SURFACE HYDROPHOBICITY OF THE INTESTINAL-TRACT

To quantitate surface hydrophobicity of the intestine, we measured contact angles formed with water droplets in multiple regions of rabbit intestine at varying ages (suckling, weanling, and adult) and after dinitrochlorobenzene-induced colitis. Contact angles were measured using novel methods: axisymmetric drop-shape analysis-contact diameter for contact angles < 90-degrees and axisymmetric drop-shape analysis-maximum diameter for contact angles > 90-degrees. To determine whether mucus was present on the surface of intestine used, indirect immunofluorescence was performed using antibody specific to goblet cell mucin. To confirm that intestinal mucus could be responsible for the physical properties of surface mucosa, surface tensions of mucus prepared from distal ileum, distal colon, and inflamed distal colon of adult rabbits were measured by axisymmetric drop-shape analysis on pendant drops. Contact angles of adult small intestine [duodenum, 38.0 +/- 11.2-degrees (SD); jejunum, 44.0 +/- 22.9-degrees; ileum, 56.4 +/- 23.3-degrees] were less than proximal colon (93.2 +/- 6.7-degrees; P < 0.05) and distal colon (86.4 +/- 24.2-degrees; P < 0.05). Contact angles on proximal colon from suckling rabbits (53.2 +/- 8.4-degrees) were less than both weanling (93.2 +/- 23.3-degrees; P < 0.05) and adult rabbits (93.2 +/- 6.7-degrees; P < 0.05). Contact angles on inflamed adult distal colon (54.7 +/- 20.6-degrees) were decreased from values on normal distal colons (86.4 +/- 24.2-degrees). Indirect immunofluorescence demonstrated that mucin was present in both vacuoles of goblet cells and on the colonic surface. Pendant drop analysis showed that ileal mucus had a greater surface tension [51.89 +/- 0.98 (SD) mJ/m2] compared with mucus from inflamed distal colon (47.11 +/- 0.29 mJ/m2; P < 0.01). In addition, surface tension of mucus prepared from inflamed distal colon was greater than normal distal colonic mucus (34.26 mJ/m2; P < 0.01). We conclude that intestinal hydrophobicity is altered by maturational changes, regional differences, and mucosal inflammation. Changes in physical properties of the intestinal mucosa are likely due to alterations in the mucous layer overlying intestinal epithelium.