Growth hormone-independent cardiotropic activities of growth hormone-releasing peptides in normal subjects, in patients with growth hormone deficiency, and in patients with idiopathic or ischemic dilated cardiomyopathy

Hexarelin modulates lung mechanics, inflammation, and fibrosis in acute lung injury

Introduction:

Acute respiratory distress syndrome (ARDS) is an acute form of diffuse lung injury characterized by (i) an intense inflammatory response, (ii) increased pulmonary vascular permeability, and (iii) the loss of respiratory pulmonary tissue. In this article we explore the therapeutic potential of hexarelin, a synthetic hexapeptide growth hormone secretagogue (GHS), in an experimental model of ARDS. Hexarelin has anti-inflammatory properties and demonstrates cardiovascular-protective activities including the inhibition of cardiomyocyte apoptosis and cardiac fibrosis, both of which may involve the angiotensin-converting enzyme (ACE) system.

Methods:

In our experimental model, ARDS was induced by the instillation of 100 mM HCl into the right bronchus; these mice were treated with hexarelin (320 μg/kg, ip) before (Pre) or after (Post) HCl challenge, or with vehicle. Respiratory system compliance, blood gas analysis, and differential cell counts in a selective bronchoalveolar lavage (BAL) were determined 6 or 24 hours after HCl instillation. In an extended study, mice were observed for a subsequent 14 days in order to assess lung fibrosis.

Results:

Hexarelin induced a significant improvement in lung compliance and a reduction of the number of total immune cells in BAL 24 hours after HCl instillation, accompanied with a lower recruitment of neutrophils compared with the vehicle group. At day 14, hexarelin-treated mice presented with less pulmonary collagen deposition compared with vehicle-treated controls.

Conclusions:

Our data suggest that hexarelin can inhibit the early phase of the inflammatory response in a murine model of HCl-induced ARDS, thereby blunting lung remodeling processes and fibrotic development.

Ghrelin Derangements in Idiopathic Dilated Cardiomyopathy: Impact of Myocardial Disease Duration and Left Ventricular Ejection Fraction

Background: Ghrelin may exert positive effects on cardiac structure and function in heart failure (HF) patients. Methods: We assessed ghrelin levels in 266 dilated cardiomyopathy (DCM) patients and in 200 age, gender and body mass index (BMI) matched controls. Further, we evaluated the expression of ghrelin and growth hormone secretagogue-receptor (GHSR) in the myocardium of 41 DCM patients and in 11 controls. Results: DCM patients had significantly lower levels of total, acylated and unacylated ghrelin when compared to controls (p < 0.05 for all). In controls, we observed a negative correlation of ghrelin with age, male gender and BMI. These correlations were lost in the DCM group, except for male gender. Total ghrelin was higher in patients with more recent diagnosis when compared to patients with longer duration of the DCM (p = 0.033). Further, total ghrelin was higher in patients with lower left ventricular systolic function (<40% LVEF, vs. 40% ≤ LVEF < 49% vs. LVEF ≥ 50%: 480.8, vs. 429.7, vs. 329.5 pg/mL, respectively, p = 0.05). Ghrelin prepropeptide was expressed more in DCM patients than in controls (p = 0.0293) while GHSR was expressed less in DCM patients (p < 0.001). Furthermore, ghrelin showed an inverse correlation with its receptor (ρ = −0.406, p = 0.009), and this receptor showed a significant inverse correlation with Interleukin-1β (ρ = −0.422, p = 0.0103). Conclusion: DCM duration and severity are accompanied by alterations in the ghrelin–GHSR system.

A Linear Fragment of Unacylated Ghrelin (UAG6-13) Protects Against Myocardial Ischemia/Reperfusion Injury in Mice in a Growth Hormone Secretagogue Receptor-Independent Manner

Unacylated ghrelin (UAG), the most abundant form of ghrelin in circulation, has been shown to exert cardioprotective effect in experimental cardiopathies. The present study aimed to investigate the cardioprotective effect of a linear bioactive fragment of UAG against myocardial ischemia-induced injury and dysfunction in C57BL/6 wild type mice and the mechanisms involved. Treatments were administered at doses of 100 (UAG), 1,000 and 3,000 (UAG_6-13) nmol/kg at 12 h interval during 14 days prior to 30 min left coronary artery ligation and reperfusion for a period of 6 or 48 h. The infarct area was decreased in a dose-dependent manner at 48 h of reperfusion, with a reduction of 54% at the highest dose of UAG_6-13 tested. Myocardial hemodynamics were improved as demonstrated by an increase in cardiac output, maximum first derivative of left ventricular pressure, and preload recruitable stroke work, a load-independent contractility index. Six hours after reperfusion, circulating levels of IL-6 and TNF-α pro-inflammatory cytokines were reduced, and the effect was maintained at 48 h for TNF-α. 5' AMP-activated protein kinase (AMPK) was activated, while acetyl-CoA carboxylase (ACC) activity was inhibited, along with a decrease in apoptotic protein levels. In isolated hearts, the effect of UAG_6-13 was unaffected by the presence of D-Lys³-GHRP-6, a ghrelin receptor (GHSR1a) antagonist, suggesting that the peptide acted through a GHSR1a-independent pathway. The results support the therapeutic application of UAG bioactive peptide fragments against myocardial ischemia/reperfusion injury.

Synthetic Growth Hormone-Releasing Peptides (GHRPs): A Historical Appraisal of the Evidences Supporting Their Cytoprotective Effects

BACKGROUND

Growth hormone-releasing peptides (GHRPs) constitute a group of small synthetic peptides that stimulate the growth hormone secretion and the downstream axis activity. Mounting evidences since the early 1980s delineated unexpected pharmacological cardioprotective and cytoprotective properties for the GHRPs. However, despite intense basic pharmacological research, alternatives to prevent cell and tissue demise before lethal insults have remained as an empty niche in the clinical armamentarium. Here, we have rigorously reviewed the investigational development of GHRPs and their clinical niching perspectives.

METHODOLOGY

PubMed/MEDLINE databases, including original research and review articles, were explored. The search design was date escalated from 1980 and included articles in English only.

RESULTS AND CONCLUSIONS

GHRPs bind to two different receptors (GHS-R1a and CD36), which redundantly or independently exert relevant biological effects. GHRPs' binding to CD36 activates prosurvival pathways such as PI-3K/AKT1, thus reducing cellular death. Furthermore, GHRPs decrease reactive oxygen species (ROS) spillover, enhance the antioxidant defenses, and reduce inflammation. These cytoprotective abilities have been revealed in cardiac, neuronal, gastrointestinal, and hepatic cells, representing a comprehensive spectrum of protection of parenchymal organs. Antifibrotic effects have been attributed to some of the GHRPs by counteracting fibrogenic cytokines. In addition, GHRP family members have shown a potent myotropic effect by promoting anabolia and inhibiting catabolia. Finally, GHRPs exhibit a broad safety profile in preclinical and clinical settings. Despite these fragmented lines incite to envision multiple pharmacological uses for GHRPs, especially as a myocardial reperfusion damage-attenuating candidate, this family of "drugable" peptides awaits for a definitive clinical niche.

The cardiovascular action of hexarelin

Hexarelin, a synthetic growth hormone-releasing peptide, can bind to and activate the growth hormone secretagogue receptor (GHSR) in the brain similar to its natural analog ghrelin. However, the peripheral distribution of GHSR in the heart and blood vessels suggests that hexarelin might have direct cardiovascular actions beyond growth hormone release and neuroendocrine effects. Furthermore, the non-GHSR CD36 had been demonstrated to be a specific cardiac receptor for hexarelin and to mediate its cardioprotective effects. When compared with ghrelin, hexarelin is chemically more stable and functionally more potent. Therefore, it may be a promising therapeutic agent for some cardiovascular conditions. In this concise review, we discuss the current evidence for the cardiovascular action of hexarelin.

Ghrelin in cardiovascular disease and atherogenesis

Although initially associated with regulation of appetite, the cardiovascular system has also been recognized as a potentially important target for ghrelin. Moreover, a limited number of clinical studies suggest a role for ghrelin in the treatment of congestive heart failure. So far reported cardiovascular effects of growth hormone secretagogues and/or ghrelin include lowering of peripheral resistance, either direct at the vascular level and/or by modulating sympathetic nervous activity. Other observed effects indicate possible improvement of contractility and cardioprotective effects both in vivo and in vitro.Taken together, these results offer an interesting perspective on the future where further studies aiming at evaluating a role of GHS and ghrelin in the treatment of cardiovascular disease are warranted.

Cardiovascular actions of the ghrelin gene-derived peptides and growth hormone-releasing hormone

In 1976, small peptide growth hormone secretagogues (GHSs) were discovered and found to promote growth hormone (GH) release from the pituitary. The GHS receptor (GHS-R) was subsequently cloned, and its endogenous ligand ghrelin was later isolated from the stomach. Ghrelin is a 28-amino acid peptide, whose acylation is essential for binding to GHS-R type 1a and for the endocrine functions, including stimulation of GH secretion and subsequent food intake. Unacylated ghrelin, the other ghrelin form, although devoid of GHS-R binding is an active peptide, sharing many peripheral effects with acylated ghrelin (AG). The ghrelin system is broadly expressed in myocardial tissues, where it exerts different functions. Indeed, ghrelin inhibits cardiomyocyte and endothelial cell apoptosis, and improves left ventricular (LV) function during ischemia–reperfusion (I/R) injury. In rats with heart failure (HF), ghrelin improves LV dysfunction and attenuates the development of cardiac cachexia. Similarly, ghrelin exerts vasodilatory effects in humans, improves cardiac function and decreases systemic vascular resistance in patients with chronic HF. Obestatin is a recently identified ghrelin gene peptide. The physiological role of obestatin and its binding to the putative GPR39 receptor are still unclear, although protective effects have been demonstrated in the pancreas and heart. Similarly to AG, the hypothalamic peptide growth hormone-releasing hormone (GHRH) stimulates GH release from the pituitary, through binding to the GHRH-receptor. Besides its proliferative effects in different cell types, at the cardiovascular level GHRH inhibits cardiomyocyte apoptosis, and reduces infarct size in both isolated rat heart after I/R and in vivo after myocardial infarction. Therefore, both ghrelin and GHRH exert cardioprotective effects, which make them candidate targets for therapeutic intervention in cardiovascular dysfunctions.

Cardiovascular effects of intravenous ghrelin infusion in healthy young men

Ghrelin infusion improves cardiac function in patients suffering from cardiac failure, and bolus administration of ghrelin increases cardiac output in healthy subjects. The cardiovascular effects of more continuous intravenous ghrelin exposure remain to be studied. We therefore studied the cardiovascular effects of a constant infusion of human ghrelin at a rate of 5 pmol/kg per minute for 180 min. Fifteen healthy, young (aged 23.2 +/- 0.5 yr), normal-weight (23.0 +/- 0.4 kg/m(2)) men volunteered in a randomized double-blind, placebo-controlled crossover study. With the subjects remaining fasting, peak myocardial systolic velocity S', tissue tracking TT, left ventricular ejection fraction EF, and endothelium-dependent flow-mediated vasodilatation were measured. Ghrelin infusion increased S' 9% (P = 0.002) and TT 10% (P < 0.001), whereas EF, resting blood flow velocity, and endothelium-dependent flow-mediated vasodilatation did not change (P = 0.13). This was associated with a peak in serum growth hormone after 60 min of infusion (37.77 +/- 5.27 ng/ml, P < 0.001), a doubling of free fatty acid levels (P = 0.001), and a 1.6-fold increase in cortisol levels (P < 0.05), whereas glucose and catecholamine levels were constant. In conclusion, supraphysiological levels of ghrelin stimulate left ventricular function in terms of S' and TT in healthy young normal-weight men without changing resting blood flow velocity and endothelium-dependent flow-mediated vasodilatation. The effects did not translate into detectable increments in EF.

Growth-hormone-releasing peptide 6 (GHRP6) prevents oxidant cytotoxicity and reduces myocardial necrosis in a model of acute myocardial infarction

Therapies aimed at enhancing cardiomyocyte survival following myocardial injury are urgently required. As GHRP6 [GH (growth hormone)-releasing peptide 6] has been shown to stimulate GH secretion and has beneficial cardiovascular effects, the aim of the present study was to determine whether GHRP6 administration reduces myocardial infarct size following acute coronary occlusion in vivo. Female Cuban Creole pigs were anaesthetized, monitored and instrumented to ensure a complete sudden left circumflex artery occlusion for 1 h, followed by a 72 h reperfusion/survival period. Animals were screened clinically before surgery and assigned randomly to receive either GHRP6 (400 μg/kg of body weight) or normal saline. Hearts were processed, and the area at risk and the infarct size were determined. CK-MB (creatine kinase MB) and CRP (C-reactive protein) levels and pathological Q-wave-affected leads were analysed and compared. Evaluation of the myocardial effect of GHRP6 also included quantitative histopathology, local IGF-I (insulin-growth factor-I) expression and oxidative stress markers. GHRP6 treatment did not have any influence on mortality during surgery associated with rhythm and conductance disturbances during ischaemia. Infarct mass and thickness were reduced by 78% and 50% respectively, by GHRP6 compared with saline (P<0.01). More than 50% of the GHRP6-treated pigs did not exhibit pathogological Q waves in any of the ECG leads. Quantitative histopathology and CK-MB and CRP serum levels confirmed the reduction in GHRP6-mediated necrosis (all P<0.05). Levels of oxidative stress markers suggested that GHRP6 prevented myocardial injury via a decrease in reactive oxygen species and by the preservation of antioxidant defence systems (all P<0.05). Myocardial IGF-I transcription was not amplified by GHRP6 treatment compared with the increase induced by the ischaemic episode in relation to expression in intact hearts (P<0.01). In conclusion, GHRP6 exhibits antioxidant effects which may partially contribute to reduce myocardial ischaemic damage.

Effects of ghrelin and synthetic GH secretagogues on the cardiovascular system

Ghrelin, a newly discovered endogenous hormone that is produced by the stomach, and synthetic peptides have been identified recently as potent growth-hormone secretagogues. This effect is exerted through interaction with a specific G-protein-coupled receptor, GHS-R1a, which is expressed mainly in the hypothalamus-pituitary complex. A study of the peripheral distribution of GHS receptors has shown that it is also present in cardiovascular tissue, which has led to the exploration of the cardiovascular functions of ghrelin and synthetic, growth-hormone-releasing peptides. These ligands have several cardiovascular activities, including a cardioprotective effect against myocardial ischemia, and vasoactive and cardiotropic effects in both experimental models and humans. These effects are mediated by the interaction of these ligands with binding sites, including GHS-1Ra, for which the signalling pathways are not documented fully. Identification of the cardiac and vascular binding sites for ghrelin and synthetic, growth-hormone-releasing peptides will provide new perspectives for treating cardiovascular diseases with these ligands.

Ghrelin and GHS on cardiovascular applications/functions

Although initially recognised for their GH-releasing properties, the cardiovascular system has been recognised as a potentially important target for GH secretagogues (GHS). Moreover, a limited number of studies also indicate cardiovascular effects of ghrelin. So far reported cardiovascular effects of GHS and/or ghrelin include lowering of peripheral resistance, possible improvement of contractility and cardioprotective effects both in vivo and in vitro. Taken together, these results offer an interesting perspective on the future where further studies aiming at evaluating a role of GHS and ghrelin in the treatment of cardiovascular disease are warranted.

Influence of growth hormone on cardiovascular health and disease

Experimental and clinical studies indicate that growth hormone (GH) and insulin-like growth factor-1 (IGF-1) are involved in heart development. Impaired cardiovascular function, as recently demonstrated, could potentially reduce life expectancy both in GH deficiency (GHD) and excess. Patients with childhood- or adult-onset GHD may have both cardiac structural and functional abnormalities, i.e. reduced cardiac mass, reduced diastolic filling, and impaired left ventricular response to peak exercise. In addition, GHD patients may present with an increase in vascular intima-media thickness and a higher occurrence of atheromatous plaques that can further aggravate the hemodynamic conditions and contribute to the increased cardiovascular and cerebrovascular risk. However, some evidence has been provided to show that cardiovascular abnormalities can be partially reversed after somatropin (recombinant GH) therapy in patients with GHD. Recently, somatropin administration was shown to induce improvement in hemodynamics and clinical status in some patients with heart failure. Although these data need to be confirmed in more extensive studies, such promising results open new perspectives for somatropin therapy. The role of GH secretagogues in heart failure is still unknown.

GH-releasing peptides improve cardiac dysfunction and cachexia and suppress stress-related hormones and cardiomyocyte apoptosis in rats with heart failure

Growth hormone (GH)-releasing peptides (GHRP), a class of synthetic peptidyl GH secretagogues, have been reported to exert a cardioprotective effect on cardiac ischemia. However, whether GHRP have a beneficial effect on chronic heart failure (CHF) is unclear, and the present work aims to clarify this issue. At 9 wk after pressure-overload CHF was created by abdominal aortic banding in rats, one of four variants of GHRP (GHRP-1, -2, and -6 and hexarelin, 100 mug/kg) or saline was injected subcutaneously twice a day for 3 wk. Echocardiography and cardiac catheterization were performed to monitor cardiac function and obtain blood samples for hormone assay. GHRP treatment significantly improved left ventricular (LV) function and remodeling in CHF rats, as indicated by increased LV ejection fraction, LV end-systolic pressure, and diastolic posterior wall thickness and decreased LV end-diastolic pressure and LV end-diastolic dimension. GHRP also significantly alleviated development of cardiac cachexia, as shown by increases in body weight and tibial length in CHF rats. Plasma CA, renin, ANG II, aldosterone, endothelin-1, and atrial natriuretic peptide were significantly elevated in CHF rats but were significantly decreased in GHRP-treated CHF rats. GHRP suppressed cardiomyocyte apoptosis and increased cardiac GH secretagogue receptor mRNA expression in CHF rats. GHRP also decreased myocardial creatine kinase release in hypophysectomized rats subjected to acute myocardial ischemia. We conclude that chronic administration of GHRP alleviates LV dysfunction, pathological remodeling, and cardiac cachexia in CHF rats, at least in part by suppressing stress-induced neurohormonal activations and cardiomyocyte apoptosis.

There are no acute cardiac effects of a single iv dose of human ghrelin in severe growth hormone deficient patients

It has previously been suggested that ghrelin mediates GH-independent biologic activities on the heart. We investigated the acute effects on cardiac contraction of a single iv administration of human ghrelin (in a dose of 1 microg/kg) in severe untreated GH deficient subjects. Prior to the ghrelin infusion, an echocardiographic examination was performed at rest (baseline), after physiologic saline and during dobutamine stress echocardiography (DSE) to exclude a preexisting (subclinical) myocardial dysfunction. To evaluate the acute cardiac effect of infusion and during DSE the velocity of left ventricular (LV) wall contraction was measured continuously by echocardiography. Despite severe GH deficiency we observed in all subjects a normal cardiac function at rest after physiologic saline and during DSE. No acute changes in cardiac performance or cardiac parameters could be observed after a single iv dose of ghrelin. Also, no important increase in GH secretion was detected after ghrelin administration. Our study suggests that, in contrast to hexarelin, a single iv administration of ghrelin in a physiological dose has no acute effects on cardiac function in severe GH deficiency. This suggests that GH-independent effects of ghrelin play no important role in the acute regulation of cardiac function in man.

Biological, physiological, pathophysiological, and pharmacological aspects of ghrelin

Ghrelin is a peptide predominantly produced by the stomach. Ghrelin displays strong GH-releasing activity. This activity is mediated by the activation of the so-called GH secretagogue receptor type 1a. This receptor had been shown to be specific for a family of synthetic, peptidyl and nonpeptidyl GH secretagogues. Apart from a potent GH-releasing action, ghrelin has other activities including stimulation of lactotroph and corticotroph function, influence on the pituitary gonadal axis, stimulation of appetite, control of energy balance, influence on sleep and behavior, control of gastric motility and acid secretion, and influence on pancreatic exocrine and endocrine function as well as on glucose metabolism. Cardiovascular actions and modulation of proliferation of neoplastic cells, as well as of the immune system, are other actions of ghrelin. Therefore, we consider ghrelin a gastrointestinal peptide contributing to the regulation of diverse functions of the gut-brain axis. So, there is indeed a possibility that ghrelin analogs, acting as either agonists or antagonists, might have clinical impact.

The positive inotropic and calcium-mobilizing effects of growth hormone-releasing peptides on rat heart

GH-releasing peptides (GHRP) are synthetic peptides exerting GH-dependent or GH-independent effects via GH secretagogue receptor on many organs, including the heart. The underlying mechanisms of the cardiotropic properties of GHRP are poorly understood. This study investigates these effects of four GHRP in isolated perfused heart preparations and isolated neonatal and adult ventricular myocytes. The calcium response of cardiocytes to GHRP was visualized using confocal microscopy. All tested GHRP facilitated both ventricular contraction and relaxation in a dose-dependent manner, moderately decreasing coronary flow, but not modifying heart rate. GHRP induced a biphasic increase in intracellular free Ca2+ of the cardiocytes, consisting of a transient phase (phase 1), followed by a plateau phase (phase 2). Phase 1 was abolished by pretreatment with thapsigargin, a Ca2+-adenosine triphosphatase inhibitor of the sarcoplasmic reticulum. The phase 2 response was eliminated by removing extracellular free Ca2+, by verapamil, a voltage-gated Ca2+ channel blocker, or by 24-h pretreatment with phorbol 12-myristate 13-acetate, down-regulating protein kinase C. In isolated (denervated) heart, GHRP have a direct cardiotropic, without chronotropic, effect. GHRP elevate myocardial intracellular free Ca2+ through activating Ca2+ influx via voltage-gated Ca2+ channels and triggering Ca2+ release from thapsigargin-sensitive intracellular Ca2+ stores. Protein kinase C mediates the GHRP-induced Ca2+ influx, but not Ca2+ release. These finding support a number of roles for GHRP in the cardiovascular system.

Preliminary observations on the effects of acute infusion of growth hormone on coronary vasculature and on myocardial function and energetics of an isolated and blood-perfused heart

Recent studies have shown that growth hormone (GH) deficiency may deteriorate post-ischemic myocardial reperfusion damage. Furthermore, GH has been reported to be a promising therapeutic option in the treatment of chronic myocardial dysfunction. However, the exact mechanisms of action of GH on the cardiovascular system, particularly in the acute setting, are still unclear. The aim of our study consisted of monitoring the acute effects of GH infusion on isolated blood-perfused rabbit heart according to dose-response pattern and during ischemic conditions to test its anti-ischemic property. Seven blood-donors perfused isolated hearts were used as experimental model. The mechanical and metabolic data of the isolated organs were continuously monitored. Under aerobic conditions, dose-response curves were initially tested after intracoronary infusion of GH at increasing dosages (1, 2, 3 mg/l). After a stabilization period, the effects of GH infusion (5 mg/kg) administered 30 minutes prior to acute global myocardial ischemia (30 minutes) were also investigated. At the doses tested, GH did not induce any changes either in the developed or in the diastolic pressures of the isolated organ. However, transient reduction of the coronary perfusion pressure was observed at the dosage of 3 mg/l. During the ischemia/reperfusion study, at the dosages used in this study, GH did not modify either the degree of stunning in the early reperfusion or the recovery of the developed pressure at the end of reperfusion. In addition, GH did not prevent either the increase of diastolic pressure during ischemia or the release of lactate and CPK during reperfusion. Tissue content of high-energy phosphates was also not changed by GH infusion. In our experimental model, acute GH infusion did not reduce the ischemic/reperfusion damage of the myocardium. However, GH transiently induced coronary vasodilation without modifying the myocardial contractility. Acute effects of GH appear, therefore, to predominantly relate to vascular dilation suggesting that the effects on myocardial contractility may require long-lasting intake being likely linked to enhancement of specific protein synthesis or gene expression of cardiac myocytes.

Effects of acute hexarelin administration on cardiac performance in patients with coronary artery disease during by-pass surgery

Growth hormone (GH) secretagogues are synthetic molecules with neuroendocrine but also cardiovascular activities mediated by specific GH secretagogue-receptors. The acute administration of hexarelin, a peptidyl GH secretagogue, increases left ventricular ejection fraction in normal subjects and even in patients with severe GH deficiency. We evaluated cardiac performances in patients with coronary artery disease after acute administration of hexarelin (2.0 microg/kg, i.v.) compared to that in patients given with GH-releasing hormone (GHRH; 2.0 microg/kg, i.v.), recombinant human (rh)-GH (10.0 microg/kg, i.v.) or placebo. Cardiac performance was studied in 24 male patients (age [mean +/- S.E.M.]: 59.5 +/- 1.1 years; body mass index: 24.6 +/- 0.9 kg/m(2); left ventricular ejection fraction: 57.2 +/- 1.4%) with coronary artery disease undergoing by-pass surgery during general anesthesia. Left ventricular ejection fraction, left ventricular end diastolic volume, cardiac index and cardiac output were evaluated by intraoperative omniplane transoesophageal echocardiography while wedge pressure, central venous pressure, mean arterial pressure and systemic vascular resistance index were evaluated by systemic and pulmonary arterial catheterization. RhGH, GHRH and placebo did not exert any hemodynamic effect while hexarelin induced a prompt (after +10 min) increase in left ventricular ejection fraction (P < 0.001), cardiac index (P < 0.001) and cardiac output (P < 0.001) lasting up to +90 min without any variation in left ventricular end diastolic volume. Accordingly, hexarelin induced a reduction of wedge pressure (P < 0.01). These changes occurred in the presence of increased mean arterial pressure (P < 0.05) and transient decrease of central venous pressure (P < 0.05 at +30 min only) but no change in systemic vascular resistance index. Heart rate after hexarelin was similar to that after placebo. Hexarelin induced a slight increase in GH levels which was similar to that after GHRH but far lower (P < 0.01) than that after rhGH. Thus, in patients with coronary artery disease undergoing by-pass surgery, the acute administration of hexarelin clearly improves cardiac performance without any relevant variation in systemic vascular resistance. The cardiotropic effect of hexarelin is not shared by GHRH or by rhGH, indicating that it is not mediated by the increase in circulating GH levels but more likely reflects activation of specific cardiovascular GH secretagogue receptors.