Acute cardiovascular and hormonal effects of GH and hexarelin, a syntheticGH-releasing peptide, in humans

Reduced cardiac mass and performances are present in GH deficiency and are counteracted by rhGH replacement. GH and IGF-I possess specific myocardial receptors and have been reported able to exert an acute inotropic effect. S ynthetic GH secretagogues (GHS) possess specific pituitary and hypothalamic but even myocardial receptors. In 7 male volunteers, we studied cardiac pe rformance by radionuclide angiocardiography after iv administration of rhGH or hexarelin (HEX), a peptidyl GHS. The administration of rhGH or HEX incr eased circulating GH levels to the same extent (AUC: 1594.6+/-88.1 vs 1739. 3+/-262.2 mu g/l/min for 90 min) while aldosterone and catecholamine levels did not change; HEX, but not rhGH, significantly increased cortisol levels . Left ventricular ejection fraction (LVEF), mean blood pressure (MBP) and heart rate (HR) were unaffected by rhGH (62.4+/-2.1 vs 62.1+/-2.3%, 90.6+/- 3.4 vs 92.0+/-2.5 mm Hg, 62.3+/-1.8 vs 66.7+/-2.7 bpm). HEX increased LVEF (70.7+/-3.0 vs 64.0+/-1.5%, p<0.03) without significant changes in MBP and HR (92.8+/-4.7 vs 92.4+/-3.2 mmHg, 63.1+/-2.1 vs 67.0+/-2.9 bpm). LVEF sign ificantly raised at 15 min, peaked at 30 min and lasted up to 60 min after HEX. These findings suggest that in man, the acute administration of Hexare lin exerts a short-lasting, positive inotropic effect. This effect seems GH -independent and might be mediated by specific GHS myocardial receptors. (J . Endocrinol. Invest. 22: 266-272, 1999) (C)1999, Editrice Kurtis.