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Department of Biomedical Sciences and Biotechnology, University of Brescia, Brescia, Italy
1 Department of Pharmacology, University of Milano, Milano, Italy
2 Department of Experimental and Environmental Medicine and Biotechnologies, University of Milano-Bicocca, Monza, Italy
3 Department of Medical and Surgical Sciences, University of Brescia, Brescia, Italy
(Requests for offprints should be addressed to D Cocchi, Department of Biomedical Sciences and Biotechnology, University of Brescia, Viale Europa 11, 25123 Brescia, Italy; Email: cocchi{at}med.unibs.it)
It has previously been reported that growth hormone secretagogues (GHS) may have a role in the regulation of bone metabolism in animals and humans. In this study we evaluated the effect of ghrelin, the endogenous ligand of GHS receptors, on the proliferation rate and on osteoblast activity in primary cultures of rat calvaria osteoblasts. In the same experiments, we compared the effects of ghrelin with those of hexarelin (HEXA) and EP-40737, two synthetic GHS with different characteristics. Both ghrelin and HEXA (10–11–10–8 M) significantly stimulated osteoblast proliferation at low concentrations (10–10 M). Surprisingly, EP-40737 demonstrated an antiproliferative effect at 10–9–10–8 M, whereas lower concentrations had no effect on cell proliferation. Ghrelin and HEXA significantly increased alkaline phosphatase (ALP) and osteocalcin (OC) production. At variance with these peptides, EP-40737 did not significantly stimulate ALP and OC. The mRNA for GHS-R1a receptors and the corresponding protein were detected in calvarial osteoblasts by RT-PCR and Western blot respectively, indicating that ghrelin and GHS may bind and activate this specific receptor. We conclude that endogenous ghrelin and synthetic GHS modulate proliferation and differentiation of rat osteoblasts, probably by acting on their specific receptor.
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