Role of the mucous surface coat, dietary bulk and mucosal cell turnover in the intestinal disposition of benzo(a)pyrene (BaP)

The dispositon of ³H-benzo(a)pyrene (BaP) equivalents from the diet was examined at the lumen-mucosal cell interface of the proximal, medial and distal regions of the catfish intestine. ³H-BaP (500 μd, 20 μg/kg) was administered via gavage in maintenance diet to two groups of catfish. One group was fed daily after dosing while the other was fasted until collection of intestinal tissues. Autoradiography of cryosectioned tissues and computer-enhanced image analysis allowed examination of BaP disposition. BaP was found to selectively localize at high concentrations in the mucous surface coat and corresponding villi of the colon. Supplemental feeding of uncontaminated diet lowered BaP concentrations in these regions. In a similar but separate experiment, ³H-thymidine (666 μCi) was administered to two groups of catfish by i.p. injection to examine mucosal cell turnover in relation to BaP turnover. ³H-Thymidine incorporation was greatest in the distal regions of both fasted and fed groups. Thymidine dynamics indicated that feeding was related to only marginal changes in cell turnover, which suggests that losses in intravillus BaP with feeding may not be wholly explained by intestinal cell turnover. Results from this study suggest that the mucous surface coat of the intestine is a major factor in the regional disposition of dietary carcinogens and removal of BaP from this mucin layer is related to the intake of dietary bulk.