Ghrelin, the endogenous ligand for GH secretagogue receptors, has been reported to influence acid gastric secretion and motility, but its potential gastroprotective effect is unknown. The aims of this study were 1) to examine the effects of central and peripheral administration of ghrelin on ethanol-induced gastric ulcers in conscious rats, and 2) to investigate the possible roles of nitric oxide (NO), vagal nerve, and sensory fibers in the gastric effects of ghrelin. Ghrelin was administered either intracerebroventricularly or sc 30 min before ethanol, and mucosal lesions were examined macroscopically. Additionally, rats were either treated with the inhibitor of NO synthesis N(omega)-nitro-L-arginine methyl ester (L-NAME) or underwent bilateral cervical vagotomy or capsaicin-induced sensory denervation. Conventional histology and immunohistochemistry for ghrelin, gastrin, and somatostatin were performed on gastric specimens from representative rats. Central ghrelin (4-4,000 ng/rat) dose-dependently reduced ethanol-induced gastric ulcers by 39-77%. Subcutaneous ghrelin administration (80 micro g/kg) reduced ulcer depth only. L-NAME and capsaicin, but not vagotomy, prevented the gastroprotective effect of central ghrelin (4000 ng/rat). This is the first evidence that ghrelin exerts a potent central gastroprotective activity against ethanol-induced lesions. The gastroprotective effect of ghrelin is mediated by endogenous NO release and requires the integrity of sensory nerve fibers.

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.

Background and purpose: Ghrelin, a gut-brain peptide, is considered a gastroprotective factor in gastric mucosa. We investigated the role of prostaglandins (PG) and the possible interplay between PGs and nitric oxide (NO) in ghrelin gastroprotection against ethanol (EtOH)-induced gastric lesions. Experimental approach: We examined the effects of (1) central ghrelin (4 mg per rat) injection on PGE 2 accumulation in normal or EtOH-lesioned gastric mucosa, (2) pretreatment with indomethacin (10 mg kg À1 , p.o.), a non-selective cyclooxygenase (COX) inhibitor, and with a selective COX-1, SC560 (5 mg kg À1 , p.o.) or COX-2 inhibitor, celecoxib (3.5 mg kg À1 , p.o.) on ghrelin gastroprotection against 50% EtOH (1 mL per rat)-induced gastric lesions, (3) the NO synthase inhibitor, L-NAME (70 mg kg À1 , s.c), on gastric PGE 2 content in ghrelin-treated rats and (4) central ghrelin on the expression of constitutive and inducible NOS and COX mRNA and on the localization of the immunoreactivity for COX-2 in the gastric mucosa exposed to EtOH. Key results: Ghrelin increased PGE 2 in normal mucosa, whereas, it reversed the EtOH-induced PGE 2 surge. Ghrelin had no effect on mucosal COX-1 expression but reduced the EtOH-induced increase in COX-2 expression and immunoreactivity. Indomethacin and SC560, but not celecoxib, removed ghrelin gastroprotection. L-NAME prevented the PGE 2 surge induced by ghrelin and, like indomethacin, reduced EtOH-induced PGE 2 increase. Ghrelin enhanced eNOS expression and reduced iNOS mRNA. Conclusions and implications:This study shows that COX-1-derived PGs are mainly involved in ghrelin gastroprotection and that the constitutive-derived NO together with PGE 2 are involved in ghrelin gastroprotective activity.

We examined the possible central and peripheral effects of synthetic growth hormone secretagogues (GHS), hexarelin (Hexa) and EP 40737 (D-Thr-D-Trp (2-Me)-Ala- Trp-D-Phe-Lys-NH₂), and of their endogenous counterpart, ghrelin, on gastric acid secretion. The compounds were administered intracerebroventricularly (i.c.v.) or subcutaneously (s.c.) in conscious male rats and the volume of gastric secretion and gastric acid output were examined 3 h after pylorus ligation (Shay-test). Central Hexa, EP 40737 and ghrelin administration (from 0.1 pmol to 1 nmol/rat, i.c.v.) significantly inhibited gastric acid secretion. The maximum inhibitory effect on gastric acid output was detected at the dose of 10 pmol/rat, i.c.v. for Hexa (–51.3%), of 100 pmol/rat, i.c.v. for EP 40737 (–70%) and of 1 pmol/rat, i.c.v. for ghrelin (–60%). All peptides were less effective at the highest dose used (1 nmol/rat, i.c.v.). Hexa, EP 40737 and ghrelin injected s.c. did not modify gastric acid secretion. The inhibitory action of Hexa on gastric acid secretion seems to involve brain somatostatinergic system since Hexa (10 pmol/rat, i.c.v.) did not inhibit gastric acid secretion in rats pretreated (4 h before) with cysteamine (300 mg/kg, s.c.), a depletor of endogenous somatostatin. These results show that synthetic GHS and ghrelin exert a central long-lasting inhibitory effect on gastric acid secretion in conscious pylorus-ligated rats. The fact that very low doses of ghrelin and GHS inhibit gastric secretion, provide evidence for a tonic inhibitory role of the peptides in the central control of gastric secretory function.