The vagus is inhibitory of insulin secretion under fasting conditions

The involvement of the vagus in the insulin response during the early phase of absorption of a meal has been demonstrated recently. The extent of this vagal influence was investigated during fasting in an anesthetized porcine model. Portal and systemic insulin were evaluated together with glycemia during cooling and sectioning of both cervical vagal trunks in 12 splanchnicotomized or sham-operated pigs. In sham-operated animals, portal and systemic insulin were significantly and reversibly increased by cooling (173 and 123%, respectively). Portal insulin peaked 20 min after the onset of cooling but declined slowly while cooling was still activated. In contrast, systemic insulin was increased evenly along cooling. Section of the vagus was also associated with a portal and systemic insulin increase (144 and 117%) but to a lesser extent than cooling. In both treatments, portal and systemic insulin increases were either reduced (vagal cooling) or eliminated (vagal section) in splanchnicotomized animals. We conclude that the vagus exerts an inhibitory activity on interdigestive insulin secretion that is partly mediated by the splanchnic nerves.