A new steroidal saponin from Agave brittoniana and its biphasic effect on the Na+-ATPase activity

A new steroidal saponin, 3-{(O-6-deoxy-alpha-L-mannopyranosyl-(1 -> 4)-O-beta-D-glucopyranosyl-(l 3)-O-[O-beta-D-glucopyranosyl-(1 -> 3)-beta-D-glucopyranosyl-(1 -> 2)]-O-beta-D-glucopyranosyl-(1 -> 4)-beta-D-galactopyranosyl)oxyl}-6-hydroxy-(3 beta,5 alpha,6 alpha,25R)-spirostan-12-one, was isolated from Agave brittoniana Trel. The structure was determined by extensive NMR spectroscopy studies and chemical conversions. Its effects on the Na+-ATPase and (Na++K+)-ATPase activities of the proximal tubule from pig kidney were evaluated. It was observed that this steroidal saponin exerts a biphasic effect on the Na+-ATPase activity. It is concluded that the effect of the aqueous extract as a diuretic is due, at least in part, to the action of saponin on the ouabain-insensitive Na+-ATPase.