Regression of cardiac hypertrophy in spontaneously hypertensive rats by enalapril and the expression of contractile proteins

Effects of hypertension and exercise on cardiac proteome remodelling

Left ventricle hypertrophy is a common outcome of pressure overload stimulus closely associated with hypertension. This process is triggered by adverse molecular signalling, gene expression, and proteome alteration. Proteomic research has revealed that several molecular targets are associated with pathologic cardiac hypertrophy, including angiotensin II, endothelin-1 and isoproterenol. Several metabolic, contractile, and stress-related proteins are shown to be altered in cardiac hypertrophy derived by hypertension. On the other hand, exercise is a nonpharmacologic agent used for hypertension treatment, where cardiac hypertrophy induced by exercise training is characterized by improvement in cardiac function and resistance against ischemic insult. Despite the scarcity of proteomic research performed with exercise, healthy and pathologic heart proteomes are shown to be modulated in a completely different way. Hence, the altered proteome induced by exercise is mostly associated with cardioprotective aspects such as contractile and metabolic improvement and physiologic cardiac hypertrophy. The present review, therefore, describes relevant studies involving the molecular characteristics and alterations from hypertensive-induced and exercise-induced hypertrophy, as well as the main proteomic research performed in this field. Furthermore, proteomic research into the effect of hypertension on other target-demerged organs is examined.

Enalapril decreases cardiac mass and fetal gene expression without affecting the expression of endothelin-1, transforming growth factor β-1, or cardiotrophin-1 in the healthy normotensive rat

Angiotensin II can induce cardiac hypertrophy by stimulating the release of growth factors. ACE inhibitors reduce angiotensin II levels and cardiac hypertrophy, but their effects on the healthy heart are largely unexplored. We hypothesized that ACE inhibition decreases left ventricular mass in normotensive animals and that this is associated with altered expression of cardiac fetal genes, growth factors, and endothelial nitric oxide synthase (eNOS). Wistar rats (n = 7 per group) were orally administered with enalapril twice daily for a total daily dose of 5 mg·kg–1·d–1 (ENAP5) or 15 mg·kg–1·d–1 (ENAP15) or vehicle. Systolic blood pressure was measured by the tail-cuff method. Left ventricular expression of cardiac myosin heavy chain-α (MYH6) and -β (MYH7), atrial natriuretic peptide (ANP), endothelin-1 (ET-1), transforming growth factor β-1 (TGFβ-1), cardiotrophin-1 (CT-1), and renal renin were examined by real-time PCR, and eNOS using Western blot. Blood pressure was decreased only in ENAP15 animals (p < 0.05 vs. Control), whereas left ventricular mass decreased after both doses of enalapril (p < 0.05 vs. Control). MYH7 and ANP were reduced in ENAP15, while no changes in ET-1, TGFβ-1, CT-1, and MYH6 mRNA or eNOS protein were observed. Renal renin dose-dependently increased after enalapril treatment. Enalapril significantly decreased left ventricular mass even after 1 week treatment in the normotensive rat. This was associated with a decreased expression of the fetal genes MYH7 and ANP, but not expression of ET-1, CT-1, or TGFβ-1.

Comparative study of the effects of lacidipine and enalapril on the left ventricular cardiomyocyte remodeling in spontaneously hypertensive rats

Antihypertensive medications are the most efficient drugs in achieving regression of myocardial hypertrophy in both clinical studies and animal models of hypertension. Nevertheless, there is a lack of clear and concise comparative study of their effects on the modulation of cardiomyocyte morphology and function. Here, we assessed the tissue-protective actions of 2 of these drugs, the calcium channel blocker lacidipine (3 mg/kg/day) and the angiotensin-converting enzyme-inhibitor enalapril (10 mg/kg/day) in vivo, after 8 weeks of treatment of 12-week-old spontaneously hypertensive rats, as well as in vitro, after short-term (4 min) application to isolated cardiomyocytes. Left ventricular hypertrophy (LVH) was compared at organ, tissue, and single-cell level. Our data showed that both drugs prevented the LVH of 20-week-old spontaneously hypertensive rats, but only lacidipine significantly decreased the cardiomyocyte size. Similarly, the single-cell contractility was significantly lowered in lacidipine-treated rats only. The effect of lacidipine was initiated shortly after exposure to the drug in a dose-dependent manner at 0.5 Hz, as well as at 2 Hz, with EC(50) of 10(-7) mol/L. These results can help in understanding the effects of these drugs on the prevention of LVH.

Chronic β-adrenoceptor stimulation and cardiac hypertrophy with no induction of circulating renin

The hemodynamic and cardiac effects of isoproterenol were examined in rats submitted to chronic salt loading (1% NaCl as drinking water) to prevent activation of the systemic renin-angiotensin system. Isoproterenol treatment for 1 week resulted in 36% and 44% (P<0.05) increase in left ventricle mass in both control and chronic salt loading rats and induction of cardiac angiotensin-converting enzyme activity and expression (P<0.05) with no changes in serum angiotensin-converting enzyme. Plasma renin activity decreased significantly with chronic salt loading and failed to increase by isoproterenol treatment, whereas it increased 2.33 fold (P<0.05) in animals kept on regular chow. Isoproterenol treatment leads to transient increase in heart rate and cardiac output while blood pressure remained unchanged. Altogether, these data provide evidence that isoproterenol induced hypertrophy is associated with cardiac induction of angiotensin-converting enzyme and daily transient hemodynamic overload even in the absence of systemic activation of renin-angiotensin system.

Significant target organs for hypertension and cardiac hypertrophy by angiotensin-converting enzyme inhibitors

To clarify the mechanisms by which angiotensin-converting enzyme (ACE) inhibitors lower blood pressure or inhibit cardiac hypertrophy, we analyzed the correlations among tissue ACE activities, blood pressure and cardiac hypertrophy. In spontaneously hypertensive rats (SHR), blood pressure, heart weight and ACE activities in plasma and various tissues were measured 3, 24 and 48 h after repeated daily treatment for 2 weeks with the ACE inhibitors trandolapril, perindopril, temocapril and enalapril. For all four ACE inhibitors, blood pressure and ACE activities in the plasma, aorta and kidney were significantly reduced 3 h after the last treatment. Although hypotensive effects were maintained at 24 h, ACE activities in plasma were not suppressed by temocapril and enalapril. Even at 3 h, enalapril could not suppress ACE activity in the brain, and temocapril and enalapril could not inhibit ACE activities in the heart. Significant correlations between ACE activity in the aorta and blood pressure were observed for all four ACE inhibitors, while the ACE activities in the heart and brain were not correlated with changes in blood pressure. Significant decreases in the ratio of heart weight to body weight were observed in SHR treated with trandolapril and perindopril, whereas they were not observed with temocapril and enalapril. The ratio of heart weight to body weight was significantly correlated with ACE activity in the heart. ACE activities in vascular tissues and the heart may be important targets in terms of the ability of ACE inhibitors to lower blood pressure or inhibit cardiac hypertrophy, respectively.

Bioenergetic remodeling of heart during treatment of spontaneously hypertensive rats with enalapril

We used spontaneously hypertensive rats to study remodeling of cardiac bioenergetics associated with changes in blood pressure. Blood pressure was manipulated with aggressive antihypertensive treatment combining low dietary salt and the angiotensin-converting enzyme inhibitor enalapril. Successive cycles of 2 wk on, 2 wk off treatment led to rapid, reversible changes in left ventricular (LV) mass (30% change in <10 days). Despite changes in LV mass, specific activities of bioenergetic (cytochrome-c oxidase, citrate synthase, lactate dehydrogenase) and reactive oxygen species (ROS) (total cellular superoxide dismutase) enzymes were actively maintained within relatively narrow ranges regardless of treatment duration, organismal age, or transmural region. Although enalapril led to parallel declines in mitochondrial enzyme content and ventricular mass, total ventricular mtDNA content was unaffected. Altered enzymatic content occurred without significant changes in relevant mRNA and protein levels. Transcript levels of gene products involved in mtDNA maintenance (Tfam), mitochondrial protein degradation (LON protease), fusion (fuzzy onion homolog), and fission (dynamin-like protein, synaptojanin-2alpha) were also unchanged. In contrast, enalapril-mediated ventricular and mitochondrial remodeling was accompanied by a twofold increase in specific activity of catalase, an indicator of oxidative stress, suggesting that rapid cardiac adaptation is accompanied by tight regulation of mitochondrial enzyme activities and increased ROS production.

Taurine attenuates hypertrophy induced by angiotensin II in cultured neonatal rat cardiac myocytes

The effect of taurine on angiotensin II-induced changes in cell morphology and biochemistry of the cultured neonatal cardiomyocyte was examined. Angiotensin II (1-100 nM) alone caused a slow increase in the surface area of the myocyte accompanied by an induction of the expression of atrial natriuretic peptide (ANP) and an upregulation of transforming growth factor beta(1) gene (TGF-beta(1)). The signaling pathway of angiotensin II (1-100 nM) was found to proceed through protein kinase C and the rapid activation of mitogen-activated protein (MAP) kinases. Pretreatment of the myocyte with taurine (20 mM) in the absence of angiotensin II had no visible effect on cell size or growth rate. However, the cells that were pretreated with taurine (20 mM) for 24 h exhibited reduced responsiveness to angiotensin II (100 nM) relative to surface cell area enlargement and the upregulation of the late and growth factor genes(ANP, TGF-beta(1)). Angiotensin II-mediated activation of the MAP kinases (extracellular signal-regulated protein kinase 1/2: ERK1/2) was not blocked by taurine. Taurine reduced the phosphorylation of a 29-kDa protein, a reaction which was enhanced by angiotensin II and appears to involve protein kinase C step. The results indicate that taurine is an effective inhibitor of certain aspects of angiotensin II action.

MET-88, a gamma-butyrobetaine hydroxylase inhibitor, improves cardiac SR Ca2+ uptake activity in rats with congestive heart failure following myocardial infarction

We previously reported that MET-88, 3-(2,2,2-trimethylhydrazinium) propionate, improved left ventricular diastolic dysfunction induced by congestive heart failure (CHF) in rats. The present study was designed to investigate the mechanism by which MET-88 improved the cardiac relaxation impaired in CHF rats. The left coronary artery of the animals was ligated, and the rats were then orally administered vehicle (control), MET-88 at 50 or 100 mg/kg or captopril at 20 mg/kg for 20 days. Myocytes were isolated from the non-infarcted region in the left ventricle, and cell shortening and [Ca2+]i transients were measured with a video-edge detector and by fluorescence analysis, respectively. In CHF control rats, the diastolic phase of cell shortening was prolonged compared with that of the sham-operated (sham) rats. This prolongation was prevented by treatment with MET-88 at 100 mg/kg or captopril at 20 mg/kg. CHF control rats also showed an increase in the decay time of [Ca2+]i transients compared with sham rats. MET-88 at 100 mg/kg and captopril at 20 mg/kg attenuated the increase in decay time of [Ca2+]i transients. Ca2+ uptake activity of the sarcoplasmic reticulum (SR) isolated from the non-infarcted region in the left ventricle was measured, and Lineweaver-Burk plot analysis of the activity was performed. CHF control rats revealed a decrease in the Vmax for SR Ca2+ uptake activity without alteration in Kd. MET-88 at 100 mg/kg significantly prevented the decrease in Vmax, but had no effect on Kd. Also, treatment with MET-88 at 100 mg/kg improved myocardial high-energy phosphate levels impaired in CHF rats. These results suggest that one of the mechanisms by which MET-88 improved cardiac relaxation in CHF rats is based on the amelioration of [Ca2+]i transients through increase of SR Ca2+ uptake activity.

Beneficial effects of MET-88, a gamma-butyrobetaine hydroxylase inhibitor in rats with heart failure following myocardial infarction

Myocardial ischemia can cause myocardial infarction and as a consequence, heart failure. 3-(2,2,2-trimethylhydrazinium) propionate (MET-88) inhibits gamma-butyrobetaine hydroxylase and has cardioprotective effects on the ischemic heart. We now examined the effects of MET-88 in rats with congestive heart failure following myocardial infarction. Congestive heart failure was produced by left coronary artery ligation in rats. MET-88 at 100 mg/kg/day was orally administered from the 2nd day after surgery. We performed a survival study for 181 days, and measured ventricular remodeling, cardiac function, and myocardial high-energy phosphate levels after treatment for 20 days. MET-88 prolonged survival with a median 50% survival of 103 days compared to 79 days for the heart-failure control rats. The expansion of the left ventricular cavity (ventricular remodeling) in heart-failure rats was prevented by treatment with MET-88, and the effect of MET-88 was similar to that of captopril at 20 mg/kg. MET-88 attenuated the rise in right atrial pressure in heart-failure rats and augmented cardiac functional adaptability against an increased load. Also, MET-88 improved the myocardial energy state in heart-failure rats. The present results indicate that MET-88 improves the pathosis in rats with heart failure induced by myocardial infarction.

Angiotensin II-induced cardiomyocyte hypertrophy and cardiac fibrosis in stroke-prone spontaneously hypertensive rats

Angiotensin-converting enzyme inhibitors (ACEIs) cause regression of hypertensive left ventricular hypertrophy (LVH) by reducing angiotensin II, increasing bradykinin, or both. The mechanisms of these cardioprotective effects remain controversial. The aims of this study were to determine whether the cardioprotective effects of ACEIs are mediated by reducing angiotensin II and whether ACEIs ameliorate the morphologic, physiologic, and biochemical changes in the hearts of stroke-prone spontaneously hypertensive rats (SHRSPs). Male SHRSPs were treated with hydralazine, captopril, or candesartan, an angiotensin II type 1 receptor (AT1R) antagonist, from age 12 to 24 weeks. We measured systolic blood pressure (SBP), left ventricular weight (LVW), left ventricular (LV) myocyte cross-sectional area (myocyte size), LV Interstitial collagen volume fraction (ICVF), perivascular collagen area/luminal area ratio (PVCA/LA), the medial area to luminal area ratio (MA/LA), the relative amount of V3 myosin heavy chain (MHCV3), and coronary reserve maximum (coronary flow max/ventricular weight (CFmax/VW)). These parameters were compared with those of untreated SHRSPs and Wistar-Kyoto rats (WKYs). SHRSPs exhibited decreased coronary reserve and LVH with an increase in myocyte size, PVCA/LA, MA/LA, and MHCV3 at 12 weeks of age. In addition to these changes, 24-week-old SHRSPs showed an increase in ICVF. The LVW, coronary reserve, myocyte size, PVCA/LA, ICVF, and MHCV3 of SHRSPs treated with captopril or candesartan all approached control values. In contrast, hydralazine decreased only ICVF. These results suggest that ACEIs regress LVH and normalize coronary reserve by modulating the effects of angiotensin II via AT1R on the induction of cardiomyocyte hypertrophy, perivascular fibrosis, and medial thickening of intramyocardial coronary arteries in SHRSPs. We concluded that these effects, in addition to the reduction of SBP, are important in causing the regression of LVH.

Ontogenetic aspects of hypertension development: analysis in the rat

In this review, we attempt to outline the age-dependent interactions of principal systems controlling the structure and function of the cardiovascular system in immature rats developing hypertension. We focus our attention on the cardiovascular effects of various pharmacological, nutritional, and behavioral interventions applied at different stages of ontogeny. Several distinct critical periods (developmental windows), in which particular stimuli affect the further development of the cardiovascular phenotype, are specified in the rat. It is evident that short-term transient treatment of genetically hypertensive rats with certain antihypertensive drugs in prepuberty and puberty (at the age of 4-10 wk) has long-term beneficial effects on further development of their cardiovascular apparatus. This juvenile critical period coincides with the period of high susceptibility to the hypertensive effects of increased salt intake. If the hypertensive process develops after this critical period (due to early antihypertensive treatment or late administration of certain hypertensive stimuli, e.g., high salt intake), blood pressure elevation, cardiovascular hypertrophy, connective tissue accumulation, and end-organ damage are considerably attenuated compared with rats developing hypertension during the juvenile critical period. As far as the role of various electrolytes in blood pressure modulation is concerned, prohypertensive effects of dietary Na+ and antihypertensive effects of dietary Ca2+ are enhanced in immature animals, whereas vascular protective and antihypertensive effects of dietary K+ are almost independent of age. At a given level of dietary electrolyte intake, the balance between dietary carbohydrate and fat intake can modify blood pressure even in rats with established hypertension, but dietary protein intake affects the blood pressure development in immature animals only. Dietary protein restriction during gestation, as well as altered mother-offspring interactions in the suckling period, might have important long-term hypertensive consequences. The critical periods (developmental windows) should be respected in the future pharmacological or gene therapy of human hypertension.

Troponin I phosphorylation and myofilament calcium sensitivity during decompensated cardiac hypertrophy

We have measured myocyte cell shortening, troponin-I (Tn-I) phosphorylation, Ca2+ dependence of actomyosin adenosinetriphosphatase (ATPase) activity, adenosine 3',5'-cyclic monophosphate (cAMP) levels, and myofibrillar isoform expression in the spontaneously hypertensive rat (SHR) during decompensated cardiac hypertrophy (76 wk old) and in age-matched Wistar-Kyoto rat (WKY) controls. The decreased inotropic response to beta-adrenergic stimulation previously observed in myocytes from 26-wk-old SHR was further reduced at 76 wk of age. In response to beta-adrenergic stimulation, Tn-I phosphorylation was greater in the 76-wk-old SHR than in the WKY, although cAMP-dependent protein kinase A (PKA)-dependent Tn-I phosphorylation in the SHR did not increase with progression from compensated (26 wk) to decompensated (76 wk) hypertrophy. We also observed a dissociation between the increased PKA-dependent Tn-I phosphorylation and decreased cAMP levels in the 76-wk-old SHR versus WKY during beta-adrenergic stimulation. Baseline Tn-I phosphorylation was significantly reduced in 76-wk-old SHR versus WKY and was associated with decreased basal cAMP levels and increased Ca2+ sensitivity of actomyosin ATPase activity. The change in myofilament Ca2+ sensitivity during beta-adrenergic stimulation in the 76-wk-old SHR (0.65 pCa units) was over twofold greater than in the 76-wk-old WKY (0.30 pCa units). We also determined whether embryonic troponin T isoforms were reexpressed in decompensated hypertrophy and observed significant reexpression of the embryonic cardiac troponin T isoforms in the 76-wk-old SHR. The significant decrease in Ca2+ sensitivity with beta-adrenergic stimulation in 76-wk-old SHR may contribute to the severely impaired inotropic response during decompensated hypertrophy in the SHR.

A novel angiotensin II-receptor antagonist, 606A, induces regression of cardiac hypertrophy, augments endothelium-dependent relaxation and improves renal function in stroke-prone spontaneously hypertensive rats

It is well-known that cardiac hypertrophy and arterial and renal dysfunction are serious complications of hypertension. Therefore, we investigated the chronic effects of 606A (2-propyl-3-[2'(1H-tetrazole-5-yl)biphenyl-4-yl]methyl-5-acetyl-4,5,6,7- tetrahydro imidazo [4,5-c]pyridine-4-carboxylic acid disodium salt), a novel AT1-receptor antagonist, on these complications of hypertension in stroke-prone spontaneously hypertensive rats (SHRSP) using Wistar Kyoto rats (WKY) as the control. After 8 weeks treatment from 16 weeks of age with 606A by a subcutaneously implanted osmotic pump, cardiac function, cardiac weight, acetylcholine-induced endothelium-dependent relaxation in the isolated aorta and renal function were estimated. Furthermore, wall thickness of the left ventricle was studied morphologically. We found that 606A (0.3 mg, 1 mg and 3 mg/head/day) dose-dependently lowered blood pressure without any effects on heart rate in SHRSP. Long-term treatments with 606A significantly reduced cardiac weight, left ventricular wall thickness and left ventricular end diastolic pressure, whereas it did not affect cardiac contractility. Endothelium-dependent relaxation of the aorta was recovered, and total protein excretion as well as total protein excretion/creatinine excretion ratio was reduced to the level of WKY by the treatment. These results suggest that 606A not only has a hypotensive effect but also protects cardiac, renal and vascular tissues from complications of hypertension. Thus, 606A could be an useful drug for treatment of hypertension.

Efficient inhibition of the development of cardiac remodeling by a long-acting calcium antagonist amlodipine

The purpose of the present study was to examine the effects of a long-acting calcium antagonist, amlodipine, on the development of cardiac remodeling. Dihydropyridine calcium antagonists have been used widely for many years in the treatment of hypertension and angina pectoris. It has been reported, however, that a prototype of dihydropyridines, nifedipine, does not reduce mortality of patients with ischemic heart disease, possibly because of reflex stimulation of the sympathetic nervous system. A calcium antagonist, amlodipine, has been reported to have potential benefits by virtue of a gradual onset of action and a long duration of effects. Amlodipine (8 mg/kg per day, once a day) or nifedipine (24 mg/kg per day, three times a day) was administered to spontaneously hypertensive 12-week-old rats for 12 weeks. Left ventricular wall thickness was measured by echocardiography, and relative amounts of myosin heavy chain isoforms were assessed by pyrophosphate gels. Expressions of "fetal type" genes and type 1 collagen gene were examined by Northern blot analysis. Amlodipine and nifedipine both markedly reduced systolic blood pressure. However, the decrease in systolic blood pressure caused by nifedipine continued for no more than 8 hours, whereas the blood pressure-lowering effect of amlodipine continued for more than 16 hours post dose. Amlodipine markedly reduced left ventricular wall thickness, whereas nifedipine only weakly attenuated an increase in the wall thickness. Amlodipine, but not nifedipine, prevented an increase in the relative amount of V3 myosin heavy chain isoform and suppressed an increase in mRNA levels of beta-myosin heavy chain, skeletal alpha-actin, and type 1 collagen. Unlike nifedipine, amlodipine effectively prevented cardiac remodeling secondary to high blood pressure at biochemical levels and morphological levels. These results suggest that a long-acting calcium antagonist is more effective than a short-acting one in preventing organ injury in hypertensive subjects.

Inhibition of carnitine synthesis protects against left ventricular dysfunction in rats with myocardial ischemia

During myocardial ischemia, inhibition of the carnitine-mediated transportation of fatty acid may be beneficial because it facilitates glucose utilization and prevents an accumulation of fatty acid metabolites. We orally administered 3-(2,2,2-trimethyl hydrazinium) propionate (MET), an inhibitor of carnitine synthesis, for 20 days to rats. Then we evaluated left ventricular (LV) function during brief ischemia by using a buffer-perfused isovolumic heart model. After 15 min of reoxygenation after the transient ischemia, LV peak systolic pressure (PSP) almost completely returned to the baseline level in rats given MET (96 +/- 4%), whereas it was only partially (77 +/- 16%) recovered in the placebo-treated rats. We induced myocardial infarction in other rats by ligating the left anterior descending coronary artery. Then the animals were given MET for 20 days, and LV function was compared. In the placebo-treated rats (with myocardial infarction, but without drug treatment), LVPSP was lower than that in the sham group [108 +/- 19 (n = 10) vs. 136 +/- 15 mm Hg (n = 13); p < 0.05], and the time constant (T) of LV pressure decay was elongated (36 +/- 4 vs. 30 +/- 7 ms; p < 0.05). In MET-treated groups, however, neither PSP nor T differed from those in the sham group. In conclusion, inhibition of the carnitine-mediated transportation of fatty acid by MET protected against left ventricular dysfunction in acute and chronic myocardial ischemia.

Molecular mechanism of angiotensin II type I and type II receptors in cardiac hypertrophy of spontaneously hypertensive rats

We administered angiotensin (Ang) II receptor type 1 (AT1) blockade (losartan; 10 or 40 mg/kg per day), type II receptor (AT2) blockades (PD123319; 100 mg/kg per day), or angiotensin-converting enzyme (ACE) inhibitor (enalapril; 30 mg/kg per day) to spontaneously hypertensive rats (SHR) from 10 to 20 weeks of age. At the end of the treatment, high doses of losartan and enalapril significantly reduced the arterial systolic blood pressure compared with the untreated SHR to the level of WKY rats. But low doses of losartan and PD123319 were without effect. High doses of losartan and enalapril also significantly reduced both the left ventricular (LV) weight and the ratio of LV to body weight compared with the untreated SHR, which were still larger than that of WKY rats. However, the collagen concentration of SHR treated with high doses of losartan or enalapril was completely reduced to the level of WKY rats. Using reverse transcription polymerase chain reaction, we examined the mRNA expression for ACE, AT1, and AT2 in experimental animals. The enhanced AT1 mRNA expression was significantly decreased in the SHR treated with a high dose of losartan or PD123319 compared with the untreated SHR. The level of ACE mRNA was also decreased in the SHR treated with a high dose of losartan or enalapril. The level of AT2 mRNA was not significantly different between the Wistar-Kyoto rats and the SHR; however, this expression was decreased significantly after the treatment with a high dose of losartan or PD123319. These results indicate that AT1 receptor and ACE, but not AT2 receptor, play a crucial role in the remodeling of matrix tissue but a smaller role in the development of the hypertrophy of LV myocyte in SHR and that the LV/body weight changes do not fully account for the complete suppression of hypertension.

Long-term inhibition of the renin-angiotensin system in genetic hypertension: analysis of the impact on blood pressure and cardiovascular structural changes

OBJECTIVE

To compare, using data from published studies, the efficacy of chronic inhibition of the renin-angiotensin system in inducing persistent downregulation of hemodynamic and cardiovascular structural changes in an adult rat with established genetic hypertension with the widely accepted known downregulation in young genetically hypertensive rats.

STUDY SELECTION

We report on 36 studies that satisfied our inclusion criteria (angiotensin converting enzyme inhibitor or angiotensin II receptor antagonist treatment that lowered arterial pressure levels for at least 3 weeks). Of the 24 studies concerning developing hypertensive rats, a significant number (n = 17) also examined the persistence of any hemodynamic or cardiovascular effects after withdrawal of treatment. Conversely, of 15 studies using adult rats only seven and three reported on post-treatment hemodynamic and cardiovascular structural indices respectively.

RESULTS

During treatment the hemodynamic and cardiovascular structural changes produced were qualitatively and quantitatively similar in the young and adult treated rats. Critical assessment of the persistence of these effects after withdrawal of treatment again found qualitatively similar responses. However, the strength of this finding is limited by the paucity of studies concerning adult rats in which equivalent treatment durations and equipressor doses of treatments were compared between these two age groups.

CONCLUSIONS

Blockade of the renin-angiotensin system appears to have an efficacy in reversing established hypertension and hypertrophy similar to that with which it prevents the development of hypertension and hypertrophy. This partial 'cure' of hypertension after withdrawal of treatment is clearly evident when treatment is initiated during the development of hypertension and appears to be similar even when treatment is initiated in established hypertension.

Steady-state pharmacokinetics and pharmacodynamics of imidaprilat, an active metabolite of imidapril, a new angiotensin-converting enzyme inhibitor in spontaneously hypertensive rats

Imidapril, a new angiotensin-converting enzyme (ACE) inhibitor, was infused subcutaneously at the rates of 9, 30, 90, and 300 micrograms/rat/day for 4 weeks via an osmotic pump implanted under the skin in the back of male spontaneously hypertensive rats (SHRs). Plasma concentrations of imidaprilat as an active metabolite of imidapril, systolic blood pressure (SBP), and plasma ACE activity were determined periodically. These results were also compared with those of enalapril. The plasma concentrations of an active metabolite of both the imidapril and enalapril groups increased according to the doses and showed almost the same plasma concentrations at the same doses. Both groups significantly inhibited plasma ACE activity and reduced SBP, and these actions were maintained for 4 weeks. At the lowest dose studied (9 micrograms/rat/day), imidapril was more potent than enalapril in inhibiting plasma ACE (maximum 2.5-fold difference), but this difference was reduced at higher doses. In contrast, significant differences in SBP effects were observed only at the highest dose studied (300 micrograms/rat/day). Also, the imidapril group significantly decreased the relative heart weight at the rate of 300 micrograms/rat/day. Furthermore, good correlations between plasma imidaprilat concentration and plasma ACE activity or SBP were observed, suggesting that plasma concentration may be a useful marker of pharmacological effects. However, a poor relationship between plasma ACE activity and SBP for enalapril was observed, suggesting that this may not be an adequate marker of pharmacologic efficacy of ACE inhibitors in general. The clinical relevance of these findings is not known at present.

Angiotensin II mediates mechanical stress-induced cardiac hypertrophy

In order to elucidate the signal transduction pathway from external mechanical stress to nuclear gene expression in mechanical stress-induced cardiac hypertrophy, we examined the time course of activation of Raf-1 kinase (Raf-1), mitogen-activated protein kinase kinase (MAPKK) and MAP kinases (MAPKs) in neonatal rat cardiac myocytes. Mechanical stretch transiently activated Raf-1 and MAPKK with a peak at 2 and 5 min after stretch, respectively. In addition, MAPKs were maximally activated at 8 min after stretch. Next, the relationship between stretch-induced hypertrophy and the cardiac reninangiotensin system was investigated. When the stretch-conditioned culture medium was transferred to non-stretched cardiac myocytes, the medium activated MAPK activity slightly but significantly, and the activation was completely blocked by the type I angiotensin II (AngII) receptor antagonist, CV-11974. Moreover, in in vivo studies using spontaneously hypertensive rats, hypertension-induced cardiac hypertrophy was significantly reduced by treatment with subpressure doses of CV-11974. In addition, CV-11974 reduced the isozymic transition of MHC from VI to V3 and inhibited the accumulation of collagen fibers in the extracellular space of the myocardium. These results suggest that mechanical stress activates the protein kinase cascade of phosphorylation in cardiac myocytes in the order of Raf-1, MAPKK and MAPKs. AngII, which is secreted from stretched myocytes, possibly activates these protein kinases. Moreover, it was shown that CV-11974 causes regression of cardiac hypertrophy and has cardioprotective effects on hypertrophied myocardium in vivo.

Functional significance of alterations in cardiac contractile protein isoforms

Multiple closely related, yet distinct, isoforms exist for each of the cardiac contractile proteins. The isoform composition of the heart changes in response to developmental and physiologic cues. This paper reviews the molecular basis for cardiac contractile protein isoform diversity and the functional consequences of isoform shifts.

Enalapril does not prevent the myocardial ischemia caused by the chronic inhibition of nitric oxide synthesis

In rats, chronic administration of the nitric oxide (NO) inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) causes arterial hypertension, cardiac hypertrophy and myocardial ischemic alterations such as necrosis and fibrosis. In this study, we evaluated the effect of 8 weeks of treatment with enalapril maleate on cardiac weight and on the development of the histological alterations induced by L-NAME. Enalapril significantly inhibited the development of both arterial hypertension (117.2 +/- 5.8, 161.8 +/- 8.8 and 122.0 +/- 10.6 mm Hg, for control, L-NAME- and L-NAME + enalapril-treated animals, respectively) and left ventricular hypertrophy (1.36 +/- 0.13, 1.60 +/- 0.04 and 1.48 +/- 0.05 mg/g, for control, L-NAME- and L-NAME + enalapril-treated animals, respectively), but had no effect on the myocardial lesions. These findings demonstrate that although the renin-angiotensin system plays a major role in the development of arterial hypertension and cardiac hypertrophy, it does not modulate the ischemia-induced myocardial alterations observed in this model.

Angiotensin II induces cardiac phenotypic modulation and remodeling in vivo in rats

Cardiac phenotypic modulation and remodeling appear to be involved in the pathophysiology of cardiac hypertrophy and heart failure. We undertook this study to examine whether angiotensin II (Ang II) in vivo, independent of blood pressure, contributes to cardiac phenotypic modulation and remodeling. A low dose (200 ng/kg per minute) of Ang II was continuously infused into rats by osmotic minipump for 24 hours or 3 or 7 days to examine the effects on the expression of cardiac phenotype-related or fibrosis-related genes. This Ang II dose caused a small and gradual increase in blood pressure over 7 days. Left ventricular mRNAs for skeletal alpha-actin, beta-myosin heavy chain, atrial natriuretic polypeptide, and fibronectin were already increased by 6.9-, 1.8-, 4.8-, and 1.5-fold, respectively, after 24 hours of Ang II infusion and by 6.9-, 3.3-, 7.5-, and 2.5-fold, respectively, after 3 days, whereas ventricular alpha-myosin heavy chain and smooth muscle alpha-actin mRNAs were not significantly altered by Ang II infusion. Ventricular transforming growth factor-beta 1 and types I and III collagen mRNA levels did not increase at 24 hours and began to increase by 1.4-, 2.8-, and 2.1-fold, respectively, at 3 days. An increase in left ventricular weight occurred 3 days after Ang II infusion. Treatment with TCV-116 (3 mg/kg per day), a nonpeptide selective angiotensin type 1 receptor antagonist, completely inhibited the above-mentioned Ang II-induced increases in ventricular gene expressions and weight. Hydralazine (10 mg/kg per day), which completely normalized blood pressure, did not block cardiac hypertrophy or increased cardiac gene expressions by Ang II.(ABSTRACT TRUNCATED AT 250 WORDS)

Enalapril treatment increases cardiac performance and energy reserve via the creatine kinase reaction in myocardium of Syrian myopathic hamsters with advanced heart failure

BACKGROUND

Converting enzyme inhibitor treatment of congestive heart failure slows progression to failure and reduces mortality rate. It is known whether these benefits are due solely to improved hemodynamics or also to improved myocyte energetics. This study examines the effect of enalapril treatment on both isovolumic contractile performance and its biochemical correlate, flux through the creatine kinase (CK) system, in an animal model of severely failing myocardium.

METHODS AND RESULTS

Seven-month-old Syrian cardiomyopathic (TO-2 strain) and normal golden Syrian (FIB strain) hamsters were each randomly assigned to one of three groups supplied daily with either no, low (25 mg/kg body wt), or high (100 mg/kg body wt) doses of enalapril for 12 to 14 weeks. At 10 months of age, all substrates and products and flux through the CK reaction were measured in isolated perfused hearts by 31P magnetization transfer and chemical assay. Compared with normal hamsters, the myopathic hamsters exhibited significantly lower body weights and higher biventricular heart weights, which were partially reversed by drug treatment. The Langendorff-perfused hearts showed decreased isovolumic contractile performance with identical load conditions. This was partially reversed by drug treatment. In the failing hearts, the following substrate and product concentrations and enzyme activities were decreased compared with nonfailing hearts but were unchanged by drug treatment: ATP (-28%), phosphocreatine (-48%), free creatine (-64%), ADP (-51%), and CK (-34%, primarily MM isoenzyme). Flux through the CK reaction for the untreated cardiomyopathic hamster hearts was decreased by 67%, and this decrease was almost completely reversed by enalapril treatment. The increased CK flux is due to an increase in the rate constant for the reaction, since substrate concentrations are unchanged, and is not predicted by the rate equation. In enalapril-treated failing hearts, phosphoryl transfer via the CK reaction increased with contractile performance. This was not observed in the nonfailing hearts, in which energy reserve is adequate to support changes in contractile performance.

CONCLUSIONS

Decreased flux through CK reaction leads to decreased capacity for ATP synthesis and may contribute to decreased contractile performance in cardiomyopathic hamster hearts. Enalapril treatment results in increased phosphoryl transfer through the CK reaction in failing myocardium, and this increase is coupled to improved cardiac performance. Decreased CK flux in failing hearts is due to a combination of decreased Vmax and lower guanidino pool; this mechanism fails to explain changes in CK flux in enalapril-treated failing hearts.

Role of regulatory proteins (troponin-tropomyosin) in pathologic states

In vertebrate striated muscle, troponin-tropomyosin is responsible, in part, not only for transducing the effect of calcium on contractile protein activation, but also for inhibiting actin and myosin interaction when calcium is absent. The regulatory troponin (Tn) complex displays several molecular and calcium binding variations in cardiac muscles of different species and undergoes genetic changes with development and in various pathologic states. Extensive reviews on the role of tropomyosin (Tm) and Tn in the regulation of striated muscle contraction have been published describing the molecular mechanisms involved in contractile protein regulation. In our studies, we have found an increase in Mg2+ ATPase activity in cardiac myofibrils from dystrophic hamsters and in rats with chronic coronary artery narrowing. The abnormalities in myofibrillar ATPase activity from cardiomyopathic hamsters were largely corrected by recombining the preparations with a TnTm complex isolated from normal hamsters indicating that the TnTm may play a major role in altered myocardial function. We have also observed down regulation of Ca2+ Mg2+ ATPase of myofibrils from hypertrophic guinea pig hearts, myocardial infarcted rats and diabetic-hypertensive rat hearts. In myosin from diabetic rats, this abnormality was substantially corrected by adding troponin-tropomyosin complex from control hearts. All of these disease models are associated with decreased ATPase activities of pure myosin and in the case of rat and hamster models, shifts of myosin heavy chain from alpha to beta predominate. In summary, there are three main troponin subunit components which might alter myofibrillar function however, very few direct links of molecular alterations in the regulatory proteins to physiologic and pathologic function have been demonstrated so far.

Dose-dependent effects of perindopril on blood pressure and small-artery structure

Long-term treatment of young spontaneously hypertensive rats (SHR) with angiotensin-converting enzyme (ACE) inhibitors has a persistent effect on blood pressure when treatment is withdrawn. The aim of the present study was to determine whether this effect could be mediated by the effect of treatment on resistance-artery structure. We determined the dose dependence of ACE-inhibitor therapy on blood pressure and small-artery structure during treatment and on the recovery of blood pressure when treatment was withdrawn. SHR (40 per group) were treated from age 4 to 24 weeks with one of three doses of perindopril (0.4, 0.8, or 1.5 mg/kg per day). Control groups were untreated SHR and Wistar-Kyoto rats. At 24 weeks, treatment was stopped and small arteries were taken from half of the rats from the mesenteric, femoral, cerebral, and coronary vascular beds for morphological and functional measurements. The blood pressure of the other half of the rats was followed until 36 weeks of age. During treatment, perindopril caused a dose-dependent reduction in blood pressure and in the media-lumen ratio and media area of the small arteries, whereas there was a dose-dependent increase in lumen diameter. The effect of treatment on the structure of arteries from the different vascular beds was homogeneous. Compared with values from Wistar-Kyoto rats, blood pressure normalization in SHR was not associated with full normalization of structure. After withdrawal of treatment, there was an inverse relation between perindopril dose and the persistent effect.(ABSTRACT TRUNCATED AT 250 WORDS)

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

BACKGROUND

Previous studies have demonstrated that angiotensin II (Ang II) acts as a growth-promoting factor directly on cardiac myocytes and that angiotensin-converting enzyme inhibitor induces regression of hypertrophied hearts both in experimental animals and in humans. These results suggest that the renin-angiotensin system (RAS) is involved in the formation of left ventricular hypertrophy (LVH). To elucidate the role of RAS in the progression of cardiac hypertrophy, we evaluated the effect of an Ang II receptor antagonist on LVH in spontaneously hypertensive rats (SHRs) and investigated the molecular mechanisms by which antagonizing Ang II receptors reduces cell hypertrophy of myocytes using the in vitro model of mechanical stretch.

METHODS AND RESULTS

In the in vivo study, we treated SHRs with the nonpeptide Ang II receptor antagonist TCV-116 (0.1, 1, or 10 mg/kg per day) or hydralazine (10 mg/kg per day). Blood pressure was measured by the tail-cuff method, and wall thickness of left ventricle was serially monitored using M-mode echocardiography. Rats were killed at the age of 13, 17, 21, or 25 weeks, and left ventricular (LV) weight, transverse diameter of cardiomyocytes, relative amount of V3 myosin heavy chain (MHC), and degree of interstitial collagen accumulation were examined. Untreated SHRs progressively developed severe hypertension, but treatment with TCV-116 or hydralazine inhibited the increase in blood pressure. Treatment with TCV-116 reduced LV weight, LV wall thickness, transverse diameter of myocytes, relative amount of V3 MHC, and interstitial fibrosis, whereas treatment with hydralazine slightly prevented an increase in LV wall thickness but did not exert significant reduction in other parameters. In the in vitro study, neonatal rat cardiomyocytes were cultured on deformable silicone dishes and mechanically stretched with or without pretreatment of CV-11974 (an active metabolite of TCV-116), and [3H]phenylalanine incorporation, activity of mitogen-activated protein (MAP) kinase, and c-fos mRNA expression were analyzed. Pretreatment of cultured cardiomyocytes with 10(-7) mol/L CV-11974 inhibited an increase in [3H]phenylalanine incorporation, MAP kinase activity, and c-fos gene expression induced by stretch of cardiomyocytes.

CONCLUSIONS

The Ang II receptor antagonist TCV-116 induced regression of cardiac hypertrophy and had cardioprotective effects on hypertrophied myocardium in vivo, and antagonizing Ang II receptors inhibited intracellular signaling of stretch-mediated cardiomyocyte hypertrophy in vitro. These results suggest a crucial role of the cardiac RAS in the development of LVH produced by pressure overload.

Replacement of salt by a novel potassium- and magnesium-enriched salt alternative improves the cardiovascular effects of ramipril

1. The influence of salt (sodium chloride; NaCl) (an additional 6% in the diet) and that of a novel sodium-reduced, potassium-, magnesium-, and L-lysine-enriched salt alternative on the cardiovascular effects of ramipril was studied in stroke-prone spontaneously hypertensive rats in a 6-week study. The intake of sodium chloride was adjusted to the same level by adding the salt alternative at a 1.75 times higher amount than regular salt. 2. Salt produced a marked rise in blood pressure and induced cardiac hypertrophy and significant mortality, while the salt alternative neither increased blood pressure nor caused any mortality and produced less cardiac hypertrophy than salt. 3. Ramipril treatment at a daily dose of 3 mg kg-1 normalized blood pressure and prevented the development of cardiac hypertrophy of rats on control diet. These effects of ramipril were blocked by the addition of salt but were only slightly attenuated by the addition of the salt alternative. The mortality in the salt group was prevented by ramipril. 4. Responses of mesenteric arterial rings in vitro were examined at the end of the study. Salt, but not the salt alternative, increased vascular contractile responses to noradrenaline. Ramipril treatment improved the arterial relaxation responses to acetylcholine and to sodium nitroprusside. The vascular relaxation enhancing effect of ramipril was blocked by salt but only slightly attenuated by the salt alternative. 5. Ramipril treatment did not significantly increase plasma renin activity in the presence or in the absence of salt supplementation. The salt alternative did not cause hyperkalaemia, either alone or in combination with ramipril treatment. 6. Both salt supplementations, irrespective of ramipril treatment, induced a six to eight fold increase in the urinary excretion of calcium. There was an expected 90 to 140% rise in the urinary excretion of magnesium and 200% rise in the urinary excretion of potassium in the salt alternative group. Salt also produced an approximately 50% increase in magnesuria.7. Our findings suggest that replacement of salt by the potassium-, magnesium- and L-lysine-enriched salt alternative improves the cardiovascular effects of ramipril. In the present study the beneficial effect was related to the increased intakes of potassium and/or magnesium and L-lysine from the salt alternative because the amount of sodium chloride was the same.

Carvedilol, a novel cardiovascular agent, inhibits development of vascular and ventricular hypertrophy in spontaneously hypertensive rats

The effects of carvedilol, a novel cardiovascular agent, were evaluated in developing spontaneously hypertensive rats (SHR) for effects on hemodynamics, and the ability to effect the development of left ventricular, and vascular hypertrophy associated with chronic hypertension. Chronic oral administration of low dose carvedilol (20 mg/kg/day) was initiated when rats were 5 weeks of age, and experiments progressed until 14 weeks of age. Carvedilol-treated SHR had significantly reduced systolic blood pressures and heart rates throughout the duration of the experiment, and had significantly reduced ventricle/body weights by approximately 9.0%. Morphologic analysis of tertiary branches of the mesenteric artery revealed that carvedilol-treated SHR had significant reductions in medial cross-sectional area. Carvedilol produced concentration-dependent inhibition of basal [3H]thymidine incorporation in cultured SHR vascular smooth muscle cells, as well as by stimulation produced by PDGF (1 nM), EDGF (1 nM), thrombin (0.5 U/ml), or endothelin-1 (1 nM), indicating that carvedilol had direct anti-mitogenic activity. The present studies demonstrate that low dose carvedilol produced sustained reductions in blood pressure and heart rate in developing SHR that were accompanied by significant inhibition in the development of vascular and myocardial hypertrophy. The morphological changes induced by carvedilol may be mediated by a combination of hemodynamic effects, as well as by direct anti-mitogenic effects on vascular smooth muscle.

Effect of early onset angiotensin converting enzyme inhibition on myocardial capillaries

We investigated the preventive effects of long-term treatment with the angiotensin converting enzyme inhibitor ramipril on myocardial left ventricular hypertrophy and capillary length density in spontaneously hypertensive rats. Rats were treated in utero and subsequently up to 20 weeks of age with a high dose (1 mg/kg per day) or with a low dose (0.01 mg/kg per day) of ramipril. Animals given a high dose of ramipril remained normotensive, whereas those given a low dose developed hypertension in parallel to vehicle-treated controls. At the end of the treatment period, converting enzyme activity in heart tissue was inhibited dose-dependently in the treated groups. Both groups revealed an increase in myocardial capillary length density together with increased myocardial glycogen and reduced citric acid concentrations. Left ventricular mass was reduced only in high dose- but not in low dose-treated animals. Our results demonstrate that early onset treatment with a converting enzyme inhibitor can induce myocardial capillary proliferation, even at doses too low to antagonize the development of hypertension or left ventricular hypertrophy. We hypothesize that potentiation of kinins is responsible for this effect, probably by augmenting myocardial blood flow, which is a well-known trigger mechanism of angiogenesis in the heart.

Verapamil blocks basal and angiotensin II-induced RNA synthesis of rat aortic vascular smooth muscle cells

We evaluated VER effect on RNA synthesis of quiescent and angiotensin II (AII)- stimulated cultured rat aortic vascular smooth muscle cells (VSMC). In a dose-dependent manner, VER decreased [3H]uridine uptake by quiescent VSMCs (ED50 7 x 10(-6)M), an effect that was shared by other calcium antagonists, but to a variable degree. VER caused a significant effect within 3 hours and attained a maximal effect at 7 hours. In addition VER caused a 22 +/- 2% decrease in [3H]uridine uptake by VSMCs stimulated with 10% fetal bovine serum, while it completely abolished [3H]uridine uptake by VSMCs induced by AII. We conclude that VER decreases basal and inhibits AII-induced increase in mRNA synthesis of VSMCs. These data may explain in part how VER causes a decrease in vascular resistance and alters the vasoconstrictor effect of AII.

Mechanisms of cardiac growth. The role of the renin-angiotensin system

Hypertension is associated with cardiac hypertrophy, which is a structural adaptation of the heart in order to attenuate the systolic stress on the left ventricle. As cardiac myocytes cannot divide, they increase in mass and volume, probably by activating second messengers and proto-oncogenes involved in cellular differentiation and proliferation. Various mechanisms, such as pressure overload and angiotensin II (Ang II), have been proposed to trigger cardiocyte growth and left-ventricular hypertrophy (LVH). In both cases, activation of second messenger routes which increase the intracellular calcium concentration, protooncogene expression, and protein synthesis have been demonstrated. Ang II also facilitates the action of another trophic agent for cardiocytes, which is noradrenaline (NA). In addition, the prevention and reversal of LVH by inhibitors of angiotensin-converting enzyme (ACE) suggests a key role for Ang II. However, no conclusive evidence has demonstrated the role of a single pathophysiologic factor in LVH. Therefore, it is more attractive to suggest a link between high blood pressure, renin-angiotensin and other vasoactive systems, such as the adrenergic system, which might together lead in a synergistic way to cardiac hypertrophy.