ABSTRACT
AIMS: To investigate the anorectic effect of L-arginine (L-Arg) in rodents. METHODS: We investigated the effects of L-Arg on food intake, and the role of the anorectic gut hormones glucagon-like peptide-1 (GLP-1) and peptide YY (PYY), the G-protein-coupled receptor family C group 6 member A (GPRC6A) and the vagus nerve in mediating these effects in rodents. RESULTS: Oral gavage of L-Arg reduced food intake in rodents, and chronically reduced cumulative food intake in diet-induced obese mice. Lack of the GPRC6A in mice and subdiaphragmatic vagal deafferentation in rats did not influence these anorectic effects. L-Arg stimulated GLP-1 and PYY release in vitro and in vivo. Pharmacological blockade of GLP-1 and PYY receptors did not influence the anorectic effect of L-Arg. L-Arg-mediated PYY release modulated net ion transport across the gut mucosa. Intracerebroventricular (i.c.v.) and intraperitoneal (i.p.) administration of L-Arg suppressed food intake in rats. CONCLUSIONS: L-Arg reduced food intake and stimulated gut hormone release in rodents. The anorectic effect of L-Arg is unlikely to be mediated by GLP-1 and PYY, does not require GPRC6A signalling and is not mediated via the vagus. I.c.v. and i.p. administration of L-Arg suppressed food intake in rats, suggesting that L-Arg may act on the brain to influence food intake. Further work is required to determine the mechanisms by which L-Arg suppresses food intake and its utility in the treatment of obesity.
Subject(s)
Appetite Depressants/therapeutic use , Arginine/therapeutic use , Dietary Supplements , Gastrointestinal Agents/therapeutic use , Glucagon-Like Peptide 1/agonists , Obesity/diet therapy , Peptide YY/agonists , Animals , Appetite Depressants/administration & dosage , Appetite Depressants/adverse effects , Appetite Depressants/pharmacology , Arginine/administration & dosage , Arginine/adverse effects , Cells, Cultured , Dietary Supplements/adverse effects , Energy Intake/drug effects , Energy Metabolism/drug effects , Gastrointestinal Agents/administration & dosage , Gastrointestinal Agents/adverse effects , Gastrointestinal Agents/pharmacology , Glucagon-Like Peptide 1/blood , Glucagon-Like Peptide 1/metabolism , In Vitro Techniques , Injections, Intraperitoneal , Injections, Intraventricular , Intestinal Mucosa/cytology , Intestinal Mucosa/drug effects , Intestinal Mucosa/metabolism , Intestinal Mucosa/pathology , Male , Mice, Inbred C57BL , Mice, Knockout , Obesity/drug therapy , Obesity/metabolism , Obesity/pathology , Peptide YY/blood , Peptide YY/metabolism , Random Allocation , Rats, Wistar , Receptors, G-Protein-Coupled/agonists , Receptors, G-Protein-Coupled/antagonists & inhibitors , Receptors, G-Protein-Coupled/genetics , Receptors, G-Protein-Coupled/metabolism , Weight Loss/drug effectsABSTRACT
BACKGROUND: High-protein diets promote weight loss and subsequent weight maintenance, but are difficult to adhere to. The mechanisms by which protein exerts these effects remain unclear. However, the amino acids produced by protein digestion may have a role in driving protein-induced satiety. METHODS: We tested the effects of a range of amino acids on food intake in rodents and identified l-cysteine as the most anorexigenic. Using rodents we further studied the effect of l-cysteine on food intake, behaviour and energy expenditure. We proceeded to investigate its effect on neuronal activation in the hypothalamus and brainstem before investigating its effect on gastric emptying and gut hormone release. The effect of l-cysteine on appetite scores and gut hormone release was then investigated in humans. RESULTS: l-Cysteine dose-dependently decreased food intake in both rats and mice following oral gavage and intraperitoneal administration. This effect did not appear to be secondary to behavioural or aversive side effects. l-Cysteine increased neuronal activation in the area postrema and delayed gastric emptying. It suppressed plasma acyl ghrelin levels and did not reduce food intake in transgenic ghrelin-overexpressing mice. Repeated l-cysteine administration decreased food intake in rats and obese mice. l-Cysteine reduced hunger and plasma acyl ghrelin levels in humans. CONCLUSIONS: Further work is required to determine the chronic effect of l-cysteine in rodents and humans on appetite and body weight, and whether l-cysteine contributes towards protein-induced satiety.