A preliminary study of growth hormone in the treatment of dilated cardiomyopathy

Treatment with growth hormone enhances contractile reserve and intracellular calcium transients in myocytes from rats with postinfarction heart failure

BACKGROUND

Recombinant human growth hormone (GH) improves in vivo cardiac function in rats with postinfarction heart failure (MI). We examined the effects of growth hormone (14 days of 3.5 mg. kg-1. d-1 begun 4 weeks after MI) on contractile reserve in left ventricular myocytes from rats with chronic postinfarction heart failure.

METHODS AND RESULTS

Cell shortening and [Ca2+]i were measured with the indicator fluo 3 in myocytes from MI, MI+GH, control, and normal animals treated with GH (C+GH) under stimulation at 0.5 Hz at 37 degrees C. Cell length was similar in MI and MI+GH rats (150+/-5 and 157+/-5 microm) and was greater in these groups than in the control and C+GH groups (140+/-4 and 139+/-4 microm, P<0.05). At baseline perfusate calcium of 1.2 mmol/L, myocyte fractional shortening and [Ca2+]i transients were similar among the 4 groups. We then assessed contractile reserve by measuring the increase in myocyte fractional shortening in the presence of high-perfusate calcium of 3.5 mmol/L. In the control and C+GH groups, myocyte fractional shortening and peak systolic [Ca2+]i were similarly increased in the presence of high-perfusate calcium. In the presence of high-perfusate calcium, both myocyte fractional shortening and peak systolic [Ca2+]i were depressed in the MI compared with the control groups. In contrast, myocyte fractional shortening (14.1+/-.9% versus 11.1+/-.9%, P<0.05) and peak systolic [Ca2+]i (647+/-43 versus 509+/-37 nmol/L, P<0.05) were significantly higher in MI+GH than in MI rats and were comparable to controls. Left ventricular myocyte expression of sarcoplasmic reticulum Ca2+ ATPase 2 (SERCA-2) and left ventricular SERCA-2 protein levels were increased in MI+GH compared with MI rats.

CONCLUSIONS

Calcium-dependent contractile reserve is depressed in myocytes from rats with postinfarction heart failure. Long-term growth hormone therapy increases contractile reserve by restoring normal augmentation of systolic [Ca2+]i in myocytes from rats with postinfarction heart failure.

Growth hormone and the heart

Until a few years ago, growth hormone (GH) and insulin-like growth factor-1 (IGF-1) were considered essential only to the control of linear growth, glucose homeostasis, and for the maintenance of skeletal muscle mass. A large body of evidence recently coming from animal and human studies has unequivocally proven that the heart is a target organ for the GH/IGF-1 axis. Specifically GH exerts both direct and indirect cardiovascular actions. Among the direct effects, the ability of GH to trigger cardiac tissue growth plays a pivotal role. Another direct effect is to augment cardiac contractility, independent of myocardial growth. Direct effects of GH also include the improvement of myocardial energetics and mechanical efficiency. Indirect effects of GH on the heart include decreased peripheral vascular resistance (PVR), expansion of blood volume, increased glomerular filtration rate, enhanced respiratory activity, increased skeletal muscle performance, and psychological well-being. Among them, the most consistently found is the decrease of PVR. GH may also raise preload through its sodium-retaining action and its interference with the hormonal system that regulates water and electrolyte metabolism. Particularly important is the effect of GH on skeletal muscle mass and performance. Taking into account that heart failure is characterized by left ventricular dilation, reduced cardiac contractility, and increase of wall stress and peripheral vascular resistance, GH may be beneficial for treatment of heart failure. Animal studies and preliminary human trials have confirmed the validity of the GH approach to the treatment of heart failure. Larger placebo-controlled human studies represent the main focus of future investigations.

Role of TGF-beta1 in platelet-mediated cardioprotection during ischemia-reperfusion in isolated rat hearts

Platelets protect myocardium against ischemia-reperfusion injury. This study examined the role of platelet-derived TGF-beta1 in cardioprotection during ischemia-reperfusion. Isolated Sprague Dawley rat hearts were perfused with K-H buffer and subjected to 25 min of global ischemia followed by 30 min of reperfusion. Ischemia-reperfusion resulted in myocardial dysfunction indicated by increase in CPP and LVEDP, and decrease in dLVP. Perfusion of hearts with washed platelets or supernatant of aggregated platelets attenuated (P < 0.01) of myocardial dysfunction following ischemia-reperfusion. Ischemia-reperfusion resulted in a decrease in myocardial TGF-beta1 determined by immunohistochemistry. ELISA showed an increase in latent TGF-beta1, but a decrease in active TGF-beta1. Perfusion of hearts with platelets or aggregated platelet supernatant preserved myocardial TGF-beta1 content upon ischemia-reperfusion. Perfusion of hearts with recombinant TGF-beta1 also resulted in cardioprotection following ischemia-reperfusion qualitatively similar to that observed with platelets or aggregated platelet supernatants. RT-PCR analysis showed an increase in myocardial TGF-beta1 mRNA following ischemia-reperfusion. These observations indicate that platelets protect the myocardium against ischemia-reperfusion-mediated dysfunction at least in part by releasing TGF-beta1. Increase in both TGF-beta1 mRNA and latent TGF-beta1 does not indicate a defect in the translation of mRNA. Reduction in myocardial TGF-beta1 following ischemia-reperfusion suggests a defect in the conversion of latent TGF-beta1 to active TGF-beta1.

Effect of oxymetholone on left ventricular dimensions in heart failure secondary to idiopathic dilated cardiomyopathy or to mitral or aortic regurgitation

This study suggests that the short-term administration of a small dosage of anabolic steroids may have a beneficial effect on the deteriorated myocardium, although long-standing exposure to a larger dosage of anabolic steroids may induce myocardial and systemic complications.

Insulin-like growth factor I stimulates cardiac myosin heavy chain and actin synthesis in the awake rat

To determine the effect of insulin-like growth factor I (IGF-I) on cardiac contractile protein synthesis in vivo, we measured L-[ring-2, 6-3H]phenylalanine incorporation into myosin heavy chain and actin during intravenous infusions (4 h) of either saline or IGF-I (1 microgram. kg-1. min-1) in awake rats. After an overnight fast, IGF-I increased myosin synthesis by 29% compared with saline (11.5 +/- 0.8 vs. 8.9 +/- 0.6%/day, P < 0.01) and actin synthesis by 26% (7.2 +/- 0.3 vs. 5.7 +/- 0.3%/day, P < 0.01), with similar effects in left and right ventricles and a comparable effect on mixed cardiac protein. When amino acids were infused with IGF-I, a further increase in myosin synthesis was observed (P < 0.01). In fed rats, despite higher baseline synthesis rates than in fasted rats (P < 0. 01), IGF-I also increased the synthesis of myosin (12.3 +/- 0.5 vs. 9.9 +/- 0.5%/day, P < 0.01) and actin (8.8 +/- 0.3 vs. 7.5 +/- 0. 2%/day, P < 0.01) compared with saline. IGF-I infusion had no hypoglycemic effect and did not change heart rate or blood pressure. Thus relatively low-dose IGF-I has a direct action in vivo to acutely increase heart contractile protein synthesis in both fasted and fed awake rats.

New method to evaluate myocyte remodeling from formalin-fixed biopsy and autopsy material

BACKGROUND

Excessive lengthening of cardiac myocytes attributed to series addition of sarcomeres is a consistent feature of left ventricular dilation in chronic heart failure. Currently, it is not feasible to assess myocyte dimensions, particularly myocyte length, in a manner that is of potential diagnostic usefulness.

METHODS AND RESULTS

Isolated myocytes from three groups of normal rats (100, 200, and 300 g) were obtained by using two different methods: (1) digestion of formalin-fixed myocardial tissue using potassium hydroxide (KOH) and (2) retrograde aortic perfusion of fresh hearts with collagenase. There was no difference in mean cell length between the two methods. The KOH method was also used to isolate intact, rod-shaped myocytes from formalin-fixed human cadaver left ventricles (control, n = 3; heart failure, n = 3) and from human right ventricle biopsy specimens (n = 6). Confirming our previous work using collagenase-isolated myocytes from fresh human explants, left ventricular myocytes from failing hearts showed longer mean cell length compared with control hearts. Data from human right ventricle biopsy specimens confirmed our previous finding in rats that myocyte lengthening is less pronounced in this chamber in heart failure.

CONCLUSIONS

The KOH method can be used to obtain reliable measurements of myocyte length and other cellular parameters from myocardial biopsies and autopsy material. Such data may be useful in the diagnostic assessment of remodeling associated with heart failure.

Etiology and response to drug treatment in heart failure

Clinical trials in heart failure (HF) tend to randomize patients according to demographic characteristics and severity of left ventricular dysfunction, without taking account of the precise diagnosis. This article reviews results from recent trials suggesting that the etiology of HF, and particularly whether it is ischemic or nonischemic, may influence the long-term prognosis and the response to treatment. Some studies, but not all, suggest that nonischemic HF has a better prognosis than ischemic HF. The data on the benefits of angiotensin-converting enzyme inhibitors in ischemic versus nonischemic HF are conflicting. Carvedilol, and recently, bisoprolol have been shown to reduce mortality in ischemic and nonischemic HF, whereas metoprolol has, to date, improved prognosis only in dilated cardiomyopathy. Better responses to digoxin, amlodipine and amiodarone have been reported in non-ischemic HF. There is at present no clear explanation for the apparent therapeutic differences between ischemic and nonischemic HF. Absence of a rigorous definition of "nonischemic HF" in many studies makes interpretation of the results difficult. Further studies to clarify the effects of etiology of HF on the response to treatment could be particularly important for preventing progression to more advanced stages, in which any type of drug therapy may have limited value in prolonging survival. An individualized therapeutic approach, based on etiology of HF and possibly other factors such as plasma drug levels or the levels of neurohormones, could result in major progress in treating HF patients.

Apoptosis in the failing heart

Apoptosis is a tightly regulated, energy-requiring process of programmed cell death. While necrosis is a form of cell death that results from acute cellular injury, apoptosis is controlled autodigestion of the cell that occurs through activation of endogenous proteases. This process results in the cleavage of chromatin into oligonucleosome-length DNA fragments and its multiples. This DNA fragmentation demonstrates a characteristic laddering pattern on DNA agarose gel electrophoresis. The heart undergoes extensive remodeling during embryogenesis wherein apoptosis significantly contributes to the development of the cardiac chambers and correct routing of the great vessels. Pathologic stimuli can also result in apoptosis and include ischemia, hypoxia, inflammation, cytokines, growth factors, and toxic agents. Better understanding of the molecular mechanisms responsible for regulating apoptosis in the failing myocardium may soon lead to strategies aimed at preventing further myocyte loss and enhancing myocyte replacement through regulated cell growth.

The effects of recombinant human growth hormone on cardiopulmonary function in elective abdominal aortic aneurysm repair

OBJECTIVES

Cardiorespiratory complications are the predominant source of morbidity in patients undergoing major surgery. Recombinant human growth hormone (rhGH) has previously been shown to be effective in improving respiratory and cardiac function in compromised patients.

DESIGN

The aim of this study was to assess the effects of perioperative rhGH on cardiac function in 33 patients undergoing elective infrarenal abdominal aortic aneurysm repair.

METHODS

Patients were randomised to one of three groups: placebo for 6 days before and after surgery (control, n = 12); genotropin (GH) 0.3 units/kg/day for 6 days before and after surgery (pre and postop GH, n = 10) and placebo for 6 days before and GH (0.3 units/kg/day) for 6 days after surgery (postop EH, n = 11). Patients were assessed on days 7 and 1 before and days 7, 14 and 50 after operation. Intraoperative cardiac index (CI) was measured after induction of anaesthesia, before and after aortic cross-clamping, after aortic unclamping and at the end of surgery.

RESULTS

Pretreatment with GH resulted in a significantly higher heart rate during surgery and was associated with a trend towards higher cardiac index (CI) (p < 0.067) at all stages of surgery. Mean arterial blood pressure at the stage of aortic unclamping was significantly higher in patients treated with GH preoperatively.

CONCLUSIONS

Larger studies are required to evaluate the beneficial effects of GH in aortic surgery. However, data from this pilot study suggests that perioperative GH administration may result in improved cardiac performance during aortic surgery.

Growth hormone preserves cardiac sarcoplasmic reticulum Ca2+ release channels (ryanodine receptors) and enhances cardiac function in cardiomyopathic hamsters

OBJECTIVE

Growth hormone (GH) improves cardiac function in experimental models of heart failure and human dilated cardiomyopathy. However, the mechanism by which GH increases myocardial contractility is not entirely clear. Our aim was to examine the effects of GH on cardiac function and cardiac sarcoplasmic reticulum Ca2+ release channels (ryanodine receptors, RyR) in the hearts of UM-X7.1 cardiomyopathic hamsters during the development of heart failure.

METHODS

Experimental and healthy control hamsters were examined at the age of 20 weeks. Recombinant human GH (2 mg/kg/day, s.c.) or vehicle was then administered for 3 weeks. We examined (i) the in vivo left ventricular (LV) size and LV systolic function using transthoracic echocardiography, (ii) the density (Bmax) and affinity (Kd) of high-affinity [3H] ryanodine binding sites in crude homogenates from normal and cardiomyopathic hamster hearts.

RESULTS

Vehicle-treated UM-X7.1 hamsters exhibited significant increases in left ventricular end-diastolic diameter and end-systolic diameter (LVESd), and a significant decrease in LV fractional shortening (FS). GH-treatment attenuated the increase in LVESd and reduced the LV chamber size, and also significantly increased LVFS. Vehicle-treated UM-X7.1 hamsters exhibited a significantly lower Bmax than control hamsters (0.34 +/- 0.04 vs 0.44 +/- 0.06 pmol/mg, p < 0.05), and the treatment with GH in UM-X7.1 hamsters significantly attenuated the reduction of Bmax (0.42 +/- 0.03 pmol/mg vs vehicle-treated group (0.34 +/- 0.04 pmol/mg), p < 0.05). Kd did not differ significantly between the experimental groups. In normal control hamsters, GH treatment with this dose did not significantly enhance LV systolic function or the density of RyRs. There was no significant difference in terms of the connective-tissue volume-fraction, myocyte size and capillary density between the GH- and vehicle-treated groups of UM-X7.1 hamsters.

CONCLUSIONS

GH treatment may improve cardiac function by preserving the density of RyRs and enhancing cellular function in cardiomyopathic hamster hearts.

Angiotensin II blockade followed by growth hormone as adjunctive therapy after experimental myocardial infarction

BACKGROUND

Recombinant human growth hormone (rhGH) has shown beneficial effects on cardiac function after myocardial infarction (MI) in rats. High-dose angiotensin II (AT1) receptor blockade in normal rats inhibited the hypertrophic effect of growth hormone (GH), therefore we investigated whether GH effects after MI would be enhanced by giving it in sequence after remodeling had been inhibited by prior AT1 blockade (losartan, L).

METHODS AND RESULTS

Rats given losartan for 10 weeks after MI followed by rhGH for 2 weeks (2 mg/kg twice a day, GH plus losartan) were compared with rats given losartan for 10 weeks followed by placebo for 2 weeks (placebo plus losartan group) and with untreated controls (n = 17-20/group). Average MI sizes and left ventricular (LV) end diastolic (ED) dimensions (echocardiography) did not differ between groups. In GH and losartan, body weight (BW) was increased but left ventricular weight (LVW)/BW was reduced, and the LV fractional shortening and LV dP/dtmax (catheter tip micromanometer) were increased compared with the control group (20.3 vs 15.4% and 5579 vs 4699 mmHg/s, respectively, P < .05). The cardiac index also was significantly increased. In the placebo plus losartan group, the LVW/BW was also reduced and the cardiac index increased versus controls. Stroke volume was increased in GH plus losartan group compared with both placebo plus losartan and controls, and the systemic vascular resistance was significantly decreased only in the GH plus losartan group. The ED posterior wall thickness (noninfarcted wall) was increased in GH plus losartan compared with both control and placebo plus losartan. Left ventricular end diastolic pressure reduction was not significant in GH plus losartan group versus controls but was reduced in placebo plus losartan group, whereas LV relaxation (tau) was improved in both groups versus control rats. Thus, persistent remodeling effects caused by prior AT1 blockade undoubtedly contributed to some responses, but short-term GH given in sequence after chronic AT1 blockade had favorable actions on the failing heart and peripheral circulation by increasing LV wall thickness with partial reversal of unfavorable remodeling, lowering of vascular resistance, improvement of LV contractility, and enhanced LV systolic function and cardiac index relatively late after experimental MI.

Functional impact of an increase in ventricular mass after myocardial damage and its attenuation by converting enzyme inhibition

BACKGROUND

A increase in left ventricular mass after ventricular damage has been identified as an initial response to injury. However, the functional significance of this response has not been clearly established and is the focus of this study.

METHODS AND RESULTS

Twelve mongrel dogs underwent transmyocardial direct current shock to produce transmural left ventricular damage. Six were assigned to converting enzyme inhibitor therapy initiated 24 hours after damage and continued for 4 weeks. The remaining six dogs served as a control group. Left ventricular structure (mass and end diastolic volume) and systolic function (regional and global ejection fraction at rest and during afterload stress) were assessed by magnetic resonance imaging before damage and at the end of the 4-week period. After myocardial damage, left ventricular mass increased from 93.6 +/- 4.0 to 107.5 +/- 3.4 gm in the control group (P < .01) with no change in ventricular volume. Ramipril-treated dogs displayed a reduction in mass (83.2 +/- 2.2 to 74.6 +/- 2.9 gm, P < .05). In the control group, there was greater reduction in global ejection fraction in response to afterload stress at 4 weeks compared with baseline (-16 +/- 4 vs -4 +/- 3%, P = .03). Ejection fraction response to afterload stress was maintained at 4 weeks in the converting enzyme inhibitor-treated group (-5 +/- 3 vs - 1 +/- 4%) and was different at 4 weeks from the control group (-1 +/- 4 vs -16 +/- 4%, P = .004).

CONCLUSION

The increase in left ventricular mass noted after direct current shock was associated with the impairment of systolic function during afterload stress. Inhibition of this mass increase results in preservation of function, thus further supporting the concept that attenuation of ventricular remodeling should be a therapeutic goal.

Deficient insulin-like growth factor I in chronic heart failure predicts altered body composition, anabolic deficiency, cytokine and neurohormonal activation

BACKGROUND

Recent studies of growth hormone supplementation in chronic heart failure have been associated with variable results. Acquired abnormalities of biochemical parameters of the growth hormone insulin-like growth factor I axis have been associated with severe chronic heart failure. There are suggestions of an acquired growth hormone resistance with deficient insulin-like growth factor I in some patients.

OBJECTIVES

Therefore, we set out to investigate the clinical and functional status and the degree of cytokine and neurohormonal alteration of chronic heart failure patients with deficient insulin-like growth factor I responses.

METHODS

Patients with chronic heart failure were divided into two groups according to their insulin-like growth factor I levels (classified according to the manufacturer's assay range in normal controls): low insulin-like growth factor I <104 (n = 20; 89 +/- 9.6 ng/ml), and normal/high >104 ng/ml (n = 32; 169 +/- 52 ng/ml). Between groups there was no difference in age (low versus high: 65.3 +/- 12.1 versus 61.6 +/- 9.1 years, p = 0.21), body mass index, aerobic capacity (peak oxygen consumption: low versus high: 15.5 +/- 5.2 versus 17.3 +/- 6.3 mL/kg/min, p = 0.23), left ventricular ejection fraction, New York Heart Association classification.

RESULTS

During quadriceps strength testing, patients with low insulin-like growth factor I had reduced absolute strength (-24%), and strength per unit area muscle (- 14%) than patients with normal/high insulin-like growth factor I. Leg muscle cross-sectional area was lower in the low insulin-like growth factor I group (-12% and -13% for right and left legs, respectively). These alterations were accompanied by increased levels of growth hormone (+145%), tumor necrosis factor-alpha (+46%), cortisol/ dehydroepiandrosterone ratio (+60%), noradrenaline (+49%) and adrenaline (+136%) (all at least p < 0.05).

CONCLUSIONS

Patients with low insulin-like growth factor I levels show signs of altered body composition, cytokine and neuroendocrine activation, to a greater extent than patients with normal/high levels.

Insulin-like growth factor-1 but not growth hormone augments mammalian myocardial contractility by sensitizing the myofilament to Ca2+ through a wortmannin-sensitive pathway: studies in rat and ferret isolated muscles

A growing body of evidence has been accumulated recently suggesting that growth hormone (GH) and insulin-like growth factor-1 (IGF-1) affect cardiac function, but their mechanism(s) of action is unclear. In the present study, GH and IGF-1 were administered to isolated isovolumic aequorin-loaded rat whole hearts and ferret papillary muscles. Although GH had no effect on the indices of cardiac function, IGF-1 increased isovolumic developed pressure by 24% above baseline. The aequorin transients were abbreviated and demonstrated decreased amplitude. The positive inotropic effects of IGF-1 were not associated with increased intracellular Ca2+ availability to the contractile machinery but to a significant increase of myofilament Ca2+ sensitivity. Accordingly, the Ca2+-force relationship obtained under steady-state conditions in tetanized muscle was shifted significantly to the left (EC50, 0.44+/-0.02 versus 0.52+/-0.03 micromol/L with and without IGF-1 in the perfusate, respectively; P<0.05); maximal Ca2+-activated tetanic pressure was increased significantly by 12% (211+/-3 versus 235+/-2 mm Hg in controls and IGF-1-treated hearts, respectively; P<0.01). The positive inotropic actions of IGF-1 were not associated with changes in either pHi or high-energy phosphate content, as assessed by 31P nuclear magnetic resonance spectroscopy, and were blocked by the phosphatidylinositol 3-kinase inhibitor wortmannin. Concomitant administration of IGF binding protein-3 blocked IGF-1-positive inotropic action in ferret papillary muscles. In conclusion, IGF-1 is an endogenous peptide that through a wortmannin-sensitive pathway displays distinct positive inotropic properties by sensitizing the myofilaments to Ca2+ without increasing myocyte [Ca2+]i.

Growth hormone: a new therapy for heart failure?

There is now little doubt that growth hormone (GH) and insulin-like growth factor-1 (IGF-1) play a role in cardiac development and in cardiovascular physiology in adult life. Congenital lack of GH is associated with defective cardiac growth, ventricular wall thinning, and impaired systolic function. These abnormalities limit exercise capacity and contribute to the poor quality of life in patients with GH deficiency. In addition, studies with in vitro muscle preparations have shown that IGF-1 affects myocardial contractility by a direct mechanism. These findings suggested that GH would benefit patients affected by heart failure. Indeed, GH and/or IGF-1 have proven beneficial in various models of experimental heart failure. Tested in patients with classes II-IV heart failure, they improved cardiac performance and clinical status. These effects were associated with improved myocardial energetics and de-activation of the neurohormonal system. Because of the uncontrolled nature of the studies and the small number of cases examined, conclusions as to the effectiveness of GH and IGF-1 must await the results from larger trials.

Recombinant human growth hormone: old and novel uses

Recent studies of the growth hormone insulinlike growth factor I (IGFI) axis suggest that these hormones are involved in several physiologic processes, in addition to growth. Thus, several lines of evidence indicate an increasingly important role for recombinant human growth hormone as a part of the modern therapeutic armamentarium. In addition to the treatment of children with growth hormone deficiency, administration of growth hormone appears to be of considerable benefit to girls with Turner syndrome, children with chronic renal failure, and adults with growth hormone deficiency or human immunodeficiency virus (HIV) wasting syndrome. Moreover, its therapeutic use is being investigated in other conditions, such as children with idiopathic short stature, the healthy elderly, and the critically ill. However, long-term surveillance among growth hormone recipients is needed to fully evaluate its risk-benefit profile.

Enalapril restores depressed circulating insulin-like growth factor 1 in patients with chronic heart failure

BACKGROUND

Congestive heart failure (CHF) is characterized by increased activity of the renin-angiotensin system. Recent experimental studies have shown that infusion of angiotensin II results in depressed plasma levels of insulin-like growth factor 1 (IGF-1) and weight loss. We have previously reported that stable patients with CHF have decreased activity of the growth hormone (GH)-IGF1 axis. We have hypothesized, therefore, that angiotensin-converting enzyme (ACE) inhibition therapy should restore GH-IGF1 activity in CHF patients.

METHODS AND RESULTS

Nine patients with stable CHF who were taking digitalis and diuretics, New York Heart Association functional class III were studied before and after 8 weeks of therapy with Enalapril (10 mg twice daily). We measured IGF1 levels, radionuclide left ventricular ejection fraction (EF) and peak oxygen consumption (PVO2). We found that 7 of 9 patients had abnormally low levels of IGF1 (0.2-0.5 mU/ml). IGF1 levels reverted to normal after Enalapril therapy (0.36 +/- 0.03 to 0.8 +/- 0.14 mU/ml, P = .004). This was associated with a significant increase in EF (27.4 +/- 1.1 to 31.4 +/- 0.9%) and PVO2 (14.8 +/- 1.2 to 18.6 +/- 1.5 ml/kg/min) values (P < .05).

CONCLUSION

Chronic ACE inhibition therapy restored previously reduced IGF1 plasma levels in patients with CHF, most likely by reducing angiotensin II activity.

Randomised, double-blind, placebo-controlled trial of human recombinant growth hormone in patients with chronic heart failure due to dilated cardiomyopathy

BACKGROUND

Some studies have suggested that treatment with recombinant human growth hormone (rhGH) increases left-ventricular mass and improves haemodynamic and functional status in patients with heart failure due to dilated cardiomyopathy. We did a double-blind, randomised, placebo-controlled study of rhGH in patients with chronic heart failure due to dilated cardiomyopathy.

METHODS

50 patients (43 men) were randomly allocated treatment with subcutaneous rhGH (2 IU daily) or placebo for a minimum of 12 weeks. The primary endpoints were the effects on left-ventricular mass and systolic wall stress. The secondary endpoints were the effects on left-ventricular size and function. Data were analysed by intention to treat.

FINDINGS

Patients in the rhGH group had an increase in left-ventricular mass compared with those in the placebo group (27%, p=0.0001). There was no significant difference in left-ventricular systolic wall stress, mean blood pressure, or systemic vascular resistance between the two groups. New York Heart Association functional class, left-ventricular ejection fraction, and distance on the 6 min walking test were unchanged. The change in serum insulin-like growth factor (IGF)-I concentrations (rhGH 77 ng/mL; placebo -19 ng/mL, GH vs placebo p=0.0001) was significantly related to the change in left-ventricular mass (r=0.55, p=0.0001). One patient in the rhGH group was withdrawn at 6 weeks because of worsening heart failure.

INTERPRETATION

There is a significant increase in left-ventricular mass in patients with dilated cardiomyopathy given rhGH but this is not accompanied by an improvement in clinical status. Changes in left-ventricular mass are related to changes in serum IGF-I concentrations. Whether a longer treatment period would provide clinical benefits and decrease mortality is unknown.

Left ventricular structure and function in children infected with human immunodeficiency virus: the prospective P2C2 HIV Multicenter Study. Pediatric Pulmonary and Cardiac Complications of Vertically Transmitted HIV Infection (P2C2 HIV) Study Group

BACKGROUND

The frequency of, course of, and factors associated with cardiovascular abnormalities in pediatric HIV are incompletely understood.

METHODS AND RESULTS

A baseline echocardiogram (median age, 2.1 years) and 2 years of follow-up every 4 months were obtained as part of a prospective study on 196 vertically HIV-infected children. Age- or body surface area-adjusted z scores were calculated by use of data from normal control subjects. Although 88% had symptomatic HIV infection, only 2 had CHF at enrollment, with a 2-year cumulative incidence of 4.7% (95% CI, 1.5% to 7.9%). All mean cardiac measurements were abnormal at baseline (decreased left ventricular fractional shortening [LV FS] and contractility and increased heart rate and LV dimension, mass, and wall stresses). Most of the abnormal baseline cardiac measurements correlated with depressed CD4 cell count z scores and the presence of HIV encephalopathy. Heart rate and LV mass showed significantly progressive abnormalities, whereas FS and contractility tended to decline. No association was seen between longitudinal changes in FS and CD4 cell count z score. Children who developed encephalopathy during follow-up had depressed initial FS, and FS continued to decline during follow-up.

CONCLUSIONS

Subclinical cardiac abnormalities in HIV-infected children are common, persistent, and often progressive. Dilated cardiomyopathy (depressed contractility and dilatation) and inappropriate LV hypertrophy (elevated LV mass in the setting of decreased height and weight) were noted. Depressed LV function correlated with immune dysfunction at baseline but not longitudinally, suggesting that the CD4 cell count may not be a useful surrogate marker of HIV-associated LV dysfunction. However, the development of encephalopathy may signal a decline in FS.

Orally active growth hormone secretagogues: state of the art and clinical perspectives

Growth hormone secretagogues (GHS) are synthetic, non-natural peptidyl and nonpeptidyl molecules with potent stimulatory effect on somatotrope secretion. They have no structural homology with growth hormone-releasing hormone (GHRH) and act via a specific receptor, which has now been cloned and is present at both the pituitary and hypothalamic level. This evidence strongly suggests the existence of a still unknown natural GHS-like ligand. Several data favour the hypothesis that GHS could counteract somatostatinergic activity at both the pituitary and hypothalamic level and/or, at least partially, via a GHRH-mediated mechanism. However, the possibility that they act via an unknown hypothalamic factor remains open. GH-releasing peptide-6 (GHRP-6) is the first hexapeptide studied extensively in humans. More recently, peptidyl superanalogues GHRP-1, GHRP-2 and hexarelin, and nonpeptidyl mimetics, such as the spiroindoline derivative MK-677, have been synthesized and their effects have been studied in humans. The GH-releasing activity of GHS is marked, dose related and reproducible after intravenous, subcutaneous, intranasal and even oral administration. The effect of GHS is partially desensitized but prolonged, intermittent oral administration increases insulin-like growth factor I (IGF-I) levels. The GH-releasing effect of GHS undergoes age-related variations; it increases from birth to puberty, remains similar in adulthood and decreases with ageing. The effect of GHS on GH release is synergistic with that of GHRH, while it is only partially refractory to inhibitory influences, which nearly abolish the effect of GHRH. GHS maintain their GH-releasing activity in some somatotrope hypersecretory states such as acromegaly, anorexia nervosa, hyperthyroidism and critical illness. The GH response to GHS has been reported clear although reduced in GH deficiency, obesity and hypothyroidism, while it is strongly reduced in patients with pituitary stalk disconnection or Cushing's syndrome. In short children, elderly subjects, critically ill patients and even in adult patients with GH deficiency an increase of IGF-I has been shown after GHS treatment. These data indicate that treatment with orally active GHS in humans enhances the activity of the GH-IGF-I axis and could be clinically useful.

Is there a role for growth hormone in the clinical management of burn injuries?

GH is a potent anabolic agent that offers distinct advantages to the hypercatabolic paediatric burns patient. GH can be administered with minimal risk of untoward side-effects in this patient group. GH reduces the catabolic effects of trauma, both directly and indirectly, through stimulation of protein synthesis. Accelerated wound healing and reduction in tissue-wasting effects are clear benefits that reduce the overall morbidity associated with burn injury in children. Further applications of GH treatment will stem from ongoing investigations that are examining alternative delivery methods, long-term treatment beyond the acute hospitalization phase, and combination therapy with beta-blockers, antiglucocorticoids or other growth factors.

Effects of growth hormone and insulin-like growth factor I in experimental heart failure

These studies suggest that IGF-I and GH have generally favourable effects on the failing heart. They further demonstrate the ability of the severely depressed and failing heart to respond to the trophic and inotropic effects of GH. There is, however, a need for a better understanding of the mechanism of the contractility effect, the character of the hypertrophy observed (whether it is a more favourable type than that secondary to mechanical overload) and the vascular actions, both trophic and vasodilatory. In addition, the degree to which high-dose ACE inhibition or angiotensin II receptor blockade may inhibit some of these effects requires further study. Finally, it is clear that additional experimental studies and clinical trials are needed to investigate the long-term effects of GH on morbidity and mortality in heart failure, as well as the possible side-effects and other actions, such as the potential of GH to enhance skeletal muscle size and strength.

[Growth hormone: a magical potion?]

INTRODUCTION

The various components of the growth hormone (GH)-insulin-like growth factor (IGF-I) axis and their binding proteins have many peripheral effects, mainly on bone, growth, activation of main cellular functions, energy metabolism and protein anabolism. They contribute to adapt an individual to circumstances of life and illness.

CURRENT KNOWLEDGE AND KEY POINTS

The unlimited supply of recombinant GH makes it possible to treat not only children with short stature but other disorders. In adults with GH deficiency, it has a marked effect on subjective well-being and body composition, and improves physical activity. GH may be promoted in new therapeutic areas such as severe hypercatabolic and denutrition states, dilated cardiomyopathy and several other more hypothetical areas. GH is not a wonder drug increasing physical performances in sport competitors or fighting against senescence.

FUTURE PROSPECTS AND PROJECTS

GH is a new therapeutic tool. Its efficacy must be evaluated through double-blind, placebo-controlled clinical trials. Currently, only benefits on psychological and physical symptoms of GH deficiency in adults have been validated.

Effects of constitutive overexpression of insulin-like growth factor-1 on the mechanical characteristics and molecular properties of ventricular myocytes

Recently, insulin-like growth factor-1 (IGF-1) has been claimed to positively influence the cardiac performance of the decompensated heart. On this basis, the effects of constitutive overexpression of IGF-1 on the mechanical behavior of myocytes were examined in transgenic mice in which the cDNA for the human IGF-1B was placed under the control of a rat alpha-myosin heavy chain promoter. In mice heterozygous for the transgene and in nontransgenic littermates at 2.5 months of age, the alterations in Ca2+ sensitivity of tension development, unloaded shortening velocity, and sarcomere compliance were measured in skinned myocytes. The quantities and state of phosphorylation of myofilament proteins in these enzymatically dissociated ventricular myocytes were also examined. The overexpression of IGF-1 was characterized by a nearly 15% reduction in myofilament isometric tension at submaximum Ca2+ levels in the physiological range, whereas developed tension at maximum activation was unchanged. In contrast, unloaded velocity of shortening was increased 39% in myocytes from transgenic mice. Moreover, resting tension in these cells was reduced by 24% to 33%. Myocytes from nontransgenic mice pretreated with IGF-1 failed to reveal changes in myofilament Ca2+ sensitivity and unloaded velocity of shortening. The quantities of C protein, troponin I, and myosin light chain-2 were comparable in transgenic and nontransgenic mice, but their endogenous state of phosphorylation increased 117%, 100%, and 100%, respectively. Troponin T content was not altered, and myosin isozymes were essentially 100% V1 in both groups of mice. In conclusion, constitutive overexpression of IGF-1 may influence positively the performance of myocytes by enhancing shortening velocity and cellular compliance.

The failing human heart does not release nitrogen oxides

It has been suggested that the myocardial production of nitric oxide, as a consequence of expression of the inducible isoform of nitric oxide synthase (NOS), plays an important role in the pathophysiology of heart failure. We determined the net cardiac production of nitrogen oxides (NOx), as a measure of NOS activity, by performing arterial and coronary sinus sampling in healthy control subjects (n=6) and patients with end-stage heart failure (n=10). The arterial plasma NOx concentration was significantly elevated in heart failure patients (58.4 +/- 7.0 vs 36.9 +/- 4.9 microM, p<0.05). However, we found net extraction of NOx across the heart, with no difference between the two groups. Therefore, the heart does not appear to be a source of NOx in heart failure, and this study does not support a pathophysiological role for NOx in this condition.

Safety and hemodynamic effects of intravenous triiodothyronine in advanced congestive heart failure

Most patients with advanced congestive heart failure have altered thyroid hormone metabolism. A low triiodothyronine level is associated with impaired hemodynamics and is an independent predictor of poor survival. This study sought to evaluate safety and hemodynamic effects of short-term intravenous administration of triiodothyronine in patients with advanced heart failure. An intravenous bolus dose of triiodothyronine, with or without a 6- to 12-hour infusion (cumulative dose 0. 1 5 to 2.7 microg/kg), was administered to 23 patients with advanced heart failure (mean left ventricular ejection fraction 0.22 +/- 0.01). Cardiac rhythm and hemodynamic status were monitored for 12 hours, and basal metabolic rate by indirect calorimetry, echocardiographic parameters of systolic function and valvular regurgitation, thyroid hormone, and catecholamine levels were measured at baseline and at 4 to 6 hours. Triiodothyronine was well tolerated without episodes of ischemia or clinical arrhythmia. There was no significant change in heart rate or metabolic rate and there was minimal increase in core temperature. Cardiac output increased with a reduction in systemic vascular resistance in patients receiving the largest dose, consistent with a peripheral vasodilatory effect. Acute intravenous administration of triiodothyronine is well tolerated in patients with advanced heart failure, establishing the basis for further investigation into the safety and potential hemodynamic benefits of longer infusions, combined infusion with inotropic agents, oral triiodothyronine replacement therapy, and new triiodothyronine analogs.

Selective increase in cardiac IGF-1 in a rat model of ventricular hypertrophy

There is evidence that insulin-like growth factor-1 (IGF-1) plays a role in the development of left ventricular hypertrophy, but it is uncertain whether cardiac IGF-1 changes before or after hypertension is established, and whether circulating IGF-1 are involved in cardiac hypertrophy. We have investigated changes in circulating and left ventricular IGF-1 and in the expression of the IGF-1 gene in the left ventricles of rats during the development of hypertensive left ventricular hypertrophy (Goldblatt model; 2 kidney-1 clamped). Our results show that the left ventricular contents of IGF-1 and its mRNA were increased at one and four weeks of hypertension and hypertrophy, and that both returned to control values after nine weeks. These changes were unrelated to the seric concentration of IGF-1 in the blood. These results show that local rather than circulating IGF-1 levels contributed to the development of renovascular hypertensive left ventricular hypertrophy.

Lack of beneficial effects of growth hormone treatment in conscious dogs during development of heart failure

The effects of chronic treatment with growth hormone (porcine GH, 0.56 mg.kg-1.day-1 s.c.) were examined in dogs with heart failure induced by rapid ventricular pacing (240 beats/min) for 4 wk. Fourteen conscious dogs were studied 2-3 wk after surgical instrumentation with catheters in the descending aorta and left atrium, a pressure gauge in the left ventricle (LV), a flow probe around the ascending aorta, pacing leads on the ventricular free wall and left atrium, and ultrasonic crystals on the opposing anterior and posterior endomyocardium of the LV. GH treatment for 4 wk significantly increased both body weight and plasma insulin-like growth factor 1 (IGF-1) compared with vehicle-treated dogs (P < 0.01, +2.0 +/- 0.5 vs. +0.3 +/- 1.1 kg; 1,043 +/- 218 vs. 241 +/- 64 ng/ml, respectively). However, the changes in resting LV systolic (i.e., both isovolumic and ejection phases) and diastolic function (i.e., isovolumic relaxation time constant tau) and the systemic vascular resistance were similar for the GH- and vehicle-treated groups during the development of heart failure. LV contractile reserve, assessed with step infusion of isoproterenol or dobutamine challenge, was markedly attenuated after heart failure, but there were no differences between the GH- and vehicle-treated groups. During the progression of heart failure, the increases in plasma atrial natriuretic peptide correlated (P < 0.01) directly with left atrial pressure and inversely with LV circumferential fiber shortening. However, GH treatment did not substantially modify these relationships. In addition, renal function and myocardial ultrastructure at the advanced stage of heart failure also showed similar changes for the GH- and vehicle-treated groups. We conclude that in conscious dogs during the development of congestive heart failure produced by rapid ventricular pacing, GH at a dose that increases body weight and plasma IGF-1 levels does not affect LV performance or systemic vascular dynamics.

Growth hormone-releasing peptides and their analogs

Growth hormone-releasing peptides (GHRPs) are a series of hepta (GHRP-1)- and hexapeptides (GHRP-2, GHRP-6, Hexarelin) that have been shown to be effective releasers of GH in animals and humans. More recently, a series of nonpeptidyl GH secretagogues (L-692,429, L-692,585, MK-0677) were discovered using GHRP-6 as a template. Some cyclic peptides as well as penta-, tetra-, and pseudotripeptides have also been described. This review summarizes recent developments in our understanding of the GHRPs, as well as the current nonpeptide pharmacologic analogs. GHRPs and their analogs have no structural homology with GHRH and act via specific receptors present at either the pituitary or the hypothalamic level. The GHRP receptor has recently been cloned and it does not show sequence homology with other G-protein-coupled receptors known so far. This evidence strongly suggests the existence of a natural GHRP-like ligand which, however, has not yet been found. Although the exact mechanism of action of GHRPs has not been fully established, there is probably a dual site of action on both the pituitary and the hypothalamus, possibly involving regulatory factors in addition to GHRH and somatostatin. Moreover, the possibility that GHRPs act via an unknown hypothalamic factor (U factor) is still open. The marked GH-releasing activity of GHRPs is reproducible and dose-related after intravenous, subcutaneous, intranasal, and even oral administration. The GH-releasing effect of GHRPs is the same in both sexes, but undergoes age-related variations. It increases from birth to puberty and decreases in aging. The GH-releasing activity of GHRPs is synergistic with that of GHRH and not affected by opioid receptor antagonists, while it is only blunted by inhibitory influences that are known to nearly abolish the effect of GHRH, such as neurotransmitters, glucose, free fatty acids, glucocorticoids, rhGH, and even exogenous somatostatin. GHRPs maintain their GH-releasing effect in somatotrope hypersecretory states, such as acromegaly, anorexia nervosa, and hyperthyroidism. On the other hand, GHRPs and their analogs have been reported to be effective in idiopathic short stature, in some situations of GH deficiency, in obesity, and in hypothyroidism, while in patients with pituitary stalk disconnection and in Cushing's syndrome the somatotrope responsiveness to GHRPs is almost absent. A potential role in the treatment of short stature, aging, catabolic states, and dilated cardiomyopathy has been envisaged.

Clenbuterol induces cardiac hypertrophy with normal functional, morphological and molecular features

OBJECTIVE

Several pharmacological agents have been shown to produce 'physiological' or 'pathological' hypertrophy based on their functional characteristics. The aim of this study was to examine the features of cardiac hypertrophy induced by the selective beta 2-adrenergic agonist, clenbuterol.

METHODS

Cardiac hypertrophy was induced in 7-week-old Sprague-Dawley rats by daily injections of clenbuterol for 3 weeks. Thyroxine and isoproterenol were also used to produce cardiac hypertrophy to serve as positive controls for physiological and pathological hypertrophy, respectively. Left ventricular function was determined using an isolated rat heart preparation. Ventricular samples were used for morphological examination while interstitial collagen was measured using high-pressure liquid chromatography. Expression of sarcoplasmic reticulum Ca(2+)-ATPase2a (SERCA2a) and phospholamban (PLB) were measured by dot blot analysis.

RESULTS

Clenbuterol treatment induced 26% left ventricular hypertrophy. These hearts demonstrated normal systolic isovolumic parameters and diastolic (active relaxation and passive stiffness) function. In addition, left ventricular concentration of collagen and morphology was normal as were the expression of SERCA2a and PLB mRNA.

CONCLUSION

These results suggest that clenbuterol-induced hypertrophy is 'physiological' in terms of its function, extracellular structure and gene expression.

Coronary constriction impairs cardiac function and induces myocardial damage and ventricular remodeling in mice

To establish whether coronary artery narrowing (CAN) in mice was accompanied by depressed ventricular function, tissue injury, and modifications in cardiac anatomy, the left coronary artery was constricted in FVB/N mice and the animals were killed 7 days later. CAN consisted of a 53% reduction in luminal diameter, which resulted in a twofold increase in left ventricular end-diastolic pressure. Left ventricular systolic pressure and left ventricular + and -dP/dt decreased 15, 21, and 11%, respectively. Left ventricular weight-to-body weight ratio increased 33%. This hypertrophic adaptation was characterized by a 9 and 20% increase in the longitudinal and transverse cavitary diameters, which provoked a 1.5-fold expansion in chamber volume. In contrast, wall thickness decreased 15%. These anatomic and functional changes induced a threefold elevation in diastolic stress. Foci of reparative fibrosis were found in the endomyocardium and epimyocardium, involving 2-3% of the tissue. Finally, myocyte loss in the ventricle was 15%, and myocyte hypertrophy was 38%. Impaired ventricular function, diastolic Laplace overloading, myocyte loss, and decompensated eccentric hypertrophy in mice after CAN mimic the ischemic cardiomyopathic heart in humans.

Pharmacological modulation of pressure-overload cardiac hypertrophy: changes in ventricular function, extracellular matrix, and gene expression

BACKGROUND

Appropriate cardiac hypertrophy (CH) is necessary in several clinical settings, such as pulmonary artery banding in the two-stage arterial switch operation for transposition of the great arteries. Pressure-overload CH, however, produces ventricular dysfunction due to structural and molecular changes. The beta2-adrenergic receptor agonist clenbuterol has been shown to induce CH without such adverse effects to the rat heart. This study was performed to determine its effects on left ventricular (LV) function, structure, and gene expression in pressure-overload CH.

METHODS AND RESULTS

Sprague-Dawley rats were assigned to one of four groups: 1, sham-operated (n=15); 2, banding of ascending aorta (n=22); 3, banding+clenbuterol (n=18); and 4, banding+thyroxine (n= 17). At the end of 3 weeks, groups 2, 3, and 4 showed an increase in LV mass index of 49.7+/-5.1%, 66.1+/-3.8%, and 47.6+/-4.6%, respectively, relative to group 1. A subgroup with severe CH (>50%) in group 2 was found to have significantly impaired developed pressure and diastolic relaxation and an increase in passive stiffness, with significantly reduced LV expression of sarcoplasmic reticulum Ca2+-ATPase2a (SERCA2a) mRNA and increased LV collagen concentration. In comparison, similarly hypertrophied animals in groups 3 and 4 demonstrated improved developed pressure, normal relaxation and diastolic stiffness with normal collagen concentration, and a greater abundance of SERCA2a mRNA.

CONCLUSIONS

Clenbuterol administration in conjunction with pressure overload produces a specific type of CH with preserved LV function. In addition, an increase in LV mass was associated with less fibrosis and greater expression of SERCA2a mRNA than banding alone.

Thyroid hormone improves function and Ca2+ handling in pressure overload hypertrophy. Association with increased sarcoplasmic reticulum Ca2+-ATPase and alpha-myosin heavy chain in rat hearts

We asked whether thyroid hormone (T4) would improve heart function in left ventricular hypertrophy (LVH) induced by pressure overload (aortic banding). After banding for 10-22 wk, rats were treated with T4 or saline for 10-14 d. Isovolumic LV pressure and cytosolic [Ca2+] (indo-1) were assessed in perfused hearts. Sarcoplasmic reticulum Ca2+-ATPase (SERCA), phospholamban, and alpha- and beta-myosin heavy chain (MHC) proteins were assayed in homogenates of myocytes isolated from the same hearts. Of 14 banded hearts treated with saline, 8 had compensated LVH with normal function (LVHcomp), whereas 6 had abnormal contraction, relaxation, and calcium handling (LVHdecomp). In contrast, banded animals treated with T4 had no myocardial dysfunction; these hearts had increased contractility, and faster relaxation and cytosolic [Ca2+] decline compared with LVHcomp and LVHdecomp. Myocytes from banded hearts treated with T4 were hypertrophied but had increased concentrations of alpha-MHC and SERCA proteins, similar to physiological hypertrophy induced by exercise. Thus thyroid hormone improves LV function and calcium handling in pressure overload hypertrophy, and these beneficial effects are related to changes in myocyte gene expression. Induction of physiological hypertrophy by thyroid hormone-like signaling might be a therapeutic strategy for treating cardiac dysfunction in pathological hypertrophy and heart failure.

Insulin-like growth factor-1 receptor and its ligand regulate the reentry of adult ventricular myocytes into the cell cycle

To determine whether insulin-like growth factor-1 (IGF-1) stimulation in vitro of ventricular myocytes isolated from infarcted hearts is characterized by the reentry of cells into the cell cycle, the expression and kinase activity of cyclins E, A, and B and DNA synthesis were evaluated 5 days after coronary artery occlusion and 24 and 48 h following the addition of IGF-1. Myocytes surviving an acute myocardial infarction were employed because of their increase in surface insulin-like growth factor-1 receptors (IGF-1R). Western blot analysis documented that IGF-1 resulted in an upregulation of cyclins D1, E, A, and B in viable postinfarcted myocytes. Cyclin E- and A-associated histone H1 kinase activity and cyclin D1-associated retinoblastoma protein-associated kinase activity also increased, but cyclin B kinase activity was not enhanced by IGF-1. These changes in cyclins and kinase activities were characterized by a significant increase in the number of cells labeled by bromodeoxyuridine, from approximately 630/10(6) to nearly 9, 000/10(6) myocytes. This latter value was reduced by more than 50% by antisense oligodeoxynucleotide to IGF-1R mRNA. However, IGF-1 stimulation did not induce nuclear mitotic division and cytokinesis. In conclusion, the growth-promoting effect of IGF-1 on adult myocytes is regulated by the density of IGF-1R, which conditions the activation of the replicatory machinery of the cells. The failure of IGF-1 to enhance cyclin B kinase activity may be responsible for a block in the cell cycle and the inability of myocytes to progress through the M phase and subsequently divide.

Insulin-like growth factor-I rapidly activates multiple signal transduction pathways in cultured rat cardiac myocytes

In response to insulin-like growth factor-I (IGF-I), neonatal rat cardiac myocytes exhibit a hypertrophic response. The elucidation of the IGF-I signal transduction system in these cells remains unknown. We show here that cardiac myocytes present a single class of high affinity receptors (12,446 +/- 3,669 binding sites/cell) with a dissociation constant of 0.36 +/- 0.10 nM. Two different beta-subunits of IGF-I receptor were detected, and their autophosphorylation was followed by increases in the phosphotyrosine content of extracellular signal-regulated kinases (ERKs), insulin receptor substrate 1, phospholipase C-gamma1, and phosphatidylinositol 3-kinase. IGF-I transiently activates c-Raf in cultured neonatal cardiac myocytes, whereas A-raf is activated much less than c-Raf. Two peaks of ERK activity (ERK1 and ERK2) were resolved in cardiac myocytes treated with IGF-I by fast protein liquid chromatography, both being stimulated by IGF-I (with EC50 values for the stimulation of ERK1 and ERK2 by IGF-I of 0.10 and 0. 12 nM, respectively). Maximal activation of ERK2 (12-fold) and ERK1 (8.3-fold) activities was attained after a 5-min exposure to IGF-I. Maximal activation of p90 S6 kinase by IGF-I was achieved after 10 min, and then the activity decreased slowly. Interestingly, IGF-I stimulates incorporation of [3H]phenylalanine (1.6-fold) without any effect on [3H]thymidine incorporation. These data suggest that IGF-I activates multiple signal transduction pathways in cardiac myocytes some of which may be relevant to the hypertrophic response of the heart.

Is growth hormone good for the heart?

Growth hormone (GH), probably acting indirectly through locally produced insulin-like growth factor I, stimulates myocardial hypertrophy and increases myocyte contractility. In experimental models insulin-like growth factor I appears to be a key regulator of ventricular hypertrophy. Many adults with growth hormone deficiency (GHD) have reduced left ventricular mass, a lower ejection fraction, and reduced exercise tolerance. Elevated serum lipid levels, increased visceral fat, and early atheroma formation may contribute to an increased mortality rate from cardiovascular disease in these persons, but GH replacement therapy appears to correct many of these abnormalities. GH excess (acromegaly) results in cardiac hypertrophy that can progress to cardiac failure. Treatment with octreotide at least partially reverses cardiac hypertrophy and dysfunction. GH treatment may induce beneficial cardiac hypertrophy in adults without GHD who have dilated cardiomyopathy. Significant cardiac dysfunction has not been reported in children with GHD who are treated with GH, nor have adverse cardiac effects been reported with GH in short children without GHD, including those with Turner syndrome. We now have extensive experience with the therapeutic use of GH in children with cardiac structural abnormalities (e.g., Turner and Noonan syndromes, congenital heart disease), and such use appears to be safe. Furthermore, cardiac complications of GH in children without cardiac disease are rare. Continued observation to ensure that GH therapy has no long-term effects on cardiac anatomy or function in children is necessary.

Acromegalic cardiomyopathy: evaluation of the left ventricular diastolic function in the subclinical stage

It is recently shown that the majority of acromegalic patients without concomitant heart disease have diastolic dysfunction at rest. The aim of this study is to evaluate left ventricular diastolic function in normotensive acromegalic patients without any evidence of heart disease. Eleven acromegalic patients and 16 normal subjects of comparable age and sex distribution were studied by echocardiography. Left ventricular end-diastolic diameter, interventricular septal thickness, left ventricular posterior wall thickness, left ventricular end-diastolic volume and stroke volume were found to be significantly higher in acromegalic patients. Left ventricular mass and left ventricular mass index increased significantly in acromegalics in comparison with controls (229.16 +/- 46.11 g versus 167.17 +/- 24.57 g and 124.99 +/- 26.91 g/m2 versus 95.09 +/- 13.29 g/m2 respectively, p < 0.001). Mitral A wave desceleration rate and isovolumetric relaxation time (IVRT)-two of the studied parameters of left ventricular diastolic filling- were significantly prolonged in patients as compared with controls (p = 0.03 and p < 0.001 respectively). Four (36%) of the acromegalic patients had peak early/late diastolic mitral velocity ratio lower than 1, indicating diastolic dysfunction. All of the patients had IVRT longer than 90 ms (mean + 2 standart deviations of normals). It is concluded that in acromegalic patients without any other evidence of heart disease left ventricular diastolic function is impaired. This indicates a specific cardiomyopathy exists in the subclinical stage. IVRT is found to be more sensitive than other studied parameters for detecting diastolic dysfunction at this stage.

Growth hormone attenuates early left ventricular remodeling and improves cardiac function in rats with large myocardial infarction

OBJECTIVES

We sought to investigate the cardiac effects of growth hormone (GH) administration during the early phase of pathologic remodeling in a rat model of large myocardial infarction (MI).

BACKGROUND

Recent evidence suggests that exogenous administration of GH evokes a hypertrophic response and increases left ventricular (LV) function in vivo in rats with normal or chronically failing hearts. We hypothesized that these effects would attenuate ventricular remodeling early after MI.

METHODS

Fifty-eight male rats underwent sham operation (n = 19) or had induced MI (n = 39). The day after the operation, the infarcted rats were randomized to receive 3 weeks of treatment with GH, 3 mg/kg body weight per day (n = 19) or placebo (n = 20). Echocardiography, catheterization and isolated whole heart preparations were used to define cardiac structure and function.

RESULTS

Growth hormone caused hypertrophy of the noninfarcted myocardium in a concentric pattern, as noted by higher echocardiographic relative wall thickness at 3 weeks and by morphometric histologic examination. Left ventricular dilation was reduced in the GH-treated versus placebo group (echocardiographic LV diastolic diameter to body weight ratio 2.9 +/- 0.1 vs. 3.5 +/- 0.2 cm/kg; p < 0.05). In vivo and in vitro cardiac function was improved after GH treatment. Despite elevated insulin-like growth factor-1 (IGF-1) serum levels in GH-treated rats, myocardial IGF-I messenger ribonucleic acid was not different among the three groups, suggesting that an increase in its local expression does not appear necessary to yield the observed effects.

CONCLUSIONS

These data demonstrate that early treatment of large MI with GH attenuates the early pathologic LV remodeling and improves LV function.

Growth hormone in adults: indications and implications

Adults with hypopituitarism and documented growth hormone deficiency are now eligible for replacement therapy. What are the guidelines for diagnosis and treatment? More broadly, what are the implications for other adults with hyposomatotropism-namely, the elderly? And is there a therapeutic role for the hormone in patients with disease states such as osteoporosis, heart failure, and acute catabolic illness?