Effect of oral contraceptives on the plasma concentration of pyridoxal phosphate

Abstract

The plasma concentrations of pyridoxal phosphate (PLP) in 55 women who had been using oral contraceptive agents (OCA) for 6 months or more were compared with those of 77 nonusers. The PLP content was assayed enzymatically with tyrosine decarbosylase apoenzyme. Mean PLP of OCA users 7.8 plus or minus 3.7 ng/m1 was significantly lower than that for the controls 9.4 plus or minus 4.2 ng/m1 (p less than .05). Mean PLP of OCA users was significantly lower than controls in the 25-29 and 30-34 year age groups (p less than .001 and p less than .02 respectively). 10 subjects were followed sequentially from 2 weeks before OCA therapy for a duration of 3 months or more. There was a decrease in PLP in 9 of the subjects within 3 months followed by a return toward pretreatment levels in most of the subjects by 6 months. Tryptophan load tests were done concurrently with PLP measurements in 15 OCA users and 6 nonusers. In nonusers of comparable age (20-25) the xanthurenic acid (XA) excretion was 27.1 plus or minus 5.7 mcmoles/8hours. 11 of 15 OCA USERS HAD ELEVATED XANTHURENIC ACID EXCRETION (LESS THAN 38.5 15 OCA USERS HAD ELEVATED XANTHURENIC ACID EXCRETION (38.5 MCMOLES/8HOURS) BUT plasma PLP was less than 4.7 ng/m1 in only 4 of them. These results are consistent with the view that OCA induce an increased requirement for pyridoxine hydrochloride (vitamin B6). Although the majority of OCA users can correct the relative deficiency state naturally a substantial number remain deficient suggesting the need for vitamin B6 supplementation.