Growth Hormone Releasers: Arginine / Hexarelin
L-arginine reduces heart rate and improves hemodynamics in severe congestive heart failureBocchi EA, Vilella de Moraes AV, Esteves-Filho A, Bacal F, Auler JO, Carmona MJ, Bellotti G, Ramires AF. Heart Institute, Medical School of Sao Paulo University, Brazil.
BACKGROUND: Stimulated endothelium-derived relaxing factor-mediated vasodilation and conduit artery distensibility are impaired in congestive heart failure (CHF). L-arginine could have a potentially beneficial role in CHF, acting through the nitric oxide (NO)-L-arginine pathway or by growth hormone increment. HYPOTHESIS: This study was undertaken to investigate the effects of L-arginine on heart rate, hemodynamics, and left ventricular (LV) function in CHF.
METHODS: In seven patients (aged 39 +/- 8 years) with CHF, we obtained the following parameters using echocardiography and an LV Millar Mikro-Tip catheter simultaneously under four conditions: basal, during NO inhalation (40 ppm), in basal condition before L-arginine infusion, and after L-arginine intravenous infusion (mean dose 30.4 +/- 1.9 g). RESULTS: Nitric oxide inhalation increased pulmonary capillary wedge pressure from 25 +/- 9 to 31 +/- 7 mmHg (p < 0.05), but did not change echocardiographic variables or LV contractility by elastance determination. L-arginine decreased heart rate (from 88 +/- 15 to 80 +/- 16 beats/min, p<0.005), mean systemic arterial pressure (from 84 +/- 17 to 70 +/- 18 mmHg, p < 0.007), and systemic vascular resistance (from 24 +/- 8 to 15 +/- 6 Wood units, p<0.003). L-arginine increased right atrial pressure (from 7 +/- 2 to 10 +/- 3 mmHg, p<0.04), cardiac output (from 3.4 +/- 0.7 to 4.1 +/- 0.8 l/min, p < 0.009), and stroke volume (from 40 +/- 9 to 54 +/- 14 ml, p < 0.008). The ratios of pulmonary vascular resistance to systemic vascular resistance at baseline and during NO inhalation were 0.09 and 0.075, respectively, and with L-arginine this increased from 0.09 to 0.12.
CONCLUSION: L-arginine exerted no effect on contractility; however, by acting on systemic vascular resistance it improved cardiac performance. L-arginine showed a negative chronotropic effect. The possible beneficial effect of L-arginine on reversing endothelial dysfunction in CHF without changing LV contractility should be the subject of further investigations.
Arginine nutrition and cardiovascular functionWu G, Meininger CJ. Department of Animal Science and Faculty of Nutrition, Texas A&M University, College Station, 77843, USA.
L-Arginine (Arg) is the substrate for the synthesis of nitric oxide (NO), the endothelium-derived relaxing factor essential for regulating vascular tone and hemodynamics. NO stimulates angiogenesis, but inhibits endothelin-1 release, leukocyte adhesion, platelet aggregation, superoxide generation, the expression of vascular cell adhesion molecules and monocyte chemotactic peptides, and smooth muscle cell proliferation. Arg exerts its vascular actions also through NO-independent effects, including membrane depolarization, syntheses of creatine, proline and polyamines, secretion of insulin, growth hormone, glucagon and prolactin, plasmin generation and fibrinogenolysis, superoxide scavenging and inhibition of leukocyte adhesion to nonendothelial matrix. Compelling evidence shows that enteral or parenteral administration of Arg reverses endothelial dysfunction associated with major cardiovascular risk factors (hypercholesterolemia, smoking, hypertension, diabetes, obesity/insulin resistance and aging) and ameliorates many common cardiovascular disorders (coronary and peripheral arterial disease, ischemia/reperfusion injury, and heart failure). Dietary Arg supplementation may represent a potentially novel nutritional strategy for preventing and treating cardiovascular disease.
Arginine: Clinical potential of a semi-essential aminoAppleton J. Department chair, National College of Naturopathic Medicine, Portland, OR 97201, USA. email@example.com
Arginine, a semi-essential amino acid, is involved in numerous areas of human biochemistry, including ammonia detoxification, hormone secretion, and immune modulation. Arginine is also well known as a precursor to nitric oxide (NO), a key component of endothelial-derived relaxing factor, an endogenous messenger molecule involved in a variety of endothelium-dependent physiological effects in the cardiovascular system. Because of arginine's NO-stimulating effects, it can be utilized in therapeutic regimens for angina pectoris, congestive heart failure, hypertension, coronary heart disease, preeclampsia, intermittent claudication, and erectile dysfunction. In addition, arginine has been studied in the treatment of HIV/AIDS, athletic performance, burns and trauma, cancer, diabetes and syndrome X, gastrointestinal diseases, male and female infertility, interstitial cystitis, immunomodulation, and senile dementia. Toxicity, dosage considerations, and contraindications are also reviewed.
Diagnosis of growth hormone deficiency in adultsKorbonits M, Besser M. Department of Endocrinology, St. Bartholomew's Hospital, London, UK.
The potential effects of growth hormone (GH) deficiency in adults and the importance of GH secretion in adult life have only been recognized and documented recently. It has been suggested that GH-deficient adults may have premature mortality, abnormalities in body composition and bone density with impaired physical performance and psychological well-being, which are sometimes improved by GH replacement. It is essential, therefore, to establish reliable standards to define GH deficiency in adults. Patients with possible GH deficiency often have primary pituitary or hypothalamic disorders or have undergone surgery or radiotherapy, and thus show evidence of a failure of one of the other pituitary hormones. Several biochemical approaches have been studied to define GH deficiency in the adult and no universal consensus has yet been reached. The most widely established criterion is the peak serum GH concentration achieved during a provocative test, usually the insulin tolerance test (ITT), or following other pharmacological stimuli (e.g. glucagon, arginine, clonidine or GH-releasing factor) but, alternatively, a more physiological stimulus (such as sleep, fasting or exercise) has been used. Spontaneous circulating levels of hormones of the GH axis [24-hour integrated GH concentration, serum insulin-like growth factor I (IGF-I) or IGF-binding protein-3] have been used in the diagnosis of childhood GH deficiency. They have been tested in adults as well but seem to have a more limited role. There are several factors complicating the evaluation of these results. Basal and stimulated GH and IGF-I levels decline with age and with obesity, levels tend to be higher in females and are dependent on nutritional and physical status. The ITT potentially has some risk attached, e.g. in the presence of ischaemic heart disease, but it has proved to be safe in general when used in specialized departments. Other tests are less reliable; releasing hormone tests only assess the readily releasable stores within the pituitary and not the physiological secretory status. The 'cut-off' point for the definition of subnormal responses ideally needs to be set for each provocative test, for each age group, for each degree of obesity and for both sexes. There is considerable variability in GH assays among different laboratories, which makes it difficult to compare hormone levels. The reproducibility of provocative tests can also be variable. An advantage of the hypoglycaemia and glucagon tests is that they allow simultaneous assessment of the adrenocorticotropic hormone reserve.
Effect of digoxin on the somatotroph responsiveness to growth hormone-releasing hormone (GHRH) alone or combined with arginine in normal young volunteersBroglio F, Benso A, Gottero C, Vito LD, Granata R, Arvat E, Bobbio M, Trevi G, Ghigo E. Department of Internal Medicine, University of Turin, Italy.
BACKGROUND: The activity of the GH/IGF-I axis, known to play a major role in myocardial structure and function, has been reported to be altered in patients with chronic heart failure.
AIM AND DESIGN OF THE STUDY: In order to evaluate the possibility that clinically used cardioactive drugs may exert neuroendocrine influences on somatotroph secretion, we studied the effects of pretreatment with enalapril (20 mg/day orally for 3 days), furosemide (20 mg i.v. as a bolus at -5 minutes) or digoxin (0.25 mg orally 4x/day for 3 days) on the GH response to growth hormone-releasing hormone (GHRH) (1.0 microg/ kg i.v. as a bolus at 0 minutes) in 12 healthy male adults (age [mean +/- SEM] 30.2 +/- 1.4 years; BMI 22.7 +/- 0.7 kg/ m2). In a subgroup of 8 subjects the same study was performed testing the GH response to GHRH + arginine (ARG; 0.5 g/kg i.v. from 0 to + 30 minutes).
RESULTS The GH response to GHRH (1,304.1 +/- 248-5 microg/l/h) was not modified by enalapril (1,368.7 +/- 171.2 microg/l/h) or by furosemide (1,269.3 +/- 185.2 microg/l/h) but was significantly blunted by digoxin (613.6 +/- 73.2 microg/l/h, P < 0.05). On the other hand digoxin, enalapril and furosemide did not modify the GH response to GHRH +ARG.
CONCLUSIONS: Digoxin, but not enalapril or furosemide, inhibits the GH response to GHRH in normal subjects. The blunting effect of digoxin on the GHRH-induced GH response is counteracted by arginine. These findings show that digoxin possesses an inhibitory effect on somatotroph secretion that may be mediated at the hypothalamic level.
Improvement of cardiac output and liver blood flow and reduction of pulmonary vascular resistance by intravenous infusion of L-arginine during the early reperfusion period in pig liver transplantationLangle F, Steininger R, Waldmann E, Grunberger T, Benditte H, Mittlbock M, Soliman T, Schindl M, Windberger U, Muhlbacher F, Roth E. Department of Surgery, University of Vienna, Austria.
BACKGROUND: The release of liver arginase after orthotopic liver transplantation (OLT) causes a deficiency of L-arginine and nitrite in the plasma. This deficiency is possibly related to pulmonary hypertension and reduced hepatic blood flow, which are commonly observed in the immediate reperfusion period. The aim of this study was to evaluate the impact of L-arginine supplementation on metabolic and hemodynamic parameters during liver reperfusion after OLT in pigs.
METHODS: Thirteen pig OLTs (control group, n=6; arginine group, n=7) were performed by a standard technique. Cold ischemic time was 20 hr. L-Arginine was infused at a dosage of 500 mg/kg body weight into the donor pigs (30 min before liver explantation) and also into the recipients (over a period of 3 hr from the beginning of the reperfusion period). At the end of the experimental study, the pigs were killed with an overdose of potassium.
RESULTS: In the control group, liver revascularization increased plasma arginase concentrations (+615%) and reduced plasma levels of L-arginine (-87%), nitrite (-82%), and nitrate (-53%). Infusion of L-arginine increased plasma levels of L-arginine from 94+/-21 micromol/L to 1674+/-252 micromol/L (P<0.001), L-ornithine from 46+/-8 micromol/L to 2215+/-465 micromol/L (P<0.001), and L-citrulline from 58+/-8 micromol/L to 116+/-34 micromol/L (P<0.001), but had no effect on plasma levels of nitrite and nitrate. Administration of L-arginine in the donor pigs did not produce any systemic or organ-specific hemodynamic alterations. Infusion of L-arginine into the recipient pigs improved cardiac performance (increase in heart rate [+61%, P=0.017] and cardiac index [+53%, P=0.005], reduction in pulmonary capillary wedge pressure [-54%, P=0.014]). Moreover L-arginine infusion increased oxygen consumption (+65%, P=0.003), reduced pulmonary vascular resistance index (P=0.001), stimulated portal venous blood flow (P=0.014), and elevated body temperature during the reperfusion period (P=0.007).
CONCLUSIONS: From these data, we conclude that the infusion of L-arginine during OLT improves the hemodynamic performance of the heart, lung, and liver.
GH-independent cardiotropic activities of hexarelin in patients with severe left ventricular dysfunction due to dilated and ischemic cardiomyopathyImazio M, Bobbio M, Broglio F, Benso A, Podio V, Valetto MR, Bisi G, Ghigo E, Trevi GP. Division of Cardiology, University Internal Medicine Department, Turin, Italy.
AIM: To investigate acute cardiotropic activities of hexarelin in patients with severe left ventricular dysfunction due to ischemic (iCMP) and dilated cardiomyopathy (dCMP). METHODS AND RESULTS: We studied the effect of intravenous hexarelin administration on growth hormone (GH) levels and left ventricular ejection fraction (LVEF) evaluated by radionuclide angiography in eight patients with dCMP (age 53.0+/-2.8, LVEF 16.7+/-2.1%) and five patients with iCMP (age 52.0+/-2.8 years, LVEF 22.6+/-2.1). Results were compared with a group of seven normal subjects (age 37.4+/-3.4 years, LVEF 64.0+/-1.5%) and seven patients with severe growth-hormone deficiency (GHD; age 42.0+/-4.4 years, LVEF 50.0+/-1.9%) previously studied with the same methodology. In dCMP and iCMP patients hexarelin induced a similar significant (P<0.05) increase in GH levels. In iCMP patients hexarelin induced a LVEF increase (peak LVEF 26.2+/-2.5%, P<0.05) as observed in normals and GHD, while in dCMP LVEF was unchanged (peak LVEF 17.7+/-1.7, P=NS). In all groups other hemodynamic parameters were unchanged. CONCLUSIONS: Acute hexarelin administration increases LVEF in iCMP patients (as in normals and GHD) but not in dCMP patients in spite of a similar GH releasing effect and basal LVEF. A possible explanation of the positive inotropic effect of hexarelin in iCMP could be a direct stimulation on viable myocardium or myocardial contractile reserve.
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 cardiomyopathyBroglio F, Benso A, Valetto MR, Gottero C, Quaranta L, Podio V, Arvat E, Bobbio M, Bisi G, Ghigo E. Department of Internal Medicine, University of Turin, Italy.
Growth hormone releasing peptides (GHRPs) are synthetic molecules endowed with potent neuroendocrine activities mediated by specific receptors in the pituitary and in the central nervous system. GHRPs receptors have been reported even in perpheral tissues, particularly in the myocardium, where they probably mediate growth hormone (GH)-independent activities. We studied in humans the cardiac effects of hexarelin administration in 7 normal adults, in 7 severe GH-deficient patients, and in 12 patients with severe dilated cardiomyopathy. Left ventricular ejection fraction (LVEF), mean blood pressure (MBP), heart rate (HR), and GH levels were evaluated at baseline and every 15 min up to 60 min after acute 2.0 microg/kg iv hexarelin administration. Basal LVEF in dilated cardiomyopathy was impaired and lower (p < 0.001) than in GH deficiency, in turn lower (p< 0.001) than in normal subjects. Hexarelin signficantly (p < 0.05) increased LVEF in normal and in GH-deficient subjects, but not in dilated cardiomyopathy, without significant variations in MBP and HR. Hexeralin significantly (p < 0.05) increased GH levels in normal subjects and in dilated cardiomyopathy but not in GH deficiency. These findings suggest that, in humans, the acute administration of hexarelin exerts a GH-independent positive inotropic effect likely mediated by specific GHRPs myocardial receptors.
The growth hormone secretagogue hexarelin improves cardiac function in rats after experimental myocardial infarctionTivesten A, Bollano E, Caidahl K, Kujacic V, Sun XY, Hedner T, Hjalmarson A, Bengtsson BA, Isgaard J. Research Center for Endocrinology and Metabolism, the Department of Internal Medicine, Sahlgrenska University Hospital, Goteborg, Sweden.
Several studies have shown that GH can enhance cardiac performance in rats after experimental myocardial infarction and in humans with congestive heart failure. In the present study, the hemodynamic effects of hexarelin (Hex), an analog of GH-releasing peptide-6 and a potent GH secretagogue, were compared with the effects of GH. Four weeks after ligation of the left coronary artery male rats were treated sc twice daily with hexarelin [10 microg/kg x day (Hex10) or 100 microg/kg x day (Hex100)], recombinant human GH (2.5 mg/kg x day), or 0.9% NaCl for 2 weeks. Transthoracic echocardiography was performed before and after the treatment period. GH, but not Hex, increased body weight gain. GH and Hex100 decreased total peripheral resistance (P < 0.05) and increased stroke volume (P < 0.05 and P < 0.01, respectively) and stroke volume index (P = 0.06 and P < 0.01, respectively) vs. NaCl. Cardiac output was increased by GH and Hex100 (P < 0.05), and cardiac index was increased by Hex100 with a borderline significance for GH (P = 0.06). In conclusion, Hex improves cardiac function and decreases peripheral resistance to a similar extent as exogenous GH in rats postmyocardial infarction. The mechanisms of these effects are unclear; they could be mediated by GH or a direct effect of Hex on the cardiovascular system.
The role of the GH/IGF-I axis for cardiac function and structureIsgaard J, Tivesten A, Friberg P, Bengtsson BA. Research Center for Endocrinology and Metabolism, Sahlgrenska University Hospital, Goteborg, Sweden. firstname.lastname@example.org
There is ample evidence to support a role for the GH/IGF-I axis in regulation of cardiac growth, structure and function. GH may act directly on the heart or through circulating IGF-I (Fig. 1). Moreover, GH has been found to regulate local production of IGF-I in the heart. Both the GH-R and IGF-I-R are expressed in cardiac tissue. Hence, the IGF-I-R receptor can theoretically be activated through locally produced IGF-I acting via autocrine/paracrine mechanisms, or via circulating IGF-I exerting its effects as an endocrine agent. During conditions of pressure and volume overload, an increased systolic wall stress triggers an induction of gene expression of IGF-I GH-R and possibly IGF-J-R implying a potential role for the GH/IGF-I axis in the development of adaptive hypertrophy of the heart and vessels. Cardiovascular effects of GH in clinical studies include beneficial effects on contractility, exercise performance and TPR, and experimental studies suggest an increased Ca2+ responsiveness as one possible underlying cause, although effects of GH and IGF-I on apoptosis may possibly also play a role. The GH secretagogue hexarelin improves cardiac function after experimental myocardial infarction either through an increased GH secretion or possibly through a cardiac GHS receptor, although this needs further investigation. Moreover, it is clear that further basic and clinical studies are required to gain insight into the GH and IGF-I mechanisms of action and to monitor long-term effects when GH is administered as substitution therapy or as an agent in the treatment of congestive heart failure.
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