Vitamin form comparisons

Preferably, high pressure Hquid chromatography (hplc) is used to separate the active pre- and cis-isomers of vitamin D from other isomers and allows their analysis by comparison with the chromatograph of a sample of pure reference i j -vitainin D, which is equiUbrated to a mixture of pre- and cis-isomers (82,84,85). This method is more sensitive and provides information on isomer distribution as well as the active pre- and cis-isomer content of a vitamin D sample. It is appHcable to most forms of vitamin D, including the more dilute formulations, ie, multivitamin preparations containing at least 1 lU/g (AOAC Methods 979.24 980.26 981.17 982.29 985.27) (82). The practical problem of isolation of the vitamin material from interfering and extraneous components is the limiting factor in the assay of low level formulations. 

Tetronic acids exist predominantly in the dioxo form (32) in solvents of low polarity, while the existence of the monoenol form (33) has been established in other solvents by infrared " and ultraviolet spectral comparisons- and from dipole moment data. " Haynes and Pliramer " have recently reviewed the structure of these compounds [see also reference 28(a)], and the tautomerism of vitamin A (34), which has a related structure, has also been surveyed.- Analogous compounds carrying an amino group in the 3-position are also know n. ... 

Lead has been shown to decrease circulating levels of the active form of vitamin D (1,25-dihydroxy-vitamin D) in children. The conversion of vitamin D to this active hormonal form takes place via hydroxylation to 25-hydroxyvitamin D in the liver, followed by 1-hydroxylation in the mitochondria of the renal tubule by a complex cytochrome P-450 (heme-containing) system (Mahaffey et al. 1982 Rosen and Chesney 1983). Comparisons of the serum 1,25-dihydroxyvitamin D levels in children with blood lead levels of 33 g/dL with those in children with severe renal insufficiency (Rosen et al. 1980) and in children with an inborn error of vitamin D metabolism in which the 1-hydroxylase system or component... 

In summary, our bioavailability study provided for fhe firsf time data for fhe shorf-ferm bioavailability of ot-tocopherol solubilizate in comparison to regular fat-soluble preparations. Our results pointed to a higher short-term bioavailability of vitamin E in micelles versus fat-soluble forms of fhis vifamin in healthy adult volunteers both with regard to AUCs and with regard to maximum increases in plasma vitamin concentrations. 

Figure 4. Comparison of vitamin A and [3-carotene. The bond between Cls and C15 is broken as an initial step in forming vitamin A.

The commonly available source of stable vitamin E used in animal feed is synthetic DL-alpha-tocopheryl acetate. An alternative form of stable vitamin E is D-alpha-tocopheryl acetate, which is derived from plant oils (such as soybean, sunflower and maize oil). This form has a relative biopotency of more than 136% in comparison with DL-alpha-tocopheryl acetate. The potency of the fat-soluble vitamins is expressed in terms of international units (IUs). 

On the other hand, kitol is resistant to treatment with active manganese dioxide therefore, it appears that kitol has no a,j3-unsaturated hydroxyl groups. From these facts and also from a comparison of the relation between cinnamic acid and its photodimer (truxillic acid) with the relation between vitamin A and kitol, the author presumed that kitol is a dimer of vitamin A and has a cyclobutane ring formed by the carbon atoms in position 13 and 14. A probable structure is ... 

We report here the synthesis, biological activities and metabolism of the active forms of naturally occurring vitamin D analogues, especially active form of vitamin D4 (1comparison with those of l(X,25(OH)2D3. In addition, we introduce application of the synthetic procedure developed for the preparation of active forms of vitamin D analogues described here to the synthesis of biologically active natural steroids and the intermediates in ergosterol biosynthesis. 

Comparison of the two systems reveals a feature that obviously accounts for part of the differences. With vitamin D (Section V) one (cZt) form (or two if one counts the two possible chair forms of the A ring) predominates in the ground-state... 

The potencies of various tocopherols, K vitamins, ubiquinones, and similar substances in the prevention of respiratory decline have been assayed by supplementation of graded dose levels to the whole homogenate system. For each dose level, averages of at least four experiments were established. From the dose-response curves, the 50 % effective dose (EDbo) was derived. The EDso for df-a-tocopherol was found to be 1.1 ng per 3 ml of medium containing 50 mg of homogenized liver (Table VII). A comparison of the potencies of a-, /3-, 7-, and 5-tocopherols gave the same relative order of activity as the resorption sterility assay for vitamin E. df-a-To-copheryl acetate demonstrated only 3 % of the activity of the free vitamin. a-Tocopherylquinone was about 10% as active as tocopherol itself. The Simon metabolite (Simon et al., 1956) (Fig. 4) showed 40% of the activity of di-a-tocopherol, in spite of the fact that it was supplied in the quinone form. 

We previously reported the complete transformation of brushite (DCPD, dicalcium phosphate dihydrate, CaHP04-2H20) powders in less than a week to octacalcium phosphate (OCP), but not to apatitic calcium phosphate, when a commercial DMEM solution was used as the soak test medium at 37°C [42]. The removal of all the amino acids, vitamins, ucose/dextrose, phenol red, Hepes and pyruvate from the DMEM formulation and raising the Ca/P molar ratio of thus modified form of biomineralization solution from 1.99 to 2.50 led to observing much faster transformation of DCPD powders to OCP in comparison to DMEM [43]. 

A semi-quantitative determination can be made by comparison with a series of standards on the same layer, before or after carrying out a colour reaction. A flawless quantitative determination after elution has not so far been achieved as a result of the extreme instabflity of the vitamin A compounds, especially on active adsorbents. Success may perhaps be gained by conversion to the more stable anhydro-form and following then with TLC. The radioactive measurement of isotopes has been carried out frequently [68, 98]. 

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