Canine Colonic Microstructure and Function as Affected by the Level of Dietary Protein

Abstract

Fifteen adult mongrel dogs, 5-24 kg body wt, were fed one of three diets that varied in the level of dietary protein (12%, 24% or 36%). Dogs were fed their re spective diets for a minimum of 14 d before experi mentation. Colonie function was evaluated by in vivo perfusion, cecum to rectum, of 90-min duration. Tis sues were collected from the proximal, mid and distal colon for analysis of oxygen consumption rate, protein content and mucosal morphology. Oxygen consump tion rate (tissue energetics) was measured over time with glucose as the substrate. Colonie mass (1.33%, 2.45% and 2.57% body wt) and protein content (0.63, 1.10 and 1.16 g/kg body wt) (12, 24 and 36%, respec tively) were significantly less (P < 0.05) in dogs fed the 12% compared with those fed 24 and 36% protein diets. In addition, tissue energetics (0.21,0.44 and 0.57 urn O2'g~1'min~1 increased significantly with each increase in dietary protein (12, 24 and 36% protein, respectively). Significant differences were also noted in tissue energetics for the proximal, mid and distal colonie segments. Morphometric studies revealed a larger (P < 0.05) ratio of colonie surface area to mu cosal volume in dogs fed the 24% and 36% diets rel ative to those fed the 12% protein diet. Colonie trans port of sodium, chloride and individual fatty acids (acetate, propionate and butyrate) were significantly different for the various dietary protein levels. Signif icant differences in effluent pH, osmolality, bicarbon ate and base excesswere also noted among diet groups. The data suggests that the canine large bowel acts as a protein sink, accumulating protein with the in creased dietary level. Furthermore, colonie structure and tissue energetics adapt to various levels of dietary protein, resulting in a modification of the absorptivesecretory process of the bowel.