Intestinal absorption of sodium dodecyl sulfate in the rodent: evidence for paracellular absorption

Experiments were performed to define the mechanism of intestinal absorption of dodecyl sulfate (DS), an amphipathic organic anion whose chemical structure resembles that of dodecanoate, a C12 fatty acid anion. With jejunal segments perfused in single-pass fashion in the anesthetized rat, steady-state absorption of DS was concentration dependent, with the apparent permeability constant (P(app)) ranging from 4 to 22 x 10(-5) cm/s. When DS concentration was held constant and net water absorption was induced by decreasing perfusate osmolality, DS absorption increased in direct proportion to water absorption, suggesting absorption by solvent drag via the paracellular route. However, DS absorption continued even when water secretion was induced by a hypertonic perfusate. Consequently, for all experiments, DS absorption could be empirically described as the sum of two terms: 1) absorption in the absence of water absorption (P(app) = 5.6 x 10(-5) cm/s) and 2) absorption induced by water movement [(delta P(app)/delta water absorption) = 0.2 x 10(-5) cm x s(-1) x microl segment(-1) x min(-1)]. In a polarized epithelial monolayer of renal epithelial cells (Madin-Darby canine kidney cells), DS was absorbed predominantly by a paracellular pathway, as the absorption rate increased threefold when paracellular junction pore size was increased by the addition of cytochalasin D. The calculated apparent radius was 2.9 A, indicating that the cross section of the molecule, not its length, determined the rate of absorption. It is concluded that absorption of DS in the intact animal occurs slowly and mostly via the paracellular route, because the fixed negative charge on the molecule retards rapid passive entry into the enterocyte, as occurs with protonated fatty acids. That absorption of DS persisted despite net water secretion suggests a low level of transcellular absorption across the jejunal enterocyte also occurs.