Fructose Absorption and Metabolism by the Growing Chick

Experiments were conducted to evaluate whether fructose was converted to glucose during absorption in the chick. Chicks were found to absorb glucose and fructose rapidly and absorption of an orally administered dose of either hexose was essentially complete within 1 hr. Intestinal sacs incubated in vitro transported fructose from the mucosal to the serosal surface and only 17% of the hexose in the serosal fluid was glucose. Experiments with intact chicks using fructose-U-14C demonstrated that only 12% of the radioactive hexose entering the portal blood was glucose. Thus, it was concluded that only about 15% of absorbed fructose is converted to glucose during the process of absorption. However, 10 min following the intraperitoneal administration of fructose-U-14C, 97% of the hexose radioactivity in blood was present as glucose. The activity of hepatic fructokinase was observed to be high and was not influenced by fructose ingestion. It is proposed that fructose is rapidly utilized by the chick and that the liver is a major site of fructose metabolism.