Effect of medium‐chain glycerides on the intestinal absorption of phenol red: Studies on mechanisms of the promoting effect

To elucidate the mechanisms of the promoting action of medium‐chain glyceride (MCG) on the intestinal absorption of phenol red (PR), the effect of different MCG dose levels on PR absorption, the absorption kinetics of MCG itself, and the mucosal reduced glutathione (GSH) levels were investigated to determine whether or not they are related to the promoting action of MCG. The absorption of PR was found to be enhanced with an increase in MCG dose (as an emulsion in the range 0.5–4.0%). Urinary excretion of PR was reduced by absorbed MCG components, which also resulted in an increase in the AUC. Moment analysis of plasma PR concentrations after intraintestinal administration revealed a shorter mean absorption time (MAT) for the emulsion formulation than for the control. The mucosal GSH level was lowered by the administration of the MCG emulsion (2–10%) into the intestinal lumen. Pretreatment with a 4% MCG emulsion decreased GSH levels to one‐half of the control. In these cases, the level of mucosal GSH seemed to remain constant to the end of the experiment after it had decreased during the initial period. On the other hand, results from the in situ loop or recirculation study showed that enhancement of PR absorption appeared in the earlier period and then gradually decreased. The time course of the PR absorption rate, estimated from plasma concentration data, was similar to that of the MCG absorption rate. These results suggest that the promotion of intestinal absorption is related to the absorption kinetics of MCG itself, but not directly to the level of mucosal GSH.