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Endocrinology Vol. 149, No. 2 476-482
Copyright © 2008 by The Endocrine Society

Endogenous Relaxin Does Not Affect Chronic Pressure Overload-Induced Cardiac Hypertrophy and Fibrosis

Qi Xu1, Edna D. Lekgabe1, Xiao-Ming Gao, Ziqiu Ming, Geoffrey W. Tregear, Anthony M. Dart, Ross A. D. Bathgate, Chrishan S. Samuel and Xiao-Jun Du

Baker Heart Research Institute (Q.X., E.D.L., X.-M.G., Z.M., A.M.D., X.-J.D.), Melbourne, Victoria 8008, Australia; and Howard Florey Institute (E.D.L., G.W.T., R.A.D.B., C.S.S.), University of Melbourne, Melbourne, Parkville, Victoria 3010, Australia

Address all correspondence and requests for reprints to: X.-J. Du, Baker Heart Research Institute, P.O. Box 6492, St. Kilda Road Central, Melbourne, Victoria 8008, Australia. E-mail: xiaojun.du{at}baker.edu.au.


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
The effect of endogenous relaxin on the development of cardiac hypertrophy, dysfunction, and fibrosis remains completely unknown. We addressed this question by subjecting relaxin-1 deficient (Rln1–/–) and littermate control (Rln1+/+) mice of both genders to chronic transverse aortic constriction (TAC). The extent of left ventricular (LV) remodeling and dysfunction were studied by serial echocardiography over an 8-wk period and by micromanometry. The degree of hypertrophy was estimated by LV weight, cardiomyocyte size, and expression of relevant genes. Cardiac fibrosis was determined by hydroxyproline assay and quantitative histology. Expression of endogenous relaxin during the course of TAC was also examined. In response to an 8-wk period of pressure overload, TAC mice of both genotypes developed significant LV hypertrophy, fibrosis, hypertrophy related gene profile, and signs indicating congestive heart failure when compared with respective sham controls. The severity of these alterations was not statistically different between the two genotypes of either gender. Relaxin mRNA expression was up-regulated, whereas that of its receptor was unchanged in the hypertrophic myocardium of wild-type mice. Collectively, the extent of pressure overload-induced LV hypertrophy, fibrosis, and dysfunction were comparable between Rln1+/+ and Rln1–/– mice. Thus, although up-regulated in its expression, endogenous relaxin had no significant effect on the progression of cardiac maladaptation and dysfunction in the setting of chronic pressure overload.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
RELAXIN IS A 6-kDa polypeptide hormone that primarily interacts with relaxin family peptide receptor 1 (RXFP1) (1). Recent studies have demonstrated multiple biological functions of relaxin, including its ability to remodel the extracellular matrix and to stimulate the breakdown of collagen in reproductive and nonreproductive organs such as the skin, lung, kidney, liver, and heart (2, 3, 4, 5, 6, 7, 8, 9, 10). The therapeutic actions of exogenous relaxin have been potent and rapid occurring in preventing and/or reversing established cardiac fibrosis (8, 9, 10), while demonstrating cardiac protection in vitro and in vivo in the setting of ischemia or oxidative stress (10, 11, 12, 13). Furthermore, mice lacking the major circulating form of relaxin (Rln1–/–) have demonstrated that relaxin is an important endogenous regulator of collagen turnover in the aging heart and other nonreproductive organs (9, 14, 15, 16).

Experimental and clinical studies have attempted to ascertain a direct role of endogenous relaxin in the setting of cardiovascular disease. Patients with heart failure have had markedly increased expression of human relaxins in the plasma and myocardium, which was positively correlated with the severity of heart failure (17). Although there exist reports with conflicting data (18, 19), the findings of this study (17) were confirmed, at least in part, by several other clinical studies (20, 21, 22) and with recent experimental studies showing significant elevation of relaxin expression in various models of heart disease (10, 23). However, the role of endogenous relaxin in the progression of heart disease remains unclear.

Based on the documented cardiac actions of relaxin (13) and our recent findings on the antifibrotic actions of exogenous relaxin in another pressure overload model, the spontaneously hypertensive rat (12), we hypothesize that endogenous relaxin plays a beneficial role in the setting of heart disease. If this were correct, it would be expected that the Rln1–/– mice would respond poorly to an insult of disease relative to wild-type littermates. To test this possibility, we subjected Rln1–/– and littermate control (Rln1+/+) mice to chronic pressure overload by surgically induced transverse aortic constriction (TAC), and determined how the absence of endogenous relaxin affected the progression of disease, particularly involving the processes of cardiac hypertrophy, fibrosis, and dysfunction. We also measured the gene expression levels of relaxin and RXFP1 in the hypertrophic mouse myocardium. The rationale for the use of the pressure overload model is that it is a well-established model, associated with significant myocardial hypertrophy and fibrosis (24, 25, 26, 27, 28, 29), and has been widely used to document adverse effects of numerous genetic interventions (24, 25, 26, 30, 31).


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Animals and surgery
Rln1–/– and Rln1+/+ mice were generated from heterozygous (Rln1+/–) breeders with a C57Blk6Jx129SV genetic background, individually genotyped and aged to 4–5 months for these studies. In view of the fact that a gender-dependant cardiac fibrotic phenotype was observed in aging Rln1–/– mice (16), we studied male and female mice separately.

All experiments were approved by a local Animal Ethics Committee, in accordance with the National Institutes of Health guidelines. Before surgery, mice were anesthetized with an ip injection of ketamine/xylazine/atropine (100/20/1.2 mg/kg, respectively) and intubated for ventilation. With the aid of a surgical microscope, a midline incision was made at the sternum, and the aorta was dissected between the right innominate and the left carotid arteries. The aorta was then constricted by approximately 65% to a lumen size of 0.4 mm using a probe, as previously described (24, 32). Sham-operated mice were subjected to similar surgery except for the constriction of the aorta. Operated animals were monitored and studied for a period of 8 wk after surgery.

Echocardiography
Echocardiography was performed in conscious mice at 1, 4, and 8 wk after surgery using a SONOS5500 ultrasound machine (Hewlett-Packard Co., Palo Alto, CA) with a 15-MHz linear transducer, as described previously (33, 34). Mice were trained before each test for two sessions per day over a 4-d period as described previously. During training sessions each mouse was held by grasping the nape of the neck with the tail wrapped to restrain the animal (see Fig. 2Go). Preheated ultrasound transmission gel was applied to the thorax, and a probe-like object was repeatedly stroked across the chest, mimicking actual conditions of the echocardiographic examination. This training procedure was repeated three times per session, with each session lasting 5–10 min. Two-dimensional-guided M-mode images from the left ventricular (LV) short-axis view were obtained, and the following parameters were measured digitally using the leading edge technique: heart rate (HR), LV dimensions at diastole (LVDd) and systole, external LV diastolic diameter (ExLVDd), and averaged LV wall thickness at diastole (WTd). Measurements were made from three consecutive cardiac cycles and averaged. We calculated the following: LV mass index (LVMI) = (ExLVDd3 – LVDd3) x 1.055, then normalized by body weight, ratio of WTd (h):LVDd (r) (h/r) = [(ExLVDd – LVDd)/LVDd], and LV fractional shortening (FS) = (LVDd – LV dimensions at systole)/LVDd x 100%. Echocardiography and image analyses were performed in a blinded fashion using a coded system.


Figure 2
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  		FIG. 2. Serial echocardiographic examination was performed on conscious mice for LV remodeling and dysfunction after sham operation or TAC. Measures taken include WTd (A), LVMI (B), LVDd (C), h/r ratio (D), and LV FS (E) at 1, 4, and 8 wk after surgery. All values are the mean ± SE of eight to 17 per group. *, {dagger}, P < 0.05 vs. respective gender matched sham-operation group, as determined by a two-way repeated measure ANOVA. KO, knockout; W, wk.

 
Micromanometry
At 8 wk after surgery, cardiac hemodynamics was assessed by LV catheterization. Animals were anesthetized with an ip injection of ketamine/xylazine/atropine (100/10/1.2 mg/kg, respectively). A 1.4-F Millar catheter (Millar Instruments, Houston, TX) was inserted via the right carotid artery into the ascending aorta and the LV, as described previously (24). HR, aortic blood pressures, LV pressures, time constant of isovolumic pressure relaxation, and maximal rates of increase or decay of LV pressures were acquired and analyzed using Chart 5 software (AD Instruments, Colorado Springs, CO).

Morphometric measures
Under a microscope we inspected the presence of signs that indicated heart failure (chest fluid accumulation, lung congestion, and chronic atrial thrombus) (24). We measured body weight, tibial length, and weights of the left ventricle, right ventricle, atria, lungs, kidney, and liver. The left ventricle was frozen for gene expression, collagen (hydroxyproline) content analysis, or fixed for histological analyses.

Quantitative histology and hydroxyproline assay
The middle portion of the left ventricle was fixed in buffered 10% formalin solution, paraffin embedded, transversely cut into 5-µm sections, and stained with hematoxylin and eosin or 0.1% Picrosirius Red. Collagen content was analyzed by both quantitative histology and hydroxyproline assay (16). Using the Optimas 6.5 program (Media Cybernetics, Inc., Bethesda, MD), and in a blinded fashion, interstitial collagen content in the left ventricle was determined by measuring areas that positively stained (collagen) with Picrosirius Red, and results from 15–20 randomly selected fields per LV section were averaged and expressed as the percentage of a field. Myocyte cross-sectional area was taken as an average of 50–70 cells from 15 randomly selected fields (32). Hydroxyproline levels of the left ventricle were also determined chemically as described previously with values converted to collagen content (16).

Gene expression analysis
Total RNA was extracted from LV samples using TRIZOL reagent (Invitrogen Corp., Carlsbad, CA). After RNase-free DNase treatment (Promega Corp., Madison, WI), RNA (1 µg) was reverse transcribed to cDNA with the use of random primers (Promega) and Superscript III RNase H– Reverse Transcriptase (Invitrogen). RNA transcripts of atrial natriuretic peptide (ANP), β-myosin heavy chain (MHC), {alpha}-MHC, sarcoendoplasmic reticulum Ca2+-ATPase (SERCA2a), RXFP1, relaxin-1 (Rln1), and glyceraldehyde phosphate dehydrogenase (GAPDH) were determined by SYBR Green PCR using Master Mix (Invitrogen) and specifically designed primers with an ABI PRISM 7700 Sequence Detection System (Applied Biosystems, Foster, CA), as we described previously (32). PCR efficiency of various genes was predetermined to be comparable, and gene expression levels were normalized by that of GAPDH.

Statistical analysis
Results are expressed as the mean ± SE or percentages. Echocardiography data were analyzed by two-way ANOVA for repeated measures, followed by an independent t test if necessary, whereas all other results were analyzed by two-way ANOVA (to account for the two variables: genotype and TAC) with a Bonferroni post hoc test and unpaired Student’s t test, or by Fisher’s exact test. P < 0.05 indicates statistical significance.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Expression of relaxin and RXFP1 in the hypertrophied mouse heart
The lack of Rln1 mRNA expression in the heart of Rln1–/– mice has previously been demonstrated by our group (16). The gene expression of both Rln1 and RXFP1 in the hypertrophic LV myocardium of wild-type male animals was examined by real-time PCR. There was a 2-fold increase in the mRNA expression of Rln1 at 4 and 8 wk after TAC (both P < 0.05 vs. that measured in sham controls; Fig. 1AGo). In contrast, the mRNA levels of RXFP1 remained unchanged in the hypertrophic heart compared with that measured in sham controls (Fig. 1BGo).


Figure 1
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  		FIG. 1. Gene expression of Rln1 (A) and RXFP1 (B) in the hypertrophic LV myocardium of wild-type mice subjected to pressure overload for 4 and 8 wk. All values are the mean ± SE of six to eight samples per group. The sham-operated group contains a mixture of animals, 4 and 8 wk after surgery. *, P < 0.05 vs. sham-operated control.

 
Pathological events and cardiac hypertrophy
After excluding surgery related deaths within the first 24 h, all sham-operated mice and a total of 68 mice with TAC survived. Eight mice died within 1 wk after surgery; five mice (three male Rln1+/+ and two female Rln1–/–) died of heart failure, and three mice (two female Rln1+/+ and one male Rln1–/–) died of large artery rupture. By 8 wk after TAC, about 30–40% of male and female Rln1+/+ mice had signs that indicated the presence of congestive left heart failure, i.e. massive pleural effusion, severe lung congestion (defined as lung wet weight over sham group mean + 3 SD), and chronic atrial thrombus (Table 1Go) (24). In comparison, male and female Rln1–/– animals with TAC had similar incidences of heart failure.


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  		TABLE 1. Body weights, organ weights, myocyte size, and incidence of pathological events detected by autopsy

 
Body weight and tibia length measured at termination were very similar between respective sham-operated and TAC groups, and as a result of this, the heart and organ weights were expressed as absolute values. The weights of the left ventricle, right ventricle, atria, and lungs of mice subjected to TAC increased significantly (all P < 0.05) over respective sham-operated controls (Table 1Go), whereas weights of the liver and kidney remained unchanged (data not shown). Heart and LV weights increased by 64–90% in males and by 110–135% in female mice with TAC (Table 1Go). The atrial wet weight of TAC mice was doubled and that of lungs increased by 70% vs. that measured in sham-operated controls, indicative of congestive heart failure. In all cases involving the increase in cardiac chamber and lung weights, there was no genotype-dependent difference observed in the TAC mice (Table 1Go). Furthermore, sham-operated mice of both genders and genotypes had similar LV cardiomyocyte size, whereas cardiomyocyte size was significantly enlarged by 54–84% in both genders of mice, 8 wk after TAC, regardless of genotype.

TAC mice had markedly increased systolic arterial pressure, LV systolic pressure, and pulse pressure over sham-operated values (all P < 0.01; Table 2Go). However, there was no significant difference in the TAC-induced increments of these parameters in both genders of Rln1+/+ and Rln1–/– mice, indicating a similar degree of pressure overload. In addition, LV end-diastolic pressure was increased to a similar degree in female Rln1+/+ and Rln1–/– mice with TAC (Table 2Go).


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  		TABLE 2. Effects of TAC for 8 wk on hemodynamics by micromanometry

 
Functional assessments
To follow the time-dependent development of hypertrophic growth and LV dysfunction, echocardiography was performed on conscious mice at 1, 4, and 8 wk after TAC surgery. Male and female mice of both genotypes showed a significant increase in WTd as early as 1 wk after TAC and onwards (Fig. 2AGo). A progressive increase in LV hypertrophy, measured as LVMI, was also noticed in all TAC groups (Fig. 2BGo). In this study LV mass by echocardiography at 8 wk after TAC correlated well with LV weight (r = 0.857; n = 90; P < 0.001). LV chamber size increased significantly from wk 4 in all TAC groups and was further enlarged at wk 8 (Fig. 2CGo). LV h/r ratio, derived from WTd and radius of LV dimension, was largely maintained in male mice with TAC but significantly increased in female mice with TAC during the early phase of TAC, indicating concentric hypertrophy (Fig. 2DGo). Furthermore, in TAC mice of both genders, eccentric hypertrophy become apparent during the late stage of the study period, as indicated by less further changes or even a reduction in WTd from that measured at wk 1 after TAC, together with a progressive LV dilatation (Fig. 2Go, B and D). In conscious and restrained male and female mice of both genotypes, FS was also reduced moderately at wk 1 and more profoundly at 4 and 8 wk after TAC (Fig. 2EGo). However, in all cases there were no genotype-dependent differences in these observations.

Interstitial collagen content
LV fibrosis was assessed by quantitative histology and the hydroxyproline assay (Fig. 3Go). By histology, a 5- to 6-fold increase in collagen content was observed in hearts of 6- to 7-month-old TAC mice of both genders (Fig. 3Go, A and B), compared with that measured in sham controls. The hydroxyproline assay revealed a 30–50% increase in collagen content relative to sham-operated controls (Fig. 3CGo). Once more, there were no differences in collagen content between Rln1+/+ and Rln1–/– animals with TAC.


Figure 3
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  		FIG. 3. Collagen content by histological and biochemical determination. A, Representative LV sections stained with 0.1% Picrosirius red from all groups as indicated (magnification, x20). B, Percent LV interstitial collagen content quantified from Picrosirius red-stained sections with results expressed as percent collagen content relative to the sham-control group of the same gender. C, Collagen concentration in the left ventricle determined by hydroxyproline assay with results expressed as relative values seen in their gender-matched sham-control mice (µg/mg dry weight tissue). All values are the mean ± SE from six mice per group. *, P < 0.05, {dagger}, P < 0.05; **, P< 0.01; {dagger}{dagger}, P < 0.01 vs. respective sham control.

 
Hypertrophy related gene expression
Hypertrophied LV tissues (from TAC mice) showed a multifold up-regulation in ANP and β-MHC mRNA expression, whereas that of {alpha}-MHC and SERCA2a was down-regulated by about 50% (all P < 0.05 vs. sham-control values; Fig. 4Go). However, there were no differences in the expression pattern of all genes tested in Rln1+/+ and Rln1–/– mice with sham operation or TAC of either gender (P > 0.05).


Figure 4
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  		FIG. 4. Expression of ANP (top-left panel), β-MHC (top-right panel), {alpha}-MHC (bottom-left panel), SERCA2a (bottom-right panel) normalized by GAPDH. All values are the mean ± SE from five to six mice per group. *, P < 0.05; **, P < 0.01; {dagger}, P < 0.05; {dagger}{dagger}, P < 0.01 vs. respective sham-control group.

 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
Using relaxin-deficient mice, we examined the role of endogenous relaxin in a chronic pressure overload model of cardiac remodeling and dysfunction. We showed that expression of Rln1 mRNA in the hypertrophic heart of wild-type mice was up-regulated, a finding in keeping with several clinical and experimental reports (10, 17, 20, 21, 22, 23). However, our results showed comparable changes between Rln1+/+ and Rln1–/– mice in the severity of cardiac hypertrophy, fibrosis, and ventricular dysfunction, and importantly, these findings were not influenced by gender. Thus, our data suggest that endogenous relaxin does not appear to affect the development of myocardial hypertrophy, collagen buildup, LV remodeling and dysfunction due to chronic pressure overload.

Although an up-regulation of relaxin mRNA expression in the compromised heart and an increase in plasma relaxin levels have been documented by experimental and clinical studies (10, 17, 22, 23), the significance of this elevation of endogenous relaxin (by cardiac and noncardiac sources) remains unexplored. Recent studies, including ours, have demonstrated that relaxin is a potent but safe antifibrotic factor (8, 9, 10, 13, 14, 15, 16) when applied exogenously, suggesting that endogenous relaxin may similarly protect the injured heart from the progression of fibrosis. This is supported by the findings that Rln1–/– male mice develop an age-dependent cardiac fibrosis (16), whereas administering exogenous relaxin at pharmacological doses was able to reverse preexisting fibrosis in Rln1–/– male mice and in other experimental models of heart disease (8, 9, 10). It is plausible that the 2-fold increase in relaxin mRNA that was measured in Rln1+/+ animals with TAC might not have been enough to produce the therapeutic effects seen with pharmacological doses of exogenous relaxin (8, 9). Because assay methods to detect relaxin protein levels in mice are currently unavailable, this possibility remains to be tested in the future. In addition, expression of RXFP1 in the setting of heart disease remains completely unexplored. Previous studies have shown that cardiomyocytes and cardiac fibroblasts express RXFP1 mRNA (9, 13), while specific relaxin binding to the myocardium has also been documented (35). We observed that RXFP1 gene expression in the hypertrophied myocardium of wild-type animals was unchanged when compared with levels measured in the respective sham-operated control mice.

There has been controversy surrounding the influence by relaxin on heart function (13). In a previous study, we did not observe any functional differences between aged Rln1–/– and Rln1+/+ mice at either baseline or with β-adrenergic stimulation (16). In the present study, a varying degree of LV dysfunction was documented in mice during the course of pressure overload. Again though, the extent of LV dysfunction after chronic pressure overload was comparable between Rln1–/– and Rln1+/+ animals. This is in keeping with the similar degree of myocardial hypertrophy and interstitial fibrosis observed between the genotypes. Collectively, there is no evidence that endogenous relaxin might affect cardiac function directly. It is worth pointing out that in the majority of previous studies on mice with TAC, echocardiography was performed under anesthetized conditions. According to these studies, a maintained FS was consistently reported within the first few weeks after surgery, whereas LV dysfunction and chamber dilatation become detectable at later stages (36, 37, 38). By performing echocardiography on conscious mice, we have revealed a significant although moderate decline in FS as early as 1 wk after TAC. Meanwhile, LV chamber dilation was observed during the early stages of TAC-induced injury. Thus, performing echocardiography in conscious animals appears to have improved the sensitivity of detecting cardiac dysfunction and remodeling without the confounding influence of anesthetics, as shown by previous studies (33, 34, 39).

In contrast to the well-documented antifibrotic actions of relaxin, there have been very few studies that have evaluated the effects of relaxin on cardiomyocytes, per se, during the process of cardiac hypertrophy. One recent study has revealed that myocardial relaxin levels negatively correlated with hypertrophic indices in vitro (23). In our study there was no significant genotypical difference in parameters of hypertrophic growth in response to pressure overload. This apparent lack of influence by endogenous relaxin on the degree of pressure overload-induced hypertrophy is in keeping with our recent study on the spontaneously hypertensive rat model, showing a lack of an effect by exogenously administered relaxin on indices of cardiac hypertrophy (8). Using cultured cardiomyocytes, we also showed that the extent of cardiomyocyte hypertrophy stimulated by the {alpha}1-adrenergic agonist, phenylephrine, was not affected by the addition of relaxin (12). However, relaxin was potent in inhibiting cardiomyocyte hypertrophy stimulated by cardiac fibroblast-conditioned medium (12), indicating that a paracrine function of fibroblasts most likely promotes cardiomyocyte hypertrophy, which is abolished by relaxin through its ability to inhibit fibroblast proliferation and differentiation/activation (9, 12, 13). Thus, our findings from the current study imply that at least within the time course studied, fibroblast-derived factors might not have played a significant role in promoting TAC-induced hypertrophic growth.

The presence of myocardial fibrosis in the hypertrophic heart was confirmed by hydroxyproline assay and quantitative histology, in keeping with previous reports (32, 40). However, once again, there was no significant disparity in TAC-induced collagen deposition between the genotypes. It is noteworthy that the beneficial effects of exogenous relaxin were observed in experimental models of heart disease, when cardiac fibrosis was the consequence of cardiomyopathy (9, 10) or hypertension (8), as a result of activated pro-fibrotic hormonal factors, such as the renin-angiotensin system and cytokines (TGF-β1) (28), known to be effectively inhibited by relaxin (18). In this regard, the TAC model may be different in that an increased biomechanical stress (or wall stress) is the major cause of the interstitial fibrosis, particular during the early phase of disease progression, suggesting that the experimental setting chosen may have contributed to the lack of an effect of endogenous relaxin.

In conclusion, our findings collectively suggest that endogenous relaxin does not play a pivotal role in the process of pressure overload-mediated myocardial remodeling and dysfunction. However, the protective potential of endogenous relaxin cannot be excluded in heart disease of other etiology, such as cardiomyopathy and ischemic heart disease, or from other organs undergoing inflammation- and cytokine-induced fibrosis (41, 42). Thus, additional studies are required to confirm the potential role of endogenous relaxin in the heart by subjecting Rln1–/– mice to other models of experimental heart disease. In addition, considering the low and sometimes undetectable levels of circulating and/or organ levels of endogenous relaxin, our findings do not contradict the beneficial effects achieved by administration of exogenous relaxin at pharmacological doses on the diseased heart (3, 4, 5, 6, 7, 8, 9) and other organs (12, 29, 32).


   Footnotes
 
This work was supported by grants from the National Heart Foundation of Australia (G04M1524), the Australian Research Council (LP0560620), and the National Health and Medical Research Council of Australia (225108). C.S.S. is a National Health and Medical Research Council/National Heart Foundation of Australia Career Development Fellow, and G.W.T., A.M.D., R.A.D.B., and X.-J.D. are National Health and Medical Research Council Fellows.

Disclosure Statement: The authors have nothing to declare.

First Published Online November 8, 2007

1 Q.X. and E.D.L. contributed equally to this work. Back

Abbreviations: ANP, Atrial natriuretic peptide; ExLVDd, external left ventricular diastolic diameter; FS, fractional shortening; GAPDH, glyceraldehyde phosphate dehydrogenase; h/r, ratio of diastolic wall thickness and radius of LV dimension; HR, heart rate; LV, left ventricular; LVDd, LV dimensions at diastole; LVMI, LV mass index; MHC, myosin heavy chain; Rln1, relaxin-1; Rln1–/–, relaxin-1 deficient; Rln1+/+, littermate control; RXFP1, relaxin family peptide receptor 1; SERCA2a, sarcoendoplasmic reticulum Ca2+ATPase; TAC, transverse aortic constriction; WTd, LV wall thickness at diastole.

Received September 4, 2007.

Accepted for publication October 26, 2007.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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