Role of the rat liver in the disposal of a glucose gavage

An oral gavage of either 3, 1 or 0.1 mmoles of glucose was given to rats under standard feeding conditions or food deprived for 24 hr. The blood flow of the portal and suprahepatic veins as well as the hepatic balances for glucose, lactate, alanine and pyruvate were estimated.In fed rats, after the administration of an oral 3 mmoles load, the liver actually released 310 µmoles of glucose and 90 of lactate, amounts that could be accounted for by the uptake of alanine (148 µmoles) and small loss of glycogen (275 µmoles of glycosyl residues). In starved rats, however, the liver took a very high proportion (c. 71%) of the glucose absorbed, both as glucose (780 µmoles), lactate and pyruvate (892 µmoles) or alanine (134 µmoles). The synthesis of glycogen was considerably limited, accounting for only 205 µmoles, and leaving practically one mmol of glucose equivalent energy available for liver function and the synthesis of other compounds. Practically all glycogen was synthesized directly from glucose, since the synthesis from 3 C carriers was less than a 5%. Smaller gavages (1 or 0.1 mmoles) resulted in a much lower liver uptake activity.The strikingly different activity of the liver with respect to the available glucose and 3 C fragments could not be explained alone by the circulating levels of these compounds, suggesting a very deep influence of the intestine in hepatic function. The liver plays a very passive role in fed animals, with a very small involvement in the disposal of a glucose load, whereas it takes on an important role when the overall availability of energy is diminished.