Effect of oral contraceptives and pyridoxine on the metabolism of vitamin B6 and on plasma tryptophan and alpha-amino nitrogen

The effect of supplementary pyridoxine on the metabolism of vitamin B6 as well as plasma tryptophan and α-amino nitrogen was determined in women using oral contraceptive agents. Ten women who were taking oral contraceptive agents and 11 who had never taken them served as subjects. Blood from the various biochemical measurements was drawn from fasting subjects before and after they had received an oral dose of 50 mg of pyridoxine-HCl daily fo 2 days. The use of oral contraceptive agents had no effect on the levels of blood vitamin B6, plasma pyridoxal phosphate, and plasma tryptophan. The activity of erythrocyte glutamic oxaloacetic transaminase was higher (P < 0.05) in the oral contraceptive agent users than in the nonusers but the stimulation in vitro by pyridoxal phosphate was similar for the two groups. Plasma α-amino nitrogen was slightly lower in the oral contraceptive agent users than in the nonusers, but the difference was not statistically significant. The rise in blood vitamin B6 in response to pyridoxine was similar in the two groups, but the rise in plasma pyridoxal phosphate tended to be lower in the oral contraceptive agent treated subjects. Following pyridoxine supplementation, the basal activity of erythrocyte glutamic oxalocetic transaminase increased (P < 0.01) in both groups of subjects and the stimulation in vitro by pyridoxal phosphate decreased correspondingly. Plasma tryptophan and α-amino nitrogen were unaffected by the supplementary pyridoxine.