Similar cardiovascular effects of growth hormone and insulin-like growth factor-I in rats after experimental myocardial infarction

Involvement of two distinct signalling pathways in IGF-1-mediated central control of hypotensive effects in normotensive and hypertensive rats

AIMS

Insulin-like growth factor-1 (IGF-1) is abundantly expressed in the nucleus tractus solitarii (NTS). In a previous study, we revealed that the induction of nitric oxide (NO) production in the NTS reduces blood pressure (BP). It is well known that both acute administration and chronic administration of IGF-I reduce BP. The aim of this study was to evaluate the short-term hypotensive effect of IGF-1 in the NTS and to delineate the underlying molecular mechanisms of IGF-1 in the NTS of normotensive WKY rats and spontaneously hypertensive rats (SHRs).

METHOD

Microinjections of the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 and the MAP kinase-ERK kinase (MEK) inhibitor PD98059 into the NTS in WKY rats and SHRs were used to study the involvement of IGF-1-induced depressor effects.

RESULT

An IGF-1 (7.7 pmol) injection into the NTS resulted in a significant decrease in BP and HR in WKY rats and SHRs. Immunoblotting and immunohistochemical analysis showed that the microinjection of LY294002 (0.6 pmol) or PD98059 (3.0 pmol) into the NTS attenuated the IGF-1-induced depressor effects and Akt or ERK phosphorylation in WKY rats. An attenuation effect of LY294002, but not PD98059, was found in the SHRs. However, the mRNA and protein expression levels of the IGF-1R showed no significant differences in the NTS of the WKY rats and the SHRs.

CONCLUSION

These results suggest that distinct Akt and ERK signalling pathways mediated the IGF-1 control of the central depressor effects in WKY rats and SHRs. ERK signalling defects may be associated with the development of hypertension.

Pre-weaning growth hormone treatment reverses hypertension and endothelial dysfunction in adult male offspring of mothers undernourished during pregnancy

Maternal undernutrition results in elevated blood pressure (BP) and endothelial dysfunction in adult offspring. However, few studies have investigated interventions during early life to ameliorate the programming of hypertension and vascular disorders. We have utilised a model of maternal undernutrition to examine the effects of pre-weaning growth hormone (GH) treatment on BP and vascular function in adulthood. Female Sprague-Dawley rats were fed either a standard control diet (CON) or 50% of CON intake throughout pregnancy (UN). From neonatal day 3 until weaning (day 21), CON and UN pups received either saline (CON-S, UN-S) or GH (2.5 ug/g/day)(CON-GH, UN-GH). All dams were fed ad libitum throughout lactation. Male offspring were fed a standard diet until the end of the study. Systolic blood pressure (SBP) was measured at day 150 by tail cuff plethysmography. At day 160, intact mesenteric vessels mounted on a pressure myograph. Responses to pressure, agonist-induced constriction and endothelium-dependent vasodilators were investigated to determine vascular function. SBP was increased in UN-S groups and normalised in UN-GH groups (CON-S 121±2 mmHg, CON-GH 115±3, UN-S 146±3, UN-GH 127±2). Pressure mediated dilation was reduced in UN-S offspring and normalised in UN-GH groups. Vessels from UN-S offspring demonstrated a reduced constrictor response to phenylephrine and reduced vasodilator response to acetylcholine (ACh). Furthermore, UN-S offspring vessels displayed a reduced vasodilator response in the presence of L-NG-Nitroarginine Methyl Ester (L-NAME), carbenoxolone (CBX), L-NAME and CBX, Tram-34 and Apamin. UN-GH vessels showed little difference in responses when compared to CON and significantly increased vasodilator responses when compared to UN-S offspring. Pre-weaning GH treatment reverses the negative effects of maternal UN on SBP and vasomotor function in adult offspring. These data suggest that developmental cardiovascular programming is potentially reversible by early life GH treatment and that GH can reverse the vascular adaptations resulting from maternal undernutrition.

Importance of circulating IGF-1 for normal cardiac morphology, function and post infarction remodeling

IGF-1 plays an important role in cardiovascular homeostasis, and plasma levels of IGF-1 correlate inversely with systolic function in heart failure. It is not known to what extent circulating IGF-1 secreted by the liver and local autocrine/paracrine IGF-1 expressed in the myocardium contribute to these beneficial effects on cardiac function and morphology. In the present study, we used a mouse model of liver-specific inducible deletion of the IGF-1 gene (LI-IGF-1 -/- mouse) in an attempt to evaluate the importance of circulating IGF-I on cardiac morphology and function under normal and pathological conditions, with an emphasis on its regulatory role in myocardial phosphocreatine metabolism. Echocardiography was performed in LI-IGF-1 -/- and control mice at rest and during dobutamine stress, both at baseline and post myocardial infarction (MI). High-energy phosphate metabolites were compared between LI-IGF-1 -/- and control mice at 4 weeks post MI. We found that LI-IGF-1 -/- mice had significantly greater left ventricular dimensions at baseline and showed a greater relative increase in cardiac dimensions, as well as deterioration of cardiac function, post MI. Myocardial creatine content was 17.9% lower in LI-IGF-1 -/- mice, whereas there was no detectable difference in high-energy nucleotides. These findings indicate an important role of circulating IGF-1 in preserving cardiac structure and function both in physiological settings and post MI.

IGF-1 and atherothrombosis: relevance to pathophysiology and therapy

IGF-1 (insulin-like growth factor-1) plays a unique role in the cell protection of multiple systems, where its fine-tuned signal transduction helps to preserve tissues from hypoxia, ischaemia and oxidative stress, thus mediating functional homoeostatic adjustments. In contrast, its deprivation results in apoptosis and dysfunction. Many prospective epidemiological surveys have associated low IGF-1 levels with late mortality, MI (myocardial infarction), HF (heart failure) and diabetes. Interventional studies suggest that IGF-1 has anti-atherogenic actions, owing to its multifaceted impact on cardiovascular risk factors and diseases. The metabolic ability of IGF-1 in coupling vasodilation with improved function plays a key role in these actions. The endothelial-protective, anti-platelet and anti-thrombotic activities of IGF-1 exert critical effects in preventing both vascular damage and mechanisms that lead to unstable coronary plaques and syndromes. The pro-survival and anti-inflammatory short-term properties of IGF-1 appear to reduce infarct size and improve LV (left ventricular) remodelling after MI. An immune-modulatory ability, which is able to suppress 'friendly fire' and autoreactivity, is a proposed important additional mechanism explaining the anti-thrombotic and anti-remodelling activities of IGF-1. The concern of cancer risk raised by long-term therapy with IGF-1, however, deserves further study. In the present review, we discuss the large body of published evidence and review data on rhIGF-1 (recombinant human IGF-1) administration in cardiovascular disease and diabetes, with a focus on dosage and safety issues. Perhaps the time has come for the regenerative properties of IGF-1 to be assessed as a new pharmacological tool in cardiovascular medicine.

Cardiac effects of 3 months treatment of acromegaly evaluated by magnetic resonance imaging and B-type natriuretic peptides

Long-term treatment of acromegaly prevents aggravation and reverses associated heart disease. A previous study has shown a temporary increase in serum levels of the N-terminal fraction of pro B-type natriuretic peptide (NT-proBNP) suggesting an initial decline in cardiac function when treatment of acromegaly is initiated. This was a three months prospective study investigating short-term cardiac effects of treatment in acromegalic patients. Cardiac function was evaluated by the gold standard method cardiac magnetic resonance imaging (CMRI) and circulating levels of B-type natriuretic peptides (BNP and NT-proBNP). CMRI was performed at baseline and after 3 months of treatment. Levels of IGF-I, BNP and NT-proBNP were measured after 0, 1, 2 and 3 months. Eight patients (5 males and 3 females, mean age 53 ± 12 years (range 30-70)) and 8 matched healthy control subjects were included. Median IGF-I Z-score decreased from 4.5 (range 2.5-6.4) to 2.3 (-0.1 to 3.3). At baseline the patients had increased left ventricle mass index (LVMI) compared to control subjects (ΔLVMI 35 g/m(2) (95% CI 8-63 g/m(2), P = 0.016). After 3 months of treatment there was an increase in end-diastolic volume index EDVI (ΔEDVI 9 mL/m(2) (95% CI 3-14), P = 0.007) and an increase in levels of BNP (median (ranges) 7 (0.58-286) vs. 20 (1-489) pg/mL, P = 0.033) and of NT-proBNP (63 (20-1004) vs. 80 (20-3391) pg/mL, P = 0.027). Assessed by the highly sensitive and precise CMRI method, 3 months treatment of acromegaly resulted in an increase in EDVI, and increased levels of BNP and NT-proBNP suggesting an initial decrease in cardiac function.

Cardioprotective effects of growth hormone-releasing hormone agonist after myocardial infarction

Whether the growth hormone (GH)/insulin-like growth factor 1(IGF-1) axis exerts cardioprotective effects remains controversial; and the underlying mechanism(s) for such actions are unclear. Here we tested the hypothesis that growth hormone-releasing hormone (GHRH) directly activates cellular reparative mechanisms within the injured heart, in a GH/IGF-1 independent fashion. After experimental myocardial infarction (MI), rats were randomly assigned to receive, during a 4-week period, either placebo (n = 14), rat recombinant GH (n = 8) or JI-38 (n = 8; 50 microg/kg per day), a potent GHRH agonist. JI-38 did not elevate serum levels of GH or IGF-1, but it markedly attenuated the degree of cardiac functional decline and remodeling after injury. In contrast, GH administration markedly elevated body weight, heart weight, and circulating GH and IGF-1, but it did not offset the decline in cardiac structure and function. Whereas both JI-38 and GH augmented levels of cardiac precursor cell proliferation, only JI-38 increased antiapoptotic gene expression. The receptor for GHRH was detectable on myocytes, supporting direct activation of cardiac signal transduction. Collectively, these findings demonstrate that within the heart, GHRH agonists can activate cardiac repair after MI, suggesting the existence of a potential signaling pathway based on GHRH in the heart. The phenotypic profile of the response to a potent GHRH agonist has therapeutic implications.

Insulin glargine reduces carotid intimal hyperplasia after balloon catheter injury in Zucker fatty rats possibly by reduction in oxidative stress

Diabetes and impaired glucose tolerance are associated with increased cardiovascular disease morbidity and mortality particularly after vascular injury. Since insulin is frequently used in such patients, the effect of glulisine (short acting) and glargine (long acting) were tested in Zucker fatty rat carotid artery subjected to balloon catheter injury. Insulin-resistant Zucker fatty rats were sc injected 0.45 mg/kg/d of glargine (once) or glulisine (twice) for 1 week before, and 3 weeks after balloon injury. Fasting and postprandial glucose was measured twice weekly. Injured and uninjured carotid arteries, liver, and aorta were harvested after 3 weeks of injury. Carotid sections were H&E stained for measuring intima/media ratio or immunostained for nitrotyrosine. Serum and aortic protein were analyzed for IGF-1 and 8-isoprostane, respectively. Carotid intima/media ratio was significantly reduced in the glargine group [0.9 +/- 0.1-control; 0.6 +/- 0.1-glulisine; 0.4 +/- 0.1-glargine, P < 0.05]. Serum IGF-1 levels were higher in both insulins, but significant only in glargine group [567 +/- 121 (ng/ml)-control; 1059 +/- 150 (ng/ml)-glargine; P < 0.05]. The aortic 8-isoprostane levels decreased significantly in the glargine group [(921 vs. 2566 pg/mg protein; P < 0.05]. Compared to control nitrotyrosine staining intensity was significantly lower in both groups of insulin-treated rats; the lowest level was in the glargine group. Insulin glargine attenuates carotid intimal hyperplasia in nondiabetic Zucker fatty rat independent of glucose levels and support a valuable function for insulin in vascular disease that merits additional investigations.

Randomised comparison of growth hormone versus IGF-1 on early post-myocardial infarction ventricular remodelling in rats

OBJECTIVE

Growth hormone and insulin-like growth factor-1 participate in post-myocardial infarction healing, but their relative importance is unclear. We compared the treatment effects of these agents on left ventricular remodelling.

DESIGN

Wistar rats were randomised into a single dose of either growth hormone (0.5microg, n=29), or insulin-like growth factor-1 (0.5microg, n=27), delivered by direct intramyocardial punctures, and were compared with controls (n=30). Five minutes after treatment, myocardial infarction was generated by permanent ligation of the left coronary artery. Twenty-four hours post-ligation, serum levels of catecholamines were measured using radioimmunoassay and infarct size as well as infarct expansion index were calculated. The expression of genes related to extracellular matrix and angiogenesis was measured using polymerase chain reaction.

RESULTS

Infarct expansion index was lower in growth hormone-treated rats (0.28+/-0.03, p=0.007) and in insulin-like growth factor-1-treated rats (0.35+/-0.03, p=0.044) compared to controls (0.51+/-0.06). Infarct size was significantly (p=0.0076) lower in growth hormone-treated rats (32.2+/-2.0%) and marginally (p=0.094) lower in insulin-like growth factor-1-treated rats (36.2+/-2.3%) compared to controls (42.0+/-2.7%). Survival rates were comparable in the three groups. Epinephrine was lower in the growth hormone group (2.8+/-0.2microg/l) compared to either controls (5.0+/-0.6microg/l, p=0.007), or to insulin-like growth factor-1-treated rats (6.3+/-0.6microg/l, p=0.0001). Collagen I and III expression in the infarct zone was higher in the growth hormone group compared to either the insulin-like growth factor-1 group or to controls.

CONCLUSIONS

Both growth hormone and insulin-like-growth factor-1 decrease early infarct expansion, but growth hormone results in more favourable extracellular matrix remodelling and sympathetic activation.

Recombinant bovine growth hormone-induced reduction of atrial natriuretic peptide is associated with improved left ventricular contractility and reverse remodeling in cardiomyopathic UM-X7.1 hamsters with congestive heart failure

OBJECTIVE

To assess the effect of short-term treatment with GH on left ventricular contractility and remodeling, after the development of heart failure in cardiomyopathic hamsters (CMH).

DESIGN

Two groups of 200-day-old UM-X7.1 CMH received daily subcutaneous injections of recombinant bovine (rb) GH (1mg/kg/day) or 0.9% NaCl for 40 days. Golden Syrian hamsters (GSH) were used as controls. At 240-day-old, the hamsters were randomly subjected to (i) assessment of left ventricular systolic function in a Langendorff perfused mode followed by the determination of the passive diastolic pressure-volume relationship and morphometric measurements; (ii) assessment of left ventricular mRNA expression of genes belonging to the fetal gene program including atrial (ANP) and brain (BNP) natriuretic peptides and cardiac myosin heavy chain isoforms and of the circulating levels of the natriuretic peptides.

RESULTS

Hearts from CMH were hypertrophied and dilated (p<0.05) compared to hearts from GSH, along with a approximately 10-fold increase in the circulating ANP and BNP levels. Left ventricular BNP and ANP mRNAs were elevated by 2- and 3-fold, respectively, compared to GSH. rbGH reduced both ANP mRNA and ANP circulating levels by 34% (p<0.01) but did not significantly modulate BNP levels. This effect was associated with a preserved systolic function and reverse remodeling as assessed by a leftward shift of the passive diastolic pressure-volume relationship indicating reduced ventricular dilatation.

CONCLUSIONS

The data show that a short-term administration of GH in the terminal phase of the disease confers cardioprotection by attenuating systolic dysfunction and by inducing beneficial reverse remodeling.

Early, intracoronary growth hormone administration attenuates ventricular remodeling in a porcine model of myocardial infarction

OBJECTIVE

Ventricular remodeling is a common corollary of myocardial infarction. We hypothesized that this process may be attenuated by growth hormone, administered as a single high-dose, selectively in the infarct zone, early postmyocardial infarction.

DESIGN

In 35 pigs (29+/-4 kg), myocardial infarction was generated by inflation of an over-the-wire angioplasty balloon in the circumflex artery for 60 min and 5 further pigs were sham-operated. Ten minutes after reperfusion, the pigs were randomized (2:1) to either growth hormone (1 IU/kg) (n=23) or normal saline (n=12), delivered via the balloon catheter. All survivors were treated with captopril and were sacrificed 4 weeks after myocardial infarction.

RESULTS

Compared to controls, growth hormone-treated animals displayed lower heart weight (4.1+/-0.5 g/kg body weight, versus 3.4+/-0.4 g/kg, respectively, p=0.003) and dimensions (left ventricular short axis diameter 46+/-7 mm versus 37+/-6 mm, p=0.01; right ventricular short axis diameter 38+/-7 mm versus 30+/-5 mm p=0.001). Growth hormone increased wall thickness in the infarct (6.0+/-1.8 in controls versus 9.9+/-3.7 in treated animals, p=0.004) and non-infarct zones (10.6+/-1.8 in controls versus 15.5+/-3.8 in treated animals, p=0.0006) and produced higher (p<0.05) microvascular density in both zones.

CONCLUSION

Intracoronary administration of growth hormone attenuates left and right ventricular remodeling by inducing hypertrophy and by enhancing angiogenesis.

Somatostatin Analogue Mimics Acute Ischemic Preconditioning in a Rat Model of Myocardial Infarction

We tested the hypothesis that octreotide, a somatostatin analogue, can mimic ischemic preconditioning (PC) to provide cardioprotection against myocardial infarction. An ischemia-reperfusion model of adult Wistar rats was used. Infarct size was expressed as a percentage of the area at risk under different treatment protocols. Octreotide PC (35 microg/Kg 20 minutes before ischemia-reperfusion) significantly decreased infarct size (18 +/- 4%) versus control (60 +/- 7%). The somatostatin receptor antagonist cyclo-somatostatin (0.5 mg/Kg) could blunt the above cardioprotection. Administration of either chelerythrine (a protein kinase C inhibitor, 2 mg/Kg) or genistein (a tyrosine kinase inhibitor, 5 mg/Kg) could also block octreotide PC (54 +/- 7% and 58 +/- 6%, respectively). Pretreatment with the mitochondrial ATP-sensitive potassium channel antagonist 5-hydroxydecanoic acid (5-HD) and the sarcolemmal ATP-sensitive potassium channel antagonist glibenclamide could abolish the effects of octreotide PC (54 +/- 6% and 52 +/- 6%). Chelerythrine, however, had no effect on octreotide PC. In conclusion, the present study demonstrates that octreotide can mimic ischemic PC to reduce infarct size. Acute effects of octreotide PC involve the activation of protein kinase C, tyrosine kinase C, and mitochondrial ATP-sensitive potassium channels, but not systemic IGF-I activation.

Local myocardial overexpression of growth hormone attenuates postinfarction remodeling and preserves cardiac function

BACKGROUND

Ventricular remodeling with chamber dilation and wall thinning is seen in postinfarction heart failure. Growth hormone induces myocardial hypertrophy when oversecreted. We hypothesized that localized myocardial hypertrophy induced by gene transfer of growth hormone could inhibit remodeling and preserve cardiac function after myocardial infarction.

METHODS

Rats underwent direct intramyocardial injection of adenovirus encoding either human growth hormone (n = 9) or empty null vector as control (n = 9) 3 weeks after ligation of the left anterior descending coronary artery. Analysis of the following was performed 3 weeks after delivery: hemodynamics, ventricular geometry, cardiomyocyte fiber size, and serum growth hormone levels.

RESULTS

The growth hormone group had significantly better systolic cardiac function as measured by maximum left ventricular pressure (73.6 +/- 6.9 mm Hg versus control 63.7 +/- 7.8 mm Hg, p < 0.05) and maximum dP/dt (2845 +/- 453 mm Hg/s versus 1949 +/- 605 mm Hg/s, p < 0.005), and diastolic function as measured by minimum dP/dt (-2520 +/- 402 mm Hg/s versus -1500 +/- 774 mm Hg/s, p < 0.01). Ventricular geometry was preserved in the growth hormone group (ventricular diameter 12.2 +/- 0.7 mm versus control 13.1 +/- 0.4 mm, p < 0.05; borderzone wall thickness 2.0 +/- 0.2 mm versus 1.5 +/- 0.1 mm, p < 0.001), and was associated with cardiomyocyte hypertrophy (6.09 +/- 0.63 microm versus 4.66 +/- 0.55 microm, p < 0.005). Local myocardial expression of growth hormone was confirmed, whereas serum levels were undetectable after 3 weeks.

CONCLUSIONS

Local myocardial overexpression of growth hormone after myocardial infarction resulted in cardiomyocyte hypertrophy, attenuated ventricular remodeling, and improved systolic and diastolic cardiac function. The induction of localized myocardial hypertrophy presents a novel therapeutic approach for the treatment of ischemic heart failure.