Fourth ventricular administration of ghrelin induces relaxation of the proximal stomach in the rat

The effects of fourth ventricular administration of ghrelin on motility of the proximal stomach were examined in anesthetized rats. Intragastric pressure (IGP) was measured using a balloon situated in the proximal part of the stomach. Administration of ghrelin into the fourth ventricle induced relaxation of the proximal stomach in a dose-dependent manner. Significant reduction of IGP was observed at doses of 3, 10, or 30 pmol. The administration of ghrelin (10 or 30 pmol) with growth hormone secretagogue receptor (GHS-R) antagonist ([D-Lys3] GHRP-6; 1 nmol) into the fourth ventricle did not induce a significant change in IGP. The sole administration of [D-Lys3] GHRP-6 also did not induce a significant change in IGP. Bilateral sectioning of the vagi at the cervical level abolished the relaxation induced by the administration of ghrelin (10 or 30 pmol) into the fourth ventricle, suggesting that relaxation induced by ghrelin is mediated by vagal preganglionic neurons. Microinjections of ghrelin (200 fmol) into the caudal part of the dorsal vagal complex (DVC) induced obvious relaxation of the proximal stomach. Similar injections into the intermediate part of the DVC did not induce significant change. Dose-response analyses revealed that the microinjection of 2 fmol of ghrelin into the caudal DVC significantly reduced IGP. These results revealed that ghrelin induced relaxation in the proximal stomach via GHS-R situated in the caudal DVC.