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, gl ucose homeostasis, and for the maintenance of skeletal muscle mass. A large body of evidence recently coming from animal and human studies has unequiv ocally proven that the heart is a target organ for the GH/IGF-1 axis. Speci fically GH exerts both direct and indirect cardiovascular actions. Among th e 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 imp rovement of myocardial energetics and mechanical efficiency. Indirect effec ts of GH on the heart include decreased peripheral vascular resistance (PVR ), expansion of blood volume, increased glomerular filtration rate, enhance d respiratory activity, increased skeletal muscle performance, and psycholo gical wellbeing. 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 characteriz ed by left ventricular dilation, reduced cardiac contractility, and increas e of wall stress and peripheral vascular resistance, GH may be beneficial f or treatment of heart failure. Animal studies and preliminary human trials have confirmed the validity of the GH approach to the treatment of heart fa ilure. Larger placebo-controlled human studies represent the main focus of future investigations.