EFFECT OF AGING ON THE BIOAVAILABILITY OF VITAMIN-B6 IN RATS

An age-related decline in vitamin B-6 status has been demonstrated in humans and rodents. In this study, the bioavailability of vitamin B-6 was evaluated in 3- and 20-month-old, male Fischer 344 rats by administration of a single, oral dose of [H-3]pyridoxine. In addition, plasma pyridoxal 5'-phosphate concentration and alkaline phosphatase and erythrocyte aspartate aminotransferase activity were measured. Plasma pyridoxal phosphate concentration was 75% lower in the aged rats compared with the 3-month-old rats. Plasma alkaline phosphatase activity was reduced and erythrocyte aspartate aminotransferase activity increased in the aged rats. There was no difference in the stimulation of erythrocyte aspartate aminotransferase activity with pyridoxal phosphate. Approximately 99% of the radioisotope was absorbed by rats from both age groups. No differences were observed in the tissue distribution of [H-3]vitamin B-6 between the two age groups or the retention of radioactivity by the various tissues examined. The urinary excretion of total H-3, as well as [H-3]4-pyridoxic acid, was not different between the two age groups. Reduced plasma pyridoxal phosphate concentration with aging does not appear to be the result of decreased intestinal absorption of vitamin B-6, increased plasma alkaline phosphatase activity, or altered metabolic utilization of vitamin B-6. Based on this information, plasma pyridoxal phosphate concentration may not be an adequate assessment parameter for vitamin B-6 status as affected by aging.