Glucagon effects on the human small intestine.

Area of Science:

• Gastroenterology
• Endocrinology
• Physiology

Background:

• Glucagon is a hormone primarily known for its role in glucose metabolism.
• Its effects on gastrointestinal motility, particularly the small intestine, are less understood.
• Investigating glucagon's impact on intestinal function is crucial for understanding digestive processes.

Purpose of the Study:

• To investigate the effects of intravenously administered glucagon on small intestinal function in healthy volunteers.
• To determine the dose-dependent effects of glucagon on jejunal contractions, transit time, and absorption.
• To differentiate glucagon's effects from those of concurrent insulin and glucose level changes.

Main Methods:

• Healthy volunteers received intravenous glucagon via bolus injection and continuous infusion.
• Plasma glucagon concentrations were monitored.
• Jejunal contractions, intestinal transit time (mean transit time - MTT), and water/electrolyte absorption were measured.
• Effects were correlated with specific plasma glucagon levels.

Main Results:

• High glucagon concentrations (>800 pg/ml) abolished jejunal contractions for over 4 minutes after a latency period.
• Glucagon infusion (>720 pg/ml) caused jejunal dilatation and increased MTT.
• Inhibition of water/electrolyte absorption occurred only at very high glucagon levels (>1760 pg/ml).
• Effects on motility were independent of insulin and glucose changes.

Conclusions:

• Short-term, high-dose glucagon inhibits intestinal tone, contractions, and propulsion.
• A significant latency period suggests glucagon does not directly act on intestinal smooth muscle.
• The observed effects on motility occur at non-physiological glucagon levels.
• Minor effects on absorption are limited to a narrow, high concentration range.