Effects of ghrelin and other neuropeptides (CART, MCH, orexin A and B, and GLP-1) on the release of insulin from isolated rat islets.
OBJECTIVE
Ghrelin, a neuropeptide containing 28 amino acids, shows a reciprocal diurnal plasma fluctuation to that of plasma insulin. The aim of this study is to clarify the dose and glucose-dependency of ghrelin on the insulin secretion and to compare its effect with that of other neuropeptides-GLP-1, CART (55-102), CART (55-76), CART (62-76), MCH, orexin A, and B.


METHODS
Rat islets were incubated with 1 pmol/l-1 micromol/l of ghrelin, CART fragments, MCH, orexin A or B, or GLP-1 (n = 16-32) in the presence of 16.7 mmol/l glucose. Ghrelin (10 nmol/l) was added to islets at glucose concentrations of 3.3, 6.6, 16.7 and 25 mmol/l, respectively (n = 28-32). Also, INS-1E cells were incubated with ghrelin (1 nmol/l) in the presence of glucose (3.3, 6.6, 16.7, and 25 mmol/l). In addition, we measured the mRNA expression of the ghrelin receptor using RT-PCR.


RESULTS
Ghrelin inhibited insulin secretion from islets and INS-1E cells in a dose- and glucose-dependent manner. Neither 10 pmol/l-1 micromol/l of CART fragments, MCH, orexin A, nor orexin B changed the insulin secretion at 16.7 mmol/l glucose, while GLP-1, as expected, stimulated the insulin release from rat islets. Interestingly, ghrelin receptors were expressed both in islets, INS-1E, MIN 6 and alpha cell Tca-9 lines.


CONCLUSIONS
Ghrelin inhibits the insulin secretion in vitro in a dose- and glucose-dependent manner. Beta cells contain ghrelin receptors. CART fragments did not affect the insulin secretion. Ghrelin may play a physiological role for the regulation of insulin secretion.
Colombo
Michele
M
Department of Endocrinology and Metabolism C, Aarhus Amtssygehus, Aarhus University Hospital, Aarhus University, Denmark. Mcolombo@dadlnet.dk
Gregersen
Søren
S
Xiao
Jianzhong
J
Hermansen
Kjeld
K
D000818:Animals; D002352:Carrier Proteins / Q000494:pharmacology; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation / Q000187:drug effects; D054439:Ghrelin; D005934:Glucagon / Q000494:pharmacology; D052216:Glucagon-Like Peptide 1; D005947:Glucose / Q000494:pharmacology; D007028:Hypothalamic Hormones / Q000494:pharmacology; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D047908:Intracellular Signaling Peptides and Proteins; D007515:Islets of Langerhans / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008543:Melanins / Q000494:pharmacology; D009419:Nerve Tissue Proteins; D009479:Neuropeptides / Q000494:pharmacology*; D064446:Orexin Receptors; D000068797:Orexins; D010446:Peptide Fragments / Q000494:pharmacology; D036361:Peptide Hormones / Q000494:pharmacology*; D010907:Pituitary Hormones / Q000494:pharmacology; D011498:Protein Precursors / Q000494:pharmacology; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D051381:Rats; D043562:Receptors, G-Protein-Coupled / Q000235:genetics; D054440:Receptors, Ghrelin; D018013:Receptors, Neuropeptide; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000098882:Cocaine- and Amphetamine-Regulated Transcript Protein
D002352:Carrier Proteins; D054439:Ghrelin; D005934:Glucagon; D052216:Glucagon-Like Peptide 1; D005947:Glucose; D007028:Hypothalamic Hormones; D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D008543:Melanins; D009419:Nerve Tissue Proteins; D009479:Neuropeptides; D064446:Orexin Receptors; D000068797:Orexins; D010446:Peptide Fragments; D036361:Peptide Hormones; D010907:Pituitary Hormones; D011498:Protein Precursors; D012333:RNA, Messenger; D043562:Receptors, G-Protein-Coupled; D054440:Receptors, Ghrelin; D018013:Receptors, Neuropeptide; C428723:cocaine- and amphetamine-regulated transcript protein (55-102); D000098882:Cocaine- and Amphetamine-Regulated Transcript Protein; C019463:melanin-concentrating hormone