Glucagon receptor knockout mice display increased insulin sensitivity and impaired beta-cell function

Area of Science:

• Endocrinology
• Metabolism
• Molecular Biology

Background:

• Glucagon receptor knockout (Gcgr(-/-)) mice exhibit lower blood glucose and better glucose tolerance.
• Previous studies noted hyperglucagonemia and elevated glucagon-like peptide-1 (GLP-1) in Gcgr(-/-) mice.
• The specific roles of glucagon receptor signaling in islet function and insulin sensitivity remain unclear.

Purpose of the Study:

• To investigate the impact of glucagon receptor signaling on beta-cell function.
• To determine the effect of glucagon receptor disruption on insulin sensitivity.
• To elucidate the compensatory mechanisms involved in glucose homeostasis in Gcgr(-/-) mice.

Main Methods:

• Hyperinsulinemic-euglycemic clamp studies in Gcgr(-/-) and wild-type mice.
• Assessment of acute insulin response (AIR) to intravenous glucose and other secretagogues.
• Analysis of insulin secretion and glucose oxidation in isolated islets from Gcgr(-/-) mice.

Main Results:

• Gcgr(-/-) mice demonstrated enhanced insulin sensitivity, indicated by a higher glucose infusion rate during clamp studies.
• The acute insulin response to glucose was elevated in Gcgr(-/-) mice but blunted by a GLP-1 receptor antagonist.
• Isolated islets from Gcgr(-/-) mice showed impaired insulin secretion and reduced glucose oxidation.
• AIR to other secretagogues like arginine and cholecystokinin octapeptide was reduced, while carbachol response was unaffected.

Conclusions:

• Glucagon receptor signaling is essential for normal beta-cell function.
• Disruption of glucagon signaling improves insulin action.
• Elevated GLP-1 levels in Gcgr(-/-) mice compensate for impaired beta-cell function in vivo.