Truncal and hepatic vagotomy reduce suppression of feeding by jejunal lipid infusions

Two experiments investigated mechanisms underlying the decrease in food intake produced by lipid infusions into the jejunum. In Experiment 1, male Sprague-Dawley rats with truncal abdominal vagotomy (TVx), selective hepatic-branch vagotomy (HVx), or sham vagotomy received repeated 7 h infusions of linoleic acid (LA), corn oil (CO), or saline through indwelling jejnnal catheters. Cumulative food intake was measured at 1, 3, 6, and 23 h. LA and, to a lesser extent, CO suppressed food intake in excess of the caloric value of the load. This effect was eliminated by TVx, which significantly attenuated the suppression of intake produced by both lipids at 3 and 6 h and also at 23 h when LA was infused. HVx attenuated suppression at 23 h on tests with LA and at 3 and 6 h on CO tests. Experiment 2 showed that jejunal infusion of LA had no effect on multi-unit activity of afferent fibers in the left splanchnic nerve in anesthetized rats. Thus, these results provide further evidence that satiating effects of intestinal lipid infusions are mediated by the vagal fibers, some of which lie within the hepatic branch. However, because significant suppression of food intake remained after TVx, and because of the negative results of Experiment 2, these lipid infusions engage as yet unidentified mechanisms independent of the vagus.