Further Investigations of Enhancing Effect of Medium-Chain Triglycerides on d-α-Tocopherol Acetate Absorption from Lecithin-Dispersed Preparations in Rat Small Intestine

The effect of medium-chain triglycerides (MCTG) in lecithin-dispersed d-α-tocopherol acetate (VEA) preparation on intestinal absorption of VEA was investigated in rats using the in situ loop experiment. When VEA preparations containing soybean phosphatidylcholine (PC) and various amounts of MCTG were administered, the amount of VEA absorbed in 2 h was not significantly different among them. However, the amounts of total VE, sum of VEA and d-α-tocopherol (VE), remaining in the luminal fluid and the intestinal tissue were dependent on the MCTG content. Total VE remaining in the intestinal tissue after the administration of a VEA/PC/MCTG (5/16/1 by weight) preparation was nearly twice of VEA/PC (5/16) preparation, although the effect of MCTG varied with the increase or decrease in the MCTG content. Moreover, the increased tissue accumulation of total VE by the VEA/PC/MCTG (5/16/1) preparation resulted in an increase in the plasma VE concentration after the removal of the luminal fluid. No effect of pretreatment with PC/MCTG (1/1) dispersion on the tissue accumulation of total VE from VEA/PC (5/16) preparation was observed. Furthermore, the plasma concentration of VE from VEA and/or VE taken up in the tissue from the VEA/PC preparation was not increased by the treatment with the PC/MCTG dispersion. These results suggest that MCTG should coexist in the luminal VEA preparation to enhance the mucosal uptake. A similar enhancing effect was also observed by the addition of the metabolite of MCTG, a medium-chain fatty acid. When caprylic acid was added to the VEA/PC preparation, the tissue accumulation of total VE was also increased in comparison with the VEA/PC preparation, and the increased amount was not significantly different from VEA/PC/MCTG (5/16/1) preparation.