Estimation of absorption enhancement by medium-chain fatty acids in rat large intestine

The absorption enhancement by the sodium salts of several fatty acids was i nvestigated in rat large intestine for model compounds having a wide range of molecular weight. Sodium caprylate (C8), sodium caprate (C10), sodium la urate (C12), which are categorized in medium-chain fatty acid, and sodium o leate (C18:1), long-chain unsaturated fatty acid, were employed as lipoidal adjuvants. Phenol red (MW=354.4), glycyrrhizin (822.9), fluorescein isothi ocyanate-dextran-4 (FD-4, 4400), FD-10 (9400) and FD-40 (38900) were select ed as model compounds for the assessment of the enhancing effect of the lip oidal adjuvants. The absorption of phenol red was promoted at the highest l evel, about 20 times higher by C12 and C18:1 than the control. The absorpti on rate - time profiles calculated by deconvolution method showed that C12 takes effect most rapidly and efficiently. In the case of glycyrrhizin, fou r adjuvants including C12 showed almost the same improvement of the absorpt ion, about 30-40 times larger than the control. C8 and sodium citrate did n ot significantly enhance the absorption of those model compounds. For FD-4, FD-10 and FD-40, C10, C12 and C18:1 revealed almost the same enhancing eff ect and the absorption of FD-4, FD-10 and FD-40 was enhanced about 80 times , 1000-1800 times and about 200 times, respectively, larger than the contro l. The enhancement ratio, the ratio of AUC with adjuvant to AUC of control, suggests that these lipoidal adjuvants would improve most efficiently the absorption of the compound having the molecular weight of around 10000. Fur thermore, C12 was suggested to be an effective adjuvant for the compounds w ith the wide range of molecular weight.