ORALLY APPLIED ENDOTOXIN STIMULATES COLONIC MUCIN RELEASING CELLS IN GERM-FREE RATS

During microbial colonization of germfree (GF) rats, mucin releasing c ells proliferate and upregulate their mucin synthesis. The present stu dy determines the effect of lipopolysaccharide (LPS) as a bacterial ce ll membrane constituent for this development. Increasing quantities of LPS from E. coli O:55 B:5 (3.5 to 350 mu g/100 g body weight (bw)) we re applied perorally to GF rats (AS/Ztm). One day after challenge, LPS concentrations up to 35 mu g LPS/100 g bw had generated a dose-depend ent hypertrophy and hyperplasia of mucin secreting cells. A further pr oliferative response was determined in the proximal colon after applic ation of 350 mu g LPS/100 g bw, the distal colon displayed a lesser re activity. Epithelial lesions were observed in both levels. Five days a fter challenge, the histological phenomena were considerably reduced. All sections of challenged animals evidenced mononuclear cell infiltra tions. Secreted mucins were isolated and separated into adherent and l uminal mucin constituents, respectively. An application of 3.5 and 35 mu g LPS/100 g bw stimulated the secretion of both constituents, the l atter ones in a more pronounced manner. The application of 350 mu g LP S/100 g bw rendered a submaximal release of both mucin constituents. R esults suggest a stimulating effect of LPS on mucin secreting cells an d mucin release, most probably generated by mononuclear cells.