Localization of ghrelin-like peptide in the gastrointestinal tract of the golden apple snail (Pomacea canaliculata) and changing of its concentration during fasting

Ghrelin is an endogenous hormone detected in the gastrointestinal tracts (GI) of various species. In the present study, ghrelin-like peptide (ghrelin-LP) was identified in the GI tract of the golden apple snail, Pomacea canaliculata. Using immunohistochemistry, the result revealed an immunoreactivity (-ir) of ghrelin-LP in regions of the GI tract. The ghrelin-LP-ir was observed in both opened-type and closed-type cells of the esophagus, stomach, and small and large intestines. The highest density of ghrelin-LP immunoreactive cells was found in the esophagus and the least density was detected in the stomach. The highest percentages of the opened-type and closed-type cells were present in the esophagus and small intestine, respectively. In immunoblotting, the molecular weight of ghrelin-LP was related to the human ghrelin peptide (∼13 kDa). Moreover, the concentration of ghrelin-LP was significantly higher in snails that were fasted for 24 h compared with fed snails. The concentration decreased after refeeding. The present study could be useful for understanding the physiological role of ghrelin-LP in mollusk species.