Insulin Release in Response to Vagal Stimulation in Anaesthetized Cats

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Abstract
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 ug and constituted about 2% of the total pancreatic insulin content. 15-20 min was needed for the release mechanism to recover.