The effect of fasting on rat portal venous and aortic blood glucose, lactate, alanine, and glutamine.

Using a chronically catheterized rat model, the effect of fasting on portal venous, aortic, and venous blood concentration minus aortic blood concentration ([PV-A]) blood glucose, lactate, alanine, and glutamine concentrations was determined. It has been postulated that the intestine is a source of lactate and alanine, precursors for glycogen synthesis, in the fed state. After 48 h of fasting portal venous glucose, lactate, and alanine blood concentrations decreased by 31, 28, and 41%, respectively. Portal venous glutamine concentration was not affected by fasting. A glucose [PV-A] was not found in either fed or fasted states. Whereas the lactate [PV-A] was not present in fed rats, it was negative in fasted rats. Alanine [PV-A] was positive in fed and fasted rats. The glutamine [PV-A] was negative in fed and fasted rats. These data indicate that portal venous concentrations of the gluconeogenic precursors, lactate and alanine, decrease in fasted rats. In fasted rats intestinal utilization of lactate increases as reflected by a negative [PV-A]. Fasting did not affect alanine production by the intestine or glutamine utilization. Despite these changes with fasting, we conclude that the intestine does not appear to be able to maintain portal venous blood concentrations of gluconeogenic precursors.