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

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 μg/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 significantly (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.