Internal signals cause large changes in food intake in one-way crossed intestines rats

Fifteen pairs of parabiotic rats had either a surgical operation in which a 15 or 30 cm segment of upper small intestine was disconnected from the digestive tract of one rat in the pair and reconnected to the transected duodenum of its partner or had control surgery. Food eaten by one rat in the pair went to the rat's own stomach, traveled through 5 cm of its upper duodenum and then crossed into the isolated segment of the partner's small intestine. After traversing the 15 or 30 cm isolated segment, the remaining unabsorbed food crossed back into the lower duodenum of the rat that fed. Food eaten by the partner went through its own digestive tract, but bypassed the isolated segment of its own upper small intestine. The operation produced a large and sustained change in food intake of both rats in a pair. For the rats with 30 cm crossed segments, the rat that lost intestinal chyme into its partner ate 3.6 times as much food as did its partner for a period of many months. At sacrifice, the rats that ate more, weighed less and had less body fat. These large changes in food intake may be caused by internal changes associated with changes in the amount of food absorbed into each rat or by differential stimulation of the lower digestive tracts. The results clearly show that there is a major internal control mechanism for the amount of food eaten.