Identification and Characterization of a New Growth Hormone-Releasing Peptide Receptor in the Heart

• Published in: Circulation research Vol. 85; no. 9; pp. 796 - 802
• Main Authors: Bodart, V, Bouchard, J F, McNicoll, N, Escher, E, Carrière, P, Ghigo, E, Sejlitz, T, Sirois, M G, Lamontagne, D, Ong, H
• Format: Journal Article
• Language: English
• Published: Hagerstown, MD American Heart Association, Inc 29.10.1999; Lippincott; Lippincott Williams & Wilkins Ovid Technologies
• Subjects: Animals; Biological and medical sciences; Coronary Vessels - physiology; Fundamental and applied biological sciences. Psychology; Heart; Heart - physiology; Hormones - metabolism; Male; Oligopeptides - metabolism; Radioligand Assay; Rats; Rats, Sprague-Dawley; Receptors, Neuropeptide - isolation & purification; Receptors, Neuropeptide - physiology; Receptors, Pituitary Hormone-Regulating Hormone - isolation & purification; Receptors, Pituitary Hormone-Regulating Hormone - physiology; Signal Transduction - physiology; Vascular Resistance - physiology; Vertebrates: cardiovascular system; Heart; Rat; Somatotropin releasing factor; Rodentia; Coronary artery; Photoaffinity labelling; Hexapeptide; Signal transduction; Vertebrata; Mammalia; Vascular resistance; Blood vessel; Animal; Peptidergic receptor; Circulatory system
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.res.85.9.796

Hexarelin, a synthetic hexapeptide of the growth hormone-releasing peptide (GHRP) family with strong growth hormone (GH)-releasing activity, features protecting activity against postischemic ventricular dysfunction in hearts from GH-deficient and senescent rats. To document whether hexarelin action is mediated through specific cardiac receptors, perfusion of Langendorff rat hearts with hexarelin and binding studies were carried out. In the Langendorff rat heart system, hexarelin induced a dose-dependent increase in coronary perfusion pressure. Nifedipine, chelerythrine, and bisindolylmaleimide partially inhibited the vasoconstriction induced by hexarelin, suggesting that this effect was mediated at least in part by L-type Ca channels and protein kinase C. In contrast, diclofenac and 1-(7-carboxyheptyl)imidazole were without effect, suggesting that prostaglandins and thromboxanes were not involved in the coronary vasoconstriction induced by hexarelin. To characterize the hexarelin binding sites in the rat heart, [I]Tyr-Bpa-Ala-hexarelin was used as photoactivatable radioligand in saturation and competitive binding studies. We specifically labeled a hexarelin receptor with an Mr of 84 000 in rat cardiac membranes. Saturation binding curves revealed a single class of binding sites with a Kd of 14.5 nmol/L and a density of 91 fmol/mg of protein. Competition binding studies gave an IC50 of 2.9 μmol/L for hexarelin; MK-0677 and EP51389, both potent GH secretagogues, did not displace the binding of the photoactivatable derivative from rat cardiac membranes. Interestingly, both compounds were devoid of any vasoconstrictive activity. These results suggest the existence of a new class of hexarelin receptor in the heart, whose role in the regulation of the coronary vascular tone is yet to be determined.