A depletion-repletion folate bioassay based on growth and tissue folate concentrations of rats

To improve standardization of a folate bioassay, folate-depleted rats were repleted with a folate-free amino acid-based diet supplemented with 29 levels of folic acid. Growth was the main response variable and body tissue folate concentrations were also assessed. Because a positive correlation was observed between low levels of dietary folic acid and growth and little or no correlation was observed between high levels and growth, six regression models with a steep slope for low levels and a shallow or zero slope for high levels of dietary folic acid were evaluated. The model referred to as the "two-phase regression" or "change-point" model best described the relationship. Depleted rats needed 674 +/- 71 nmol folic acid/kg diet to reach their full growth potential. This value is biologically sensible, and this regression model is well established in the statistical literature. The change-point model is highly recommended to characterize the growth response, because growth is a functional response and, in the range of 226 to 680 nmol folic acid/kg, this response is linear, which is an additional advantage. Linear responses are easier to interpret because of complicated issues of interpretation and confidence intervals with nonlinearities. Linear regressions described serum and liver folate responses, whereas exponentials described whole blood and carcass folate responses. Depleted rats needed 5920 and 5780 nmol folic acid/kg diet to maximize their whole blood and carcass folates, respectively.

Analysis of milk-based infant formula. Phase V. Vitamins A and E, folic acid, and pantothenic acid: Food and Drug Administration-Infant Formula Council: collaborative study

In 1982, the U.S. Food and Drug Administration, the Infant Formula Council and its member companies, contract laboratories, and other government laboratories began a study of analytical methods for the nutrients listed in the Infant Formula Act of 1980 (P.L. 96-359). Four phases of the study have been completed and are discussed in earlier reports. The present report provides data on Phase V, in which 13 laboratories collaboratively studied individual methods for folic acid, pantothenic acid, and vitamin E, in addition to 2 methods for vitamin A. Vitamins A and E are determined by liquid chromatography. Folic acid and pantothenic acid are determined by microbiological methods using acidimetric and/or turbidimetric assays as the determinative step. In most cases, relative standard deviations for repeatability, RSDr, and reproducibility, RSDR, are as good as those that would be predicted from other collaborative studies. RSDr and RSDR values obtained for the 5 methods are 9.35 and 25.44% for folic acid, 4.59 and 10.23% for pantothenic acid, 8.46 and 11.69% for vitamin E, 3.62 and 9.72% for vitamin A (retinol isomers), and 4.9 and 10.5% for vitamin A (retinol). The 5 methods have been adopted first action by AOAC International.

[Determination of the folic acid content of vegetables and fruits using high-performance liquid chromatography (HPLC)]

The folic acid content of vegetables (including potatoes) and fruits was determined by means of high-performance liquid chromatography (HPLC). Free folate (monoglutamate forms) and total folate (monoglutamate+polyglutamate forms) are differentiated. Vegetables contained 27-187 micrograms/100 g and fruits 10-80 micrograms/100 g total folate. The free folate portion ranged from 6.3% to 96.8% (mean 35%) in vegetables and from 11.6% to 89.0% (mean 56%) in fruits. In addition, the results of the quantification of the main folate derivatives tetrahydrofolic acid (THF), 5-methyltetrahydrofolic acid (5-CH3-THF) and 5-formyltetrahydrofolic acid (5-CHO-THF) are presented. The mean values were 70% 5-CH3-THF, 20% 5-CHO-THF and 10% THF. Their total, resulting from the addition of pteroylglutamate equivalences, is comparable with the results of microbiological methods reported in the tables of nutritive values.

A thin-layer chromatographic method to determine process impurities in leucovorin calcium

A densitometric thin-layer chromatographic method for the analysis of process impurities in leucovorin calcium was developed and validated. Using this method, folic acid, N10-formyldihydrofolic acid, p-aminobenzoic acid, and N-(4-aminobenzoyl)-L-glutamic acid were monitored with a limit of detection of approximately 0.1% each. Both absorbance and fluorescence densitometric evaluations were utilized; fluorescence evaluation selectively detected impurities that were not chromatographically resolved from leucovorin.

Effect of smoking on folate levels in buccal mucosal cells

The objective of the study was to document the existence of localized deficiency of folate in a tissue exposed to cigarette smoke, by analysis of oral and circulatory levels of this vitamin in smokers and non-smokers. Buccal mucosal cells and blood samples were collected from 25 smokers and 34 non-smokers. The Health Habits and History Questionnaire was completed by each subject. A 96-well plate L. casei assay, along with preincubation with a folate-free chick pancreas pteroyl-gamma-glutamyl hydrolase, was used to quantitate total buccal mucosal cell folates. The reproducibility (CV 5 to 7%) and recovery (95 to 106%) of the folate assay were satisfactory. Smokers had significantly lower buccal mucosal cell folate levels than did non-smokers. The mean plasma folate level of smokers although within normal limits, was also significantly lower than that of non-smokers. There were no significant differences in mean dietary folate intake or in alcohol consumption between the 2 groups. The strength of the positive association between smoking and plasma and buccal mucosal cell folate deficiency (by any definition) was moderate to strong and statistically significant. Our results indicate that cigarette smoking may result in a localized folate deficiency in buccal mucosal cells, independent of the plasma folate levels.

Methyl group metabolism in the pancreas of folate-deficient rats

Several studies have suggested that the metabolism of one-carbon compounds may have a special role in the function of the exocrine pancreas. An amino acid-defined diet was used to produce folate deficiency in a group of male rats. These rats were compared with a group of rats pair-fed the same diet supplemented with adequate folate and with a third group fed the folate-supplemented diet with ad libitum access. Pancreatic folate concentrations were already severely depleted after 4 wk of feeding the deficient diet (0.95 +/- 0.10, 5.81 +/- 0.29 and 4.58 +/- 0.30 nmol/g for the deficient, pair-fed control and ad libitum-fed control groups, respectively). The level of folate present in the pancreas of nondeficient animals was second only to that reported for liver. Urinary amylase excretion by animals in the deficient group was higher than that by the other groups (245.5 +/- 21.9, compared with 181.9 +/- 14.5 and 195.3 +/- 10.9 units/mg creatinine for the deficient, pair-fed control and ad libitum-fed control groups, respectively) after 4 wk. The ratio of S-adenosylmethionine to S-adenosylhomocysteine was 18.6 +/- 1.6 and 14.5 +/- 1.0 after 4 wk for the ad libitum-fed control and pair-fed control groups, respectively, but was significantly lower at 6.3 +/- 1.1 for the deficient group. These results indicate a profound effect of folate deficiency upon methyl group metabolism of the pancreas and suggest that this may result in decreased pancreatic function.

Vitamin B12 metabolism in multiple sclerosis

We have previously described 10 patients with multiple sclerosis (MS) and unusual vitamin B12 deficiency. We have therefore studied vitamin B12 metabolism in 29 consecutive cases of MS, 17 neurological controls, and 31 normal subjects. Patients with MS had significantly lower serum vitamin B12 levels and significantly higher unsaturated R-binder capacities than neurological and normal controls, and they were significantly macrocytic compared with normal controls. Nine patients with MS had serum vitamin B12 levels less than 147 pmol/L and, in the absence of anemia, this subgroup was significantly macrocytic and had significantly lower red blood cell folate levels than neurological and normal controls. Nine patients with MS had raised plasma unsaturated R-binder capacities, including three patients with very high values. There is a significant association between MS and disturbed vitamin B12 metabolism. Vitamin B12 deficiency should always be looked for in patients with MS. The cause of the vitamin B12 disorder and the nature of the overlap with MS deserve further investigation. Coexisting vitamin B12 deficiency might aggravate MS or impair recovery from MS.

Prevalence of folate deficiency in emergency department patients with alcohol-related illness or injury

To assess the prevalence of folate deficiency in emergency department patients with alcohol-related illness or injury, a prospective, nonconsecutive case series with nonrandomized controls was used. All patients presenting to a 60,000-visit public hospital emergency department with alcohol-related illness or injury were eligible; patients were excluded if they had received folate in our health care facility within the previous 4 months. An alcohol and brief dietary history was obtained, and a complete blood cell count and red blood cell folate level was performed on each patient. Analysis was undertaken by chi 2 to evaluate the prevalence of folate deficiency in the alcohol-related versus the control population. One hundred three patients were entered into the study. Three patients were subsequently excluded from analysis. Of 52 study patients, three (5.8%) were found to be folate deficient. Of 48 controls, two (4.2%) were found to be folate deficient. This difference is not statistically significant (P greater than .05, chi 2; mean difference 1.6%, 95% confidence interval -6.9% to 10.1%). The prevalence of folate deficiency in patients presenting to this emergency department with alcohol-related illness or injury is low, and does not differ from the general emergency department population. Empiric folate therapy in these patients is not indicated.

Phenytoin-folate interactions: differing effects of the sodium salt and the free acid of phenytoin

Chronic phenytoin (PHT) treatment has long been associated with folate deficiency. It has been suggested that pH changes in the gut associated with PHT ingestion may be responsible for decreased folate uptake either by direct inhibition of folate transport into the intestinal mucosa or by inhibition of folate conjugase activity. To examine these possibilities, rats were gavaged chronically with PHT using either the sodium salt (NaPHT) or the free acid (HPHT) in the presence of folic acid as the dietary source of folate. The NaPHT caused a greater depletion of folate in the liver and brain and a significant increase in methylenetetrahydrofolate reductase activity in the liver. The HPHT caused a significantly decreased weight gain over the 8 weeks of treatment and resulted in a much higher liver PHT concentration and a slightly lower plasma PHT concentration. These data support the hypothesis that PHT-induced changes in pH in the gut affect the enterohepatic circulation of folate.

Folate and vitamin B12 concentrations in maternal and fetal blood, and amniotic fluid in second trimester pregnancies complicated by neural tube defects

OBJECTIVE

To investigate maternal and fetal folate and vitamin B12 concentrations in pregnancies affected by neural tube defects (NTD).

DESIGN

Measurement of folate and vitamin B12 concentrations in amniotic fluid, fetal blood and maternal blood samples in midgestation.

SUBJECTS

32 women undergoing termination of pregnancy at 14-21 weeks gestation for social reasons (n = 24) or for fetuses with neural tube defects (n = 8).

INTERVENTIONS

Fetoscopy before intra-amniotic injection of prostaglandins.

RESULTS

In normal pregnancies there was a positive correlation between maternal and fetal serum folate, and the fetal serum and red blood cell folate concentrations were higher than the maternal. There were no differences in amniotic fluid, maternal blood or fetal blood folate concentrations between pregnancies with NTD and normal pregnancies. Although amniotic fluid vitamin B12 was lower in pregnancies with NTD, maternal serum vitamin B12 concentration was not reduced.

CONCLUSION

In this small group of pregnancies with NTD at mid-gestation there is no evidence to suggest folate or vitamin B12 deficiency.

Folate-deficient human lymphoblasts: changes in deoxynucleotide metabolism and thymidylate cycle activities

Peripheral blood lymphocytes of healthy volunteers cultured with phytohaemagglutinin in folate-deficient medium exhibit megaloblastic maturation with reduced intracellular folate content. We have employed this in vitro model for megaloblastic maturation to determine accompanying changes in cellular thymidylate cycle activities and deoxynucleotide levels. Folate-deficient cells exhibit a two-fold increase in thymidine kinase and thymidylate synthase activities. These increased activities were reduced to those of folate-replete cells by co-culture of folate-deficient cells with thymidine. Folate deficiency was accompanied by reduced cellular levels of thymidine triphosphate (TTP) and deoxyguanosine triphosphate (dGTP). Exogenous deoxyuridine produced no increase in the reduced levels of TTP of folate-deficient cells but effected a two-fold increase in cellular deoxycytidine triphosphate. Exogenous thymidine increased the reduced TTP levels of folate-deficient cells and corrected the reduced dGTP level; the increase in cellular TTP accompanying exogenous thymidine was more pronounced in folate-deficient cells. These in vitro findings are compatible with a block in de novo thymidylate synthesis and explain in part the reported in vivo changes for the deoxynucleotide pool in megaloblastic marrow cells due to folate or vitamin B12 deficiency.

[Intraerythrocyte folates and leukocytic neutrophil segmentation in macrocytosis in patients with liver disease]

The problem of macrocytosis above all concerns deficiences and the study of these aspects is particularly important in hepatopathic patients for therapeutic purposes. A state of deficiency can also be revealed in morphological terms by the assessment of the hypersegmentation of polymorphonucleate neutrophil leucocytes. In the group of hepatopathic patients included in the study there was no significant differences in vitamin B12 concentrations in comparison to normal values, whereas mean levels of serum folates were decreased, although still within the normal range. It is worth underlining that to evaluate vitamin B12 it is necessary to measure analogous inefficient components from a metabolic point of view and the assessment of serum folates is not important as an index of normal erythropoietic activity. To overcome this limitation, we assayed intraerythrocytic folates which are vitamin-B12-dependent and these too proved to be within the normal range. Leucocyte hypersegmentation was also excluded by evaluating the mean of PMN lobes. A clearly normal RDW was also observed in macrocytic anemia in hepatopathic patients and this may represent a further difference from hepatocytic macrocytosis.

Use of the deoxyuridine suppression test to evaluate localized folate deficiency in rat colonic epithelium

In this study the deoxyuridine suppression test (dUST) was performed on isolated rat colonocytes to establish its value as an indicator of folate status in the colonic epithelium. [3H]thymidine incorporation into DNA was suppressed greater than 90% by deoxyuridine (dU) concentrations greater than 2.5 mumol/L. Preincubation of cells with 5-fluorouracil (1-100 mumol/L) but not methotrexate (10-100 mumol/L) resulted in a significant decrease in the degree of suppression. The dUST performed on colonocytes from folate-deficient animals displayed less suppression than on colonocytes from folate-replete animals (P less than 0.05). The abnormal degree of suppression was corrected by adding 100 mumol folinic acid/L. There was a negative correlation between the degree of suppression and the folate concentration of the colonic epithelium (P less than 0.001). These data indicate that the dUST is useful for detecting folate deficiency in the colonic epithelium and may therefore be valuable in assessing a deficiency state localized to that epithelium.

Uridine enhances expression of the fragile X chromosome in human lymphocytes

We have studied the effect of uridine on the expression of fragile X (fra[X]) in lymphocyte cultures established in the folate and thymidine deficient medium TC199. The results indicate that uridine enhances the expression of fra(X) and gives a higher mitotic rate. The excess of uridine during DNA synthesis might further promote the previously suggested cycle of misincorporation and removal of deoxyuridine monophosphate when the pool of deoxythymidine triphosphate is continuously depleted.

Pteroylpolyglutamates in human milk

Considerable variation exists in reported values for total folate content and the pteroylpolyglutamate (PteGlun) content of human milk. We investigated possible methodological sources of this variation. In two laboratories, milk folate content (with and without folate conjugase) was determined microbiologically. No differences in total milk folate or PteGlun (n greater than 3) content were found between laboratories. PteGlun was found to comprise a significant fraction of total milk folate (28%). Use of rennin did not alter total folate content nor the percent of PteGlun in human milk. Heating (121 degrees C for 5 min) increased folate concentrations (190%, P less than 0.0001), indicating that release of folate from binding protein is necessary for folate utilization by Lactobacillus casei. Although human milk folate conjugase, (FC) activity was approximately one-twentieth that of plasma FC activity, it was not sufficient to autolyze endogenous PteGlun. Thus, microbiological protocols that do not use folate conjugase and do not release folate from binding proteins will seriously underestimate milk folate values.

Effects of a parenteral supplement of folic acid and its interaction with level of feed intake on hepatic tissues and growth performance of young dairy heifers

Forty-seven dairy heifers of approximately 10 d of age were assigned to a factorial experiment in which a supplement of folic acid (0 or 40 mg) administered weekly by i.m. injection and level of feed intake were the two factors studied. The heifers were weaned after 5 wk of experimentation. Following weaning, and until the end of the experiment, 11 wk later, they had ad libitum access to grass hay and concentrates at two different levels, ad libitum or restricted, to allow a body weight gain of 700 g/d. A supplement of folic acid (P less than .05) and ad libitum access to feed (P less than .05) increased the mean concentration of serum folates. Blood hemoglobin and packed cell volume were not affected by the level of feed intake. However, they were both increased (P less than .05) by the supplement of folic acid. Average daily gain was analyzed over three different periods: 0 to 5 wk (before weaning), 5 to 10 wk, and 10 to 16 wk. Average daily gain was increased by the supplement of folic acid during the second period (P less than .05) and by ad libitum access to feed during the last two periods (P less than .05). Ad libitum access to feed increased (P less than .05) weight of the liver, decreased the (P less than .05) concentrations of RNA and DNA, and increased (P less than .05) the ratios of protein/DNA and RNA/DNA. The supplement of folic acid decreased (P less than .05) weight of the liver and increased the ratio RNA/DNA (P less than .05). These effects of supplement of folic acid on growth performance and on hematological cells may reflect a lack of folic acid during the weeks after weaning.

Folate status assessment

This paper is a review of established methods of folate status assessment and the primary factors that increase the risk of folate deficiency, including physiological life cycle changes. The first stage of folate depletion can be assessed by measuring serum folate levels, which drop prior to tissue depletion, and which are paralleled by a reduction in red blood cell (RBC) folate. Functional changes associated with abnormalities in biochemical pathways can be monitored by the deoxyuridine suppression test. Cell division, including erythropoiesis, becomes impaired in the same time sequence as changes in biochemical functions, as evidenced by abnormal erythrocyte morphology and a reduction in hemoglobin concentration. In addition to inadequate dietary folate intake, key factors that may impair folate utilization and thus status include alcohol consumption, smoking, and specific drugs. Folate requirements may increase during various phases of the life cycle due to physiological stresses such as pregnancy and lactation. Folate status may also be compromised during adolescence and in senescence for diverse reasons that require special emphasis on factors such as biological maturity and socioeconomic status, as well as chronic use of alcohol, drugs, and smoking.

Interaction of gamma interferon and 5-fluorouracil in the H630 human colon carcinoma cell line

The antiproliferative effects and pharmacological interactions of 5-fluorouracil (5-FU) in combination with gamma interferon (IFN-gamma) were determined against the human colon carcinoma H630 cell line in vitro. H630 was 9-fold more resistant to 5-FU, as compared to a relatively sensitive human colon line (C1). IFN-gamma showed modest antiproliferative activity against the H630 line, with a 50% inhibitory concentration of 440 units/ml. Simultaneous treatment of H630 with subinhibitory concentrations of IFN-gamma and 5-FU produced a significant enhancement of the 5-FU-associated growth inhibition. The growth-inhibitory activity of the combination against H630 was prevented by the addition of 20 microM thymidine. Thymidylate synthase (TS) activity was measured by both the 5-fluoro-2'-deoxyuridine-5'-monophosphate binding and catalytic assays, using cytosolic extracts. A 24-h exposure to 1 microM 5-FU in the H630 line resulted in a 3.1-fold increase in the total amount of TS, while in the 5-FU/IFN-gamma-treated cells TS remained unchanged from non-drug-treated control levels. Moreover, we found that free thymidylate synthase in the 5-FU/IFN-gamma-treated cells was significantly decreased, as compared to the cells treated with 5-FU alone. Incorporation of 5-FU into both the RNA and DNA fractions did not change with the addition of IFN-gamma. Accumulation of the fluoropyrimidine metabolites 5-fluoro-2'-deoxyuridine-5'-monophosphate and 5-fluorouridine-5'-triphosphate remained the same for 5-FU alone and the combination treatment. These findings suggest that acute TS induction by 5-FU may provide an important mechanism by which human colon carcinoma cells express decreased sensitivity to 5-FU and that IFN-gamma can reverse the development of resistance to 5-FU in the H630 line by inhibiting the overexpression of TS that results from 5-FU exposure. These studies contribute to a growing understanding of the complex interaction between 5-FU and IFN-gamma.

Application of a tri-enzyme extraction for total folate determination in foods

A tri-enzyme digestion procedure using chicken pancreas conjugase, alpha-amylase, and Pronase was evaluated to determine its usefulness in the microbiological quantitation of total folate in foods. Folate values obtained by traditional conjugase digestion were compared to those obtained by the tri-enzyme method for 12 food products that represent diverse matrixes. The tri-enzyme treatment increased measurable folate from most foods when compared to levels found after conjugase digestion. Largest increases were noted for tuna fish (51%) and yogurt (33%) after tri-enzyme digestion. For the 12 foods, a mean increase of 19% in measurable folate was obtained with tri-enzyme treatment. The study shows that traditional conjugase treatment does not completely free folate from complex food matrixes before microbiological analysis. Further, as other investigations have suggested, current accepted methods for folate analysis may be underestimating folate levels in foods.

Methotrexate therapy in rheumatoid arthritis patients diminishes lectin-induced mononuclear cell proliferation

Methotrexate (MTX) is an anti-folate drug used in cancer chemotherapy because of its anti-proliferative effects. However, it is unclear whether the anti-proliferative effects of MTX contribute to the efficacy of low-dose MTX in the treatment of rheumatoid arthritis (RA). To date, either no change or a paradoxical increase in lectin-induced proliferation has been observed in cultures of peripheral blood mononuclear cells (PBMC) from MTX-treated RA patients (RA + MTX). In these earlier studies, high folate-containing media and tritiated thymidine (3H-TdR) were used. Our studies were designed to test the hypothesis that the use of a culture medium with a low folate content along with tritiated deoxyuridine (3H-UdR) permits detection of diminished phytohemagglutinin (PHA)-induced proliferative responses of PBMC from RA + MTX. The data demonstrate decreased PHA-induced cellular proliferation of cultured PBMC from RA + MTX compared with controls. When comparing the PBMC proliferative responses in high vs low folate medium, a significantly greater increase (P less than 0.05) in proliferation occurs in the cells from RA + MTX cultured in the high folate medium. This suggests that an in vivo folate-deficient state of the cells from RA + MTX may be corrected in vitro when a high folate medium is used in culture. We conclude that the use of 3H-UdR and a medium containing folate within the normal range of plasma folate levels eliminates artifacts associated with the use of high folate medium and 3H-TdR, which obscures the anti-proliferative effect of MTX in RA patients.

Interaction of methotrexate polyglutamates and dihydrofolate during leucovorin rescue in a human breast cancer cell line (MCF-7)

Previous investigations have suggested that high-dose methotrexate with leucovorin rescue is a potentially useful strategy for overcoming antifolate resistance. Interactions between methotrexate (MTX) and leucovorin and their respective metabolites appear to occur at multiple intracellular sites, including dihydrofolate reductase (MTX/MTX polyglutamates versus dihydrofolate) and other folate-dependent enzymes (MTX polyglutamates versus reduced folate substrates). The present studies were designed to test the ability of dihydrofolate to compete with methotrexate and methotrexate polyglutamates for dihydrofolate reductase activity using an intact human breast carcinoma cell line (MCF-7) as the model system. Exposure of the breast cells to methotrexate for 24 h resulted in a concentration-dependent formation of methotrexate polyglutamates that markedly exceeded the dihydrofolate reductase-binding capacity for up to 24 h after the removal of drug from the growth media. Under these conditions of dihydrofolate reductase inhibition, we found that tritium-labeled dihydrofolate was capable of competing with methotrexate and its metabolites for dihydrofolate reductase activity as evidenced by the appearance of tritium-labeled reduced folates in the treated cells. We found the interaction between dihydrofolate and methotrexate to be dependent on the exposure concentrations of both methotrexate and dihydrofolate. These studies provide direct evidence that competition during leucovorin rescue occurs at the level of dihydrofolate reductase between methotrexate polyglutamates and dihydrofolate polyglutamates in intact human cells.

Vitamin B12 and folate levels in long-term vegans

Serum vitamin B12, serum folate and red blood cell (RBC) folate levels were examined among 36 strict vegans of 5-35 years' duration. Vitamin B12 levels among the vegans were generally lower than in a control population. Most of the vegans had vitamin B12 values less than 200 pg/ml. RBC folate levels were normal but serum folate levels among the vegans were higher than among the controls. None of the vegans had any hematologic evidence of vitamin B12 deficiency, however four of them had neurologic complaints. Long-standing vegans should be monitored for vitamin B12 levels.

Modulation of pteroylpolyglutamate concentration and length in response to altered folate nutrition in a comprehensive range of rat tissues

For a range of rat tissue extracts, the concentrations of total folates and of short-chain pteroylpolyglutamates were assayed by Lactobacillus casei with and without conjugase treatment, respectively, and the concentration and chain length of H4PteGlnn and 5,10-CH2-H4PteGlnn together were assayed after binding to thymidylate synthase and tritiated fluorodeoxyuridylate. For rats fed a nonpurified diet and consuming 26 micrograms of folic acid daily, the respective concentrations of these total folates, short-chain folates and thymidylate synthase bindable folates were, in nmol/g, 10.2, 2.5 and 3.5 in liver, 3.9, 1.8 and 2.0 in kidney, 4.2, 1.2 and 1.0 in bone marrow, 2.3, 0.6 and 0.2 in adrenal, 2.1, 0.3 and 0.5 in spleen, 2.1, 0.9 and 0.8 in jejunal smooth muscle, 1.2, 0.9 and 0.2 in jejunal mucosa, 1.0, 0.3 and 0.6 in testis, 0.7, 0.1 and 0.2 in heart, 0.3, 0.1 and 0.1 in skeletal muscle, 0.5, 0.1 and 0.3 in brain and 0.7, 0.002 and 0 in erythrocytes. The predominant pteroylpolyglutamate chain length was 6 residues in all tissues except kidney, jejunal mucosa, skeletal muscle and brain, in which the value was 5 residues. A folate-deficient diet (30 ng/d) fed for 3 wk resulted in a depression in the total folate concentration of all tissues (except brain); the depression was generally greater for short-chain than for long-chain folates and was accompanied by a lengthening of the pteroylpolyglutamate chain. Opposite results followed folate excess of 4 to 5.4 mg/d. The fractional change in the folate concentration of the individual tissues, following perturbation of dietary folate, did not vary greatly among tissues.(ABSTRACT TRUNCATED AT 250 WORDS)