Age variation of vitamin B 6 metabolism in man

Abstract

1. (1) An account is given of a study on the pyridoxal phosphate content in plasma from 59 normal human subjects of different ages carried out by a sensitive method using the apoenzyme of tyrosine decarboxylase and 14C-labelled tyrosine for the determination. A striking decrease with age was found. 2. (2) Further to investigate this finding, tryptophan tolerance tests were performed on eleven normal human subjects aged over 60 years with low plasma pyridoxal phosphate values. The xanthurenic acid excretion in urine was high, but returned to normal after administration of vitamin B 6. The pyridoxal phosphate content in plasma also rose greatly as a consequence of the treatment. 3. (3) In another group (405 hospital in-patients) the S-GOT levels were determined directly and in the presence of excess pyridoxal phosphate. The increase in the transaminase activity was found to be significantly higher among the older subjects. Three patients with a two- to threefold increase in S-GOT level after administration of pyridoxal phosphate were found to have a low pyridoxal phosphate content in plasma and a pathological tryptophan tolerance test. In one of the three the values did not return to normal after intake of vitamin B 6, and a defect in absorption or in phosphorylation of the vitamin is thought to be responsible. 4. (4) From the results of the investigation it is concluded that the vitamin B 6 metabolism becomes altered with higher ages.