Lymphatic and portal venous transport of alpha-tocopherol and cholesterol

The absorption of ³H-α-tocopherol was studied in rats after intraduodenal administration in micellar solutions. Net absorption from mixed micelles in lymph fistula rats was 66%, but only 42% appeared in lymph and 3% was excreted in urine. Administration of ³H-α-tocopherol in taurocholate micelles reduced both the rate of absorption into lymph and the proportion carried in chylomicrons. In studies with lymph and bile duct cannulated rats, up to 8% of the radioactivity was excreted in bile, irrespective of whether the cannula was in the mesenteric or thoracic lymph duct. These findings suggested that radioactivity was being absorbed via the portal vein, which was confirmed by demonstrating a higher concentration in portal than in aortic plasma. Radioactivity in plasma partly consisted of polar metabolites, in contrast to lymph where over 90% was free α-tocopherol. In parallel experiments with ¹⁴C-cholesterol, significant amounts of radioactivity were excreted in bile and the ratio of portal: aortic radioactivity again suggested absorption via the portal route. The majority of ¹⁴C-cholesterol in portal plasma was free sterol, in contrast to lymph where it was mainly esterified. These results suggest that small amounts of both α-tocopherol and free cholesterol can be transported from the intestine via the portal vein, although under normal circumstances absorption of both compounds occurs mainly via the lymphatic pathway.