Contribution of luminal concentration of nutrients and osmolality to postprandial intestinal hyperemia in dogs.

Intestinal blood flow is increased during digestion. This study assesses if the concentration of nutrients and/or osmolality of chyme in the intestinal lumen are factors determining the hyperemia. Six digested food mixtures containing different concentrations of nutrients and/or having different osmolalities were placed into the jejunal lumen, and their effects on local venous outflow compared. The 100% (999 mOsm/kg), 33% (291 mOsm/kg), and 20% (183 mOsm/kg) food mixtures all increased flow, but the 10% food mixture (94 mOsm/kg) did not. The hyperemic effect of 33 and 20% food was similar, but 100% food produced a greater increase in flow than did 33 or 20% food. Luminal placement of a 30% solution of a nonabsorbable substance polyethylene glycol (1000 mOsm/kg) did not alter flow. Also, the vascular effects of 20 or 10% food mixtures were not altered when these mixtures were made isotonic by the addition of NaCl. These studies indicate that lumen osmolality, within a range of 180 to 1000 mOsm/kg, is not a significant factor contributing to the local hyperemia occurring when nutrients are in the gut lumen. However, the concentration of nutrients in the lumen is a factor determining the local hyperemia.