Effect of Vagotomy and Vagal Stimulation on Insulin Secretion

The influence of the vagus nerve on insulin secretion in the dog has been confirmed by studies involving both vagotomy and vagal stimulation. Following vagotomy, a fall in portal vein insulin levels occurs. Following stimulation of both the right and left vagus, insulin levels rise abruptly, peak within five minutes and rapidly return to baseline levels. A small rise in blood glucose, which occurs simultaneously, cannot be blocked by phentolamine, an alpha-adrenergic blocking agent. When given alone, phentolamine stimulates insulin secretion. Atropine inhibits both the glucose and insulin rises following vagal stimulation. Only a portion of releasable insulin appears to be under vagal control. Glucose mediated insulin release and net glucose utilization are not significantly affected by vagotomy.