converting enzyme after myocardial infarction. Hypertension
35. Passier RCJJ, Smits JFM, Verluyten MJA, Studer R, Drexler H, Daemen MJAP. Activation of angiotensin-converting enzyme expression in infarct zone following myocardial infarction. Am J Physiol
36. Drexler H, Lindpaintner K, Lu W, Schieffer B, Ganten D. Transient increase in the expression of cardiac angiotensinogen in a rat model of myocardial infarction and failure [Abstract]. Circulation
37. Meggs LG, Coupet J, Huang H, et al. Regulation of angiotensin II receptors on ventricular myocytes after myocardial infarction in rats. Circ Res
38. Nio Y, Matsubara H, Murasawa S, Kanasaki M, Inada M. Regulation of gene transcription of angiotensin II receptor subtypes in myocardial infarction. J Clin Invest
39. Dostal DE, Baker KM. Angiotensin II stimulation of left ventricular hypertrophy in adult rat heart: mediation by the AT1
receptor. Am J Hypertens
40. Helin K, Tikkanen I, Hohenthal U, Fyhrquist F. Inhibition of either angiotensin-converting enzyme or neutral endopeptidase induces both enzymes. Eur J Pharmacol
41. Hartman JC, Wall TM, Hullinger TG, Shebuski RJ. Reduction of myocardial infarct size in rabbits by ramiprilat: reversal by the bradykinin antagonist HOE 140. J Cardiovasc Pharmacol
42. Ehring T, Baumgart D, Krajcar M, Hümmelgen M, Kompa S, Heusch G. Attenuation of myocardial stunning by the ACE inhibitor ramiprilat through a signal cascade of bradykinin and prostaglandins but not nitric oxide. Circulation
43. Kojima M, Shiojima I, Yamazaki T, et al. Angiotensin II receptor antagonist TCV-116 induces regression of hypertensive left ventricular hypertrophy in vivo and inhibits the intracellular signaling pathway of stretch-mediated cardiomyocyte hypertrophy in vitro. Circulation
44. Raya TE, Fonken SJ, Lee RW, et al. Hemodynamic effects of direct angiotensin II blockade compared to converting enzyme inhibition in rat model of heart failure. Am J Hypertens
45. Nishikimi T, Yamagishi H, Takeuchi K, Takeda T. An angiotensin II receptor antagonist attenuates left ventricular dilatation after myocardial infarction in the hypertensive rat. Cardiovasc Res
46. Linz W, Schölkens BA. A specific B2
-bradykinin receptor antagonist HOE 140 abolishes the antihypertrophic effect of ramipril. Br J Pharmacol
47. Sun Y, Ratajska A, Weber KT. Bradykinin receptor and tissue ACE binding in myocardial fibrosis: response to chronic angiotensin II or aldosterone administration in rats. J Mol Cell Cardiol