Effects of glucagon-like peptide 1 (7-36 amide) on glucose kinetics during somatostatin-induced suppression of insulin secretion in healthy men.

Glucagon-like peptide 1 (GLP-1) is known to stimulate insulin secretion and biosynthesis, but has also been shown to decrease insulin requirements in type 1 diabetic subjects suggesting insulin-independent effects. To assess whether GLP-1 exerts also direct effects on whole-body glucose metabolism, 6,6-D2-glucose kinetics were measured in 8 healthy volunteers receiving once GLP-1, once saline during hyperglycemic glucose clamping, while somatostatin with replacement amounts of insulin, glucagon and growth hormone was infused. Even though endogenous insulin secretion could not be blocked completely (increased plasma concentrations of C-peptide and proinsulin), somatostatin infusion resulted in stable insulin and glucagon plasma levels in both protocols (GLP-1 vs. placebo: NS). After 3 h of GLP-1 infusion, peripheral glucose disappearance significantly increased compared to placebo (p < 0.03) despite of somatostatin-induced suppression of insulin and glucagon secretion. Thus, GLP-1 infusion seems to have direct stimulatory effects on peripheral glucose metabolism in man.