L-arginine promotes gut hormone release and reduces food intake in rodents

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.

Keywords: GLP-1; animal pharmacology; body composition; energy regulation; obesity therapy.

Figure 1

Effect of oral administration of L‐arginine (L‐Arg) on food intake, body weight and energy expenditure in rodents. Effect of oral gavage (o.g.) of control (water) and 8 and 16 mmol/kg L‐Arg on food intake in male rats (A) after an overnight fast [n = 9–10; ##P < 0.01 vs. L‐Arg (8 mmol/kg), ***P < 0.001 vs. water control] and (B) ad libitum fed at the beginning of dark phase (n = 12–16; *P < 0.05, **P < 0.01, ***P < 0.01 vs. water control, #P < 0.05 vs. 8 mmol/kg L‐Arg) at 0–1, 1–2, 2–4, 4–8 and 0–24 h after administration. (C) Effect of o.g. of control (water) and 8, 16 and 24 mmol/kg L‐Arg on food intake in male mice after an overnight fast at 0–1, 1–2, 2–4, 4–8 and 0–24 h after administration (n = 8–9; *P < 0.05, ***P < 0.001 vs. water control; #P < 0.05, ##P < 0.01 vs. 8 mmol/kg L‐Arg; $P < 0.05 vs. 16 mmol/kg L‐Arg). Effect of o.g. of control (water) or 24 mmol/kg L‐Arg in ad libitum‐fed mice during the early light phase (D) (n = 10 per group), and (E) early dark phase (n = 10 per group) at 0–1, 1–2, 2–4, 4–8, and 0–24 h after administration (*P < 0.05, **P < 0.01 ***P < 0.001 vs. control). Effect of repeated o.g. administration of L‐Arg on food intake (F) and body weight (G) in diet‐induced obese (DIO) mice. Effect of three times daily o.g. administration of control (water; black circles, solid line) or 16 mmol/kg L‐Arg (white circles, dotted line) on cumulative food intake and body weight change in DIO mice during a period of 5 days (n = 9 per group; *P < 0.05, ***P < 0.001 vs. vehicle). Effect of o.g. administration of control (water; black circles, solid line) or 24 mmol/kg L‐Arg (white circles, dotted line) on cumulative food intake (H), O ₂ consumption (I) and CO ₂ production (J) and respiratory exchange ratio (RER) (K) in mice injected at early light phase and placed in comprehensive laboratory animal monitoring system cages. The o.g. was performed at 09:00 hours and food was returned at 17:00 hours, as indicated by the dotted line. Recordings were taken over a period of 24 h and at subsequent 24‐min intervals after administration. The shaded areas represent the dark phase from 19:00 hours (n = 12 per group; *P < 0.05, **P < 0.01, ***P < 0.001 vs. water control). All data are presented as mean ± standard error of the mean.

Figure 2

Effect of L‐arginine (L‐Arg) on food intake in G‐protein‐coupled receptor family C group 6 member A (GPRC6a)‐KO mice and rats after subdiaphragmatic vagal deafferentation (SDA) surgery. Effect of oral gavage (o.g.) administration of (A) control (water) or 16 mmol/kg L‐Arg, and (B) control (water) or 24 mmol/kg L‐Arg on 0–1‐h food intake in wildtype and GPRC6a‐KO mice with ad libitum access to food injected at the beginning of dark phase [*P < 0.05, **P < 0.01 vs. water control (n = 4, crossover)]. (C) Effect of o.g. of control (water) and 16 mmol/kg L‐Arg on 0–1‐h food intake in male rats that underwent sham or SDA surgery (n = 9–10, crossover; ***P < 0.001 vs. control). All data are presented as mean ± standard error of the mean.

Figure 3

Effect of L‐arginine (L‐Arg) on gut hormone release. Effect of L‐Arg on (A) glucagon‐like peptide‐1 (GLP‐1) and (B) peptide YY (PYY) release from primary mice colonic L‐cells incubated with 1, 10 and 100 mM L‐Arg and IBMX‐forskolin mix (10 µM, each) for 2 h. The release is shown as percentages of total hormone contained for each well in the experiment (n = 9 plates from nine mice; *P < 0.05, **P < 0.01, ***P < 0.001 vs. control). Data presented as mean ± standard error of the mean (s.e.m.). Effect of oral gavage (o.g.) administration of control (water) and 16 mmol/kg L‐Arg on (C) GLP‐1, and (D) PYY in overnight fasted male rats at 30 and 90 min after administration (n = 6–8; *P < 0.05, ***P < 0.001 vs. water control, ##P < 0.01 vs. 12 mmol/kg L‐Arg). Data are presented as mean ± s.e.m. Effect of intra‐ileal administration of saline and 1 M L‐Arg on plasma GLP‐1 and PYY concentrations in overnight fasted (E) anaesthetized mice and (F) rats. Blood samples were taken from mice at 30 min, and from rats at 0, 15, 30, 45 and 60 min after administration (n = 4–5 per group; *P < 0.05 vs. control). Mice results are expressed as mean ± s.e.m. Rat results are expressed as area under the curve (AUC) mean ± s.e.m.

Figure 4

Effect of L‐arginine (L‐Arg)‐mediated gut hormone release on food intake and gut function. Effect of intraperitoneal administration of a mixture of 400 nmol/kg exendin 9‐39 and 5.26 µmol/kg BIIE0246 on the anorectic effect of oral gavage of 24 mmol/kg L‐Arg in (A) fasted mice during early light phase (n = 10) and (B) ad libitum ‐fed mice during dark phase (n = 10) in the 0–1‐h period after administration (*P < 0.05, ***P < 0.001 vs. vehicle control group). Data are presented as mean ± standard error of the mean (s.e.m.). (C) Representative recordings from mouse colon mucosa showing a biphasic I_sc change to apical L‐Arg (1 mM, upper) compared with minor effects to apical D‐Arg (1 mM, lower). Basolateral vasoactive intestinal peptide (10 nM) pre‐treatment increased I_sc, and subsequent control PYY (10 nM, basolateral) anti‐secretory responses are evident. Basal I_sc values (in μA) are shown to the left of each trace (exposed mucosal area, 0.14 cm²). Responses to apical L‐Arg, D‐Arg and control PYY responses in ileum (D, F and H) and colon (E, G and I) colon are shown after either vehicle (+DMSO, 0.03%) or Y₁R antagonist BIBO3304 (+BIBO, 300 nM). Responses are the mean ± s.e.m. from observation numbers in parenthesis. Only L‐Arg 2° I_sc reductions were sensitive to BIBO treatment in (D) ileum and (E) colon mucosae. Note PYY responses in the ileum (H) are attributable to Y ₂ signalling (and thus are not significantly reduced by BIBO) while Y₁R signalling predominates in the mouse colon and is BIBO‐sensitive (I). *P < 0.05, **P < 0.01. All data are presented as mean ± s.e.m.

Figure 5

Effect of intraperitoneal (i.p.) and intracerebroventricular (i.c.v.) administration of L‐arginine (L‐Arg) on food intake in rodents. Effect of i.p. administration of (A) control (saline), 4, and 8 mmol/kg L‐Arg on food intake in fasted male rats (n = 8–9, *P < 0.05, **P < 0.01 vs. control) and (B) control (saline), 4, 8 and 12 mmol/kg L‐Arg in fasted male mice (n = 7–9; *P < 0.05, **P < 0.01, ***P < 0.001 vs. control; $$P < 0.01, $$$P < 0.001 vs. 4 mmol/kg L‐Arg; ##P < 0.01, ###P < 0.001 vs. 8 mmol/kg L‐Arg) at 0–1, 1–2, 2–4, 4–8 and 0–8 h after administration during early light phase. (C) Effect of i.c.v. administration of control (saline) and 4 µM L‐Arg on food intake in male rats following an overnight fast at 0–1, 1–2, 2–4, 4–8 and 0–24 h after administration (n = 8–9; *p < 0.05 vs. control). All data are presented as mean ± s.e.m.