Metabolism of tritiated D-alpha-tocopherol and D-alpha-tocopheryl succinate in intraruminally dosed sheep

The comparative disposition (absorption, plasma disposition, tissue distribution) of D-alpha-tocopherol and of D-alpha-tocopheryl succinate (forms of vitamin E) was investigated in 10 ruminally cannulated wethers. Tritiated tocopherols (4 microCi/kg BW) were administered directly into the rumen. Plasma and ruminal fluid activity were regularly measured from the time of administration to 96 h after administration. Radioactivity in lymph was measured in four additional wethers dosed intraruminally (100 microCi) with the same tritiated compounds. Lymph was collected from the cannulated thoracic duct during the first 24 h after the administration. Wethers were killed and selected tissues were measured for their tocopherol activity. Plasma and ruminal fluid specific activity vs time were modeled using appropriate compartmental and noncompartmental approaches. It was shown that there was a large difference in the relative bioavailability of the two compounds with a four times higher (P < .05) relative availability of D-alpha-tocopherol than of D-alpha-tocopheryl succinate. This was explained in terms of incomplete hydrolysis of tocopheryl succinate before absorption. By direct ruminal fluid measurement, it was estimated that tocopherol behaves similarly to a soluble ruminal marker with a ruminal transit time of approximately 19 h. In plasma, the total mean residence time was 148 h for D-alpha-tocopherol and 106 h for D-alpha-tocopheryl succinate. The lymph activity was mainly associated with tocopherol both after tocopherol and tocopheryl succinate administration. Tissue concentration of radioactivity was higher (P < .05) for sheep dosed with tocopherol than for those dosed with the tocopheryl succinate, confirming the difference in bioavailability of the two compounds.