Physical and chemical changes in porcine gastric mucus in the normal and ulcerated status

Master Thesis


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University of Cape Town

It has been reported that there is a 100% incidence of ulceration of the squamous pars oesophagea of the pig's stomach following bile duct ligation. The reproducibility of this model has made possible its use in the investigation of the biochemical aspects of mucus secretion in both the normal state and at various states of ulceration. The main findings are summarised below: Mucus scrapings of the cardiac gland region of the pig stomach had a higher water and total protein content in the pre-ulcerated, ulcerated and post-ulcerated states. Gel chromatography on Sepharose CL-4B indicated larger amounts of degraded mucins relative to native mucins in the samples obtained from pre-ulcerated, ulcerated and post-ulcerated stomachs, as compared with the normal and control samples. The amounts of purified mucins obtained after isopycnic centrifugation in CsCl and gel chromatography on Sepharose CL-2B decreased from the normals and controls to the bile duct-ligated pigs. An analysis on SDS-PAGE revealed a considerable degree of proteolytic degradation of the pig gastric mucins in the bile duct-ligated pigs as compared with the normal and control animals. Staining reagents specific for both the protein and the carbohydrate components of the mucus glycoprotein were employed in gel electrophoresis, which also revealed the presence of contaminating protein, viz. haemoglobin, pepsin, albumin and smaller glycoproteins, to a greater extent in the ulcerated than in the normal and control states. Since pig gastric mucins contain 75% of carbohydrate, the determination of the proportions of monosaccharide constituents was essential. This was performed by GLC analysis of the alditol acetate derivatives of the sugars, which were characterised by mass spectrometry as well as by their retention times, relative to standards, on both packed and capillary columns. The most striking changes indicated by the GLC analyses were a decrease in the fucose content of the mucins from the normal to the ulcerated states and an increase in the proportion of N-acetylglucosamine in mucins from sham-operated animals. The control (sham-operated) pig behaved very similarly to the normal pig for up to 24 hours after the surgical procedure. At 48 hours, however, slight changes resembling those following bile duct ligation occurred. This could be due to the trauma of the sham-operation, which involved the surgical insertion of a cannula in the body region of the pig's stomach. It is possible that, under such stress biosynthesis of the mucins may be affected.