The vagus is inhibitory of the late postprandial insulin secretion in conscious pigs

The vagus is involved in the cephalic phase of insulin secretion but its role in the meal absorption phase of insulin release remains to be defined. The aim of this study was therefore to evaluate the role of the vagus in the early and the late meal absorption phases of insulin secretion. In six pigs, venous insulin profiles were compared in intact animals, after ventral or dorsal vagal trunk section, and after section of both vagal trunks (truncal vagotomy). Since gastric emptying could be modified by vagotomy, it was recorded concomitantly by gamma scintigraphy. Semi-solid (porridge) and liquid (glucose 10%) meals were tested. Truncal vagotomy significantly increased insulin release compare to intact animals after glucose (63.8%) and porridge (174.4%) meals in the early and the late absorption phases of insulin secretion, respectively. For the glucose meal, this effect could be explained by a vagally mediated change in gastric emptying rate, since insulin concentrations for a similar amount of nutrient propelled to the duodenum were not different in intact and truncal vagotomized animals. In contrast, after the porridge meal, truncal vagotomy was associated with a second, later occurring increase in circulating insulin, which could not be explained by changes in gastric emptying rate. These results demonstrate for the first time an inhibitory role of the vagus in the late meal absorption phase of insulin release.