Absorption kinetics of some carbohydrates in conscious pigs. 2. Quantitative aspects.

Concentrations of reducing sugars, glucose, fructose and lactic acid in blood obtained from arterial and portal catheters were measured together with the portal hepatic blood flow-rate for periods of 8-24 h in twenty-six unanaesthetized pigs (mean body-weight 51 kg). The animals received experimental meals containing different amounts (100-1600 g) of different sugars (glucose fifteen meals, sucrose twenty-four meals, lactose fourteen meals, maize starch nineteen meals) together with a protein-mineral-vitamin mixture (150 g) 6-8 after implantation of the catheters and an electromagnetic flow probe. Because the portal blood flow pattern did not differ between test meals, net absorption followed the same trends as for porto-arterial concentration differences (R erat et al. 1984). Apart from lactose, the amounts of reducing sugars appearing in the portal vein correlated with the intake of the test meal, but the absorption pattern was different for each sugar. The appearance of reducing sugars was faster and earlier after intake of glucose than after sucrose and the same was the case for sucrose relative to maize starch. The differences between the three carbohydrates tended to increase with the level of intake. With a test meal containing 1 kg carbohydrate, i.e. a normal meal in a 50 kg pig, digestion of sucrose and maize starch was not finished 8 h after the meal since only 60 and 52% respectively of their hydrolysis products were recovered in the portal blood. In the case of lactose, the amounts of reducing sugars appearing in the portal blood were always very small and constant (113-118 g within 8 h) whatever the level of intake, i.e. 30 and 15% of their hydrolysis products for intakes of 400 and 800 g respectively. Depending on the carbohydrate ingested, the uptake of glucose by the gut cell wall ranged from 14 to 21 g/h and the production of lactic acid from 2.5 to 3.5 g/h.