Role of growth hormone in chronic heart failure. Therapeutic implications.

Abstract

Congestive heart failure is a multiple aetiology, high prevalence, poor prognosis cardiovascular disorder. Medical treatment of dilated cardiomyopathy is aimed at alleviating the symptoms of heart failure. Diuretics, ACE inhibitors and very recently, beta-blockers have been shown to have favourable effects on symptoms, exercise capacity and mortality. Growth hormone (GH) and insulin-like growth factor (IGF)-1 are involved in several physiological processes such as the control of muscle mass and function, body composition and regulation of nutrient metabolism. The roles of GH and IGF-1 as modulators of myocardial structure and function are well established. Receptors for both GH and IGF-1 are expressed by cardiac myocytes; therefore, GH may act directly on the heart or via the induction of local or systemic IGF-1, whereas IGF-1 may act by endocrine, paracrine or autocrine mechanisms. Patients with acromegaly have an increased propensity to develop ventricular hypertrophy and cardiovascular diseases and, in addition, an impaired cardiac efficiency is observed in patients with GH deficiency. Animal models of pressure and volume overload have demonstrated up-regulation of cardiac IGF-1 production and expression of GH and IGF-1 receptors, implying that the local regulation of these factors is influenced by haemodynamic changes. Moreover, experimental studies suggest that GH and IGF-1 have stimulatory effects on myocardial contractility, possibly mediated by changes in intracellular calcium handling. Heart failure is caused by ventricular dilatation with abnormal wall thickening, which leads to impaired cardiac performance; therefore, based on the evidence available for GH we would expect beneficial effects from the use of GH in these patients. Several papers highlight the positive influence of GH in the regulation of heart development and performance. In patients with GH deficiency, GH administration dramatically improves cardiac function. In small nonblind studies, both short and long term GH treatment have demonstrated beneficial effects in patients with heart failure secondary to ischaemic or idiophatic cardiomyopathy. Recently, two randomised, placebo-controlled studies, did not show significant GH-mediated improvement in cardiac performance in patients with dilated cardiomyopathy, despite significant increases in IGF-1. Acquired GH resistance, might be an important feature of severe heart failure and explain the different responses to GH therapy seen in different patients. Whether GH treatment will finally find a place, and with which modalities, in the treatment of heart failure remains to be established.