On the role of the mouth and gut in the control of saccharin and sugar intake: a reexamination of the sham-feeding preparation.

Adult female rats, each fitted with a gastric fistula, were tested for their "normal-feeding" (fistula closed) and "sham-feeding" (fistula open) response to saccharin and sugar solutions under a variety of conditions. When hungry, rats consumed no more of a 0.2% saccharin solution with their fistula open than they did with their fistula closed. Increasing or decreasing the saccharin concentration did not increase the amount of solution sham fed, but adding a small amount of glucose (3%) to the saccharin solution did increase the amount sham fed. Thirsty rats, unlike hungry, significantly increased their 0.2% saccharin solution intake when tested with an open fistula. When tested with a 32% glucose solution, hungry rats consumed up to six times more solution with their fistula open than with their fistula closed. The hungry rats also sham fed significantly more of the 32% glucose solution than of the 0.2% saccharin solution or 0.2% saccharin + 3% glucose solution. Sham-feeding of a 32% sucrose solution significantly elevated blood glucose levels, but blocking this effect by adding acarbose, a drug that inhibits sucrose digestion, did not reduce the amount of solution sham fed. Several possible explanations for the differential sham-feeding response to saccharin and sugar solutions are discussed.