Effect of luminal perfusion rate on duodenal alkalinization in the rat in vivo and in vitro.

This study investigates the effects of luminal perfusion rate on the observed rate of alkalinization of an unbuffered saline by anesthetized rat distal duodenum. Increases in perfusion rate (range 0.3-22 ml/min) increased both alkalinization (3-15 mumol/cm hr) and intraluminal pressure (6-22 mm Hg). Increases in pressure (6-30 mm Hg) at constant perfusion rate (3 ml/min) did not change alkalinization. The effect of perfusion rate on alkalinization was rapid, reversible, and could be repeated several times. It was unaffected by indomethacin (10 mg/kg subcutaneously) or tetrodotoxin (1 mg/ml in perfusate). A limited in vitro study at two flow rates (0.3 and 22 ml/min) showed a similar enhancement of alkalinization. It is concluded that the rate of alkalinization is increased by raising the perfusion rate of the lumen both in vivo and in vitro. The mechanism remains to be established but may involve the reduction of a diffusion barrier between the mucosa and luminal bulk fluid. These results may have implications for the movement of other substances across intestinal segments.