Insulin secretion in the conscious mouse is biphasic and pulsatile

Area of Science:

• Endocrinology
• Physiology
• Metabolism

Background:

• Most species exhibit biphasic insulin secretion in response to glucose.
• Mouse islets in vitro typically lack a robust second phase of insulin secretion.
• Previous studies have not extensively investigated this phenomenon in vivo.

Purpose of the Study:

• To compare in vivo insulin secretion in conscious mice with in vitro secretion from isolated mouse islets.
• To determine if the diminished second phase of insulin secretion in isolated mouse islets is an artifact of isolation.

Main Methods:

• Conscious mice underwent surgical implantation of carotid artery and jugular vein catheters.
• A hyperglycemic clamp was used to raise plasma glucose levels.
• Arterial plasma insulin response was measured frequently in transfused mice to maintain blood volume.

Main Results:

• In vivo, glucose elevation induced a significant first-phase insulin peak (403% above basal) followed by a robust second phase (289% above basal).
• Isolated mouse islets showed a similar first phase but a significantly blunted second phase (169% above basal).
• In vivo insulin secretion exhibited pulsatile patterns, absent in isolated islets.

Conclusions:

• Conscious mice demonstrate biphasic and pulsatile insulin secretion in response to glucose, consistent with other species.
• The isolation process appears to abrogate the mechanisms responsible for robust second-phase insulin secretion.
• In vivo studies are crucial for understanding the complete physiological response of pancreatic islets.