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Obestatin stimulates GH release from somatotroph cells, which indicates that this peptide can act directly on the pituitary. Based on the incapability of obestatin to cross the blood Linsitinib barrier [28], it is not possible to talk about a peripheral control of GH secretion by obestatin. However the expression of preproghrelin at hypothalamic level [29] prompted us to speculate about the involvement of the hypothalamus in obestatin-mediated stimulation of GH release. A direct involvement would suppose that hypothalamic obestatin was secreted into the portal system to exert its action on somatotroph cells that modulate GH secretion. An indirect involvement would imply that other factor(s) might be involved in the regulation of the pituitary expression of preproghrelin and obestatin secretion that would modulate GH synthesis and/or secretion. Thus, obestatin might be included in the series of stimulatory releasing factors that control the GH release from somatotrophs.
Acknowledgments
We thank Prof. Dr. I.C.A.F. Robinson (Division of Neurophysiology, National Institute for Medical Research, The Ridgeway, Mill Hill, London, UK) for providing GC cell line. Dr. A.B. Crujeiras is root hairs greatly acknowledged for helpful discussions. This work was supported by Grants from the FIS and the Instituto de Salud Carlos III, Ministerio de Ciencia e Innovación and Xunta de Galicia. CIBER is an initiative of Instituto de Salud Carlos III (Ministerio de Ciencia e Innovación, Spain). Instituto de Salud Carlos III (Ministerio de Ciencia e Innovación, Spain) and Xunta de Galicia (SERGAS) funded the work of Y. Pazos and J.P. Cami?a through a research-staff stabilization contract. L.M. Seoane is a recipient of a Research Contract “Miguel Servet” from the Instituto de Salud Carlos III (Ministerio de Ciencia e Innovación) in the Complejo Hospitalario Universitario de Santiago de Compostela.