Elevated blood pyruvate levels and decreased retention of thiamin in rats mildly depleted of vitamin B 12

Abstract

Nine-moth-old rats that were mildly depleted of vitamin B 12 and their controls were subjected to 26 days of thiamin deficiency. All rats had been equilibrated with the control level of thiamin (500 μg/ 100 g diet) for the previous 8 months. The four subgroups (11 rats/ subgroup) included: controls (CC), vitamin B 12-depleted (BD), thiamin deficient (TD) and vitamin B 12 depleted rats made thiamin deficient (BD+TD). At the initiation of the thiamin deficiency period, BD-rats were excreting 3 times more methylmalonic acid than their controls. This was indicative of a significant, although mild, depletion of vitamin B 12. The mild depletion of vitamin B 12 (BD) led to a 49% increased loss of thiamin in urine, whereas 26 days of thiamin deficiency (TD and BD+TD) was accompanied by decreased losses of thiamin in urine. Urinary losses of thiamin were equivalent to 24% of ingested thiamin for controls (CC), but these losses of thiamin were doubled (46%) in rats depleted of vitamin B 12 (BD). Because of their reduced intakes of food, BD-rats received only 78% as much thiamin as the controls (CC), and they retained a similar relative amount (69%) of thiamin in their liver. Thiamin deficient rats (TD) retained only 7% as much thiamin in their liver. The least amount of thiamin was retained in liver when rats had a thiamin deficiency combined with the mild depletion of vitamin B 12 (BD+TD). The mild depletion of vitamin B 12 (BD) and thiamin deficiency (TD) promoted equivalent increases in blood pyruvate. Rats mildly depleted of vitamin B 12 have an inhibited ability to retain absorbed thiamin, and the resulting depletion of thiamin leads to major increases in blood pyruvate.