Dietary resistant starch increases hypothalamic POMC expression in rats

Abstract

Resistant starch (RS) is fermentable dietary fiber. Inclusion of RS in the diet causes decreased body fat accumulation and altered gut hormone profile. This study investigates the effect of feeding RS on the neuropeptide messenger RNA (mRNA) expressions in the arcuate nucleus (ARC) of the hypothalamus and whether vagal afferent nerves are involved. The rats were injected intraperitoneally with capsaicin to destroy unmyelinated small vagal afferent nerve fibers. The cholecystokinin (CCK) food suppression test was performed to validate the effectiveness of the capsaicin treatment. Then, capsaicin-treated rats and vehicle-treated rats were subdivided into a control diet or a RS diet group, and fed the corresponding diet for 65 days. At the end of study, body fat, food intake, plasma peptide YY (PYY) and glucagon-like peptide 1 (GLP-1), and hypothalamic pro-opiomelanocortin (POMC), neuropeptide Y (NPY), agouti-related peptide (AgRP) gene expressions were measured. RS-fed rats had decreased body fat, increased POMC expression in the hypothalamic ARC, and elevated plasma PYY and GLP-1 in both the capsaicin and vehicle-treated rats. Hypothalamic NPY and AgRP gene expressions were not changed by RS or capsaicin. Therefore, destruction of the capsaicin-sensitive afferent nerves did not alter the response to RS in rats. These findings suggest that dietary RS might reduce body fat through increasing the hypothalamic POMC expression and vagal afferent nerves are not involved in this process. This is the first study to show that dietary RS can alter hypothalamic POMC expression.

Figure 1

Dietary Resistant Starch increases (a) pro-opiomelanocortin (POMC), but not (b) neuropeptide Y (NPY), and (c) agouti-related peptide (AgRP) messenger RNA (mRNA) expressions in arcuate nucleus of Resistant Starch–fed rats treated with vehicle or capsaicin. Data are mean ± s.e.m. for group of 7–9 rats. For POMC mRNA expression, diet: P < 0.05, capsaicin: P > 0.05, Interaction: P > 0.05 by two-way ANOVA. For NPY and AgRP, there were no significant effects on diet, capsaicin, and interaction. *P < 0.05 vs. controls within the same treatment (vehicle or capsaicin).

Figure 2

(a) Total body fat and (b) percentage of body fat/disemboweled body weight were decreased in Resistant Starch–fed rats treated with vehicle or capsaicin. Data are mean ± s.e.m. for group of 10–11 rats. Two-way ANOVA analysis indicates there were significant diet (P < 0.001) and a significant capsaicin treatment effects (P < 0.01), with no interaction effect. *P < 0.05 vs. controls within the same treatment (vehicle or capsaicin).

Figure 3

(a) Plasma total peptide YY (PYY) and (b) total glucagon-like peptide 1 (GLP-1) concentrations were increased in rats fed Resistant Starch. Data are mean ± s.e.m. for group of 10–11 rats. For both a and b, there was a significant diet effect (P < 0.001) but not a capsaicin treatment effect (P > 0.05) and no interaction effect (P > 0.05). *P < 0.05 vs. controls within the same treatment (vehicle or capsaicin). PM, pmol/l.