Behavioral effects of vagotomy in humans

Animal experiments and clinical observations have demonstrated significant effects of vagotomy on body weight. Weight loss or inability to regain are partly due to impaired motility and secretomotor activity of the vagus nerve causing disturbances in digestion which, however, are not sufficient to explain most of the weight deficit after vagotomy in animals or morbidly obese patients. The body weight deficit is also due to reduced caloric intake with changes in the quantity and quality of food and liquid intake, the latter accounting for more than one-third of the total reduction in caloric intake. Obese patients have consistent decreases in hunger ratings after vagotomy and also reveal changed hedonic ratings and estimations of taste intensity. Validation of vagotomy studies requires tests of vagal integrity to confirm the completeness of the surgery and rule out regeneration of nerve tissue or recruitment of function. Tests of completeness of vagotomy are difficult to perform and evaluate in morbidly obese patients due to insulin resistance. The finding of an inadequate gastric acid response to insulin hypoglycemia implies a defect hypothalamic response to hypoglycemic stress in these patients. A new postoperative test of completeness of vagotomy based on disrupted drinking after intravenous hypertonic saline challenge is introduced as an attractive alternative to the potentially hazardous insulin test.