Studies of the degraded carrageenan-induced colitis of rabbits. II. Changes in the epithelial glycoprotein O-acylated sialic acids associated with the induction and healing phases.

Rabbits fed freely with a 1% aqueous solution of degraded carrageenan developed a progressive colitis characterized after five days by severe inflammation and mucosal ulceration of the caecum. Histochemical and chemical studies indicated that there was a marked reduction in intracellular mucin and in the proportion of the epithelial glycoprotein sialic acids with substituents in the side chain and at position C4. Changes in the O-acylated sialic acids occurred rapidly and, apparently, prior to either mucosal ulceration or a significant inflammatory response. Following the removal of carrageenan from the diet, there was evidence of progressive healing characterized by re- epitheliazation and a reduction in the inflammatory response until, at 12 days, the mucosa was comparatively normal. Healing was accompanied by an apparent increase in intracellular mucin and in the proportion of the epithelial glycoprotein sialic acids with substituents in the side chain and at position C4. Animals sacrificed 20 days after withdrawal of the carrageenan showed a renewal of ulceration characterized by an active inflammatory process, congestion, haemorrhage, and an inflammatory exudate consisting of a massive aggregation of eosinophils together with lymphocytes and plasma cells. This was accompanied by a reduction in the proportion of side chain and C4 substituted sialic acids.