[en] The intestinal absorption and in vivo turnover kinetics of [³H]folic acid (FA) and (6S)-5-formyl-[³H]tetrahydrofolate (5-CHO-THF) were examined to determine whether differences exist in the inherent bioavailability of these forms of the vitamin. Following oral administration of 2 μCi/100 g body weight (in 50 mM sodium ascorbate, pH 7), a biphasic pattern of urinary tritium excretion was observed for each labeled folate. The following kinetic results were obtained (n=9). Little tritium was found in the GI tract after 8 hours, which indicated nearly complete absorption of each folate. HPLC analysis of urine revealed similar excretory patterns over 0-8 days post-dose for each folate administered, and the patterns of hepatic [³H]folates were equivalent when examined after 8 hours and 4 days post-dose. These findings indicate that the bioavailability FA and 5-formyl-THF is equivalent

[en] [³H]5'-O-(beta-D-glucopyranosyl) pyridoxine (PN-glucoside) and [¹⁴C]pyridoxine (PN) were orally administered to lactating rats. Milk was collected from the dam, and the stomach contents and liver were collected from the suckling pups 24 and 48 h after administration. Analysis of the isotopic ratio (³H/¹⁴C) in the milk and stomach contents indicated that the secretion of ³H in the milk was 20-25% as great as the secretion of ¹⁴C. The only labeled form of ³H and ¹⁴C in the stomach contents was pyridoxal phosphate (PLP), indicating that PN-glucoside was hydrolyzed to PN and subsequently metabolized prior to secretion by the mammary gland. The isotopic ratio in the livers of the pups was similar to that of the stomach contents. Furthermore, the relative distribution of the two isotopes among the hepatic metabolites of the pups was similar. The results of this study indicate that intact PN-glucoside is not secreted in milk, although vitamin B-6 derived from the limited hydrolysis and metabolism of PN-glucoside is delivered to the mammary gland for secretion

[en] The synthesis and in vivo application of stable-isotopically labeled folic acid was investigated to devise methods suitable for studies of folate metabolism in human subjects. Glutamate-labeled tetradeutero-pteroylglutamic acid (d4-folic acid) was prepared by mixed anhydride coupling of N10-trifluoroacetylpteroic acid and dimethyl L-[3,3,4,4-2H4]glutamic acid, saponification in sodium deuteroxide, and chromatographic purification. Retention of the isotopic label was verified by proton NMR and mass spectrometry of the para-aminobenzoylglutamic acid product of C9-N10 bond cleavage. A method was devised for determination of of isotopic enrichment of urinary d4-folates derived from orally administered d4-folic acid using affinity chromatographic purification, chemical cleavage of the C9-N10 bond, HPLC isolation of the p-[2H4]aminobenzoylglutamate product, followed by negative-ion chemical-ionization gas chromatography/mass spectrometry. Data concerning the urinary excretion of d4-folates derived from an oral dose of d4-folic acid in an adult human are presented

[en] [3H]5'-O-(beta-D-glucopyranosyl) pyridoxine (PN-glucoside) and [14C]pyridoxine (PN) were administered orally or intraperitoneally to vitamin B-6-adequate or -deficient rats. Analysis of intestinal contents and feces indicated effective intestinal absorption of PN-glucoside relative to PN. There was greater retention of 14C than 3H in the liver and carcass regardless of the route of administration of the radiolabeled vitamins. There was no major difference in the relative distribution of 3H and 14C among the vitamin B-6 metabolites in the liver between the treatment groups, and no [3H]PN-glucoside was detected in any of the livers. For all groups, the majority of the 3H administered was detected in the urine within 24 h. Less excretion of both 3H and 14C in the urine was observed for the deficient rats. There was no major difference in the relative proportion of urinary [3H]PN-glucoside or [3H]4-PA between rats fed or injected with the radiolabeled vitamins. These results indicate that vitamin B-6 status influences the clearance of metabolites derived from PN and PN-glucoside, as well as the clearance of intact PN-glucoside. Vitamin B-6 status, however, has little or no effect on the utilization of PN-glucoside. This study also suggests that the intestine is the primary site of the limited conversion of PN-glucoside to biologically active PN in the rat

[en] The effect of thermal processing on the bioavailability of vitamin B₆ in liver and muscle was examined by radioisotopic enrichment of these tissues. Rats were fed a single gelled test meal containing rat liver or muscle intrinsically enriched by vascular perfusion with [³H]vitamin B₆ or a gelled test meal containing [³H]pyridoxine (PN). Diets were extrinsically enriched with [¹⁴C]PN to permit a direct comparison of enrichment methods. Absorption and metabolism were examined by analysis of tissues and excreta 24 h after the test meal had been consumed. The bioavailability of [³H]B₆ vitamers in the raw tissues was equivalent to that of [³H]PN in controls. Thermal processing of the tissues (121⁰C, 45 min) induced destruction of 25-30% of the [³H]B₆ vitamers and weakly reduced (≤10%) the utilization of the remaining[³H]B₆ vitamers. The presence of monosodium glutamate (MSG) during thermal processing did not alter the results. The utilization of [¹⁴C]PN was unaffected by diet composition. These data demonstrate the high bioavailability of vitamin B₆ in animal-derived foods and support the use of isotopic enrichment methods as an alternative to conventional bioassay procedures

[en] The problems encountered are described and the solutions found to obtain these results. (author)

[en] The TFTR Prototype Neutral Beam Power Supply (PNBPS) has been tested with regard to its fault interruption performance up to 80 kV accelerator voltage. The energy into a faulting load has been determined and the extrapolation to the designed operating level of 120 kV is well within the specified limits. The accelerator floating deck modulator was additionally operated to 120 kV output voltage at the nominal current of 65 A for 250 ms. Described are the problems encountered and the solutions found to obtain these results

[en] A method was devised for the synthesis of 3', 5'-[²H₂]folic acid (d₂-folic acid) for use in studies of folate metabolism in human beings. Labeling was accomplished by catalytic dehalogenation of 3', 5'-dibromofolate with deuterium gas and palladium/carbon catalyst. d₂-Folic acid was separated from reduced forms and residual 3'-monobromofolate by chromatography on DEAE-Sephadex. Analysis by proton NMR and mass spectrometry indicated 70-75% deuteration of the 3',5'-positions and lack of deuteration at other carbons. (author)

[en] The bioavailability of orally administered mono- and polyglutamyl folates was examined in humans by using stable-isotope methods. [3',5'-2H2]Folic acid (d2-FA) and [3',5'-2H2]pteroylhexaglutamate (d2-PteGlu6) were prepared for oral administration and (glu-2H4)folic acid (d4-FA) was prepared for intravenous (iv) injection. In two trials, adult males (n = 7) on a folate saturation regimen (2 mg/d) were given a single 677-nmol oral dose of either d2-FA or d2-PteGlu6 in apple juice along with an iv injection of 502 nmol d4-FA as a control. Urine was collected for 48 h and the isotope labeling of urinary folates determined by mass spectrometry. The excretion ratio of urinary folates (% of d2-folate dose/% of d4-folate dose) resulting from oral d2-FA and iv d4-FA was 1.45 +/- 0.10 (mean +/- SEM) whereas the ratio for oral d2-PteGlu6 and iv d4-FA was 0.67 +/- 0.04. These results indicate that the d2-PteGlu6 is available to humans as a source of folate although its bioavailability is substantially less than that of d2-FA under these conditions