EFFECTS OF SOME PURIFIED ALFALFA (MEDICAGO-SATIVA) SAPONINS ON TRANSMURAL POTENTIAL DIFFERENCE IN MAMMALIAN SMALL-INTESTINE

The effect of a range of structurally divergent alfalfa saponins on th e potential difference (PD) across the rat small intestine has been ex amined in vitro. Typically, there was an immediate reduction in PD, al though there was considerable variation in response to particular comp ounds. Among the glycosides of medicagenic acid, bisdesmosides contain ing four sugar moieties had activities equal to the monodesmoside and to medicagenic acid itself. The exception was 3Glc,28Glc-medicagenic a cid, which did not affect the membrane potential. Zanhic acid glycosid es reduced the PD to a much greater extent than medicagenic acid deriv ed compounds. The tridesmoside of zanhic acid was the most active comp ound tested. This compound is however not precipitated by cholesterol and hence would not have been present in the 'biologically active' fra ctions used in previous studies. The present data show that both the l ipophilic aglycone portion of saponins, and the sugar composition can influence the ability of these compounds to depolarise the intestinal mucosa. The observations are discussed in the light of antinutritional properties of alfalfa saponins when fed to monogastric animals.