Effects on glucagon-like peptide-1 secretion by distal ileal administration of nutrients

The aim of this study was to investigate the effects of nutrients (glucose, fat, and amino acid) on glucagon-like peptide-1 (GLP-1) secretion by the L cell in the distal ileum and insulin level in peripheral blood.

Ninety-six Wistar rats were randomly allocated into 12 groups, with 8 rats in each group: glucose-10 cm, glucose-15 cm, glucose-20 cm, fat-10 cm, fat-15 cm, fat-20 cm, amino acid-10 cm, amino acid-15 cm, amino acid-20 cm, control-10 cm, control-15 cm, and control-20 cm. Blood samples were collected at 0, 30, 60, 90, and 120 min after in vivo distal ileal perfusion of nutrients or normal saline (control groups). Blood glucose level was assessed by a handheld glucometer. Plasma GLP-1 and insulin level were evaluated by ELISA. GLP-1 level was also evaluated by immunohistochemistry analysis of GLP-1 expression in ileal mucosa and scanning electron microscope analysis of ultrastructural changes of L cells.

Under administration of nutrients in the distal ileum of equal length, GLP-1 levels were greatest for fat, then glucose, and then amino acid (the peak concentration of GLP-1 in the fat-10 cm group, the glucose-10 cm group, the amino acid-10 cm group, and the control-10 cm group was 29.76 ± 1.32, 28.54 ± 1.29, 26.30 ± 1.26, and 22.52 ± 1.22 pmol/L, respectively, with p < 0.05). Under administration of nutrients in the distal ileum of equal length, insulin levels were also greatest for fat, then glucose, and then amino acid (the peak concentration of insulin in the fat-10 cm group, the glucose-10 cm group, the amino acid-10 cm group, and the control-10 cm group was 30.10 ± 1.33, 27.17 ± 1.27, 22.98 ± 1.31, and 12.40 ± 1.11 mU/L, respectively, with p < 0.05). Under administration of the same nutrients, the longer the distal ileum was stimulated, the greater the GLP-1 and insulin levels.

Long distal ileal administration of fat more efficiently stimulated GLP-1 secretion, resulting in enhanced insulin secretion.