Studies of the degraded carrageenan-induced colitis of rabbits. I. Changes in the epithelial glycoprotein O-acylated sialic acids associated with ulceration.

Ulceration of the large intestine, induced in New Zealand white rabbits by the administration of 1% w/v degraded carrageenan for periods of up to nine weeks, was studied by a combination of histochemical and chemical procedures for the identification of O-acylated sialic acid. The onset of the disease was rapid, visible faecal blood being observed within five days. Caecal ulceration was diffuse throughout the mucosa being more prominent and frequent on the transverse folds. In some cases large, discrete ulcers were observed in the rectal portion of the lower colon, while in a small number of cases there were ulcers at the caecal end of the upper colon. The ulceration was characterized by oedema, congestion, haemorrhage, inflammation and mucosal ulceration. The inflammatory exudate consisted of macrophages, lymphocytes, a few plasma cells and, in animals treated for a long period, aggregates of eosinophils. The ulceration was associated with a marked reduction in the proportion of the caecal epithelial glycoprotein sialic acids which were neuraminidase-resistant and/or substituted in the side chain. Histochemical studies indicated that changes in side chain substitution were more marked at the margins of the ulcers and could be observed in sections of colon that showed no evidence of ulceration.