Intestinal sphingolipid excretion associated with feeding of phytohemagglutinin lectin (Phaseolus vulgaris) to germ-free and conventional rats

Abstract

Intestinal sphingolipids of feces of germ-free and conventional rats were analyzed during the pair feeding of a complete defined diet containing phytohemagglutinin lectin (PHA) from red kidney beans (Phaseolus vulgaris) as 1% dietary protein in comparison to casein fed controls. Phytohemagglutinin in the diet increased the total fecal excretion of sphingomyelins (18-fold for germ-free and 20-fold for conventional rats), of non-acid glycosphingolipids (3.5-fold for germ-free and 9-fold for conventional rats) and also of the gangliosides (2.5-fold) for the germ-free rats compared to controls. For germ-free rats the increase of non-acid glycolipids was ascribed to an effect of the lectin strictly on the small intestinal mucosa, while for conventional rats an effect was seen also on the large intestinal mucosa. Increase of fecal gangliosides of germ-free rats was due mainly to an increased excretion of N-acetylneuraminosyl-lactosylceramide, a ganglioside species restricted to epithelial cells of duodenum, of upper jejunum and of large intestines. The effects on glycolipid excretion observed in germ-free rats and the rather similar effects seen in conventional animals suggested that the influence of dietary PHA was due directly to effects elicited by PHA binding to the enterocyte brush border membrane and not to secondary effects induced by increase in the luminal microflora.