Stimulation of fluid intake by carbohydrates: interaction between taste and calories.

Rats were trained in an apparatus that infused water or nutritive fluids into their stomachs every time that they drank flavored fluids. Rats given saccharin to drink by mouth drank more fluid than rats given cherry-flavored water to drink. Furthermore, rats given saccharin to drink ingested much more fluid if they were given intragastric infusions of 6% carbohydrate than intragastric infusions of plain water. This stimulatory effect of carbohydrate infusion occurred within 1 or 2 days of training and was very large, amounting to > or = 70% increase in fluid intake compared with rats drinking saccharin and infused with water. On the other hand, infusions of 6% carbohydrate had no effect on the intake of rats given cherry-flavored water to drink. In an attempt to determine whether rats could be trained to respond to cherry flavor at all, rats were infused with a liquid diet whenever they drank cherry or saccharin-flavored water. When dry food was withheld, the rats learned to increase fluid intake so as to feed themselves. The rats given saccharin to drink acquired this task more readily than rats given cherry flavor to drink, but both groups took in normal amounts of food by the end of the 10-day training period. It is concluded that it is much easier to condition an increase in fluid intake with intragastric infusions of carbohydrate than with an arbitrary nonsweet flavor.