The ghrelin system in acinar cells: localization, expression, and regulation in the exocrine pancreas.
OBJECTIVE
Ghrelin and its receptor are expressed abundantly in the stomach and pituitary. Recently, a ghrelin system, consisting of both ligand and receptor, has also been found to exist in the endocrine cells of pancreatic islets. This ghrelin system may play a role in regulating insulin secretion and glucose homeostasis. The aim of the present study was to investigate whether a functional ghrelin system also exists in the exocrine pancreas.


METHODS
Precise localization and expression of ghrelin and its receptor in rat pancreatic acinar cells were examined by immunocytochemistry and Western blot, whereas messenger RNA levels were examined by semiquantitative reverse transcription-polymerase chain reaction. The roles of physiological and pathophysiological conditions, such as gastric acid inhibition, starvation, and acute pancreatitis, in regulation of ghrelin and its receptor were also examined.


RESULTS
Both ghrelin and its receptor were detected, at both protein and messenger RNA levels, in the acinar cells of the exocrine pancreas. Ghrelin receptor expression was up-regulated by gastric acid inhibition and down-regulated by acute pancreatitis, whereas levels remained unchanged after food deprivation. In contrast, ghrelin expression did not exhibit significant changes in any condition.


CONCLUSIONS
Our data indicate that a ghrelin system exists in the acinar cells of the exocrine pancreas. This system is subject to regulation by physiological and pathophysiological stimuli and may thus regulate exocrine functions by paracrine and/or autocrine mechanisms.
Lai
Kit Ching
KC
Department of Physiology, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, Hong Kong, China.
Cheng
Christopher H K
CH
Leung
Po Sing
PS
D000126:Achlorhydria / Q000139:chemically induced / Q000503:physiopathology; D000208:Acute Disease; D000818:Animals; D019898:Autocrine Communication; D002108:Ceruletide / Q000633:toxicity; D005508:Food Deprivation; D005744:Gastric Acid / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D054439:Ghrelin; D008297:Male; D009853:Omeprazole / Q000494:pharmacology; D046790:Pancreas, Exocrine / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D010195:Pancreatitis / Q000139:chemically induced / Q000503:physiopathology; D019899:Paracrine Communication; D036361:Peptide Hormones / Q000032:analysis / Q000096:biosynthesis / Q000502:physiology*; D012333:RNA, Messenger / Q000032:analysis; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D043562:Receptors, G-Protein-Coupled / Q000032:analysis / Q000096:biosynthesis / Q000502:physiology*; D054440:Receptors, Ghrelin
D054439:Ghrelin; D036361:Peptide Hormones; D012333:RNA, Messenger; D043562:Receptors, G-Protein-Coupled; D054440:Receptors, Ghrelin; D002108:Ceruletide; D009853:Omeprazole