Hepatic portal glucose infusions decrease food intake and increase food preference.

We examined the contribution of experimental factors to the hepatic control of food intake. Rats with either hepatic portal or jugular catheters were infused four times with glucose (4.5 mg/min) and equitonic saline (2 ml/2 h). During the infusions their food contained nonnutritive chocolate or chicken flavor, depending on the infusate received. Hepatic portal glucose decreased food intake relative to saline and no infusion conditions, but jugular glucose did not. When allowed to choose between the flavors associated with each infusate, rats with hepatic portal catheters preferred the flavor eaten during glucose infusion, and rats with jugular catheters showed no preference. These results suggest that a mechanism located in the liver can reduce food intake without producing malaise and that portal glucose can act as an unconditioned stimulus for the acquisition of a learned food preference. Several reports that hepatic portal infusions do not alter feeding behavior may be explained by a failure to control for previous experience in the test situation.