Insulin within islets is a physiologic glucagon release inhibitor

Area of Science:

• Endocrinology
• Pancreatic Physiology

Background:

• Insulin's role in regulating glucagon secretion is not fully understood.
• Intra-islet paracrine signaling is a potential mechanism for hormonal control.

Purpose of the Study:

• To investigate the physiological control of glucagon secretion by intra-islet insulin.
• To determine if insulin directly restrains glucagon release from pancreatic alpha cells.

Main Methods:

• Isolated rat pancreata were perfused with anti-insulin serum or control serum.
• Glucose concentration was maintained at 100 mg/dl.
• Radioactive tracers were used to assess antibody distribution and insulin binding capacity.

Main Results:

• Perfusion with anti-insulin serum caused a rapid, significant, and dramatic increase in glucagon secretion.
• Glucagon levels peaked at three times baseline and returned to normal upon cessation of antiserum perfusion.
• Minimal antibody remained in the pancreas after perfusion, suggesting limited intravascular insulin neutralization.

Conclusions:

• Insulin exerts a physiological restraint on alpha cell glucagon secretion.
• Loss of insulin's inhibitory action may initiate hyperglucagonemia in insulin-deficient states.
• Insulin's inhibitory effect likely occurs predominantly within the intravascular compartment.