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

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Abstract
Reduced cardiac mass and performances are present in GH deficiency and are coun-teracted by rhGH replacement. GH and IGF-I possess specific myocardial receptors and have been reported able to exert an acute inotropic effect. Synthetic GH secretagogues (GHS) possess specific pituitary and hypothalamic but even myocar-dial receptors. In 7 male volunteers, we studied cardiac performance by radionuclide angiocardiography after iv administration of rhGH or hexare-lin (HEX), a peptidyl GHS. The administration of rhGH or HEX increased circulating GH levels to the same extent (AUC: 1594.6±88.1 vs 1739.3±262.2 μg/l/min for 90 min) while aldosterone and cate-cholamine 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%, pvs 67.0±2.9 bpm). LVEF significantly 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 Hexarelin exerts a short-lasting, positive inotropic effect. This effect seems GH-in-dependent and might be mediated by specific GHS myocardial receptors.

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