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Changes in Pyridoxal Phosphate and Pyridoxamine Phosphate in Blood, Liver and Brain in the Pregnant Mouse¹

David Furth-Walker^*, David Leibman^* and Andrew Smolen^*,,2

^* Institute for Behavioral Genetics School of Pharmacy, Molecular and Environmental Toxicology Program, University of Colorado, Boulder, CO 80309-0447

A decrease in plasma pyridoxal-5'-phosphate (PLP) occurs during pregnancy in humans and experimental animals for reasons that are not known. To determine if mice also develop decreased plasma PLP concentrations during pregnancy, and if plasma PLP levels in pregnancy reflect tissue levels of PLP and pyridoxamine-5'-phosphate (PMP), we measured PLP concentrations in plasma, erythrocytes and whole blood, and liver and brain PLP and PMP in control and pregnant mice. Mice were fed a nonpurified diet containing 8.13 mg pyridoxine-HCl/kg. The PLP analyses were performed with our newly developed apotryptophanase method in which the substrate S-benzyl-L-cysteine is hydrolyzed to benzyl mercaptan, reacted with Ellman's reagent and measured spectrophotometrically. During pregnancy, plasma PLP levels decreased 50% below control levels, but erythrocyte and whole blood PLP levels increased 2.9- and 1.6-fold, respectively. Liver PLP and PMP decreased 25%, in parallel with plasma PLP, but brain PLP and PMP concentrations were unchanged during pregnancy. These results suggest that metabolism or utilization of vitamin B-6 is altered in pregnancy, and that plasma PLP concentrations alone may not be a good indicator of nutritional status in pregnancy.

KEY WORDS: • pregnancy • vitamin B-6 • apotryptophanase • mice • pyridoxal-5'-phosphate • pyridoxamine-5'-phosphate

¹ Supported by grants from the National Institute of Child Health and Human Development, HD 21709, and the National Institute of Neurological and Communicative Disorders and Stroke, NS 20748.

² To whom correspondence should be sent.

Manuscript received 26 September 1988. Revision accepted 14 February 1989.