Effects of ingestion of a green seaweed, Ulva lactuca, upon caecal and colonic mucosas in the germ-free rat and in the heteroxenic rat harbouring a human bacterial flora

Effect of ingestion of green seaweed, Ulva lactuca, (70 g kg(-1)) during a 6-week period on caecal and colonic mucosas was studied in germ-free (GF) r ats and in heteroxenic (HE) rats harbouring a human bacterial flora (GF rat s associated with a human flora). The pH and sulphide concentration of the caecal contents, crypt morphometry, mitotic index and mucin types in the ca ecal and distal colonic mucosas were determined. In the GF caecum, Ulva str ongly increased crypt depth and mucin-containing cells irrespective of the mucin type studied (neutral, acidic or sulphated) compared to the control d iet but had no significant effect on mitotic index. The crypt depth and muc in-containing cells in the caecum were higher in HE than in GF control rats . They were slightly but significantly increased by Ulva. In the distal col on mucosa of GF rats, Ulva decreased crypt depth and cell number as well as sulphomucin-containing cells. Conversely, in the HE rats, it increased cry pt depth and reduced the number of neutral mucin-containing cells. These re sults show that Ulva lactuca exerts an intrinsic effect on mucosal morphome try and on mucin biosynthesis in GF rats. No pathological alteration was ob served in the mucosas and no significant modification of the mitotic index or sulphide production was observed in HE rats. (C) 1999 Society of Chemica l Industry.