METABOLISM OF TRITIATED D-ALPHA-TOCOPHEROL AND D-ALPHA-TOCOPHERYL SUCCINATE IN INTRARUMINALLY DOSED SHEEP

The comparative disposition (absorption, plasma disposition, tissue di stribution) of D-alpha-tocopherol and of D-alpha-tocopheryl succinate (forms of vitamin E) was investigated in 10 rumically cannulated wethe rs. Tritiated tocopherols (4 mu Ci/kg BW) were administered directly i nto the rumen. Plasma and ruminal fluid activity were regularly measur ed from the time of administration to 96 h after administration. Radio activity in lymph was measured in four additional wethers dosed intrar uminally (100 mu Ci) with the same tritiated compounds. Lymph was coll ected from the cannulated thoracic duct during the first 24 h after th e administration. Wethers were killed and selected tissues were measur ed for their tocopherol activity. Plasma and ruminal fluid specific ac tivity vs time were modeled using appropriate compartmental and noncom partmental 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 incomplet e hydrolysis of tocopheryl succinate before absorption. By direct rumi nal fluid measurement, it was estimated that tocopherol behaves simila rly to a soluble ruminal marker with a ruminal transit time of approxi mately 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 radio activity 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.