[Biologic membrane functions in health and disease. Effects of bile acids and laxatives on the mucosal transfer].

The morphologica and biochemical asymmetry of the intestinal epithelium is the precondition for the net transfer of sodium and water from the lumen to the bloodstream. Dihydroxy bile acids and diphenol laxatives belong to the group of drugs which are capable of inhibiting or reversing this net transfer in rats and humans. This property is characterized as antiabsorptive and hydragogue. In addition to their pharmacologic action, pathophysiologic (cholagenic diarrhea) and toxic symptoms (hypokalemia and secondary aldosteronism) can be ascribed to this property. Dihydroxy bile acids and diphenal laxatives render the junctions more permeable. Their mechanism of action can therefore be explained by stating that, due to increased intercellular permeability, the asymmetry of the system is lost and absorption thus comes to a standstill. Since slight hydrostatic pressure on the subepithelial side suffices to reverse the net transfer, it is assumed that in vivo the filtration pressure of the capillaries is the motive force for net transfer into the lumen.