The in vitro uptake and kinetics of release of palmitic acid and taurodeoxycholate from hamster small intestinal segments

Abstract

1. 1. Everted sacs from hamster proximal and distal small intestine were incubated for 10 min at 37° in a micellar solution containing labeled palmitic acid, sodium taurodeoxycholate and inulin. After incubation, efflux of the labeled compounds from the intestinal mucosa was measured by sequential 1-min rinsings in separate 20-ml volume of ice-cold Krebs-Ringer phosphate buffer for a total of 25 min. The radio-activity in each rinsing solution, tissue homogenates and serosal fluids was assayed. 2. 2. The uptake of labeled taurodeoxycholate and inulin by the proximal and distal small intestine was not significantly different. However, the amount of [I- 14C] palmitic acid taken up by the proximal small intestine was significantly greater. 3. 3. A considerable fraction of the labeled substances taken up during the initial incubation could be released by rinsing. The distal small intestine released a greater fraction of labeled palmitic acid and its release appeared to be inversely related to the esterifying capacity of the intestine. Proportionately greater amounts of [ 3H] taurodeoxycholate and [ 14C]inulin than that of [1- 14C]palmitic acid were released by both proximal and distal small intestine. 4. 4. Analysis of the kinetics of efflux of each substance indicated that efflux occurred from two compartments, one rapidly and one slowly turning over. The characteristics of efflux of labeled palmitic acid and taurodeoxycholate from the rapidly turning over compartment were similar to those of labeled inulin suggesting that they occupied the extracellular fluid space. The characteristics of efflux from the slowly turning over compartment were different for each substance, and no conclusions could be drawn regarding the location of this compartment. However, the finding that the efflux of [1- 14C]palmitic acid and [ 3H]taurodeoxycholate from this compartment was slower than that of [ 14C]inulin indicate that superticial binding sites may be involved in the reversible uptake of these substances. In addition the ratio of [ 3H]taurodeoxycholate to [1- 124C]palmitic acid in this compartment was greatly in excess of the 10:1 ratio of the micellar incubation medium indicating that the efflux of [ 3H]taurodeoxycholate exceeded that of [1- 14C]palmitic acid.