Changes in pyridoxal phosphate and pyridoxamine phosphate in blood, liver and brain in the pregnant mouse

Direct and Functional Biomarkers of Vitamin B6 Status

Measures of B6 status are categorized as direct biomarkers and as functional biomarkers. Direct biomarkers measure B6 vitamers in plasma/serum, urine and erythrocytes, and among these plasma pyridoxal 5'-phosphate (PLP) is most commonly used. Functional biomarkers include erythrocyte transaminase activities and, more recently, plasma levels of metabolites involved in PLP-dependent reactions, such as the kynurenine pathway, one-carbon metabolism, transsulfuration (cystathionine), and glycine decarboxylation (serine and glycine). Vitamin B6 status is best assessed by using a combination of biomarkers because of the influence of potential confounders, such as inflammation, alkaline phosphatase activity, low serum albumin, renal function, and inorganic phosphate. Ratios between substrate-products pairs have recently been investigated as a strategy to attenuate such influence. These efforts have provided promising new markers such as the PAr index, the 3-hydroxykynurenine:xanthurenic acid ratio, and the oxoglutarate:glutamate ratio. Targeted metabolic profiling or untargeted metabolomics based on mass spectrometry allow the simultaneous quantification of a large number of metabolites, which are currently evaluated as functional biomarkers, using data reduction statistics.

Preliminary evidence of reduced occipital GABA concentrations in puerperal women: a 1H-MRS study

RATIONALE

Childbirth is associated with rapid neuroendocrine fluctuations, which are thought to contribute to the phatogenesis of postpartum major depression (PPD).

OBJECTIVES

The aim of this proton magnetic resonance spectroscopy (1H-MRS) study was two-fold; 1) to examine whether puerperium is associated with alterations in occipital cortex gamma-aminobutyric acid (GABA) concentrations and 2) to determine whether such alterations may be more prominent in women with PPD.

MATERIALS AND METHODS

Nine women with PPD, 14 postpartum healthy controls, and ten healthy follicular phase females underwent 1H-MRS at 2.1 Tesla to measure occipital cortex GABA concentrations. Postpartum women were scanned within 6 months of delivery and prior to resumption of menstruation. Healthy non-puerperal controls, drawn from a historical sample, were scanned during the early to mid-follicular phase when ovarian hormone levels would be similar to those found in the puerperium. GABA data were analyzed using analysis of covariance, and regression models were used to explore the relationship between cortical GABA concentrations and blood levels of estradiol, progesterone, and neurosteroids.

RESULTS

Cortical GABA and plasma allopregnanolone (ALLO) concentrations were reduced in both groups of postpartum women, regardless of PPD diagnosis, compared to healthy follicular phase women. There was no correlation between cortical GABA concentrations and estradiol, progesterone, ALLO, or pregnenolone (PREG).

CONCLUSIONS

This study is the first to describe reductions in occipital cortex GABA levels in the postpartum period, a time of increased vulnerability to mood disturbances in women. The concomitant reduction in peripheral ALLO levels provides further evidence of alterations in the balance between cortical excitation and inhibition during the puerperium. Women with PPD may represent a subgroup of women who fail to adequately adapt to this alteration in the neuroendocrine milieu.

Vitamin B6 deficiency and dietary fats: effects on lipid composition and glutathione peroxidase activity in rat liver

Dietary selenium, vitamin B6 and fatty acids modulate both tissue acyl composition by regulating polyunsaturated fatty acid metabolism and antioxidant defences by influencing glutathione peroxidase activity. Alteration in the intake of one of them could therefore lead to different results depending on the intake of the others. To clarify this complex relationship, in the present study we have evaluated the modifications occurring in fatty acid composition and glutathione peroxidase activity in total liver and liver microsomes of rats fed diets containing the same amount of selenium, but different vitamin B6 content and fatty acid composition. Our data indicate that both acyl composition and glutathione peroxidase activity are greatly influenced not only by vitamin B6 deficiency, but also by the diet unsaturation degree. This study underlines that not only selenium availability but also other nutrients can modulate glutathione peroxidase activity.

Correlation between dietary polyunsaturated fatty acids and plasma homocysteine concentration in vitamin B6-deficient rats

BACKGROUND AND AIM

Vitamin B6 as cofactor of Delta6 desaturase is involved in polyunsaturated fatty acid metabolism; moreover, it is a cofactor of the trans-sulfuration pathway of homocysteine. Some studies report that low concentrations of pyridoxine, by increasing homocysteine levels, are associated with coronary artery disease, and carotid and arterial lesions. The aim of this study was to verify whether different dietary amounts of polyunsaturated fatty acids associated with low content of vitamin B6 could modulate homocysteinemia.

METHODS AND RESULTS

Thirty-two rats were divided into two groups, one fed a diet with adequate vitamin B6 content the other a diet containing low amount of the same vitamin. Within each group, rats were divided into two subgroups differing in the polyunsaturated fatty acid content of the diet (63 and 33%, respectively). The vitamin B6-deficient diet induced an increase in homocysteine concentration compared to the vitamin B6-normal diet. This increase was tenfold in the subgroup fed high polyunsaturated fatty acid levels and twofold in the other subgroup. The fatty acid composition of liver phospholipids showed a lower arachidonic acid relative molar content and a lower 20:4/18:2 ratio in vitamin B6-deficient groups compared with B6-normal groups.

CONCLUSIONS

On the basis of the different biological functions of pyridoxine and considering that some factors closely related to atherosclerosis are vitamin B(6) dependent, adequate pyridoxine availability could be necessary to assure a normal long chain fatty acid metabolism and to reduce the risk linked to hyperhomocysteinemia.

Vitamin B6 deficiency decreases the glucose utilization in cognitive brain structures of rats

The effects of vitamin B(6) deficiency on metabolic activities of brain structures were studied. Male Sprague-Dawley weanling rats received one of the following diets: (1) 7 mg pyridoxine HCl/kg (control group); (2) 0 mg pyridoxine HCl/kg (vitamin B(6)-deficient group); or (3) 7 mg pyridoxine HCl/kg with food intake restricted in quantity to that consumed by the deficient group (pair-fed control group). After 8 weeks of dietary treatment, rats in all three groups received an intravenous injection of 2-deoxy-[(14)C] glucose (100 microCi/kg). Vitamin B(6) status was evaluated by plasma pyridoxal 5'-phosphate concentrations. The vitamin B(6)-deficient group had significantly lower levels of plasma pyridoxal 5'-phosphate than did the control and pair-fed groups. The local cerebral glucose utilization rates in structures of the limbic system, basal ganglia, sensory motor system, and hypothalamic system were determined. The local cerebral glucose utilization rates in each of the four brain regions in the deficient animals were approximately 50% lower (P < 0.05) than in the control group. Results of the present study suggest that serious cognitive deficit may occur in vitamin B(6)-deficient animals.

Effects of different dietary amounts of LCPUFA n3 and vitamin B6 on lipid composition and antioxidant defences in rat kidney

Our previous report demonstrated that, when vitamin deficiency is associated with high contents of long chain polyunsaturated fatty acids (LCPUFA) n3, lipid peroxidation susceptibility in rat heart and liver increases. In this paper, we evaluated the effect of the same dietary administration on lipid composition and antioxidant defenses of rat kidney. Results showed that vitamin B(6) deficiency, when associated with a fish oil diet, as compared to vegetable oil condition, increased relative kidney weight and decreased pyridoxal-5P contents. The different LCPUFA n3 dietary contents produced, on kidney phospholipids, effects interlaced with those of vitamin B(6) deficiency; in particular fish oil and vitamin B(6) deficient diet caused a significant decrease of arachidonic acid showing that the processes of elongation and desaturation of linoleic acid were slowed. Also, peroxidation susceptibility was higher, as demonstrated both by increased TBARS formation and glutathione peroxidase activity, and by decreased vitamin E contents and reduced glutathione/oxidized glutathione ratio.

Renal calcium phosphate and oxalate deposition in prolonged vitamin B6 deficiency: studies on a rat model of urolithiasis

OBJECTIVE

To determine the effect on kidney oxalate-salt deposition of a prolonged diet which induced vitamin B6 deficiency in adult rats, as there are reports of the pathogenic involvement of vitamin B6 deficiency in the formation of renal calcium oxalate calculi.

MATERIALS AND METHODS

The study comprised 24 6-month-old male albino Wistar rats; 12 were fed with a purified vitamin B6-deficient diet and the others provided with the same diet but supplemented with 6 mg/kg of vitamin B6. After 12 weeks, all rats were killed, and their kidneys fixed in formalin and routinely processed to paraffin for morphological examination; some fragments were fixed in glutaraldehyde and prepared for ultrastructural examination. From each rat consecutive sections of both kidneys were cut and stained with haematoxylin and eosin, periodic-acid Schiff, Sirius red and the Von Kossa method for calcium. Sections were examined in polarized light and by electron microscopy.

RESULTS

The histopathological and ultrastructural features of the kidney of vitamin B6-deficient rats were those of tubular-interstitial nephritis, characterized by tubular atrophy, interstitial fibrosis and chronic inflammatory infiltration. Oxalate and phosphate crystals were present in the papillary and parenchymal connective tissue. Ultrastructural features confirmed severe tubular epithelial lesions and the presence of an interstitial and intraepithelial inflammatory infiltrate; there was mild interstitial fibrosis. None of these features were apparent in the kidney of control rats.

CONCLUSIONS

Histopathological and ultrastructural data indicate that a prolonged vitamin B6-deficient diet may contribute to the formation and deposition of calcium phosphate and oxalate crystals, which lead to severe damage of the renal parenchyma. This phenomenon may occur not only in growing rats, which have more active protein metabolism and consequently higher vitamin B6 requirements, but also in adult rats.

Effects of short-term dietary administration of marginal levels of vitamin B(6)and fish oil on lipid composition and antioxidant defences in rat tissues

Previous reports have shown that vitamin B(6)deficiency leads to peroxidative stress in rat organs. In this paper, we evaluated the effects on lipid peroxidation of short-term (six weeks) dietary administration of marginal contents of vitamin B(6). A further risk factor of susceptibility to peroxidation was the presence of fish oil with higher contents of n-3 polyunsaturated fatty acid (LCPUFA). The contemporaneous vitamin B(6)deficiency and presence of fish oil caused a C18:2 increase, a C20:4 decrease, and replacement of some n-6 LCPUFA with n-3 LCPUFA, without changes in the unsaturation index. In liver, TBARS production did not show any differences between dietary conditions, whereas the activities of glutathione-dependent enzymes were stimulated. In heart, fish oil increased lipid peroxidation, especially in the vitamin B(6)-deficient group.

Relationships between Pregnancy and Vitamin B-6 Nutriture on Brain 3-Hydroxykynurenine Concentrations in Mice

The kynurenine (KYN) pathway of tryptophan metabolism produces several neuroactive metabolites, including 3-hydroxykynurenine (3HK). The pathway is subject to regulation by a number of effectors including pregnancy and availability of vitamin B-6. Vitamin B-6 depleted humans and animals excrete abnormally high concentrations of KYN metabolites in urine. In pregnancy, vitamin B-6 deficiency is commonly seen, and tryptophan metabolism is often found to be altered. We measured concentrations of 3HK in brains of DBA/2Ibg and A/Ibg mice as functions of pregnancy and dietary level of vitamin B-6. Pregnant DBA mice are more susceptible to flurothyl-induced seizures than controls, pregnant A mice are not. Significant elevations of 3HK were found in brains of pregnant mice, and the increases were greater in the pregnancy-associated seizure prone DBA, than in the A mice. In the A mice, brain 3HK concentrations were negatively correlated with dietary vitamin B-6 levels, as expected; however, in the DBA mice these correlations were positive, indicating an unusual response to vitamin B-6 restriction. The accumulation of a cytotoxic, excitatory metabolite, 3HK, in brain may contribute to the increased seizure susceptibility of susceptible pregnant mice, perhaps though its effects as an endogenous modulator of excitatory amino acid receptor systems.

The influence of dietary restriction on vitamin B-6 vitamer distribution and on vitamin B-6 metabolizing enzymes in rats

OBJECTIVE

The purpose of this study was to assess the effect of dietary restriction on tissue distribution of vitamin B-6 vitamers and activities of vitamin B-6 metabolizing enzymes in rats.

METHODS

Male rats were subjected to a 40% dietary restriction for 10, 20 or 40 weeks. The tissue vitamin B-6 vitamer concentrations and activities of the vitamin B-6 metabolizing enzymes of the animals were determined.

RESULTS

The plasma pyridoxal 5'-phosphate (PLP) concentrations of the diet-restricted (DR) rats were comparable to those of the control group at week ten but were significantly lower at weeks 20 and 40. These significantly lower levels of plasma PLP in DR rats might in part be related to lower hepatic pyridoxal kinase and pyridoxamine (pyridoxine) 5'-phosphate oxidase activities. The urinary 4-pyridoxic acid excretion of the DR groups responded to the reduced food intake and were lower at weeks 10 and 20. Tissue levels of PLP were not affected by dietary restriction. In contrast, greater levels of pyridoxamine 5'-phosphate were found in liver, kidney and heart of the DR animals.

CONCLUSION

The duration of dietary restriction influenced the distribution of vitamin B-6 vitamers. When plasma PLP is used to evaluate vitamin B-6 status, the length of dietary restriction should be considered.

Restoration of rat liver L-threonine dehydratase activity by pyridoxamine 5'-phosphate: the half-transaminating activity of L-threonine dehydratase and its regulatory role

When a highly purified preparation of rat liver l-threonine deaminase (l-TDH, EC 4.2.1.16) was 99% inactivated by dialysis, removing bound pyridoxal 5'-phosphate (PLP), the apoenzyme was reactivated not only by PLP but also by pyridoxamine 5'-phosphate (PMP). When purified by HPLC, the commercial PMP used in the incubation mixture was found to contain only extremely small amounts of PLP, which could not account for restoration of l-threonine dehydratase activity. HPLC analysis of the assay mixtures showed that during incubation, sufficient PLP had been formed for reactivation of the apoenzyme. The apoenzyme evidently bound PMP and triggered transamination between PMP and the keto acids, which either contaminated, or were formed by the minimal amount of PLP-holoenzyme always present even in the dialyzed preparation. When sufficient PLP was formed, the PLP-holoenzyme and the original 'true' l-threonine dehydratase activity were restored. When PMP was incubated with the apoenzyme in the presence of small quantities of keto acids (pyruvate or 2-oxobutyrate) small amounts of l-alanine or l-aminobutyrate were formed. The reaction was not reversible; l-alanine and l-aminobutyrate did not react with the PLP-holoenzyme. No transaminating activity occurred with other amino acids. These results show that l-threonine dehydratase exists in two forms: the well known stable apoenzyme-PLP (hydrolase deaminating) and the transient apoenzyme-PMP (non-reversible half-transaminating). Half-transamination has the biological role of keeping the activity of the 'true' l-TDH constant and of regulating intracellular levels of pyruvate, alanine, oxobutyric acid, l-aminobutyric acid, l-threonine and l-serine.

Dual influence of aging and vitamin B6 deficiency on delta-6-desaturation of essential fatty acids in rat liver microsomes

Delta-6-desaturase (D6D) activity is influenced by many nutritional and non-nutritional factors, among which one of the most important is aging. D6D activity could be susceptible to the dual influence of aging itself and of nutritional deficiencies, due to the reduced intake and/or absorption of essential nutrients. Particularly, vitamin B6 deficiency might be a crucial factor for D6D activity in aged people. Using 20 month old Sprague-Dawley rats fed a diet with a subnormal level of vitamin B6, we evaluated D6D activity for linoleic acid (LA) and alpha-linolenic acid (ALA) in liver microsomes, and the fatty acid composition of microsomal total lipids. We observed a diminished D6D activity for LA and also for ALA in vitamin B6-deficient animals, being approximately 63% and 81% respectively of the corresponding activity in control rats. As a consequence, significant modifications in the relative molar content of microsomal fatty acids were observed. The content of arachidonic and docosahexaenoic acid, the main products of the conversion of LA and ALA respectively, decreased, LA content increased and a decrease in the unsaturation index was observed in liver microsomes of B6-deficient rats. The foregoing results suggest that the impairment of D6D activity by vitamin B6 deficiency might be an important factor in decreasing the synthesis of n-6 and n-3 PUFAs. This may be particularly important in aging, where D6D activity is already impaired.

Chronic exercise affects vitamin B-6 metabolism but not requirement of growing rats

The effect of chronic exercise (forced swimming) on vitamin B-6 status and metabolism was studied in growing male rats fed deficient (0 mg pyridoxine-HCl/kg), suboptimal (2 mg pyridoxine-HCl/kg) or control (7 mg pyridoxine-HCl/kg) diets for 9 wk. Sedentary rats were fed the same diets. Body weight gain was lower in deficient rats than in both other dietary groups. Sedentary rats were heavier than trained rats of all diet groups. Erythrocyte aspartate aminotransferase, urinary 4-pyridoxic acid excretion, blood (plasma and erythrocytes) and tissue B-6 vitamers were measured. Urinary 4-pyridoxic acid, plasma pyridoxal 5'-phosphate and erythrocyte aspartate aminotransferase values of exercised and sedentary rats responded to changes in dietary pyridoxine but were not different from one another. After 9 wk of vitamin B-6 depletion, tissue concentrations of pyridoxal 5'-phosphate and pyridoxamine 5;5'-phosphate were 41-66% and 26-49% lower, respectively, in the deficient groups than in the control groups. Larger percentage differences occurred in plasma than in tissues (95 vs. 22-66%). In liver, pyridoxal 5'-phosphate concentrations were lower, whereas pyridoxal concentrations were higher in trained than in sedentary rats. In gastrocnemius muscle, pyridoxal 5'-phosphate, pyridoxamine 5'-phosphate and total vitamin B-6 concentrations were higher in trained than in sedentary rats. Concentrations of vitamin B-6 compounds in heart, kidneys, brain and adrenals were not affected by training. On the basis of the vitamin B-6-dependent variables measured in this study, we conclude that prolonged exercise affects the metabolism of vitamin B-6, but does not increase the vitamin B-6 requirement in growing rats.

Response of kynurenine pathway enzymes to pregnancy and dietary level of vitamin B-6

The kynurenine pathway of tryptophan metabolism produces several neuroactive metabolites including 3-hydroxykynurenine, kynurenic acid, and quinolinic acid. This pathway is sensitive to reductions in vitamin B-6 availability because two key enzymes, kynurenine aminotransferase (KAT) and kynureninase (KYNase), require pyridoxal 5'-phosphate. During pregnancy abnormal concentrations of kynurenine metabolites are also found. We measured the effects of pregnancy and vitamin B-6 availability on KAT and KYNase in liver. DBA/2Ibg and A/Ibg mice were fed diets containing 0.25, 0.5, 2.0, 3.6, or 7.0 mg/kg pyridoxine-HCl (PN-HCl) for 4 weeks. Mitochondrial KAT and cytosolic KYNase were measured in control mice and pregnant mice on gestational days 16-18. The response of the two inbred strains was similar throughout. There were no marked alterations in KAT activity as a function of diet or pregnancy. In contrast, KYNase activities were significantly reduced by dietary restriction of vitamin B-6, and pregnant mice had significantly lower activity than nonpregnant controls for all but the highest dietary level of PN-HCl. These data show that pregnancy has a more pronounced effect on KYNase activity than vitamin B-6 restriction, and that the effects of pregnancy and diet are additive. The alteration in the kynurenine pathway in pregnancy is due to a reduction in KYNase activity, which is resistant to alleviation by vitamin B-6 supplementation.

Aminotransferase activities in mouse, Mus domesticus, erythrocytes separated according to age

Erythrocyte aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities are often used as indices of vitamin B-6 nutritional status; however, results using a mixed population of erythrocytes can be quite variable. Erythrocytes from two strains of mice (Mus domesticus), A/Ibg and DBA/Ibg, were separated according to age by centrifugation through discontinuous Percoll density gradients into three fractions: top (least dense, youngest), middle and bottom (most dense, oldest). A sufficient yield of age-fractionated erythrocytes was obtained from a single mouse for all of the enzyme measurements. The activities of AST, ALT and three age-marker enzymes, pyruvate kinase, acetylcholinesterase and hexokinase, were found to be significantly higher in the youngest cell fractions, and declined in the older, more dense fractions. A mice had significantly lower AST and ALT activities in the age separated fractions than did DBA mice. The measurement of enzyme activities in low density, young cells may be especially useful in studies involving conditions in which the proportion of young erythrocytes may be elevated with respect to the entire erythrocyte mass.

Alterations in regional brain GABA concentration and turnover during pregnancy

During pregnancy, mice are more susceptible to flurothyl-induced seizures than are nonpregnant control mice. The potential role of brain GABA in mediating this behavior was examined in the present study. GABA concentrations in the cerebellum, hippocampus, striatum, midbrain, and cortex from individual control, pregnant (days 17-18) and delivery-day Heterogeneous Stock mice were assayed using a fluorometric method. Turnover of GABA was assessed by inhibiting metabolism with aminooxyacetic acid and measuring GABA accumulation over the next 2 h. Steady-state GABA concentrations decreased significantly from control in all brain regions during pregnancy. Reductions in GABA concentrations were approximately 25-30% in the affected regions. At parturition, GABA concentrations in the cerebellum and cortex returned to control levels, but hippocampal, striatal, and midbrain GABA levels remained significantly depressed. All the indices of GABA turnover--first-order rate constant, half-life, initial rate of synthesis, and turnover rate (product of first-order rate constant and initial concentration)--showed a significant reduction in pregnancy, which was continued through the time of delivery in all brain regions except the hippocampus. Half-life values for GABA increased nearly fourfold in the cerebellum and cortex. These results show that there is a significant alteration in GABAergic systems during pregnancy and parturition. We suggest that the reduction in GABA turnover is a compensatory anticonvulsant mechanism to offset the inherent seizure susceptibility brought about by the reduced level of the major inhibitory neurotransmitter in the brain.

Strain, sex and developmental profiles of cocaine metabolizing enzymes in mice

Cocaine is a potent hepatotoxin in laboratory mice, although the cocaine-induced hepatotoxicity (CIH) is due to the action of a metabolite of cocaine. Cocaine can be hydrolyzed by serum cholinesterase (ChE) to inactive products, or be oxidized by hepatic cytochrome P-450 and FAD-containing monooxygenase (FADM). The oxidative pathway is thought to be responsible for production of the hepatotoxic metabolite of cocaine, presumably norcocaine nitroxide. Female mice are much more resistant to CIH than males of the same strain. We have found that immature male mice are as resistant as females to the development of CIH. Males did not show any CIH until the onset of puberty (30 days of age), indicating that the development of CIH in males was under hormonal control. To determine if the major cocaine-metabolizing enzymes were responsible for the regulation of CIH, we measured the activities of ChE, cocaine N-demethylation (CND) and FADM as a function of sex in C57BL/6Ibg and DBA/2Ibg mice 20-21, 30 +/- 1 and 65 +/- 5 days of age. There was a significant sex difference in ChE activity (females higher than males) but no effect of age. Cocaine N-demethylation increased in both males and females with age, but there was no consistent sex difference. Activity of FADM declined in males as a function of age, but remained constant in females. The lack of a consistent correlation between enzyme activities and sex-, strain-, and age-dependent differences in susceptibility to CIH, do not support a regulatory role for ChE, CND or FADM in mediating the hepatotoxic response.

Developmental expression of cocaine hepatotoxicity in the mouse

Cocaine may be metabolized either by ester hydrolysis to inactive products or by oxidation via a cytochrome P-450 and FAD-monooxygenase pathway to a hepatotoxic metabolite, presumably norcocaine nitroxide. Mice are the species most susceptible to cocaine-induced hepatotoxicity (CIH), and marked strain differences in response have been found. Female mice are very resistant to CIH, whereas males are susceptible, indicating that hormonal factors may be involved. We treated mice of 5 inbred strains with cocaine at three ages: 20 days (weanling), 30 days (adolescent) and 60 days (adult). The CIH response was assessed by measurement of plasma alanine aminotransferase (ALT) activity 18 hours later. For each of the strains females of all three age groups were resistant to CIH, and males did not begin to develop CIH until approximately 30 days of age. The degree of CIH in 30-day-old males was intermediate between the levels found in 20-day-old males and adult males. These data suggest that the enzyme, or enzymes, responsible for the production of the toxic metabolite are absent, or at very low levels, in female and immature male mice, and that they are either inducible by androgens or are repressed by estrogens or progestins. It is possible that these enzymes may be involved in the production of toxic metabolites of compounds other than cocaine.

Pyridoxal 5'-phosphate and pyridoxamine 5'-phosphate concentrations in blood and tissues of mice fed ethanol-containing liquid diets

The effects of chronic ethanol administration on vitamin B-6 metabolism were studied in female Long-Sleep (LS) and Short-Sleep (SS) mice. Animals were fed an ethanol containing liquid diet (AIN-76) for four weeks. Concentration of ethanol in the diet increased from 10 to 25% ethanol-derived calories (EDC) during weeks 1-3 and was maintained at 30% EDC for 1 additional week. We measured concentrations of pyridoxal 5'-phosphate (PLP) in plasma, erythrocytes and whole blood, and liver and brain PLP and pyridoxamine 5'-phosphate (PMP) in ethanol-fed and pair-fed control mice. Chronic ethanol administration significantly increased PMP and total (PLP + PMP) levels in the liver of SS mice. In LS mice ethanol feeding significantly decreased PMP and total (PLP + PMP) levels in the brain, but these values were still within normal limits. These results suggest that both control and ethanol-containing liquid diets are nutritionally adequate with respect to vitamin B-6, and that chronic ethanol administration does not adversely affect vitamin B-6 metabolism in adult mice.