GH-releasing peptides (GHRP) are synthetic peptides exerting GH-dependent or GH-independent effects via GH secretagogue receptor on many organs, including the heart. The underlying mechanisms of the cardiotropic properties of GHRP are poorly understood. This study investigates these effects of four GHRP in isolated perfused heart preparations and isolated neonatal and adult ventricular myocytes. The calcium response of cardiocytes to GHRP was visualized using confocal microscopy. All tested

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... facilitated both ventricular contraction and relaxation in a dose-dependent manner, moderately decreasing coronary flow, but not modifying heart rate. GHRP induced a biphasic increase in intracellular free Ca 2؉ of the cardiocytes, consisting of a transient phase (phase 1), followed by a plateau phase (phase 2). Phase 1 was abolished by pretreatment with thapsigargin, a Ca 2؉ -adenosine triphosphatase inhibitor of the sarcoplasmic reticulum.