Metabolism of the nicotinic acid moiety of d,l-.ALPHA.-tocopheryl nicotinate.

: The metabolism of the nicotinic acid (NA) moiety of d,l-alpha-tocopheryl nicotinate (TN) was investigated using radiolabeled TN, with the labeled moiety of the molecule being either NA or tocopherol, and labeled NA. After a single orally administered dose of TN to normal rats, the level of this radiolabeled compound increased gradually in the blood. After the oral administration of NA, the level increased and decreased rapidly initially before coming to a stable level of elevation. Urinary metabolites from rats administered TN were compared with those from rats administered NA. In the case of NA administration, the main metabolites in the urine were nicotinuric acid and NA, while NA was the main metabolite in the urine from rats given TN. These results indicate that the metabolism of the NA moiety of TN differs from that of free NA. The tocopherol moiety of TN was taken up by red blood cell membranes and the NA moiety was distributed among red blood cell contents. The main metabolite in both red blood cell contents and liver after a single orally administered dose of TN was nicotine amide. To determine the metabolism and distribution of TN incorporated into the cellular organelles of the liver, TN was injected intravenously to normal rats and the livers subjected to cell fractionation. TN was distributed in nuclear, mitochondrial, lysosomal, microsomal and supernatant fractions in unchanged form. Several metabolites of TN were detected as minor components in these organelles as well.