Interactions between hemolytic saponins, bile salts and small intestinal mucosa in the rat

The interaction between bile salts and saponins from Gypsophylla was investigated in vitro, using changes in transmural potential difference across isolated lengths of rat jejunum as an index of the capacity of the saponin to affect the permeability of intestinal mucosal cells. The addition of saponin (ca. 5 mM) to taurocholic acid in buffered saline (pH 7.4) led to a significant increase in viscosity, indicating the formation of a polymer. The viscosity of the solution was highest at low molar ratios of bile salt to saponin (0.5-2.0). Under these conditions there was an inhibition of the permeating effect of saponins on the gut, as judged by the rate of decline in transmural PD. There was no evidence of inflammation or functional damage to the jejunal mucosa of rats fed a diet containing Gypsophylla saponin (ca. 1.5% w/w) for 7 d but changes in villus morphology were observed. There was also evidence of an increased rate of mucosal cell proliferation. Serum cholesterol levels were significantly lower in saponin-fed rats than in controls, while the cholesterol content of the cecal contents was increased. These results suggest that despite the protective effect of bile salts, Gypsophylla saponins interact with the mucosa of the proximal small intestine in vivo, but at the dietary level used in this study the mucosa was protected by an enhanced rate of cell replacement. The loss of cholesterol via exfoliated mucosal cells may contribute to the hypocholesterolemic effect of saponins in rats.