Carrier-mediated transport of riboflavin in the rat colon

Carriers involved in riboflavin transport have generally been presumed to b e localized in the upper small intestine. However, using a closed loop tech nique, we found that in the rat colon the absorption of riboflavin could be significantly reduced by raising the concentration from 0.1 to 200 muM and by adding lumiflavin, an analogue of riboflavin, These results suggest tha t saturable transport by the carrier that is specific for riboflavin and an alogues may also be involved in riboflavin absorption in the colon. At the lower concentration of 0.1 muM, carrier-mediated transport was suggested to prevail, compared with passive transport, both in the colon and the small intestine. Furthermore, carrier-mediated transport in the colon was compara ble with that in the small intestine. This study is the first to suggest ca rrier-mediated riboflavin transport in the colon. Although the riboflavin t ransport system in the colon needs to be subjected to more detailed investi gation of its transport functions and role in riboflavin absorption after o ral administration, it would be of interest to explore potential use of thi s carrier as a system for drug delivery. Copyright (C) 2000 John Wiley & So ns, Ltd.