Effect of catch-up growth after food restriction on the entero-insular axis in rats

Abstract

Background: Catch-up growth after food restriction (CUGFR) is characterized by a significant change in food intake which could theoretically lead to the change in glucagon-like peptide-1 (GLP-1) secretion that consequently results in altered functions of pancreatic islets.

Methods: Experimental rats were divided into two groups. Rats in CUGFR group were put on food-restriction for 4 weeks, and then allowed full access to food for 0, 2, 4 weeks respectively while rats in the control group were offered ad libitum access to food. Plasma glucose, insulin and GLP-1 level during OGTT were measured in all the rats. Moreover, morphology of intestinal mucosa, number of L cells, beta cell mass, incretin effect and the expression of GLP-1 receptor (GLP-1R) gene in the islets were also determined.

Results: The size of pancreatic islets, insulin concentration, plasma GLP-1 concentration, incretin effect, villus height-to-crypt depth ratio and L cells were all significantly decreased in CUGFR group at the end of a 4-week food-restriction period as compared with the controls. Insulin concentration and the villus height-to-crypt depth ratio were increased and finally exceeded the level of the control group over a 4-week catch-up period. Nevertheless, at the conclusion of the study, islet size, L cells number, plasma GLP-1 concentration and incretin effect increased but failed to reach the levels of the controls.

Conclusion: CUGFR decreases incretin effect and disturbs the entero-insular axis partially by decreasing GLP-1 concentration, which might be responsible for the increased risk of metabolic disorder during CUGFR.

Figure 1

The diagram of experiment design. Rats were divided into NC group (n = 18) and CUGFR group (n = 18). The arrows indicate the specific days on which rats were sacrificed.

Figure 2

Food intake and body weight during food restriction and re-feeding stage. All values are expressed as means ± SD (n = 6). *P ≤ 0.05 versus NC group; **P ≤ 0.01 versus NC group. The arrows indicate the specific days on which oral glucose tolerance tests (OGTTs) were performed.

Figure 3

HE Staining (×400 magnification) and insulin immunofluorescence staining (×200 magnification) in a rat pancreatic islet. Islet cells in the NC (A1 and B1) and CUGFR (A2 and B2) groups 4 weeks after catch-up growth with HE staining (A1 and A2) and insulin fluorescence staining (B1 and B2). Green fluorescence shows cells positive for insulin.

Figure 4

Effect of catch-up growth on beta cell relative area and mass. After insulin staining of rat pancreatic islet, the area positively stained for insulin was quantified by Image Pro Plus software. Values are means ± SD (n = 6). *P < 0.05 versus NC group. **P < 0.01 versus NC group.

Figure 5

Effect of catch-up growth on islet function and GLP-1 concentration. Plasma glucose (A), insulin (B), GLP-1(C) levels and AUC_Insulin, AUC_Glucose, AUC_GLP-1 during a 1-hour OGTT, which was conducted 0 (A1, B1 and C1), 2 (A2, B2 and C2) and 4 (A3, B3 and C3) weeks after catch-up growth in the NC (red) and CUGFR (green) groups, were measured. Data are expressed as means ± SD of six rats in each group. *P ≤ 0.05 versus NC group; **P ≤ 0.01 versus NC group.

Figure 6

Effect of catch-up growth on GLP-1R mRNA expression in islets. A1. RT-PCR products from RNA extracted from rat (n = 5-6 per group) pancreatic islets. The beta actin control was comparable in all groups. A2. The statistical results of real time quantitative PCR products from RNA extracted from rat pancreatic islets. Data are expressed as means ± SD. *P ≤ 0.05 versus NC group.

Figure 7

Time course of the glucose and insulin following oral and IV glucose in the normal and catch-up growth rats. Plasma glucose (A1, A2, A3) and insulin (B1, B2, B3) concentrations in rats of NC group (red) or CUGFR group (green) during oral glucose tolerance test (solid line) and intravenous glucose infusion test (broken lines) designed to match the oral glucose curve in six rats, were detected after catch up growth for 0 (A1, B1), 2(A2, B2) and 4 (A3, B3) weeks. Data are expressed as means ± SD.

Figure 8

Effect of catch-up growth on the incretin effect. Data are expressed as means ± SD. The incretin effect was calculated by comparing the insulin response to oral and matched IV glucose load. * P ≤ 0.05 versus NC group.

Figure 9

HE Staining (×200 magnification) and glucagon staining (×400 magnification) in rat ileum. Ileal villus observed in the CUGFR0 (A1) and CUGFR2 (A2) groups with HE staining and NC4 (B1) and CUGFR4 (B2) groups with glucagon staining. Arrow shows a glucagon-positive cell.

Figure 10

Effect of catch-up growth on glucagon-positive cells per high-power field. To quantify the expression of glucagon, an average of 50 sections of rat ileum from each of two animals were examined. The number of cells immunoreactive for glucagon was determined. Data are expressed as means ± SD. *P ≤ 0.05 versus NC group; **P ≤ 0.01 versus NC group.