The effect of lipids on taurocholate absorption from intestinal loops in the rat

The rates of uptake and serosal transfer of [14C]-labelled taurocholate (7.77 mM in bicarbonate buffer, pH 6.5) were determined in situ in ligated segments of rat intestine in the presence of lipids. Oleic acid, monoolein, lecithin, and lysolecithin enhanced taurocholate uptake and transfer in the jejunum, each lipid exhibiting an optimal concentration at which the bile acid fluxes were maximal. The maximal rates of bile acid uptake observed with the various lipids were close to four times the uptake rates found with the lipid-free taurocholate medium, whereas serosal transfer rates under optimal conditions were enhanced about six-fold. The optimal concentrations differed widely among the various lipids, being inversely related to the lipids' polarity. Simultaneous measurement of taurocholate and [3H]-labelled oleic acid showed that under optimal conditions, when the molar concentration of oleic acid was about equal to that of the bile acid, the fatty acid and bile acid also exhibited closely similar rates of absorption. At other fatty acid concentrations, the fractional rate of absorption of the bile acid was much lower than that of the fatty acid. The rates of uptake and serosal transfer of pure taurocholate by the ileum exceeded those of the jejunum by factors of about 7 and 15, respectively, but in the presence of lipids this difference in absorptive capacity for bile acid between the distal and proximal segment largely disappeared.