Ghrelin stimulates gastric motility of the guinea pig through activation of a capsaicin-sensitive neural pathway: in vivo and in vitro functional studies.
BACKGROUND
Ghrelin stimulates gastric motility in rats, mice and humans. Although ghrelin and the ghrelin receptor are known to be expressed in the guinea-pig gastrointestinal tract, the effects of ghrelin on gastric motility have not been examined. Aim of the present study was to clarify the motor-stimulating action of ghrelin in the guinea-pig stomach.


METHODS
Gastric motility was measured as intraluminal pressure changes using a balloon inserted in the stomach of urethane-anaesthetized guinea pigs. The effects of ghrelin on gastric muscle contraction and [(3)H]-efflux from [(3)H]-choline-loaded strips were investigated in vitro.


RESULTS
Ghrelin (0.3-30 microg kg(-1), i.v.) increased gastric motility in a dose-dependent manner but des-acyl ghrelin was ineffective. The action of ghrelin was completely inhibited by hexamethonium and D-Lys(3)-growth-hormone releasing peptide-6. Atropine partially decreased the stimulatory action of ghrelin. In capsaicin-pretreated guinea pigs, the ghrelin-induced response was markedly decreased. Ghrelin (1 micromol L(-1)) did not affect [(3)H]-efflux in non-stimulated preparations but significantly decreased electrical field stimulation (EFS)-induced [(3)H]-efflux. L-Nitro arginine methylester (L-NAME) attenuated the inhibition of [(3)H]-efflux by ghrelin. Ghrelin did not cause any mechanical changes in gastric strips. Electrical field stimulation caused relaxation of gastric strips, which changed to atropine-sensitive contraction in the presence of L-NAME. Relaxation induced by EFS was slightly potentiated, but the EFS-induced contraction was not affected by ghrelin.


CONCLUSIONS
Ghrelin stimulates gastric motility of the guinea pig through activation of capsaicin-sensitive vago-vagal reflex pathway including efferent cholinergic neurons. Peripheral ghrelin receptors on enteric nitrergic nerves might affect the ghrelin-induced gastric action by releasing nitric oxide.
Department of Pharmacology, School of Veterinary Medicine, Rakuno Gakuen University, Ebetsu, Hokkaido, Japan.
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Nakamura
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Onaga
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Kitazawa
D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002211:Capsaicin / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004525:Efferent Pathways / Q000187:drug effects / Q000502:physiology*; D004558:Electric Stimulation; D005260:Female; D005769:Gastrointestinal Motility / Q000187:drug effects / Q000502:physiology*; D054439:Ghrelin / Q000494:pharmacology / Q000502:physiology*; D006168:Guinea Pigs; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D010276:Parasympatholytics / Q000494:pharmacology; D011706:Pyloric Antrum / Q000187:drug effects / Q000502:physiology*; D014630:Vagus Nerve / Q000187:drug effects / Q000502:physiology
D054439:Ghrelin; D010276:Parasympatholytics; D001285:Atropine; D000109:Acetylcholine; D002211:Capsaicin