Vagotomy suppresses cephalic phase insulin release in sheep

The effect of selective vagotomy of the abomasum, pylorus, duodenum and liv er on insulin release during the cephalic phase of digestion was investigat ed in wethers and lactating ewes. Electrical stimulation of the cervical va gus nerves was carried out to test the completeness of the vagotomies perfo rmed. In experiment 1, using wethers, the abomasal, pyloric and duodenal br anches (ADV; n = 7) or the hepatic, abomasal, pyloric and duodenal branches (HADV; n = 10) of the ventral and/or dorsal vague nerves were cut; a third group of wethers underwent sham-operation (SO; n = 8). In experiment 2, va gotomy (ADV; n = 5) or sham-operations (SO; n = 5) were carried out in lact ating ewes. Jugular blood was drawn before and after presentation of food f or glucose and insulin determination (experiments 1 and 2) or before, durin g and after the electrical stimulation of the peripheral ends of the cut ce rvical vagus nerves in randomly selected lactating ewes (experiment 3: ADV = 3, SO = 3) and wethers (experiment 4: ADV = 4, HADV = 4, SO = 4), for det ermination of insulin only. Presentation of food caused an immediate and si gnificant (P < 0.05) rise in plasma insulin levels in SO animals compared w ith ADV or HADV wethers (experiment 1) or ADV ewes (experiment 2) without a ny significant change in blood glucose concentrations. In comparison with t he SO group the baseline-corrected areas under the insulin response curve w ere significantly (P < 0.05) smaller for the respective vagotomized groups for periods 1-2, 2-4 and 4-6 min (experiment 1) and 1-2 and 2-4 min (experi ment 2) after presentation of food. Total area under the response curve for 10 min was significantly (P < 0.05) lower (experiment 1) and tended (P < 0 10) to be lower (experiment 2) for the vagotomized groups compared with th at of the control groups. Direct electrical stimulation of the cervical vag us nerves raised plasma insulin concentrations to significantly (P < 0.05) higher levels in the SO ewes but not in the ADV ewes (experiment 3). It was also evident that in experiment 1, HADV did not have any additive effect o ver that achieved by ADV alone. These results indicate that the vagal inner vation of the gut mediates insulin release during the cephalic phase of fee ding in sheep. It is concluded thar insulin secretion from the pancreatic b eta-cells in response to either food-related reflex activation of the vagal nuclei in the hypothalamus or direct cervical vagus nerve stimulation is m ediated through the vagal efferent fibres carried in the abomasal, pyloric and duodenal branches of the vagus nerves in sheep.