Licking rate of rats is reduced by intraduodenal and intraportal glucose infusion

The effect of isotonic glucose, urea, and NaCl solutions (0.5 ml) delivered directly to the duodenum or portal system on the rate of drinking a 3.2% glucose or a 3.4% sucrose solution was investigated in rats. Both duodenal and portal glucose infusions produced a decrease in licking rate when the licking test vas administered immediately after the infusion. The effect diminished with increasing time intervals between the infusion and the test. Infusions of urea by both the duodenal and portal routes had effects similar to those produced by glucose but the magnitude of the effect was smaller. Control infusions of isotonic NaCl into the portal vein indicate that the depressing effect of portal glucose and urea on licking rate was chemospecific rather than due to local hypervolemia. Intrajugular infusions of glucose did not alter lick rates, suggesting that the chemoreceptors involved in the effects produced by portal infusions are located in the liver.