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*Cardiomyopathy
Endocrinology Vol. 143, No. 12 4846-4855
Copyright © 2002 by The Endocrine Society

ARTICLE

Effect of Chronic Treatment with Bovine Recombinant Growth Hormone on Cardiac Dysfunction and Lesion Progression in UM-X7.1 Cardiomyopathic Hamsters

Sylvie Marleau, Nathalie Lapointe1, Julie Massicotte1, Catia Céméus, Gaëtan Jasmin, Louis Dumont, Martin G. Sirois, Jean-Lucien Rouleau, Patrick du Souich and Huy Ong

Faculty of Pharmacy (S.M., C.C., H.O.) and Departments of Pharmacology (J.M., L.D., M.G.S., P.d.S., H.O.) and Pathology (G.J.), Faculty of Medicine, Université de Montréal, Montréal, Québec, Canada H3C 3J7; Montréal Heart Institute (M.G.S.), Montréal, Québec, Canada H1T 1C8; and Department of Cardiology (N.L., J.-L.R.), Toronto University Health Network, Toronto, Ontario, Canada H1T 1C8

Address all correspondence and requests for reprints to: Dr. Huy Ong, Faculty of Pharmacy, Université de Montréal, P.O. Box 6128, Station Downtown, Montréal, Québec, Canada H3C 3J7. E-mail: huy.ong{at}umontreal.ca.


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
In view of the potentially beneficial effect of GH on ventricular function of humans suffering from idiopathic dilated cardiomyopathy, we undertook a study to evaluate the optimal time to initiate treatment with GH and its duration in UM-X7.1 cardiomyopathic hamsters (CMH). GH (1 mg/kg·d) therapy was initiated either in the early or late (30 and 160 d old, respectively) phases of the disease and continued until death at 240 d of age. Age- and sex-matched Golden Syrian hamsters (GSH) were used as controls. Basal IGF-1 levels in serum were reduced by nearly half in CMH compared with GSH but were increased within a physiological range in male hamsters. In contrast, female hamsters presented elevated basal serum IGF-1 levels that were not further elevated by GH administration, as reported in experimental models and humans. Accordingly, the present study will focus on the effects of GH therapy on cardiac performance in male hamsters.

GH did not improve ventricular function when starting at a late stage of the disease compared with CMH controls. Maximum rate of left ventricular pressure development decreased by approximately 64% in CMH treated early with recombinant bovine GH. Ventricular dysfunction was associated with morphologic indices of hypertrophy, ventricular dilatation, and extensive fibrosis. Mortality was strikingly increased in GH-treated CMH for 210 d (four males and eight females), as opposed to four females (and no male) in the vehicle-treated group. These results suggest that chronic treatment with recombinant bovine GH in CMH, starting at an early stage of lesion development, is associated with a reduced cardiac performance at the terminal stage of the disease.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
GH DEFICIENCY (GHD) in adults has been associated with an increased prevalence of cardiovascular morbidity and mortality (1, 2). In particular, the development of GHD in childhood results in reduced cardiac output at rest and during exercise secondary to a reduction in myocardial wall thickness. These symptoms have been associated with the development of a dilated form of cardiomyopathy leading to heart failure (HF). Treatment of these patients with GH improves left ventricular function, reduces diastolic blood pressure, reduces the carotid media thickness, and modulates the profile of lipoproteins by increasing HDL and the overall well-being of patients (2, 3). These observations suggest that patients suffering from severe cardiac failure resulting from dilated cardiomyopathy, but without GHD may respond to GH.

The idiopathic form of dilated cardiomyopathy (IDC) is characterized by considerable interstitial fibrosis with loss of myocytes, significant ventricular dilatation, and reduced contractility. IDC invariably leads to a progressive systolic dysfunction, which is associated with a very poor prognosis (4). In 1996, Fazio et al. (5) reported an increase in left ventricular mass (LVM) and cardiac output, as well as reduced secretion of norepinephrine and reduced plasma levels of aldosterone in a small number of patients with IDC treated with recombinant human (rh) GH at a dose of 0.15 IU/kg·wk during 3 months. The overall improvement of the cardiac status in these patients was associated with an improved exercise tolerance and myocardial energetics. In contrast, a double-blind study from Osterziel et al. (1998) (6) performed in a larger group of patients with dilated cardiomyopathy did not show beneficial effects of rhGH therapy when administered at a dose of 2 IU/d for 3 months, in spite of an increase in LVM and IGF-1 levels. Similarly, Isgaard et al. (1998) (7) reported that rhGH treatment, at a dose of 0.1 IU/kg·wk during 1 wk followed by 0.25 IU/kg·wk during 3 months in patients with New York Heart Association class II and III congestive heart failure of different etiologies (8), increased IGF-1 levels but did not improve cardiac function. Conflicting results have been also reported for GH therapy in patients with ischemic cardiac failure treated for up to 6 months (9). These apparent discrepancies could be related to differences in the timing of initiation of treatment in the disease process, in dosing regimens and/or in duration of GH treatment. In view of the potential benefit of GH therapy in patients suffering from cardiac failure secondary to idiopathic dilated cardiomyopathy that respond poorly to conventional heart failure therapy, additional studies aimed to characterize the optimal time and duration to start GH treatment have been performed.

In the present study, we thus evaluated the effects of GH on cardiac performance in the Syrian cardiomyopathic hamster (CMH) model of IDC. We studied the UM-X7.1 strain of CMH, which derived from the BIO 14.6 strain that presents hereditary abnormalities in both cardiac and skeletal muscles due to an inherited mutation in the gene coding for {delta}sarcoglycan of the dystrophin complex (10). This model features traits of the human idiopathic cardiomyopathy (11, 12). In this model, heart lesions are rarely seen before 30–40 d after birth, after which three phases are generally observed in the course of the disease: 1) the phase of necrosis that usually extends from 30–100 d and is followed by 2) healing, fibrosis, mild cardiac hypertrophy, and dilatation between 100–160 d after birth and, 3) the terminal phase of the disease that is associated with an increase in ventricular dilatation and heart failure until death (life span rarely exceed 300 d) (12, 13, 14). In this CMH model, we assessed the optimal time for GH administration on cardiac function and disease progression. Recombinant bovine (rb) GH was administered at a fixed dose of 1 mg/kg·d from either 30 or 160 d after birth until they were killed at 240 d. Hence, in this study, the pharmacological effects of daily GH injections were investigated before and after the onset of dilated cardiomyopathy in CMH. The effects of GH therapy on cardiac contractility index, the passive left ventricular pressure-volume relationship, cardiac fibrosis and morphometry were assessed. The major observation in the present study is that rbGH therapy in CMH, initiated at an early phase of the disease, does not prevent disease progression; it is rather associated with a significant impairment in ventricular function in the late phase of the disease, as assessed in the isolated Langendorff’s heart model.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Animals
The experiments were conducted on male and female Golden Syrian hamsters (GSH) (Charles River, St-Constant, Québec, Canada) and CMH of the UM-X7.1 line were provided by Dr. G. Jasmin (Department of Pathology, Faculty of Medicine, Université de Montréal, Montréal, Québec, Canada). The animals were housed in cages (less than five per cage) and fed with standard chow diet and water ad libitum. GH or vehicle treatment was begun in either 30- (early) or 160-d-old (late) CMH as well as in age- and sex-matched GSH. The animal study protocol was reviewed and approved by the institutional Animal Ethics Committee of the Université de Montréal and conducted in accordance with the Canadian Council on Animal Care guidelines for use of experimental animals.

GH preparations
rbGH was kindly provided by Monsanto (St. Louis, MO). Stock solutions of rbGH (10 mg/ml) were prepared by adding sterile water to the lyophilized rbGH. One-milliliter aliquots were frozen at -80 C. One aliquot was diluted 1/10 with 0.9% NaCl and kept for a maximum of 7 d at 4 C and used for daily sc injections, administered between 0800 h and 1100 h. Long-term efficacy of rbGH preparation in hamsters has been assessed by monitoring serum IGF-1 levels and weight gain at the end and throughout the study period, respectively.

Study protocol and systolic function
Male and female CMH were assigned to one of four groups (n = 15–17 hamsters per group): groups 1 and 2 received daily injections of either rbGH (1 mg/kg, 100 µl/100 g) (group 1) or 0.9% NaCl (group 2), starting at 30 d (early) and continued for another 210 d after birth in both groups. Group 3 received daily injections of rbGH (1 mg/kg) and group 4, 0.9% NaCl, starting at 160 d and continued another 80 d in both groups.

At 240 d, the animals in all groups were anesthetized with chloral hydrate (30 mg/100 g) ip 30 min after the sc administration of the morning dose of rbGH or 0.9% NaCl and received 1000 IU of heparin ip. One milliliter of blood was taken from the jugular vein, the heart superfused with cold saline, after which the aorta was isolated and the heart rapidly dissected out. The hearts were retrogradely perfused according to the Langendorff’s method with oxygenated modified Krebs-Ringer buffer (Ca2+,1.25 mM) at 37 C, and at a pressure of 140 cm of H2O. A latex balloon (no. 5 or 6, Hugo-Sachs Electronik, March-Hugstetten, Germany) was introduced into the left ventricle through the left atrium and connected to a pressure transducer. The hearts were permitted to beat freely for a 15-min stabilization period. Left ventricular systolic and diastolic pressures were obtained with the ventricular balloon filled with 0.9% NaCl to obtain a diastolic pressure of 5 mm Hg. Left ventricular pressure was computed as systolic minus diastolic pressure. After a 15-min equilibration period, the left ventricular (LV) pressure, its first derivative, LV + maximal rate of pressure rise (dP/dtmax), and heart rate were registered with a Grass recorder (Model 7400, Astro-Med Inc., West Warwick, RI). Once the isovolumetric pressures were recorded, the hearts were arrested in diastole by infusing a solution of potassium chloride (20 mM). The isolated heart model allows assessment of intrinsic ventricular performance without systemic influences (15, 16).

Passive pressure-volume relationship
To eliminate the influence of the right ventricle, it was cut off once the heart was removed from the Langendorff’s perfusion system. A double-lumen catheter (PE-50 inside PE-200) was inserted 6 mm into the left ventricle via the aorta. The atrioventricular groove was ligated and the ventricle emptied of all remaining Krebs-Henseleit’s solution. A negative pressure (-5 mm Hg) was created in the ventricle, using a syringe connected to a three-way stopcock placed between the ventricle and a pressure transducer. A quantity of 0.9% NaCl was infused at a rate of 0.68 ml/min via one lumen while the intraventricular pressure was continuously recorded on a Gould recorder 2600s (Cleveland, OH) by means of the other lumen. The ventricular volumes at pressures of -5, 0, 2.5, 5, 10, 15, 20, and 30 mm Hg were used to plot the curves of the pressure-volume relationship (17).

Planimetry and histology evaluations
Once the pressure-volume relationship was assessed, the hearts were filled with Krebs Ringer’s solution to a filling pressure of 15 mm Hg, sealed, and fixed in its distended form in 10% PBS-buffered formalin for 24 h. The hearts were cut midway between base and apex, and cross-sectional slices were obtained 1 mm above and below the middle cut, and inserted into a cassette for continued fixing, dehydration and embedding in paraffin in preparation for histologic studies. Representative cross-sections of each heart were stained with Masson’s trichrome stain and mounted on a slide for projection to a magnification of x10. Extent of fibrosis in the myocardium was assessed using image analysis (Scion Imaging Software, Scion Corp., Frederick, MD) as previously described (18) and by expressing the results in terms of % collagen over the whole left ventricular surface area.

Ventricular cavity and surface, endocardial and epicardial diameters, as well as endocardial and epicardial circumferences were measured by planimetry as previously described (17). Wall thickness was calculated as the mean of three measurements obtained at different sites. Myocardial area was calculated as the difference between left ventricular surface including ventricular vessels and left ventricular cavity, as previously described (18).

Serum IGF-1 measurement
Serum was obtained from the blood and frozen at -20 C until assayed for measurement of IGF-1 levels. The serum concentrations of IGF-1 were determined by RIA on hydrochloric acid-ethanol extracts using radiolabeled human IGF-1 (Nichols Institute Diagnostics, San Juan Capistrano, CA). The assay was performed according to manufacturer’s instructions.

Statistical analysis
Data are expressed as mean ± SEM. Comparisons between groups were performed using a one-way ANOVA followed by pair-wise multiple comparisons using the Student-Newman-Keuls method. Comparisons between the passive diastolic pressure-volume curves was done using a multivariate ANOVA useful for growth curves (19), followed by the Bonferroni rule for pair-wise comparisons between curves. Differences were considered significant at P < 0.05.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Effect of rbGH on body and heart weight and IGF-l serum levels
Male GSH and CMH receiving daily sc injections of rbGH for either 80 (late treatment) or 210 (early treatment) d had a significant increase in body weight (BW) compared with their respective controls (Fig. 1Go, A and B). Male GSH treated for 210 d with rbGH had a BW of 235 ± 9 g compared with 180 ± 7 g for vehicle treated GSH (P < 0.05). Male CMH treated for 210 d with rbGH had a BW of 199 ± 8 g compared with 118 ± 3 g for vehicle-treated CMH (P < 0.05). Similar results were observed for hamsters treated for 80 d (Fig. 1BGo), and female hamsters (data not shown). Heart weight increased in proportion with BW in GSH inasmuch as the heart to BW ratios, as well as the ratios of LV weight to BW, were not significantly changed by GH treatment in both early and late treated GSH. Heart to BW ratios were increased in untreated (vehicle) CMH compared with GSH, suggesting cardiac hypertrophy in CMH (Tables 1Go and 2Go). rbGH treatment in CMH when adjusted to BW (heart weight to BW ratio) prevented cardiac hypertrophy in early treated CMH and attenuated it in late treated CMH as compared with vehicle.



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  		Figure 1. Cumulative mean BW in male GSH and CMH aged 30 d (A) and 160 d (B) when initiating treatment with vehicle (0.9% NaCl) (open symbol) or rbGH, 1 mg/kg·d sc (closed symbol). Data represent the mean value of n = 5–7 hamsters (surviving at 240 d) in each group.

 

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  		Table 1. Cardiac morphologic characteristics of 240-d-old male GSH and CMH after 210 d of treatment with rbGH or vehicle, starting at 30 d after birth (early treatment)

 

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  		Table 2. Cardiac morphologic characteristics of 240-d-old GSH and CMH after 80 d of treatment with rbGH or vehicle, starting at 160 d after birth (late treatment)

 
Levels of IGF-1 in serum were higher in male GH-treated GSH and CMH compared with their controls, indicating responsiveness to GH treatment (Fig. 2Go). CMH had lower levels of IGF-1 in serum than GSH. Elevated basal levels of IGF-1 were found in female serum, 804 ± 55 ng/ml and 365 ± 31 ng/ml in GSH and CMH, respectively, in hamsters treated for 210 d. GH treatment did not further elevate IGF-1 serum concentrations (data not shown). No antibovine GH antibodies were detected in GSH as well as in CMH sera (data not shown).



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  		Figure 2. Serum IGF-1 levels in male GSH and CMH treated with vehicle (open bar) or with 1 mg/kg·d rbGH (solid bar) for 210 d (A), starting 30 d after birth (early treatment) and for 80 d (B), starting 160 d after birth (late treatment). Data are presented as the mean ± SEM of n = 5–6 hamsters. *, P < 0.01 and **, P < 0.001 compared with vehicle; ##, P < 0.001 CMH compared with GSH.

 
Cardiac planimetry and histologic evaluation
The morphologic characteristics of hearts from male GSH and CMH receiving daily sc injections of rbGH for 80 or 210 d are presented in Tables 1Go and 2Go, respectively. GSH hearts from hamsters treated with rbGH from 160 d after birth (late treatment) had no difference in epicardial and endocardial circumference; myocardial area and myocardial thickness compared with control hearts, whereas hearts from GSH treated with rbGH for 210 d had an increase in epicardial circumference and myocardial area (Table 1Go). Hearts from CMH treated with rbGH for 210 d had an increase in endocardial and epicardial circumference, indicating that significant ventricular dilatation occurred in these hearts compared with hearts from CMH treated with 0.9% NaCl over this period. Myocardial area and thickness did not change.

Treatment with rbGH did not significantly alter cardiac fibrosis in GSH (data not shown). Prolonged treatment with rbGH for either 210 (Fig. 3AGo) or 80 (Fig. 3BGo) significantly increased the extent of collagen staining in 240-d-old CMH. Figure 4Go illustrates collagen staining with Masson’s trichrome in GHS and CMH treated for 210 d with either vehicle or rbGH.



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  		Figure 3. Percentage collagen in left ventricle from male GSH and CMH treated with vehicle (open bar) or with 1 mg/kg·d rbGH (solid bar) for 210 d (A), starting 30 d after birth and for 80 d (B), starting 160 d after birth (**, P < 0.001 compared with vehicle).

 


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  		Figure 4. Trichrome Masson stain of hearts from GSH treated with 0.9% NaCl and CMH treated with either 0.9% NaCl or rbGH (1 mg/kg·d) for 210 d.

 
Systolic function
The maximum rate of pressure development in isolated-heart preparations and ventricular pressure were decreased by approximately 64% in CMH treated with rbGH for 210 d as compared with CMH controls (Fig. 5Go, A and C). Heart rate (Fig. 5EGo) was reduced by 23% in CMH treated with rbGH for 210 d. These results suggest that a prolonged treatment with rbGH at a fixed dose of 1 mg/kg·d in CMH, starting at an early stage of lesion development, is associated with reduced cardiac performance at the terminal stage of the disease. In contrast, GH administration in CMH aged 160 d until death, at 240 d, did not significantly alter cardiac performance (Fig. 5Go, B, D, and F). Interestingly, CMH controls had relatively preserved cardiac performance as compared with GSH.



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  		Figure 5. Cardiac parameters in isolated male GSH and CMH hearts. Hamsters have been treated with vehicle (open bar) or with rbGH (1 mg/kg·d) (solid bar) for 210 d (A), starting 30 d after birth and for 80 d (B), starting 160 d after birth. Data are presented as the mean ± SEM of n = 4–6 hearts per group, according to the number of surviving hamsters and viable hearts at 240 d. *, P < 0.05 and **, P < 0.001 compared with vehicle.

 
Diastolic pressure-volume relationship
The passive pressure-volume relationships were obtained after the hearts were arrested in diastole by switching to a Krebs-Henseleit solution with a high K+ solution (20 mM). In both vehicle and rbGH-treated CMH, early treatment was associated with a leftward shift of the passive pressure-volume curves compared with that of GHS curves, consistent with the increase in cardiac fibrosis in CMH. For the group of rbGH-treated CMH, a rightward shift of the passive pressure-volume relationship of CMH was found compared with that of vehicle-treated CMH, consistent with ventricular dilatation (Fig. 6Go).



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  		Figure 6. Passive pressure-volume relationships of the GSH and CMH hearts treated for 210 d. Male GSH (square symbols) and CMH (circle symbols) were treated with vehicle (0.9% NaCl) (open symbol) or rbGH, 1 mg/kg·d sc (closed symbol). Data represent the mean value of n = 4–5 hamsters (surviving at 240 d) in each group. *, P < 0.05 compared with 0.09% NaCl-treated CMH.

 
Survival rate in CMH and GSH
Figure 7Go shows the survival rate curve of CMH (male and female) throughout the course of the experiments. As shown in the figure, mortality is strikingly increased in CMH treated with rbGH, in particular in the group treated for 210 d (early treatment).



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  		Figure 7. Survival rate in CMH that have been treated with vehicle (dash line) or rbGH (1 mg/kg·d) (solid line) for 210 d, starting 30 d after birth and for 80 d, starting 160 d after birth in male (A) and female (B).

 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
The effects of GH therapy on the cardiovascular system have been well demonstrated in disorders with excessive or deficient GH protection. Effectively, the substitutions of GH in GH deficiency conditions resulted in an increase of ventricular wall mass, an improvement of cardiac function and a reduction of vascular resistance (20, 21). These beneficial effects of GH on cardiac function in patients with GH deficiency and in experimental myocardial infarction in rats (22, 23) have led to the evaluation of this hormone in the treatment of idiopathic dilated cardiomyopathy. GH therapy in human patients with heart failure secondary to IDC or other conditions led to conflicting results, with LV hypertrophy associated with either improvement of heart function (5, 24, 25, 26), or not (6, 8). These discrepancies may stem from different durations of treatment and doses used between studies and it has been suggested that individual therapeutic regimens may be required for successful GH therapy of heart failure (23). In the present study, we have investigated the optimal time to start treatment and its duration with a fixed dose of GH in cardiomyopathic hamsters, a genetic model featuring traits of the human disease.

The UM-X7.1 cardiomyopathic hamster strain established at the Université de Montréal is a subline of the original BIO 14.6 strain of the Bio-Research Institute (Cambridge, MA) (13, 14). The cardiomyopathy in this strain shows similar features to that of the human disease, including substantial and diffuse fibrosis (4), which in diseased animals accompanies the myolitic and calcification process, cardiac hypertrophy, circulatory failure and ventricular dilation in the terminal phase of the disease (13, 14). Most animals die from congestive heart failure (13). Hence, this model provides unique possibilities of studying the effect of pharmacological treatments on disease progression. The present study was designed to address the effect of a prolonged administration of GH on disease evolution in CMH, initiating the therapy either at the early (30 d after birth) or late (160 d after birth) phase of the disease until they were killed at 240 d of age. Previous studies on the effects of GH on cardiac function in experimental models of cardiac failure in the rat and in CMH were restricted to short periods (3–4 wk) of rhGH administration, due to the development of antihuman GH antibodies during GH therapy. In the present study, appearance of anti-GH antibodies has been circumvented by using rbGH, which shares high sequence homology with the hamster GH sequence (86%), hence low immunogenic properties in CMH (27). No detectable hamster antibovine GH antibody levels were detected by ELISA in GSH and CMH (data not shown).

Interestingly, IGF-1 serum levels were nearly 2-fold lower in untreated CMH compared with GSH (Fig. 2Go). These observations are in agreement with alterations in the somatotrophic system in patients with IDC, inasmuch as serum levels of IGF-1 in these patients are diminished in relation to the severity of heart failure (28). Reduced levels of IGF-1 may be related to a decreased sensitivity to GH (28). Alternatively, reduced IGF-1 levels could be related to peripheral GH resistance and to the increase of IGFBP-3 circulating levels (29). In addition, whereas male hamsters responded to GH by a physiological increase in IGF-1 serum levels, female hamsters had elevated IGF-1 basal levels and their response to GH (in terms of IGF-1 increase) appeared to be blunted. Gender dimorphism in the response to GH has been reported in both in experimental models and humans (30, 31, 32, 33) and may be linked to gonadal steroids (32). In the present study, gender dimorphism in the response to GH was associated with an increase mortality rate in female CMH (Fig. 7Go). Although it appears that prolonged GH therapy exerted more deleterious effects in female than in male CMH, we cannot exclude that female CMH may have been more affected by the disease from the very beginning of the study.

The dose of GH (1 mg/kg·d) was selected on the basis of preliminary results showing that BW increase, as well as heart to BW ratio did not differ between 1 and 3 mg/kg rbGH administered for 40 d in 200-d-old CMH (data not shown). A daily dose of 1 mg/kg·d of rbGH induced a steady increase in the mean BW in both GSH and CMH, further supporting a response to the trophic effect of GH throughout the experimental period (Fig. 1Go). The dose of GH used in our study is relatively modest compared with that used in experimental heart failure models (2–4 mg/kg·d) (34).

Most studies on the effect of GH treatment on experimental cardiac failure have used a post-infarction heart failure model in rats. These studies have consistently shown that rhGH (2–3 mg/kg·d) in surviving animals improved cardiac performance, as shown by enhanced myocardial contractility and reduced left ventricular end-diastolic pressure and peripheral vascular resistance (23, 34). Beneficial effects have also been found after combined IGF-1 and GH in experimental heart failure (22). These studies provided experimental evidence for a potentially beneficial role of GH in preserving cardiac function in experimental heart failure secondary to myocardial infarction, but studies in models mimicking human dilated cardiomyopathy are scarce. Recently, Ryoke et al. (35) studied the effects of a 21-d treatment with rhGH (2 mg/kg twice daily) in CMH (CHF 147, a derivative of the UM-X7.1 CMH line) aged 4 and 10 months, respectively. Short-term GH treatment had favorable effects in the 4-month CMH, which was characterized by an increase in the LV dP/dtmax, reduced LV wall stress, and no increase in the preload (left ventricular end-diastolic pressure), indicating enhanced myocardial contractility. However, in the 10-month CMH, GH did not exert any beneficial effect on cardiac function, even when combining GH treatment with ACE inhibitors to prevent cardiac remodeling. These discrepancies could be related to the increase LV fibrosis in older CMH (35).

The major findings in the present study are that daily treatment with sc injections of rbGH at a fixed dose of 1 mg/kg in 30-d-old CMH, until death at 240 d, is associated with a significant impairment in ventricular function. Isolated hearts from these hamsters showed depressed myocardial contractility, as both LV developed pressure and LV +dP/dtmax, were markedly reduced. In addition, ventricular dysfunction was associated with morphologic indices of ventricular dilatation and extensive fibrosis that further extend with GH therapy. Consistent with extensive cardiac fibrosis in CMH, the passive pressure-volume relationships were shift to the left compared with that of GHS. Furthermore, an increase in ventricular dilatation appears to occur from the rightward shift of the pressure-volume curve of rbGH-treated CMH. Paradoxically, CMH treated 210 d with rbGH therapy had a decrease in cardiac hypertrophy as compared with their CMH controls as judged by a significant decrease in LV weight/BW ratio. Indeed, despite an impressive increase in BW, 210-d GH-treated CMH had a significant decrease in LV weight/BW ratio compared with all groups including the GSH groups. Although part of this difference could be explained by an increase in edema or fluid retention in 240-d-old GH-treated CMH, no clinical difference between the two CMH groups was noted. Compatible with inadequate cardiac hypertrophy in the 210-d-old GH-treated CMH is the decrease in myocardial thickness as compared with the control GSH that had much thicker myocardium despite similar BW. The morphologic changes in late (80 d) treated CMH were directionally similar but less marked.

The reason for a reduced heart rate in CMH after a prolonged treatment with GH is unclear; however, ß-adrenergic dysfunction in heart failure is well established. In CMH, ß-adrenergic receptors are functionally uncoupled from the Gs protein at the early stage of the disease. This phenomenon may result from the increased sympathetic tone associated with this pathology, as exemplified by the increased urinary excretion of norepinephrine in 50-d-old CMH (13). Yet, whether ß-adrenergic dysfunction is associated with receptor down-regulation is controversial and different studies reported either no change (CHF 147 strain) or a significant decrease in receptor numbers in 210- to 220-d-old CMH (UM-X7.1) (12). Whether ß-adrenergic receptor uncoupling to signaling pathways and/or receptor down-regulation contributed to the altered cardiac hemodynamics observed in the present study remain to be investigated. In addition to its anabolic and cardiac effects, GH is known to regulate glucose and lipid metabolism (36). Under GH excess conditions such as acromegaly or high dose GH treatment, the diabetogenic action of GH becomes apparent. Whether prolonged GH therapy significantly modulated glucose metabolism in the present study appears unlikely considering that a 5 mg/kg daily dose of biosynthetic human GH administered to 105-d-old female rat for 80 d did not modify the final blood glucose levels (37).

Overall, our results show that a prolonged administration of rbGH in CMH did not prevent development of ventricular dilatation, nor did it avert systolic dysfunction. Moreover, collagen deposition in GH-treated CMH increased, which may have compromised both systolic and diastolic function, and survival at 240 d in long-term-treated CMH was clearly reduced. Hence, ventricular remodeling in CMH did not benefit from chronic (210 d) GH therapy. In contrast, daily administration of GH in CMH from 160 d after birth, when the animals undertook the terminal phase of the disease, did not appear to improve or worsen ventricular function compared with CMH controls, despite increased interstitial fibrosis (Figs. 3Go and 4Go). In agreement, Ryoke et al. (35) showed that GH had few beneficial effects at 10 months in hamsters with severe heart failure, but our results clearly show that a sustained administration may be detrimental. To our knowledge, the present study is the first describing the effect of span life therapy with GH on the cardiovascular function. Our observations may have negative implications for the use of long-term GH therapy as a means to improve cardiac performance in IDC patients. Yet, selected patients may benefit from GH therapy (5, 38, 39). Keeping in mind the increased cardiovascular risk with prolonged administration of GH at pharmacological doses, the benefit/risk ratio of GH adjunct in IDC therapy of patients may require continuous individual assessment.


   Acknowledgments
 
Recombinant bovine GH was kindly supplied by Monsanto Co. (St. Louis, MO). The authors are grateful to Mrs. Lucie Héroux and Dominique Lauzier for skillful technical assistance.


   Footnotes
 
This work was supported by Pharmacia-Upjohn and the Canadian Institutes of Health Research.

1 N.L. and J.M. contributed equally to this work. Back

Abbreviations: BW, Body weight; CMH, cardiomyopathic hamsters; dP/dtmax, maximal rate of pressure rise; GHD, GH deficiency; GSH, Golden Syrian hamsters; HF, heart failure; IDC, idiopathic form of dilated cardiomyopathy; LV, left ventricular; LVM, left ventricular mass; rb, recombinant bovine; rh, recombinant human.

Received July 30, 2002.

Accepted for publication August 22, 2002.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Merola B, Cittadini A, Colao A, Longobardi S, Fazio S, Sabatini D, Saccá L, Lombardi G 1993 Cardiac structural and functional abnormalities in adult patients with growth hormone deficiency. J Clin Endocrinol Metab 77:1658–1661[Abstract]
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S. Marleau, M. Mulumba, D. Lamontagne, and H. Ong
Cardiac and peripheral actions of growth hormone and its releasing peptides: Relevance for the treatment of cardiomyopathies
Cardiovasc Res, January 1, 2006; 69(1): 26 - 35.
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