Prediction of the Relative Passive-transfer Rates of Short-chain Fatty Acids across Lipid Membranes

Abstract

A VAST quantity of literature has accumulated concerning the mechanism of lipid transfer across the intestinal wall, yet the process still remains largely unclear¹. One point which seems definitely established is the difference between the transfer of short-chain fatty acids, which appear free in the liver portal blood, and the long-chain acids (>C₁₀), which appear mainly in lymph in the form of triglycerides². Whereas the latter transfer system is complex, involving emulsification, micelle formation and enzymatic esterification, the former may be relatively simple, involving a combination of a fatty acid permease and passive penetration. Smyth³ and Barry and Smyth⁴ have demonstrated that fatty acids containing from two to six carbons are actively transported from the mucosal to the serosal side of intestinal sacs in vitro. Higher concentrations of fatty acids suppress in vitro active transport, the suppression being more pronounced with increasing chain length, but this inhibition does not seem to influence the rate of disappearance of fatty acids from inside the intestine in vivo⁴. The possible contribution of passive transport is therefore of some interest.