Vagotomy suppresses cephalic phase insulin release in sheep

Area of Science:

• Physiology
• Neuroendocrinology
• Gastroenterology

Background:

• The cephalic phase of digestion involves neural reflexes preparing the body for nutrient intake.
• The vagus nerve plays a critical role in mediating these cephalic phase responses, including insulin release.
• Understanding the specific vagal pathways involved in insulin secretion is essential for comprehending digestive physiology.

Purpose of the Study:

• To investigate the effect of selective vagotomy of the abomasum, pylorus, duodenum, and liver on insulin release during the cephalic phase of digestion in sheep.
• To determine the specific vagal efferent fibers responsible for mediating cephalic phase insulin release.

Main Methods:

• Selective vagotomy of specific abdominal organs (abomasum, pylorus, duodenum, liver) in wethers and lactating ewes.
• Sham-operations as controls.
• Electrical stimulation of cervical vagus nerves to assess vagotomy completeness and nerve function.
• Measurement of plasma glucose and insulin levels before and after food presentation and/or nerve stimulation.

Main Results:

• Food presentation caused a significant rise in plasma insulin in sham-operated animals but not in vagotomized sheep.
• Vagotomy of the abomasal, pyloric, and duodenal branches (ADV) significantly reduced insulin response compared to controls.
• Hepatic, abomasal, pyloric, and duodenal vagotomy (HADV) showed no additive effect over ADV.
• Electrical stimulation of vagus nerves increased insulin in sham-operated ewes but not in vagotomized ewes.

Conclusions:

• Vagal innervation of the gut mediates insulin release during the cephalic phase of feeding in sheep.
• Insulin secretion is mediated through vagal efferent fibers in the abomasal, pyloric, and duodenal branches of the vagus nerves.
• These findings elucidate the neural control of insulin secretion in response to food stimuli in ruminants.