Insulin release in response to vagal stimulation in anaesthetized cats

Peripheral and portal plasma insulin concentrations were determined in eviscerated cats before, during and after vagal stimulation. Basal peripheral insulin levels averaged 2.4 ng/ml and portal levels 18 ng/ml. The portal blood flow was recorded continuously, thus enabling the insulin output/min to be calculated. In addition, the total insulin content of the pancreas was determined, which permitted quantitative comparisons of insulin release and pancreatic insulin content to be made. About 2% of the insulin store was released during one hour under basal conditions. Unilateral vagal stimulation with frequencies ranging between 1 and 20 Hz induced an almost immediate release of insulin into the portal vein. Following stimulation with frequencies of 3-4 Hz, the release mechanism was fatigued by a total of 2000-3000 impulses. The insulin output produced by such a supramaximal stimulation averaged 1.5 microgram and constituted about 2% of the total pancreatic insulin content. 15-20 min was needed for the release mechanism to recover.