Gastrointestinal absorption of quaternary ammonium compounds correlated to their binding to small intestinal brush border membrane in rat

The relationship between absorption of quaternary ammonium compounds (QACs) from rat intestine and their in-vitro binding to isolated brush-border membrane has been examined, using a series of n-alkyltrimethylammoniums. The binding of these QACs gradually increased with each extension of unbranched hydrocarbon chain from octyltrimethylammonium to tetradecyltrimethylammonium. However, hexyltrimethylammonium and heptyltrimethylammonium failed to bind to the membrane. On the other hand, the disappearance of these QACs from rat jejunal loop also increased with the length of hydrocarbon chain over the range of 8.9 to 71.3%. A good correlation was found between binding to the brush-border membrane and disappearance from jejunal loop. From these results, it was suggested that the size of the hydrophobic part of a QAC molecule was a principal determinant of both absorption and membrane binding, and that the absorption of QACs with an appropriate sized hydrophobic part, was closely associated with the degree of binding to the membrane.