Biochemical Effects in Animals

The complexity of deoxypyridoxine effects is evident from the difference in response depending on the amount of B₆ available. Deoxypyridoxine reduced the fall in plasma pyridoxal phosphate in deficient animals but caused a fall in the normal B₆ animals. pector examined vitamin B₆ transport by brain slices and choroid plexuses from rabbits in vitro. Rosen concluded that vitamin antagonists may affect only selected enzymes and need not inhibit all biochemical functions of the vitamin. Vitamin B₆ has an important role in tryptophan metabolism. B₆ deficiency alone tended to reduce the plasma concentrations of essential amino acids but had little effect on the nonessential amino acids. Iwanowska found no change in the activity of aspartate or alanine aminotransferases in the blood of rats treated with up to 400 µg deoxypyridoxine per day with or without adequate B₆. A series of in vitro studies demonstrated that 4'-deoxypyridoxine-5'-phosphate, but not deoxypyridoxine itself, would inhibit tyrosine decarboxylase.