Mice treated with 200 µl enema containing 30 µM FTU, APF or BPF for 2h. Colorectal mucosa tissue was scrapped, homogenized, spun and the fluorescence of the supernatant was quantified, converted to fmole, normalized by mucosa tissue weight. Tissue retention was examined for up to 5 days, BPF is greater than APF at all time points (One way ANOVA p < 0.05, n = 4).