Abstract

BACKGROUND
Ghrelin is a newly discovered gut peptide, produced mainly in the stomach, which is secreted into the circulating blood and acts on the hypothalamus and the pituitary gland. Although ghrelin was originally identified as an endogenous growth hormone secretagogue, recent studies have suggested its role is in the regulation of food intake and energy homeostasis. The aim of this study was to investigate changes in the expression of ghrelin in the stomach, and of its receptors in the hypothalamus and the pituitary gland in relation to the feeding state. METHODS: Sprague Dawley male rats, divided into 3 groups, freely fed, fasted for 48 hrs and fasted for 48 hrs followed by feeding for 24 hrs, were investigated. The stomach fundus, the hypothalamus and the pituitary glands were collected. The gastric ghrelin mRNA expression was determined by Northern blot analysis and the ghrelin protein by immunohistochemistry. The ghrelin receptor mRNA levels in the hypothalamus and anterior pituitary gland were determined by real time PCR. RESULTS: The ghrelin mRNA levels in the stomach were increased by fasting but reduced again by allowing feeding. The number of ghrelin-immunoreactive gastric epithelial cells tended to increase with fasting. Moreover, the ghrelin receptor mRNA levels increased fold in the hypothalamus, and about 3 fold in the anterior pituitary gland harvested from the rats that had fasted for 48 hrs compared to those that were freely fed. CONCLUSION: Our data demonstrate that expression of both ghrelin in stomach and its receptor in target organs increased in the fasted state, which would be helpful for magnifying the orexigenic effect of ghrelin in the negative energy balance state. Dynamic changes in ghrelin and ghrelin receptor according to altered metabolic state may suggest a physiologic role of ghrelin in the regulation of energy homeostasis.

• Keywords: Ghrelin;Growth hormone secretagogue receptor;Fasting;Stomach;Hypothalamus;Pituitary gland;