Both acyl and des-acyl ghrelin regulate adiposity and glucose metabolism via CNS ghrelin receptors. Short Title: CNS ghrelin receptor regulation of metabolism

Ghrelin receptors (GHSRs) in the central nervous system (CNS) mediate hyperphagia and adiposity induced by acyl ghrelin (AG). Evidence suggests that des-acyl ghrelin (dAG) has biological activity through GHSR independent mechanisms. We combined in vitro and in vivo approaches to test possible GHSR-mediated biological activity of dAG. Both AG (100nM) and dAG (100nM) significantly increased IP3 formation in HEK-293 cells transfected with human GHSR. As expected, intracerebroventricular (icv) infusion of AG in mice increased fat mass (FM), in comparison with the saline-infused controls. Icv-dAG also increased FM at the highest dose tested (5 nmol/day). Chronic icv infusion of AG or dAG increased glucose-stimulated insulin secretion (GSIS). Subcutaneously infused AG regulated FM and GSIS in comparison to saline-infused control mice, whereas dAG failed to regulate these parameters even with doses that were efficacious when delivered icv. Furthermore, icv-dAG failed to regulate FM and induce hyperinsulinemia in GHSR deficient (Ghsr-/-) mice. In addition, a hyperinsulinemiceuglycemic clamp suggests that icv-dAG impairs glucose clearance without affecting endogenous glucose production. Taken together, these data demonstrate that dAG is an agonist of GHSR and regulates body adiposity and peripheral glucose metabolism through a CNS GHSR-dependent mechanism.