American Journal of Clinical Nutrition, Vol 24, 297-303, Copyright © 1971 by The American Society for Clinical Nutrition, Inc.

Oral contraceptives and vitamin B₆ metabolism

¹ Department of Environmental Medicine, State University of New York, Downstate Medical Center, Brooklyn, New York 11203
² Associate Professor, School of Household Economics, University of Alberta, Edmonton 7, Alberta, Canada
³ Present address: Department of Pediatrics, Dalhousie University, Halifax, Nova Scotia, Canada

Five young women who were taking oral contraceptive pills, and five young women who were not, consumed a diet of known composition for 6 days. On the morning of the 6th day a fasting blood sample was taken, followed by the administration of a 2-g load dose of l-tryptophan. Continuous 24-hr urine samples were collected and composited so that days 1-4 were pooled, whereas samples from day 5 and day 6 were considered to be the preload sample and the postload sample. Urine was analyzed for XA, KA, K, and OH-K, and for vitamin B₆. The fasting blood sample was analyzed for plasma amino acid levels and the amount of GOT and GPT in the erythrocytes.

The levels of the tryptophan metabolites excreted on days 1-4 compared with that collected on day 5 were not statistically different for either the control or experimental group. Urinary XA increased after taking the dose of tryptophan in both the control and experimental subjects and this increase was significant at a P < 0.001 for the experimental group. Increases were also noted posttryptophan for KA and K again for both groups of subjects. The higher levels of tryptophan metabolites observed preload in the control subjects have been attributed to the effect of endogenous steroid production as the load dose was administered at the point of ovulation. It has been postulated that the greater affinity of the transaminase enzymes for vitamin B₆ than that of the kynureninase enzymes might account for the increased amounts of XA and KA in the experimental subjects. The excretion of OH-K was similar in both groups.

The excretion of vitamin B₆ in the urine was not significantly changed throughout the study. The slight decrease noted posttryptophan could be an adaptation of subjects to a diet containing slightly less vitamin B₆ than in the usual diet consumed.

The levels of the essential amino acids in the plasma of the experimental subjects were significantly lower for phenylalanine and methionine compared with control subjects. There was no significant difference between groups for the levels of threonine, lysine, leucine, or isoleucine, although the levels of lysine, leucine, and isoleucine were lower for the experimental subjects.

The levels of the nonessential amino acids analyzed, except histidine and aspartic acid, were lower in the experimental subjects compared with control subjects. This difference was highly significant for glycine, proline, arginine, and tyrosine.

The total essential amino acids were not significantly different between groups but the total nonessential amino acids were significant at a P < 0.002.

The GOT levels in the red blood cell were statistically higher in the experimental group than the control group. This difference was also evident when the enzyme system was activated by the in vitro addition of pyridoxal phosphate. The GPT levels in the erythrocyte were the same for both groups.

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