Comparison of the Effects of Various C-Terminal and NTerminal Fragment Peptides of Glucagon-Like Peptide-1 on Insulin and Glucagon Release from the Isolated Perfused Rat Pancreas*

Truncated glucagon-like peptide-1 (GLP-1) possesses a potent stimulatory activity for insulin secretion and a slight inhibiting activity for glucagon secretion. The aim of this paper is to examine the activities of N- and C-terminal fragments of GLP-1 using a rat pancreas perfusion system. Concerning the N-terminal portion, GLP-l(7–37) amide elicited a clear insulinotropic activity at 0.1 or 1 nM with the perfusate containing 5.5 mM glucose and 5 mM arginine, while 10 nM GLP-l-(1–37) amide, -(6–37) amide, and -(8–37) amide did not. Concerning the C-terminal portion, GLP-l-(7–37) amide, -(7–37), and -(7–36) amide had a similar potency of insulinotropic activity, and GLP-l-(7–35) was less potent; 0.1 nM GLP-l-(7–35) did not stimulate insulin release, nor did 10 nM GLP-1-(7–20). Glucagon release was significantly suppressed by 1 and 10 nM GLP-l-(7–37) amide, 10 nM GLP-l-(7–37), and 1 nM GLP-l-(7–36) amide. Other fragment peptides of GLP-1, including GLP-l-(7–35), had no effect. From these results it is concluded that histidine at position 7 of GLP-1 as a free N-terminal amino acid is very important in GLP-l's insulinotropic activity and probably in glucagon-inhibiting activity, and that C-terminal amidation and three C-terminal amino acids are less important for these activities.