Background: Ghrelin is the endogenous ligand for the growth hormone secretagogue receptor (GHSR). Ghrelin regulates feeding activity and interdigestive contractions of the stomach in rodents. To investigate the role of endogenous ghrelin in the digestive system, we have developed GHSR-mutant rats, named FHH-Ghsr(m1Mcwi), using the Fawn-Hooded Hypertensive (FHH) parental strain.
Methods: N-ethyl-N-nitrosourea (ENU) was used as a mutagen. Genomic DNA prepared from a tail clip was analyzed using the targeting induced local lesions in genomes (TILLING) approach. The non-synonymous mutation in position 343 (NM_032075) led to the generation of a premature stop codon, causing deletion of the last 22 amino acids at the C-terminal of ghrelin receptor protein. Spontaneous and ghrelin-stimulated food intake was measured in wild-type (WT) FHH and FHH-Ghsr(m1Mcwi) rats. For interdigestive motility recording, two strain gauge transducers were sutured on the antrum and duodenum. Spontaneous gastroduodenal contractions were recorded in freely moving conscious rats.
Results: Ghrelin (40 μg/kg) failed to stimulate food intake in the mutant rats, while spontaneous food intake was not significantly different between the WT rats and FHH-Ghsr(m1Mcwi) rats. Phase III-like contractions were observed in stomach and duodenum both in the WT and FHH-Ghsr(m1Mcwi) rats. In the WT rats, ghrelin (12 μg/kg) administration enhanced spontaneous phase III-like contractions, and a GHSR antagonist, (D-lys3)GHRP-6 (0.28 mg/kg), abolished the spontaneous phase III-like contractions. In FHH-Ghsr(m1Mcwi) rats, ghrelin and (D-lys3)GHRP-6 did not affect phase III-like contractions.
Conclusions: It is suggested that the intact GHSR structure is essential for the ghrelin-dependent regulation of interdigestive motility and feeding behavior. Even in FHH-Ghsr(m1Mcwi) rats, spontaneous gastric phase III-like contractions were still observed, suggesting the development of a compensatory mechanism to maintain these contractions.