A role for the vagus nerve in the etiology and maintenance of the hyperinsulinemia of genetically obese fa/fa rats.

It is demonstrated that pre-obese Zucker rats, studied before weaning (17 days of age), at a time when they were indistinguishable from lean controls, do hypersecrete insulin in response to glucose or arginine administration when compared to their lean littermates in spite of normal basal insulin levels. When arginine is used as the stimulus, it is shown that pre-obese pups hypersecrete glucagon as well as insulin, the net result of insulin and glucagon oversecretion being probably the observed normoglycemia of these animals. Furthermore, these early substrate-induced increases in pancreatic hormonal secretion could be reduced toward normal values by acute pre-treatment of the pre-obese rats with the cholinergic inhibitor, atropine. It is suggested the parasympathetic nervous system plays a role in genetically obese fa/fa rats in bringing about an early increased substrate-induced insulin release, a defect which could be one of the causes involved in the development of their obesity syndrome. In adult animals, the involvement of the parasympathetic nervous system in insulin oversecretion is less clear probably due to the presence of an increased B cell mass. However, using three different experimental approaches, it could be seen that an increased vagal tone acting at the B cells in obese animals participate to their insulin hypersecretion.