Active transport of salicylate by rat jejunum.

Using an improved segmented flow technique the uptake of salicylate in low concentration (1-3 mM) by rat jejunum is found to be steady for ca. 30 min, and is proportional to lumen concentration. At higher lumen concentrations (6-8 mM) the rate of uptake falls from the beginning to very low levels. At low lumen concentrations the tissue fluid concentration rises to approximately three times the lumen concentration without significant effect on the uptake rate. This rise is an exponential function of the net water transport across the intestinal wall. The rate constant is of the same order of magnitude as those found earlier for equilibration of tissue fluid with glucose and wash-out of protein from the tissue fluid. The uptake of salicylate is inhibited irreversibly by 2,4-dinitrophenol (2-4 x 10(-5) M).