Rat bioassay of wheat bran folate and effects of intestinal bacteria.

This study estimates the folate endogenous to a food material (wheat bran) and examines the role of intestinal bacteria in the rat bioassay for folate. After a 4-wk folate depletion period, rats were fed for an additional 4 wk basal diets with or without 0.5% phthalylsulfacetamide and with 100, 200 or 300 g of wheat bran; or 50, 100 or 150 g of xylan; or 0, 0.25, 0.50 or 0.75 mg of folic acid added per kg of basal diet. Xylan increased both liver and fecal folate, and this effect was nearly eliminated by phthalylsulfacetamide. Wheat bran contributed 1.6 micrograms of available folate per g of wheat bran without phthalylsulfacetamide in an apparently valid slope-ratio analysis. With the addition of phthalylsulfacetamide, liver folate increased in rats fed wheat bran diets and decreased in rats fed folic acid diets. The slope-ratio analysis for wheat bran folate with phthalylsulfacetamide became invalid due to a lack of intersection. Phthalylsulfacetamide had no effect on fecal folate excretion from rats fed the wheat bran diets. Further studies are needed on a variety of foods with and without phthalylsulfacetamide to evaluate the effect and importance of intestinal folate synthesis in the rat.

Folate bioavailability in humans: effects of wheat bran and beans.

The effect of wheat bran or California small white beans in the diet on absorption of monoglutamyl (PteGlu) and heptaglutamyl folic acid (PteGlu7) was studied in six men confined to a metabolic unit. Relative folate absorption was determined by measuring 24-h urinary folate excretion and serum folate levels at 0, 1, and 2 h after ingestion of a formula meal containing 1.13 mumol PteGlu or PteGlu7 (500 micrograms PteGlu equivalent). Serum data showed PteGlu absorption was more rapid than PteGlu7 absorption. Urinary excretion of PteGlu7 was 63% (50 less than or equal to mean less than or equal to 76%) of PteGlu excretion. Addition of 30 g wheat bran to the formula meal accelerated PteGlu absorption whereas PteGlu7 absorption was not significantly affected by either food. Effects of the two foods were qualitatively different. Wheat bran increased the absorption of PteGlu relative to PteGlu7 whereas beans minimized the difference between PteGlu and PteGlu7 serum areas.

Computerized semiautomated microbiological assay of folacin.

A semiautomated microbiological folacin assay system is described. A microcomputer controls sample dilutions, medium addition, turbidity determination, and data acquisition. Assay capacity is 600 tubes per day, approximately twice that of comparable manual assays. Using the automated equipment, more samples can be compared within one assay, eliminating many sources of between-assay variation in large studies. Additional advantages of this system are reduced human errors, flexibility of assay design, and multifunctional component equipment. Folacin results from chicken liver, spinach, and breakfast cereal samples show equivalent precision for manual and automated assays.

Folic acid utilization from high fiber diets in rats.

This study was designed to examine the effect of several sources of dietary fiber on the utilization of folic acid added to the diets of rats. Weanling rats were given a low folacin basal diet for 21 days, divided into various groups and then fed folic acid (pteroylglutamic acid) and/or fiber-supplemented diets for 7 or 8 days. The slope of the liver folacin response was measured as an indicator for utilization of added folic acid. Fecal folacin excretion was measured as an indicator of unabsorbed dietary folacin plus folacin synthesis by intestinal bacteria. There was no detectable effect of cellulose, xylan, pectin or wheat bran on the utilization of added folic acid. Liver and fecal folacin content indicated that some fiber sources contributed additional available folacin to the animals from intestinal synthesis or naturally occurring folacin. Cellulose acted as a simple dietary dilutant and had no significant effect on the utilization of added folic acid or total fecal folacin excretion. Xylan stimulated intestinal folacin synthesis, and this was reflected in higher fecal and liver folacin content. Wheat bran and beans (two varieties of each) contained measurable folacin or stimulated synthesis of bacterial folacin, which appeared to be available to the rat.

Integrated saturation model for tissue micronutrient concentrations applied to liver folacin.

A mathematical model for tissue micronutrient concentration as a function of dietary nutrient concentration, time, and growth rate is derived from assumptions of saturable nutrient storage capacity and reversible storage and depletion processes. The model is tested using liver folacin concentration data from rats. The estimated maximum liver concentration (16.8 micrograms/g), and half-life (8 days) of liver folacin are compared to more direct observations in the literature. The intake producing the half-maximal liver folacin concentration (1.3 mg folic acid/kg diet) compares well to the 1978 NRC recommendation for the rat. The estimated model parameters obtained from animals at two to three months of age are used successfully to predict additional observations from younger, more rapidly growing animals. The model has potential application in predicting the effects of food enrichment or therapeutic nutrient supplementation programs, and in the development of bioassay methods and recommended intakes.

Development of a folacin bioassay in rats.

The objective of this study was to determine if the relationship between dietary folic acid and liver folacin concentration could serve as a quantitative standard response curve for a folacin bioassay. This paper examines the time required for liver folacin depletion, the effect of the supplementation period on the range of the linear response and the precision of the standard curve. Male weanling Fisher strain rats were offered a low folacin diet for 31 days. At the end of the depletion period rats were assigned to diets containing 0. 0.25, 0.5, 1.0, 2.0 or 4.0 mg added folic acid/kg of diet. Total liver folacin was measured on three animals from each group after 2, 4, 7, 14, and 28 days on the repletion diets. The liver folacin response curves at 7, 14, and 28 days had a linear range of 4, 2, and 1 mg of folic acid per kg of diet with standard errors equal to 11, 6, and 7% of the slopes respectively. The 28 day repletion period gives the most sensitive standard range. These responses establish that liver folacin concentration is suitable for use as the response variable in the folacin bioassay. With appropriate controls the model should be useful for bioassay of folacin in natural materials.