ABSTRACT
SCOPE: The gastrointestinal (GI) tract senses and responds to intraluminal nutrients and these interactions often affect GI functions. We found that, among basic amino acids, l-ornithine (Orn) and l-lysine (Lys) stimulated but l-arginine (Arg) suppressed GI motility after oral administration (24 mmol/kg) in mice (Orn and Lys, 14.3 and 26.4% promotion; Arg, 7.7% suppression). We investigated the mechanism of the action of Orn and Lys on GI motility. METHODS AND RESULTS: Orn-induced promotion of small intestinal transit was significantly inhibited (p<0.05) by oral administration of capsazepine, a transient receptor potential vanilloid 1 (TRPV1) antagonist. Moreover, the stimulatory effect of Orn and Lys was abolished in TRPV1-knockout mice. In TRPV1-transfected HEK293 cells, Orn and Lys (10 mM) evoked Ca2+ influx, which was blocked by ruthenium red, a TRP channel antagonist. These results suggest that Orn and Lys promote GI motility via activation of TRPV1. The GI motility stimulation by Orn and Lys was also blocked by atropine, a muscarinic acetylcholine receptor (mAChR) antagonist, or NG -nitro-l-arginine methyl ester, a nitric oxide (NO) synthase inhibitor. CONCLUSION: Orally administered Orn and Lys stimulate GI motility via TRPV1, mAChR and NO synthase in mice.
Subject(s)
Calcium Signaling , Gastrointestinal Motility , Lysine/administration & dosage , Ornithine/administration & dosage , TRPV Cation Channels/agonists , Up-Regulation , Animals , Arginine/administration & dosage , Arginine/metabolism , Calcium Signaling/drug effects , Capsaicin/analogs & derivatives , Capsaicin/pharmacology , Down-Regulation/drug effects , Gastrointestinal Motility/drug effects , HEK293 Cells , Humans , Intestine, Small/drug effects , Intestine, Small/physiology , Lysine/metabolism , Male , Membrane Transport Modulators/pharmacology , Mice, Inbred C57BL , Mice, Knockout , Mice, Mutant Strains , Ornithine/metabolism , Rats , Recombinant Proteins/chemistry , Recombinant Proteins/metabolism , Ruthenium Red/pharmacology , TRPV Cation Channels/antagonists & inhibitors , TRPV Cation Channels/genetics , TRPV Cation Channels/metabolism , Up-Regulation/drug effectsABSTRACT
We found that intraduodenal administration of l-ornithine (l-Orn) stimulates growth hormone (GH) secretion in Wistar rats, and then investigated its mechanism. GH-releasing activity after intraduodenal administration of l-Orn was blocked by [d-Lys3]-GHRP-6, an antagonist of the ghrelin receptor; however, l-Orn (100 µM) has no affinity for the ghrelin receptor, suggesting that the GH-releasing activity of l-Orn is mediated via ghrelin release and activation of the ghrelin receptor. Intraduodenally administered l-Orn increased ghrelin mRNA expression in the duodenum but not in the stomach or hypothalamus. In addition, l-Orn-induced GH-releasing activity was inhibited by propranolol, an antagonist of ß-adrenergic receptor, which is known to be coupled to ghrelin release. In conclusion, intraduodenally administered l-Orn stimulates GH secretion through the sympathetic nervous and ghrelin systems.
Subject(s)
Ghrelin/metabolism , Growth Hormone/metabolism , Ornithine/metabolism , Animals , Duodenum/metabolism , Hypothalamus/metabolism , Male , Rats , Rats, Wistar , Receptors, Ghrelin/metabolismABSTRACT
It is well known that large dose of leucine reduces the food intake and causes growth retardation in experimental animals when leucine is given with a low-protein diet. However, the mechanism for the anorectic effect of leucine has not yet been clarified. We demonstrate here that the anorectic effect of leucine was significantly reduced in a vagotomized rat.
