Effects of some purified alfalfa (Medic ago sativa) saponins on transmural potential difference in mammalian small intestine

The effect of a range of structurally divergent alfalfa saponins on the potential difference (PD) across the rat small intestine has been examined in vitro Typically, there was an immediate reduction in PD, although there was considerable variation in response to particular compounds. Among the glycosides of medicagenic acid, bisdesmosides containing four sugar moieties had activities equal to the monodesmoside and to medicagenic acid itself. The exception was 3Glc, 28Glc-medicagenic acid, which did not affect the membrane potential. Zanhic acid glycosides reduced the PD to a much greater extent than medicagenic acid derived compounds. The tridesmoside of zanhic acid was the most active compound tested. This compound is however not precipitated by cholesterol and hence would not have been present in the ‘biologically active’ fractions used in previous studies. The present data show that both the lipophilic aglyconc portion of saponins, and the sugar composition can influence the ability of these compounds to depolarized the intestinal mucosa. The observations are discussed in the light of anti nutritional properties of alfalfa saponins when fed to monogastric animals.